No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Increased Sensitivity of Sensory Neurons to Tumor Necrosis Factor α in Rats With Chronic Compression of the Lumbar Ganglia
Abstract
Proinflammatory cytokines may sensitize primary sensory neurons and facilitate development of neuropathic pain processes after peripheral nerve injury. The goal of this study was to determine whether responses of dorsal root ganglion (DRG) neurons to exogenous tumor necrosis factor α (TNF-α) are altered in a chronically compressed DRG (CCD) injury model. Extracellular recordings from teased dorsal root microfilaments demonstrated that acute topical application of TNF-α to the DRG for 15 min evoked C- and Aβ-fiber responses in both normal and CCD rats. However, the response latency was significantly shorter, and the peak discharge rate was higher, in CCD fibers than in normal fibers. Intracellular recordings from small- and large-sized neurons showed that TNF-α induced greater depolarization and greater decrease in rheobase in CCD neurons than in normal neurons. The proportion of both small- and large-sized neurons that were responsive to TNF-α increased significantly after CCD injury. Furthermore, TNF-α altered the discharge patterns of large, spontaneously active neurons in addition to enhancing their discharge rates. However, the depolarization caused by TNF-α in such neurons was minor (<2 mV). Inflammatory cytokines such as TNF-α increased the sensitivity of sensory neurons in normal and CCD rats. The CCD injury itself, on the other hand, increased neuronal responses to inflammatory cytokines.
... [19] Neuroinflammation is precipitated by TNFα activation of inflammatory cells that produce TNFα and other pro-inflammatory cytokines, which sensitize primary afferent sensory nerve fibers. [18,87,89] Microglial cells at 1 st , 2 nd , and 3 rd order synapses become activated and produce TNFα, indicating spread of the neuroinflammation along the neuroaxis. [53,56] Altogether, the increased levels of TNFα, TNFα-induced neuroplastic changes, and loss of sensory gating along the neuroaxis leads to altered sympathetic outflow and potentially altered parasympathetic output, which fails to dampen inflammation at all levels of the reflex arc. ...
... Many studies suggest that TNFα-induced ectopic activity, or abnormal neural activity, sensitizes primary afferent neurons after injury. [86][87][88] TNFα that was applied to rat dorsal root ganglions (DRG) in vivo mediated peripheral sensitization, or a reduction in the mechanical thresholds of fibers with an associated increase in their receptive field size. [88] Application of TNFα to rat DRG neuron cultures increased transient voltage-activated sodium channel currents through TNF receptor-1 (TNFR-1). ...
... [86] Direct application of TNFα to cultured DRG neurons from rats with chronic compression of lumbar ganglia evoked greater action potentials and enhanced neuronal excitability when compared to control neurons. [87] Both TNFα and its receptor (TNFR-1) are upregulated in glia and neurons following peripheral nerve injury. [89] Peripheral sensitization along with continued TNFα-induced anterograde transmission of information along the afferent pathway may, thus, contribute to the development of central sensitization at both the levels of the spinal cord and supra-spinal sites. ...
It is well known that unresolved chronic pain results in decreased quality of life, inability to interact with others, and an overall patient disability, even to the point of not being able to perform one’s activities of daily living. Complex regional pain syndrome (CRPS) constitutes chronic pain with a neuroinflammatory component that culminates in disabilities and impairment, as well as comorbid disease onset. CRPS often affects a limb following a trauma (sprain, strain and fracture) to the limb or immobilization (i.e. casting). [1] There are two diagnostic categories for CRPS: CRPS-1 occurs in the absence of an identifiable nerve lesion, and CRPS-2 arises in the presence of an identifiable nerve injury. Both CRPS-1 and -2 display similar symptoms, but only the latter type meets the formal classification of neuropathic pain. The CRPS-1 subtype distinction is less thoroughly described in the literature, because the microscopic nerve damage would be hard to detect clinically. [2] In addition to pain out of proportion to the initial injury, other CRPS symptoms due to damage to nerves controlling temperature and blood flow frequently do not appear until much after the injury, and therefore, patients often experience a delay in diagnosis. [3, 4] Unfortunately, delayed diagnosis may translate to ineffective treatment, because early initiation of treatment is important to prevent a vicious cycle of ongoing, chronic pain that becomes even more difficult to treat medically.
... 16,27,33,34,74,75 TNFα can induce inflammatory pain since it directly sensitizes sensory neurons through a reduction in the firing thresholds, which contributes to maintenance of pain. [76][77][78][79][80][81] An electrophysiology study demonstrated TNFα application to rat nociceptive neurons decreased response latency and increased spontaneous firing frequency, supporting the role of TNFα sensitizing peripheral nerves on the cellular level. 76 TNFα has also been shown to induce pain on the behavioral level. ...
... [76][77][78][79][80][81] An electrophysiology study demonstrated TNFα application to rat nociceptive neurons decreased response latency and increased spontaneous firing frequency, supporting the role of TNFα sensitizing peripheral nerves on the cellular level. 76 TNFα has also been shown to induce pain on the behavioral level. TNFα injection directly into rat hindpaws resulted in increased hyperalgesia demonstrating a role of TNFα in the initiation of inflammatory pain, and this painful behavior was inhibited by local TNFα inhibition, demonstrating the potential of local TNFα inhibition to alleviate the inflammatory pain in the periphery. ...
Painful intervertebral disc (IVD) degeneration has tremendous societal costs and few effective therapies. Intradiscal tumor necrosis factor‐alpha (TNFα) is commonly associated with low back pain, but the direct relationship remains unclear. Treatment strategies for low back pain require improved understanding of the complex relationships between pain, intradiscal pro‐inflammatory cytokines, and structural IVD degeneration. A rat in vivo lumbar IVD puncture model was used to determine the role of TNFα in initiating painful IVD degeneration and to identify statistical relationships between painful behavior, IVD degeneration, and intradiscal pro‐inflammatory cytokine expression. Lumbar IVDs were punctured anteriorly and injected with TNFα, anti‐TNFα, or saline and compared with sham and naive controls for mechanical hindpaw pain threshold, IVD degeneration, IVD height, and intradiscal TNFα and IL‐1β expressions. TNFα injection increased pain and IVD degeneration whereas anti‐TNFα alleviated pain to control levels. Multivariate step‐wise linear regression identified pain threshold was predicted by IVD and intradiscal TNFα expression. Painful behavior was also linearly associated with IVD height loss, intradiscal TNFα and IL‐1β. The significant associations between IVD degeneration, height loss, inflammation, and painful behavior highlights the multifactorial nature of painful IVD degeneration and the challenges to diagnose and treat a specific underlying factor. We concluded that TNFα is an initiator of painful IVD degeneration and its early inhibition can mitigate pain and degeneration. Intradiscal TNFα inhibition following IVD injury may warrant investigation for its potential to alter downstream painful IVD degeneration processes.
This article is protected by copyright. All rights reserved
... abnormalities reflecting current nerve pathology, but also to predict neuronal dysfunction associated with a putative late-onset phenotype. Rheobase, threshold potential, and resting membrane potential as key parameters reflecting membrane excitability [18,41,46] were not different compared to controls (Fig. 4). Interestingly, we found a reduced AP firing frequency for S126G neurons when stimulated with 2× rheobase current, while no difference was observed for both lower and higher suprathreshold currents. ...
Fabry disease (FD) is a life-limiting disorder characterized by intracellular globotriaosylceramide (Gb3) accumulations. The underlying α-galactosidase A (α-GAL A) deficiency is caused by variants in the gene GLA. Variants of unknown significance (VUS) are frequently found in GLA and challenge clinical management. Here, we investigated a 49-year old man with cryptogenic lacunar cerebral stroke and the chance finding of the VUS S126G, who was sent to our center for diagnosis and initiation of a costly and life-long FD-specific treatment. We combined clinical examination with in vitro investigations of dermal fibroblasts (HDF), induced pluripotent stem cells (iPSC), and iPSC-derived sensory neurons. We analyzed α-GAL A activity in iPSC, Gb3 accumulation in all three cell types, and action potential firing in sensory neurons. Neurological examination and small nerve fiber assessment was normal except for reduced distal skin innervation. S126G iPSC showed normal α-GAL A activity compared to controls and no Gb3 deposits were found in all three cell types. Baseline electrophysiological characteristics of S126G neurons showed no difference compared to healthy controls as investigated by patch-clamp recordings. We pioneer multi-level cellular characterization of the VUS S126G using three cell types derived from a patient and provide further evidence for the benign nature of S126G in GLA, which is of great importance in the management of such cases in clinical practice.
... Complete transection of the nerve is associated with an increase in the release of glutamate along with other markers and activation of N-methyl-D-aspartate (NMDA) receptors, leading to allodynia. 10,11 Diagnosis of neuropathic pain is based on proper clinical, physical, and neurological examination. Patients usually present with shooting, burning pain along with tingling numbness, allodynia, and hyperalgesia. ...
Background: Post-operative neuropathic pain is one of the most dreadful complications following lumbar spine surgeries. Owing to the similarities in the pathophysiological and biochemical mechanisms underlying epilepsy and neuropathic pain, many anti-epileptic drugs (AEDs) like pregabalin and gabapentin are being used in the treatment of post-operative neuropathic pain. Methods: This prospective and observational study included a total of 60 patients out of 261 patients undergoing lumbar discectomy surgery, who postoperatively had neuropathic pain as diagnosed with LANSS score; and were randomly divided into pregabalin (n=30) and gabapentin (n=30) supplementation groups, and the efficacy was compared with respect to visual analog scale (VAS) score (clinically) and Oswestry disability index (ODI) score (functionally) at pre-operative and post-operative follow-ups; and also, total analgesia consumed. Results: No statistical differences were observed between any of the demographic variables and surgical levels operated upon between the two groups. Both the groups showed significant improvements in clinical (VAS) and functional (ODI) outcome as compared to pre-operative status. Leeds assessment of neuropathic symptoms and signs scale (LANSS) score was significantly increased in both the groups postoperatively till the 3rdmonthfollow-up, after which there was a significant decrease in the score. The Pregabalin group showed significant (p<0.05) improvement in VAS and ODI scores at the post operative 1st, 3rd, and 6th month, as compared to the gabapentin group; however, at other follow-ups the difference was insignificant. Total analgesia consumed was significantly higher in the gabapentin group. Conclusions: Our study concluded that both pregabalin and gabapentin are highly effective in the treatment of early post-operative neuropathic pain; showing encouraging clinical and functional improvements. Pregabalin had significantly better outcomes on short-term follow-ups; however, on longer follow-ups, both had similar beneficial outcomes. Pregabalin supplementation showed a significant analgesia-sparing effect as compared to gabapentin.
... Numerous studies have demonstrated a link between TNF-α and different types of pain (Schafers et al., 2008;Zhang & An, 2007). TNF-α drives nociceptor sensitization by regulation of TRPV1 expression and sensitization of DRG neurons (Constantin et al., 2008;He et al., 2010;Jin & Gereau, 2006;Liu, Li, Brull, & Zhang, 2002;Park et al., 2011;Wei, Qiu, Jin, Liu, & Hu, 2021). TNF-α further promotes neuropathic pain by inducing glial activation and central sensitization Bezzi et al., 2001;Kawasaki, Zhang, Cheng, & Ji, 2008;Zhong et al., 2010). ...
It is generally believed that immune activation can elicit pain through production of inflammatory mediators that can activate nociceptive sensory neurons. Emerging evidence suggests that immune activation may also contribute to the resolution of pain by producing distinct pro-resolution/anti-inflammatory mediators. Recent research into the connection between the immune and nervous systems has opened new avenues for immunotherapy in pain management. This review provides an overview of the most utilized forms of immunotherapies (e.g., biologics) and highlight their potential for immune and neuronal modulation in chronic pain. Specifically, we discuss pain-related immunotherapy mechanisms that target inflammatory cytokine pathways, the PD-L1/PD-1 pathway, and the cGAS/STING pathway. This review also highlights cell-based immunotherapies targeting macrophages, T cells, and mesenchymal stromal cells for chronic pain management.
... Accumulating evidences indicate that abnormal production of inflammatory cytokines mediates neuroinflammation and sensitize neurons to induce hyperalgesia or allodynia in neuropathic pain or radiculopathy [28]. In the current study, the SNI rats presented with significant reduced pain changed in SNs, the results showed that the expressions of IL-33, IL-6 and IL-1β significantly increased nearly 2.5fold, 2-fold and 2-fold separately after SNI; similarly, the changes were decreased by administration of LA (Fig. 6 A, D-F). ...
Neuropathic pain is a debilitating chronic disorder, significantly causing personal and social burdens, in which activated neuroinflammation is one major contributor. Thymic stromal lymphopoietin (TSLP) and interleukin (IL)-33 is important for chronic inflammation. Linalyl acetate (LA) is main component of lavender oil with an anti-inflammatory property through TSLP signaling. The aim of the study is to investigate how LA regulates mechanical hyperalgesia after sciatic nerve injury (SNI). Adult Sprague-Dawley male rats were separated into 3 groups: control group, SNI group and SNI with LA group. LA was administrated intraperitoneally one day before SNI. Pain behavior test was evaluated through calibration forceps testing. Ipsilateral sciatic nerves (SNs), dorsal root ganglions (DRGs) and spinal cord were collected for immunofluorescence staining and Western blotting analyses. SNI rats were more sensitive to hyperalgesia response to mechanical stimulus since operation, which was accompanied by spinal cord glial cells reactions and DRG neuro-glial interaction. LA could relieve the pain sensation, proinflammatory cytokines and decrease the expression of TSLP/TSLPR complex. Also, LA could reduce inflammation through reducing IL-33 signaling. This study is the first to indicate that LA can modulate pain through TSLP/TSLPR and IL-33 signaling after nerve injury.
... Neurons expressing mCherry were observed in DRG of controls and DREADDs animals ( Figure 2C). Diameter sizes of transduced afferents are presented in a histogram in Figure 2D, with preferential targeting occurring in cells that are medium and large in size (Li and Zhao, 1998;Liu et al., 2002). To calculate transduction efficiencies of viral vectors (fraction of dsRed+ cells to total cells in adjacent sections), Fluorescent Nissl was used to visualize total cells in the DRG ( Figure 2E). ...
Neuromodulatory therapies for spinal cord injury (SCI) such as electrical epidural stimulation (EES) are increasingly effective at improving patient outcomes. These improvements are thought to be due, at least in part, to plasticity in neuronal circuits. Precisely which circuits are influenced and which afferent classes are most effective in stimulating change remain important open questions. Genetic tools, such as Designer Receptors Exclusively Activated by Designer Drugs (DREADDs), support targeted and reversible neuromodulation as well as histological characterization of manipulated neurons. We therefore transduced and activated lumbar large diameter peripheral afferents with excitatory (hM3Dq) DREADDs, in a manner analogous to EES, in a rat hemisection model, to begin to trace plasticity and observe concomitant locomotor changes. Chronic DREADDs activation, coupled with thrice weekly treadmill training, was observed to increase afferent fluorescent labeling within motor pools and Clarke's column when compared to control animals. This plasticity may underlie kinematic differences that we observed across stages of recovery, including an increased and less variable hindquarters height in DREADDs animals, shorter step durations, a more flexed ankle joint early in recovery, a less variable ankle joint angle in swing phase, but a more variable hip joint angle. Withdrawal of DREADDs agonist, clozapine- N -oxide (CNO) left these kinematic differences largely unaffected; suggesting that DREADDs activation is not necessary for them later in recovery. However, we observed an intermittent “buckling” phenomenon in DREADDs animals without CNO activation, that did not occur with CNO re-administration. Future studies could use more refined genetic targeted of specific afferent classes, and utilize muscle recordings to find where afferent modulation is most influential in altering motor output.
