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Zarrouki F, Goutal S, Vacca O, Garcia L, Tournier N, Goyenvalle A, Vaillend C. Abnormal Expression of Synaptic and Extrasynaptic GABAA Receptor Subunits in the Dystrophin-Deficient mdx Mouse. Int J Mol Sci 2022; 23:ijms232012617. [PMID: 36293496 PMCID: PMC9604073 DOI: 10.3390/ijms232012617] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2022] [Revised: 09/21/2022] [Accepted: 10/11/2022] [Indexed: 11/17/2022] Open
Abstract
Duchenne muscular dystrophy (DMD) is a neurodevelopmental disorder primarily caused by the loss of the full-length Dp427 dystrophin in both muscle and brain. The basis of the central comorbidities in DMD is unclear. Brain dystrophin plays a role in the clustering of central gamma-aminobutyric acid A receptors (GABAARs), and its loss in the mdx mouse alters the clustering of some synaptic subunits in central inhibitory synapses. However, the diversity of GABAergic alterations in this model is still fragmentary. In this study, the analysis of in vivo PET imaging of a benzodiazepine-binding site radioligand revealed that the global density of central GABAARs is unaffected in mdx compared with WT mice. In contrast, semi-quantitative immunoblots and immunofluorescence confocal imaging in tissue sections revealed complex and differential patterns of alterations of the expression levels and/or clustered distribution of a variety of synaptic and extrasynaptic GABAAR subunits in the hippocampus, cerebellum, cortex, and spinal cord. Hence, dystrophin loss not only affects the stabilization of synaptic GABAARs but also influences the subunit composition of GABAARs subtypes at both synaptic and extrasynaptic sites. This study provides new molecular outcome measures and new routes to evaluate the impact of treatments aimed at compensating alterations of the nervous system in DMD.
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Affiliation(s)
- Faouzi Zarrouki
- Université Paris-Saclay, CNRS, Institut des Neurosciences Paris Saclay, 91400 Saclay, France
- Université Paris-Saclay, UVSQ, Inserm, END-ICAP, 78000 Versailles, France
| | - Sébastien Goutal
- Université Paris-Saclay, INSERM, CNRS, CEA, Laboratoire d’Imagerie Biomédicale Multimodale (BioMaps), Service Hospitalier Frédéric Joliot, 91401 Orsay, France
| | - Ophélie Vacca
- Université Paris-Saclay, UVSQ, Inserm, END-ICAP, 78000 Versailles, France
| | - Luis Garcia
- Université Paris-Saclay, UVSQ, Inserm, END-ICAP, 78000 Versailles, France
| | - Nicolas Tournier
- Université Paris-Saclay, INSERM, CNRS, CEA, Laboratoire d’Imagerie Biomédicale Multimodale (BioMaps), Service Hospitalier Frédéric Joliot, 91401 Orsay, France
| | - Aurélie Goyenvalle
- Université Paris-Saclay, UVSQ, Inserm, END-ICAP, 78000 Versailles, France
| | - Cyrille Vaillend
- Université Paris-Saclay, CNRS, Institut des Neurosciences Paris Saclay, 91400 Saclay, France
- Correspondence:
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Abstract
We aimed to investigate a sexually dimorphic role of calcitonin gene-related peptide (CGRP) in rodent models of pain. Based on findings in migraine where CGRP has a preferential pain-promoting effect in female rodents, we hypothesized that CGRP antagonists and antibodies would attenuate pain sensitization more efficaciously in female than male mice and rats. In hyperalgesic priming induced by activation of interleukin 6 signaling, CGRP receptor antagonists olcegepant and CGRP8-37 both given intrathecally, blocked, and reversed hyperalgesic priming only in females. A monoclonal antibody against CGRP, given systemically, blocked priming specifically in female rodents but failed to reverse it. In the spared nerve injury model, there was a transient effect of both CGRP antagonists, given intrathecally, on mechanical hypersensitivity in female mice only. Consistent with these findings, intrathecally applied CGRP caused a long-lasting, dose-dependent mechanical hypersensitivity in female mice but more transient effects in males. This CGRP-induced mechanical hypersensitivity was reversed by olcegepant and the KCC2 enhancer CLP257, suggesting a role for anionic plasticity in the dorsal horn in the pain-promoting effects of CGRP in females. In spinal dorsal horn slices, CGRP shifted GABAA reversal potentials to significantly more positive values, but, again, only in female mice. Therefore, CGRP may regulate KCC2 expression and/or activity downstream of CGRP receptors specifically in females. However, KCC2 hypofunction promotes mechanical pain hypersensitivity in both sexes because CLP257 alleviated hyperalgesic priming in male and female mice. We conclude that CGRP promotes pain plasticity in female rodents but has a limited impact in males.SIGNIFICANCE STATEMENT The majority of patients impacted by chronic pain are women. Mechanistic studies in rodents are creating a clear picture that molecular events promoting chronic pain are different in male and female animals. We sought to build on evidence showing that CGRP is a more potent and efficacious promoter of headache in female than in male rodents. To test this, we used hyperalgesic priming and the spared nerve injury neuropathic pain models in mice. Our findings show a clear sex dimorphism wherein CGRP promotes pain in female but not male mice, likely via a centrally mediated mechanism of action. Our work suggests that CGRP receptor antagonists could be tested for efficacy in women for a broader variety of pain conditions.
