ArticleLiterature Review

GABA puts a stop to pain

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Abstract

A lack of inhibition, particularly that mediated by gamma-amino butyric acid (GABA), the main inhibitory transmitter of the central nervous system (CNS), is responsible for many pain states. Until recently, few GABA acting drugs were available and were prescribed mostly for relieving muscle spasms, anxiety and epilepsy, but rarely for pain. The basic metabolic pathway of GABA is well known and we are now beginning to understand the function of this neurotransmitter in the complex circuitry underlying pain, especially in the context of nerve injury. Analgesic compounds are now being developed targeting GABA transporters as well as GABA associated enzymes and receptors. Some GABA analogs act by inhibiting ion channels, a property that contributes to their analgesic effects. However, despite considerable progress in developing new compounds, the use of systemically acting GABAergic drugs is limited by unwanted side-effects on systems other than those involved in pain, and by the fact that in certain areas of the brain, GABA can enhance rather than reduce pain. The advent of new drugs targeting subtypes of GABA receptors and transporters and the possibility of using newly developed delivery systems, such as intrathecal pumps and viral vectors, to target specific areas of the nervous system will likely help circumvent these problems.

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... 16 GABA is abundant in the spinal cord, it is presented by interneurons only and not by the projection neurons. 17 GABAergic interneurons are localized largely in superficial laminae, while some are in deeper laminae of the dorsal and ventral horn. The inhibitory part of the GABAergic system is also distributed through various synaptic organizations that are axosomatic or axoaxonic. ...
... The direct antinociceptive descending inhibition through GABA and glycine pathways also help in controlling nociceptive inputs, which are activated by bulbospinal projections of the brain stem. 17 In contrast to this, some reports suggest that inhibitory GAB-Aergic transmission may transmit pain impulses rather than inhibiting them. Nevertheless, the activation of GABAA and GABAB receptors, in general, have shown antinociceptive effects. ...
... Derivatives of hydrazine inhibit the binding of this cofactor and thus reduce the activity of GATs to raise GABA. 17 Although tiagabine is the only clinically approved GAT inhibitor for NP, several molecules and drugs are under investigation for the same. 17,88 In a recent study, novel functionalized amino acids that were designed and synthesized exhibited inhibitory effects on mGAT4 and mGAT2 transporters and showed analgesic effects in preclinical studies of 3 different NP mod-els. ...
Article
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Traumatic spinal cord injury (SCI) is the devastating neurological damage to the spinal cord that becomes more complicated in the secondary phase. The secondary injury comes with inevitable long-lasting complications, such as chronic neuropathic pain (CNP) and spasticity which interfere with day to day activities of SCI patients. Mechanisms underlying CNP post-SCI are complex and remain refractory to current medical treatment. Due to the damage, extensive inhibitory, excitatory tone dysregulation causes maladaptive synaptic transmissions, further altering the nociceptive and nonnociceptive pathways. Excitotoxicity mediated GABAergic cell loss, downregulation of glutamate acid decarboxylase enzyme, upregulation of gamma-aminobutyric acid (GABA) transporters, overactivation of glutamate receptors are some of the key evidence for hypoactive inhibitory tone contributing to CNP and spasticity post-SCI. Restoring the inhibitory GABAergic tone and preventing damage-induced excitotoxicity by employing various strategies provide neuroprotective and analgesic effects. The present article will discuss CNP and spasticity post-SCI, understanding their pathophysiological mechanisms, especially GABA-glutamate-related mechanisms, therapeutic interventions targeting them, and progress regarding how regulating the excitatory-inhibitory tone may lead to more targeted treatments for these distressing complications. Taking background knowledge of GABAergic analgesia and recent advancements, we aim to highlight how far we have reached in promoting inhibitory GABAergic tone for SCI-CNP and spasticity.
... γ-Aminobutyric acid (GABA) is well known as the main inhibitory neurotransmitter of the CNS, and its low levels are responsible for many pain states. Additionally, the experimental data and clinical studies clearly confirm an important role of GABA in the mechanism and treatment of epileptic seizures [6]. However, recent studies have provided strong evidences that GABA B receptors are also localized in the periphery; surprising in this context is the finding of GABA localization at the terminal endings of corneal nociceptors [7]. ...
... Synthesis of esters based on monocyclic terpenes and GABA (1)(2)(3)(4) was carried out via Steglich esterification with N,N′-dicyclohexylcarbodiimide (DCC) and 4-dimethylaminopyridine (DMAP) as a catalyst in dichloromethane (DCM). The following terpenes were used for esters preparation: L-menthol (5), thymol (6), carvacrol (7), and guaiacol (8). Of these esters, compounds 1 and 2 had been prepared previously and are only shown herein for comparison. ...
... Boc-protected GABA was not obtained commercially and has been synthesized according to the literature procedure [21]. Structures of the obtained compound were established by 1 H-NMR spectroscopy on a AVANCE DRX 500 (500 MHz) instrument (Bruker, Davis, CA, USA) using DMSO-d 6 and CDCl 3 as solvents and TMS as an internal standard. FAB mass spectrum was obtained on a VG 70-70EQ mass spectrometer (VG Analytical Ltd., Manchester, UK) equipped with Xe ion gun (8 kV); the sample was mixed with m-nitrobenzyl-alcohol matrix. ...
Article
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Novel esters of γ-aminobutyric acid (GABA) with monocyclic terpenes were synthesized via Steglich esterification and characterized by 1 H-NMR, IR and mass spectral studies. Their anticonvulsant, analgesic and anti-inflammatory activities were evaluated by a PTZ-induced convulsion model, AITC-induced hyperalgesia and AITC-induced paw edema, respectively. All studied esters, as well as their parent terpenes, were found to produce antinociceptive effects in the AITC-induced model and attenuate acute pain more than the reference drug benzocaine after their topical application. GABA esters of L-menthol and thymol were also shown to exceed the reference drug ibuprofen in their ability to decrease the inflammatory state induced by intraplantar injection of the TRPA1 activator AITC. The present findings indicate that GABA esters of carvacrol and guaiacol are not a classical prodrug and possess their own pharmacological activity. Prolonged antiseizure action of the ester based on the amino acid and guaiacol (200 mg/kg) was revealed at 24 h after oral administration. Furthermore, orally co-administered gidazepam (1 mg/kg) and GABA esters of L-menthol, thymol and carvacrol produce synergistic seizure prevention effects.
... GABAergic inhibitory neurotransmission in the central nervous system plays an important role in regulating nociceptive pathways in supraspinal areas, such as the PAG, insular cortex and ACC, as well as in the spinal cord. These may be potential mechanisms underlying the outcome of analgesia regarding both affective and sensitive discriminative components of pain (Jasmin et al., 2004;Juarez-salinas et al., 2019). Therefore, it would be possible for ESI-induced antinociception to involve GABAergic signaling through the pIC and pain-related areas. ...
... In addition, the results obtained here show a decrease in the hypersensitivity of Sham animals after mBIC administration. Considering that a facilitation effect involving PAG and RVM has an important GABA A -dependent contribution to the development of hypersensitivity in the CCI model (Jasmin et al., 2004), intrathecal administration of mBIC may have influenced the activity of this facilitatory pathway, resulting in the observed antinociceptive response. ...
... The cingulate cortex has a known connectivity with the insula (Lu et al., 2016) and contains a large number of GABAergic terminals and GABA A receptors responsible for regulating pain-associated behavioral responses (LaGraize, 2007). Moreover, the inhibition of the PAG and rostroventromedial medulla (RVM) is important to modulate efferent projections of the descending pain modulatory pathway (Calejesan et al., 2000;Jasmin et al., 2004). Regarding the hippocampus, increased GABA signaling accompanies deficits in spatial learning (Saffarpour et al., 2017). ...
Article
The insula has emerged as a critical target for electrical stimulation since it influences pathological pain states. We investigated the effects of repetitive electrical stimulation of the insular cortex (ESI) on mechanical nociception, and general locomotor activity in rats subjected to chronic constriction injury (CCI) of the sciatic nerve. We also studied neuroplastic changes in central pain areas and the involvement of GABAergic signaling on ESI effects. CCI rats had electrodes implanted in the left agranular posterior insular cortex (pIC), and mechanical sensitivity was evaluated before and after one or five daily consecutive ESIs (15 min each, 60 Hz, 210 μs, 1 V). Five ESIs (repetitive ESI) induced sustained mechanical antinociception from the first to the last behavioral assessment without interfering with locomotor activity. A marked increase in Fos immunoreactivity in pIC and a decrease in the anterior and mid-cingulate cortex, periaqueductal gray and hippocampus were noticed after five ESIs. The intrathecal administration of the GABAA receptor antagonist bicuculline methiodide reversed the stimulation-induced antinociception after five ESIs. ESI increased GAD65 levels in pIC but did not interfere with GABA, glutamate or glycine levels. No changes in GFAP immunoreactivity were found in this work. Altogether, the results indicate the efficacy of repetitive ESI for the treatment of experimental neuropathic pain and suggest a potential influence of pIC in regulating pain pathways partially through modulating GABAergic signaling.
... A potentiation of inhibitory neurotransmission should in principle allow compensating for this loss. Benzodiazepines, which facilitate the action of GABA at GABA A receptors exert clear analgesic or antihyperalgesic actions after local spinal application, both in animal models of pain (Clavier et al., 1992;Sumida et al., 1995) and in patients (Tucker et al., 2004a;Tucker et al., 2004b), for a comprehensive review see (Jasmin et al., 2004). This thesis uses an integrative approach combining pharmacological, behavioral, electrophysiological and morphological experiments in wild type and genetically modified mice to unravel the identity and the localization of the GABA A receptor subtypes mediating this analgesia. ...
... Importantly, spinally injected diazepam is not effective against pain in non-inflamed or noninjured animals but only reverses pathologically increased pain sensitivity, a finding that is in good agreement with the notion that benzodiazepines are generally not analgesic (Jasmin et al., 2004). Therefore its action should be considered as anti-hyperalgesic rather than anagesic. ...
... A possible mechanism to reverse these effects is through treatment with benzodiazepines (Knabl, Witschi et al. 2008;Knabl, Zeilhofer et al. 2009;Zeilhofer, Witschi et al. 2009) which augment spinal GABAergic neurotransmission postsynaptically. This notion is supported by the efficacy of spinally applied benzodiazepines for chronic pain conditions in humans (for review see (Jasmin, Wu et al. 2004)); and their efficacy in preclinical pain models (Knabl, Witschi et al. 2008;Knabl, Zeilhofer et al. 2009). ...
... Critically, benzodiazepines that "spare" α1-containing subunits do not induce sedation yet achieve analgesia in all of these models (Knabl, Witschi et al. 2008;Munro, Lopez-Garcia et al. 2008;Knabl, Zeilhofer et al. 2009). Our results with intrathecal MZL are consistent with previous electrophysiological experiments in the SNL model (Kontinen and Dickenson 2000); with behavioral and biochemical experiments in the chronic constriction injury model of PNI (Lim, Lim et al. 2006); with experiments in rats with chronic inflammation of the hindpaw from complete Freund's adjuvant (CFA) injection (Anseloni and Gold 2008); and with reports of alleviation of pain in humans with spinal benzodiazepines (Jasmin, Wu et al. 2004). Hence, these results provide further support for a spinal site of action for anti-allodynic effects of benzodiazepines after PNI. ...
... Subsequently, after GAT-1 cloning and functional characterization (Guastella et al., 1990), tiagabine was demonstrated to interact specifically with it (Borden et al., 1994;Borden, 1996) and to be a clinically effective antiepileptic drug (Suzdak and Jansen, 1995;Schousboe and White, 2009;Froestl, 2011). The selectivity of tiagabine for GAT-1 confines its action to those regions of the central nervous system where the transporter plays a large role (neocortex, cerebellum, and hippocampus; Jasmin et al., 2004). Tiagabine has also been found to exert antinociceptive, anxiolytic-like, sedative, and antidepressant-like actions (Jasmin et al., 2004;Sałat et al., 2015). ...
... The selectivity of tiagabine for GAT-1 confines its action to those regions of the central nervous system where the transporter plays a large role (neocortex, cerebellum, and hippocampus; Jasmin et al., 2004). Tiagabine has also been found to exert antinociceptive, anxiolytic-like, sedative, and antidepressant-like actions (Jasmin et al., 2004;Sałat et al., 2015). Finally, tiagabine monotherapy appears to improve the performance of epilepsy patients on a number of neuropsychological tests (Dodrill et al., 1998), an effect that seems to relate to the report that heterozygous mice show greater learning and memory compared to wild-type and homozygous GAT-1 −/− mice (Shi et al., 2012). ...
Article
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γ-Aminobutyric acid (GABA) transporter (GAT)-1, the major GABA transporter in the brain, plays a key role in modulating GABA signaling and is involved in the pathophysiology of several neuropsychiatric diseases, including epilepsy. The original description of GAT-1 as a neuronal transporter has guided the interpretation of the findings of all physiological, pharmacological, genetic, or clinical studies. However, evidence published in the past few years, some of which is briefly reviewed herein, does not seem to be consistent with a neurocentric view of GAT-1 function and calls for more detailed analysis of its localization. We therefore performed a thorough systematic assessment of GAT-1 localization in neocortex and subcortical white matter. In line with earlier work, we found that GAT-1 was robustly expressed in axon terminals forming symmetric synapses and in astrocytic processes, whereas its astrocytic expression was more diffuse than expected and, even more surprisingly, immature and mature oligodendrocytes and microglial cells also expressed the transporter. These data indicate that the era of “neuronal” and “glial” GABA transporters has finally come to a close and provide a wider perspective from which to view GABA-mediated physiological phenomena. In addition, given the well-known involvement of astrocytes, oligodendrocytes, and microglial cells in physiological as well as pathological conditions, the demonstration of functional GAT-1 in these cells is expected to provide greater insight into the phenomena occurring in the diseased brain as well as to prompt a reassessment of earlier findings.
... Among the eight free AAs (Thr, Ala, Pro, Phe, Cys, Tau, Orn, and GABA) increased by AP supplementation, five AAs such as Thr, Ala, Pro, Cys, and Tau were reported to yield gut-protective effects on gut health [3,[5][6][7][20][21][22][23][24]. Dietary Thr supplementation may promote intestinal health by modulating gut mucins and inflammation [5,6]. ...
... In this study, GABA in the cecum contents was clearly detected in the NPAP group but was undetected in the other groups. GABA is an inhibitory neurotransmitter in the nervous system and suppresses the sensation of pain and anxiety [24]. Recurrent abdominal pain is a common and costly health-care problem attributed partially to visceral hypersensitivity. ...