... 195,[210][211][212] These mediators act not only on neurons but also on neighboring SGCs facilitating paracrine and autocrine positive feedback. [213][214][215] SGCs represent a source of ATP through vesicular-or channel-mediated . Soluble mediators are released from the sensory neuron soma and readily bind to receptors on SGC and also serve as chemoattractant for macrophages and T cells: Glutamate activate N-methyl-D-aspartic acid (NMDA) glutamatergic receptors, substance P (SP) binds to neurokinin 1 receptor (NK1R), C-C motif chemokine ligand 2 (CCL2) binds to C-C motif chemokine receptor 2 (CCR2), calcitonin gene-related peptide (CGRP) binds to CGRP receptors (CGRPR), adenosine triphosphate (ATP) binds to various purinoceptors (P2X, P2Y), damage associated molecular patterns (DAMPs) bind to toll-like receptors (TLR2, TLR4). ...
Chronic pain remains a public health problem and contributes to the ongoing opioid epidemic. Current pain management therapies still leave many patients with poorly controlled pain, thus new or improved treatments are desperately needed. One major challenge in pain research is the translation of preclinical findings into effective clinical practice. The local neuroimmune interface plays an important role in the initiation and maintenance of chronic pain and is therefore a promising target for novel therapeutic development. Neurons interface with immune and immunocompetent cells in many distinct microenvironments along the nociceptive circuitry. The local neuroimmune interface can modulate the activity and property of the neurons to affect peripheral and central sensitization. In this review, we highlight a specific subset of many neuroimmune interfaces. In the central nervous system, we examine the interface between neurons and microglia, astrocytes, and T lymphocytes. In the periphery, we profile the interface between neurons in the dorsal root ganglion with T lymphocytes, satellite glial cells, and macrophages. To bridge the gap between preclinical research and clinical practice, we review the preclinical studies of each neuroimmune interface, discuss current clinical treatments in pain medicine that may exert its action at the neuroimmune interface, and highlight opportunities for future clinical research efforts.
... Studies have shown that TNF-α facilitates heat-induced CGRP release from nociceptor terminals in the skin [79] and sensitizes peripheral Aβ-and C-fibers [80][81][82][83]. This sensitization of peripheral primary afferents by TNF-α results from the abnormal expression of voltage-gated sodium channels (VGSCs) in the dorsal root ganglia (DRG) [84][85][86]. ...
The neuroimmune mechanism underlying neuropathic pain has been extensively studied. Tumor necrosis factor-alpha (TNF-α), a key pro-inflammatory cytokine that drives cytokine storm and stimulates a cascade of other cytokines in pain-related pathways, induces and modulates neuropathic pain by facilitating peripheral (primary afferents) and central (spinal cord) sensitization. Functionally, TNF-α controls the balance between cell survival and death by inducing an inflammatory response and two programmed cell death mechanisms (apoptosis and necroptosis). Necroptosis, a novel form of programmed cell death, is receiving increasing attraction and may trigger neuroinflammation to promote neuropathic pain. Chronic pain is often accompanied by adverse pain-associated emotional reactions and cognitive disorders. Overproduction of TNF-α in supraspinal structures such as the anterior cingulate cortex (ACC) and hippocampus plays an important role in pain-associated emotional disorders and memory deficits and also participates in the modulation of pain transduction. At present, studies reporting on the role of the TNF-α–necroptosis pathway in pain-related disorders are lacking. This review indicates the important research prospects of this pathway in pain modulation based on its role in anxiety, depression and memory deficits associated with other neurodegenerative diseases. In addition, we have summarized studies related to the underlying mechanisms of neuropathic pain mediated by TNF-α and discussed the role of the TNF-α–necroptosis pathway in detail, which may represent an avenue for future therapeutic intervention.
... Blockade of ZNF382 binding to silencer or genetic deletion of silencer not only reversed the ZNF382 suppression on Cxcl13 transcription but also impaired the inhibitory effect of ZNF382 on SNLinduced nociceptive hypersensitivity. Given that increased DRG CXCL13 contributed to neuropathic pain through ERKmediated production of inflammatory mediators (e.g., TNFα; Jiang et al., 2016;Zhang et al., 2016) and that increased DRG TNFα elevated nociceptor excitability and induced hyperalgesia through enhancing voltage-gated sodium channel function in DRG neurons (Liu et al., 2002;Leo et al., 2015;Fischer et al., 2017), the anti-nociceptive effect produced by ZNF382 overexpression in neuropathic pain likely results from the silencing of CXCL13 and subsequent inactivation of ERK signaling pathway in injured DRG. Inactive ERK signaling pathway may cause the reductions in DRG neuronal excitability and (Latremoliere and Woolf, 2009), resulting in the attenuation of central sensitization in the SC dorsal horn. ...
Nerve injury–induced changes of gene expression in dorsal root ganglion (DRG) are critical for neuropathic pain genesis. However, how these changes occur remains elusive. Here we report the down-regulation of zinc finger protein 382 (ZNF382) in injured DRG neurons after nerve injury. Rescuing this down-regulation attenuates nociceptive hypersensitivity. Conversely, mimicking this down-regulation produces neuropathic pain symptoms, which are alleviated by C-X-C motif chemokine 13 (CXCL13) knockdown or its receptor CXCR5 knockout. Mechanistically, an identified cis-acting silencer at distal upstream of the Cxcl13 promoter suppresses Cxcl13 transcription via binding to ZNF382. Blocking this binding or genetically deleting this silencer abolishes the ZNF382 suppression on Cxcl13 transcription and impairs ZNF382-induced antinociception. Moreover, ZNF382 down-regulation disrupts the repressive epigenetic complex containing histone deacetylase 1 and SET domain bifurcated 1 at the silencer-promoter loop, resulting in Cxcl13 transcriptional activation. Thus, ZNF382 down-regulation is required for neuropathic pain likely through silencer-based epigenetic disinhibition of CXCL13, a key neuropathic pain player, in DRG neurons.
... In this context, several studies have indicated that primary sensory neurons may express receptors for proinflammatory cytokines/chemokines, including for those peripheral macrophage-derived cytokines (eg, IL-1b, TNF, and IL-6 receptors). 131,138 Based on that, several studies have analysed the possible effects of these cytokines on the excitability of primary sensory neurons. 151,159 For example, both TNF and IL-1b are able to enhance the excitability of cultured primary sensory neurons in vitro. ...
The peripheral nervous system comprises an infinity of neural networks that act in the communication between the central nervous system and the most diverse tissues of the body. Along with the extension of the primary sensory neurons (axons and cell bodies), a population of resident macrophages has been described. These newly called sensory neuron–associated macrophages (sNAMs) seem to play an essential role in physiological and pathophysiological processes, including infection, autoimmunity, nerve degeneration/regeneration, and chronic neuropathic pain. After different types of peripheral nerve injury, there is an increase in the number and activation of sNAMs in the sciatic nerve and sensory ganglia. The activation of sNAMs and their participation in neuropathic pain development depends on the stimulation of pattern recognition receptors such as Toll-like receptors and Nod-like receptors, chemokines/cytokines, and microRNAs. On activation, sNAMs trigger the production of critical inflammatory mediators such as proinflammatory cytokines (eg, TNF and IL-1β) and reactive oxygen species that can act in the amplification of primary sensory neurons sensitization. On the other hand, there is evidence that sNAMs can produce antinociceptive mediators (eg, IL-10) that counteract neuropathic pain development. This review will present the cellular and molecular mechanisms behind the participation of sNAMs in peripheral nerve injury–induced neuropathic pain development. Understanding how sNAMs are activated and responding to nerve injury can help set novel targets for the control of neuropathic pain.
... It has been well established that TNF-a produces a persistent hyperexcitability through gene transcription in DRG ( He et al., 2010;Huang et al., 2014;Tamura et al., 2014;Zang et al., 2010) and in cortical neurons ( Chen et al., 2015). TNF-a has also been repeatedly demonstrated to induce an acute excitation of DRG neurons ( Liu et al., 2002;Zhang et al., 2002) and of subfornical organ neurons (Simpson and Ferguson, 2017). TNF-a enhances sodium currents in DRG neurons within minutes (Jin and Gereau, 2006). ...
It is well known that nuclear factor-kappaB (NF-κB) regulates neuronal structures and functions by nuclear transcription. Here, we showed that phospho-p65 (p-p65), an active form of NF-κB subunit, reversibly interacted with Nav1.7 channels in the membrane of dorsal root ganglion (DRG) neurons of rats. The interaction increased Nav1.7 currents by slowing inactivation of Nav1.7 channels and facilitating their recovery from inactivation, which may increase the resting state of the channels ready for activation. In cultured DRG neurons TNF-α upregulated the membrane p-p65 and enhanced Nav1.7 currents within 5 min but did not affect nuclear NF-κB within 40 min. This non-transcriptional effect on Nav1.7 may underlie a rapid regulation of the sensibility of the somatosensory system. Both NF-κB and Nav1.7 channels are critically implicated in many physiological functions and diseases. Our finding may shed new light on the investigation into the underlying mechanisms.
... Endometriotic lesion sites also exhibit increased neuroangiogenesis, which could be attributed to localized inflammation (Asante and Taylor, 2011;Arnold et al., 2012;Di Spiezio Sardo et al., 2015). Inflammatory molecules and neuropeptides might directly activate or sensitize sprouting sensory fibers in the tissues or excite nociceptive neurons, which resulted in pain and/or mechanical hypersensitivity (Liu et al., 2002;Mckinnon et al., 2015). Prolonged exposure of sensory neurons to inflammatory mediators would then lead to central sensitization (Arnold et al., 2012) and cause estrogenindependent pain (Woolf and Salter, 2000), as observed in some patients with endometriosis and persistent pelvic pain (Neziri et al., 2010;As-Sanie et al., 2013;Brawn et al., 2014). ...
Pain is the most severe and common symptom of endometriosis. Its underlying pathogenetic mechanism is poorly understood. Nerve sensitization is a particular research challenge, due to the limitations of general endometriosis models and sampling nerve tissue from patients. The chemokine fractalkine (FKN) has been demonstrated to play a key role in various forms of neuropathic pain, while its role in endometriotic pain is unknown. Our study was designed to explore the function of FKN in the development and maintenance of peripheral hyperalgesia and central sensitization in endometriosis using a novel endometriosis animal model developed in our laboratory. After modeling, behavioral tests were carried out and the optimal time for molecular changes was obtained. We extracted ectopic tissues and L4–6 spinal cords to detect peripheral and central roles for FKN, respectively. To assess morphologic characteristics of endometriosis-like lesions—as well as expression and location of FKN/CX3CR1—we performed H&E staining, immunostaining, and western blotting analyses. Furthermore, inhibition of FKN expression in the spinal cord was achieved by intrathecal administration of an FKN-neutralizing antibody to demonstrate its function. Our results showed that implanted autologous uterine tissue around the sciatic nerve induced endometriosis-like lesions and produced mechanical hyperalgesia and allodynia. FKN was highly expressed on macrophages, whereas its receptor CX3CR1 was overexpressed in the myelin sheath of sciatic nerve fibers. Overexpressed FKN was also observed in neurons. CX3CR1/pp38-MAPK was upregulated in activated microglia in the spinal dorsal horn. Intrathecal administration of FKN-neutralizing antibody not only reversed the established mechanical hyperalgesia and allodynia, but also inhibited the expression of CX3CR1/pp38-MAPK in activated microglia, which was essential for the persistence of central sensitization. We concluded that the FKN/CX3CR1 signaling pathway might be one of the mechanisms of peripheral hyperalgesia in endometriosis, which requires further studies. Spinal FKN is important for the development and maintenance of central sensitization in endometriosis, and it may further serve as a novel therapeutic target to relieve persistent pain associated with endometriosis.
... Substantial data reveal pro-nociceptive roles for TNF in chronic pain [22][23][24] , and increases in levels of TNF in the brain impact peripheral hypersensitivity [9,14,25,26] . Thus, whether the increase is central, peripheral or both, TNF facilitates pain [27,28] , and lowering of TNF is antinociceptive [12,14,[29][30][31][32][33][34] . Spread of inflammation occurs along the neuroaxis (CNS and peripheral nervous system, PNS) during neuropathic pain, providing an explanation for its chronicity [35] . ...
... Radiculopathic symptoms are not always present with nerve root compression and can occur in its absence [7,8]. In animal models, the direct application of NP to the nerve roots without mechanical compression causes an abnormal production of inflammatory mediators and cytokines [10,13,[33][34][35][36][37][38], which rapidly sensitize primary afferents and induce neural-immune interactions [39,40]. This leads to the production and secretion of cytokines, excitatory amino acids, COX-2, and prostaglandins, which induces the hyperexcitability of spinal dorsal horn neurons as well as hyperalgesia [41,42]. ...
Background:
Immune and inflammatory responses occurring in the spinal cord play a pivotal role in the progression of radicular pain caused by intervertebral disk herniation. Interleukin-33 (IL-33) orchestrates inflammatory responses in a wide range of inflammatory and autoimmune disorders of the nervous system. Thus, the purpose of this study is to investigate the expression of IL-33 and its receptor ST2 in the dorsal spinal cord and to elucidate whether the inhibition of spinal IL-33 expression significantly attenuates pain-related behaviors in rat models of noncompressive lumbar disc herniation.
Methods:
Lentiviral vectors encoding short hairpin RNAs that target IL-33 (LV-shIL-33) were constructed for gene silencing. Rat models of noncompressive lumber disk herniation were established, and the spines of rats were injected with LV-shIL-33 (5 or 10 μl) on the first day after the operation. Mechanical thresholds were evaluated during an observation period of 21 days. Moreover, the expression levels of spinal tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), interleukin-6 (IL-6), and cyclooxygenase 2 (COX-2) and the activation of the mitogen-activated protein kinases (MAPK) and nuclear factor-κB (NF-κB) pathways were evaluated to gain insight into the mechanisms related to the contribution of IL-33/ST2 signaling to radicular pain.
Results:
The application of nucleus pulposus (NP) to the dorsal root ganglion (DRG) induced an increase in IL-33 and ST2 expression in the spinal cord, mainly in the dorsal horn neurons, astrocytes, and oligodendrocytes. Spinally delivered LV-shIL-33 knocked down the expression of IL-33 and markedly attenuated mechanical allodynia. In addition, spinal administration of LV-shIL-33 reduced the overexpression of spinal IL-1β, TNF-α, and COX-2 and attenuated the activation of C-Jun N-terminal kinase (JNK), extracellular signal-regulated kinase (ERK), and NF-κB/p65 but not p38.
Conclusions:
This study indicates that spinal IL-33/ST2 signaling plays an important role in the development and progression of radicular pain in rat models of noncompressive lumber disk herniation. Thus, the inhibition of spinal IL-33 expression may provide a potential treatment to manage radicular pain caused by intervertebral disk herniation.
... The cytokine profile was similar to that seen in the LID model (20)(21)(22). In addition, sensory neurons showed increased sensitivity to many pro-inflammatory cytokines after implementation of the CCD model (23,24). It is documented that the NFκB pathway is involved in these models (25,26) and one of the major mechanisms of steroid anti-inflammatory effects is suppression of this pathway. ...
Aim of review
Low back pain is a major health problem in United States and worldwide. In this review, we aim to show that mineralocorticoid receptor (MR) activation has a critical role in the initiation of immune and inflammatory responses, which in turn can impact the effectiveness of the currently used steroids for epidural injections in low back pain management since most steroids activate MR in addition to the primary target, glucocorticoid receptor (GR). Moreover, we would like to determine some of the benefits of blocking the MR-induced negative effects. Overall, we propose a novel therapeutic approach for low back pain management by using a combination of a MR antagonist and a GR agonist in the epidural injections.
Method
We will first introduce the societal cost of low back pain and discuss how epidural steroid injections became a popular treatment for this condition. We will then describe several preclinical models used for the study of low back pain conditions and the findings with respect to the role of MR in the development of inflammatory low back pain.
