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Yorgason JT, Wadsworth HA, Anderson EJ, Williams BM, Brundage JN, Hedges DM, Stockard AL, Jones ST, Arthur SB, Hansen DM, Schilaty ND, Jang EY, Lee AM, Wallner M, Steffensen SC. Modulation of dopamine release by ethanol is mediated by atypical GABA A receptors on cholinergic interneurons in the nucleus accumbens. Addict Biol 2022; 27:e13108. [PMID: 34713509 DOI: 10.1111/adb.13108] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2021] [Revised: 08/31/2021] [Accepted: 09/24/2021] [Indexed: 12/18/2022]
Abstract
Previous studies indicate that moderate-to-high ethanol (EtOH) concentrations enhance dopamine (DA) neurotransmission in the mesolimbic DA system from the ventral tegmental area (VTA) and projecting to the nucleus accumbens core (NAc). However, voltammetry studies demonstrate that moderate-to-high EtOH concentrations decrease evoked DA release at NAc terminals. The involvement of γ-aminobutyric acid (GABA) receptors (GABAA Rs), glycine (GLY) receptors (GLYRs) and cholinergic interneurons (CINs) in mediating EtOH inhibition of evoked NAc DA release were examined. Fast scan cyclic voltammetry, electrophysiology, optogenetics and immunohistochemistry techniques were used to evaluate the effects of acute and chronic EtOH exposure on DA release and CIN activity in C57/BL6, CD-1, transgenic mice and δ-subunit knockout (KO) mice (δ-/-). Ethanol decreased DA release in mice with an IC50 of 80 mM ex vivo and 2.0 g/kg in vivo. GABA and GLY decreased evoked DA release at 1-10 mM. Typical GABAA R agonists inhibited DA release at high concentrations. Typical GABAA R antagonists had minimal effects on EtOH inhibition of evoked DA release. However, EtOH inhibition of DA release was blocked by the α4 β3 δ GABAA R antagonist Ro15-4513, the GLYR antagonist strychnine and by the GABA ρ1 (Rho-1) antagonist TPMPA (10 μM) and reduced significantly in GABAA R δ-/- mice. Rho-1 expression was observed in CINs. Ethanol inhibited GABAergic synaptic input to CINs from the VTA and enhanced firing rate, both of which were blocked by TPMPA. Results herein suggest that EtOH inhibition of DA release in the NAc is modulated by GLYRs and atypical GABAA Rs on CINs containing δ- and Rho-subunits.
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Affiliation(s)
- Jordan T Yorgason
- Department of Cellular Biology and Physiology, Brigham Young University, Provo, Utah, USA
| | - Hillary A Wadsworth
- Department of Psychology and Center for Neuroscience, Brigham Young University, Provo, Utah, USA
| | - Elizabeth J Anderson
- Department of Psychology and Center for Neuroscience, Brigham Young University, Provo, Utah, USA
| | - Benjamin M Williams
- Department of Psychology and Center for Neuroscience, Brigham Young University, Provo, Utah, USA
| | - James N Brundage
- Department of Psychology and Center for Neuroscience, Brigham Young University, Provo, Utah, USA
| | - David M Hedges
- Enterprise Information Management, Billings Clinic, Billings, Montana, USA
| | - Alyssa L Stockard
- Department of Psychology and Center for Neuroscience, Brigham Young University, Provo, Utah, USA
| | - Stephen T Jones
- Department of Psychology and Center for Neuroscience, Brigham Young University, Provo, Utah, USA
| | - Summer B Arthur
- Department of Psychology and Center for Neuroscience, Brigham Young University, Provo, Utah, USA
| | - David Micah Hansen
- Department of Psychology and Center for Neuroscience, Brigham Young University, Provo, Utah, USA
| | - Nathan D Schilaty
- Department of Physiology & Biomedical Engineering, Mayo Clinic, Rochester, Minnesota, United States
| | - Eun Young Jang
- Research Center for Convergence Toxicology, Korea Institute of Toxicology, Daejeon, South Korea
| | - Anna M Lee
- Department of Pharmacology, University of Minnesota, Minneapolis, Minnesota, USA
| | - Martin Wallner
- Department of Molecular and Medical Pharmacology, University of California Los Angeles, Los Angeles, California, USA
| | - Scott C Steffensen
- Department of Psychology and Center for Neuroscience, Brigham Young University, Provo, Utah, USA
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Sparrow EL, James S, Hussain K, Beers SA, Cragg MS, Bogdanov YD. Activation of GABA(A) receptors inhibits T cell proliferation. PLoS One 2021; 16:e0251632. [PMID: 34014994 PMCID: PMC8136847 DOI: 10.1371/journal.pone.0251632] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2020] [Accepted: 04/29/2021] [Indexed: 11/18/2022] Open
Abstract
BACKGROUND The major sites for fast synaptic inhibition in the central nervous system (CNS) are ion channels activated by γ-aminobutyric acid (GABA). These receptors are referred as GABA(A) receptors (GABA(A)R). Recent evidence indicates a role of GABA(A)R in modulating the immune response. This work aimed to discern the role of GABA and GABA(A)Rs in human and mouse T cell activity. METHODS Mouse splenocytes or human peripheral blood mononuclear cells (PBMCs) were activated with anti-CD3 antibodies and the proliferation of both CD8+ and CD4+ T cells assessed through flow cytometry. Subsequently, the effects on T cell proliferation of either GABA(A)R modulation by diazepam that is also capable of activating mitochondrial based translocator protein (TSPO), alprazolam and allopregnanolone or inhibition by bicucculine methiodide (BMI) and (1,2,5,6-Tetrahydropyridin-4-yl)methylphosphinic acid (TPMPA) were assessed. RESULTS Positive modulation of GABA(A)Rs either by benzodiazepines or the neurosteroid allopregnanolone inhibits both mouse and human T cell proliferation. GABAergic inhibition of T cell proliferation by benzodiazepines could be rescued by GABA(A)R blocking. Our data suggest that benzodiazepines influence T cell proliferation through both TSPO and GABA(A)Rs activation. CONCLUSIONS We conclude that activation of GABA(A)Rs provides immunosuppression by inhibiting T cell proliferation.