Article
Our recent study indicated that dietary Aspergillus oryzae-derived protease preparation (AP), through its enzymatic activity, exerted a bifidogenic effect in rats. We hypothesized that dietary AP links to protein degradation and subsequently elevates gut-protective amino acids (AAs) in rats fed adequate protein diet. In this study, dietary AP markedly increased the relative abundance of Bifidobacterium and Lactobacillus and the levels of free threonine, alanine, proline, taurine, ornithine, phenylalanine, cystine, and γ-aminobutyric acid in the cecum contents of rats fed with an adequate protein diet, but not in those fed with a low-protein diet. The elevated AAs, except ornithine and phenylalanine, potentially have gut-related health benefits. Some of the AP-modulated free AAs appeared to be associated with the relative abundance of Bifidobacterium and Lactobacillus. Thus, AP combined with adequate protein diet is likely to increase the levels of cecum beneficial free AAs, which is partially associated with the relative abundance of the probiotics.
... Although most of the studies to determine the mechanisms underlying the anti-addictive and anti-nociceptive effects of coronaridine congeners have been oriented toward AChRs, it is plausible that modulation of GABA A Rs also plays a role in these activities, considering that these receptors are involved in pain [9] and addiction [10]. In this regard, determining the functional and structural features of the interaction of (+)-catharanthine with the GABA A R is an important and necessary step for the advancement of this hypothesis and might help to shed light on the anti-addictive properties of these compounds given that several other GABA A R potentiators, including benzodiazepines, barbiturates, and ethanol, can induce tolerance and dependence [11][12][13][14]. ...
... After two consecutive applications of EC 5 GABA, (+)-catharanthine was co-applied with EC 5 GABA, followed by another application of EC 5 GABA to demonstrate washout of the effect. The experiments on receptors containing the α1 (Q241L), β3(M286C), or β2(N265S) mutated subunits were performed following similar protocols, activating the receptors with a low (EC [5][6][7][8][9][10][11][12][13][14][15] ) concentration of GABA. The potentiating effect of a modulator was calculated as (I peak,GABA+modulator / I peak,GABA ) − 1, and expressed as % change in response to GABA. ...
Article
(+)-Catharanthine, a coronaridine congener, potentiates the γ-aminobutyric acid type A receptor (GABAAR) and induces sedation through a non-benzodiazepine mechanism, but the specific site of action and intrinsic mechanism have not been defined. Here, we describe GABAAR subtype selectivity and location of the putative binding site for (+)-catharanthine using electrophysiological, site-directed mutagenesis, functional competition, and molecular docking experiments. Electrophysiological and in silico experiments showed that (+)-catharanthine potentiates the responses to low, subsaturating GABA at β2/3-containing GABAARs 2.4-3.5 times more efficaciously than at β1-containing GABAARs. The activity of (+)-catharanthine is reduced by the β2(N265S) mutation that decreases GABAAR potentiation by loreclezole, but not by the β3(M286C) or α1(Q241L) mutations that reduce receptor potentiation by R(+)-etomidate or neurosteroids, respectively. Competitive functional experiments indicated that the binding site for (+)-catharanthine overlaps that for loreclezole, but not those for R(+)-etomidate or potentiating neurosteroids. Molecular docking experiments suggested that (+)-catharanthine binds at the β(+)/α(-) intersubunit interface near the TM2-TM3 loop, where it forms H-bonds with β2-D282 (TM3), β2-K279 (TM2-TM3 loop), and β2-N265 and β2-R269 (TM2). Site-directed mutagenesis experiments supported the in silico results, demonstrating that the K279A and D282A substitutions, that lead to a loss of H-bonding ability of the mutated residue, and the N265S mutation, impair the gating efficacy of (+)-catharanthine. We infer that (+)-catharanthine potentiates the GABAAR through several H-bond interactions with a binding site located in the β(+)/α(-) interface in the transmembrane domain, near the TM2-TM3 loop, where it overlaps with loreclezole binding site.
... Following the cloning and functional characterization of GAT-1 (Guastella et al., 1990), the major GABA transporter in the mammalian central nervous system, it became soon evident that tiagabine specifically interacts with the GAT-1 transporter (Borden, 1996;Borden et al., 1994), and that it is clinically effective as antiepileptic drug (Froestl, 2011;Schousboe and White, 2009;Suzdak and Jansen, 1995). Tiagabine's selectivity toward GAT-1 limits its activity to regions of the CNS in which GAT-1 plays a significant role (neocortex, cerebellum, and hippocampus) (Jasmin et al., 2004). In addition, tiagabine, besides its anticonvulsant effect, has antinociceptive, anxiolytic-like, sedative and antidepressant-like properties (Jasmin et al., 2004;Salat et al., 2015). ...
... Tiagabine's selectivity toward GAT-1 limits its activity to regions of the CNS in which GAT-1 plays a significant role (neocortex, cerebellum, and hippocampus) (Jasmin et al., 2004). In addition, tiagabine, besides its anticonvulsant effect, has antinociceptive, anxiolytic-like, sedative and antidepressant-like properties (Jasmin et al., 2004;Salat et al., 2015). ...
Article
Stimulated by the results of a recent paper on the effects of tiagabine, a selective inhibitor of the main GABA transporter GAT-1, on oligodendrogenesis, we verified the possibility that GAT-1 may be expressed in oligodendrocytes using immunocytochemical methods and functional assays. Light microscopic analysis of the subcortical white matter of all animals revealed the presence of numerous GAT-1+ cells of different size (from 3 to 29 µm) and morphology. An electron microscope analysis revealed that, besides fibrous astrocytes and interstitial neurons, GAT-1 immunoreactivity was present in immature and mature oligodendrocytes. Co-localization studies between GAT-1 and markers specific for oligodendrocytes (NG2 and RIP) showed that about 12% of GAT-1 positive cells in the white matter were immature oligodendrocytes, while about 15% were mature oligodendrocytes. In vitro functional assays showed that oligodendrocytes exhibit tiagabine-sensitive Na(+) -dependent GABA uptake. Although relationships between GABA and oligodendrocytes have been known for many years, this is the first demonstration that GAT-1 is expressed in oligodendrocytes. The present results on the one hand definitely closes the era of "neuronal" and "glial" GABA transporters, on the other they suggest that oligodendrocytes may contribute to pathophysiology of the several diseases in which GAT-1 have been implicated to date. GLIA 2017.
... On the other hand, Allo stimulates GABA receptors at multiple sites of the nervous system. One potential site of action of GABA agonist is in the dorsal horn of the spinal cord, where GABA suppresses afferent nociceptive input [25]. However, GABA is also involved in the regulation of descending pain modulatory pathways originating from the rostroventral medulla (RVM) and periaqueductal gray (PAG). ...
Article
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Background: To identify a new strategy for postoperative pain management, we investigated the analgesic effects of allopregnanolone (Allo) in an incisional pain model, and also assessed its effects on the activities of the primary afferent fibers at the dorsal horn. Methods: In experiment 1, 45 rats were assigned to Control, Allo small-dose (0.16 mg/kg), and Allo large-dose (1.6 mg/kg) groups (n = 15 in each). The weight bearing and mechanical withdrawal thresholds of the hind limb were measured before and at 2, 24, 48, and 168 h after Brennan's surgery. In experiment 2, 16 rats were assigned to Control and Allo (0.16 mg/kg) groups (n = 8 in each). The degree of spontaneous pain was measured using the grimace scale after the surgery. Activities of the primary afferent fibers in the spinal cord (L6) were evaluated using immunohistochemical staining. Results: In experiment 1, the withdrawal threshold of the Allo small-dose group was significantly higher than that of the Control group at 2 h after surgery. Intergroup differences in weight bearing were not significant. In experiment 2, intergroup differences in the grimace scale scores were not significant. Substance P release in the Allo (0.16 mg/kg) group was significantly lower than that in the Control group. Conclusions: Systemic administration of Allo inhibited mechanical allodynia and activities of the primary afferent fibers at the dorsal horn in a rat postoperative pain model. Allo was proposed as a candidate for postoperative pain management.
... In both cases, neurotransmitters (e.g. glutamate [excitatory effect, enhances pain] and gamma-aminobutyric acid [GABA; inhibitory effect, reduces pain]) transfer nociceptive impulses via neurons to the spinal cord which are then passed to the brain stem via ascending pathways where they are interpreted within higher centers [35][36][37][38] . Descending pathways simultaneously modify pain perception via the noradrenergic pain regulation system 37,39 . ...
Article
Objective: Pain is one of the most common reasons for an individual to consult their primary care physician, with the majority of chronic pain being treated in the primary care setting. However, many primary care physicians/non-pain medicine specialists lack enough awareness, education and skills to manage pain patients appropriately, and there is currently no clear, common consensus/formal definition of `pain chronification’. Methods: This article, based on an international Change Pain Chronic Advisory Board meeting which was held in Wiesbaden, Germany, in October 2016, provides primary care physicians/non-pain medicine specialists with a narrative overview of pain chronification, including underlying physiological and psychosocial processes, predictive factors for pain chronification, a brief summary of preventive strategies, and the role of primary care physicians and non-pain medicine specialists in the holistic management of pain chronification. Results: Based on currently available evidence, we propose the following consensus-based definition of pain chronification which provides a common framework to raise awareness among non-pain medicine specialists: `Pain chronification describes the process of transient pain progressing into persistent pain; pain processing changes as a result of an imbalance between pain amplification and pain inhibition; genetic, environmental and bio-psychosocial factors determine the risk, the degree, and time-course of chronification.’ Conclusion: Early intervention plays an important role in preventing pain chronification and, as key influencers in the management of patients with acute pain, it is critical that primary care physicians are equipped with the necessary awareness, education and skills to manage pain patients appropriately.
... Özelleşmiş bu duyusal nöronlardan glutamat gibi eksitatör nörotransmitterlerin salınması ağrıyı arttırıcı, GABA gibi inhibitör nörotransmitterlerin salınması ise ağrıyı azaltıcı yönde etki yapar. [11][12][13] Somatik ve visseral yapıların ağrı duyusu, A-delta lifleri ile medulla spinaliste Lamina 1 ve 5'te, C lifleriyle Lamina 1 ve 2'de ikinci sıra nöronlarla sinaps yapar. Somatik yapılarda bulunan nosiseptörler mekanik, kimyasal ve termal uyaranlara karşı hassasken visseral yapılardaki nosiseptörler başlıca gerilme, iskemi ve distansiyona karşı hassastır. ...
... Borneol was recognised as a GABA mediator which may be responsible for pain states. 21,22 In Southeastern Asia, camphor is widely used to treat sprains, swellings and inflammation. In Thai Traditional Medicine it was added into the recipe as a pest deterrent and preservative. ...
Article
Full-text available
Myofascial pain syndrome (MPS) is a chronic pain disorder which causes musculoskeletal pain and inflammation in the body's soft tissues. Thai Traditional Medicine uses hot herbal compresses as analgesic and anti-inflammatory treatment. There are no scientifically validated follow-up studies after treatment using hot herbal compresses. Effects of hot herbal compresses as an alternative treatment for MPS in the upper trapezius muscle compared with the standard treatment (diclofenac) were examined. Sixty patients with myofascial pain syndrome in the upper trapezius muscle were randomly divided into two groups and assigned to receive either hot herbal compress or nonsteroidal anti-inflammatory drug (diclofenac) treatment for 2 weeks. Clinical assessments included visual analogue scale (VAS) for pain score, cervical range of motion (CROM) for the neck and pressure pain threshold (PPT) tolerability before and after treatment. Within the groups, all treatments caused significant improvement in VAS and marginally increased effectiveness in PPT; however, only hot herbal compress treatment improved CROM. Hot herbal compress was more effective than diclofenac in all tests. Results provided comparable clinical efficacy between hot herbal compress and diclofenac after 2 weeks of treatment. Hot herbal compress proved to be an effective complementary or alternative treatment for MPS in the upper trapezius muscle. © 2018 Center for Food and Biomolecules, National Taiwan University
... Moreover, drugs that enhance GABA-mediated inhibitory transmission, and subsequently affect neuronal repetitive firing, can be of relevance in alleviating several painful syndromes, since they can produce a membrane stabilizing effect on sensory neurons and/or enhance intrinsic analgesic responses (Jasmin et al., 2004;Enna and McCarson, 2006). This evidence may help to explain the fact that most of the studies presented in Box 1 (64%) are studies of the possible effect of plants of this genus on pain management (or simple screening for analgesic drugs, which was the most common type of study described). ...
Article
Full-text available
Many people use medicinal plants to relieve disorders related to the central nervous system (CNS), such as depression, epilepsy, anxiety and pain, even though the effectiveness of most of them has not yet been proven through scientific studies. Plants of the Lippia genus (Verbenaceae) are widely used in ethnobotany as a food, for seasoning and in antiseptic remedies. They are also marketed and used for the treatment of different types of pain, including stomachache, abdominal pain and headache, as well as being used as sedatives, anxiolytics and anticonvulsants. Despite their widespread use, there are no reviews on the CNS profile of plants of this genus. Therefore, the databases MEDLINE-PubMed, Embase, Scopus and Web of Science were searched using the terms Lippia and biologic activity. Thirty-five papers were found. Eleven species of Lippia showed CNS activity, with leaves and the aerial parts of plants being the most commonly used, especially in aqueous and ethanol extracts or volatile oil (VO). The species are composed mainly of terpenoids and phenylpropanoids, including polyketides, flavonoids and in less quantity some alkaloids. Although several species of Lippia present analgesic activity, most studies have not explored the mechanisms responsible for this effect, however, there is some evidence that volatile oils and constituents of the extracts may be responsible for the relief of some CNS disorders, but the effects on pain modulation seem to be the most exploited so far.
... 43,44 Importantly, inhibitory interneurons, such as GABAergic neurons, are involved in antinociceptive processing in the ACC sites. 45,46 In this study, we found that in vivo inhibition of GABA A receptors in the ACC reduces mechanical thresholds. On the other hand, the McN-A-343-induced antinociceptive effect was attenuated by co-injection of the GABA A antagonist bicuculline. ...
Article
Full-text available
Cholinergic systems regulate the synaptic transmission resulting in the contribution of the nociceptive behaviors. Anterior cingulate cortex is a key cortical area to play roles in nociception and chronic pain. However, the effect of the activation of cholinergic system for nociception is still unknown in the cortical area. Here, we tested whether the activation of cholinergic receptors can regulate nociceptive behaviors in adult rat anterior cingulate cortex by integrative methods including behavior, immunohistochemical, and electrophysiological methods.
