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Normal DRG neuron development and reduced central innervation in CKO mice. A-E, In situ hybridization with indicated probes on transverse sections through lumbar DRG of P21 control (Ctrl ) and CKO mice. F, Double staining on transverse P21 lumbar spinal cord sections with CGRP immunostaining (red) and IB4 binding (green).
Source publication
Spatial and temporal cues govern the genesis of a diverse array of neurons located in the dorsal spinal cord, including dI1-dI6, dILA, and dILB subtypes, but their physiological functions are poorly understood. Here we generated a new line of conditional knock-out (CKO) mice, in which the homeobox gene Tlx3 was removed in dI5 and dILB cells. In the...
Contexts in source publication
Context 1
... marked by the expres- sion of various neurotrophin receptors, including TrkC, TrkB, and Ret (Lallemend and Ernfors, 2012), as well as by the expres- sion of VGLUT1 ( Li et al., 2003). In CKO mice, DRG neuron development and survival were unaffected, as suggested by the grossly normal expression of TrkA, TrkB, TrkC, CGRP, and Ret ( Fig. 3A-E). This is consistent with the lack of Lbx1 expression in DRG ( Gross et al., 2002;Müller et al., 2002), and unaffected Tlx3 expression in Tlx3 F/F ;Lbx1 Cre/ CKO mice (data not ...
Context 2
... normal differentiation of DRG neurons, we found that there are much fewer CGRP and IB4 nerve terminals in CKO dorsal spinal cord, although their relative dorsoventral pro- jection pattern remained (Fig. 3F ). In contrast, innervation of VGLUT1 low threshold mechanoreceptors to the deep dorsal horn and to the ventral motor neurons was largely unaffected (data not shown). Thus, developmental impairment of a large subset of Tlx3-dependent excitatory neurons in the superficial dorsal horn results in reduced innervation by CGRP and IB4 ...
Citations
... Furthermore, the immunostaining results revealed a higher proportion of sensory neurons positive for calretinin in the injury border of the co-transplantation group than that in the OPC-alone transplantation group and the control group [41][42][43] (Fig. 8c, d). However, the calcitonin gene-related peptide (CGRP) signals, which labeled the axons of sensory neurons [44][45][46][47][48], were detected around the lesion area, the abundance of CGRP signals tended to increase in the transplanted groups, but there was not statistically different among the three groups (Additional file 1: Fig. S4a, S4b). The results suggested that co-transplantation of iPSC-derived OPCs culture together with HUVECs might have promoted the recovery of sensory functions in SCI rats. ...
Background
Spinal cord injury (SCI) is a devastating disease that causes extensive damage to oligodendrocytes and neurons leading to demyelination and axonal degeneration. In this study, we co-transplanted cell grafts containing oligodendrocyte progenitor cells (OPCs) derived from human-induced pluripotent stem cells (iPSCs) combined with human umbilical vein endothelial cells (HUVECs), which were reported to promote OPCs survival and migration, into rat contusion models to promote functional recovery after SCI.
Methods
OPCs were derived from iPSCs and identified by immunofluorescence at different time points. Functional assays in vitro were performed to evaluate the effect of HUVECs on the proliferation, migration, and survival of OPCs by co-culture and migration assay, as well as on the neuronal axonal growth. A combination of OPCs and HUVECs was transplanted into the rat contusive model. Upon 8 weeks, immunofluorescence staining was performed to test the safety of transplanted cells and to observe the neuronal repairment, myelination, and neural circuit reconstruction at the injured area; also, the functional recovery was assessed by Basso, Beattie, and Bresnahan open-field scale, Ladder climb, SEP, and MEP. Furthermore, the effect of HUVECs on grafts was also determined in vivo.
Results
Data showed that HUVECs promote the proliferation, migration, and survival of OPCs both in vitro and in vivo. Furthermore, 8 weeks upon engraftment, the rats with OPCs and HUVECs co-transplantation noticeably facilitated remyelination, enhanced functional connection between the grafts and the host and promoted functional recovery. In addition, compared with the OPCs-alone transplantation, the co-transplantation generated more sensory neurons at the lesion border and significantly improved the sensory functional recovery.
Conclusions
Our study demonstrates that transplantation of OPCs combined with HUVECs significantly enhances both motor and sensory functional recovery after SCI. No significance was observed between OPCs combined with HUVECs group and OPCs-alone group in motor function recovery, while the sensory function recovery was significantly promoted in OPCs combined with HUVECs groups compared with the other two groups. These findings provide novel insights into the field of SCI research.