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Affiliation(s)
- Emma L. Sparrow
- Antibody and Vaccine Group, Centre for Cancer Immunology, MP127, University of Southampton Faculty of Medicine, Southampton, Hants, United Kingdom
| | - Sonya James
- Antibody and Vaccine Group, Centre for Cancer Immunology, MP127, University of Southampton Faculty of Medicine, Southampton, Hants, United Kingdom
| | - Khiyam Hussain
- Antibody and Vaccine Group, Centre for Cancer Immunology, MP127, University of Southampton Faculty of Medicine, Southampton, Hants, United Kingdom
| | - Stephen A. Beers
- Antibody and Vaccine Group, Centre for Cancer Immunology, MP127, University of Southampton Faculty of Medicine, Southampton, Hants, United Kingdom
| | - Mark S. Cragg
- Antibody and Vaccine Group, Centre for Cancer Immunology, MP127, University of Southampton Faculty of Medicine, Southampton, Hants, United Kingdom
| | - Yury D. Bogdanov
- Antibody and Vaccine Group, Centre for Cancer Immunology, MP127, University of Southampton Faculty of Medicine, Southampton, Hants, United Kingdom
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Eliasen JN, Krall J, Frølund B, Kohlmeier KA. Sex-specific alterations in GABA receptor-mediated responses in laterodorsal tegmentum are associated with prenatal exposure to nicotine. Dev Neurobiol 2020; 80:178-199. [PMID: 32628361 DOI: 10.1002/dneu.22772] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2020] [Revised: 06/23/2020] [Accepted: 06/23/2020] [Indexed: 12/14/2022]
Abstract
Smoking during pregnancy is associated with deleterious physiological and cognitive effects on the offspring, which are likely due to nicotine-induced alteration in the development of neurotransmitter systems. Prenatal nicotine exposure (PNE) in rodents is associated with changes in behaviors controlled in part by the pontine laterodorsal tegmentum (LDT), and LDT excitatory signaling is altered in a sex and age-dependent manner by PNE. As effects on GABAergic LDT signaling are unknown, we used calcium imaging to evaluate GABAA receptor- (GABAA R as well as GABAA -ρ R) and GABAB receptor (GABAB R)-mediated calcium responses in LDT brain slices from female and male PNE mice in two different age groups. Overall, in older PNE females, changes in calcium induced by stimulation of GABAA R and GABAB R, including GABAA -ρ R were shifted toward calcium rises. In both young and old males, PNE was associated with alterations in calcium mediated by all three receptors; however, the GABAA R was the most affected. These results show for the first time that PNE is associated with alterations in GABAergic transmission in the LDT in a sex- and age-dependent manner, and these data are the first to show PNE-associated alterations in functionality of GABA receptors in any nucleus. PNE-associated alterations in LDT GABAergic transmission within the LDT would be expected to alter output to target regions and could play a role in LDT-implicated, negative behavioral outcomes following gestational exposure to smoking. Accordingly, our data provide further supportive evidence of the importance of eliminating the consumption of nicotine during pregnancy.
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Affiliation(s)
- Jannik Nicklas Eliasen
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Jacob Krall
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Bente Frølund
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Kristi A Kohlmeier
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
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The Benzodiazepine Binding Sites of GABAA Receptors. Trends Pharmacol Sci 2018; 39:659-671. [DOI: 10.1016/j.tips.2018.03.006] [Citation(s) in RCA: 107] [Impact Index Per Article: 17.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2018] [Revised: 03/15/2018] [Accepted: 03/22/2018] [Indexed: 11/24/2022]
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Persistent GABAA/C responses to gabazine, taurine and beta-alanine in rat hypoglossal motoneurons. Neuroscience 2016; 330:191-204. [PMID: 27246441 DOI: 10.1016/j.neuroscience.2016.05.048] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2016] [Revised: 05/19/2016] [Accepted: 05/24/2016] [Indexed: 11/22/2022]
Abstract
In hypoglossal motoneurons, a sustained anionic current, sensitive to a blocker of ρ-containing GABA receptors, (1,2,5,6-tetrahydropyridin-4-yl)methylphosphinic acid (TPMPA) and insensitive to bicuculline, was previously shown to be activated by gabazine. In order to better characterize the receptors involved, the sensitivity of this atypical response to pentobarbital (30μM), allopregnanolone (0.3μM) and midazolam (0.5μM) was first investigated. Pentobarbital potentiated the response, whereas the steroid and the benzodiazepine were ineffective. The results indicate the involvement of hybrid heteromeric receptors, including at least a GABA receptor ρ subunit and a γ subunit, accounting for the pentobarbital-sensitivity. The effects of the endogenous β amino acids, taurine and β-alanine, which are released under various pathological conditions and show neuroprotective properties, were then studied. In the presence of the glycine receptor blocker strychnine (1μM), both taurine (0.3-1mM) and β-alanine (0.3mM) activated sustained anionic currents, which were partly blocked by TPMPA (100μM). Thus, both β amino acids activated ρ-containing GABA receptors in hypoglossal motoneurons. Bicuculline (20μM) reduced responses to taurine and β-alanine, but small sustained responses persisted in the presence of both strychnine and bicuculline. Responses to β-alanine were slightly increased by allopregnanolone, indicating a contribution of the bicuculline- and neurosteroid-sensitive GABAA receptors underlying tonic inhibition in these motoneurons. Since sustained activation of anionic channels inhibits most mature principal neurons, the ρ-containing GABA receptors permanently activated by taurine and β-alanine might contribute to some of their neuroprotective properties under damaging overexcitatory situations.
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Tadavarty R, Hwang J, Rajput P, Soja P, Kumar U, Sastry B. Are presynaptic GABA-Cρ2 receptors involved in anti-nociception? Neurosci Lett 2015; 606:145-50. [DOI: 10.1016/j.neulet.2015.08.049] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2015] [Revised: 08/25/2015] [Accepted: 08/26/2015] [Indexed: 11/24/2022]
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Popova E. GABAergic neurotransmission and retinal ganglion cell function. J Comp Physiol A Neuroethol Sens Neural Behav Physiol 2015; 201:261-83. [PMID: 25656810 DOI: 10.1007/s00359-015-0981-z] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2014] [Revised: 01/19/2015] [Accepted: 01/21/2015] [Indexed: 01/13/2023]
Abstract
Ganglion cells are the output retinal neurons that convey visual information to the brain. There are ~20 different types of ganglion cells, each encoding a specific aspect of the visual scene as spatial and temporal contrast, orientation, direction of movement, presence of looming stimuli; etc. Ganglion cell functioning depends on the intrinsic properties of ganglion cell's membrane as well as on the excitatory and inhibitory inputs that these cells receive from other retinal neurons. GABA is one of the most abundant inhibitory neurotransmitters in the retina. How it modulates the activity of different types of ganglion cells and what is its significance in extracting the basic features from visual scene are questions with fundamental importance in visual neuroscience. The present review summarizes current data concerning the types of membrane receptors that mediate GABA action in proximal retina; the effects of GABA and its antagonists on the ganglion cell light-evoked postsynaptic potentials and spike discharges; the action of GABAergic agents on centre-surround organization of the receptive fields and feature related ganglion cell activity. Special emphasis is put on the GABA action regarding the ON-OFF and sustained-transient ganglion cell dichotomy in both nonmammalian and mammalian retina.