Recent findings
MR has pro-inflammatory effects in many tissues which can counteract the anti-inflammatory effects induced by GR activation. Blocking MR using the selective MR antagonist eplerenone can reduce pain and sensory neuron excitability in experimental models of low back pain. Moreover, combining the MR antagonist with clinically used steroids is more effective in reducing pain behaviors than using the steroids alone.
Summary
MR antagonists are promising candidates to increase the effectiveness of currently used steroids. Since the activation of the MR is evident in preclinical models of low back pain, blocking its deleterious effects can be beneficial in managing inflammatory pain conditions.
... Indeed, levels of PGE 2 have been shown to be elevated within 5 min following TBI [194]. In addition to these direct activators or TRP channels, cytokines like IL-1, IL-6, and TNFα may sensitize sensory neurons, lowering the threshold for release of neuropeptides [195,196]. ...
Background
The neuroinflammatory response following traumatic brain injury (TBI) is known to be a key secondary injury factor that can drive ongoing neuronal injury. Despite this, treatments that have targeted aspects of the inflammatory pathway have not shown significant efficacy in clinical trials. Main bodyWe suggest that this may be because classical inflammation only represents part of the story, with activation of neurogenic inflammation potentially one of the key initiating inflammatory events following TBI. Indeed, evidence suggests that the transient receptor potential cation channels (TRP channels), TRPV1 and TRPA1, are polymodal receptors that are activated by a variety of stimuli associated with TBI, including mechanical shear stress, leading to the release of neuropeptides such as substance P (SP). SP augments many aspects of the classical inflammatory response via activation of microglia and astrocytes, degranulation of mast cells, and promoting leukocyte migration. Furthermore, SP may initiate the earliest changes seen in blood-brain barrier (BBB) permeability, namely the increased transcellular transport of plasma proteins via activation of caveolae. This is in line with reports that alterations in transcellular transport are seen first following TBI, prior to decreases in expression of tight-junction proteins such as claudin-5 and occludin. Indeed, the receptor for SP, the tachykinin NK1 receptor, is found in caveolae and its activation following TBI may allow influx of albumin and other plasma proteins which directly augment the inflammatory response by activating astrocytes and microglia. Conclusions
As such, the neurogenic inflammatory response can exacerbate classical inflammation via a positive feedback loop, with classical inflammatory mediators such as bradykinin and prostaglandins then further stimulating TRP receptors. Accordingly, complete inhibition of neuroinflammation following TBI may require the inhibition of both classical and neurogenic inflammatory pathways.
... Whole-cell perforated patch clamp recordings in cultured rat hippocampal neurons showed that long-term treatment with TNF-α increases Ca 2+ current density through L-type voltage-dependent channels, but it decreases currents induced by glutamate, NMDA, AMPA, and kainate. Neurons pre-treated with TNF-α exhibited increased intracellular Ca 2+ concentrations following membrane depolarization, but reduced intracellular Ca 2+ concentration in response to excitatory amino acids [151,152]. Inflammatory mediators such as nitric oxide (NO) and TNF-α are released from glia-enriched mix culture in response to hypoxia/reoxygenation [153,154]. TNF-α also modulates synaptic maturation and neuronal branching in the hippocampus by controlling the expression of synaptic vesicle-associated proteins [155]. ...
Cytokines are inducible, secretory proteins that mediate intercellular communication in the immune system. They are grouped in families referred as tumour necrosis factors, interleukins, interferons and colony stimulating factors. In recent years, it is clear that some of these proteins and their receptors are also produced in the central nervous system (CNS) by specific neural cell lineages under physiological and pathological conditions. The data we have hitherto let us suggest that cytokines play an important role in the regulation of both excitatory and inhibitory neurotransmission in the CNS. Growing evidence indicates that, in addition to the hormones of hypothalamic, pituitary and gonadal origin, autocrine/paracrine regulators play important roles in the reproductive functions. Cytokines, originally known as immunoregulatory proteins, may affect the neuroendocrine events of reproduction, ovarian/testis function, endometrium, the developing embryo, placenta and parturition. Cytokines can modulate and mediate the actions of hormones at their target cells and, in the opposite way, hormones may regulate the production and action of cytokines at three different levels: cytokine secretion, cytokine receptor expression and cellular responses. Cytokines may also function in an endocrine manner affecting distant targets. In addition, many cells in the reproductive system also produce cytokines independently of the presence of leukocytes, thus reproductive tissues are sites of cytokine action and production. There is compelling evidence that cytokines, in fact, play an important regulatory role in the development and normal function of ovarian and testicular tissues, and are surveyed as the important regulators of steroidogenesis and gamete production. Cytokines interfere with steroidogenesis at the level of testes, and ovaries. For instance, secretory products of macrophages are involved in the regulation of steroidogenesis, Sertoli cell activity, and germ cell survival in the human testes. In conclusion, cytokines interact with steroidogenesis in a systemic and complex manner, influencing development, function, and hormone production of the testes, and ovaries. Thus a variety of clinical situations may be due to cytokine action in the gonads. Therapeutic manipulation of the immune system may affect reproductive function. The aim of this chapter is to provide a summary of the extensive literature dealing with cytokines in central nervous system function, and gonadal biology, and to follow this with some speculation concerning the significance of these molecules in interactions between the immune system and the neuroendocrine system. This knowledge could be fundamental for the proposal of new therapeutic approaches to neurological, psychiatric and reproductive disorders.
... Inflammatory mediators, e.g., TNFα, nerve growth factor (NGF) and ATP are upregulated and released from those non-neuronal cells. They act directly on their receptors at sensory neurons, nerve fibers and their terminals [47][48][49][50] or indirectly through the release of prostanoids, e.g. PGE2 [51]. ...
Background
We have previously shown that endogenously active purinergic P2X7 receptors (P2X7Rs) in satellite glial cells of dorsal root ganglia (DRGs) stimulate ATP release. The ATP activates P2Y1Rs located in the enwrapped neuronal somata, resulting in down-regulation of P2X3Rs. This P2X7R-P2Y1-P2X3R inhibitory control significantly reduces P2X3R-mediated nociceptive responses. The underlying mechanism by which the activation of P2Y1Rs inhibits the expression of P2X3Rs remains unexplored.
Results
Examining the effect of the activation of p38 mitogen-activated protein kinase on the expression of P2X3Rs in DRGs, we found that the p38 activator, anisomycin (Anis), reduced the expression of P2X3Rs. Blocking the activity of SGCs by the glial Krebs cycle inhibitor, fluorocitrate, did not change the effect of Anis. These results suggest that neuronal p38 plays a major role in the inhibition of P2X3R expression. Western blotting analyses showed that inhibiting P2Y1Rs by MRS2179 (MRS) or blocking P2X7Rs by either oxATP or A740003 reduced pp38 and increased P2X3R expression in DRGs. These results are further supported by the immunohistochemical study showing that P2X7R and P2Y1R antagonists reduce the percentage of pp38-positive neurons. These observations suggest that activation of P2X7Rs and P2Y1Rs promotes p38 activity to exert inhibitory control on P2X3R expression. Since activation of p38 by Anis in the presence of either A740003 or MRS could overcome the block of P2X7R-P2Y1R inhibitory control, p38 in DRG neurons is downstream of P2Y1Rs. In addition, inhibition of p38 by SB202190 was found to prevent the P2X7R and P2Y1R block of P2X3R expression and increase P2X3R-mediated nociceptive flinch behaviors.
Conclusions
p38 in DRG neurons downstream of P2Y1R is necessary and sufficient for the P2X7R-P2Y1R inhibitory control of P2X3R expression.
... Rather than nerves, dorsal root ganglia can also be injured to generate experimental neuropathic pain. Thus, Liu et al. (2002) inserted a small stainless steel rod (4 mm in length and 0.5-0.8 mm in diameter) into the L5 and/or L4 intervertebral foramen to produce foramen stenosis. ...
Neuropathic pain, caused by lesions of central or peripheral nervous system, is difficult to treat because of its resistance to classical antalgic treatments. Most of pharmacotherapeutic treatments of neuropathic pain (antidepressants, anticonvulsants) currently used are only based on empirical data and are not specifically aimed at relieving pain. Better knowledge of the mechanisms underlying neuropathic pain is an absolute prerequesite to develop new and innovative treatments. With the aim of contributing to elucidate these mechanisms, I developed two models of neuropathic pain in rats, and studied their behavioral, pharmacological, cellular and biochemical characteristics. The first model consisted of the induction of central neuropathic pain by complete transection of the spinal cord at T8-T9 level. The second one consisted of the administration of BDNF (Brain Derived Neurotrophic Factor; which implication in nociceptive signaling pathways is well established in the literature), directly at the spinal level, via intrathecal (i.t.) injection. In both cases, pro-algesic consequences of these interventions have been compared to those induced by unilateral ligation of the sciatic nerve, which is still considered as a classical, although not really satisfactory, model of peripheral neuropathic pain. From the second day after spinal cord transection up to (at least) 2 months later, lesioned rats developed a strong mechanical allodynia (von Frey filaments test) within a limited cutaneous territory just rostral to the surgical scar. This effect really reflected central neuropathic pain because it did not occur in control, " sham operated " animals, that underwent the same surgical intervention except the spinal cord transection. Mechanical allodynia was associated with marked overexpression of markers of neuronal injury (ATF-3), microglial activation (OX-42, P2X4, P2X7 and TLR4 receptors), astrocyte activation (GFAP), as well as upregulation of transcripts encoding BDNF and pro-inflammatory cytokines (IL-1ß, IL-6 and TNF-α, but only transiently for the latter cytokine), in dorsal root ganglia and/or spinal cord. Therefore, spinal cord transection triggered a strong neuroinflammatory reaction, like that occurring after peripheral nerve lesion, but with different time course and amplitude. On the other hand, intrathecal injection of an infra-nanomolar dose of BDNF (0.3 - 3.0 ng) also induced a strong mechanical allodynia and hyperalgesia at hindpaw level, which developed within 3-5 days and lasted for at least two weeks. However, in sharp contrast with spinal cord transection (and sciatic nerve ligation), i.t. injection of BDNF did not induce any microglial activation and/or proinflammatory cytokines upregulation. Intrathecal (exogenous) BDNF-induced (endogenous) BDNF auto-induction might play a key role in the maintenance of i.t. BDNF-induced hyperalgesia as the latter can be reversed by pharmacological blockade of the BDNF receptor TrkB (with cyclotraxin B at 20 mg/kg i.p., which also reversed sciatic nerve ligation-induced hyperalgesia). Pharmacological investigations showed that the opioid antalgic drug tapentadol and anticonvulsants such as pregabalin and gabapentin efficiently reduced neuropathic pain in i.t. BDNF i.t. as well as in sciatic nerve-ligated rats. Accordingly, intrathecal injection of BDNF might represent a new non-surgical model of neuropathic pain in rats. Moreover, our results indicate that blockade of BDNF-TrkB signaling could open new therapeutic perspectives for alleviating peripheral neuropathic pain. This innovative pharmacological approach should also be explored in the case of central neuropathic pain caused by spinal cord injury.
... Whole-cell perforated patch clamp recordings in cultured rat hippocampal neurons showed that long-term treatment with TNF-α increases Ca 2+ current density through L-type voltage-dependent channels, but it decreases currents induced by glutamate, NMDA, AMPA, and kainate. Neurons pre-treated with TNF-α exhibited increased intracellular Ca 2+ concentrations following membrane depolarization, but reduced intracellular Ca 2+ concentration in response to excitatory amino acids [151,152]. Inflammatory mediators such as nitric oxide (NO) and TNF-α are released from glia-enriched mix culture in response to hypoxia/reoxygenation [153,154]. TNF-α also modulates synaptic maturation and neuronal branching in the hippocampus by controlling the expression of synaptic vesicle-associated proteins [155]. ...
... TNFα has been demonstrated to decrease outward K + currents in retinal ganglion neurons (Diem et al. 2001) and inhibit K + currents in small dorsal root sensory neurons (Liu et al. 2008b) that may produce increased excitability of afferent fibers. Furthermore, treatment of dorsal root ganglion with TNFα evokes neuronal discharge in both A and C-fibers and causes mechanical sensitization (Liu et al. 2002;Ozaktay et al. 2006). These results suggest that TNFα may increase the excitability of afferent fibers by directly modulating the ion channels. ...
... The role of TNF-␣ in pain mechanisms has been investigated extensively. For example, the direct exposure of uninjured DRG neurons to TNF-␣ can lead to the development of ongoing activity (Leem and Bove 2002;Liu et al. 2002;Sorkin et al. 1997;Zhang et al. 2002), although there is substantial controversy over the extent of this effect (Leem and Bove 2002). Following nerve injury, however, it is in agreement that TNF-␣ can further sensitize neurons and increase the rate of firing from those neurons that are already ongoing Schafers et al. 2003). ...
subgroup of inflamed C-fiber axons in a α CCL2 has similar excitatory effects to TNF-You might find this additional info useful... 56 articles, 17 of which can be accessed free at: This article cites http://jn.physiology.org/content/106/6/2838.full.html#ref-list-1 including high resolution figures, can be found at: Updated information and services http://jn.physiology.org/content/106/6/2838.full.html can be found at: Journal of Neurophysiology about Additional material and information http://www.the-aps.org/publications/jn This infomation is current as of January 10, 2012.
... It has been demonstrated that herniated disc tissues release IL-1b, which affects the somatosen-sory neural response at the dorsal root level [5]. Previous studies have also shown that TNF-a in the nucleus pulposus plays an important role in radicular pain and that sensory neurons display increased sensitivity to TNF-a in a rat CCD model [6,7]. ...
Dorsal root ganglia (DRG) are vulnerable to physical injury of the intervertebral foramen, and chronic compression of the DRG (CCD) an result in nerve root damage with persistent morbidity. The purpose of this study was to evaluate the effects of low level laser therapy (LLLT) on the DRG in a CCD model and to determine the mechanisms underlying these effects. CCD rats had L-shaped stainless-steel rods inserted into the fourth and fifth lumbar intervertebral foramen, and the rats were then subjected to 0 or 8 J/cm2 LLLT for 8 consecutive days following CCD surgery. Pain and heat stimuli were applied to test for hyperalgesia following CCD. The levels of TNF-α, IL-1β and growth-associated protein-43 (GAP-43) messenger RNA (mRNA) expression were measured via real-time PCR, and protein expression levels were analyzed through immunohistochemical analyses. Our data indicate that LLLT significantly decreased the tolerable sensitivity to pain and heat stimuli in the CCD groups. The expression levels of the pro-inflammatory cytokines TNF-α and IL-1β were increased following CCD, and we found that these increases could be reduced by the application of LLLT. Furthermore, the expression of GAP-43 was enhanced by LLLT. In conclusion, LLLT was able to enhance neural regeneration in rats following CCD and improve rat ambulatory behavior. The therapeutic effects of LLLT on the DRG during CCD may be exerted through suppression of the inflammatory response and induction of neuronal repair genes. These results suggest potential clinical applications for LLLT in the treatment of compression-induced neuronal disorders.
... The cells in the nucleus pulposus can produce several cytokines [23,24] including TNF-a which is suggested to be a factor of importance in the pathophysiology of disc herniation and sciatic pain and has, e.g. been shown to increase neuronal excitability in primary nociceptive neurons when applied locally [25]. ...
Purpose
To investigate the effects on evoked thalamic neuronal activity of application of notochordal cells and chondrocyte-like cells derived from nucleus pulposus (NP) onto a dorsal root ganglion (DRG) and to compare these effects with a previously reported increased thalamic activity induced by NP.
Methods
Nucleus pulposus was harvested from tail discs of adult rats and the disc cells were separated into two cell populations, notochordal cells and chondrocyte-like cells. The two cell populations were applied separately, or in combination, to the L4 DRG of anaesthetised female Sprague–Dawley rats during acute electrophysiological experiments. In control experiments, cell suspension medium was applied on the DRG. Recordings from the contralateral thalamus were sampled for 40 min while electrically stimulating the ipsilateral sciatic nerve at above Aδ-fibre thresholds.
