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Query: UMLS:C0030193 (pain)
 261,466 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The use of cell lines utilized as biologic "minipumps" to provide antinociceptive molecules, such as GABA, in animal models of pain is a newly developing area in transplantation biology. The neuronal cell line, RN33B, derived from E13 brain stem raphe and immortalized with the SV40 temperature-sensitive allele of large T antigen (tsTag), was transfected with rat GAD67 cDNA (glutamate decarboxylase, the synthetic enzyme for GABA), and the GABAergic cell line, 33G10.17, was isolated. The 33G10.17 cells transfected with the GAD67 gene expressed GAD67 protein and synthesized low levels of GABA at permissive temperature (33 degrees C), when the cells were proliferating, and increased GAD67 and GABA during differentiation at nonpermissive temperature (39 degrees C) in vitro, because GAD67 protein expression was upregulated with differentiation. A control cell line, 33V1, transfected with the vector alone, contained no GAD67 or GABA at either temperature. These cell lines were used as grafts in a model of chronic neuropathic pain induced by unilateral chronic constriction injury (CCI) of the sciatic nerve. Pain-related behaviors, including cold and tactile allodynia and thermal and tactile hyperalgesia, were evaluated after CCI in the affected hind paw. When 33G10.17 and 33V1 cells were transplanted in the lumbar subarachnoid space of the spinal cord 1 week after CCI, they survived greater than 7 weeks on the pia mater around the spinal cord. Furthermore, the tactile and cold allodynia and tactile and thermal hyperalgesia induced by CCI was significantly reduced during the 2-7-week period after grafts of 33G10.17 cells. The maximal effect on chronic pain behaviors with the GABAergic grafts occurred 2-3 weeks after transplantation. Transplants of 33V1 control cells had no effect on the allodynia and hyperalgesia induced by CCI. These data suggest that a chronically applied, low local dose of GABA presumably supplied by transplanted cells near the spinal dorsal horn was able to reverse the development of chronic neuropathic pain following CCI. The use of neural cell lines that are able to deliver inhibitory neurotransmitters, such as GABA, in a model of chronic pain offers a novel approach to pain management.
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PMID:Transplants of neuronal cells bioengineered to synthesize GABA alleviate chronic neuropathic pain. 1033 78

The inhibitory neurotransmitter GABA is synthesized by glutamic acid decarboxylase (GAD), and two isoforms of this enzyme exist: GAD65 and GAD67. Immunocytochemical studies of the spinal cord have shown that whilst both are present in the dorsal horn, GAD67 is the predominant form in the ventral horn. The present study was carried out to determine the pattern of coexistence of the two GAD isoforms in axonal boutons in different laminae of the cord, and also to examine the relation of the GADs to the glycine transporter GLYT2 (a marker for glycinergic axons), since many spinal neurons are thought to use GABA and glycine as co-transmitters. Virtually all GAD-immunoreactive boutons throughout the spinal grey matter were labelled by both GAD65 and GAD67 antibodies; however, the relative intensity of staining with the two antibodies varied considerably. In the ventral horn, most immunoreactive boutons showed much stronger labelling with the GAD67 antibody, and many of these were also GLYT2 immunoreactive. However, clusters of boutons with high levels of GAD65 immunoreactivity were observed in the motor nuclei, and these were not labelled with the GLYT2 antibody. In the dorsal horn, some GAD-immunoreactive boutons had relatively high levels of labelling with either GAD65 or GAD67 antibody, whilst others showed a similar degree of labelling with both antibodies. GLYT2 immunoreactivity was associated with many GAD-immunoreactive boutons; however, this did not appear to be related to the pattern of GAD expression. It has recently been reported that there is selective depletion of GAD65, accompanied by a loss of GABAergic inhibition, in the ipsilateral dorsal horn in rats that have undergone peripheral nerve injuries [J Neurosci 22 (2002) 6724]. Our finding that some boutons in the superficial laminae showed relatively high levels of GAD65 and low levels of GAD67 immunoreactivity is therefore significant, since a reduction in GABA synthesis in these axons may contribute to neuropathic pain.
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PMID:Distribution and colocalisation of glutamate decarboxylase isoforms in the rat spinal cord. 1277 May 60