... Moreover, drugs that enhance GABA-mediated inhibitory transmission, and subsequently affect neuronal repetitive firing, can be of relevance in alleviating several painful syndromes, since they can produce a membrane stabilizing effect on sensory neurons and/or enhance intrinsic analgesic responses (Jasmin et al., 2004;Enna and McCarson, 2006). This evidence may help to explain the fact that most of the studies presented in Box 1 (64%) are studies of the possible effect of plants of this genus on pain management (or simple screening for analgesic drugs, which was the most common type of study described). ...
Article
Full-text available
Many people use medicinal plants to relieve disorders related to the central nervous system, such as depression, epilepsy, anxiety and pain, even though the effectiveness of most of them has not yet been proven through scientific studies. Plants of the Lippia genus, Verbenaceae, are widely used in ethnobotany as a food, for seasoning and in antiseptic remedies. They are also marketed and used for the treatment of different types of pain, including stomach ache, abdominal pain and headache, as well as being used as sedatives, anxiolytics and anticonvulsants. Despite their widespread use, there are no reviews on the central nervous system profile of plants of this genus. Therefore, the databases Medline-PubMed, Embase, Scopus and Web of Science were searched using the terms Lippia and biologic activity. Thirty-five papers were found. Eleven species of Lippia showed central nervous system activity, with leaves and the aerial parts of plants being the most commonly used, especially in aqueous and ethanol extracts or volatile oil. The species are composed mainly of terpenoids and phenylpropanoids, including polyketides, flavonoids and in less quantity some alkaloids. Although several species of Lippia present analgesic activity, most studies have not explored the mechanisms responsible for this effect, however, there is some evidence that volatile oils and constituents of the extracts may be responsible for the relief of some CNS disorders, but the effects on pain modulation seem to be the most exploited so far.
... GABA is a nonprotein amino acid which induces hypotensive, diuretic, and tranquilizer effect. It also functions as pain regulating and some pain relieving drugs currently on the market act by targeting GABA receptors (Jasmin et al. 2004). The important role of GABA in mood disorders was first postulated back in 1980, and over the last decades much data has emerged to support the hypothesis. ...
Chapter
The roles of intestinal microorganisms in communication between the gut and brain are gaining increasing recognition. Microbiome driven gut-to-brain communication has been shown to influence stress-related responses in both human and animal models. Sufficient preclinical data are supporting the view that probiotic microorganisms have antidepression potentials. Preclinical evaluations in animal and human models suggested that certain probiotic strains possess anxiolytic activity, similar to antidepressants. The antidepressive effect may be mediated via the vagus nerve, spinal cord, immune systems, or neuroendocrine systems. Such bacterial interactions which cross the interdisciplinary field of microbiology and neurobiology have raised possible alternatives of microbial endocrinology as a natural way to combat stress and/or depression. This current review will address some of the current evidence, possible pathways, and targets of postulated mechanisms.
... GABA is functionally recognized as an inhibitory neurotransmitter in the mammalian central nervous system and is used in pharmaceutical industries due to its several physiological functions in animal systems (Rashmi et al. 2018) such as anti-cancer (Schuller et al. 2008), hyposensitive (Inoue et al. 2003), analgesic (Jasmin et al. 2004), antidepressant, diuretic, tranquilizing (Streeter et al. 2007), anti-epileptic (Landmark 2007) and anti-diabetic properties (Kanwal et al. 2015;Rashmi et al. 2018). GABA enhances growth hormone, plasma concentration, harmonizes circadian rhythms, treats movement disorders and regulates sleep and reproductive functions. ...
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γ-aminobutyric acid (GABA) is a ubiquitous non-protein amino acid widely distributed in prokaryotes and eukaryotes. Recently, it is gaining momentum to treat several human diseases. It is synthesized from glutamate, by glutamate decarboxylase a key enzyme in GABA shunt pathway and has been considered as one of the important bioactive compounds produced in response to several environmental stresses. GABA works as a signalling molecule that plays crucial role in biological organisms under adverse conditions. So far, the metabolism of GABA is extensively studied in plants and other eukaryotes, although in cyanobacteria GABA is less studied than in other prokaryotes. Hence the present review highlights the metabolic pathways of GABA production in cyanobacteria particularly the possible ways (via modifying the exogenous growth conditions and regulating gene expression) to enhance the endogenous GABA pool and its extraction in cost effective way to meet the rising demand due to its diverse physiological functions on human health. Alternatively, we discuss the effects of various environmental stresses in augmenting intracellular production in algal cells. Besides this, the review also emphasizes on different commercial applications of this compound in various industrial sectors such as pharmaceutical industry, food, beverages and dairy industry, bioplastics and biofuel production.
... However, although anecdotal reports suggest some efficacy of classical BDZ in chronic pain patients, classical BDZ are usually not considered as first line therapeutics in these patients (Jasmin et al., 2004). ...
Article
Im Rückenmark sind GABAAR sowohl postsynaptisch auf intrinsischen Neuronen des Hinterhorns als auch auf den Terminalen primär afferenter Nozizeptoren exprimiert, wo sie durch primärafferente Depolarisation (engl. primary afferent depolrization, PAD) zur präsynaptischen Hemmung beitragen. Die meisten dieser präsynaptischen GABAAR gehören zum 2 Typ. Im ersten Teilprojekt der vorliegenden Dissertation untersuchten wir Mäuse, deren Nozizeptoren entweder keine 2 GABAAR exprimierten (sns-2-/-) oder aufgrund einer Punktmutation insensitiv gegenüber Diazepam waren (sns-2R/-). Basale Schmerzschwellen sowie entzündliche und neuropathische Neuropathie waren in beiden Mausstämmen unverändert. Im Entzündungsschmerzmodell war jedoch der antihyperalgetische Effekt von intrathekal injiziertem Diazepam signifikant vermindert. Im zweiten Teilprojekt sollte der mögliche Beitrag supraspinaler 2 GABAAR zur Antihyperalgesie untersucht werden. Ein solcher Beitrag könnte etwa in einer Aufhebung angstvermittelter Hyperalgesie oder in einem genuinen antihyperalgetischen Effekt bestehen. Hierzu wurden HoxB8-2-/- Mäuse, denen 2 GABAAR im Rückenmark und in der Peripherie fehlen, systemisch mit HZ166 behandelt. HZ166 ist ein neu entwickelter Agonist an der Benzodiazepin-Bindungsstelle von GABAAR mit reduzierten sedativen Eigenschaften. Die selektive Ablation spinaler und peripherer GABAAR führte zu einem kompletten Verlust der 2-vermittelten Komponente der HZ166-induzierten Antihyperalgesie im Neuropathiemodell. Diese Ergebnisse zeigen, dass supraspinale 2 GABAAR nicht wesentlich zur HZ166- vermittlelten Antihyperalgesie beitragen, und legen damit auch nahe, dass indirekte Effekte, die z.B. durch die anxiolytische Wirkung zustande kommen könnten, keine wesentliche Rolle spielen. Im dritten Teilprojekt wurde daher die molekulare Zusammensetzung der GABAAR-Subtypen im Hinterhorn des Rückenmarks einer detaillierten Analyse unterzogen. Histologische Färbung von verschiedenen Markerproteinen im selben Schnitt und hochsensitive Detektionsmethoden zeigten, dass die Verteilung der GABAAR im Hinterhorn des Rückenmarks einen sehr hohen Organisationgrad aufweist. Insbesondere 2 und 3 GABAAR zeigten eine strategisch äusserst effektive Verteilung auf Nociceptorterminalen und auf exzitatorischen und inhibitorischen Interneuronen. Die Ergebnisse dieser Untersuchungen belegen, dass 2, 3 und 5 GABAAR auf prä- und postsynaptischen Kompartimenten spezifischer Neuronentypen lokalisiert sind, die eine zentrale Rolle für die GABAerge Kontrolle der Nociception spielen.
... Modulation of the pain signal in the dorsal horn involves local inhibitory and facilitatory interneurons as well as diverse excitatory and inhibitory neurotransmitters. This central sensitization is thought to be mediated largely through the N-methyl-Daspartate (NMDA) receptor complex [25]. ...
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Pain is a homeostatic mechanism that intervenes to protect the organism from harmful stimuli that could damage its integrity. It is made up of two components: the sensory-discriminative component, which identifies the provenance and characteristics of the type of pain; and the affective-motivational component, on which emotional reflexes, following the painful sensation, depend.There is a system for pain control at an encephalic and spinal level, principally made up of the periaqueductal grey matter, the periventricular area, the nucleus raphe magnus, and the pain-inhibition complex situated in the posterior horns of the spinal cord. Through the activation of these pain-control systems, the nervous system suppresses the afference of pain signals. Endogenous opioids represent another analgesic system.In the course of various studies on pain transmission in Down patients, the reduced tolerance of pain and the incapacity to give a qualitative and quantitative description emerged in a powerful way. All of these aspects cause difficulty in evaluating pain. This is linked to several learning difficulties. However, it cannot be excluded that in these anomalies of pain perception, both the anatomical and the neurotransmitter alteration, typical of this syndrome, may hold a certain importance.This fact may have important clinical repercussions that could affect the choice of therapeutic and rehabilitative schemes for treatment of pathologies in which pain is the dominant symptom, such as postoperative pain. It could influence research on analgesics that are more suitable for these patients, the evaluation of the depth of analgesia during surgical operation, and ultimately, absence of obvious pain manifestations. In conclusion, alterations of the central nervous system, neurotransmitters, pain transmission, and all related problems should be considered in the management of pain in patients with Down's syndrome, especially by algologists and anesthesiologists.
... In the spinal cord, the incoming signals are then modulated, transmitted to second order neurons by neurotransmitters, and passed to the brain stem via ascending pathways ( Figure 1). For example, glutamate has an excitatory effect and enhances pain, whereas gamma-aminobutyric acid (GABA) has an inhibitory effect and reduces pain 15,16 . The brain stem essentially acts as a mediator of transmission to higher centers, where the pain signals are interpreted 17,18 . ...
... Oral GABA administration was reported to relieve anxiety (Abdou et al., 2006), improve mood (Sakashita et al., 2019), and reduce symptoms of premenstrual syndrome (Rapkin and Akopians, 2012). In addition, GABA also supports the physiologic adjustment of pituitary gland function and controls growth hormone secretion from the pituitary gland (Acs et al., 1987), promotes muscle protein synthesis (Olarescu et al., 2000), stabilizes blood pressure , and relieves pain (Jasmin et al., 2004). On the contrary, the higher capability of glutamate degradation I was observed in the healthy group. ...
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Migraine is a very common, multifactorial, and recurrent central nervous system disorder that causes throbbing headache, photophobia, phonophobia, nausea, and disability. Migraine occurs more often in females, and its complex physiopathology is not yet fully understood. An increasing number of gastrointestinal disorders have been linked to the occurrence of migraine suggesting that gut microbiota might play a pivotal role in migraine through the gut–brain axis. In the present work, we performed a metagenome-wide association study (MWAS) to determine the relationship between gut microbiota and migraine by analyzing 108 shotgun-sequenced fecal samples obtained from elderly women who suffer from migraine and matched healthy controls. Notably, the alpha diversity was significantly decreased in the migraine group at species, genus, and Kyoto Encyclopedia of Genes and Genomes (KEGG) orthologous levels. Firmicutes, especially the “unfriendly” Clostridium spp., were significantly enriched in the migraine group. Conversely, the healthy controls held more beneficial microorganisms, such as Faecalibacterium prausnitzii, Bifidobacterium adolescentis, and Methanobrevibacter smithii. For functional modules, the migraine group was enriched in gut–brain modules (GBMs) including kynurenine degradation and γ-aminobutyric acid (GABA) synthesis. However, the healthy controls held higher gut metabolic modules (GMMs) including glycolysis, homoacetogenesis, and GBMs including quinolinic acid degradation and S-adenosyl methionine (SAM) synthesis. The differences in gut microbiota composition and function between the migraine and healthy groups provided new information as well as novel therapeutic targets and strategies for migraine treatment, which could help to improve the early diagnosis of the disease, as well as the long-term prognosis and the life quality of patients suffering from migraine.
... A reduction of GABAergic inhibition has been shown to play a prominent role in chronic pain development and in pain maintenance [62]. It is therefore no surprise that GABA receptor agonists have proven effective as an analgesic agent, but important side effects limit its long-term use [63,64]. Identification of a state of disinhibition at such an early stage of recovery in patients with a fracture is of particular clinical relevance in this population since high initial pain is considered a risk factor for chronic pain development [65]. ...
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Objective Primary motor (M1) cortical excitability alterations are involved in the development and maintenance of chronic pain. Less is known about M1-cortical excitability implications in the acute phase of an orthopedic trauma. This study aims to assess acute M1-cortical excitability in patients with an isolated upper limb fracture (IULF) in relation to pain intensity. Methods Eighty-four (56 IULF patients <14 days post-trauma and 28 healthy controls). IULF patients were divided into two subgroups according to pain intensity (mild versus moderate to severe pain). A single transcranial magnetic stimulation (TMS) session was performed over M1 to compare groups on resting motor threshold (rMT), short-intracortical inhibition (SICI), intracortical facilitation (ICF), and long-interval cortical inhibition (LICI). Results Reduced SICI and ICF were found in IULF patients with moderate to severe pain, whereas mild pain was not associated with M1 alterations. Age, sex, and time since the accident had no influence on TMS measures. Discussion These findings show altered M1 in the context of acute moderate to severe pain, suggesting early signs of altered GABAergic inhibitory and glutamatergic facilitatory activities.
... The observed increase in alpha activity during tonic deep-tissue pain may therefore be reflecting a lack of inhibition possibly mediated by the neurotransmitter gammaaminobutyric acid (GABA) (Klimesch et al. 2007;Başar and Güntekin 2008). Increased GABA levels have been previously measured in the ACC and R-AI with MR spectroscopy during tonic painful stimulation (Jasmin et al. 2005;LaGraize and Fuchs 2007;Kupers et al. 2009). The neurotransmitter GABA is involved in the cortical modulation of pain trough inhibition of synapses in the brain (Olsen and Sieghart 2009). ...