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Affiliation(s)
- E Popova
- Department of Physiology, Medical Faculty, Medical University, 1431, Sofia, Bulgaria,
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Wong LW, Tae HS, Cromer BA. Role of the ρ1 GABA(C) receptor N-terminus in assembly, trafficking and function. ACS Chem Neurosci 2014; 5:1266-77. [PMID: 25347026 DOI: 10.1021/cn500220t] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
Abstract
The GABAC receptor and closely related GABAA receptor are members of the pentameric ligand-gated ion channels (pLGICs) superfamily and mediate inhibitory fast synaptic transmission in the nervous system. Each pLGIC subunit comprises an N-terminal extracellular agonist-binding domain followed by a channel domain and a variable intracellular domain. Available structural information shows that the core of the agonist-binding domain is a β sandwich of ten β-strands, which form the agonist-binding pocket at the subunit interface. This β-sandwich is preceded by an N-terminal α-helix in eukaryotic structures but not in prokaryotic structures. The N-terminal α-helix has been shown to be functionally essential in α7 nicotinic acetylcholine receptors. Sequence analysis of GABAC and GABAA receptors predicts an α-helix in a similar position but preceded by 8 to 46 additional residues, of unknown function, which we term the N-terminal extension. To test the functional role of both the N-terminal extension and the putative N-terminal α-helix in the ρ1 GABAC receptor, we created a series of deletions from the N-terminus. The N-terminal extension was not functionally essential, but its removal did reduce both cell surface expression and cooperativity of agonist-gated channel function. Further deletion of the putative N-terminal α-helix abolished receptor function by preventing cell-surface expression. Our results further demonstrate the essential role of the N-terminal α-helix in the assembly and trafficking of eukaryotic pLGICs. They also provide evidence that the N-terminal extension, although not essential, contributes to receptor assembly, trafficking and conformational changes associated with ligand gating.
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Affiliation(s)
- Lik-Wei Wong
- Health
Innovation Research Institute, School of Medical Sciences, RMIT University, Bundoora, Victoria 3083, Australia
- Department
of Pharmacology and Therapeutics, University of Melbourne, Parkville, Victoria 3010, Australia
| | - Han-Shen Tae
- Health
Innovation Research Institute, School of Medical Sciences, RMIT University, Bundoora, Victoria 3083, Australia
| | - Brett A. Cromer
- Health
Innovation Research Institute, School of Medical Sciences, RMIT University, Bundoora, Victoria 3083, Australia
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Jones SM, Palmer MJ. Pharmacological analysis of the activation and receptor properties of the tonic GABA(C)R current in retinal bipolar cell terminals. PLoS One 2011; 6:e24892. [PMID: 21949779 PMCID: PMC3174224 DOI: 10.1371/journal.pone.0024892] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2011] [Accepted: 08/22/2011] [Indexed: 11/29/2022] Open
Abstract
GABAergic inhibition in the central nervous system (CNS) can occur via rapid, transient postsynaptic currents and via a tonic increase in membrane conductance, mediated by synaptic and extrasynaptic GABAA receptors (GABAARs) respectively. Retinal bipolar cells (BCs) exhibit a tonic current mediated by GABACRs in their axon terminal, in addition to synaptic GABAAR and GABACR currents, which strongly regulate BC output. The tonic GABACR current in BC terminals (BCTs) is not dependent on vesicular GABA release, but properties such as the alternative source of GABA and the identity of the GABACRs remain unknown. Following a recent report that tonic GABA release from cerebellar glial cells is mediated by Bestrophin 1 anion channels, we have investigated their role in non-vesicular GABA release in the retina. Using patch-clamp recordings from BCTs in goldfish retinal slices, we find that the tonic GABACR current is not reduced by the anion channel inhibitors NPPB or flufenamic acid but is reduced by DIDS, which decreases the tonic current without directly affecting GABACRs. All three drugs also exhibit non-specific effects including inhibition of GABA transporters. GABACR ρ subunits can form homomeric and heteromeric receptors that differ in their properties, but BC GABACRs are thought to be ρ1-ρ2 heteromers. To investigate whether GABACRs mediating tonic and synaptic currents may differ in their subunit composition, as is the case for GABAARs, we have examined the effects of two antagonists that show partial ρ subunit selectivity: picrotoxin and cyclothiazide. Tonic and synaptic GABACR currents were differentially affected by both drugs, suggesting that a population of homomeric ρ1 receptors contributes to the tonic current. These results extend our understanding of the multiple forms of GABAergic inhibition that exist in the CNS and contribute to visual signal processing in the retina.