Neuropathic pain after spinal cord injury (SCI) represents a difficult problem that is commonly refractory to conventional medical management. To determine if spinal release of gamma-amino butyric acid (GABA) could reduce below-level central neuropathic pain after SCI, we constructed a replication-incompetent herpes simplex virus (HSV)-based vector encoding one isoform of human glutamic acid decarboxylase (GAD67). Dorsal root ganglion (DRG) neurons transduced in vitro or in vivo by subcutaneous inoculation produced GAD and released GABA constitutively. T13 spinal cord hemisection resulted in central neuropathic pain manifested by mechanical allodynia and thermal hyperalgesia. Subcutaneous inoculation of the vector into both feet reduced both manifestations of below-level SCI pain; the vector-mediated effect was partially reversed by intrathecal bicuculline or phaclofen at doses that did not affect thresholds in normal or injured uninoculated animals. Vector-mediated GABA release attenuated the increase in spinal calcitonin gene-related peptide immunoreactivity caused by cord hemisection. These results suggest that HSV-mediated gene transfer to DRG could be used to treat below-level central neuropathic pain after incomplete SCI.
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PMID:Peripherally delivered glutamic acid decarboxylase gene therapy for spinal cord injury pain. 1523 42

The processing of sensory, including nociceptive, information in spinal dorsal horn is critically modulated by spinal GABAergic neurones. For example, blockade of spinal GABA(A) receptors leads to pain evoked by normally innocuous tactile stimulation (tactile allodynia) in rats. GABAergic dorsal horn neurones have been classified neurochemically and morphologically, but little is known about their physiological properties. We used a transgenic mouse strain coexpressing enhanced green fluorescent protein (EGFP) and the GABA-synthesizing enzyme GAD67 to investigate the properties of a subgroup of GABAergic neurones. Immunohistochemistry showed that EGFP-expressing neurones accounted for about one-third of the GABAergic neurones in lamina II of the spinal dorsal horn. They constituted a neurochemically rather heterogeneous group where 27% of the neurones coexpressed glycine, 23% coexpressed parvalbumin and 14% coexpressed neuronal nitric oxide synthase (nNOS). We found almost no expression of protein kinase Cgamma (PKCgamma) in EGFP-labelled neurones but a high costaining with PKCbetaII (78%). The whole-cell patch-clamp technique was used to intracellularly label and physiologically characterize EGFP- and non-EGFP-expressing lamina II neurones in spinal cord slices. Sixty-two per cent of the EGFP-labelled neurones were islet cells while the morphology of non-EGFP-labelled neurones was more variable. When stimulated by rectangular current injections, EGFP-expressing neurones typically exhibited an initial bursting firing pattern while non-EGFP-expressing neurones were either of the gap or the delayed firing type. EGFP-expressing neurones received a greater proportion of monosynaptic input from the dorsal root, especially from primary afferent C-fibres. In conclusion, EGFP expression defined a substantial but, with respect to the measured parameters, rather inhomogeneous subgroup of GABAergic neurones in spinal lamina II. These results provide a base to elucidate the functional roles of this subgroup of GABAergic lamina II neurones, e.g. for nociception.
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PMID:Physiological, neurochemical and morphological properties of a subgroup of GABAergic spinal lamina II neurones identified by expression of green fluorescent protein in mice. 1528 47

Aberrant GABAergic inhibition in spinal dorsal horn may underlie some forms of neuropathic pain. Potential, but yet unexplored, mechanisms include reduced excitability, abnormal discharge patterns or altered synaptic input of spinal GABAergic neurons. To test these hypotheses, we quantitatively compared active and passive membrane properties, firing patterns in response to depolarizing current steps and synaptic input of GABAergic neurons in spinal dorsal horn lamina II of neuropathic and of control animals. Transgenic mice were used which expressed enhanced green fluorescent protein (EGFP) controlled by the GAD67 promoter, thereby labelling one-third of all spinal GABAergic neurons. In all neuropathic mice included in this study, chronic constriction injury of one sciatic nerve led to tactile allodynia and thermal hyperalgesia. Control mice were sham-operated. Membrane excitability of GABAergic neurons from neuropathic or sham-treated animals was indistinguishable. The most frequent firing patterns observed in neuropathic and sham-operated animals were the initial burst (neuropathic: 46%, sham-treated: 42%), the gap (neuropathic: 31%, sham-treated: 29%) and the tonic firing pattern (neuropathic: 16%, sham-treated: 24%). The synaptic input from dorsal root afferents was similar in neuropathic and in control animals. Thus, a reduced membrane excitability, altered firing patterns or changes in synaptic input of this group of GABAergic neurons in lamina II of the spinal cord dorsal horn are unlikely causes for neuropathic pain.
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PMID:Physiological properties of spinal lamina II GABAergic neurons in mice following peripheral nerve injury. 1705 34

