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Visceral hyperalgesia in transgenic mice induced by intracolon injection of capsaicin. Behavioral reactions (abdominal licking, stretching, squashing the lower abdomen against floor and abdominal retractions) evoked by intracolonic injection of vehicle solution or 0.1% capsaicin in WT and Tg mice. A. Number of behaviors observed in each 5 min period over a total observation time of 20 min post-administration. ***Indicates the other three groups which were significantly different from capsaicin-treated Tg mice during the first 5 min observation period (p < 0.001). B. Number of behaviors observed in the total 20 min period post-administration. Data are shown as mean ± s.e.m. (n = 5-11, *p < 0.05, **p < 0.01, ***p < 0.001).
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Dysfunction of brain-gut interaction is thought to underlie visceral hypersensitivity which causes unexplained abdominal pain syndromes. However, the mechanism by which alteration of brain function in the brain-gut axis influences the perception of visceral pain remains largely elusive. In this study we investigated whether altered brain activity c...
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Context 1
... further investigate whether altered excitability in the forebrain affects the pain sensation of abdominal viscera where most nerve endings are embedded deep within the wall of the organ, an intraluminal injection of capsaicin into the colon was performed to induce visceral pain. Intracolon administration of vehicle solution into either WT mice or Tg mice induced similar behavioral responses with a small amount of abdominal licking, which was clearly separate from normal grooming activ- ity ( Figure 5). Intracolon administration of 0.1% capsaicin into Tg mice evoked significant behavioral responses with abdominal licking, stretching, squashing of the lower abdomen against floor and abdominal retractions, as compared with the group of WT mice ( Figure 5). ...Context 2
... administration of vehicle solution into either WT mice or Tg mice induced similar behavioral responses with a small amount of abdominal licking, which was clearly separate from normal grooming activ- ity ( Figure 5). Intracolon administration of 0.1% capsaicin into Tg mice evoked significant behavioral responses with abdominal licking, stretching, squashing of the lower abdomen against floor and abdominal retractions, as compared with the group of WT mice ( Figure 5). These results indicate that Tg mice are more sensitive to visceral pain induced by intracolon chemical stimulation. ...Citations
... [37][38][39][40] To explore the consequences of M-current suppression for the epileptic phenotype, a homozygous model was created bearing the variant p.(S559A), which attenuates the neurotransmitter-induced M-current suppression. 41 In addition, studies of the p.(G279S) variant allowed highlighting of the role of Kcnq2-related neuronal hyperexcitability in the forebrain for the perception of visceral pain, 42 on the fear memory trace, 43 and to study the relationship between the peptide hormone ghrelin and Kcnq2 in the context of dopaminergic neurotransmission. 44 Kcnq2deficient mouse models generated from 2000 to 2022 are presented in Table 1. ...
Variants in the Kv7.2 channel subunit encoded by the KCNQ2 gene cause epileptic disorders ranging from a benign form with self‐limited epileptic seizures and normal development to severe forms with intractable epileptic seizures and encephalopathy. The biological mechanisms involved in these neurological diseases are still unclear. The disease remains intractable in patients affected by the severe form. Over the past 20 years, KCNQ2 models have been developed to elucidate pathological mechanisms and to identify new therapeutic targets. The diversity of Kcnq2 mouse models has proven invaluable to access neuronal networks and evaluate the associated cognitive deficits. This review summarizes the available models and their contribution to our current understanding of KCNQ2 epileptic disorders.
... Therefore, decreasing 5-HT transmission by blocking 5-HT 2A R or enhancing inhibitory Kv7 channels may produce similar effects on PFC related behaviors. Although previous studies suggest that activation of Kv7 channels can ameliorate pain by reducing excitability in nociceptive inputs [21,22], the role of 5-HT 2A R and Kv7 in PFC in the context of chronic pain remains unclear. ...
Chronic pain remains a disabling disease with limited therapeutic options. Pyramidal neurons in the prefrontal cortex (PFC) express excitatory Gq-coupled 5-HT2A receptors (5-HT2AR) and their effector system, the inhibitory Kv7 ion channel. While recent publications show these cells innervate brainstem regions important for regulating pain, the cellular mechanisms underlying the transition to chronic pain are not well understood. The present study examined whether local blockade of 5-HT2AR or enhanced Kv7 ion channel activity in the PFC would attenuate mechanical allodynia associated with spared nerve injury (SNI) in rats. Following SNI, we show that inhibition of PFC 5-HT2ARs with M100907 or opening of PFC Kv7 channels with retigabine reduced mechanical allodynia. Parallel proteomic and RNAScope experiments evaluated 5-HT2AR/Kv7 channel protein and mRNA. Our results support the role of 5-HT2ARs and Kv7 channels in the PFC in the maintenance of chronic pain.