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Affiliation(s)
- Stefanie M. Jones
- Neuroscience Group, Institute for Science and Technology in Medicine, Keele University, Keele, United Kingdom
| | - Mary J. Palmer
- Neuroscience Group, Institute for Science and Technology in Medicine, Keele University, Keele, United Kingdom
- * E-mail:
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Lewis A, Wilson N, Stearns G, Johnson N, Nelson R, Brockerhoff SE. Celsr3 is required for normal development of GABA circuits in the inner retina. PLoS Genet 2011; 7:e1002239. [PMID: 21852962 PMCID: PMC3154962 DOI: 10.1371/journal.pgen.1002239] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2011] [Accepted: 06/28/2011] [Indexed: 12/30/2022] Open
Abstract
The identity of the specific molecules required for the process of retinal circuitry formation is largely unknown. Here we report a newly identified zebrafish mutant in which the absence of the atypical cadherin, Celsr3, leads to a specific defect in the development of GABAergic signaling in the inner retina. This mutant lacks an optokinetic response (OKR), the ability to visually track rotating illuminated stripes, and develops a super-normal b-wave in the electroretinogram (ERG). We find that celsr3 mRNA is abundant in the amacrine and ganglion cells of the retina, however its loss does not affect synaptic lamination within the inner plexiform layer (IPL) or amacrine cell number. We localize the ERG defect pharmacologically to a late-stage disruption in GABAergic modulation of ON-bipolar cell pathway and find that the DNQX-sensitive fast b1 component of the ERG is specifically affected in this mutant. Consistently, we find an increase in GABA receptors on mutant ON-bipolar terminals, providing a direct link between the observed physiological changes and alterations in GABA signaling components. Finally, using blastula transplantation, we show that the lack of an OKR is due, at least partially, to Celsr3-mediated defects within the brain. These findings support the previously postulated inner retina origin for the b1 component and reveal a new role for Celsr3 in the normal development of ON visual pathway circuitry in the inner retina. Visual information is transmitted through the retina from photoreceptors to bipolars to ganglion cells, the output neurons connecting to the brain. This vertical transmission of information is modulated by inhibitory lateral interneurons. Normal vision requires the proper transmission and processing of these neuronal signals. In the inner retina, amacrine cells are the main class of inhibitory interneurons. They modulate the information from bipolar to ganglion cells and are functionally responsible for adjusting image brightness and for detecting motion. Physiological studies have revealed important aspects of the mechanisms of inhibitory modulation, and anatomical studies have identified the many amacrine subclasses and their non-random arrangement within the retina. Although cell–cell interactions are thought to be critical for establishing the important physiological and morphological features of this cell class, the precise molecules and their functions are mostly unknown. In this paper we report the discovery of a mutant that identifies the atypical cell adhesion molecule, Celsr3, as critical for proper development of GABA-signaling pathways in the inner retina.
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Affiliation(s)
- Alaron Lewis
- Department of Biochemistry, University of Washington, Seattle, Washington, United States of America
| | - Neil Wilson
- Department of Biochemistry, University of Washington, Seattle, Washington, United States of America
| | - George Stearns
- Department of Biochemistry, University of Washington, Seattle, Washington, United States of America
| | - Nicolas Johnson
- Department of Biochemistry, University of Washington, Seattle, Washington, United States of America
| | - Ralph Nelson
- Basic Neurosciences Program, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Rockville, Maryland, United States of America
| | - Susan E. Brockerhoff
- Department of Biochemistry, University of Washington, Seattle, Washington, United States of America
- * E-mail:
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Cheng ZY, Chebib M, Schmid KL. rho1 GABAC receptors are expressed in fibrous and cartilaginous layers of chick sclera and located on sclera fibroblasts and chondrocytes. J Neurochem 2011; 118:281-7. [DOI: 10.1111/j.1471-4159.2011.07300.x] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Memic A, Volgina VV, Gussin HA, Pepperberg DR, Kay BK. Generation of recombinant guinea pig antibody fragments to the human GABAC receptor. J Immunol Methods 2011; 368:36-44. [PMID: 21362428 DOI: 10.1016/j.jim.2011.02.010] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2010] [Revised: 12/22/2010] [Accepted: 02/22/2011] [Indexed: 10/18/2022]
Abstract
To generate monoclonal antibodies to the human ρ1 GABA(C) receptor, a ligand-gated chloride ion channel that is activated by the neurotransmitter γ-aminobutyric acid (GABA), we recovered the immunoglobulin variable heavy chain (V(H)) and light chain (V(L)) regions of a guinea pig immunized with a 14-mer peptide segment of the N-terminal extracellular domain of the ρ1 subunit. Oligonucleotide primers were designed and used to amplify the V(H) and V(L) regions of guinea pig RNA by the reverse transcriptase polymerase chain reaction. The amplified and cloned V(H) and V(L) regions were transferred together into a phagemid vector, yielding a library of 5×10(6) members, which displayed chimeric fragments of antigen binding (Fabs) with guinea pig variable and human constant regions fused to protein III of M13 bacteriophage. Through affinity selection of this phage-display library with the biotinylated 14-mer peptide segment of GABA(C), we isolated four different antibody fragments that bound specifically to the immunogenic peptide. Phage particles displaying two of these antibodies, but not negative controls, bound selectively to the surface of neuroblastoma cells expressing the ρ1 GABA(C) receptor. Such antibody fragments will be useful in future studies involving targeting of specific neural tissues that express the GABA(C) receptor.
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Affiliation(s)
- Adnan Memic
- Department of Biological Sciences, University of Illinois at Chicago, 60607, USA
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Neurovascular interaction and the pathophysiology of diabetic retinopathy. EXPERIMENTAL DIABETES RESEARCH 2011; 2011:693426. [PMID: 21747832 PMCID: PMC3124285 DOI: 10.1155/2011/693426] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/13/2010] [Revised: 01/11/2011] [Accepted: 01/25/2011] [Indexed: 01/08/2023]
Abstract
Diabetic retinopathy (DR) is the most severe of the several ocular complications of diabetes, and in the United States it is the leading cause of blindness among adults 20 to 74 years of age. Despite recent advances in our understanding of the pathogenesis of DR, there is a pressing need to develop novel therapeutic treatments that are both safe and efficacious. In the present paper, we identify a key mechanism involved in the development of the disease, namely, the interaction between neuronal and vascular activities. Numerous pathological conditions in the CNS have been linked to abnormalities in the relationship between these systems. We suggest that a similar situation arises in the diabetic retina, and we propose a logical strategy aimed at therapeutic intervention.
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Flores-Gracia C, Nuche-Bricaire A, Crespo-Ramírez M, Miledi R, Fuxe K, Pérez de la Mora M. GABA(A) ρ receptor mechanisms in the rat amygdala and its role in the modulation of fear and anxiety. Psychopharmacology (Berl) 2010; 212:475-84. [PMID: 20689940 DOI: 10.1007/s00213-010-1973-x] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/17/2010] [Accepted: 07/20/2010] [Indexed: 11/28/2022]
Abstract
RATIONALE Accumulating evidence for the presence of GABA(A) ρ receptors within the amygdala which differ from other members of the GABA(A) receptor family in both subunit composition and functional properties has been recently obtained. OBJECTIVES This work was conducted to study whether GABA(A) ρ receptors may have a putative role in the amygdaloid modulation of fear and anxiety. RESULTS It was found that the bilateral intra-amygdaloid administration (6-240 pmol/side) of (1,2,5,6-tetrahydropyridine-4-yl)methylphosphinic acid, a selective GABA(A) ρ receptor antagonist, reduced dose-dependently the exploration of the open arms of the elevated plus-maze without affecting locomotion and increased the plasma levels of corticosterone. In contrast, bicuculline in the dose range used (1.8-60 pmol/side) induced seizures, but had no effects on the exploration of the maze. CONCLUSIONS It is suggested that GABA(A) ρ receptors may have a role in the amygdaloid modulation of fear and anxiety.