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Positive allosteric modulators of nonbenzodiazepine γ-aminobutyric acidA receptor subtypes for the treatment of chronic pain. Pain 2019; 160:198-209. [PMID: 30204648 DOI: 10.1097/j.pain.0000000000001392] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Chronic neuropathic pain may be caused, in part, by loss of inhibition in spinal pain processing pathways due to attenuation of local GABAergic tone. Nociception and nocifensive behaviors are reduced after enhancement of tonically activated extrasynaptic GABAAR-mediated currents by agonist ligands for δ subunit-containing GABAARs. However, typical ligands that target δ subunit-containing GABAARs are limited due to sedative effects at higher doses. We used the spinal nerve ligation (SNL) and gp120 models of experimental neuropathic pain to evaluate compound 2-261, a nonbenzodiazepine site positive allosteric modulator of α4β3δ GABAARs optimized to be nonsedative by selective activation of β2/3-subunit-containing GABAARs over receptor subtypes incorporating β1 subunits. Similar levels of 2-261 were detected in the brain and plasma after intraperitoneal administration. Although systemic 2-261 did not alter sensory thresholds in sham-operated animals, it significantly reversed SNL-induced thermal and tactile hypersensitivity in a GABAAR-dependent fashion. Intrathecal 2-261 produced conditioned place preference and elevated dopamine levels in the nucleus accumbens of nerve-injured, but not sham-operated, rats. In addition, systemic pretreatment with 2-261 blocked conditioned place preference from spinal clonidine in SNL rats. Moreover, 2-261 reversed thermal hyperalgesia and partially reversed tactile allodynia in the gp120 model of HIV-related neuropathic pain. The effects of 2-261 likely required interaction with the α4β3δ GABAAR because 2-301, a close structural analog of 2-261 with limited extrasynaptic receptor efficacy, was not active. Thus, 2-261 may produce pain relief with diminished side effects through selective modulation of β2/3-subunit-containing extrasynaptic GABAARs.
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Liu JP, He YT, Duan XL, Suo ZW, Yang X, Hu XD. Enhanced Activities of δ Subunit-containing GABAA Receptors Blocked Spinal Long-term Potentiation and Attenuated Formalin-induced Spontaneous Pain. Neuroscience 2018; 371:155-165. [DOI: 10.1016/j.neuroscience.2017.12.002] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2017] [Revised: 11/11/2017] [Accepted: 12/02/2017] [Indexed: 01/22/2023]
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Kitayama T. The Role of K +-Cl --Cotransporter-2 in Neuropathic Pain. Neurochem Res 2018; 43:110-115. [PMID: 28677029 DOI: 10.1007/s11064-017-2344-3] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2017] [Revised: 06/09/2017] [Accepted: 06/26/2017] [Indexed: 01/21/2023]
Abstract
The pain sensory system normally functions under a fine balance between excitation and inhibition. When this balance is perturbed for some reason, it leads to neuropathic pain. There is accumulating evidence that attributes this pain generation to specific dysfunctions of the inhibitory system in the spinal cord. One possible mechanism leading to the induction of these dysfunctions is the down-regulation of K+-Cl--cotransporter-2 (KCC2) expression. In fact, various neuropathic pain models indicate a decrease of KCC2 expression in the spinal cord. The alteration of KCC2 expression affects GABAergic and glycinergic neurotransmissions, because KCC2 is a potassium-chloride exporter and serves to maintain intracellular chloride concentration. When there is a low level of KCC2 expression, GABAergic and glycinergic neurotransmissions transform from inhibitory signals to excitatory signals. In this review, the hypothesis that an alteration of KCC2 expression has a crucial influence on the initiation/development or maintenance of neuropathic pain is discussed. In addition, it is suggested that the alteration of inhibitory signals is dependent on the time after peripheral nerve injury.