... However, neurons that process heat signals in the spinal cord remain unclear. Nevertheless, developmental deletion of transcriptional factors, including Hoxb8, Pbx3, lmx1b, Tlx3, or TR4 results in neuronal loss in the superficial layers and diminishes the response to heat as well as mechanical, cold, and pruritogenic stimuli (Holstege et al., 2008;Rottkamp et al., 2008;Szabo et al., 2015;Wang et al., 2013;Xu et al., 2013). The identity of heat-processing neurons in the spinal cord is yet to be revealed. ...
Heat perception enables acute avoidance responses to prevent tissue damage and maintain body thermal homeostasis. Unlike other modalities, how heat signals are processed in the spinal cord remains unclear. By single-cell gene profiling, we identified ErbB4, a transmembrane tyrosine kinase, as a novel marker of heat-sensitive spinal neurons in mice. Ablating spinal ErbB4+ neurons attenuates heat sensation. These neurons receive monosynaptic inputs from TRPV1+ nociceptors and form excitatory synapses onto target neurons. Activation of ErbB4+ neurons enhances the heat response, while inhibition reduces the heat response. We showed that heat sensation is regulated by NRG1, an activator of ErbB4, and it involves dynamic activity of the tyrosine kinase that promotes glutamatergic transmission. Evidence indicates that the NRG1-ErbB4 signaling is also engaged in hypersensitivity of pathological pain. Together, these results identify a spinal neuron connection consisting of ErbB4+ neurons for heat sensation and reveal a regulatory mechanism by the NRG1-ErbB4 signaling.
... Genetic ablation in mouse embryos has also previously shown that Tlx1/3 positively regulate the expression of the vesicular glutamate transporter Slc17a6/Vglut2 (Fremeau et al., 2001), as well as a set of synaptic transmission genes characteristic of the glutamatergic phenotype, such as genes encoding for neuropeptides Grp, Tac1, Cck, Sst, Adcyap1 and Nts; neuropeptide receptors Grpr, Galr1, Npy1r, and Tacr1; glutamate receptors Gria2, Gria3, Grin3a, and Grin3b; GABA receptors Gabra1, Gabra5, and Gabrb2, and signaling molecule Prkcg/PKC gama (Cheng et al., 2004;Li et al., 2006;Xu et al., 2008Xu et al., , 2013Guo et al., 2012). Strikingly, we found prominent Tlx3 binding to a large number of these genes, namely Slc17a6, Cck, Adcyap1, Nts, Galr1, Npy1r, Grin3a, and Gabrb2 (Supplementary Table 1 and Figures 2A,B). ...
... This role is exerted redundantly with Tlx1 where both factors are co-expressed, namely at more rostral regions (Cheng et al., 2004). Several Tlx3-dependent genes were previously identified in mouse dorsal spinal cord through gene targeting studies in mice (Qian et al., 2002;Cheng et al., 2004Cheng et al., , 2005Li et al., 2006;Xu et al., 2008Xu et al., , 2013Guo et al., 2012). However, understanding how this protein functions has been compromised by the lack of data on direct molecular interactions. ...
... Virtually all genes known to be specifically expressed in Tlx3 + glutamatergic neurons, including transcription factors and terminal effector genes, are dependent on Tlx3, since their expression is markedly reduced or eliminated in Tlx3 knockout mice (Qian et al., 2002;Cheng et al., 2004Cheng et al., , 2005Li et al., 2006;Xu et al., 2008Xu et al., , 2013Guo et al., 2012). ...
The spinal cord dorsal horn is a major station for integration and relay of somatosensory information and comprises both excitatory and inhibitory neuronal populations. The homeobox gene Tlx3 acts as a selector gene to control the development of late-born excitatory (dILB) neurons by specifying glutamatergic transmitter fate in dorsal spinal cord. However, since Tlx3 direct transcriptional targets remain largely unknown, it remains to be uncovered how Tlx3 functions to promote excitatory cell fate. Here we combined a genomics approach based on chromatin immunoprecipitation followed by next generation sequencing (ChIP-seq) and expression profiling, with validation experiments in Tlx3 null embryos, to characterize the transcriptional program of Tlx3 in mouse embryonic dorsal spinal cord. We found most dILB neuron specific genes previously identified to be directly activated by Tlx3. Surprisingly, we found Tlx3 also directly represses many genes associated with the alternative inhibitory dILA neuronal fate. In both cases, direct targets include transcription factors and terminal differentiation genes, showing that Tlx3 directly controls cell identity at distinct levels. Our findings provide a molecular frame for the master regulatory role of Tlx3 in developing glutamatergic dILB neurons. In addition, they suggest a novel function for Tlx3 as direct repressor of GABAergic dILA identity, pointing to how generation of the two alternative cell fates being tightly coupled.