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Affiliation(s)
- Candy Flores-Gracia
- Division of Neurosciences, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Apartado Postal 70-253, 04510, Mexico City, Mexico
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Olsen RW, Sieghart W. International Union of Pharmacology. LXX. Subtypes of gamma-aminobutyric acid(A) receptors: classification on the basis of subunit composition, pharmacology, and function. Update. Pharmacol Rev 2008; 60:243-60. [PMID: 18790874 DOI: 10.1124/pr.108.00505] [Citation(s) in RCA: 788] [Impact Index Per Article: 49.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
In this review we attempt to summarize experimental evidence on the existence of defined native GABA(A) receptor subtypes and to produce a list of receptors that actually seem to exist according to current knowledge. This will serve to update the most recent classification of GABA(A) receptors (Pharmacol Rev 50:291-313, 1998) approved by the Nomenclature Committee of the International Union of Pharmacology. GABA(A) receptors are chloride channels that mediate the major form of fast inhibitory neurotransmission in the central nervous system. They are members of the Cys-loop pentameric ligand-gated ion channel (LGIC) superfamily and share structural and functional homology with other members of that family. GABA(A) receptors are assembled from a family of 19 homologous subunit gene products and form numerous, mostly hetero-oligomeric, pentamers. Such receptor subtypes with properties that depend on subunit composition vary in topography and ontogeny, in cellular and subcellular localization, in their role in brain circuits and behaviors, in their mechanisms of regulation, and in their pharmacology. We propose several criteria, which can be applied to all the members of the LGIC superfamily, for including a receptor subtype on a list of native hetero-oligomeric subtypes. With these criteria, we develop a working GABA(A) receptor list, which currently includes 26 members, but will undoubtedly be modified and grow as information expands. The list is divided into three categories of native receptor subtypes: "identified," "existence with high probability," and "tentative."
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Affiliation(s)
- Richard W Olsen
- Department of Molecular and Medical Pharmacology, Geffen School of Medicine at UCLA, Room CHS 23-120, 650 Young Drive South, Los Angeles, CA 90095-1735, USA.
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16
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Lobo IA, Harris RA. GABA(A) receptors and alcohol. Pharmacol Biochem Behav 2008; 90:90-4. [PMID: 18423561 DOI: 10.1016/j.pbb.2008.03.006] [Citation(s) in RCA: 126] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/28/2007] [Revised: 02/19/2008] [Accepted: 03/05/2008] [Indexed: 12/31/2022]
Abstract
There is substantial evidence that GABAergic neurotransmission is important for many behavioral actions of ethanol and there are reports spanning more than 30 years of literature showing that low to moderate (3-30 mM) concentrations of ethanol enhance GABAergic neurotransmission. A key question is which GABA receptor subunits are sensitive to low concentrations of ethanol in vivo and in vitro. Recent evidence points to a role for extrasynaptic receptors. Another question is which behavioral actions of alcohol result from enhancement of GABAergic neurotransmission. Some clues are beginning to emerge from studies of knock-out and knock-in mice and from genetic analysis of human alcoholics. These approaches are converging on a role for GABAergic actions in regulating alcohol consumption and, perhaps, the development of alcoholism.
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Affiliation(s)
- Ingrid A Lobo
- Waggoner Center for Alcohol and Addiction Research, Section of Neurobiology and Institute for Cellular and Molecular Biology, The University of Texas at Austin, Austin, TX 78712, United States
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17
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Li W, Jin X, Covey DF, Steinbach JH. Neuroactive steroids and human recombinant rho1 GABAC receptors. J Pharmacol Exp Ther 2007; 323:236-47. [PMID: 17636008 DOI: 10.1124/jpet.107.127365] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The gamma-aminobutyric acid type C (GABAC) receptor is structurally related to the GABAA receptors, yet quite distinct physiologically and pharmacologically. Neuroactive steroids are known to be potent and efficacious modulators of the GABAA receptor, but they are less well characterized in their actions on the GABAC receptor. We have examined the actions of neuroactive steroids and analogs on rho1 (GABAC) receptors expressed in Xenopus laevis oocytes, with two goals in mind. First, we tested a larger number of endogenous steroids, to determine whether particularly potent steroids could be found. Second, we examined the structure-activity relationship for steroid actions, and some mechanistic features, to determine the possible numbers of steroid binding sites and mechanisms of action. In total, 41 compounds were examined. Estradiols are inhibitors, essentially equipotent with picrotoxinin. No endogenous steroid tested was highly efficacious at potentiation. The results of the structure-activity studies and the effects of two mutations to the second transmembrane region of the rho1 GABAC receptor indicate that there are several mechanisms by which steroids can inhibit the receptor. Surprisingly, estradiol shares some features with picrotoxin. Inhibition by negatively charged compounds was not sensitive to membrane potential, and inhibition by all compounds tested was reduced at higher concentrations of GABA. The data indicate that the binding sites mediating potentiation and inhibition differ from each other and that there are several (three or more) mechanisms for producing inhibition.