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Affiliation(s)
- Tomoya Kitayama
- Department of Pharmacy, School of Pharmacy and Pharmaceutical Science, Mukogawa Women's University, 11-68 Koshien-Kyubanmachi, Nishinomiya, Hyogo, 663-8179, Japan.
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Neuroligin 2 regulates spinal GABAergic plasticity in hyperalgesic priming, a model of the transition from acute to chronic pain. Pain 2017; 157:1314-1324. [PMID: 26859820 DOI: 10.1097/j.pain.0000000000000513] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Plasticity in inhibitory receptors, neurotransmission, and networks is an important mechanism for nociceptive signal amplification in the spinal dorsal horn. We studied potential changes in GABAergic pharmacology and its underlying mechanisms in hyperalgesic priming, a model of the transition from acute to chronic pain. We find that while GABAA agonists and positive allosteric modulators reduce mechanical hypersensitivity to an acute insult, they fail to do so during the maintenance phase of hyperalgesic priming. In contrast, GABAA antagonism promotes antinociception and a reduction in facial grimacing after the transition to a chronic pain state. During the maintenance phase of hyperalgesic priming, we observed increased neuroligin (nlgn) 2 expression in the spinal dorsal horn. This protein increase was associated with an increase in nlgn2A splice variant mRNA, which promotes inhibitory synaptogenesis. Disruption of nlgn2 function with the peptide inhibitor, neurolide 2, produced mechanical hypersensitivity in naive mice but reversed hyperalgesic priming in mice previously exposed to brain-derived neurotrophic factor. Neurolide 2 treatment also reverses the change in polarity in GABAergic pharmacology observed in the maintenance of hyperalgesic priming. We propose that increased nlgn2 expression is associated with hyperalgesic priming where it promotes dysregulation of inhibitory networks. Our observations reveal new mechanisms involved in the spinal maintenance of a pain plasticity and further suggest that disinhibitory mechanisms are central features of neuroplasticity in the spinal dorsal horn.
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Lin CR, Cheng JK, Wu CH, Chen KH, Liu CK. Epigenetic suppression of potassium-chloride co-transporter 2 expression in inflammatory pain induced by complete Freund's adjuvant (CFA). Eur J Pain 2017; 21:309-321. [PMID: 27506893 DOI: 10.1002/ejp.925] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 07/07/2016] [Indexed: 12/14/2022]
Abstract
BACKGROUND Multiple mechanisms contribute to the stimulus-evoked pain hypersensitivity that may be experienced after peripheral inflammation. Persistent pathological stimuli in many pain conditions affect the expression of certain genes through epigenetic alternations. The main purpose of our study was to investigate the role of epigenetic modification on potassium-chloride co-transporter 2 (KCC2) gene expression in the persistence of inflammatory pain. METHODS Persistent inflammatory pain was induced through the injection of complete Freund's adjuvant (CFA) in the left hind paw of rats. Acetyl-histone H3 and H4 level was determined by chromatin immunoprecipitation in the spinal dorsal horn. Pain behaviour and inhibitory synaptic function of spinal cord were determined before and after CFA injection. KCC2 expression was determined by real time RT-PCR and Western blot. Intrathecal KCC2 siRNA (2 μg per 10 μL per rat) or HDAC inhibitor (10 μg per 10 μL per rat) was injected once daily for 3 days before CFA injection. RESULTS Persistent inflammatory pain epigenetically suppressed KCC2 expression through histone deacetylase (HDAC)-mediated histone hypoacetylation, resulting in decreased inhibitory signalling efficacy. KCC2 knock-down caused by intrathecal administration of KCC2 siRNA in naïve rats reduced KCC2 expression in the spinal cord, leading to sensitized pain behaviours and impaired inhibitory synaptic transmission in their spinal cords. Moreover, intrathecal HDAC inhibitor injection in CFA rats increased KCC2 expression, partially restoring the spinal inhibitory synaptic transmission and relieving the sensitized pain behaviour. CONCLUSION These findings suggest that the transcription of spinal KCC2 is regulated by histone acetylation epigenetically following CFA. SIGNIFICANCE Persistent pain suppresses KCC2 expression through HDAC-mediated histone hypoacetylation and consequently impairs the inhibitory function of inhibitory interneurons. Drugs such as HDAC inhibitors that suppress the influences of persistent pain on the expression of KCC2 may serve as a novel analgesic.