... Progenitors of dI5 strictly depend on Mash1, as dp3 (Helms et al., 2005). During dI5 specification, Tlx3 plays a role in correct circuit formation (Guo et al., 2012;Xu et al., 2013), in combination with expression of Lmx1b (LIM Homeobox Transcription Factor 1 Beta) (Hilinski et al., 2016). Tlx3 has been found to contrast the transcriptional programs of Lbx1 and Pax2, allowing dI5 to emerge as an excitatory IN class from the pool of adjacent class II IN which are instead inhibitory (Cheng et al., 2004;Cheng et al., 2005). ...
... Lmx1b is involved in both migration and differentiation of dI5 (Ding, 2004). A subset of dI5 has been described to express Phox2a (Paired Like Homeobox 2A) (Ding, 2004) and can be used as a reference for the class status, as with the second wave of neurogenesis dILB present a profile similar to dI5 and supports dI5 circuitry in pain (Duan et al., 2014;Szabo et al., 2015;Xu et al., 2013) and itch transmission (Sun and Chen, 2007;Szabo et al., 2015;Xu et al., 2013). Mature dI5 occupy the dorsal (deep) and ventral horns (Ding, 2004;Gross et al., 2002). ...
... Lmx1b is involved in both migration and differentiation of dI5 (Ding, 2004). A subset of dI5 has been described to express Phox2a (Paired Like Homeobox 2A) (Ding, 2004) and can be used as a reference for the class status, as with the second wave of neurogenesis dILB present a profile similar to dI5 and supports dI5 circuitry in pain (Duan et al., 2014;Szabo et al., 2015;Xu et al., 2013) and itch transmission (Sun and Chen, 2007;Szabo et al., 2015;Xu et al., 2013). Mature dI5 occupy the dorsal (deep) and ventral horns (Ding, 2004;Gross et al., 2002). ...
The spinal cord is part of the central nervous system (CNS) and develops from the embryonic invagination of the neural tube, generated as a result of primary neurulation from invagination of the neuroectoderm from the surrounding ectodermal layer. The progenitors lining the central canal within the neural tube undergo extensive proliferation resulting in two waves of neurogenesis in the mouse embryo, from which a 11 major classes of interneurons and columns of motoneurons will be specified and differentiate while migrating within the spinal cord. Identity specification of these classes heavily relies on opposing morphogen gradients in a dorsoventral axis, as well as cross-repression from the neighbouring classes. Frequently, human pregnancies present neurodevelopmental defects due to the incorrect process of neural tube closure (NTC) as last step of the neurulation, with variable clinical outcomes for the foetus according to the anteroposterior location of the defect. Studies in the past few years have shown how alterations to normal patterns of defined post-translational modifications (PTM) of histone proteins inevitably lead to defective NTC. Other developmental issues affecting cell specification and migration, and therefore the function, have been associated with disrupted PTM in the spinal cord.
Different publications implicated that lower levels of H3K79 methylation could associate with increased occurrence of defective NTC, and previous studies in Vogel’s lab defined the relevance of the well-known methyltransferase Dot1-like protein (DOT1L, responsible for H3K79 methylation) for rostral CNS development, leaving open questions with regard of its role in the caudal CNS.