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Affiliation(s)
- Wenjun Li
- Department of Anesthesiology, Washington University School of Medicine, 660 S. Euclid Ave., St. Louis, MO, USA
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18
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Frazao R, Nogueira MI, Wässle H. Colocalization of synaptic GABA(C)-receptors with GABA (A)-receptors and glycine-receptors in the rodent central nervous system. Cell Tissue Res 2007; 330:1-15. [PMID: 17610086 DOI: 10.1007/s00441-007-0446-y] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2007] [Accepted: 05/24/2007] [Indexed: 10/23/2022]
Abstract
Fast inhibition in the nervous system is preferentially mediated by GABA- and glycine-receptors. Two types of ionotropic GABA-receptor, the GABA(A)-receptor and GABA(C)-receptor, have been identified; they have specific molecular compositions, different sensitivities to GABA, different kinetics, and distinct pharmacological profiles. We have studied, by immunocytochemistry, the synaptic localization of glycine-, GABA(A)-, and GABA(C)-receptors in rodent retina, spinal cord, midbrain, and brain-stem. Antibodies specific for the alpha1 subunit of the glycine-receptor, the gamma2 subunit of the GABA(A)-receptor, and the rho subunits of the GABA(C)-receptor have been applied. Using double-immunolabeling, we have determined whether these receptors are expressed at the same postsynaptic sites. In the retina, no such colocalization was observed. However, in the spinal cord, we found the colocalization of glycine-receptors with GABA(A)- or GABA(C)-receptors and the colocalization of GABA(A)- and GABA(C)-receptors in approximately 25% of the synapses. In the midbrain and brain-stem, GABA(A)- and GABA(C)-receptors were colocalized in 10%-15% of the postsynaptic sites. We discuss the possible expression of heteromeric (hybrid) receptors assembled from GABA(A)- and GABA(C)-receptor subunits. Our results suggest that GABA(A)- and GABA(C)-receptors are colocalized in a minority of synapses of the central nervous system.
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Affiliation(s)
- Renata Frazao
- Neuroanatomie, Max-Planck-Institut für Hirnforschung, Deutschordenstrasse 46, 60528, Frankfurt/Main, Germany
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19
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Ramsey DJ, Ripps H, Qian H. Streptozotocin-induced diabetes modulates GABA receptor activity of rat retinal neurons. Exp Eye Res 2007; 85:413-22. [PMID: 17662714 PMCID: PMC2001264 DOI: 10.1016/j.exer.2007.06.005] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2007] [Revised: 05/29/2007] [Accepted: 06/01/2007] [Indexed: 11/22/2022]
Abstract
Neural deficits suggestive of involvement of the GABA signaling pathway can often be detected early in the course of diabetic retinopathy, a leading cause of blindness in the United States. To examine in greater detail the nature of the neuronal changes associated with hyperglycemia, we investigated GABA receptor activity on retinal bipolar cells in streptozotocin-induced diabetic rats; cells from age-matched normal rats served as controls. Patch-clamp recordings from isolated rod-bipolar cells revealed that diabetes enhanced the whole cell currents elicited by GABA. Responses of the GABA(C) receptor, the predominant GABA receptor on rat rod bipolar cells, exhibited a greater sensitivity to GABA, larger maximum current responses, slower response kinetics, and a smaller single channel conductance among diabetic cells relative to those recorded from normal controls. Compared with the properties of homomeric rho1 and heteromeric rho1rho2 receptors formed in a heterologous expression system, these results suggested that there was a greater contribution from the rho1 subunit in the GABA(C) receptor-mediated response of diabetic cells. The levels of mRNA, measured with real-time RT-PCR, were consistent with this finding. There was a significant enhancement in the ratio of rho1/rho2 subunit expression in the retina of diabetic animals, although the levels of GABA rho1 subunit expression were comparable in diabetic and normal retinas. Taken together, the results suggest that diabetes modifies the subunit composition of the GABA(C) receptor on retinal neurons, most likely through its effect on the efficacy of gene transcription.
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Affiliation(s)
- David J. Ramsey
- Department of Ophthalmology and Visual Sciences, University of Illinois College of Medicine, 1855 West Taylor Street, Chicago, Illinois 60612, USA
- Department of Physiology and Biophysics, University of Illinois College of Medicine, 1855 West Taylor Street, Chicago, Illinois 60612, USA
- Department of Health Policy and Administration, University of Illinois College of Medicine, 1855 West Taylor Street, Chicago, Illinois 60612, USA
| | - Harris Ripps
- Department of Ophthalmology and Visual Sciences, University of Illinois College of Medicine, 1855 West Taylor Street, Chicago, Illinois 60612, USA
- Department of Physiology and Biophysics, University of Illinois College of Medicine, 1855 West Taylor Street, Chicago, Illinois 60612, USA
- Department of Anatomy and Cell Biology, University of Illinois College of Medicine, 1855 West Taylor Street, Chicago, Illinois 60612, USA
| | - Haohua Qian
- Department of Ophthalmology and Visual Sciences, University of Illinois College of Medicine, 1855 West Taylor Street, Chicago, Illinois 60612, USA
- Department of Physiology and Biophysics, University of Illinois College of Medicine, 1855 West Taylor Street, Chicago, Illinois 60612, USA
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20
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Zhu Y, Ripps H, Qian H. A single amino acid in the second transmembrane domain of GABA rho receptors regulates channel conductance. Neurosci Lett 2007; 418:205-9. [PMID: 17398006 PMCID: PMC1942122 DOI: 10.1016/j.neulet.2007.03.020] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2007] [Revised: 03/08/2007] [Accepted: 03/11/2007] [Indexed: 10/23/2022]
Abstract
GABAC receptors, expressed predominately in vertebrate retina, are thought to be formed mainly by GABA rho subunits, each of which exhibits distinct physiological and pharmacological properties. In this study, the receptors formed by perch GABA rho subunits were expressed in HEK cells, and their single channel conductances were determined using noise analysis techniques. The receptors formed by the perch rho1A subunit gate a channel with a conductance of 0.2 pS, whereas the receptors formed by GABA rho2 subunits exhibit much higher channel conductances, i.e., 3.2 and 3.5 pS for perch rho2A and rho2B receptors, respectively. A comparison of the amino acid sequences of the channel-forming TMII regions of the various subunits suggested that a single amino acid at position 2' was a potential site for the large differential in conductance. We found that switching the serine residue at that site in the GABA rho2 subunit to the proline residue present in the rho1 subunit reduced the channel conductance to a level similar to that of the wild type rho1 receptor. Conversely, mutating proline to serine in the amino acid sequence of the rho1 receptor significantly increased its unitary conductance. These results indicate that a single amino acid in the TMII region plays an important role in determining the single channel conductance of the GABAC receptors.