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Affiliation(s)
- C-R Lin
- Department of Anesthesiology, Chang Gung Memorial Hospital-Kaohsiung Medical Center, Chang Gung University College of Medicine, Kaohsiung, Taiwan
| | - J-K Cheng
- Department of Anesthesiology, MacKay Memorial Hospital, Taipei, Taiwan
| | - C-H Wu
- Department of Anesthesiology, Chang Gung Memorial Hospital-Kaohsiung Medical Center, Chang Gung University College of Medicine, Kaohsiung, Taiwan
| | - K-H Chen
- Department of Anesthesiology, Chang Gung Memorial Hospital-Kaohsiung Medical Center, Chang Gung University College of Medicine, Kaohsiung, Taiwan
| | - C-K Liu
- Department of Anesthesiology, Chang Gung Memorial Hospital-Kaohsiung Medical Center, Chang Gung University College of Medicine, Kaohsiung, Taiwan
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Humble SR. Neurosteroids are reduced in diabetic neuropathy and may be associated with the development of neuropathic pain. F1000Res 2016; 5:1923. [PMID: 28357038 PMCID: PMC5345788 DOI: 10.12688/f1000research.9034.1] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Accepted: 07/29/2016] [Indexed: 01/10/2023] Open
Abstract
Introduction: Peripheral and central sensitisation are implicated in the development of neuropathic pain. Hypersensitivity of pain pathway neurons has been described in animal models of diabetic neuropathy, which is postulated to be related to an imbalance between inhibitory and excitatory signals within the spinal cord. GABAergic neurons within the pain pathway are vital for the transmission of painful stimuli to higher centres. A developmental change in the rate of exponential decay of GABAergic synaptic events has been observed in other types of neurons and this may be associated with fluctuations in endogenous neurosteroid tone. Methods: The whole-cell patch-clamp technique was used on slices of neural tissue. Electrophysiological recordings were obtained from wild type mice between the ages of 6 and 80 days in the spinal cord, the nucleus reticularis of the thalamus and the cerebral cortex. Recordings were also obtained from mice with diabetic neuropathy (ob/ob and db/db) between the ages of 60 and 80 days. Behavioural experiments were performed to examine mechanical and thermal nociception. Results: Electrophysiological recordings from cortical pain pathway neurons from mature type-2 diabetic mice revealed that the endogenous neurosteroid tone is reduced compared to control. However, selected neurosteroid compounds had a more pronounced effect on the GABA
A receptors of these diabetic mice. ob/ob mice exhibit mechanical hyperalgesia and allodynia, which was reduced by neurosteroids applied exogenously. Conclusions: The reduced endogenous neurosteroid tone in ob/ob mice may be linked to their hypersensitivity. Neurosteroids may exert analgesic effects in pathological pain states by attempting to restore the physiological GABAergic inhibitory tone.