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Musculoskeletal pain is a clinical condition that is characterized by ongoing pain and discomfort in the deep tissues such as muscle, bones, ligaments, nerves, and tendons. In the last decades, it was subject to extensive research due to its high prevalence. Still, a quantitative description of the electrical brain activity during musculoskeletal pain is lacking. This study aimed to characterize intracranial current source density (CSD) estimations during sustained deep-tissue experimental pain. Twenty-three healthy volunteers received three types of tonic stimuli for three minutes each: computer-controlled cuff pressure (1) below pain threshold (sustained deep-tissue no-pain, SDTnP), (2) above pain threshold (sustained deep-tissue pain, SDTP) and (3) vibrotactile stimulation (VT). The CSD in response to these stimuli was calculated in seven regions of interest (ROIs) likely involved in pain processing: contralateral anterior cingulate cortex, contralateral primary somatosensory cortex, bilateral anterior insula, contralateral dorsolateral prefrontal cortex, posterior parietal cortex and contralateral premotor cortex. Results showed that participants exhibited an overall increase in spectral power during SDTP in all seven ROIs compared to both SDTnP and VT, likely reflecting the differences in the salience of these stimuli. Moreover, we observed a difference is CSD due to the type of stimulus, likely reflecting somatosensory discrimination of stimulus intensity. These results describe the different contributions of neural oscillations within these brain regions in the processing of sustained deep-tissue pain.
... This suggests that the reward system was activated in the extroverted participants. The activation of the reward system produces increased amounts of neurotransmitters, such as dopamine and gamma-aminobutyric acid (GABA) (55), which promote a happy mood and reduce feelings of pain (56,57). Changes in these brain networks also suggest that there could be activation of the opioid system to release analgesic substances. ...
Article
Background: Placebo and nocebo responses have been increasingly gaining the attention of clinical and scientific researchers. Inconsistent conclusions from current studies indicate that different factors potentially affect both placebo and nocebo responses. Increasing evidence suggests that personality differences may affect the mechanisms of both two responses. In the present work, we explored the characteristics of neural signals of placebo and nocebo responses based on functional connectivity (FC) analysis and Granger causality analysis (GCA). Methods: A total of 34 healthy participants received conditional induction training to establish placebo and nocebo responses. Every participant completed the following experimental workflow, including scanning of baseline, experimental low back pain model establishment, scanning of acute pain status, and scanning of placebo response or nocebo response. We collect visual analogue scale (VAS) data after each scanning. Functional magnetic resonance imaging (fMRI) data from different personality groups were subjected to FC analysis and multivariate GCA (mGCA). Results: Pain scores for placebo and nocebo responses were statistically different across different personality. There are also statistically differences in the neural signals of two responses across different personality. Conclusions: The findings of the present study indicated that extroverted and introverted participants are likely to experience placebo analgesic effects and nocebo hyperalgesia effects, respectively. Both extroverted and introverted participants showed significant changes in brain networks under placebo response. Variation in emotional control and ventromedial prefrontal cortex inactivity may constitute the bulk of the personality differences in placebo analgesia. Differences in the regulation of the sensory conduction system (SCS) and release of the emotional circuit could be important factors affecting personality differences in nocebo hyperalgesia.
... [25] A possible role for targeting gamma-amino-butyric acid (GABA) receptors for pain control has been suggested. [26] Like other benzodiazepines, Midazolam is an agonist of benzodiazepine receptors acting on GABA receptors and facilitate the influx of chloride ions into neurons. The affinity of midazolam to these receptors is twice that of diazepam reflecting its increased potency. ...
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Pain relief, using opiates as a primary choice, is an important part of treating limb fractures. Yet, in order to reduce opiate consumption, other combinations have been introduced. This study aimed to compare pain reduction by a combination of morphine-midazolam with morphine injection in patients with limb fractures. A randomized double-blind study of patients with upper or lower extremity fractures was conducted. Patients' response to treatment with either morphine-midazolam solution or morphine at 15, 30, 45, 60, 120, and 180 minutes were assessed. The Kaplan-Meier curves and generalized estimating equations were examined to evaluate the success of treatment. A total of seventy-two patients aged 18-60 (80.6% male; mean age: 35±17.9 years) were included. At 15, 30, 45, and 60 minutes, successful pain control was seen in 8.83 22.2%, 33.3% and 63.9% of the patients in the morphine group, and 11.1%, 27.7%, 44.4% and 63.8% in the midazolam-morphine group. By the third hour, pain-control was achieved in all patients receiving morphine while pain persisted in one patient receiving morphine-midazolam. Log-rank test showed no significant difference between the two groups (p=0.55). Our findings revealed that adding midazolam to morphine did not improve its pain-relief profile.
... This anticonvulsant drug is a highly selective GAT1 inhibitor with IC 50 value of 0.8 mM [10,11]. The selectivity toward GAT1 is thought to limit its activity to regions of the CNS in which GAT1 plays a significant role (the cortex, cerebellum, and hippocampus) [12], and it is expected that this drug, apart from its anticonvulsant activity, may present anxiolytic, antinociceptive, and antidepressant properties which are attributed to GAT1 inhibition [7]. Although the concept of anxiolytic, antidepressant-like and antinociceptive properties of brain GAT1 inhibition is not new, so far, there are limited and rather conflicting data from animal studies regarding other than anticonvulsant properties of tiagabine. ...
Article
Tiagabine, a selective inhibitor of GABA transporter subtype 1 is used as an add-on therapy of partial seizures in humans but its mechanism of action suggests other potential medical indications for this drug. In this research we assess its pharmacological activity in several screening models of seizures, pain, anxiety and depression in mice. For pharmacological tests tiagabine was administered intraperitoneally 60min before the assay. Behavioral tests were performed using models of chemically and electrically induced seizures, thermal acute pain and formalin-induced tonic pain. Anxiolytic-like properties were evaluated using the four plate test and the elevated plus maze test. Antidepressant-like activity was assessed in the forced swim test. In addition, to exclude false positive results in these assays, the influence of tiagabine on animals' locomotor activity and motor coordination was investigated, too. Tiagabine demonstrated anticonvulsant properties in chemically induced seizures (pentylenetetrazole and pilocarpine seizures). At the dose of 100mg/kg it also elevated the seizure threshold for electrically induced seizures by 31.6% (p<0.01), but it had no activity in the maximal electroshock seizure test. Tiagabine showed anxiolytic-like and antidepressant-like effects. Although it apparently reduced animals' nociceptive responses in pain tests, these activities rather resulted from its sedative and motor-impairing properties demonstrated in the locomotor activity and the rotarod tests, respectively. The results obtained in the present study suggest that tiagabine, apart its anticonvulsant effect, has anxiolytic-like, sedative and antidepressant-like properties. In view of this, it can be potentially used in the treatment of anxiety and mood disorders. Copyright © 2014. Published by Elsevier Urban & Partner Sp. z o.o.
... Clinically, only a few studies have observed the beneficial effect of tiagabine in chronic pain (e.g., fibromyalgia and peripheral neuropathy) [214,215]. However, currently in the US, tiagabine may be prescribed off label not only for neuropathic pain patients but also to treat anxiety disorders [216]. ...
... In fact, Kishimoto et al. presented electrophysiological evidence of their co-localization on individual presynaptic GABAergic nerve terminals, and demonstrated that they synergistically inhibited GABA release in the periaqueductal gray (PAG), a structure that mediates opioid-based pain control [22]. In addition, the activation of GABA A receptors in PAG projecting neurons was shown to have a net pronociceptive effect [23]. Further support for interactions between MOP and 5-HT 1A at the cellular level comes from a study showing that they can form functional heterodimers and that signalling of one receptor in the heterodimer is inhibited by the activation of the other [24]. ...
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The importance of the dynamic interplay between the opioid and the serotonin neuromodulatory systems in chronic pain is well recognized. In this study, we investigated whether these two signalling pathways can be integrated at the single-cell level via direct interactions between the mu-opioid (MOP) and the serotonin 1A (5-HT1A) receptors. Using fluorescence cross-correlation spectroscopy (FCCS), a quantitative method with single-molecule sensitivity, we characterized in live cells MOP and 5-HT1A interactions and the effects of prolonged (18 h) exposure to selected non-peptide opioids: morphine, codeine, oxycodone and fentanyl, on the extent of these interactions. The results indicate that in the plasma membrane, MOP and 5-HT1A receptors form heterodimers that are characterized with an apparent dissociation constant = (440 ± 70) nM). Prolonged exposure to all non-peptide opioids tested facilitated MOP and 5-HT1A heterodimerization and stabilized the heterodimer complexes, albeit to a different extent: = (80 ± 70) nM), = (200 ± 70) nM, = (100 ± 70) nM and = (200 ± 70) nM. The non-peptide opioids differed also in the extent to which they affected the mitogen-activated protein kinases (MAPKs) p38 and the extracellular signal-regulated kinase (Erk1/2), with morphine, codeine and fentanyl activating both pathways, whereas oxycodone activated p38 but not ERK1/2. Acute stimulation with different non-peptide opioids differently affected the intracellular Ca2+ levels and signalling dynamics. Hypothetically, targeting MOP–5-HT1A heterodimer formation could become a new strategy to counteract opioid induced hyperalgesia and help to preserve the analgesic effects of opioids in chronic pain.
... Numerous neurotransmitter and neuromodulator systems are involved in processing nociceptive information, such as gammaaminobutyric acid (GABA) (Althaus et al., 2020;Jasmin et al., 2004;Linderoth et al., 1994), glutamate (Liaw et al., 2005), serotonin (Cortes-Altamirano et al., 2018;Messing & Lytle, 1977), substance P (Hökfelt et al., 1977;Zieglgänsberger, 2019), calcitonin gene-related peptide (CGRP) (Schou et al., 2017), endogenous opioid (Bagley & Ingram, 2020;Stone et al., 1997), and the endocannabinoid (eCB) system (Baker et al., 2003;Guindon & Hohmann, 2009;Lomazzo et al., 2015). ...
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It is becoming increasingly clear that robust sex differences exist in the processing of acute and chronic pain in both rodents and humans. However, the underlying mechanism has not been well characterized. The dorsal horn of the lumbar spinal cord is the fundamental building block of ascending and descending pain pathways. It has been shown that numerous neurotransmitter and neuromodulator systems in the spinal cord, including the endocannabinoid system and its main receptor, the cannabinoid 1 receptor (CB1R), play vital roles in processing nociceptive information. Our previous findings have shown that CB1R mRNA is widely expressed in the brain in sex‐dependent patterns. However, the sex‐, lamina‐, and cell‐type‐specific characteristics of CB1R expression in the spinal cord have not been fully described. In this study, the CB1R‐iCre‐EGFP mouse strain was generated to label and identify CB1R‐positive (CB1RGFP) cells. We reported no sex difference in CB1R expression in the lumbar dorsal horn of the spinal cord, but a dynamic distribution within superficial laminae II and III in female mice between estrus and nonestrus phases. Furthermore, the cell‐type‐specific CB1R expression pattern in the dorsal horn was similar in both sexes. Over 50% of CB1RGFP cells were GABAergic neurons, and approximately 25% were glycinergic and 20–30% were glutamatergic neurons. The CB1R‐expressing cells also represented a subset of spinal projection neurons. Overall, our work indicates a highly consistent distribution pattern of CB1RGFP cells in the dorsal horn of lumbar spinal cord in males and females. Morphological assay shows the consistent distribution pattern and cell type‐characteristics of CB1R positive cells in the dorsal horn of lumbar spinal cord from males and females, but a dynamic expression in the superficial spinal laminae of female mice between estrus and non‐estrus phases of estrous cycle.
... Gamma-aminobutyric acid (GABA) is well known as the main inhibitory neurotransmitter of the CNS, and its low level is responsible for many pain states [3]. However, recent studies have provided strong evidence that GABA B receptors are also localized in the periphery; surprising is the finding of GABA localization at the terminal endings of corneal nociceptors [4]. ...
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Analgesic activity of novel GABA esters with l-menthol (1), thymol (2), carvacrol (3) and guaiacol (4) was investigated by pharmacological models of thermal and chemical stimuli in mice after topical application in an ointment (2% w/w). The initial terpenes – l-menthol (5), thymol (6), carvacrol (7) and guaiacol (8) have also been studied under the same experimental conditions. All studied compounds were found to produce an antinociceptive effect in both thermal-and chemical-induced models of acute pain after their topical application. In the hot plate test, compound 1 demonstrated maximum analgesic activity and attenuated acute pain more than the reference drug BZC. GABA esters with l-menthol (1) and carvacrol (3), as well as l-menthol (5) itself exhibited analgesic activity which is the same or better in comparison with benzocaine in chemical-stimulated models of pain caused by either formalin or capsaicin.
Article
Viruses as therapeutic agents: science fiction becomes reality The idea of using genes as medicines was initially proposed in 1972 by Friedmann and Roblin before it was possible to identify specific genes within genomes, before the discovery of restriction enzymes to cut and paste DNA, and before the development of efficient gene delivery vehicles such as viral vectors [1]. The idea of using genes as medicines to treat diseases was a logical outcome of the identification of complex diseases resulting from mutations in single genes. If complex phenotypes were the result of mutations in a single gene, gene replacement into the right tissue at the right developmental stage should suffice to prevent or even reverse the disease progression. The implementation of this originally simple idea has ushered in a new and exciting era of therapeutic molecular medicine (i.e., gene therapy). Over the past 15 years, hundreds of gene therapy clinical trials have been implemented demonstrating therapeutic results in a growing number of genetic disorders, from relatively simple monogenic inborn errors of metabolism to complex diseases such as cancer. The techniques required to implement gene transfer began to appear in the early 1980s with the development of viral vectors (i.e., disabled viruses that could function as gene delivery vehicles). Mouse leukemia retroviruses were among the first viral vector systems that were converted into effective gene transfer vectors. By replacement of viral genes with a potentially therapeutic gene the virus was rendered incapable of replication and thus, producing disease. © Cambridge University Press 2008 and Cambridge University Press, 2009.
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More than 1.5 billion people worldwide suffer from chronic pain, yet current treatment strategies often lack efficacy or have deleterious side effects in patients. Adenosine is an inhibitory neuromodulator that was previously thought to mediate antinociception through the A1 and A2A receptor subtypes. We have since demonstrated that A3AR agonists have potent analgesic actions in preclinical rodent models of neuropathic pain and that A3AR analgesia is independent of adenosine A1 or A2A unwanted effects. Herein, we explored the contribution of the GABA inhibitory system to A3AR-mediated analgesia using well-characterized mouse and rat models of chronic constriction injury (CCI)-induced neuropathic pain. The deregulation of GABA signaling in pathophysiological pain states is well established: GABA signaling can be hampered by a reduction in extracellular GABA synthesis by GAD65 and enhanced extracellular GABA reuptake via the GABA transporter, GAT-1. In neuropathic pain, GABAAR-mediated signaling can be further disrupted by the loss of the KCC2 chloride anion gradient. Here, we demonstrate that A3AR agonists (IB-MECA and MRS5698) reverse neuropathic pain via a spinal mechanism of action that modulates GABA activity. Spinal administration of the GABAA antagonist, bicuculline, disrupted A3AR-mediated analgesia. Furthermore, A3AR-mediated analgesia was associated with reductions in CCI-related GAD65 and GAT-1 serine dephosphorylation as well as an enhancement of KCC2 serine phosphorylation and activity. Our results suggest that A3AR-mediated reversal of neuropathic pain increases modulation of GABA inhibitory neurotransmission both directly and indirectly through protection of KCC2 function, underscoring the unique utility of A3AR agonists in chronic pain. Copyright © 2015 the authors 0270-6474/15/356057-11$15.00/0.