Results
Application of notochordal cells resulted in a decrease in evoked thalamic activity within 10 min while chondrocyte-like cells did not induce any changes during the 40 min of recording. The difference in evoked thalamic activity 40 min after notochordal and chondrocyte-like cell application, respectively, was statistically significant. Neither an increased concentration of chondrocyte-like cells alone nor a combination of the two cell populations induced any changes in thalamic activity.
Conclusions
Separate exposure of the DRG to the two NP-derived cell populations induced different effects on evoked thalamic activity, but none of the tested cell samples induced an increase in neuronal activity similar to that previously observed with NP. This indicates a high complexity of the interaction between NP and nervous tissue.
... For example, TNFα not only induces transcriptional regulation of down-stream inflammatory mediators, such as induction of IL-1β, IL-6 and Nuclear Factor-B in neurons and Schwann cells (Cunha et al.,2005;Lee et al.,2009;Watkins et al.,1995), but also has a rapid sensitizing effect on primary afferent neurons. TNFα promotes heat-induced CGRP release from nociceptor terminals in skin (Opree and Kress,2000), lowers activation threshold in Aβ-and C-fibers (Junger and Sorkin,2000;Liu et al.,2002;Schäfers et al., 2003a;Zhang et al.,2002), sensitizes transient receptor potential vanilloid receptor 1 (TRPV1) (Nicol et al.,1997) and enhances TTX-resistant sodium currents in primary sensory neurons (Jin and Gereau,2006). In addition to inducing the synthesis of several sensitizers of nociceptors, IL-1β also directly activates peripheral nociceptors. ...
Systemic injection of lipopolysaccharide (LPS) induces a robust immune response as well as thermal and mechanical hyperalgesia. Spinal and peripheral glial cells have been implicated as important mediators in this hyperalgesia but the specific contributions of microglia versus astrocytes are not entirely clear. To better define these mechanisms, this study examined the febrile response, nociceptive sensitivity, glial cell reactivity and cytokine production in the dorsal root ganglion (DRG) and spinal cord in rats following systemic treatment with LPS and the effects of minocycline in countering these responses. Intraperitoneal LPS injection resulted in an increase in core body temperature and produced hyperalgesia to heat and mechanical stimuli. Western blot studies revealed increased expression of microgial cell, macrophage and satellite cell markers in DRG and microglial and astrocyte markers in spinal cord following LPS treatment. Real-time RT-PCR indicated that LPS treatment increased cytokine mRNA expression levels in both the DRG and the spinal cord. Minocycline suppressed all LPS-induced behavioral effects but not the febrile response. Moreover, minocycline prevented LPS-induced microglia/macrophage activation and cytokine responses in spinal cord and DRG, but did not affect the activation of astrocytes/satellite cells. These data demonstrate that LPS-induced changes in nociceptive sensitivity are likely mediated by activation of microglial cells and/or macrophages in the spinal cord and DRG.
... The time course of the nociceptive behavior after nerve injury and the reduced upregulation of TNFa, MCP-1/CCL2, and IL-16 in the DRG of SNS-IKKb -/mice were compatible with this idea. For TNFa and MCP-1/CCL2, pronociceptive effects have been extensively studied previously (see Liu et al, 31 Opree and Kress, 36 Parada et al,37 Shafers et al, 42 and Xu et al 56 for TNFa and see de jong et al, 9 Jung et al, 20 Thacker et al, 52 and White et al 55 for CCL2). The release of TNFa and MCP-1 increases neurogenic inflamma-tion and neuronal excitability by autocrine stimulation of the respective receptors, which are expressed on subsets of primary sensory neurons in the DRG, particularly in models of ongoing nociception, 3,8,22,55 and anti-TNFadirected treatments strongly reduce neuropathic pain in animal models. ...
Unlabelled:
Inhibitor kappa B kinase (IKK)-mediated nuclear factor-kappa B (NF-κB) activation is a major pathway for transcriptional control of various pro-inflammatory factors. We here assessed whether activation of this pathway specifically in primary nociceptive neurons of the dorsal root ganglia (DRG) contributes to the development of nociceptive hypersensitivity. Mice carrying a cre-loxP-mediated deletion of inhibitor kappa B kinase beta (IKKβ) in DRG neurons were protected from nerve injury-evoked allodynia and hyperalgesia. This effect was mimicked by systemic treatment with an IKKβ inhibitor but was not observed upon specific inhibition of IKKβ in the spinal cord, suggesting a specific role of IKKβ in the peripheral neurons. The deletion of IKKβ in DRG neurons did not affect constitutive neuronal NF-κB activity, but reduced nerve injury-evoked NF-κB stimulation in the DRG and was associated with reduced upregulation of interleukin-16, monocyte chemoattractant protein-1/chemokine (CC motif) ligand 2 (MCP-1/CCL2), and tumor necrosis factor alpha (TNFα) in the DRG. These cytokines evoked a rapid rise of intracellular calcium in subsets of primary DRG neurons. The results suggest that IKKβ-mediated NF-κB stimulation in injured primary sensory neurons promotes cytokine and chemokine production and contributes thereby to the development of chronic pain.
Perspective:
Inhibitors of IKK that do not pass the blood-brain barrier and act only in the periphery might be useful for reduction of the pro-inflammatory response in peripheral DRG neurons and reduce thereby nerve injury-evoked pain without affecting neuroprotective effects of NF-κB in the central nervous system.
... al. have demonstrated TNF-α modulation of sympathetic neuron calcium currents. 23,24 These two studies highlight direct effects of TNF-α on neurons that are independent of downstream inflammation and mediator expression. We postulate that through similar intracellular mechanisms, prolonged TNF-α exposure can result in a desensitized state in olfactory receptor neurons. ...
Background:
Despite the significant health impact of olfactory loss in chronic rhinosinusitis (CRS), the underlying pathophysiology is incompletely understood. A transgenic mouse model of olfactory inflammation induced by tumor necrosis factor-alpha (TNF-α) has provided new insights into the cellular and molecular basis of inflammatory olfactory loss. Here, we utilize systemic corticosteroids to suppress downstream cytokine expression, in order to study the direct role of TNF-α in CRS-associated olfactory dysfunction.
Methods:
Transgenic mice were induced to express TNF-α in the olfactory epithelium for 6 weeks. In a subset of mice, 1 mg/kg prednisolone was administered concurrently to inhibit downstream inflammatory responses. The olfactory epithelium (OE) was analyzed by histology and electro-olfactogram (EOG) recordings.
Results:
Treatment with prednisolone successfully prevented inflammatory infiltration over significant regions of the OE. In areas where significant subepithelial inflammation was present, a corresponding loss of olfactory neurons was observed. In contrast, areas without major inflammatory changes had normal olfactory neuron layers, despite chronic local expression of TNF-α. Prednisolone partially reversed the complete loss of olfaction in the mouse model, preserving odorant responses that were significantly diminished compared to controls, but not absent.
Conclusions:
The addition of prednisolone to the transgenic model of olfactory inflammation isolates the direct effects of induced TNF-α expression on the OE. The finding that prednisolone treatment prevents neuronal loss in some regions of the OE suggests that TNF-α does not directly cause neuronal apoptosis--rather, that subepithelial inflammation or other downstream mediators may be responsible. At the same time, EOG results imply that TNF-α directly causes physiologic dysfunction of olfactory neurons, independent of the inflammatory state. An understanding of the role of TNF-α and other inflammatory cytokines may suggest novel therapeutic strategies for CRS-associated olfactory loss.
... The role of TNF-␣ in pain mechanisms has been investigated extensively. For example, the direct exposure of uninjured DRG neurons to TNF-␣ can lead to the development of ongoing activity (Leem and Bove 2002;Liu et al. 2002;Sorkin et al. 1997;Zhang et al. 2002), although there is substantial controversy over the extent of this effect (Leem and Bove 2002). Following nerve injury, however, it is in agreement that TNF-␣ can further sensitize neurons and increase the rate of firing from those neurons that are already ongoing Schafers et al. 2003). ...
... Soluble TNFα induces hyperalgesia in normal rats [43] and increases allodynia and spontaneous pain behavior in nerve injured rats [38], an effect that correlates with increased expression of p38 MAP kinase in the DRG [40]. Application of soluble TNFα to the acutely dissociated neurons from either normal DRG or chronically compressed DRG increases the sensitivity of those cells to depolarization [26], enhances tetrodotoxin resistant sodium currents [22] and increases ectopic activity in sensory neurons [39]. Local perfusion of DRG with sTNFα induces cutaneous hyperalgesia [52]. ...
Neuropathic pain is accompanied by neuroimmune activation in dorsal horn of spinal cord. We have observed that in animal models this activation is characterized by an increased expression of transmembrane tumor necrosis factor α (mTNFα) without the release of soluble tumor necrosis factor α (sTNFα). Herein we report that the pain-related neurotransmitter peptide substance P (SP) increases the expression of mTNFα without the release of sTNFα from primary microglial cells. We modeled this interaction using an immortalized microglial cell line; exposure of these cells to SP also resulted in the increased expression of mTNFα but without any increase in the expression of the TNF-cleaving enzyme (TACE) and no release of sTNFα. In order to evaluate the biological function of uncleaved mTNFα, we transfected COS-7 cells with a mutant full-length TNFα construct resistant to cleavage by TACE. Coculture of COS-7 cells expressing the mutant TNFα with microglial cells led to microglial cell activation indicated by increased OX42 immunoreactivity and release of macrophage chemoattractant peptide 1 (CCL2) by direct cell-cell contact. These results suggest a novel pathway through which the release of SP by primary afferents activates microglial expression of mTNFα, establishing a feed-forward loop that may contribute to the establishment of chronic pain.
... Treatment of the rat paw with these cytokines reduces nociceptive thresholds and produces nociceptive hypersensitivity (Sachs et al., 2002). Acute treatment of DRG with TNFα and IL-1b increases intracellular Ca 2+ transients in neurons (Pollock et al., 2002), depolarizes membrane potentials, reduces threshold currents for action potentials and elicits spontaneous firing in DRG neurons (Liu et al., 2002;Schafers et al., 2003;Takeda et al., 2007). The mechanisms underlying these direct actions of TNFα and IL-1b on sensory neurons include a reduction of voltage-dependent K + currents (Diem et al., 2001;Takeda et al., 2008a) and an increase in Ca 2+ -dependent inward currents (Pollock et al., 2002). ...
It has been known for some time that the somata of neurons in sensory ganglia respond to electrical or chemical stimulation and release transmitters in a Ca2+-dependent manner. The function of the somatic release has not been well delineated. A unique characteristic of the ganglia is that each neuronal soma is tightly enwrapped by satellite glial cells (SGCs). The somatic membrane of a sensory neuron rarely makes synaptic contact with another neuron. As a result, the influence of somatic release on the activity of adjacent neurons is likely to be indirect and/or slow. Recent studies of neuron-SGC interactions have demonstrated that ATP released from the somata of dorsal root ganglion neurons activates SGCs. They in turn exert complex excitatory and inhibitory modulation of neuronal activity. Thus, SGCs are actively involved in the processing of afferent information. In this review, we summarize our understanding of bidirectional communication between neuronal somata and SGCs in sensory ganglia and its possible role in afferent signaling under normal and injurious conditions. The participation of purinergic receptors is emphasized because of their dominant roles in the communication.
... TNF-a could evoke action potentials in nociception neurons when applied topically to peripheral axons in vivo [4,36]. Administration of TNFa to DRG cells modulates the ion channel of nociceptive neurons [37] and evokes excitation of the neurons [38,39] and pain-related behavior [40,41]. TNF-a was also reported to increase activity of spinal dorsal horn neurons [42,12] and the antibody to TNF-a showed the opposite effect [43]. ...
Knowledge about the physiologic and pathophysiologic roles of tumor necrosis factor-alpha (TNF-alpha) in acute myocardial ischemia/infarction is still very limited. Evidence implies that TNF-alpha is involved in neural activity including nociception in peripheral and central nervous system. Current study was designed to examine the association of change in TNF-alpha and its mRNA in upper thoracic dorsal root ganglia and spinal cord (T1-T5) during acute myocardial ischemia/infarction induced by coronary artery occlusion (CAO) in rats. The experiment was performed using immunohistochemistry, enzyme immunoassay, in situ hybridization and real time reverse transcription-polymerase chain reaction techniques. At 0.5h, 1h, 3h and 6h of acute myocardial ischemia/infarction, TNF-alpha was mainly up-regulated in a sub-population of small and medium neurons and satellite cells in the dorsal root ganglia (DRG) and spinal neurons, mainly in laminae I, II and V, VI of the spinal dorsal horn of upper thoracic segments. The up-regulation of TNF-alpha mRNA was observed at 30min of CAO, which was statistically significant, compared with the control and the sham surgery groups (P<0.01). The TNF-alpha mRNA was located in the satellite cells and afferent neurons of the DRG and spinal neurons, located mainly in laminae II-VI. The findings indicate an association of up-regulation of TNF-alpha in DRG and spinal cord with acute myocardial ischemia/infarction, suggesting that TNF-alpha may be associated with the nociception initiated by acute myocardial ischemia/infarction, while the pathophysiological role needs to be studied.
... Whole-cell perforated patch-clamp recordings in cultured rat hippocampal neurons showed that long-term treatment with TNF-␣ increases Ca 2+ current density through L-type voltage-dependent channels, but it decreases currents induced by glutamate, NMDA, AMPA and kainate. Neurons pretreated with TNF-␣ exhibited increased intracellular Ca 2+ concentrations following membrane depolarization, but reduced intracellular Ca 2+ concentration in response to excitatory amino acids [80,81] . Inflammatory mediators such as nitric oxide and TNF-␣ are released from glia-enriched mix culture in response to hypoxia/reoxygenation [82,83] . ...
Cytokines are highly inducible, secretory proteins that mediate intercellular communication in the immune system. They are grouped in several protein families, namely tumor necrosis factors, interleukins, interferons and colony-stimulating factors. In recent years, evidence has elucidated that some of these proteins as well as their receptors are also produced in the central nervous system (CNS) by specific neural cell lineages under physiological and pathological conditions. Cytokines regulate a variety of processes in the CNS, including neurotransmission. The current data let us to suggest that cytokines play an important role in the regulation of both excitatory and inhibitory neurotransmission in the CNS. This knowledge could be fundamental for the proposal of new therapeutic approaches to neurological and psychiatric disorders.
Objective: Reno-renal reflexes are disturbed in cardiovascular and hypertensive conditions when elevated levels of pro-inflammatory mediators/cytokines are present within the kidney. We hypothesised that exogenously administered inflammatory cytokines TNF-α and IL-1β modulate the renal sympatho-excitatory response to chemical stimulation of renal pelvic sensory nerves.
Methods: In anaesthetised rats, intrarenal pelvic infusions of vehicle (0.9% sodium chloride (NaCl)), TNF-α (500 and 1000 ng/kg) and IL-1β (1000 ng/kg) were maintained for 30 minutes before chemical activation of renal pelvic sensory receptors was performed using randomized intrarenal pelvic infusions of hypertonic NaCl, potassium chloride (KCl), bradykinin, adenosine and capsaicin.
Results: The increase in renal sympathetic nerve activity (RSNA) in response to intrarenal pelvic hypertonic NaCl was enhanced during intrapelvic TNF-α (1000 ng/kg) and IL-1β infusions by almost 800% above vehicle with minimal changes in mean arterial pressure (MAP) and heart rate (HR). Similarly, the RSNA response to intrarenal pelvic adenosine in the presence of TNF-α (500 ng/kg), but not IL-1β, was almost 200% above vehicle but neither MAP nor HR were changed. There was a blunted sympatho-excitatory response to intrapelvic bradykinin in the presence of TNF-α (1000 ng/kg), but not IL-1β, by almost 80% below vehicle, again without effect on either MAP or HR.