Dysfunction of the spinal GABAergic system has been implicated in pain syndromes following spinal cord injury (SCI). Since lamina I is involved in nociceptive and thermal signaling, we characterized the effects of chronic SCI on the cellular properties of its GABAergic neurons fluorescently identified in spinal slices from GAD67-GFP transgenic mice. Whole cell recordings were obtained from the lumbar cord of 13- to 17-day-old mice, including those having had a thoracic segment (T8-11) removed 6-9 days prior to experiments. Following chronic SCI, the distribution, incidence, and firing classes of GFP+ cells remained similar to controls, and there were minimal changes in membrane properties in cells that responded to current injection with a single spike. In contrast, cells displaying tonic/initial burst firing had more depolarized membrane potentials, increased steady-state outward currents, and increased spike heights. Moreover, higher firing frequencies and spontaneous plateau potentials were much more prevalent after chronic SCI, and these changes occurred predominantly in cells displaying a tonic firing pattern. Persistent inward currents (PICs) were observed in a similar fraction of cells from spinal transects and may have contributed to these plateaus. Persistent Na+ and L-type Ca2+ channels likely contributed to the currents as both were identified pharmacologically. In conclusion, chronic SCI induces a plastic response in a subpopulation of lamina I GABAergic interneurons. Alterations are directed toward amplifying neuronal responsiveness. How these changes alter spinal sensory integration and whether they contribute to sensory dysfunction remains to be elucidated.
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PMID:Spinal cord injury causes plasticity in a subpopulation of lamina I GABAergic interneurons. 1848 Mar 73

The analgesic effects of morphine are mediated, in part, by periaqueductal gray (PAG) neurons that project to the rostral ventromedial medulla (RVM). Although much of the neural circuitry within the RVM has been described, the relationship between RVM neurons and PAG input and spinal output is not known. The objective of this study was to determine whether GABAergic output neurons from the PAG target RVM reticulospinal neurons. Immunocytochemistry and confocal microscopy revealed that PAG neurons project extensively to RVM neurons projecting to the spinal cord, and two-thirds of these reticulospinal neurons appear to be GABAergic (contain GAD67 immunoreactivity). The majority (71%) of PAG fibers that contact RVM reticulospinal GAD67-immunoreactive neurons also contained GAD67 immunoreactivity. Thus, there is an inhibitory projection from PAG to inhibitory RVM reticulospinal neurons. However, there were also PAG projections to the RVM that did not contain GAD67 immunoreactivity. Additional experiments were conducted to determine whether the heterogeneity in this projection can be explained by the electrophysiological character of the RVM target neurons. PAG projections to electrophysiologically defined and juxtacellularly filled ON, OFF, and Neutral cells in the RVM were examined. Similar to the pattern reported above, both GAD67- and non-GAD67-immunoreactive PAG neurons project to RVM ON, OFF, and Neutral cells in the RVM. These inputs include a GAD67-immunoreactive projection to a GAD67-immunoreactive ON cell and non-GAD67 projections to GAD67-immunoreactive OFF cells. This pattern is consistent with PAG neurons producing antinociception by direct excitation of RVM OFF cells and inhibition of ON cells.
Pain 2008 Nov 30
PMID:Periaqueductal gray neurons project to spinally projecting GABAergic neurons in the rostral ventromedial medulla. 1892 35

Endogenous pain control is, in part, mediated by descending inhibition of spinal nociception via spinal release of noradrenaline. Antinociception by activation of descending noradrenergic fibres has partially been attributed to the direct inhibition of nociceptive spinal neurons. Here, we tested the alternative hypothesis: the direct excitation of inhibitory spinal interneurons by noradrenaline. Transverse lumbar spinal cord slices were obtained from adult mice expressing enhanced green fluorescent protein (EGFP) in GABAergic neurons under control of the GAD67 promoter. Recordings were made from a total of 113 EGFP-expressing neurons and non-EGFP-expressing neurons in spinal laminae II and III with the perforated patch-clamp technique. In lamina II, where mainly nociceptive afferents terminate, noradrenaline (20 microM) depolarised significantly more EGFP-labelled (41%) than non-EGFP-labelled GABAergic neurons (4%). In contrast, noradrenaline hyperpolarised significantly more non-EGFP-labelled (46%) than EGFP-labelled GABAergic neurons (20%). In lamina III, where low threshold afferents terminate, EGFP-labelled neurons were never depolarised but either hyperpolarised (25%) or not affected (75%) by noradrenaline. Depolarisations of EGFP-labelled lamina II neurons were mimicked by the alpha(1)-adrenoceptor agonist phenylephrine (10-20 microM) and abolished by the alpha(1)-adrenoceptor antagonist prazosin (2 microM). Hyperpolarisations of EGFP- and non-EGFP-labelled neurons were abolished by the alpha(2)-adrenoceptor antagonist yohimbine (2 microM). These results show that noradrenaline directly excites inhibitory (GABAergic) lamina II interneurons in addition to its inhibitory effect on (putatively excitatory) interneurons in superficial spinal dorsal horn. Both effects of noradrenaline constitute a synergism in descending inhibition of nociceptive information in the spinal dorsal horn.
Pain 2009 Sep
PMID:Direct excitation of spinal GABAergic interneurons by noradrenaline. 1960 44