Chapter
In this section, Chapters 14–23 cover a wider range of topics dealing with the viruses that cause disease in the central nervous system (CNS). The first three chapters in the final section concern aspects of the immune response. The next three are about detection and treatment of infections and about the insects and animals that transmit the viruses to people. The final chapters focus on neurotropic viruses for gene transfers and for elimination of a brain tumor. General principles of innate immunity, with special attention to the specific problems of infections in the brain, are covered in three chapters. The first describes important and often overlooked pathways that regulate innate immune responses and control virus infections (Chapter 14). The importance of lipid mediators and alternative pathways of inflammation, as well as the ways drugs may influence them, are described. Then Chapter 15 highlights the Toll-like receptor pathway and other intracellular inflammatory pathways that are critical in the elicitation of the initial type I interferon response. This response is both antiviral and bridges innate and adaptive immunity. The influence of the neuroendocrine networks on immune responses to viral infections is detailed in the following chapter (Chapter 16). It has long been recognized that the fight-or-flight response and stress have profound influences on both acute and persistent immune responses during infections. Public health personnel rely heavily on the data associated with epidemiology as well as clinical signs to direct their diagnostic analyses when presented with a sick patient. © Cambridge University Press 2008 and Cambridge University Press, 2009.
Article
Background: The neurosteroids allopregnanolone and pregnanolone are potent positive modulators of gamma-aminobutyric acid type A receptors. Antinociceptive effects of allopregnanolone have attracted much attention because recent reports have indicated the potential of allopregnanolone as a therapeutic agent for refractory pain. However, the analgesic mechanisms of allopregnanolone are still unclear. Voltage-gated sodium channels (Na-v) are thought to play important roles in inflammatory and neuropathic pain, but there have been few investigations on the effects of allopregnanolone on sodium channels. Methods: Using voltage-clamp techniques, the effects of allopregnanolone sulfate (APAS) and pregnanolone sulfate (PAS) on sodium current were examined in Xenopus oocytes expressing Na-v 1.2, Na-v 1.6, Na-v 1.7, and Na-v 1.8 alpha subunits. Results: APAS suppressed sodium currents of Na-v 1.2, Na-v 1.6, and Na-v 1.7 at a holding potential causing half-maximal current in a concentration-dependent manner, whereas it markedly enhanced sodium current of Na-v 1.8 at a holding potential causing maximal current. Half-maximal inhibitory concentration values for Na-v 1.2, Na-v 1.6, and Na-v 1.7 were 12 +/- 4 (n = 6), 41 +/- 2 (n = 7), and 131 +/- 15 (n = 5) mu mol/l (mean +/- SEM), respectively. The effects of PAS were lower than those of APAS. From gating analysis, two compounds increased inactivation of all alpha subunits, while they showed different actions on activation of each alpha subunit. Moreover, two compounds showed a use-dependent block on Na-v 1.2, Na-v 1.6, and Na-v 1.7. Conclusion: APAS and PAS have diverse effects on sodium currents in oocytes expressing four alpha subunits. APAS inhibited the sodium currents of Na-v 1.2 most strongly.
Chapter
GABA (γ-aminobutyric acid) is a nonprotein amino acid and naturally occurs in microorganisms, plants, and animals. GABA is synthesized prominently via GABA shunt. From Krebs cycle, glucose metabolized with α-ketoglutarate and transaminated by α-oxoglutarate transaminase (GABA-T) to form glutamate. Further, glutamate is decarboxylated by glutamate decarboxylase (GAD) to form GABA. In mammalian central nervous system, GABA is present in about 25%–50% of neurons as a chief inhibitory neurotransmitter. GABA inhibitory synapses bind to specific transmembrane receptors in the plasma membrane of both pre- and postsynaptic neuronal processes. GABAA and GABAC receptors are ionotropic, activation of these receptors results in enhanced membrane ion conductance, whereas GABAB receptor is metabotropic, activation of GABAB results in increased intracellular levels of second messenger. GABA plays an important role in regulating the neuronal excitability throughout the nervous system and has several well-known physiological functions. GABA improves plasma concentration, growth hormones, and protein synthesis in the brain. The lower GABA content is associated with several psychiatric and neurological disorders, including anxiety, pain, depression, insomnia, and epilepsy. Also GABA having hypotensive, tranquilizing, diuretic, and antidiabetic effects, it regulates lipid levels in serum, inhibits cancer cell proliferation, and improves memory and the learning abilities. Along with GABA shunt, GABA synthesized through polyamine pathway as well. GABA also acts as an osmolyte in response to a range of stresses such as, mechanical, stimulation, hypoxia, cytosolic acidification, water, darkness, drought, and salt stress. Due to beneficial effects of GABA for human health, demand of GABA has increased, nowadays; it is classified as a bioactive component and used considerably in foods and pharmaceuticals. The synthetic GABA have significant side effects like drowsiness and dizziness to addiction, whereas natural GABA supplementation is nearly without side effects. Various traditional foods produced through microbial fermentation having GABA content are safe and eco-friendly. The production of GABA by living organisms (plants and microorganisms) can fulfill the demand with GABA-enriched health beneficial foods. In this chapter, general account of GABA, biosynthesis at biochemical and molecular level in microorganisms, plants, and animals along with its further metabolism in different living system, health benefits and commercial production are discussed in detail. The applications, benefits, and side effects of GABA and GABA supplements have also been discussed in details.
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The chemical interaction of nine antiepileptic drugs (tiagabine, gabapentin, pregabalin, lamotrigine, zonisamide, valproic acid, valpromide, vigabatrin, progabide) and two endogenous metabolites (4-aminobutanoic acid, 4-hydroxybutanoic acid) with a model of human GABA transporter 1 (hGAT1) is described using the molecular docking method. To establish the role of hGAT1 in chronic pain, tiagabine, a selective hGAT1 inhibitor, was assessed in the in vivo experiments for its antiallodynic properties in two mouse models of neuropathic pain. Docking analyses performed in this study provided the complex binding energies, specific hydrogen bond components, and hydrogen bond properties such as energies, distances and angles. The data of the docking studies strongly support the assumption that the antiepileptic and analgesic actions of the studied drugs can be at least in part related to the strength of their chemical interactions with hGAT1. In vivo experiments with tiagabine confirmed the involvement of hGAT1 in the regulation of the mechanical nociceptive threshold in neuropathic pain.
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As one of the essential components of traditional Chinese medicine, acupuncture has been accepted world-widely for its effectiveness in treating various disease and health conditions. Pain management is one of the least controversial therapeutic benefits of acupuncture treatment. To date, the mechanism underlying acupuncture analgesia remains poorly understood. In this review, roles of members of GABAergic neurotransmission system which has long been related to pain perception and modulation, in acupuncture analgesia are discussed.
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Acupuncture and its modified forms have been used to treat multiple medical conditions, but whether the diverse effects of acupuncture are intrinsically linked at the cellular and molecular level and how they might be connected have yet to be determined. Recently, an emerging role for the endocannabinoid system (ECS) in the regulation of a variety of physiological/pathological conditions has been identified. Overlap between the biological and therapeutic effects induced by ECS activation and acupuncture has facilitated investigations into the participation of ECS in the acupuncture-induced beneficial effects, which have shed light on the idea that the ECS may be a primary mediator and regulatory factor of acupuncture’s beneficial effects. This review seeks to provide a comprehensive summary of the existing literature concerning the role of endocannabinoid signaling in the various effects of acupuncture, and suggests a novel notion that acupuncture may restore homeostasis under different pathological conditions by regulating similar networks of signaling pathways, resulting in the activation of different reaction cascades in specific tissues in response to pathological insults.
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Therapeutic use of GABAB receptor agonists for conditions like chronic abdominal pain, overactive bladder (OAB) and gastroesophageal reflux disease (GERD) is severely affected by poor blood-brain barrier permeability and potential side effects. ADX71441 is a novel positive allosteric modulator (PAM) of the GABAB receptor that has shown encouraging results in pre-clinical models of anxiety, pain, OAB and alcohol addiction. The present study investigates the analgesic effect of ADX71441 to noxious stimulation of the urinary bladder and colon in rats. In female Sprague-Dawley rats, systemic (i.p), but not intrathecal (i.t), administration of ADX71441 produced a dose-dependent decrease in viscero-motor response (VMR) to graded urinary bladder distension (UBD) and colorectal distension (CRD). Additionally, intra-cerebroventricular (i.c.v.) administration of ADX71441 significantly decreased the VMRs to noxious UBD. In electrophysiology experiments, the drug did not attenuate the responses of UBD-sensitive pelvic nerve afferent (PNA) fibers to UBD. In contrast, ADX71441 significantly decreased the responses of UBD-responsive lumbosacral (LS) spinal neurons in spinal intact rats. However, ADX71441 did not attenuate these LS neurons in cervical (C1-C2) spinal transected rats. During cystometrogram (CMG) recordings, ADX71441 (i.p.) significantly decreased the VMR to slow infusion without affecting the number of voiding contraction. These results indicate that ADX71441 modulate bladder nociception via its effect at the supra-spinal sites without affecting the normal bladder motility and micturition reflex in naïve adult rats.
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Background This study investigated the analgesic effects of two doses (15 and 65 mg) of PF-06372865, a novel α2/α3/α5 gamma-aminobutyric acid A (GABAA) subunit selective partial positive allosteric modulator (PAM), compared with placebo and pregabalin (300 mg) as a positive control. Methods We performed a randomised placebo-controlled crossover study (NCT02238717) in 20 healthy subjects, using a battery of pain tasks (electrical, pressure, heat, cold and inflammatory pain, including a paradigm of conditioned pain modulation). Pharmacodynamic measurements were performed at baseline and up to 10 h after dose. Results A dose of 15 mg PF-06372865 increased pain tolerance thresholds (PTTs) for pressure pain at a ratio of 1.11 (90% confidence interval [CI]: 1.02, 1.22) compared with placebo. A dose of 65 mg PF-06372865 led to an increase in PTT for the cold pressor at a ratio of 1.17 (90% CI: 1.03, 1.32), and pressure pain task: 1.11 (90% CI: 1.01, 1.21). Pregabalin showed an increase in PTT for pressure pain at a ratio of 1.15 (95% CI: 1.06, 1.26) and cold pressor task: 1.31 (90% CI: 1.16, 1.48). Conclusion We conclude that PF-06372865 has analgesic potential at doses that do not induce significant sedation or other intolerable adverse events limiting its clinical use. In addition, the present study established the potential role for this battery of pain tasks as a tool in the development of analgesics with a novel mechanism of action, for the treatment of various pain states including neuropathic pain and to establish proof-of-concept. Clinical trials registration NCT0223871.
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Orofacial inflammation could activate satellite glial cells (SGCs) in the trigeminal ganglion (TG) to produce interleukin 1β (IL-1β) which plays crucial roles in the development of inflammatory pain. Recent studies have shown that gamma-amino butyric acid-B (GABA B ) receptor could modulate the expression of inflammatory cytokines in microglia and astrocytes in the spinal cord. The objective of this study was to investigate whether GABA B receptors in TG SGCs attenuate inflammatory facial pain via mediating IL-1β following inflammation and its mechanisms. Complete Freund's adjuvant (CFA) was injected into the whisker pad of rats to induce inflammation in vivo. Lipopolysaccharide (LPS) was added to culture medium to activate SGCs in vitro. Behavioral measures showed that microinjection of baclofen (a selective GABA B receptor agonist) into the TG ameliorated the mechanical allodynia of CFA-treated rats. Interestingly, baclofen pretreatment inhibited SGC activation and IL-1β production, however, preserved the decreased expression of GABA B receptors in SGCs activated by CFA in vivo and LPS in vitro. In addition, baclofen suppressed the increased expression of p-NF- κ B p65, p-I κ Bα, and p-p38 MAPK, while reversed the decreased production of I κ Bα, and further enhanced the increased expression of p-ERK(1/2) in LPS-treated SGCs in vitro. Finally, those effects of baclofen were abolished by saclofen (a specific GABA B receptor antagonist) co-administration. Altogether, these results demonstrated for the first time that activation of GABA B receptor might inhibit IL-1β production by suppressing NF- κ B and p38 MAPK signaling pathway activation and restore GABA B receptor expression in SGCs to attenuate inflammatory facial pain
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Neurotransmitter γ-aminobutyric acid (GABA) plays a principal role in the regulation of mammalian central nervous system functions. GABA evoked neurotransmission is terminated by a rapid uptake via dependent plasma membrane GABA transporters (GATs) located in the cell membrane. Potent inhibitors of these GATs are of fundamental importance for elucidation of the physiological function of these targets. Over recent years, a wide range of new GAT1-selective and less common non-GAT1-selective inhibitors have been successfully developed. This review highlights development and recent significant achievements in the field of GABA reuptake inhibitors. Special attention is paid to their pharmacological roles, structure and subtype selectivity relationships.
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Microglial cells are the immune cells of the brain that, by sensing the microenvironment, permit a correct brain development and function. They communicate with other glial cells and with neurons, releasing and responding to a number of molecules that exert effects on surrounding cells. Among these, neurotransmitters and, in particular, gamma‐aminobutyric acid (GABA) has recently gained interest in this context. We demonstrated the expression of GABA transporter 1 (GAT‐1) in microglial cells both in soma and cell processes. We show that microglial cell treatment with 1,2,5,6‐tetrahydro‐1‐[2‐[[(diphenylmethylene)amino]oxy]ethyl]‐3‐pyridinecarboxylic acid hydrochloride (NNC‐711), a potent and selective GAT‐1 inhibitor, significantly reduced Na+‐dependent GABA uptake. On the other hand, GABA uptake was significantly increased by cell treatment with (S)‐1‐[2‐[tris(4‐methoxyphenyl)methoxy]ethyl]‐3‐piperidinecarboxylic acid (SNAP‐5114), a GAT‐2/3 inhibitor, and this effect was completely blocked by the botulinum toxin BoNT/C1, that specifically cleaves and inactives syntaxin 1A (STX1A). Overall, these findings show that microglial cells express GAT‐1 and indicate that STX1A plays an important role in the regulation of GAT‐1‐dependent GABA uptake in microglia. Microglia express GABA transporter 1 (GAT‐1). GAT‐1 regulation in microglia is mediated by syntaxin 1A.