My thesis focused therefore on defining the role of DOT1L methyltransferase activity in neurulation and neurogenesis. Initially I used a small cohort of chick embryos to pharmacologically prevent DOT1L-mediated methylation during neurulation, after defining suitable experimental conditions for the EPZ5676-based treatment. Although an increase of neural tube defects (NTDs) was observed upon effective DOT1L-inhibition, the frequency of the defect did not suggest a strong dependency on DOT1L activity for NTC. As a second approach, I generated a new transgenic mouse line for conditional knockout of Dot1l (Dot1l-cKO) within the developing spinal cord and characterized the resulting phenotype at prenatal stages for morphology and physiological markers, as the Dot1l-cKO resulted in lethality at birth. The major morphological defects observed at E18.5 were marked cell death and defective distribution of marker for inhibitory interneurons. Many differentiating interneurons present only temporarily specific molecular marks at the beginning of neurogenesis and with differentiation more functional and shared markers are expressed. Additionally, previous studies in Vogel’s lab suggest a pivotal role of DOT1L in the balance between neural potency and differentiation, e.g. in the developing cortex or in the cerebellum. Thus, I focused the characterisation of the transgenic line at embryonic stages depicting the molecular heterogeneity of the developing spinal cord (E11.5-E12.5). An initial bulk RNA-seq for the whole lumbar spinal cord for control and Dot1l-cKO at E12.5 highlighted an expression trend among mutants for decreased expression of genes characteristic of active cell cycle, accompanied by an increased expression of those associated with differentiation and migration processes. Markers for dorsal progenitor classes were under-expressed in the mutant samples, while positive and negative alterations were observed widely throughout the spinal cord for markers of differentiated interneuron classes. To gain a higher resolution on the phenotype, I performed a thorough analysis of molecular markers between the first and the second wave of neurogenesis targeting all the dorsal populations (dI1, dI2, dI3, dI4/6, dI5) and partially some ventral ones (V0, V2, V3). Parallel analysis of progenitors and early postmitotic interneurons revealed the population- and time-specific sensitivity of interneurons to DOT1L activity, as dI1 subsets were differentially affected by the cKO – with dI1i being numerically affected by the cKO while the complementary dI1c subset presented altered cell positioning in the same condition. Dorsal interneuron classes as dI1 and dI5 presented early (E11.5) significant defective development, while dI2 and dI3 appeared to develop a phenotype at a later stage (E12.5). Although of minor interest for the research focus and with a less extensive KO domain I observed also ventral effects for cell positioning, suggesting extensive cross regulation within the developing system. This study represents the first direct description of the implication of DOT1L activity in spinal cord formation and development. Due to the exploratory nature of the study, many questions remain open and call for further analysis. However, clear directions emerge from this research work: DOT1L-mediated H3K79me2 is necessary for proper identity specification of defined interneuron classes, as well as for the cellular positioning of others. Loss of DOT1L methyltransferase activity in the developing spinal cord leads to aberrant cell positioning and underrepresentation of defined classes during neurogenesis, likely resulting in extensive cell death and incorrect patterning in late prenatal stages.
... Multiple subtypes of excitatory neurons in the spinal cord are involved in itch processing. Genetic deletion of the transcription factor Tlx3 or testicular orphan nuclear receptor TR4 causes the loss of excitatory neurons in laminae I and II of the dorsal spinal cord, leading to significantly impaired pruritogen-induced scratching behavior 20,21 . Recent studies have identified the molecular markers for excitatory neurons involved in the processing of chemical itch. ...
Itch, in particular chronic forms, has been widely recognized as an important clinical problem, but much less is known about the mechanisms of itch in comparison with other sensory modalities such as pain. Recently, considerable progress has been made in dissecting the circuit mechanisms of itch at both the spinal and supraspinal levels. Major components of the spinal neural circuit underlying both chemical and mechanical itch have now been identified, along with the circuits relaying ascending transmission and the descending modulation of itch. In this review, we summarize the progress in elucidating the neural circuit mechanism of itch at spinal and supraspinal levels.
... Functional studies to date have largely relied on developmental manipulations that either broadly disrupt large swaths of dorsal excitatory INs, resulting in a wide spectrum of sensory deficits (Szabo et al., 2015;Xu et al., 2013), or studies of one or two neuron populations that result in more selective sensory impairments (Abraira et al., 2017;Albisetti et al., 2019;Bourane et al., 2015a;Cheng et al., 2017;Christensen et al., 2016;Duan et al., 2014;Huang et al., 2019;Liu et al., 2018;Paixã o et al., 2019;Peirs et al., 2015;Sun and Chen, 2007). Individually, these selective studies are suggestive of labeled-line transmission, but when taken together, they show a multiplicity of IN populations regulating the same response (Albisetti et al., 2019;Christensen et al., 2016;Fatima et al., 2019;Huang et al., 2018;Mishra and Hoon, 2013;Sun and Chen, 2007). ...