Conclusion: The renal sympatho-excitatory response to renal pelvic chemoreceptor stimulation is modulated by exogenous TNF-α and IL-1β. This suggests that inflammatory mediators within the kidney can play a significant role in modulating the renal afferent nerve-mediated sympatho-excitatory response.
Satellite glial cells (SGCs) are among the most abundant non-neuronal cells in dorsal root ganglia (DRGs) and closely envelop sensory neurons that detect painful stimuli. However, little is still known about their homeostatic activities and their contribution to pain. Using single-cell RNA sequencing (scRNA-seq), we were able to obtain a unique transcriptional profile for SGCs. We found enriched expression of the tissue inhibitor metalloproteinase 3 (TIMP3) and other metalloproteinases in SGCs. Small interfering RNA and neutralizing antibody experiments revealed that TIMP3 modulates somatosensory stimuli. TIMP3 expression decreased after paclitaxel treatment, and its rescue by delivery of a recombinant TIMP3 protein reversed and prevented paclitaxel-induced pain. We also established that paclitaxel directly impacts metalloproteinase signaling in cultured SGCs, which may be used to identify potential new treatments for pain. Therefore, our results reveal a metalloproteinase signaling pathway in SGCs for proper processing of somatosensory stimuli and potential discovery of novel pain treatments.
There is burgeoning interest in the interaction between the immune and nervous systems. Pain is mediated by primary sensory neurons (nociceptors) that can respond to a variety of thermal, mechanical and chemical signals. Cytokines are now recognized as important mediators of inflammatory pain. They can induce nociceptor sensitization indirectly via mediators, wherein neurons become primed and thus become more responsive to stimulation; alternatively, there is also evidence that cytokines can directly activate neurons via their specific receptors present on the neuronal cells. We review here the evidence for and against these respective mechanisms, focusing on arthritis and inflammatory skin models. A number of striking inconsistencies amongst the conclusions made in the literature are highlighted and discussed.
Les douleurs neuropathiques sont associées dans la moelle épinière à des altérations neuronales et gliales. Ces cellules libèrent des médiateurs inflammatoires comme l'interleukine-6, jouant un rôle pro-nociceptif et qui active principalement la voie JAK/STAT3. Dans ce contexte, nous avons étudié l'implication éventuelle de la voie dans ce type de douleurs. Dans différent modèles de lésions de nerf périphérique chez le rat, la voie JAK/STAT3 spinale est activée de façon précoce et prolongée, surtout dans la microglie. L'inhibition de cette voie par un agent pharmacologique a démontré son implication dans la genèse de l'hypersensibilité douloureuse. Pour inhiber plus spécifiquement la voie JAK/STAT3, nous avons injecté dans la corne dorsale de la moelle épinière un vecteur lentiviral à fort tropisme glial (LV-SOCS3). L'injection préventive de ce vecteur chez des rats neuropathiques diminue l'expression d'IL-6, ATF3 et MCP-1 et réduit fortement l'hypersensibilité mécanique.
Neuropathic pain is a chronic disease caused by lesion of dysfunction of the central or peripheral nervous system, which affects a midrange estimate of 3% of the general population. It is a major public health problem because available treatments, which have only empirical bases, are of limited efficacy and are most often endowed with poorly tolerated side effects. Animal models are mandatory for better knowledge of underlying physiopathological mechanisms and development of really efficient and better tolerated rational therapies. Clinical observations allowed the design of numerous animal models (mainly in rats and mice), with neuropathic pain-like symptoms, particularly hyperalgesia and allodynia, which respond to alleviating drugs used in patients such as antidepressants, anticonvulsants and topical anesthetics. This review article describes the in vivo models that consist of peripheral nerve section or ligation, laser-induced nerve injury, spinal cord lesion, treatments with neurotoxic drugs (notably anticancer and antiretroviral drugs), among others. However, to date, none of these models really mimics human neuropathic pain, especially because the psychoaffective and cognitive components of human pain are difficult to assess using animal models. Recent design of innovative paradigms allowing assessment of not only hyperalgesia and allodynia, but also associated emotional, affective and cognitive dysfunctions might open new avenues for drug discovery, which is particularly needed for neuropathic pain treatment.
Intraperitoneal infection with Taenia crassiceps cysticerci in mice alters several behaviors, including sexual, aggressive, and cognitive function. Cytokines and their receptors are produced in the central nervous system (CNS) by specific neural cell lineages under physiological and pathological conditions, regulating such processes as neurotransmission. This study is aimed to determine the expression patterns of cytokines in various areas of the brain in normal and T. crassiceps-infected mice in both genders and correlate them with the pathology of the CNS and parasite counts. IL-4, IFN-γ, and TNF-α levels in the hippocampus and olfactory bulb increased significantly in infected male mice, but IL-6 was downregulated in these regions in female mice. IL-1β expression in the hippocampus was unaffected by infection in either gender. Our novel findings demonstrate a clear gender-associated pattern of cytokine expression in specific areas of the brain in mammals that parasitic infection can alter. Thus, we hypothesize that intraperitoneal infection is sensed by the CNS of the host, wherein cytokines are important messengers in the host-parasite neuroimmunoendocrine network.
Pain is usually elicited by the activation of specific visceral or non-visceral (somatic) nociceptors (“nociceptive pain”). However, it may also result from injury to or dysfunction of peripheral sensory nerve fibers or from damage to or dysfunction of the central nervous system itself (“neuropathic pain”). Although acute nociceptive pain fulfills a warning role regarding possible systemic injury, chronic and/or neuropathic pain may be maladaptive.
Cancer-related neuropathic pain generally results from compression irritation, or infiltration of nerves by the tumor, nerve trauma from operative procedures, or neuropathic pain related to the treatment of cancer itself. Management of neuropathic pain may include the use of opioids, nonsteroidal anti-inflammatory drugs (NSAIDs), antidepressants, anticonvulsants, local anesthetics, and other adjuvant medications. Intractable neuropathic pain may require the use of intraspinal delivery of medication or anesthetic and neurosurgical procedures.
The purpose of this article is to provide a global account of the mechanisms involved in the development of neuropathic pain. Particular attention is focused on cellular aspects and on the consequences of peripheral nervous system (PNS) injury. Further, therapies used for the management of cancer-related neuropathic pain are reviewed; new therapeutic approaches based on recent findings from basic research are discussed. An improved understanding of the origins of neuropathic pain should facilitate the development of novel strategies for effective treatment of cancer-related neuropathic pain.
Communication between neurons and glia in the dorsal root ganglia (DRG) and the central nervous system (CNS) is critical for nociception. Both Glial activation and proinflammatory cytokine induction underlie this communication. We investigated whether satellite glial cell (SGCs) and tumor necrosis factor alpha (TNF-α) activation in DRG participate in a 2,4,6-trinitrobenzene sulfonic acid (TNBS)-induced rat model of visceral hyperalgesia. In TNBS-treated rats, TNF-α expression increased in DRG and was colocalized to SGCs enveloping a given neuron. These SGCs were activated as visualized under electron microscopy: they had more elongated processes projecting into the connective tissue space and more gap junctions. When nerves attached to DRG (L6-S1) were stimulated with a series of electrical stimulations, TNF-α were released from DRG in TNBS treated animals compared to controls. Using a current clamp, we noted that exogenous TNF-α (2.5 ng/ml) increased DRG neuron activity and visceral pain behavioral responses were reversed by intrathecal administration of anti-TNF-α (10μg/kg per day). Based on our findings, TNF-α and SGC activation in neuron-glial communication of DRG and are critical in inflammatory visceral hyperalgesia.
Le rôle du TNF-α dans la genèse de la composante chimique de la sciatique discale est largement suggéré ; en effet, le TNF-α est impliqué dans la physiopathologie des modèles animaux de souffrance nerveuse et semble pouvoir sensibiliser une racine nerveuse à la douleur lorsque celle-ci a préalablement été soumise à une déformation mécanique ; du TNF-α a été identifié dans le nucleus pulposus et dans les cellules de Schwann dans des modèles animaux et la production locale de TNF-α endogène semble survenir à un stade précoce du processus pathologique ; l'application de TNF-α exogène induit des anomalies électrophysiologiques, histologiques et comportementales similaires à celles observées, après application de nucleus pulposus et ces effets sont plus nets en cas de compression mécanique associée ; l'utilisation de molécules inhibant le TNF-α permet de réduire ou d'inhiber les anomalies observées dans les modèles animaux ; d'autres cytokines pourraient être impliquées, comme le suggère l'action inhibitrice puissante de produits tels que la doxycycline. Deux études ouvertes ont suggéré, chez l'homme, une efficacité spectaculaire des anti-TNF-α au cours de la sciatique par hernie discale, mais la première étude contrôlée n'a pas confirmé ces données. De nombreuses questions sont ainsi posées quant à la justification de l'utilisation des anti-TNF-α dans cette pathologie, et d'autres essais contrôlés, randomisés doivent être menés.
Peripheral inflammation or injury can often result in enhanced transmission of sensory input through the spinal cord dorsal horn, this is termed central sensitization. This phenomenon, which results in pain responses from uninjured tissue, is a major clinical problem. Pharmacologic treatments must address neurochemical events in the spinal cord that contribute to central sensitization and resultant pain. This study reviews injury-induced glutamate receptor activation, changes in Ca2+ flux, and induction of calcium-dependent second messenger cascades occurring within central nociceptive afferent terminals and spinal nociceptive neurons in an attempt to explain and predict some of the relevant clinical pharmacology.
As sciatica and low back pain are among the most common medical complaints, many studies have duplicated these conditions in animals. Chronic compression of the dorsal root ganglion (CCD) is one of these models. The surgery is simple: after exposing the L4/L5 intervertebral foramina, stainless steel rods are implanted unilaterally, one rod for each vertebra, to chronically compress the lumbar dorsal root ganglion (DRG). Then, CCD can be used to simulate the clinical conditions caused by stenosis, such as a laterally herniated disc or foraminal stenosis. As the intraforaminal implantation of a rod results in neuronal somal hyperexcitability and spontaneous action potentials associated with hyperalgesia, spontaneous pain, and mechanical allodynia, CCD provides an animal model that mimics radicular pain in humans. This review concerns the mechanisms of neuronal hyperexcitability, focusing on various patterns of spontaneous discharge including one possible pain signal for mechanical allodynia - evoked bursting. Also, new data regarding its significant property of maintaining peripheral input are also discussed. Investigations using this animal model will enhance our understanding of the neural mechanisms for low back pain and sciatica. Furthermore, the peripheral location of the DRG facilitates its use as a locus for controlling pain with minimal central effects, in the hope of ultimately uncovering analgesics that block neuropathic pain without influencing physiological pain.
To evaluate the efficacy of a single direct epidural injection of tumor necrosis factor (TNF)-α inhibitor to reduce the pathological changes in nerve fiber injuries in a rat model of chronic compression of the dorsal root ganglion (CCD).
A surgical procedure for CCD was performed in 17 adult male F-344 rats. The effects of the epidural TNF-α inhibitors on CCD-induced pathological changes were investigated. Three groups of rats (n = 17) were used: (1) CCD + saline (n = 4), (2) CCD + triamcinolone (n = 5), and (3) CCD + TNF-α inhibitors (n = 8). Their dorsal root ganglia and nerve roots were removed on postoperative day 14. The intraneural edema, demyelination, and Wallerian degeneration of all 17 rats were scored pathologically.
The pathology scores of the rats in the TNF-α inhibitor treatment group (1.38 ± 0.74) indicated a mild degree of intraneural edema compared to the saline treatment group (2.25 ± 0.50, p = 0.041). In addition, rats in the TNF-α inhibitor treatment group (2.13 ± 0.35) had a mild degree of demyelination compared to the saline treatment group (2.75 ± 0.50, p = 0.038) and the triamcinolone treatment group (2.80 ± 0.45, p = 0.019). The differences in the pathology scores for Wallerian degeneration were not statistically significant in all three study groups (p = 0.658).
The epidural injection of a TNF-α inhibitor was more effective than a placebo and comparable to triamcinolone in reducing pathological nerve injury progression.
Inflammatory and immune responses following nerve injury have been shown to play an important role in neuropathic pain. Lipoxins are endogenous lipoxygenase-derived eicosanoids performing protective roles in a range of pathophysiologic processes. Here, we examined the effects of intrathecal lipoxinA4 (LXA4) on NF-κB activation and pro-inflammatory cytokine (TNF-α, IL-1β and IL-6) expression in dorsal root ganglia (DRG) following chronic compression of DRG (CCD), a model of neuropathic pain. Daily intrathecal injection of vehicle or LXA4 (10 ng or 100 ng) was performed for three successive days post-CCD. CCD induced both mechanical allodynia and thermal hyperalgesia, and increased the expression of TNF-α, IL-1β, IL-6 and NF-κB. Intrathecal injection of LXA4 prevented the development of neuropathic pain and inhibited NF-κB activation and pro-inflammatory cytokine upregulation in a dose-dependent manner. In this study, we have shown the strong protective effect of intrathecal LXA4 on the development of nociceptive behaviors induced by CCD and that these effects might be associated with its anti-inflammatory and pro-resolution properties.
Tumor necrosis factor-α (TNFα) is a proinflammatory cytokine that contributes to inflammatory and neuropathic pain. The mechanism by which TNFα modulates synaptic transmission in mouse substantia gelatinosa was studied using whole-cell patch clamp and immunohistochemistry. TNFα was confirmed to significantly increase the frequency of spontaneous EPSCs (sEPSCs) in spinal neurons and to also produce a robust decrease in the frequency of spontaneous IPSCs (sIPSCs). The enhancement of excitatory synaptic transmission by TNFα is in fact observed to be dependent on the suppression of sIPSCs, or disinhibition, in that blockade of inhibitory synaptic transmission prevents the effect of TNFα on sEPSCs but not vice versa. TNFα-induced inhibition of sIPSCs was blocked by neutralizing antibodies to TNF receptor 1 (TNFR1) but not to TNFR2 and was abolished by the p38 mitogen-activated protein kinase inhibitor SB202190 [4-(4-fluorophenyl)-2-(4-hydroxyphenyl)-5-(4-pyridyl)1H-imidazole]. TNFα rapidly inhibited spontaneous action potentials in GABAergic neurons identified in transgenic mice expressing enhanced green fluorescent protein controlled by the GAD67 promoter. This inhibitory effect was also blocked by intracellular delivery of SB202190 to the targeted cells. The inhibition of spontaneous activity in GABAergic neurons by TNFα is shown as mediated by a reduction in the hyperpolarization-activated cation current (Ih). These results suggest a novel TNFα-TNFR1-p38 pathway in spinal GABAergic neurons that may contribute to the development of neuropathic and inflammatory pain by TNFα.
Cytokines are pluripotent soluble proteins secreted by immune and glial cells and are key elements in the induction and maintenance of pain. They are categorized as pro-inflammatory cytokines, which are mostly algesic, and anti-inflammatory cytokines, which have analgesic properties. Progress has been made in understanding the mechanisms underlying the action of cytokines in pain. To date, several direct and indirect pathways are known that link cytokines with nociception or hyperalgesia. Cytokines may act via specific cytokine receptors inducing downstream signal transduction cascades, which then modulate the function of other receptors like the ionotropic glutamate receptor, the transient vanilloid receptors, or sodium channels. This receptor activation, either through amplification of the inflammatory reaction, or through direct modulation of ion channel currents, then results in pain sensation. Following up on results from animal experiments, cytokine profiles have recently been investigated in human pain states. An imbalance of pro- and anti-inflammatory cytokine expression may be of importance for individual pain susceptibility. Individual cytokine profiles may be of diagnostic importance in chronic pain states, and, in the future, might guide the choice of treatment.