... Among the wide range of activities played by H 2 S in different biological systems [36,44], the activation of Kv7 potassium channels was found to be the main mechanism underlying the abdominal pain relief mediated by E. sativa DSM, which was hampered by pretreating the animals with the Kv7 channel blocker, XE991 [4]. Interestingly, both peripheral and central Kv7 channels were found to regulate visceral sensory function in mice and humans [45][46][47]. Recently, a role for K V 7 channel in the neuronal regulation of Cl − secretion by colonic epithelium was also proposed, supporting the therapeutic potential of Kv7 channels modulators in treating pathologies associated with an hyperexcitability of enteric sensitivity terminals [48]. ...
Most therapies used in patients affected by inflammatory bowel diseases are ineffective in preventing the development of chronic visceral hypersensitivity, mainly due to inflammation-induced enteric neuroplasticity. Glucosinolates, secondary metabolites mainly of Brassicaceae with anti-inflammatory and neuroprotective properties, are effective in treating both neuropathic and arthritis pain through H2S release and Kv7 potassium channel activation. The aim of this work was to investigate the protective and anti-hyperalgesic efficacy of a defatted seed meal from Eruca sativa Mill. (Brassicaceae), rich in glucosinolates, in a rat model of colitis induced by 2,4-dinitrobenzene sulfonic acid (DNBS). The mechanisms of action were also investigated. Visceral pain was assessed by measuring the abdominal response to colorectal distension. Fifteen days after colitis induction, the acute administration of E. sativa defatted seed meal (0.1–1 g kg−1 p.o.) dose-dependently relieved pain. This effect was hampered by co-administering an H2S scavenger or a selective Kv7 blocker. Administering E. sativa (1 g kg−1) for 14 days, starting after DNBS injection, contributed to counteracting visceral pain persistence in the post-inflammatory phase of colitis by promoting colon healing from the damage and reducing enteric gliosis. E. sativa defatted seed meal might be employed as a nutraceutical tool for supporting abdominal pain relief in patients.
... In addition, SGK1.1 decreases neuronal excitability via up-regulation of neuronal M-current, linked to Kv7.2/3 potassium channels (Armas-Capote et al., 2020;Miranda et al., 2013). M-current is a subthreshold voltage-gated K + current acting as a "brake" that suppresses abnormal ectopic discharges of neurons and controls neuronal hyperexcitability (Bi et al., 2011;Miranda et al., 2013). Transgenic mice expressing a constitutively active form of SGK1 and its isoforms (B6.Tg.sgk1 mice) show increased SGK1.1 activity in the CNS and enhanced M-current levels in superior cervical ganglion neurons (Miranda et al., 2013) and hippocampal neurons (Armas-Capote et al., 2020). ...
... To assess the sensitivity to chemical noxious stimulus, a model of visceral pain induced by acetic acid 0.6% was used (Bi et al., 2011). Animals were injected i.p. with 0.3 ml of this solution and placed into a ventilated chamber with wooden bedding; 5 min after injection, the number of abdominal writhes was counted for 10 min. ...
The serum and glucocorticoid-regulated kinase 1 (SGK1) is a widely expressed protein in the Central Nervous System (CNS), involved in regulating the activity of a wide variety of ion channels and transporters and physiological functions, such as neuronal excitability. SGK1.1 is a neuronal splice isoform of SGK1, expressed exclusively in the CNS, distributed in brain and cerebellum, that decreases neuronal excitability via up-regulation of M-current, linked to Kv7.2/3 potassium channels. Strategies to maintain increased SGK1.1 activity could be helpful in decreasing neuronal hyperexcitability, as occurs in neuropathic pain. Transgenic mice overexpressing SGK1.1 (B6.Tg.sgk1) offer a particularly relevant opportunity to assess the physiological involvement of this protein in nociception.
Behavior and physiological nociception were evaluated in male and female B6.Tg.sgk1 and wild-type mice (B6.WT), characterizing nociceptive thresholds to different nociceptive stimuli (thermal, chemical and mechanical), as well as the electrophysiological properties of cutaneous sensory Aδ-fibres isolated from the saphenous nerve. The acute antinociceptive effect of morphine was also evaluated.