... The comparative functional analysis reported here provides the broad functional context necessary for understanding how sensorimotor circuits in the dorsal spinal cord are organized at a cellular level. These principles of broad circuit organization were not evaluated in previous studies using developmental mutations that typically cause pleiotropic deficits (Holstege et al., 2008;Rottkamp et al., 2008;Szabo et al., 2015;Villeda et al., 2006;Wang et al., 2013;Xu et al., 2013) or in studies targeting smaller subsets of INs (Albisetti et al., 2019;Bourane et al., 2015a;Cheng et al., 2017;Christensen et al., 2016;Duan et al., 2014;Huang et al., 2019;Liu et al., 2018;Mishra and Hoon, 2013;Paixã o et al., 2019;Peirs et al., 2015;Sun and Chen, 2007 Figures 3A and 4J), contribute to the generation of the scratch reflex independently of the GRP/GRPR pathway (Figures 4M and 4P). Although loss-of-function analyses show the CB + (Figures 4E, S4I, and S4AD) and GRPR + INs (Mishra and Hoon, 2013;Sun and Chen, 2007) are required for the chemical scratch reflex, the contribution the CR + INs make to this reflex pathway was only revealed by sufficiency experiments ( Figure 3A). ...
Cutaneous somatosensory modalities play pivotal roles in generating a wide range of sensorimotor behaviors, including protective and corrective reflexes that dynamically adapt ongoing movement and posture. How interneurons (INs) in the dorsal horn encode these modalities and transform them into stimulus-appropriate motor behaviors is not known. Here, we use an intersectional genetic approach to functionally assess the contribution that eight classes of dorsal excitatory INs make to sensorimotor reflex responses. We demonstrate that the dorsal horn is organized into spatially restricted excitatory modules composed of molecularly heterogeneous cell types. Laminae I/II INs drive chemical itch-induced scratching, laminae II/III INs generate paw withdrawal movements, and laminae III/IV INs modulate dynamic corrective reflexes. These data reveal a key principle in spinal somatosensory processing, namely, sensorimotor reflexes are driven by the differential spatial recruitment of excitatory neurons.
... However, following rhizotomy (which should destroy central terminals of primary afferents), the SP concentration in the ipsilateral dorsal horn was $20% of that seen in unoperated animals , suggesting that some of the peptide is derived from non-primary sources. Subsequent in situ hybridisation studies (Warden and Young, 1988;Xu et al., 2013) revealed a population of cells in the SDH with mRNA for Tac1, the gene that encodes SP, and SPimmunoreactive cells were identified in this region following treatment with colchicine, to block axoplasmic transport (Hokfelt et al., 1977;Hunt et al., 1981;Nahin, 1987;Leah et al., 1988;Senba et al., 1988;Yoshida et al., 1990;Ribeiro-da-Silva et al., 1991;Battaglia and Rustioni, 1992). It has since been shown that most SPexpressing dorsal horn cells are excitatory interneurons (Gutierrez-Mecinas et al., 2018;Dickie et al., 2019), with some being projection neurons that belong to the anterolateral tract (ALT) (Gutierrez-Mecinas et al., 2018;Huang et al., 2019). ...
The tachykinin peptide substance P (SP) is expressed by many interneurons and some projection neurons in the superficial dorsal horn of the spinal cord. We have recently shown that SP-expressing excitatory interneurons in lamina II correspond largely to a morphological class known as radial cells. However, little is known about their function, or their synaptic connectivity. Here we use a modification of the Brainbow technique to define the excitatory synaptic input to SP radial cells. We show that around half of their excitatory synapses (identified by expression of Homer) are from boutons with VGLUT2, which are likely to originate mainly from local interneurons. The remaining synapses presumably include primary afferents, which generally have very low levels of VGLUT2. Our results also suggest that the SP cells are preferentially innervated by a population of excitatory interneurons defined by expression of green fluorescent protein under control of the gene for gastrin-releasing peptide, and that they receive sparser input from other types of excitatory interneuron. We show that around 40% of lamina I projection neurons express Tac1, the gene encoding substance P. Finally, we show that silencing Tac1-expressing cells in the dorsal horn results in a significant reduction in reflex responses to cold and radiant heat, but does not affect withdrawal to von Frey hairs, or chloroquine-evoked itch.
... Development of other classes of inhibitory neurons, including NPY + inhibitory neurons that are involved in mechanical itch (Bourane et al. 2015) appear less affected by decreased PTF1A. The robust disruption in itch circuitry may also be modulated by a modest increase in the number of Grp neurons, excitatory neurons that are specified by TLX3 during development and are known to mediate itch information in the spinal cord (Xu et al. , 2013. Thus, the scratch phenotypes seen in the Ptf1a en-hancer mutants could result from the loss of inhibitory neurons, the increase in excitatory neurons, or a combination of these alterations. ...