Little is known about whether peripheral nerve injury during the early postnatal period modulates synaptic efficacy in the immature superficial dorsal horn (SDH) of the spinal cord, or whether the neonatal SDH network is sensitive to the proinflammatory cytokine TNFalpha under neuropathic conditions. Thus we examined the effects of TNFalpha on synaptic transmission and intrinsic membrane excitability in developing rat SDH neurons in the absence or presence of sciatic nerve damage.
The spared nerve injury (SNI) model of peripheral neuropathy at postnatal day (P)6 failed to significantly alter miniature excitatory (mEPSCs) or inhibitory (mIPSCs) postsynaptic currents in SDH neurons at P9-11. However, SNI did alter the sensitivity of excitatory synapses in the immature SDH to TNFalpha. While TNFalpha failed to influence mEPSCs or mIPSCs in slices from sham-operated controls, it significantly increased mEPSC frequency and amplitude following SNI without modulating synaptic inhibition onto the same neurons. This was accompanied by a significant decrease in the paired-pulse ratio of evoked EPSCs, suggesting TNFalpha increases the probability of glutamate release in the SDH under neuropathic conditions. Similarly, while SNI alone did not alter action potential (AP) threshold or rheobase in SDH neurons at this age, TNFalpha significantly decreased AP threshold and rheobase in the SNI group but not in sham-operated littermates. However, unlike the adult, the expression of TNFalpha in the immature dorsal horn was not significantly elevated during the first week following the SNI.
Developing SDH neurons become susceptible to regulation by TNFalpha following peripheral nerve injury in the neonate. This may include both a greater efficacy of glutamatergic synapses as well as an increase in the intrinsic excitability of immature dorsal horn neurons. However, neonatal sciatic nerve damage alone did not significantly modulate synaptic transmission or neuronal excitability in the SDH, which could reflect a relatively weak expression of TNFalpha in the injured spinal cord at early ages. The above data suggest that although the sensitivity of the SDH network to proinflammatory cytokines after nerve injury is present from the first days of life, the profile of spinal cytokine expression under neuropathic conditions may be highly age-dependent.
The effect of recombinant human tumor necrosis factor-alpha (rhTNF) on calcium currents of cultured neurons from neonatal rat superior cervical ganglia (SCG) was studied using whole-cell patch-clamp technique. We found that rhTNF-treated SCG neurons exhibited increased calcium current density without significant alteration in the steady-state parameters of activation and availability. The fraction of the current sensitive to dihydropyridines and omega-conotoxin also remained unchanged. Recovery from slow inactivation of the current, but not recovery from fast inactivation, was prolonged in rhTNF-treated cells when compared to that of control cells. We conclude that immune peptides such as rhTNF can alter cellular functions of sympathetic neurons via modulating ionic conductances. However, these changes observed in calcium currents of SCG neurons cannot account for the effect of rhTNF on norepinephrine secretion observed in a previous study. It is proposed that rhTNF exerts an additional effect at a later event in the exocytotic process.
Peripheral inflammation is characterized by heightened pain sensitivity. This hyperalgesia is the consequence of the release of inflammatory mediators, cytokines and growth factors. A key participant is the induction of the neurotrophin nerve growth factor (NGF) by interleukin-1β (IL-1β).
Tumour necrosis factor α (TNFα) has been shown both to produce hyperalgesia and to upregulate IL-1β. We have now examined whether the induction of TNFα in inflammatory lesions contributes to inflammatory sensory hypersensitivity by inducing IL-1β and NGF.
The intraplantar injection of complete Freund's adjuvant (CFA) in adult rats produced a localized inflammation of the hindpaw with a rapid (3 h) reduction in withdrawal time in the hot plate test and in the mechanical threshold for eliciting the flexion withdrawal reflex.
The CFA-induced inflammation resulted in significant elevation in the levels of TNFα, IL-1β and NGF in the inflamed paw. In the case of TNFα, an elevation was detected at 3 h, rose substantially at 6 h, peaked at 24 h and remained elevated at 5 days, with similar but smaller changes in the contralateral non-inflamed hindpaw. No increase in serum TNFα was detected at 24 h post CFA injection.
Intraplantar recombinant murine TNFα injections produce a short-lived (3–6 h) dose-dependent (50–500 ng) increase in thermal and mechanical sensitivity which was significantly attenuated by prior administration of anti-NGF antiserum.
Intraplantar TNFα (100–500 ng) also elevated at 6 but not 48 h the levels of IL-1β and NGF in the hindpaw.
A single injection of anti-TNFα antiserum, 1 h before the CFA, at a dose sufficient to reduce the effects of a 100 ng intraplantar injection of TNFα, significantly delayed the onset of the resultant inflammatory hyperalgesia and reduced IL-1β but not NGF levels measured at 24 h.
The elevation of TNFα in inflammation, by virtue of its capacity to induce IL-1β and NGF, may contribute to the initiation of inflammatory hyperalgesia.
Pain and hyperalgesia can occur when the dorsal root ganglion (DRG) and its roots are deformed mechanically in association with injuries or diseases of the spine. To evaluate the electrophysiological changes that contribute to this sensory pathology, intracellular recordings were obtained in vitro from DRGs that had received a chronic mechanical compression [chronic compression of DRG (CCD)]. The compression was produced by inserting L-shaped rods ipsilaterally into the intervertebral foramina, one at L(4) and the other at L(5) in rats 1-14 days before the recording. Control rats received a sham operation. Postoperatively, the threshold force applied by punctate stimulation of the plantar surface of the hind paw decreased significantly on the foot ipsilateral to the CCD (mechanical hyperalgesia) but changed little on the contralateral foot or on either foot for control rats. DRG somata were viewed through a microscope during recording and classified as small, medium, and large according to their diameters. CCD cells in each size category were more excitable than those of comparable size from control rats as judged by the significantly lowered threshold currents and action potential voltage thresholds. Spontaneous activity was recorded in 11% of all the CCD cells tested. The spontaneous activity and/or changes in both the threshold currents and action potential thresholds were observed as early as one day after injury. The association of cutaneous hyperalgesia with changes in the electrophysiological properties of DRG cells suggests a possible role for intrinsic alterations in the membrane properties of compressed DRG cells in the production and persistence of chronic pain after certain spinal injuries or pathologies of the spine.
Chronic compression of the dorsal root ganglion (CCD) was produced in adult rats by implanting a stainless steel rod unilaterally into the intervertebral foramen, one rod at L(4) and another at L(5). Two additional groups of rats received either a sham surgery or an acute injury consisting of a transient compression of the ganglion. Withdrawal of the hindpaw was used as evidence of a nocifensive response to mechanical and thermal stimulation of the plantar surface. In addition, extracellular electrophysiological recordings of spontaneous discharges were obtained from dorsal root fibers of formerly compressed ganglia using an in vitro nerve-DRG-dorsal root preparation. The mean threshold force of punctate indentation and the mean threshold temperature of heating required to elicit a 50% incidence of foot withdrawal ipsilateral to the CCD were significantly lower than preoperative values throughout the 35 days of postoperative testing. The number of foot withdrawals ipsilateral to the CCD during a 20-min contact with a temperature-controlled floor was significantly increased over preoperative values throughout postoperative testing when the floor was 4 degrees C (hyperalgesia) and, to a lesser extent, when it was 30 degrees C (spontaneous pain). Stroking the foot with a cotton wisp never elicited a reflex withdrawal before surgery but did so in most rats tested ipsilateral to the CCD during the first 2 postoperative weeks. In contrast, the CCD produced no changes in responses to mechanical or thermal stimuli on the contralateral foot. The sham operation and acute injury produced no change in behavior other than slight, mechanical hyperalgesia for approximately 1 day, ipsilateral to the acute injury. Ectopic spontaneous discharges generated within the chronically compressed ganglion and, occurring in the absence of blood-borne chemicals and without an intact sympathetic nervous system, were recorded from neurons with intact, conducting, myelinated or unmyelinated peripheral nerve fibers. The incidence of spontaneously active myelinated fibers was 8.61% for CCD rats versus 0.96% for previously nonsurgical rats. We hypothesize that a chronic compression of the dorsal root ganglion after certain injuries or diseases of the spine may produce, in neurons with intact axons, abnormal ectopic discharges that originate from the ganglion and potentially contribute to low back pain, sciatica, hyperalgesia, and tactile allodynia.
This study tested the hypothesis that the 17-kDa form of tumor necrosis factor-alpha is the pathophysiologic agent expressed by herniated nucleus pulposus in vivo that is primarily responsible for the histologic and behavioral manifestations of experimental sciatica associated with herniated lumbar discs.
The authors determined the molecular weight and concentration of active tumor necrosis factor-alpha in rat herniated disc and used exogenous tumor necrosis factor-alpha at the same molecular weight to study its neuropathologic effect on rat nerve root and dorsal root ganglion preparations in vivo.
Expressed by herniated nucleus pulposus in culture, tumor necrosis factor-alpha causes neuropathologic injury in nerve roots and neuropathic pain states in which mechanical allodynia is seen in response to peripheral stimuli.
Western blotting was used to identify the molecular weight of the operative tumor necrosis factor-alpha protein form, and measures of optical density were used for semiquantitative determination of concentration. Plastic-embedded nerve roots and dorsal root ganglion were used for neuropathologic evaluation, and von Frey stimulation was used to quantify mechanical allodynia.
The 17-kDa form of tumor necrosis factor-alpha is expressed by herniated nucleus pulposus at a concentration of approximately 0.48 ng per herniated rat lumbar disc. Exogenous tumor necrosis factor-alpha applied in vivo to rat nerve roots produced neuropathologic changes and behavior deficits that mimicked experimental studies with herniated nucleus pulposus applied to nerve roots.
The data reinforce other evidence that tumor necrosis factor-alpha is involved in mechanisms of neuropathic pain.
Study Design. This study tested the hypothesis that the 17-kDa form of tumor necrosis factor-alpha is the pathophysiologic agent expressed by herniated nucleus pulposus in vivo that is primarily responsible for the histologic and behavioral manifestations of experimental sciatica associated with herniated lumbar discs. Objective. The authors determined the molecular weight and concentration of active tumor necrosis factor-alpha in rat herniated disc and used exogenous tumor necrosis factor-alpha at the same molecular weight to study its neuropathologic effect on rat nerve root and dorsal root ganglion preparations in vivo. Summary of Background Data. Expressed by herniated nucleus pulposus in culture, tumor necrosis factor-alpha causes neuropathologic injury in nerve roots and neuropathic pain states in which mechanical allodynia is seen in response to peripheral stimuli. Methods. Western blotting was used to identify the molecular weight of the operative tumor necrosis factor-alpha protein form, and measures of optical density were used for semiquantitative determination of concentration. Plastic-embedded nerve roots and dorsal root ganglion were used for neuropathologic evaluation, and von Frey stimulation was used to quantify mechanical allodynia. Results. The 17-kDa form of tumor necrosis factor-alpha is expressed by herniated nucleus pulposus at a concentration of approximately 0.48 ng per herniated rat lumbar disc. Exogenous tumor necrosis factor-alpha applied in vivo to rat nerve roots produced neuropathologic changes and behavior deficits that mimicked experimental studies with herniated nucleus pulposus applied to nerve roots. Conclusions. The data reinforce other evidence that tumor necrosis factor-alpha is involved in mechanisms of neuropathic pain.
Chronic constriction injury (CCI) to peripheral nerve causes a painful neuropathy in association with a process of axonal degeneration and endoneural remodeling that involves macrophage recruitment and local increase in extracellular proteases and tumor necrosis factor alpha (TNF-α). Cell surface activation of TNF-α from its transmembrane precursor, as well as sequestration of TNF-α receptors II and I, is performed by the zinc-dependent endopeptidase family of matrix metalloproteinases (MMPs). Among TNF-α-converting MMPs, basal lamina degrading gelatinases are thought to play a role in sciatic nerve injury. In the present study, we determined the forms of TNF-α involved in the development of CCI neuropathy in rats, using Western blot analysis, and the temporal correlation of TNF-α and TNFRI protein profiles with gelatinases activity at the site of peripheral nerve injury. We observed two peaks in TNF-α protein during the first week of CCI that correspond to previously reported peaks in painful behavior. We propose that the first peak at 6 h post-CCI is due to the local expression of the cytotoxic transmembrane 26 kDa TNF-α protein released by resident Schwann cells, mast cells and macrophages. This peak in TNF-α protein expression corresponds to an increase in gelatinase B (MMP-9) activity, which is greatly upregulated as early as 3 h following CCI to rat sciatic nerve. The second peak occurs at 5 days post-CCI, and may represent TNF-α protein released by hematogenously recruited macrophages. This peak is marked by the increase in active soluble 17 kDa TNF-α and by gelatinase A (MMP-2) upregulation. These observations suggest that there is a pathogenic role for the TNF-α-converting function of MMP-2 in painful CCI neuropathy. We conclude that severe nerve injury induces MMPs, TNF-α and TNFRI, which interactively control the privileged endoneurial environment and the pathogenesis of the painful neuropathies associated with the macrophage-dependent processes of Wallerian degeneration.
Since the inflammatory process develops after transplantation to the brain, we sought to determine the presence of cytokines following a surgical trauma to the brain of an adult mouse. We report the early and marked presence of tumor necrosis factor-α and interleukin-1α in neuronal somata of the striatum following a surgical injury to the hippocampus. The expression of cytokines later extends to neuronal cells of the hippocampus, thalamus, cerebral cortex, brain stem, and cerebellum and to glial cells of the corpus callosum. By contrast, these cytokines are not expressed by neuronal cells following injury to other regions, such as the striatum, cerebellum, and cortex. This study suggests a possible role for certain neurons in the brain's early reaction to a penetrating injury.
A chronic, loose constriction of the sciatic nerve in rat produces behavioral signs of spontaneous pain and cutaneous hyperalgesia (Bennett and Xie, Pain, 33 (1988) 87–107) as well as an abnormal spontaneous activity and adrenergic sensitivity of certain dorsal root ganglion (DRG) cells with axons in the injured nerve (Kajander et al., Neurosci. Lett., 138 (1992) 225–228; Xie et al., J. Neurophysiol., 73 (1995)1811–1820) The present study investigated whether the spontaneous activity and adrenergic sensitivity were intrinsic properties of injured DRG cells and manifested in vitro, i.e., not dependent on intact blood circulation and an intact, functioning sympathetic nervous system. Two weeks after a loose constriction of the sciatic nerve, the L4 or L5 DRG with its ligated nerve and dorsal root attached was removed from the rat and placed in a chamber. Extracellular recordings were made from teased dorsal root fibers. Spontaneous activity (>0.05 imp/s in 3 min) originating within or close to the DRG was often found in C-, Aδ- and Aβ-fibers from nerve-injured rats, but was rare in fibers with peripheral axons from uninjured nerve. The incidence of various patterns of spontaneous discharge was similar to that previously recorded in vivo. Nineteen of 30 C-fibers, four of five Aδ- and three of seven Aβ-fibers from injured nerve responded to different doses of norepinephrine (NE) applied topically to the DRG. Five of seven C- and one of two Aβ-fibers from injured nerve responded to clonidine, a more selective α2 adrenergic agonist. The thresholds ranged from 500 to 10 μM, the lowest dose delivered. None of the fibers from uninjured nerve responded to NE or clonidine (500 μM). Since the experiments were carried out in vitro in the intact DRG, the existence of spontaneous activity in DRG cells in nerve-injured rats was independent of any blood borne chemicals, such as norepinephrine. We hypothesize that abnormal activity and adrenergic sensitivity in injured DRG neurons are due to an intrinsic alteration of the cell body membrane.