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Affiliation(s)
- Yujie Zhu
- Department of Ophthalmology and Visual Sciences, University of Illinois College of Medicine, 1855 West Taylor Street, Chicago, IL 60612, USA
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21
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Gussin HA, Tomlinson ID, Little DM, Warnement MR, Qian H, Rosenthal SJ, Pepperberg DR. Binding of muscimol-conjugated quantum dots to GABAC receptors. J Am Chem Soc 2007; 128:15701-13. [PMID: 17147380 PMCID: PMC2553244 DOI: 10.1021/ja064324k] [Citation(s) in RCA: 64] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Functionalization of highly fluorescent CdSe/ZnS core-shell nanocrystals (quantum dots, qdots) is an emerging technology for labeling cell surface proteins. We have synthesized a conjugate consisting of approximately 150-200 muscimols (a GABA receptor agonist) covalently joined to the qdot via a poly(ethylene glycol) (PEG) linker (approximately 78 ethylene glycol units) and investigated the binding of this muscimol-PEG-qdot conjugate to homomeric rho1 GABAC receptors expressed in Xenopus oocytes. GABAC receptors mediate inhibitory synaptic signaling at multiple locations in the central nervous system (CNS). Binding of the conjugate was analyzed quantitatively by determining the fluorescence intensity of the oocyte surface membrane in relation to that of the surrounding incubation medium. Upon 5- to 10-min incubation with muscimol-PEG-qdots (34 nM in qdot concentration), GABAC-expressing oocytes exhibited a fluorescent halo at the surface membrane that significantly exceeded the fluorescence of the incubation medium. This halo was absent following muscimol-PEG-qdot treatment of oocytes lacking GABAC receptors. Incubation of the oocyte with free muscimol (100 microM-5 mM), PEG-muscimol (500 microM), or GABA (100 microM - 5 mM) substantially reduced or eliminated the fluorescence halo produced by muscimol-PEG-qdots, and the removal of GABA or free muscimol led to a recovery of muscimol-PEG-qdot binding. Unconjugated qdots and PEG-qdots that lacked conjugated muscimol neither exhibited significant binding activity nor diminished the subsequent binding of muscimol-PEG-qdots. The results indicate that muscimol joined to qdots via a long-chain PEG linker exhibits specific binding activity at the ligand-binding pocket of expressed GABAC receptors, despite the presence of both the long PEG linker and the sterically bulky qdot.
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Affiliation(s)
- Hélène A. Gussin
- Lions of Illinois Eye Research Institute, Department of Ophthalmology and Visual Sciences, University of Illinois at Chicago, Chicago, IL 60612
| | - Ian D. Tomlinson
- Department of Chemistry, Vanderbilt University, Nashville, TN 37232
| | - Deborah M. Little
- Department of Neurology and Rehabilitation, and Center for Cognitive Medicine, University of Illinois at Chicago, Chicago, IL 60612
| | | | - Haohua Qian
- Lions of Illinois Eye Research Institute, Department of Ophthalmology and Visual Sciences, University of Illinois at Chicago, Chicago, IL 60612
| | | | - David R. Pepperberg
- Lions of Illinois Eye Research Institute, Department of Ophthalmology and Visual Sciences, University of Illinois at Chicago, Chicago, IL 60612
- Corresponding author: Dr. David R. Pepperberg, Department of Ophthalmology and Visual Sciences, University of Illinois at Chicago, 1855 W. Taylor Street, Chicago, IL 60612, Phone: 312-996-4262;Fax: 312-996-7773, Corresponding author’s email address:
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22
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Farrant M, Kaila K. The cellular, molecular and ionic basis of GABA(A) receptor signalling. PROGRESS IN BRAIN RESEARCH 2007; 160:59-87. [PMID: 17499109 DOI: 10.1016/s0079-6123(06)60005-8] [Citation(s) in RCA: 266] [Impact Index Per Article: 15.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
GABA(A) receptors mediate fast synaptic inhibition in the CNS. Whilst this is undoubtedly true, it is a gross oversimplification of their actions. The receptors themselves are diverse, being formed from a variety of subunits, each with a different temporal and spatial pattern of expression. This diversity is reflected in differences in subcellular targetting and in the subtleties of their response to GABA. While activation of the receptors leads to an inevitable increase in membrane conductance, the voltage response is dictated by the distribution of the permeant Cl(-) and HCO(3)(-) ions, which is established by anion transporters. Similar to GABA(A) receptors, the expression of these transporters is not only developmentally regulated but shows cell-specific and subcellular variation. Untangling all these complexities allows us to appreciate the variety of GABA-mediated signalling, a diverse set of phenomena encompassing both synaptic and non-synaptic functions that can be overtly excitatory as well as inhibitory.
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Affiliation(s)
- Mark Farrant
- Department of Pharmacology, UCL (University College London), Gower Street, London WC1E 6BT, UK.
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23
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Qian H, Pan Y, Choi B, Ripps H. High pH accelerates GABA deactivation on perch-rho1B receptors. Neuroscience 2006; 142:1221-30. [PMID: 16920274 DOI: 10.1016/j.neuroscience.2006.07.003] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2006] [Revised: 07/01/2006] [Accepted: 07/11/2006] [Indexed: 10/24/2022]
Abstract
The ionotropic GABA(C) receptor, formed by GABA rho subunits, is known to be modulated by a variety of endogenous compounds, as well as by changes in pH. In this study, we explore the proton sensitivity of the GABA rho subunits cloned from the perch retina, and report a novel action of high pH on the homomeric receptor formed by one of the GABA rho subunits, the perch-rho(1B) subunit. Raising extracellular pH to 9.5 significantly accelerated GABA deactivation responses elicited from oocytes expressing the perch-rho(1B) subunit, and reduced its sensitivity to GABA. The change in the kinetics of the GABA-offset response occurred without altering the maximum response amplitude, and the reduced GABA sensitivity was independent of membrane potential. Although acidification of the extracellular solution also accelerated GABA deactivation for all other GABA rho receptors examined in this study, the effects of high pH were unique to the homomeric receptor formed by the perch-rho(1B) subunit. In addition, we found that, unlike the effects on the response to the naturally occurring full agonist GABA, the responses elicited by partial agonists (imidazole-4-acetic acid (I4AA) and beta-alanine) in the presence of the high pH solution showed a significant reduction in the maximum response amplitude. When considered in terms of a model describing the activation of GABA(C) receptors, in which pH can potentially affect either the binding affinity or the rate of channel closure, the results were consistent with the view that external alkalization reduces the gating efficiency of the receptor. To identify the proton sensitive domain(s) of the perch-rho(1B) receptor, chimeras were constructed by domain swapping with other perch-rho subunits. Analysis of the pH sensitivities of the various chimeric receptors revealed that the alkaline-sensitive residues are located in the N-terminal region of the perch-rho(1B) subunit.