A long line of experimental evidence indicates that endogenous cannabinoid mechanisms play important roles in nociceptive information processing in various areas of the nervous system including the spinal cord. Although it is extensively documented that the cannabinoid-1 receptor (CB(1)-R) is strongly expressed in the superficial spinal dorsal horn, its cellular distribution is poorly defined, hampering our interpretation of the effect of cannabinoids on pain processing spinal neural circuits. Thus, we investigated the cellular distribution of CB(1)-Rs in laminae I and II of the rodent spinal dorsal horn with immunocytochemical methods. Axonal varicosities revealed a strong immunoreactivity for CB(1)-R, but no CB(1)-R expression was observed on dendrites and perikarya of neurons. Investigating the co-localization of CB(1)-R with markers of peptidergic and non-peptidergic primary afferents, and axon terminals of putative glutamatergic and GABAergic spinal neurons we found that nearly half of the peptidergic (immunoreactive for calcitonin gene-related peptide) and more than 20% of the non-peptidergic (binding isolectin B4) nociceptive primary afferents, more than one-third and approximately 20% of the axon terminals of putative glutamatergic (immunoreactive for vesicular glutamate transporter 2) and GABAergic (immunoreactive for glutamic acid decarboxylase; GAD65 and/or GAD67) spinal interneurons, respectively, were positively stained for CB(1)-R. In addition to axon terminals, almost half of the astrocytic (immunoreactive for glial fibrillary acidic protein) and nearly 80% of microglial (immunoreactive for CD11b) profiles were also immunolabeled for CB(1)-R. The findings suggest that the activity-dependent release of endogenous cannabinoids activates a complex signaling mechanism in pain processing spinal neural circuits into which both neurons and glial cells may contribute.
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PMID:Neuronal and glial localization of the cannabinoid-1 receptor in the superficial spinal dorsal horn of the rodent spinal cord. 1961 76

Abstract In this study we explore if loss of GABAergic inhibitory interneurons in the superficial dorsal horn of the spinal cord contributes to reduced GABAergic tone and neuropathic pain following spinal cord injury (SCI). A moderate contusion injury to T11 resulted in the development of mechanical hyperalgesia and thermal hyperalgesia below the level of the lesion in gad1:GFP mice that were alleviated by IP administration of the GABA transporter antagonist tiagabine. Six weeks following SCI a decreased number of GFP(+) neurons were observed in the dorsal horn of SCI animals relative to sham mice. Tissue from a mouse 2 weeks post-SCI was subsequently observed to express activated caspase-3, indicative of apoptosis, co-localized to some GFP(+) GABAergic neurons. Glutamate decarboxylase (GAD)65 and GAD67 immunohistochemical staining was reduced in the dorsal horn of SCI animals. This observation was confirmed in Western blots showing reduced immunoreactivity for GAD67, as well as GABA transporter (GAT)1. Reversal of post-SCI neuropathic pain by tiagabine suggests that reduced GABAergic tone may contribute to hyperalgesia symptoms. This is supported by the subsequent observation that SCI reduced the number of GFP(+) inhibitory neurons, and the finding that some GABAergic GFP(+) neurons undergo cell death at a time point consistent with the development of neuropathic pain following SCI. Concordantly, reductions in both GAD65 and GAD67 and GAT1 immunoreactivity also support the observation of a loss of GABAergic inhibition and the associated spinal interneurons.
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PMID:Loss of GABAergic interneurons in laminae I-III of the spinal cord dorsal horn contributes to reduced GABAergic tone and neuropathic pain after spinal cord injury. 2005 2


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