Tumor necrosis factor-alpha (TNF alpha) is a cytokine rapidly produced in the brain in response to vigorous neuronal activity and tissue injury. TNF alpha may protect neurons against excitotoxic and oxidative insults by a mechanism involving activation of the transcription factor NF-kappaB. Whole-cell perforated patch clamp recordings in cultured rat hippocampal neurons showed that long-term treatment (24-48 h) with TNF alpha increases Ca2+ current density; pharmacological analysis indicated a major increase in current through L-type voltage-dependent calcium channels. Long-term treatment with TNF alpha caused a decrease in currents induced by glutamate, NMDA, AMPA, and kainate. Shorter exposures to TNF alpha (acute; 2 h) did not alter Ca2+ current or glutamate receptor agonist-induced currents. Ceramide, an intracellular messenger that activates the transcription factor NF-kappaB, mimicked the actions of TNFs on Ca2+ current density and currents induced by glutamate receptor agonists. Cotreatment with kappaB decoy DNA abolished the effects of TNF alpha on Ca2+ current and excitatory amino acid-induced currents, demonstrating a requirement for NF-kappaB activation in the actions of TNF alpha. Neurons pretreated with TNF alpha exhibited increased intracellular Ca2+ concentrations following membrane depolarization but reduced intracellular Ca2+ concentration responses to excitatory amino acids, compared with neurons in untreated control cultures or cultures cotreated with kappaB decoy DNA. These findings suggest important roles for the transcription factor NF-kappaB in modulation of voltage-dependent calcium channels and glutamate receptors and the many physiological and pathophysiological processes in which these ion channels are involved. Such signaling mechanisms may be particularly important in injury settings such as ischemia or trauma, where TNF alpha expression is increased and NF-kappaB is activated.
Tumor necrosis factor alpha (TNF) may be involved in the pathogenic mechanisms of neuropathic pain by affecting endothelial cells and by upregulation of receptor sensitivity in afferent nerve fibers. To test the hypothesis that TNF plays a role in the vascular changes and the pain-related behavior in an experimental painful neuropathy in rats produced by tying loosely constrictive ligatures around one sciatic nerve, we investigated the effect of thalidomide, a selective blocker of TNF-production in activated macrophages. In rats in which treatment with thalidomide was started preoperatively, there was diminished mechanical allodynia and thermal hyperalgesia during the early stage of the disease. TNF immunohistochemistry revealed reduced endoneurial immunoreactivity on day 5 post surgery as compared to sham-treated animals. The pathologic vascular changes were also reduced in thalidomide-treated rats. Starting treatment with thalidomide at a time point when hyperalgesia was already present did not alter the course of the pain-related behavior. We conclude that preemptive treatment with a substance that blocks production of TNF reduces pain-related symptoms and pathologic vascular changes in the chronic constriction injury model of neuropathic pain.
The chronic constriction injury model of mononeuropathy is a direct, partial nerve injury yielding thermal hyperalgesia. The inflammation that results from this injury is believed to contribute importantly to both the neuropathological and behavioral sequelae. This study involved administering a single dose (250 ng) of interleukin-10 (IL-10), an endogenous anti-inflammatory peptide, at the site and time of a chronic constriction injury (CCI) lesion to determine if IL-10 administration could attenuate the inflammatory response of the nerve to CCI and resulting thermal hyperalgesia. In IL-10-treated animals, thermal hyperalgesia was significantly reduced following CCI (days 3, 5 and 9). Histological sections from the peripheral nerve injury site of those animals had decreased cell profiles immunoreactive for ED-1, a marker of recruited macrophages, at both times studied (2 and 5 days post-CCI). IL-10 treatment also decreased cell profiles immunoreactive for the pro-inflammatory cytokine tumor necrosis factor alpha (TNF-alpha) at day 2, but not day 5. Qualitative light microscopic assessment of neuropathology at the lesion site did not suggest substantial differences between IL-10 and vehicle-treated sections. The authors propose that initial production of TNF-alpha and perhaps other proinflammatory cytokines at the peripheral nerve lesion site importantly influences the long-term behavioral outcome of nerve injury, and that IL-10 therapy may accomplish this by downregulating the inflammatory response of the nerve to injury.
1. The properties of dorsal root ganglion cells in the lumbosacral segments were examined with intracellular electrodes about 3 weeks after section of the central (dorsal roots) or peripheral processes in the cat.
2. Chronic section of the peripheral nerve in the hind limb resulted in a reduction in conduction velocity of both the central and peripheral processes of sensory neurones.
3. Sensory neurones arising from the triceps surae and plantaris muscles were subject to ‘disuse’ conditions for about 3 weeks by section of the ventral roots combined with severance of the Achilles tendon. Under such conditions, the central and peripheral conduction velocities of these sensory neurones tended to decrease, but the decrease was significantly less than that following peripheral nerve section.
4. Chronic section of the dorsal roots produced no significant changes in conduction velocity of the central processes of muscle sensory neurones but caused a significant increase in the peripheral conduction velocity.
5. The only electrophysiological property of dorsal root ganglion cells which altered following axotomy was the time‐dependent membrane rectification in response to hyperpolarizing current pulses. The rectification characteristics were modified by chronic section of the peripheral nerve but not by chronic section of the dorsal root.
6. It is concluded that injuries in nerve fibres per se do not necessarily result in a decrease of their conduction velocity and that a decrease in their conduction velocity is associated with changes in the properties of the cell bodies.
7. It is suggested that a decrease in conduction velocity following nerve section may require the participation of changes in the neurone cell body.
Tumor necrosis factor-alpha (TNF, cachectin), a protein secreted by activated macrophages, participates in inflammatory responses and in infectious and neoplastic disease states. The mechanisms by which TNF exerts cytotoxic, hormonal, and other specific effects are obscure. Structural studies of the TNF trimer have revealed a central pore-like region. Although several amino acid side chains appear to preclude an open channel, the ability of TNF to insert into lipid vesicles raised the possibility that opening might occur in a bilayer milieu. Acidification of TNF promoted conformational changes concordant with increased surface hydrophobicity and membrane insertion. Furthermore, TNF formed pH-dependent, voltage-dependent, ion-permeable channels in planar lipid bilayer membranes and increased the sodium permeability of human U937 histiocytic lymphoma cells. Thus, some of the physiological effects of TNF may be elicited through its intrinsic ion channel-forming activity.
The hyperalgesic activities in rats of interleukin‐1β (IL‐1β), IL‐6, IL‐8, tumour necrosis factor α (TNFα) and carrageenin were investigated.
IL‐6 activated the previously delineated IL‐1/prostaglandin hyperalgesic pathway but not the IL‐8/sympathetic mediated hyperalgesic pathway.
TNFα and carrageenin activated both pathways.
Antiserum neutralizing endogenous TNFα abolished the response to carrageenin whereas antisera neutralizing endogenous IL‐1β, IL‐6 and IL‐8 each partially inhibited the response.
The combination of antisera neutralizing endogenous IL‐1β + IL‐8 or IL‐6 + IL‐8 abolished the response to carrageenin.
These results show that TNFα has an early and crucial role in the development of inflammatory hyperaglesia.
The delineation of the roles of TNFα, IL‐1β, IL‐6 and IL‐8 in the development of inflammatory hyperalgesia taken together with the finding that the production of these cytokines is inhibited by steroidal anti‐inflammatory drugs provides a mechanism of action for these drugs in the treatment of inflammatory hyperalgesia.
The ionic mechanisms of the effect of extracellularly ejected recombinant human tumor necrosis factor-alpha (rhTNF-alpha) on the membrane of identified neurons R9 and R10 of Aplysia kurodai was investigated with conventional voltage-clamp, micropressure ejection, and ion substitution techniques. Micropressure-ejected rhTNF caused a marked hyperpolarization in the unclamped neuron. Clamping the same neuron at it resting potential level (-60 mV) and reejecting rhTNF-alpha with the same dose produced a slow outward current [Io (TNF)] associated with a decrease in input membrane conductance. Io (TNF) was decreased by depolarization and increased by hyperpolarization. The extrapolated reversal potential of Io (TNF) was approximately +10 mV. Ion substitution and pharmacological experiments suggest that Io (TNF) in identified neurons R9 and R10 of A. kurodai is due to a decreased Na+ conductance but not due to an activation of the Na(+)-K+ pump. Our results demonstrate that the immunomodulator TNF can act directly on the nervous system as well as on the immune system.
Recombinant human tumor necrosis factor (rhTNF) was pressure-applied onto the the soma of identified neuron R12 in the Aplysia abdominal ganglion. rhTNF induced a slow inward current (ITNF, 80-100 s in duration, 5-10 nA in amplitude) associated with a conductance decrease. ITNF begins 1-2 s after applying rhTNF and peaks in 5-6 s. ITNF was decreased by hyperpolarization and had a reversal potential of approximately -87 mV (close to the K+ equilibrium potential). Ion substitution and pharmacological experiments suggest that ITNF is due to a decreased K+ conductance and that TNF, a product of macrophages, may form an important link in communications between nervous and immune systems.
In rats, the sciatic nerve was cut, drawn into a polythene tube with one end sealed, and a neuroma allowed to develop in the chamber. Activity in the dorsal and ventral roots terminating in the neuroma was examined between 9 days and 4 months after the section. A fraction of the small myelinated afferent fibers originating in the neuroma were carrying a steady ongoing barrage of nerve impulses. Many of the fine terminals were excited by slight mechanical distortion. The fine sprouts in the neuroma were electrically excitable. The ongoing afferent barrage was highly dependent on blood flow. It was abolished for long periods of time after a brief antidromic tetanus had invaded the active fibers. This suggests that some of the pain relief obtained from peripheral nerve stimulation may have a peripheral rather than a central mechanism. No signs of excitatory on inhibitory interaction were detected between volleys in one group of nerve fibers and the activity in other groups of fibers in the neuroma. Alpha active sympathetic amines, noradrenaline, excited the ongoing activity while beta agents, isoprenaline, had no excitatory effect. This suggests that alpha blocking agents might be useful to test if the sympathetic system is involved in particular pains.
Membrane properties of identified leech neurons with non-spiking somata were studied after axotomy. Two distinct procedures were used: the section of ganglionic roots in vivo and the isolation of cell somata in culture. The results indicated that axotomized neurons progressively developed the excitability of somatic membrane, both in vivo and in culture.
Previous experiments indicate that after peripheral nerve lesion, two sites of spontaneous ectopic impulse generation rapidly develop: the peripheral neuroma and the region of the dorsal root ganglion (DRG). In 30 adult Sprague-Dawley rats, microfilament recordings were made from either the dorsal root of L5 or the proximal sciatic nerve. The locus of the ectopic impulse generator, spontaneous firing patterns, and response to both adrenergic and hypoxic stimulation were observed in 200 spontaneously active isolated fibers. Results indicated that after sciatic transection the neuroma and the DRG behaved as independent sources of ectopic impulse generation. Spontaneous activity originating in the neuroma was responsive to adrenergic and hypoxic stimulation in 57% and 86% of fibers tested, respectively. Spontaneous activity originating in the DRG after chronic sciatic nerve transection demonstrated a response to adrenergic stimulation in 61% of fibers tested, and all fibers showed an increase in activity during hypoxic periods. Furthermore, after acute sciatic neurotomy in otherwise normal animals, spontaneous activity originating in the DRG could be recorded in a few fibers. Likewise, 48% of those fibers showed some response to topical or systemic epinephrine administration, and hypoxia produced some degree of excitation of firing in all fibers tested. Neither epinephrine administration nor hypoxic challenge produced excitation of firing in DRG neurons with intact receptive fields in normal animals. The pharmacology of adrenergic sensitivity of spontaneously active fibers from both the neuroma and the region of the DRG indicated alpha-adrenergic specificity. Furthermore, a number of fibers exhibiting spontaneous activity from both the region of the neuroma and the DRG showed either adrenergic or hypoxic sensitivity, but not both. Thus, the mechanisms of the largely excitatory actions of alpha-agonists and hypoxia on spontaneous discharges from these sites were felt to be different. These data indicate that adrenergic and/or hypoxic responsiveness is a property of (i) otherwise normal DRG neurons which demonstrate intrinsic spontaneous firing properties, (ii) neurons in chronically denervated ganglia which exhibit spontaneous activity, and (iii) some fibers within neuromas. Normal DRG neurons with intact receptive fields do not appear to increase their firing rate in response to either hypoxia or adrenergic stimulation. These findings may be relevant to the development of chronic pain in man following peripheral nerve injury.
Primary afferent neurons to the medial head of the gastrocnemius (MG) muscle were studied to determine when and where along the neuron spontaneous electrical activity begins after the peripheral nerve is damaged. Action potentials were recorded from the dorsal root and from the muscle's nerve itself as the nerve was crushed or frozen near the muscle and at intervals to 20 days afterward. Most MG units were not spontaneously active when recordings were made after the lesion. Others, which were recorded by 2 days after the lesion, fired either continuously or in intermittent trains. Some of the active units had conduction velocities in the group I fiber range. The ratio of quiet units to those with ongoing activity increased during regeneration of nerve fibers to the MG muscle. Both the peripheral terminal region of regenerating nerve fibers and the vicinity of their cell bodies initiated action potentials of spontaneous occurrence after the lesion and before the muscle had been reinnervated.
1. The ionic mechanisms of rhythmic burst firing and single spike, tonic discharge were investigated with extracellular and intracellular recordings of single neurones in the guinea-pig nucleus reticularis thalami (NRT) maintained as a slice in vitro. 2. Activation of cortical/thalamic afferents to NRT neurones resulted in a short latency burst of action potentials which could be followed by a rhythmic sequence of oscillatory burst firing. Intracellularly, this oscillatory activity was associated with an alternating sequence of low threshold Ca2+ spikes separated by after-hyperpolarizing potentials. Intracellular injection of short duration hyperpolarizing current pulses resulted in a similar sequence of oscillatory burst firing, suggesting that this activity is an intrinsic property of NRT cells. The frequency of rhythmic burst firing was highly voltage and temperature dependent and was between 7-12 Hz at -65 to -60 mV at 38 degrees C. In addition, at depolarized membrane potentials, oscillatory burst firing was typically followed by a prolonged tail of single spike activity. 3. Application of the Na+ channel poison tetrodotoxin blocked the generation of fast action potentials, but left intact the rhythmic sequence of low threshold Ca2+ spikes separated by after-hyperpolarizing potentials (AHPs). The reversal potential of the AHPs was -94 mV, suggesting that it was mediated by an increase in K+ conductance. Extracellular application of tetraethylammonium or apamin, or intracellular injection of Cs+ or the Ca2+ chelating agent EGTA, blocked the Ca2+ spike AHP, indicating that it is mediated by a Ca(2+)-activated K+ current. 4. Block of the AHP resulted in the marked enhancement of a slow after-depolarizing potential (ADP). The slow ADP occurred only following the generation of low threshold Ca2+ spikes. Replacement of extracellular Ca2+ with Mg2+ or Sr2+ resulted in an abolition of the slow ADP. In addition, the increase in [Mg2+]o resulted in an abolition of the low threshold Ca2+ spike. In contrast, replacement of extracellular Ca2+ with Ba2+ did not abolish the slow ADP. These results indicate that the ADP can be activated by either Ca2+ or Ba2+, but not by Mg2+ or Sr2+. 5. Replacement of extracellular Na+ with choline+ did not abolish the slow ADP, while replacement with N-methyl-D-glucamine+ did, indicating that the slow ADP can be supported by choline+, but not by N-methyl-D-glucamine+. Neither chemical affected the low threshold Ca2+ spike. These results are consistent with the slow ADP being mediated by a Ca(2+)-activated non-selective cation (CAN) current.(ABSTRACT TRUNCATED AT 400 WORDS)
Since the inflammatory process develops after transplantation to the brain, we sought to determine the presence of cytokines following a surgical trauma to the brain of an adult mouse. We report the early and marked presence of tumor necrosis factor-alpha and interleukin-1 alpha in neuronal somata of the striatum following a surgical injury to the hippocampus. The expression of cytokines later extends to neuronal cells of the hippocampus, thalamus, cerebral cortex, brain stem, and cerebellum and to glial cells of the corpus callosum. By contrast, these cytokines are not expressed by neuronal cells following injury to other regions, such as the striatum, cerebellum, and cortex. This study suggests a possible role for certain neurons in the brain's early reaction to a penetrating injury.