Compared with B6.WT animals, male and female B6.Tg.sgk1 mice showed increased spontaneous locomotor activity. Regarding nociception, there were no differences between transgenic and wild-type mice in heat, chemical and mechanical thresholds, but interestingly, male B6.Tg.sgk1 mice were less sensitive to cold stimulus; B6.Tg.sgk1 animals showed lower sensitivity to morphine. Electrophysiological properties of cutaneous primary afferent fibres were maintained.
This is the first demonstration that the SGK1.1 isoform is involved in nociceptive modulation, offering a protective effect against noxious cold stimulus in a sexually dimorphic manner. B6.Tg.sgk1 mice offer a particularly relevant opportunity to further analyze the involvement of this protein in nociception, and studies in models of chronic, neuropathic pain are warranted.
... The generation of our transgenic (Tg) mice expressing a dominantnegative pore mutation of rat K v 7.2/ KCNQ2 channel (rQ2-G279S) was made using a forebrain-specific αCaMKII promoter that drives specific expression in the forebrain (Bi et al., 2011). Briefly, the porelining residue Gly279 of rat KCNQ2 channel was mutated into Ser, mutant rQ2-G279S, that exerts dominant-negative effect upon co-assembly with wild-type (WT) KCNQ channel. ...
... Expression and distribution of mutant genes encoding rQ2-G279S were identified by real-time quantitative PCR and in situ hybridization. In situ hybridization showed that rQ2-G279S mutant mRNAs were highly expressed in the cortex, striatum, hippocampus, thalamus, and other forebrain regions, and they were rarely expressed in the cerebellum, almost not in the midbrain, pons, and medulla oblongata (Bi et al., 2011). Technology Co. Ltd. ...
... The analysis of Nissl-stained coronal sections of hippocampus revealed that there was no obvious structural change in adult Tg mice, compared with WT mice. In addition, we find that there is no significant difference between Tg and WT mice in spontaneous activity, and the Tg mice do not exhibit spontaneous epileptic behaviours (Bi et al., 2011). Therefore, genetic suppression of M-currents does not necessarily cause development of epilepsy. ...
Background and Purpose
Dysfunction of the prefrontal cortex (PFC) is involved in the cognitive deficits in neuropsychiatric diseases, such as schizophrenia, characterized by deficient neurotransmission known as NMDA receptor hypofrontality. Thus, enhancing prefrontal activity may alleviate hypofrontality‐induced cognitive deficits. To test this hypothesis, we investigated the effect of forebrain‐specific suppression or pharmacological inhibition of native Kv7/KCNQ/M‐current on glutamatergic hypofrontality induced by the NMDA receptor antagonist MK‐801.
Experimental Approach
The forebrain‐specific inhibition of native M‐current was generated by transgenic expression, in mice, of a dominant‐negative pore mutant G279S of Kv7.2/KCNQ2 channels that suppresses channel function. A mouse model of cognitive impairment was established by single i.p. injection of 0.1 mg·kg⁻¹ MK‐801. Mouse models of prepulse inhibition (PPI) of acoustic startle reflex and Y‐maze spontaneous alternation test were used for evaluation of cognitive behaviour. Hippocampal brain slice recordings of LTP were used to assess synaptic plasticity. Hippocampus and cortex were dissected for detecting protein expression using western blot analysis.
Key Results
Genetic suppression of Kv7 channel function in the forebrain or pharmacological inhibition of Kv7 channels by the specific blocker XE991 enhanced PPI and also alleviated MK‐801 induced cognitive decline. XE991 also attenuated MK‐801‐induced LTP deficits and increased basal synaptic transmissions. Western blot analysis revealed that inhibiting Kv7 channels resulted in elevation of pAkt1 and pGSK‐3β expressions in both hippocampus and cortex.
Conclusions and Implications
Both genetic and pharmacological inhibition of Kv7 channels alleviated PPI and cognitive deficits. Mechanistically, inhibition of Kv7 channels promotes synaptic transmission and activates Akt1/GSK‐3β signalling.
... 20 Selective ablation of KCNQ2 from the mouse forebrain results in visceral hyperalgesia suggesting that there may also be a contribution of CNS K V 7 channels to visceral pain. 21 Here, we sought to identify and confirm the role of peripheral K V 7 channels in visceral nociception by studying nerve fibres innervating the GI tract of both mouse and human. K V 7 channel subtype expression is tissue specific, with K V 7.1 highly expressed by cardiac myocytes 22 as well as in epithelial 23 and smooth muscle tissue, 24 while K V 7.2 to K V 7.5 are found in the nervous system. ...