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It has been demonstrated that smoking is associated with an increase in postoperative and chronic pain. The changes in the pain-related neural pathways responsible for these effects are unknown. Additionally, the effects of nicotine withdrawal, resulting from smoking abstinence preoperatively, has not been evaluated in terms of its impact on pain sensation. In this study, an animal model has been used to assess these effects. A rat model of long-term nicotine exposure was used. Von Frey mechanical sensory tests were performed. Western Blot and immunohistological analysis were conducted on spinal cord samples. Mechanical sensory thresholds increased in the initial period (1–3 weeks), indicating hyposensitivity. Long-term (410 weeks) and under nicotine withdrawal, the mechanical sensory thresholds decreased, indicating hyperalgesia. During short-term nicotine exposure, glutamate decarboxylase 67 (GAD67), GAD65, and μ-opioid receptors (MOR) up-regulated. Beta-endorphins down-regulated. Increased γ -aminobutyric acid (GABA) and MOR appear responsible for the hyposensitivity since the GABA receptor antagonist, bicuculline and opioid receptor antagonist, naloxone decreased the mechanical thresholds of nicotine-induced hyposensitivity. In long-term nicotine exposure, the expression of GAD67, MOR, and GABA decreased. Baclofen, a derivative of GABA, reversed the hyperalgesia seen with nicotine withdrawal. Therefore, nicotine acts as an analgesic when used acutely or short-term. Long-term exposure or nicotine withdrawal (similar to smoking cessation) results in hyperalgesia. Nicotine appears to alter pain sensitivity by affecting the expression of GAD65, GAD67, MOR, endorphins, and GABA. This may partially explain the increased pain and opioid use seen in chronic smokers in the postoperative period.
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Objective: Primary motor (M1) cortical excitability alterations are involved in the development and maintenance of chronic pain. Less is known about M1-cortical excitability implications in the acute phase of an orthopedic trauma. This study aims to assess acute M1-cortical excitability in patients with an isolated upper limb fracture (IULF) in relation to pain intensity. Methods:Eighty-four (56 IULF patients <14 days post-trauma and 28 healthy controls) performed a single transcranial magnetic stimulation (TMS) session over M1 (resting motor threshold (rMT); short-intracortical inhibition (SICI); intracortical facilitation (ICF); long-interval cortical inhibition (LICI)). IULF patients were divided into two subgroups according to pain intensity (mild versus moderate to severe pain). Results: Reduced SICI and ICF were found in IULF patients with moderate to severe pain, whereas mild pain was not associated with M1 alterations. Age, sex, and time since the accident had no influence on TMS measures. Discussion:These findings show altered M1 in the context of acute moderate to severe pain, suggesting early signs of altered GABAergic inhibitory and glutamatergic facilitatory activities.
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Communication between nerve cells depends on the balance between excitatory and inhibitory circuits. GABA, the major inhibitory neurotransmitter, regulates this balance and insufficient GABAergic activity is associated with numerous neuropathological disorders including pain. Of the various GABAA receptor subtypes, the δ-containing receptors are particularly interesting drug targets in management of chronic pain. These receptors are pentameric ligand-gated ion channels composed of α, β and δ subunits and can be activated by ambient levels of GABA to generate tonic conductance. However, only a few ligands preferentially targeting δ-containing GABAA receptors have so far been identified, limiting both pharmacological understanding and drug-discovery efforts, and more importantly, understanding of how they affect pain pathways. Here, we systemically review and discuss the known drugs and ligands with analgesics potential targeting δ-containing GABAA receptors and further integrate the biochemical nature of the receptors with clinical perspectives in pain that might generate interest among researchers and clinical physicians to encourage analgesic discovery efforts leading to more efficient therapies.
Article
Objectives: We aimed to investigate the protective potential of Punica granatum L. fruit rind extract (PFE) containing punicalagin (10.3% W/W), ellagic acid (EA) (2.7%W/W) in vincristine (75 µg/kg i.p.)- induced neuropathic pain in Wistar rats. Methods: Docking simulation studies were done on the three-dimensional (3D) structure of the GABAA and PPAR γ receptor for the binding of EA as well as punicalagin docking studies on TNF-α, and IL-6. The Present Study conceptualized a test battery to evaluate the behavioral, biochemical and histological changes. Results: Vincristine -induced significant cold allodynia, mechanical hyperalgesia, and functional deficit on 12th and 21st days. It also increased in the levels of TNF-α (Tumor necrosis factor-α), IL-6 (Interleukin-6), and MPO (Myeloperoxidase). Administration of PFE (100 and 300 mg/kg, p.o.), EA (50 mg/kg), and gabapentin (100 mg/kg) attenuated Vincristine-induced behavioral and biochemical changes significantly (P < .05). PFE showed better antinociceptive activity to EA. The histopathological evaluation also revealed the protective effects of PFE. Pretreatment of bicuculline (selective antagonist of GABAA receptors) reversed antinociceptive action of PFE, but administration of γ aminobutyric acid potentiated the action of PFE. PPAR-γ antagonist BADGE did not modify the effect of PFE. Docking results revealed that EA properly positioned into GABA and PPARγ binding site and acts as a partial agonist. Docking score of Punicalagin found to be − 9.02 kcal/mol and - 8.32 kcal/mol on IL-6 and TNFα respectively. Discussion: Conclusively, the attenuating effect of PFE may be attributed to the GABAergic system, cytokine inhibition, and anti-inflammatory activities.
Article
Neurotransmitter transporters, which remove neurotransmittesr from the synaptic cleft, are regulated by second messenger such as protein kinases and binding proteins. Neuronal acid transporters (GATs) are responsible for removing the inhibitory neurotransmitter acid (GABA) from the synaptic cleft. acid transporters 2 (GAT2/BGT1) is involved in regulating neurotransmitter recycling, but the mechanism how they are stabilized and regulated by the specific binding protein has not yet been elucidated. Here, we used the yeast two-hybrid system to identify the specific binding protein(s) that interacts with the C-terminal region of GAT2 and found a specific interaction with the mammalian LIN-7b (MALS-2). MALS-2 protein bound to the tail region of GAT2 but not to other GAT members in the yeast two-hybrid assay. The "T-X-L" motif at the C-terminal end of GAT2 is essential for interaction with MALS-2. In addition, this protein showed specific interactions in the glutathione S-transferase (GST) pull-down assay. An antibody to GAT2 specifically co-immunoprecipitated MALS associated with GAT2 from mouse brain extracts. These results suggest that MALS may stabilize GAT2 in brain.
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The effects of phorbol 12-myristate 13-acetate (PMA), a potent activator of protein kinase C (PKC), on high-affinity Na(+)-dependent gamma-aminobutyric acid (GABA) uptake were investigated in primary cultures of neurons and glial cells from rat brain cortex. Incubation of glial cells with PMA led to concentration- and time-dependent decreases in the GABA transport in glial cells. This effect could be completely suppressed by addition of the PKC inhibitor H7. The PMA effects could be mimicked by oleoylacetylglycerol, the diacylglycerol kinase inhibitor R59022 and exogenous phospholipase C. Treatment with PMA did not affect GABA transport in neuronal cells.
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Intracellular recordings from adult rat dorsal root ganglion neurones were performed in vitro and the coexistence of two gamma-aminobutyric acid (GABA) receptors on the membrane of identified A delta and C primary afferents was demonstrated. Transient applications of GABA (10(-6)-10(-2) M) evoked dose-dependent depolarizations and increased membrane conductance. The responses were mimicked by muscimol, isoguvacine, THIP and 3 amino propane sulphonic acid (3 APS); they were blocked by bicuculline and picrotoxin. Pentobarbitone induced an increase of GABA-induced depolarizations. Perfusion of tetraethylammonium (TEA, 7.5 mM) and intracellular injection of Cs+ ions unmasked the Ca2+ component of action potentials, which appeared as long-lasting plateau depolarizations. Such action potentials were shortened in the presence of methoxyverapamil (D600, 5 X 10(-6)-10(-5) M) and in a medium without Ca+ ions. Prolonged (5-10 min) perfusion of GABA (10(-9)-10(-5) M) shortened the Ca2+ component of action potentials. This effect was mimicked by baclofen (10(-7)-5 X 10(-6) M) and muscimol (5 X 10(-7)-10(-5) M) and was not affected by bicuculline perfusion (5 X 10(-6)-10(-5) M). Isoguvacine (2.5 X 10(-5) M) did not affect action potential duration. It is concluded that two GABA receptors coexist on the membrane of slow conducting primary afferents: the bicuculline-sensitive GABAA receptor mediates depolarizations and the bicuculline-insensitive GABAB receptor shortens the calcium component of action potentials.
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A new diterpenoid alkaloid, 2-acetylseptentriosine [2] (2alpha-acetoxyhetisane-1beta,9beta,19alpha-triol), has been isolated from the roots of Aconitum septentrionale, and its structure established by correlation studies and a single crystal X-ray structure determination.
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The fine structural organization of the principal sensory trigeminal nucleus was compared with that of the spinal trigeminal nucleus (subnuclei oralis, interpolaris, and the deep layers of caudalis) in adult albino rats. Direct comparisons indicate similarities between all of the subdivisions of the brainstem trigeminal complex both in the major morphological classes of neurons present and in basic patterns of synaptic connections. Major differences between the several subdivisions occur in the relative numbers and distribution of the different cell types.
Article
The present study was aimed at characterizing the GABAA receptor-mediated currents in acutely isolated glial (Müller) cells of the human retina and investigating their subcellular localization across the Müller cell membrane. Extracellular application of GABA evoked two current responses in human Müller cells: a fast transient GABAA receptor-mediated current that inactivated within 10 s and that was independent of extracellular Na+, and a sustained current that was dependent on extracellular Na+ and that was mediated by high-affinity GABA transporters. The receptor current was half-maximally activated at a GABA concentration of 32 μM, while the transporter current showed an affinity constant of 7.9 μM GABA. The receptor currents were blocked by bicuculline and picrotoxin and were also activated by muscimol or by other amino acids. The receptor currents are Cl− currents, as indicated by the close relationship between the reversal potential of these currents and the Cl− equilibrium potential. Using perforated-patch recordings, a mean intracellular Cl− concentration of 37 ± 12 mM was determined in human Müller cells. Using electrophysiological and fluorescence imaging methods, it was revealed that GABAA receptors are unevenly distributed across the Müller cell membrane, with higher densities at the endfoot, at the soma, and at the distal sclerad end of the cells. It is concluded that GABAA receptor expression may allow a sensing of retinal GABAergic neuronal signal transmission by Müller cells. © 2004 Wiley-Liss, Inc.
Article
Transection of the sciatic nerve in Rhesus monkeys and the consequent transganglionic degenerative atrophy (TDA) of central terminals of primary afferents result in transneuronal degeneration of substantia gelatinosa (SG) cells. Severe degeneration is characterized by an increased electron density of the nucleus and by conspicuous shrinkage of the cytoplasm, mitochondrial swelling, dilation of cisterns of the rough-surfaced endoplasmic reticulum, accumulation of free ribosomes and an electron-dense material in the cytoplasm. In the mild form, dilation of cisternal elements of the endoplasmic reticulum, swollen mitochondria and accumulation of free ribosomes takes place. About 10% of SG cells in segment L5 undergo the severe form whereas the rest shows signs of the mild form. Cytoplasmic alterations that occur during transneuronal degeneration seem to start at the level of subsurface cisterns. Dendrites and axons of transneuronally degenerating SG cells also show a conspicuous electron density. By analyzing the synaptic relationships of such darkened dendrites, connections in the upper dorsal horn can be deciphered. Modular units of the primary nociceptive analyzer that evaluate noxious and innocuous inputs on the basis of thin versus thick (AC/A) afferent activity and subjecting them to descending control appear to be recruited from structurally dispersed elements of synaptic glomeruli. These are arranged alongside dendritic processes of large antenna cells which relay impulses to projection cells of the spinothalamic tract.
Article
The distribution of gamma-amino-butyric acid containing neurons in the Mouse spinal cord has been studied at both the light and electron microscope levels using antibodies against GABA and revelation by the Fab-peroxidase technique. At the light microscope level immunoreactive profiles of perikarya and neuronal processes were particularly abundant in the superficial laminae (I-IV) of the dorsal horn. Scattered soma profiles were found in the other layers and more particularly in the lamina X where Liquor contacting immuno-reactive neurons could be detected. GABAergic cell bodies were very sparse in the ventral horn. Electron microscopic observations confirmed the light microscope results: terminals constituted synaptic symmetrical contacts that provide a morphological basis for inhibition in the dorsal horn and for post-synaptic inhibition of motoneurons in the ventral horn.
Article
From experiments using dissociated primary astroglial cultures from newborn rat cerebral cortex, the stimulation of monoamine receptors (α, β and 5HT) was shown to affect the high-affinity uptake kinetics of glutamate, GABA and taurine. In the presence of the α1 agonist phenylephrine, there was an increased uptake (Vmax) of glutamate, while β adrenoceptor activation slightly inhibited the glutamate uptake and stimulated the GABA and taurine uptakes. 5HT2 receptor stimulation caused a slight inhibition of the taurine uptake. The uptake rate of GABA was not affected by 5HT, α1 or α2 receptor agonists and the glutamate uptake was not affected by 5HT or α2 receptor agonists. Nor was the taurine uptake affected by α1 or α2 receptor agonists. The active uptake of aspartate was unaffected by the presence of any of the monoamine receptor agonists used in this study. When the mechanisms behind these effects were studied, the GABA uptake seemed to be mediated via the G protein—adenylate cyclase complex in the receptor domain. Moreover, the K+ channels seemed to be involved. The taurine uptake, however, did not seem to be regulated by the same mechanism. It seems more probable that there is a direct interaction between the receptor and carrier of taurine at the membrane level. The mechanism underlying the receptor-regulated glutamate uptake is at present unclear, although it does not seem to involve protein kinase C.