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Affiliation(s)
- Stephen R Humble
- Department of Anaesthetics and Pain Management, Charing Cross Hospital, Imperial College NHS Healthcare Trust London, London, W6 8RF, UK
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Lee KY, Prescott SA. Chloride dysregulation and inhibitory receptor blockade yield equivalent disinhibition of spinal neurons yet are differentially reversed by carbonic anhydrase blockade. Pain 2015; 156:2431-2437. [PMID: 26186265 DOI: 10.1097/j.pain.0000000000000301] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Synaptic inhibition plays a key role in processing somatosensory information. Blocking inhibition at the spinal level is sufficient to produce mechanical allodynia, and many neuropathic pain conditions are associated with reduced inhibition. Disinhibition of spinal neurons can arise through decreased GABAA/glycine receptor activation or through dysregulation of intracellular chloride. We hypothesized that these distinct disinhibitory mechanisms, despite all causing allodynia, are differentially susceptible to therapeutic intervention. Specifically, we predicted that reducing bicarbonate efflux by blocking carbonic anhydrase with acetazolamide (ACTZ) would counteract disinhibition caused by chloride dysregulation without affecting normal inhibition or disinhibition caused by GABAA/glycine receptor blockade. To test this, responses to innocuous tactile stimulation were recorded in vivo from rat superficial dorsal horn neurons before and after different forms of pharmacological disinhibition and again after application of ACTZ. Blocking GABAA or glycine receptors caused hyperresponsiveness equivalent to that caused by blocking the potassium chloride cotransporter KCC2, but, consistent with our predictions, only disinhibition caused by KCC2 blockade was counteracted by ACTZ. ACTZ did not alter responses of neurons with intact inhibition. As pathological downregulation of KCC2 is triggered by brain-derived neurotrophic factor, we also confirmed that ACTZ was effective against brain-derived neurotrophic factor-induced hyperresponsiveness. Our results argue that intrathecal ACTZ has antiallodynic effects only if allodynia arises through chloride dysregulation; therefore, behavioral evidence that ACTZ is antiallodynic in nerve-injured animals affirms the contribution of chloride dysregulation as a key pathological mechanism. Although different disinhibitory mechanisms are not mutually exclusive, these results demonstrate that their relative contribution dictates which specific therapies will be effective.
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Affiliation(s)
- Kwan Yeop Lee
- Neurosciences and Mental Health, The Hospital for Sick Children, Toronto, ON, Canada; Department of Physiology, University of Toronto, Toronto, ON, Canada
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Involvement of medullary GABAergic system in extraterritorial neuropathic pain mechanisms associated with inferior alveolar nerve transection. Exp Neurol 2015; 267:42-52. [DOI: 10.1016/j.expneurol.2015.02.030] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2014] [Revised: 12/03/2014] [Accepted: 02/22/2015] [Indexed: 01/15/2023]
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Synaptic Inhibition and Disinhibition in the Spinal Dorsal Horn. PROGRESS IN MOLECULAR BIOLOGY AND TRANSLATIONAL SCIENCE 2015; 131:359-83. [DOI: 10.1016/bs.pmbts.2014.11.008] [Citation(s) in RCA: 39] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
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Eaton MM, Lim YB, Covey DF, Akk G. Modulation of the human ρ1 GABAA receptor by inhibitory steroids. Psychopharmacology (Berl) 2014; 231:3467-78. [PMID: 24317445 PMCID: PMC4048647 DOI: 10.1007/s00213-013-3379-z] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/16/2013] [Accepted: 11/25/2013] [Indexed: 11/28/2022]
Abstract
RATIONALE Modulators of the ρ1 GABAA receptor may be useful in the treatment of visual, sleep, and cognitive disorders. Neuroactive steroids and analogues have been shown to modulate ρ1 receptor function, but the molecular mechanisms are poorly understood. OBJECTIVES We employed electrophysiology and voltage-clamp fluorometry to compare the actions of several neuroactive steroids and analogues on the human ρ1 GABAA receptor. RESULTS Results confirmed that P294S and T298F mutations affect modulation by steroids. The P294S mutation abolished inhibition by (3α,5β)-3-hydroxypregnan-20-one (3α5βP) while the T298F mutation eliminated inhibition by 17β-estradiol. Voltage-clamp fluorometry demonstrated that steroids differing in the presence of a charged group on C3 or nature of substituent on C17 uniquely modified fluorescence changes elicited by GABA in the extracellular domain. The I307Q mutation reversed the inhibitory effect of 3α5βP but was without effect on modulation by (3α,5β)-3-hydroxypregnan-20-one sulfate or 17β-estradiol. The effect of 3α5βP on the fluorescence change generated at Y241C was dependent on whether the steroid acted as an inhibitor or a potentiator. Further, the effect was limited to uncharged 5β-reduced steroids containing an acetyl group on C17. CONCLUSIONS The data demonstrate that steroids and analogues differ with respect to conformational changes elicited by these drugs as well as sensitivity to the effects of mutations. Steroids and analogues could be provisionally divided into three major groups based on their actions on the ρ1 GABAA receptor: 5β-reduced uncharged steroids, sulfated and carboxylated steroids, and 17β-estradiol. Further division among 5β-reduced uncharged steroids was based on substituent at position C17.