Peripheral nerve production of cytokines originates from resident and recruited macrophages, lymphocytes, mastocytes, Schwann cells, and probably neurons. Cytokines are involved in nerve lesions and repair. Tumor necrosis factor-alpha (TNF-alpha) injected into nerve induces Wallerian degeneration, whereas, interleukin-1 (IL-1) production promotes detersion by scavenger macrophages, and synthesis of neurotrophic factors (nerve growth factor-NGF- and leukemia inhibitory factor-LIF). After experimental axotomy, other neurotrophic factors, including IL-6, LIF and transforming growth factor-beta 1 (TGF-beta 1), are overexpressed in nerve and promote axonal growth until axon/Schwann cell contact. Proinflammatory cytokines are instrumental in the course of inflammatory demyelinating neuropathies. They increase vascular permeability and blood nerve barrier breakdown (TNF-alpha, vascular endothelial growth factor/ vascular permeability factor-VEGF/VPF), favor transmigration of leukocytes into nerve, induce activation and proliferation of lymphocytes (IL-1, IL-2) and macrophages (gamma-interferon-IFN-gamma), and have a direct myelinotoxic activity (TNF-alpha and TNF-beta). In addition, downregulation of the immunosuppressive cytokine TGF-beta 1 may favor the nerve inflammatory reactions.
Tumour necrosis factor-alpha, a pro-inflammatory cytokine, is expressed endoneurially following a variety of local and systemic pathophysiological insults which give rise to pain. We administered tumour necrosis factor-alpha to pentobarbital-anaesthetized rats, either topically along a restricted portion of the sciatic nerve or injected subcutaneously within the distribution of the sural nerve. Single nociceptive primary afferent fibres were assessed for ectopic discharge and receptor sensitization. Low concentrations (0.001-0.01 ng/ml) of tumour necrosis factor-alpha applied along the nerve elicited a dose-dependent, rapid onset (1-3 min) increase in discharge; higher concentrations led to reduced firing rates. C-fibres developed higher mean firing frequencies than A delta-fibres. Bursting frequency in both fibre types reached several (6) Hz. No change in mechanical threshold was observed. Intradermal injection (50 pg in 50 microliters) led to ectopic discharge and a decrease in mechanical threshold; these effects developed at different rates, suggesting multiple actions of the cytokine. Our data suggest that acute application of tumour necrosis factor-alpha to the axon can lead to aberrant electrophysiologic activity independent of peripheral receptor involvement. This low level of ectopic firing of nociceptive axons may produce wind-up in dorsal horn neurons or may, by itself, be interpreted as pain.
Tumor necrosis factor-alpha (TNF) is involved in the generation of inflammatory and neuropathic pain. The synthetic hydroxamic acid based metalloprotease inhibitor TAPI blocks cleavage of cell surface TNF and thus reduces levels of the mature 17-kDa TNF polypeptide in activated macrophages and T-cells. We have previously shown that pharmacologic inhibition of TNF production reduces pain related behaviors in mice with chronic constriction injury (CCI). Here we investigated whether blockage of TNF shedding by administration of TAPI would diminish hyperalgesia in animals with partial nerve injury. We injected 0.5 mg of the inhibitor epineurially once daily to mice with CCI for 7 days. The animals were tested for withdrawal thresholds to heat to test for thermal hyperalgesia and to von Frey hairs to assess mechanical allodynia. Mice with CCI developed thermal hyperalgesia and mechanical allodynia by day 3 after the injury. In mice treated with TAPI, a reduction of thermal hyperalgesia and mechanical allodynia of up to 50% occurred. Endoneurial TNF-immunoreactivity was reduced, but not immunoreactivity for IL-1alpha or IL-1beta. The numbers of degenerating axons and endoneurial macrophages were not affected by the treatment as compared to controls. We conclude that the metalloprotease inhibitor TAPI specifically reduces endoneurial TNF-levels after nerve injury and thereby may diminish neuropathic pain in the CCI-model.
Recent evidence points to a role of cytokines like tumor necrosis factor-alpha (TNF) in the generation of hyperalgesia not only in inflammatory, but also in neuropathic pain. We used the model of chronic constrictive injury (CCI) of one sciatic nerve in the mouse to investigate which of the two known TNF receptors is involved in the process that leads to hyperalgesia after nerve injury. Neutralizing antibodies to TNF, to the TNF receptor 1 (TNFR1), and to the TNF receptor 2 (TNFR2) were administered by epineurial injection once daily to mice with CCI. Testing of the animals' hind paws with thermal and innocuous mechanical stimuli revealed a reduction in thermal hyperalgesia and mechanical allodynia in mice treated with neutralizing antibodies to TNF and to TNFR1. Neutralizing antibodies to TNFR2 had no effect. We conclude that TNFR1, but not TNFR2, is mediating thermal hyperalgesia and mechanical allodynia after nerve injury.
Potassium currents have an important role in modulating neuronal excitability. We have investigated the effects of axotomy on three voltage-activated K(+) currents, one sustained and two transient, in cutaneous afferent dorsal root ganglion (DRG) neurons. Fourteen to 21 days after axotomy, L(4) and L(5) DRG neurons were acutely dissociated and were studied 2-8 h after plating. Whole cell patch-clamp recordings were obtained from identified cutaneous afferent neurons (46-50 microm diam); K(+) currents were isolated by blocking Na(+) and Ca(2+) currents with appropriate ion replacement and channel blockers. Separation of the current components was achieved on the basis of sensitivity to dendrotoxin or 4-aminopyridine and by the response to variation in conditioning voltage. Both control and injured neurons displayed qualitatively similar complex K(+) currents composed of distinct kinetic and pharmacological components. Three distinct K(+) current components, a sustained (I(K)) and two transient (I(A) and I(D)), were identified in variable proportions. However, total peak current was reduced by 52% in the axotomized cells when compared with control cells. Two current components were reduced after ligation, I(A) by 60%, I(K) by over 65%, compared with control cells. I(D) appeared unaffected after acute ligation. These results indicate a large reduction in overall K(+) current, resulting from reductions in I(K) and I(A), on large cutaneous afferent neurons after nerve ligation and have implications for excitability changes of injured primary afferent neurons.
Wallerian degeneration, induced after injury to a peripheral nerve, is associated with upregulation of proinflammatory cytokines, which are suggested to contribute to the development of lesion-induced neuropathic pain. In chronic constrictive injury (CCI), an animal model of injury-induced painful mononeuropathy, inhibition of synthesis, release, or function of the cytokine tumor necrosis factor-alpha (TNF) results in reduced pain-associated behavior. Here, changes of TNF content in rat sciatic nerves after CCI (days 0, 0.5, 1, 3, 7 and 14) were investigated by enzyme-linked-immunoassay. Low levels of TNF were already detectable in control nerves. Concentrations increased rapidly after CCI, with a maximum (2.7-fold) at 12 h, and remained elevated on a lower level until day 3. Baseline levels were reached again at day 14. These results indicate that TNF is produced at an early time point in the cascade of events resulting in Wallerian degeneration and hyperalgesia following peripheral nerve injury. Given that only prophylactic treatment with TNF inhibitors efficiently reduces hyperalgesia in CCI, TNF seems to contribute to the initiation of neuropathic pain in this model.
Tumor necrosis factor alpha (TNF) is a potent pro-inflammatory cytokine that produces pain and hyperalgesia following injection. Its algesic effects are due to sensitizing actions on nociceptive primary afferents and to the upregulation of other pro-inflammatory and algesic proteins. In anesthetized rats, we investigated the effect of subcutaneously injected TNF on background activity and mechanical sensitivity of C nociceptors of the sural nerve, as well as its effects on cutaneous plasma extravasation. TNF sensitized C nociceptors dose-dependently; the optimal dose (5 ng) lowered threshold in 66.7% of the tested fibers. This sensitization occurred within 30 min and could last for 2 or more hours. Injected TNF had no effect on Abeta mechanoreceptive fibers. In addition, TNF evoked ongoing activity in 14% of C nociceptors and caused significant and dose-related increases in vascular permeability in glabrous skin. Our data suggest that TNF released during disease or after tissue injury participates in the generation of hyperalgesia and inflammation.
Inhibition of proinflammatory cytokines reduces hyperalgesia in animal models of painful neuropathy. We set out to investigate the consequences of this treatment for nerve regeneration. Here we examined the sequels of epineurial application of neutralizing antibodies to tumor necrosis factor-alpha (TNF) in chronic constriction injury (CCI) of the sciatic nerve in C57/BL 6 mice. The mice were tested behaviorally for manifestations of thermal hyperalgesia and mechanical allodynia. Nerve regeneration was assessed by morphometry of myelinated nerve fibers in the sciatic nerve and of the epidermal innervation density in the glabrous skin of the hindpaws. Antibodies to TNF reduced thermal hyperalgesia and mechanical allodynia after CCI. Myelinated fiber density in the sciatic nerve was reduced to 30% of normal on day 7 after surgery, and reached 60% on day 45, with no difference between antibody-treated and untreated animals. Epidermal innervation density as shown by PGP 9.5 and CGRP immunohistochemistry was reduced to 25-47% at both time points after CCI, again without differences between antibody treated and untreated mice. Myelinated fiber density but not epidermal innervation density was correlated to thermal and mechanical withdrawal thresholds. We conclude that neutralization of endoneurial TNF attenuates pain related behavior but has no effect on nerve regeneration. Furthermore, the number of epidermal nerve fibers is not relevant to the magnitude of behavioral hyperalgesia in CCI.
The expression of interleukin-1β and tumor necrosis factor has previously been shown to be up-regulated in the spinal cord of several rat mononeuropathy models. This present study was undertaken to determine whether blocking the action of central interleukin-1β and tumor necrosis factor attenuates mechanical allodynia in a gender-specific manner in a rodent L5 spinal nerve transection model of neuropathic pain, and whether this inhibition occurs via down-regulation of the central cytokine cascade or blockade of glial activation. Interleukin-1 receptor antagonist or soluble tumor necrosis factor receptor was administered intrathecally via lumbar puncture to male Holtzman rats in a preventative pain strategy, in which therapy was initiated 1 h prior to surgery. Administration of soluble tumor necrosis factor receptor attenuated mechanical allodynia, while interleukin-1 receptor antagonist alone was unable to decrease allodynia. Interleukin-1 receptor antagonist in combination with soluble tumor necrosis factor receptor, administered to both male and female rats in a preventative pain strategy, significantly reduced mechanical allodynia in a dose-dependent manner (P<0.01). The magnitude of attenuation in allodynia was similar in both males and females. Immunohistochemistry on L5 spinal cord revealed similar astrocytic and microglial activation regardless of treatment. At days 3 and 7 post-transection, animals receiving daily interleukin-1 receptor antagonist in combination with soluble tumor necrosis factor receptor exhibited significantly less interleukin-6, but not interleukin-1β, in the L5 spinal cord compared to vehicle-treated animals. In an existing pain paradigm, in which treatment was initiated on day 7 post-transection, interleukin-1 receptor antagonist in combination with soluble tumor necrosis factor receptor attenuated mechanical allodynia (P<0.05) in male rats.
Tumor-necrosis-factor-alpha (TNF-alpha) prevented secondary death of retinal ganglion cells (RGCs) after axotomy of the optic nerve in vivo. This RGC rescue was confirmed in vitro in a mixed retinal culture model. In accordance with our previous findings, TNF-alpha decreased outward potassium currents in RGCs. Antagonism of the TNF-alpha-induced decrease in outward potassium currents with the potassium channel opener minoxidilsulfate (as verified by electrophysiology) abolished neuroprotection. Western blot analysis revealed an upregulation of phospho-Akt as a consequence of TNF-alpha-induced potassium current reduction. Inhibition of the phosphatidylinositol 3-kinase-Akt pathway with wortmannin decreased TNF-alpha-promoted RGC survival. These data point to a functionally relevant cytokine-dependent neuroprotective signaling cascade in adult CNS neurons.
To study the role of inflammatory cytokines in the initiation and persistence of radiculopathy as seen in humans, tumor necrosis factor alpha (TNF-alpha) was administered either to normal, uninjured L5 dorsal root ganglia (DRG) of rats via a hole drilled through the transverse process, or to chronically compressed L5 DRG via a hollow stainless steel rod inserted into the intervertebral foramen. In other experiments, a mixture of soluble TNF receptors (sTNF-Rs: sTNF-RIplus minussTNF-RII) was locally delivered to the chronically or acutely compressed DRG to neutralize the activity of endogenous TNF-alpha. Behavioral tests of mechanical allodynia were performed before and after TNF-alpha administration. Infusion of the normal DRG with TNF-alpha at a rate of 1 microl/h for 7 days induced ipsilateral mechanical allodynia (i.e. decreased mechanical withdrawal threshold) that lasted about 2 weeks. Infusion of the compressed DRG did not alter compression-induced allodynia within the first operative week but substantially enhanced the ipsilateral allodynia after the first postoperative week. Neutralizing the activity of endogenous TNF-alpha of the compressed DRG with sTNF-Rs reduced allodynia for 3 days, but was subsequently without effect. Similar results were obtained when sTNF-Rs were chronically administrated at the acutely compressed ganglion. Results demonstrated that exogenous TNF-alpha causes pain and mechanical allodynia when deposited at the normal DRG, and further enhances the ongoing allodynia when administrated at the compressed DRG. Results also suggest that endogenous TNF-alpha contributes to the early development of mechanical allodynia in rats with chronic DRG compression.
The pivotal role of tumour necrosis factor alpha in the development of inflammatory hyperalgesia
- Cunha Fq
- Lorenzetti Poole S
- Bb
- Ferreira Sh
CUNHA FQ, POOLE S, LORENZETTI BB, AND FERREIRA SH. The pivotal role of
tumour necrosis factor alpha in the development of inflammatory hyperalgesia. Br J Pharmacol 107: 660 -664, 1992.
The role of cytokines in nociception and chronic pain
- Deleo
- Colburn Rw
DELEO JA AND COLBURN RW. The role of cytokines in nociception and chronic
pain. In: Low Back Pain: A Scientific and Clinical Overview, edited by
Weinstein JN and Gordon SL. Am. Acad. Orthopaed. Surgeons, 1995, p.
163-185.
Reduction of potassium currents and phosphatidylinositol 3-kinase-dependent Akt phosphorylation by tumor necrosis factor-alpha rescues axotomized retinal ganglion cells from retrograde cell death in vivo
- Diem R
- Weishaupt Meyer R
- Jh
- Bahr M
DIEM R, MEYER R, WEISHAUPT JH, AND BAHR M. Reduction of potassium
currents and phosphatidylinositol 3-kinase-dependent Akt phosphorylation
by tumor necrosis factor-alpha rescues axotomized retinal ganglion cells
from retrograde cell death in vivo. J Neurosci 21: 2058 -2066, 2001.
Formation of ionpermeable channels by tumor necrosis factor-alpha
- Kagan Bl
- Baldwin Rl
- Munoz D
- Bj
KAGAN BL, BALDWIN RL, MUNOZ D, AND WISNIESKI BJ. Formation of ionpermeable channels by tumor necrosis factor-alpha. Science 255: 1427-1430, 1992.
Enhanced excitability of sensory neurons in rats with cutaneous hyperalgesia produced by chronic compression of the dorsal root ganglion
- Song Zhang J-M
- Xj
- Lamotte Rh
ZHANG J-M, SONG XJ, AND LAMOTTE RH. Enhanced excitability of sensory
neurons in rats with cutaneous hyperalgesia produced by chronic compression of the dorsal root ganglion. J Neurophysiol 82: 3359 -3366, 1999.