Article
Baclofen was administered via a chronic intrathecal catheter in the lumbar spinal subarachnoid space of awake rats. L-Baclofen was found to produce a dose-dependent, stereospecific, antinociceptive effect as measured by the tail-flick and hot plate which was not antagonized by naloxone. The effect was seen with a dose of 0.01 μg, and 0.1 μg with no apparent motor abnormalities. At 1 μg, approximately 30% of the animals tested had detectable motor impairment but all animals showed a significant degree of antinociception. In rats, at doses of 10 μg and higher, significant motor effects (flaccidity) prevented testing for analgesia. D-Baclofen was more than two orders less potent as an analgetic, but only one order less potent in ints motor effects. Similarly, in cats prepared with chronic spinal intrathecal catheters, L-Baclofen in doses of 4 and 20 μg produced a significant increase in the time required to show escape and agitation responses to a locally applied thermal probe. This effect was, as in the rat, independent of any debilition in voluntary motor function. Baclofen has therefore been clearly shown to exert an antinociceptive effect at the spinal level, in addition to its previously suggested supraspinal action. This may be compared with a similar dual site of action of morphine.
Article
The purpose of this study was to investigate the allodynic effect of bicuculline (BIC) given topically to the dorsal surface of the rat spinal cord, and to determine if spinal prostaglandins (PGs) mediate the allodynic state arising from spinal GABAA-receptor blockade. Male Sprague–Dawley rats (325–400 g) were anaesthetized with halothane and maintained with urethane for the continuous monitoring of blood pressure (MAP), heart rate (HR) and cortical electroencephalogram (EEG). A laminectomy was performed to expose the dorsal surface of the spinal cord. Unilateral application of BIC (0.1 μg in 0.1 μl) to the L5 or L6 spinal segment induced a highly localized allodynia (e.g. one or two digits) on the ipsilateral hind paw. Thus, hair deflection (brushing the hair with a cotton-tipped applicator) in the presence, but not absence of BIC, evoked an increase in MAP and HR, abrupt motor responses (MR; e.g. withdrawal of the hind leg, kicking, and/or scratching) on the affected side, and desynchrony of the EEG. BIC-allodynia was dose-dependent, yielding ED50’s (95% CI's) of 45 ng (31–65) for MAP; 68 ng (46–101) for HR and 76 ng (60–97) for MR. Allodynia was sustained for up to 2 h with repeated BIC application without any detectable change in the location or area of peripheral sensitization. Pretreatment with either the EP1- receptor antagonist, SC-51322, the cyclooxygenase (COX)-2 selective inhibitor, NS-398, or the NMDA-receptor antagonist, AP-7, inhibited BIC-allodynia in a dose-dependent manner. The results demonstrate: (a) BIC, applied to the dorsal surface of the spinal cord, induces highly localized allodynia; (b) this effect can be sustained with repeated BIC application; (c) it is evoked by NMDA-dependent afferent input; (d) spinal PGs are synthesized by constitutive COX-2 during BIC-allodynia; and (e) spinal PGs contribute to the abnormal processing of tactile input via spinal EP1-receptors.
Article
— A method is described for quantifying the GABA distribution in cat spinal cord at 200–500 μn resolution. Isolated spinal cord (L5–S1) was frozen and sectioned at about 150 μm thickness. The frozen tissue section was cut into 200 or 500 μm square blocks. The GABA content of each square tissue block was determined by enzymic micromethods and GABA distribution was mapped quantitatively. Average GABA concentrations were: 0·4 mmol/l. in white matter, 1·2 mmol/l. in ventral horn and 1·7 mmol/l. in dorsal horn. The highest concentrations of GABA (2–3 mmol/l.) were found in the dorsolateral part of dorsal horn. In order to destroy the interneurons of dorsal horn, the blood vessels supplying the dorsal horn of the lumbar enlargement were unilaterally cauterized. Seven to 30 days after operation, both the size of dorsal root potential and the GABA level in the dorsal horn were markedly reduced on the cauterized side. These results suggest that GABA is highly concentrated in the interneurons of dorsal horn and functions as a transmitter of presynaptic inhibition.
Article
Electrical field stimulation (5 Hz) evoked a prompt outflow of calcitonin gene-related peptide- and substance P-like immunoreactivities (CGRP-LI and SP-LI, respectively) from superfused slices of the dorsal but not ventral half of the rat spinal cord. The evoked outflow was abolished by tetrodotoxin, calcium-free medium or previous exposure to capsaicin, indicating that it is produced through action potentials invading the central terminals of capsaicin-sensitive primary afferents. Adenosine as well as gamma-aminobutyric acid (GABA) or the GABAB receptor agonist (-)-baclofen produced a concentration-dependent inhibition of the evoked CGRP-LI outflow. Adenosine also inhibited the evoked SP-LI outflow. These findings demonstrate that inhibition of transmitter release from primary afferent neurons should be considered as a possible mechanism of the antinociceptive action of adenosine and adenosine analogs.
Article
We have recently described extensive inhibitory interactions between inputs to the ventroposterolateral (VPL) (Roberts and Wells 1990, 1991) and ventroposteromedial (VPM) (Salt 1989) portions of the ventrobasal nucleus of the thalamus (VB). We wished to determine whether (i) the inhibition observed in the VPL was operating at the thalamic level, (ii) was dependent on GABA receptors, (iii) was demonstrable on neurons of the ventro-posteromedial nucleus of the thalamus (VPM) and (iv) was operant on test responses evoked by natural stimuli. Conditioning stimulation of sciatic nerve afferents caused inhibition of air jet evoked test responses of single VB neurons in urethane-anaesthetized rats. Both VPM and VPL neurons were subject to inhibition by conditioning stimulation of hindlimb afferents, indicating the wide-spread nature of the inhibitory process. This inhibition was reduced by the iontophoretic application of SR95531, a GABAA receptor antagonist. We conclude that there is a widely distributed inhibitory system operating in the somatic thalamus which involves both the medial and lateral portions of the nucleus and is, at least in part, mediated by GABAA receptors. The possible involvement of inhibitory processes and intrinsic membrane properties of thalamic neurones in the somatotopic plasticity of the sensory thalamus following deafferentation and in deafferentation pain is discussed.
Article
The effect of the GABAA antagonists, bicuculline and picrotoxin, in the hot plate and writhing tests in mice and the paw-pressure test in rats was assessed. Subconvulsant doses of bicuculline (1.3-4 mumol kg-1, s.c.) or picrotoxin (0.8-2.5 mumol kg-1, s.c.) induced a dose-related increase in latency of licking in the hot plate test in mice, whereas subconvulsant doses of strychnine and thiosemicarbazide (0.9 and 6 mg kg-1, s.c. respectively), did not modify the threshold to thermal stimuli in mice. The effects of bicuculline and picrotoxin were not modified by naloxone (3 mg kg-1, i.p., a dose which inhibited the antinociceptive effect of morphine) or by atropine (5 mg kg-1, i.p., a dose which prevented oxotremorine-induced antinociception) but were antagonized by the GABAB antagonist CGP 35348 (2.5 micrograms, i.c.v., a dose which prevented (+/-)baclofen-induced antinociception). Mice, rendered tolerant to baclofen-induced antinociception by twice daily injection of increasing doses of baclofen (5-18 mg kg-1, s.c.), were unresponsive to the antinociceptive effects of bicuculline and picrotoxin but still responded to morphine. Bicuculline and picrotoxin, in the same range of doses which affected the three models of antinociception used, inhibited pentobarbital-induced hypnosis. Large doses of bicuculline and picrotoxin (4 and 2.5 mumol kg-1, s.c. respectively), reduced locomotor activity and impaired rota-rod performance in mice. The changes in response to noxious stimuli, induced by bicuculline and picrotoxin, are interpreted as an antinociceptive effect. It is then suggested that this effect might depend on an indirect activation of GABAB receptors through release of GABA.(ABSTRACT TRUNCATED AT 250 WORDS)
Article
Intracellular recordings were made from sympathetic preganglionic neurons (SPNs) in transverse neonate rat spinal cord slices. Superfusion of gamma-aminobutyric acid (GABA; 25-100 microM) or (-)-baclofen (1-30 microM) consistently attenuated the excitatory postsynaptic potentials (EPSPs) evoked by stimulation of dorsal rootlets or lateral funiculus, without causing a significant change of the resting membrane potential and input resistance of the SPNs or of the depolarizations induced by pressure applications of glutamate; the IC50 for baclofen was 2.5 microM. When superfused at a higher concentration (greater than or equal to 500 microM) or ejected by pressure GABA caused a bicuculline-sensitive membrane hyperpolarization. The enantiomer (+)-baclofen (10-50 microM) and the GABAA agonist muscimol (1-10 microM) had no significant effect on the EPSPs. The GABAB receptor antagonist 2-hydroxy-saclofen caused a 10 fold rightward shift of the baclofen dose-response curve, whereas the GABAA receptor antagonist bicuculline (10-50 microM) was ineffective. Glycine had no significant effects on the EPSPs in the concentrations (10-100 microM) tested here. The results indicate that of the two putative inhibitory transmitters in the spinal cord GABA but not glycine depresses EPSPs evoked in the rat SPNs by acting on presynaptic GABAB receptors, the activation of which results in a reduction of excitatory transmitter release.
Article
Pre-embedding immunocytochemistry with antiserum to neurotensin was combined with post-embedding immunocytochemistry with GABA antiserum, in order to identify neurotensin- and GABA-containing neurons in laminae I-III of rat spinal dorsal horn. The distribution of cell bodies containing these two compounds was similar to that which has been described previously. None of the 88 neurotensin-immunoreactive neurons which were tested showed GABA-like immunoreactivity, which suggests that GABA and neurotensin exist in different cells in this region. Since both compounds are thought to be present in islet cells, it is likely that there are two neurochemically distinct populations of islet cells in lamina II of rat spinal cord.
Article
A glycoprotein that induces γ-aminobutyric acid (GABA) carriers in cultured cerebellar astrocytes was isolated and purified from conditioned media from cultured cerebellar granule cells by anion exchange chromatography, affinity chromatography, and gel filtration. Following gel filtration three fractions corresponding to Mr 30,000, 60,000, and 240,000 exhibited GABA carrier inducing activity. SDS-PAGE of the Mr 30,000 fraction revealed under non-reducing conditions three bands corresponding to Mr 30,000, 60,000, and 120,000. Under reducing conditions only the band corresponding to an Mr of 30,000 was visible. An identical N-terminal amino acid sequence and amino acid composition was found in the Mr 30,000 and the Mr 60,000 fraction from the gel filtration. These results suggest that the protein polymerizes into di- and tetramers. Computer base analysis of the N-terminal amino acid sequence revealed no obvious homology with previously reported N-terminal amino acid sequences. Application of the glycoprotein to cerebellar astrocytes led time and dose dependently to an increased GABA uptake. The effect became maximal after 24h exposure of the cells. Kinetic analysis of the GABA uptake showed that exposure of the astrocytes to the glycoprotein led to an increase in Vmax for GABA uptake without affecting Km, suggesting an increase in the number of GABA carrier molecules. Addition of actinomycin D together with the glycoprotein abolished this effect suggesting that the glycoprotein acts by stimulating de novo synthesis of GABA carriers. Hence, the newly purified protein secreted from neurons is named GABA-carrier inducing protein (GABA-CIP).
Article
In order to determine whether different morphological types of neurone in lamina III of rat spinal dorsal horn contain different neurotransmitters, a combined Golgi and immunocytochemical study was performed. Semithin sections through the cell bodies of 52 Golgi-impregnated neurones in this lamina were tested with antisera to GABA and glycine. Thirty of these cells were immunoreactive with anti-GABA antiserum and 25 of these also showed glycine-like immunoreactivity. These cells had dendrites which were oriented along the rostrocaudal axis and occupied lamina III, with some extension into lamina IV and the ventral half of lamina II. Although some of the nonimmunoreactive cells had similar morphology, many of them had dendrites which passed in a dorsal and/or ventral direction and crossed laminar boundaries. Three of the neurones which were immunoreactive with both antisera were examined with the electron microscope. These cells received a variety of synapses including some from axons which resembled low threshold myelinated mechanoreceptive primary afferents. These results indicate that there is a relationship between morphology and function for neurones in lamina III. It is suggested that the inhibitory neurones which contain both GABA and glycine selectively regulate the transmission of information from low threshold mechanoreceptive primary afferents to other dorsal horn neurones.
Article
The present study analyses the relationship of calcitonin gene-related peptide (CGRP)-immunoreactive primary afferent terminals with unlabeled and GABA-immunoreactive profiles in the primate (Macaca fascicularis) dorsal horn. One-hundred CGRP-immunoreactive terminals located in the superficial dorsal horn were quantitatively analysed and all profiles in apposition or in synaptic contact with these terminals were categorized as either axon terminals or dendrites with or without vesicles. These profiles were then further classified as to whether they were GABA-immunoreactive. All of the CGRP-immunoreactive terminals demonstrated axodendritic interactions; in addition to dendrites without vesicles, approximately half of the CGRP-immunoreactive terminals had dendrites with vesicles as postsynaptic elements. Of the dendrites with vesicles, 25/53 were GABAergic but only 3/67 of the postsynaptic dendrites without vesicles were GABAergic. GABAergic vesicle-containing dendrites were the most prominent CGRP-GABAergic interaction. Axoaxonic and dendroaxonic interactions were a rare occurrence, thus the classical anatomical substrate for primary afferent depolarization involving GABA- and CGRP-immunoreactive terminals could not be substantiated. CGRP-GABAergic interactions often involved diadic and triadic arrangements. These findings are discussed in relation to previously described primary afferent synaptology, primary afferent-GABAergic interactions and spinal cord mechanisms for modulation of noxious input.
Article
The effects of long-term (28-day) administration of several antidepressant/antipanic drugs [imipramine, desipramine, tranylcypromine and phenelzine (PLZ)] on gamma-aminobutyric acid-tranaminase (GABA-T) activity and GABA levels were investigated in rat frontal cortex. Of the drugs investigated, only PLZ inhibited GABA-T and elevated GABA levels. Additional short-term experiments were conducted with PLZ, and they demonstrated a dose-dependent inhibition of GABA-T in rat whole brain. Time-response studies on inhibition of GABA-T in whole brain demonstrated that at a dose of PLZ of 15 mg/kg i.p. inhibition of GABA-T remained relatively constant from 1 to 8 hr and that the enzyme was still inhibited by 23% at 24 hr after PLZ administration.