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Affiliation(s)
- Megan M Eaton
- Department of Anesthesiology, Washington University School of Medicine, Campus Box 8054, 660 S. Euclid Ave, St. Louis, MO, 63110, USA
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McCarson KE, Enna SJ. GABA pharmacology: the search for analgesics. Neurochem Res 2014; 39:1948-63. [PMID: 24532294 DOI: 10.1007/s11064-014-1254-x] [Citation(s) in RCA: 55] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2013] [Revised: 01/28/2014] [Accepted: 01/31/2014] [Indexed: 12/28/2022]
Abstract
Decades of research have been devoted to defining the role of GABAergic transmission in nociceptive processing. Much of this work was performed using rigid, orthosteric GABA analogs created by Povl Krogsgaard-Larsen and his associates. A relationship between GABA and pain is suggested by the anatomical distribution of GABA receptors and the ability of some GABA agonists to alter nociceptive responsiveness. Outlined in this report are data supporting this proposition, with particular emphasis on the anatomical localization and function of GABA-containing neurons and the molecular and pharmacological properties of GABAA and GABAB receptor subtypes. Reference is made to changes in overall GABAergic tone, GABA receptor expression and activity as a function of the duration and intensity of a painful stimulus or exposure to GABAergic agents. Evidence is presented that the plasticity of this receptor system may be responsible for the variability in the antinociceptive effectiveness of compounds that influence GABA transmission. These findings demonstrate that at least some types of persistent pain are associated with a regionally selective decline in GABAergic tone, highlighting the need for agents that enhance GABA activity in the affected regions without compromising GABA function over the long-term. As subtype selective positive allosteric modulators may accomplish these goals, such compounds might represent a new class of analgesic drugs.
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Affiliation(s)
- Kenneth E McCarson
- Department of Pharmacology, Toxicology, and Therapeutics, University of Kansas Medical Center, 3901 Rainbow Boulevard, Mail Stop 1018, Kansas City, KS, 66160, USA
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Inhibition of carbonic anhydrase augments GABAA receptor-mediated analgesia via a spinal mechanism of action. THE JOURNAL OF PAIN 2014; 15:395-406. [PMID: 24412803 DOI: 10.1016/j.jpain.2014.01.001] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/30/2013] [Revised: 10/22/2013] [Accepted: 01/04/2014] [Indexed: 12/21/2022]
Abstract
UNLABELLED Peripheral nerve injury (PNI) negatively influences spinal gamma-aminobutyric acid (GABA)ergic networks via a reduction in the neuron-specific potassium-chloride (K(+)-Cl(-)) cotransporter (KCC2). This process has been linked to the emergence of neuropathic allodynia. In vivo pharmacologic and modeling studies show that a loss of KCC2 function results in a decrease in the efficacy of GABAA-mediated spinal inhibition. One potential strategy to mitigate this effect entails inhibition of carbonic anhydrase activity to reduce HCO3(-)-dependent depolarization via GABAA receptors when KCC2 function is compromised. We have tested this hypothesis here. Our results show that, similarly to when KCC2 is pharmacologically blocked, PNI causes a loss of analgesic effect for neurosteroid GABAA allosteric modulators at maximally effective doses in naïve mice in the tail-flick test. Remarkably, inhibition of carbonic anhydrase activity with intrathecal acetazolamide rapidly restores an analgesic effect for these compounds, suggesting an important role of carbonic anhydrase activity in regulating GABAA-mediated analgesia after PNI. Moreover, spinal acetazolamide administration leads to a profound reduction in the mouse formalin pain test, indicating that spinal carbonic anhydrase inhibition produces analgesia when primary afferent activity is driven by chemical mediators. Finally, we demonstrate that systemic administration of acetazolamide to