Background
Chronic visceral pain is a defining symptom of many gastrointestinal disorders. The KV7 family (KV7.1–KV7.5) of voltage-gated potassium channels mediates the M current that regulates excitability in peripheral sensory nociceptors and central pain pathways. Here, we use a combination of immunohistochemistry, gut-nerve electrophysiological recordings in both mouse and human tissues, and single-cell qualitative real-time polymerase chain reaction of gut-projecting sensory neurons, to investigate the contribution of peripheral KV7 channels to visceral nociception.
Results
Immunohistochemical staining of mouse colon revealed labelling of KV7 subtypes (KV7.3 and KV7.5) with CGRP around intrinsic enteric neurons of the myenteric plexuses and within extrinsic sensory fibres along mesenteric blood vessels. Treatment with the KV7 opener retigabine almost completely abolished visceral afferent firing evoked by the algogen bradykinin, in agreement with significant co-expression of mRNA transcripts by single-cell qualitative real-time polymerase chain reaction for KCNQ subtypes and the B2 bradykinin receptor in retrogradely labelled extrinsic sensory neurons from the colon. Retigabine also attenuated responses to mechanical stimulation of the bowel following noxious distension (0–80 mmHg) in a concentration-dependent manner, whereas the KV7 blocker XE991 potentiated such responses. In human bowel tissues, KV7.3 and KV7.5 were expressed in neuronal varicosities co-labelled with synaptophysin and CGRP, and retigabine inhibited bradykinin-induced afferent activation in afferent recordings from human colon.
Conclusions
We show that KV7 channels contribute to the sensitivity of visceral sensory neurons to noxious chemical and mechanical stimuli in both mouse and human gut tissues. As such, peripherally restricted KV7 openers may represent a viable therapeutic modality for the treatment of gastrointestinal pathologies.
... 20 Selective ablation of KCNQ2 from the mouse forebrain results in visceral hyperalgesia suggesting that there may also be a contribution of CNS K V 7 channels to visceral pain. 21 Here, we sought to identify and confirm the role of peripheral K V 7 channels in visceral nociception by studying nerve fibres innervating the GI tract of both mouse and human. K V 7 channel subtype expression is tissue specific, with K V 7.1 highly expressed by cardiac myocytes 22 as well as in epithelial 23 and smooth muscle tissue, 24 while K V 7.2 to K V 7.5 are found in the nervous system. ...
\textbf{Background}$ Chronic visceral pain is a defining symptom of many gastrointestinal disorders. The K$_V$7 family (K$_V$7.1-K$_V$7.5) of voltage-gated potassium channels mediates the M current that regulates excitability in peripheral sensory nociceptors and central pain pathways. Here, we use a combination of immunohistochemistry, gut-nerve electrophysiological recordings in both mouse and human tissues, and single-cell qualitative real-time polymerase chain reaction of gut-projecting sensory neurons, to investigate the contribution of peripheral K$_V$7 channels to visceral nociception. $\textbf{Results}$ Immunohistochemical staining of mouse colon revealed labelling of K$_V$7 subtypes (K$_V$7.3 and K$_V$7.5) with CGRP around intrinsic enteric neurons of the myenteric plexuses and within extrinsic sensory fibres along mesenteric blood vessels. Treatment with the K$_V$7 opener retigabine almost completely abolished visceral afferent firing evoked by the algogen bradykinin, in agreement with significant co-expression of mRNA transcripts by single-cell qualitative real-time polymerase chain reaction for KCNQ subtypes and the B$_2$ bradykinin receptor in retrogradely labelled extrinsic sensory neurons from the colon. Retigabine also attenuated responses to mechanical stimulation of the bowel following noxious distension (0-80 mmHg) in a concentration-dependent manner, whereas the K$_V$7 blocker XE991 potentiated such responses. In human bowel tissues, K$_V$7.3 and K$_V$7.5 were expressed in neuronal varicosities co-labelled with synaptophysin and CGRP, and retigabine inhibited bradykinin-induced afferent activation in afferent recordings from human colon. $\textbf{Conclusions}$ We show that K$_V$7 channels contribute to the sensitivity of visceral sensory neurons to noxious chemical and mechanical stimuli in both mouse and human gut tissues. As such, peripherally restricted K$_V$7 openers may represent a viable therapeutic modality for the treatment of gastrointestinal pathologies.