Article
A monoclonal antibody, 115AD5, was raised against GABA coupled to bovine serum albumin. The monoclonal antibody 115AD5 also reacted with other GABA-protein conjugates. The specificity of the monoclonal antibody was corroborated by enzyme-linked immunoassay, dot-immunobinding experiments and immunostaining of rat cerebellum sections. The monoclonal antibody 115AD5 could successfully be applied on Vibratome and cryostat sections using either indirect immunofluorescence or peroxidase techniques. In rat cerebellar cortex the monoclonal antibody 115AD5 gave an intense immunoreaction in stellate cells, in Golgi neurons, and in basket cells and their processes around Purkinje cell bodies. Purkinje cell dendrites showed GABA immunoreactivity while the cell bodies were non-reactive or only weakly reactive. There was labelling in some nuclei of Purkinje cells. GABA immunoreactivity was also found in dot-like structures in the granular layer. A large population of sensory neurons in rat thoracic and lumbar spinal dorsal root ganglia presented an intense immunoreactivity for the monoclonal antibody 115AD5. Nerve bundles immunoreactive for GABA were also seen in these ganglia. In the trigeminal ganglion, a major population of sensory neurons and some of their processes presented immunoreactivity for GABA. In the sensory nodose ganglion of the vagus nerve, many neuronal cell bodies and some fibres were immunoreactive for GABA. Ligation of the vagus nerve caudal to the ganglion resulted in an increased GABA immunoreactivity in neuronal somata of the ganglion, as well as in nerve fibres on the ganglionic side of the ligature. The present results suggest that in the rat, a population of sensory neurons in thoracic and lumbar spinal dorsal root ganglia, as well as in the trigeminal and nodose ganglia contain GABA. The presence of GABA immunoreactivity in these neurons raises the possibility of a neurotransmitter or modulator role.
Article
Kainate (KA), quisqualate (QA), and alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) stimulated gamma-aminobutyric acid [3H]gamma-aminobutyric acid (GABA) release from cultured cerebellar type 2 astrocytes and from their bipotential precursors. The evoked release was prevented by the antagonist 6-cyano-2,3-dihydroxy-7-nitro-quinoxaline (CNQX). AMPA and QA applied together with KA at concentrations around or above their EC50S (20-50 microM) antagonized the stimulatory effect of KA on [3H]GABA release. On the other hand, the releasing action of KA was potentiated by concentrations of QA in the low micromolar range (2-5 microM), particularly when the concentration of KA was at the borderline of effectiveness (10 microM). KA and QA did not elevate intracellular cyclic GMP levels in astrocyte cultures, although guanylate cyclase was present in both type 2 and type 1 astrocytes. The inability of KA to elevate cyclic GMP levels in astrocytes was the only major difference in the behavior of this glutamate agonist between astroglial and neuronal cultures. The GABA transport inhibitor nipecotic acid or replacement of NaCl with LiCl abolished [3H]GABA uptake and also KA- and QA-induced release of preaccumulated [3H]GABA. Therefore, [3H]GABA was released from type 2 astrocytes and their progenitors through its Na(+)-dependent transport system, operating in an outward direction when the cells were depolarized by non-NMDA receptor agonists.
Article
This study evaluated the ability of two new, selective antagonists of the gamma-aminobutyric acidB (GABAB) receptor, phaclofen (PHAC) and 2-hydroxy-saclofen (2-OH-S), to antagonize the increase in tail-flick latency (TFL) and hot-plate latency (HPL) produced by i.t. administered baclofen (BAC) in the rat. The putative GABAB receptor antagonist delta-aminovaleric acid (DAVA) was also examined for comparative purposes. Intrathecal (i.t.) pretreatment with increasing doses of PHAC (10-100 micrograms) shifted the dose-effect relationship of i.t. administered BAC progressively to the right in a parallel manner in both the tail-flick (TF) and hot-plate (HP) test. Schild analysis of the data yielded an apparent pA2 value of 7.3 +/- 0.1 and a slope of -0.98 +/- 0.14. By comparison, PHAC did not antagonize the increase in HPL produced by i.t. injection of the serotonin1A agonist, 8-hydroxy-N,N-dipropyl-2-aminotetralin. These observations indicate that PHAC competitively and selectively antagonizes BAC and further suggest that the antinociceptive effects of i.t. administered BAC are mediated by the PHAC-sensitive subtype of the GABAB receptor. Intrathecal injection of PHAC alone did not decrease TFL or HPL, suggesting that spinal GABAB receptors involved in nociception are not tonically activated. Although i.t. pretreatment with 2-OH-S (10-30 micrograms) also antagonized the antinociceptive effects of i.t. administered BAC, increasing doses of 2-OH-S did not produce progressive, rightward shifts in the dose-effect relationship of BAC. Indeed, i.t. administration of 2-OH-S alone modestly increased TFL, but not HPL in the rat. These observations suggest that 2-OH-S may be a partial agonist at spinal GABAB receptors.(ABSTRACT TRUNCATED AT 250 WORDS)
Article
Retrograde transport and immunohistochemical double-labeling methods (Weinberg et al., 1985) were used to assess the distribution and projection status of spinal trigeminal (SpV) neurons that stain positively for glutamic acid decarboxylase (GAD) or gamma-aminobutyric acid (GABA). Large bilateral injections of diamidino yellow into the rostral and lateral pons, inclusive of V nucleus principalis and the parabrachial nucleus, retrogradely labeled large numbers of cells in each SpV subnucleus. Many cells in SpV subnuclei caudalis, interpolaris, and oralis also exhibited GABA immunoreactivity; the largest numbers were in caudalis and the smallest numbers were in oralis. However, none of the GABA- or GAD-immunoreactive SpV cells were double-labeled with diamidino yellow, though some reticular neurons displayed both GABA and the retrograde tracer. This negative result refutes a previously offered hypothesis that SpV local-circuit neurons with principalis collaterals are GABA-ergic (Jacquin et al., 1989b). These data also indicate that parabrachial-projecting SpV neurons are not GABA-ergic.
Article
The concentrations of free and peptide-bound amino acids aspartate (Asp), glutamate (Glu), glycine (Gly) and gamma-aminobutyric acid (GABA) were studied following ischemia and recirculation in the ventral and dorsal gray matter of the rabbit spinal cord. No changes in the concentration of amino acids following ten minutes (min) of ischemia and four days of recovery were found. The most significant change after 20 min, and especially 40 min, of ischemia was a decrease in free Asp and GABA levels in both parts of the gray matter. The relatively greater decrease in the concentration of free amino acids in the ventral horns corresponds with the greater morphological damage to this part of spinal cord following ischemia. Following 40 min of ischemia and recirculation decrease in peptide-bound Glu in the ventral horns and Asp and Glu in the dorsal horns was found.
Article
A postembedding immunogold study of type I synaptic glomeruli in lamina II of rat dorsal horn was carried out using antiserum to gamma-aminobutyric acid (GABA). Gold particles were concentrated over some peripheral axons and vesicle-containing dendrites within these glomeruli and both types of profile were presynaptic to central axons. These results suggest that GABA is involved in presynaptic inhibition of unmyelinated primary afferents and is released by some presynaptic dendrites within lamina II.
Article
These experiments examined the effects of intrathecally administered gamma-aminobutyric acid (GABA) agonists on the effects of intrathecally administered excitatory amino acid (EAA) agonists: N-methyl-D-aspartic acid (NMDA), quisqualic acid and kainic acid. We have found that muscimol, a GABAA receptor agonist, but not baclofen, a GABAB receptor agonist, dose-dependently inhibited caudally directed biting and scratching behavior induced by all three EAA agonists. This nonselective blockade of the expression of effects mediated by all three types of EAA receptor is in marked contrast to the selective blockade of NMDA effects seen previously in the case of mu opioids and phencyclidine receptor agonists. Inhibition by muscimol was blocked with the GABAA receptor antagonist, bicuculline. Decreased latency or hyperalgesia in the tail-flick test, found previously to be induced selectively by NMDA and blocked by an NMDA receptor antagonist, was similarly affected by muscimol but not baclofen, each given intrathecally. However, muscimol prolonged the tail-flick latency only after presentation of NMDA suggesting a possible antinociceptive effect of GABAA agonists in the presence of agonists at NMDA receptors. This study together with the preceding paper resolves GABA-mediated spinal antinociception into two components: a GABAA agonist selectively blocks nociception involving EAA receptors whereas a GABAB agonist selectively blocks substance P spinal activity (the preceding paper).
Article
Antinociceptive effects of baclofen, a gamma-aminobutyric acidB (GABAB) agonist, were studied in mice along with other GABAergic agents, all administered intrathecally (i.t.): i.e., muscimol (GABAA agonist), bicuculline (GABAA antagonist) and 5-aminovaleric acid (GABAB antagonist). After i.t. administration, none of the four compounds increased the withdrawal latency in the tail-flick test. With the intradermal hypertonic saline (6% saline) behavioral test, baclofen decreased the number of behaviors in a dose-dependent and 5-aminovaleric acid-reversible manner, whereas i.t. administered muscimol was ineffective. With the i.t. substance P (SP) behavioral test, muscimol was again ineffective, whereas the SP-induced behaviors were differentially modified by baclofen depending on the temporal order of their i.t. administration. Although baclofen, coadministered with SP, decreased the number of SP-induced behaviors, baclofen pretreatment (2-100 min before i.t. administration of SP) increased the number of behaviors in a dose-dependent and 5-aminovaleric acid-reversible manner. Two minutes after several fixed doses of baclofen were administered i.t., dose-response curves for induction of behaviors by SP (i.t.) were shifted progressively to the left by increasing doses of baclofen, suggesting that hypersensitivity to SP had developed during this time frame. Decreased responsiveness to a peripheral noxious stimulus (hypertonic saline-induced behavior) is therefore associated with hypersensitivity to i.t. applied SP (SP behavioral test). The selective action of a GABAB agonist on neurokinin-elicited behaviors shown in this study is in clear contrast to the selective action of a GABA agonist against excitatory amino acid spinal activity noted in the following paper.
Article
The purpose of the present study was to quantify the extent to which several peptides and serotonin coexist with substance P or somatostatin in selected lumbar dorsal root ganglia of the cat. The technique for the simultaneous visualization of two antigens by immunofluorescence was used to investigate the coexistence of neuropeptides in the lumbar dorsal root ganglia of colchicine-treated cats. Perikarya immunoreactive for calcitonin gene-related peptide, galanin, leu-enkephalin, somatostatin, and substance P were visualized in both the lumbar 5 and 6 dorsal root ganglia. In contrast, no immunoreactivity was observed for adipokinetic hormone, bombesin, dynorphin A, met-enkephalin, oxytocin, tyrosine hydroxylase, thyrotropin-releasing hormone, vasopressin, vasoactive intestinal peptide, or serotonin in either ganglion examined. Substance P coexisted with calcitonin-gene-related peptide, somatostatin, and leu-enkephalin. Somatostatin was colocalized with calcitonin gene-related peptide, leu-enkephalin, and substance P but coexisted with galanin minimally. The cell area of immunoreactive perikarya was also examined. Data concerning the cross-sectional area of immunoreactive cells indicated that somatostatin-immunoreactive perikarya were generally the largest population observed (up to approximately 6,000 microns2). Somatostatin and calcitonin gene-related peptide, as well as substance P and calcitonin gene-related peptide, coexisted in populations of cell bodies that had a smaller size (less than 2,000 microns2). These results suggest that certain peptides which coexist in the dorsal root ganglia may provide histochemical markers for functional groups of primary afferent neurons.
Article
The rat subcommissural organ (SCO) is a particular but adequate paradigm for the approach, in vivo, to some aspects of neuron-glia interaction in gamma-aminobutyric acid (GABA) uptake. The rat SCO ependymocytes (the main component of this structure lying at the junction of the aqueduct and the third ventricle) accumulate [3H]GABA by a highly specific uptake mechanism and receive a serotoninergic input forming typical synaptic contacts. It seems that there is a correlation between the capacity of the rat SCO ependymocytes to take up [3H]GABA and the presence of a serotonin (5-HT) innervation. Indeed, in the newborn rat, no uptake of [3H]GABA was observed before the onset of this innervation and the increased [3H]GABA accumulation in the SCO was correlated with the appearance of the 5-HT terminals in the SCO. Moreover, in the mouse, whose SCO is devoid of a 5-HT innervation, no accumulation of [3H]GABA was observed in the SCO ependymocytes. Thus, the 5-HT innervation could be involved directly or indirectly in the onset of the GABA uptake carriers. On the other hand, in adult rats parachlorophenylalanine (pCPA) treatment decreased the 5-HT content of the SCO, and increased [3H]GABA accumulation; such an augmentation was not observed when rats were treated with pCPA plus 5-hydroxytryptophan to restore the 5-HT content. However, an increase in 5-HT content of the SCO by pargyline treatment appeared to have no effect on [3H]GABA uptake. Control of GABA uptake activity by 5-HT in the SCO ependymocytes could be an interesting model for the study of a possible interaction between amino-acids and other neurotransmitters by terminating their action in the extracellular space.
Article
A recent model for control of spinal and medullary nociceptive neurons (Basbaum and Fields, 1984) incorporates a gamma-aminobutyric acid-ergic (GABA-ergic) cell into this circuitry and indicates that such elements could act as one substrate for presynaptic inhibition of primary afferents. This concept is supported by a variety of pharmacological and electrophysiological studies. We therefore examined the distribution of GABA-ergic activity in trigeminal subnucleus interpolaris (Vi) by focusing on the types of cells, together with dendritic and synaptic profiles, that are immunocytochemically labeled with an antiserum against glutamic acid decarboxylase (GAD). GAD occurred throughout Vi but was most concentrated in the ventrolateral quadrant and interstitial nucleus. It was localized to groups of small neurons with two to three primary dendrites, and within numerous punctate profiles suggestive of synaptic elements. Electron microscopy revealed labeled dendrites, some of which were postsynaptic to scalloped terminals of presumptive primary afferents. Other labeled dendritic elements, which were quite variable in size, engaged both GAD-labeled and unlabeled synapses. Most GAD synapses displayed clear round vesicles and formed contacts with unlabeled perikarya and a variety of dendritic processes. Numerous GAD-positive synapses were also incorporated into axoaxonic clusters, in which the GAD element was presynaptic to scalloped terminals. Others engaged in serial arrays with other unlabeled terminals, which, in turn, were presynaptic to dendrites. Occasionally, GAD synapses formed contacts with GAD-positive dendrites. These data show that GABA is localized to a variety of neuronal elements in ventrolateral Vi and the interstitial nucleus. These occur in spatial arrangements providing an anatomical substrate for postsynaptic modulation of activity in this area. GABA terminals also appear to be involved in a presynaptic inhibitory mechanism, which may, in some instances, affect transmission in primary afferents.
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