Peripheral somatosensory input is modulated in the dorsal spinal cord by a network of excitatory and inhibitory interneurons. PTF1A is a transcription factor essential in dorsal neural tube progenitors for specification of these inhibitory neurons. Thus, mechanisms regulating Ptf1a expression are key for generating neuronal circuits underlying somatosensory behaviors. Mutations targeted to distinct cis-regulatory elements for Ptf1a in mice, tested the in vivo contribution of each element individually and in combination. Mutations in an autoregulatory enhancer resulted in reduced levels of PTF1A, and reduced numbers of specific dorsal spinal cord inhibitory neurons, particularly those expressing Pdyn and Gal Although these mutants survive postnatally, at ∼3-5 wk they elicit a severe scratching phenotype. Behaviorally, the mutants have increased sensitivity to itch, but acute sensitivity to other sensory stimuli such as mechanical or thermal pain is unaffected. We demonstrate a requirement for positive transcriptional autoregulatory feedback to attain the level of the neuronal specification factor PTF1A necessary for generating correctly balanced neuronal circuits.
... The study of the ontogeny of excitatory spinal neurons processing distinct somatic sensory modalities showed that PKCγ neurons represent Lbx1 lineage class B neurons, with most of them persistently expressing the homeobox gene Tlx3 (Xu et al. 2013). ...
... Second, pharmacological inhibition of PKCγ using locally applied selective inhibitors (Alba-Delgado et al. 2018;Miraucourt et al. 2007Miraucourt et al. , 2009Petitjean et al. 2015;Pham Dang et al. 2016;Shumilla et al. 2005), reduction in PKCγ expression through intrathecal RNA interference (Zou et al. 2011) or genetic invalidation of PKCγ (Malmberg et al. 1997a, b;Zhao et al. 2011), all can reduce or prevent mechanical allodynia in different experimental settings. Third, alteration in the development of lamina IIi PKCγ neurons is associated with the loss of the "escape" response to dynamic mechanical stimulus (Xu et al. 2013). Finally, mechanical allodynia can be triggered by local activation of PKCγ alone (Pham Dang et al. 2016). ...
Chronic pain is a frequent and disabling condition that is significantly maintained by central sensitization, which results in pathological amplification of responses to noxious and innocuous stimuli. As such, mechanical allodynia, or pain in response to a tactile stimulus that does not normally provoke pain, is a cardinal feature of chronic pain. Recent evidence suggests that the dorsal horn excitatory interneurons that express the γ isoform of protein kinase C (PKCγ) play a critical role in the mechanism of mechanical allodynia during chronic pain. Here, we review this evidence as well as the main aspects of the development, anatomy, electrophysiology, inputs, outputs, and pathophysiology of dorsal horn PKCγ neurons. Primary afferent high-threshold neurons transmit the nociceptive message to the dorsal horn of the spinal cord and trigeminal system where it activates second-order nociceptive neurons relaying the information to the brain. In physiological conditions, low-threshold mechanoreceptor inputs activate inhibitory interneurons in the dorsal horn, which may control activation of second-order nociceptive neurons. During chronic pain, low-threshold mechanoreceptor inputs now activate PKCγ neurons that forward the message to second-order nociceptive neurons, turning thus tactile inputs into pain. Several mechanisms may contribute to opening this gate, including disinhibition, activation of local astrocytes, release of diffusible factors such as reactive oxygen species, and alteration of the descending serotoninergic control on PKCγ neurons through 5-HT2A serotonin receptors. Dorsal horn PKCγ neurons, therefore, appear as a relevant therapeutic target to alleviate mechanical allodynia during chronic pain.
... Substance P-expressing cells have been revealed by in situ hybridization for Tac1 mRNA (e.g., Xu et al., 2013), as well as with antibody against the precursor protein preprotachykinin A (PPTA), and intraspinal injection of viral vectors coding for Cre-dependent constructs into Tac1 Cre mice . These approaches have revealed that although most substance Pexpressing cells are excitatory, Tac1 mRNA and PPTA are both found in a population of inhibitory interneurons, presumably corresponding to the Gaba9 population of Häring et al. (2018). ...
Synopsis
The superficial dorsal horn of the spinal cord receives input from primary sensory neurons conveying information that is perceived as pain and itch. The vast majority of neurons in this area are interneurons, which form circuits that are essential for the behavioral expression of these percepts. The classes of neuron involved in these circuits and their functions are poorly understood, although recent studies have developed categorization schemes that account for most of these cells. This chapter highlights the important methodologies for identifying interneuron populations in the dorsal horn and discusses these populations in the light of their predicted functions.