... Stereotypic pain behaviors, such as abdominal licking, stretching, retraction, or compressing on the cage floor, are counted for 20 -30 min after irritant administration. Studies of potential mechanisms for capsaicininduced visceral pain found that pain behaviors were enhanced in a mouse with a transgenic mutation of a potassium channel in the forebrain (14) and decreased in 1 receptor knockout Themes G892 VISCERAL PAIN MODELS mice (74) or in mice with altered sensory nerve development (259). Mustard oil-induced spontaneous nocifensive behaviors can be inhibited by morphine (66), melatonin receptor agonists (35), ␣-bisabolol (116,117), and an extract from red algae (34). ...
Visceral pain describes pain emanating from the thoracic, pelvic or abdominal organs. In contrast to somatic pain, visceral pain is generally vague, poorly localized and characterized by hypersensitivity to a stimulus such as organ distension. Animal models have played a pivotal role in our understanding of the mechanisms underlying the pathophysiology of visceral pain. This review focuses on animal models of visceral pain and their translational relevance. In addition, the challenges of using animal models to develop novel therapeutic approaches to treat visceral pain will be discussed.
Copyright © 2014, American Journal of Physiology- Gastrointestinal and Liver Physiology.
... Recently, topical pharyngeolaryngeal administration of magnesium chloride in lozenge form was efficient against postoperative sore throat [8]. In contrast to these effects, is well known that intraperitoneal injection of magnesium sulfate induces visceral pain in rats and mice [9,10]. ...
... Since the discovery of retigabine's anticonvulsant properties, numerous novel Kv7 activators are being explored for their therapeutic potential in treating epilepsy (Roeloffs et al. 2008, Wulff et al. 2009, Miceli et al. 2011, Qi et al. 2011, Dalby-Brown et al. 2013, Kasteleijn-Nolst Trenité et al. 2013. Notably, in addition to epilepsy, Kv7 channel activators may also be effective in treating other diseases in which neuronal hyperexcitability represents a primary pathological component, including inflammatory or neuropathic pain (Hirano et al. 2007, Munro and Dalby-Brown 2007, Bi et al. 2011, tinnitus , as well as neuropsychiatric disorders (Redrobe andNielsen 2009, Sotty et al. 2009). ...
Stroke is a leading cause of morbidity and mortality in the United States and worldwide. However, few effective therapeutic interventions exist to treat this devastating disease. A detailed understanding of endogenous cell-adaptive mechanisms in ischemia, as well as signaling pathways leading to ischemic neurodegeneration, will critically aid in developing better treatments for stroke. In this dissertation, I investigated calcineurin-mediated signaling pathways in ischemic preconditioning and neuronal cell death. Calcineurin is a calcium/calmodulin-dependent phosphatase that regulates important neuronal functions. An ischemic preconditioning stimulus triggers calcineurin-dependent changes in the localization, phosphorylation status, and voltage-gated activation of Kv2.1 channels, which are involved in promoting neuronal tolerance in the context of otherwise lethal excitotoxic injury. Recent studies suggest that the signaling pathways mediating Kv2.1 channel regulation are complex, and may not be calcineurin activity-dependent in all cases. Additionally, how these processes contribute to neuroprotection is not well defined. In this thesis, I tested the hypothesis that Kv2.1 channel declustering may be sufficient to promote neuronal tolerance. I discovered that preconditioning leads to calcineurin-dependent increases in cyclin E1 protein levels in cortical neurons, which induces Kv2.1 dephosphorylation and dispersal of channel clusters without a concomitant shift in voltage-gated activation. Importantly, cyclin E1 over-expression reduces excitotoxic cell death in neurons. Although calcineurin is required for normal neuronal function, dysregulated calcineurin activation may be neurotoxic. In the second part of my studies, I explored the isoform-specific effects of over-expressing Regulator of calcineurin 1 (RCAN1) in neurons. I found that RCAN1 mediates isoform-dependent, distinct neuroprotective and neurotoxic cell signaling pathways through calcineurin-dependent and independent mechanisms. Thus, the studies in this dissertation provide insight into calcineurin-mediated neuronal cell survival and neurotoxic signaling pathways that may be important in the pathology of stroke and other neurodegenerative disorders.