rats with PNI produces an antiallodynic effect by itself and an enhancement of the peak analgesic effect with a change in the shape of the dose-response curve of the α1-sparing benzodiazepine L-838,417. Thus, carbonic anhydrase inhibition mitigates the negative effects of loss of KCC2 function after nerve injury in multiple species and through multiple administration routes resulting in an enhancement of analgesic effects for several GABAA allosteric modulators. We suggest that carbonic anhydrase inhibitors, many of which are clinically available, might be advantageously employed for the treatment of pathologic pain states. PERSPECTIVE Using behavioral pharmacology techniques, we show that spinal GABAA-mediated analgesia can be augmented, especially following nerve injury, via inhibition of carbonic anhydrases. Carbonic anhydrase inhibition alone also produces analgesia, suggesting these enzymes might be targeted for the treatment of pain.
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Bonin RP, De Koninck Y. Restoring ionotropic inhibition as an analgesic strategy. Neurosci Lett 2013; 557 Pt A:43-51. [PMID: 24080373 DOI: 10.1016/j.neulet.2013.09.047] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2013] [Revised: 09/11/2013] [Accepted: 09/16/2013] [Indexed: 12/31/2022]
Abstract
Neuronal inhibition in nociceptive relays of the spinal cord is essential for the proper processing of nociceptive information. In the spinal cord dorsal horn, the activity of synaptic and extrasynaptic GABAA and glycine receptors generates rapid, Cl(-)-dependent neuronal inhibition. A loss of this ionotropic inhibition, particularly through the collapse of the inhibitory Cl(-)-gradient, is a key mechanism by which pathological pain conditions develop. This review summarizes the roles of ionotropic inhibition in the regulation of nociception, and explores recent evidence that the potentiation of GABAA or glycine receptor activity or the enhancement of inhibitory drive can reverse pathological pain.
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Affiliation(s)
- Robert P Bonin
- Unité de neurosciences cellulaires et moléculaire, Centre de recherche de l'institut universitaire en santé mentale de Québec, Québec, Canada
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GABA(A) receptor modulation: potential to deliver novel pain medicines? Eur J Pharmacol 2013; 716:17-23. [PMID: 23500203 DOI: 10.1016/j.ejphar.2013.01.070] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2012] [Revised: 12/10/2012] [Accepted: 01/09/2013] [Indexed: 11/23/2022]
Abstract
GAB(A) (γ-aminobutyric acid) is abundantly expressed within the brain, and spinal cord pain circuits where it acts as the principal mediator of fast inhibitory neurotransmission. However, drugs that target GABA(A) receptor function such as the classical benzodiazepines have not been optimised to promote analgesia, are limited by side effects and are not routinely used for this purpose in humans. Compounds such as NS11394, L-838,417, HZ166 and TPA023 all bind to the same benzodiazepine site on the GABA(A) receptor to allosterically modulate receptor function and enhance the actions of GABA. By virtue of their ability to activate selected subtypes of GABA(A) receptors (principally those containing α2, α3 and α5 subunits) these compounds have been shown to possess excellent tolerability profiles in animals. Importantly, a number of these molecules also mediate profound analgesia in animal models of inflammatory and neuropathic pain. Other modulators such as neurosteroids bind to distinct sites on GABA(A) receptor α subunits, possess a unique pharmacology and are capable of targeting alternative GABA(A) receptor expressing populations. Moreover, neurosteroids also have pronounced analgesic actions in animal pain models. The continuing call for novel mechanism of action analgesics to target specific pathologies, especially in clinical neuropathic conditions, emphasizes the need to test modulators of GABA(A) receptor function in both human experimental pain models and pain patients.
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