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MESH Headings
- Animals
- Binding, Competitive/drug effects
- Binding, Competitive/physiology
- Cell Membrane/drug effects
- Cell Membrane/metabolism
- Female
- GABA Agonists/pharmacology
- Hydrogen-Ion Concentration
- Ion Channel Gating/drug effects
- Ion Channel Gating/physiology
- Ligands
- Neural Inhibition/physiology
- Neurons/metabolism
- Oocytes
- Perches
- Protein Structure, Tertiary/drug effects
- Protein Structure, Tertiary/physiology
- Protons
- Receptors, GABA/chemistry
- Receptors, GABA/drug effects
- Receptors, GABA/metabolism
- Receptors, GABA-B/chemistry
- Receptors, GABA-B/drug effects
- Receptors, GABA-B/metabolism
- Synaptic Transmission/physiology
- Time Factors
- Xenopus
- gamma-Aminobutyric Acid/metabolism
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Affiliation(s)
- H Qian
- Department of Ophthalmology and Visual Sciences, University of Illinois at Chicago, 1855 West Taylor Street, Chicago, IL 60612, USA.
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24
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Harvey VL, Duguid IC, Krasel C, Stephens GJ. Evidence that GABA rho subunits contribute to functional ionotropic GABA receptors in mouse cerebellar Purkinje cells. J Physiol 2006; 577:127-39. [PMID: 16945976 PMCID: PMC2000691 DOI: 10.1113/jphysiol.2006.112482] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Ionotropic gamma-amino butyric acid (GABA) receptors composed of heterogeneous molecular subunits are major mediators of inhibitory responses in the adult CNS. Here, we describe a novel ionotropic GABA receptor in mouse cerebellar Purkinje cells (PCs) using agents reported to have increased affinity for rho subunit-containing GABA(C) over other GABA receptors. Exogenous application of the GABA(C)-preferring agonist cis-4-aminocrotonic acid (CACA) evoked whole-cell currents in PCs, whilst equimolar concentrations of GABA evoked larger currents. CACA-evoked currents had a greater sensitivity to the selective GABA(C) antagonist (1,2,5,6-tetrahydropyridin-4-yl)methylphosphinic acid (TPMPA) than GABA-evoked currents. Focal application of agonists produced a differential response profile; CACA-evoked currents displayed a much more pronounced attenuation with increasing distance from the PC soma, displayed a slower time-to-peak and exhibited less desensitization than GABA-evoked currents. However, CACA-evoked currents were also completely blocked by bicuculline, a selective agent for GABA(A) receptors. Thus, we describe a population of ionotropic GABA receptors with a mixed GABA(A)/GABA(C) pharmacology. TPMPA reduced inhibitory synaptic transmission at interneurone-Purkinje cell (IN-PC) synapses, causing clear reductions in miniature inhibitory postsynaptic current (mIPSC) amplitude and frequency. Combined application of NO-711 (a selective GABA transporter subtype 1 (GAT-1) antagonist) and SNAP-5114 (a GAT-(2)/3/4 antagonist) induced a tonic GABA conductance in PCs; however, TPMPA had no effect on this current. Immunohistochemical studies suggest that rho subunits are expressed predominantly in PC soma and proximal dendritic compartments with a lower level of expression in more distal dendrites; this selective immunoreactivity contrasted with a more uniform distribution of GABA(A) alpha1 subunits in PCs. Finally, co-immunoprecipitation studies suggest that rho subunits can form complexes with GABA(A) receptor alpha1 subunits in the cerebellar cortex. Overall, these data suggest that rho subunits contribute to functional ionotropic receptors that mediate a component of phasic inhibitory GABAergic transmission at IN-PC synapses in the cerebellum.
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Affiliation(s)
- Victoria L Harvey
- School of Pharmacy, University of Reading, Whiteknights, PO Box 228, Reading RG6 6AJ, UK
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25
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Pan Y, Ripps H, Qian H. Random assembly of GABA rho1 and rho2 subunits in the formation of heteromeric GABA(C) receptors. Cell Mol Neurobiol 2006; 26:289-305. [PMID: 16767514 DOI: 10.1007/s10571-006-9001-8] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2005] [Accepted: 02/08/2006] [Indexed: 10/24/2022]
Abstract
1. Various combinations of the rho subunits (rho(1A), rho(1B), rho(2A), rho(2B)) of GABA(C) receptors cloned from white perch retina were expressed in Xenopus oocytes, and electrophysiological and pharmacological methods were used to test their ability to co-assemble into heteromeric receptors. Simultaneous injection of the two subunits, irrespective of their relative proportions, led invariably to the formation of a preponderance of heteromeric receptors. 2. The GABA deactivation responses elicited from these cells could be described by a single exponential decay, and their pharmacological responses deviated significantly from those expected of a simple mixture of two homomeric rho(1) and rho(2) receptors. In contrast, a double exponential function comprising fast and slow components was required to fit the GABA deactivation responses elicited from oocytes sequentially expressing rho(1) and rho(2) subunits, a condition that favors the formation of a mixture of homomeric rho(1) and rho(2) receptors. 3. Both the GABA-response kinetics and the sensitivity to picrotoxin of the heteromeric perch rho(1B)rho(2A) receptor varied with the proportion of the subunit RNA injected, indicating there is no fixed stoichiometry for their co-assembly into heteromeric rho(1)rho(2) receptors. 4. If native GABA(C) receptors in retinal neurons behave in a similar manner as in the oocyte expression system, these finding suggest that the properties of their GABA(C) receptors are likely to be influenced by the transcription/translation efficiency of GABA rho subunit genes.
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Affiliation(s)
- Yi Pan
- Department of Ophthalmology and Visual Sciences, University of Illinois, Chicago, USA
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26
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Song XQ, Meng F, Ramsey DJ, Ripps H, Qian H. The GABA rho1 subunit interacts with a cellular retinoic acid binding protein in mammalian retina. Neuroscience 2005; 136:467-75. [PMID: 16198491 DOI: 10.1016/j.neuroscience.2005.08.018] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2005] [Revised: 07/14/2005] [Accepted: 08/04/2005] [Indexed: 11/15/2022]
Abstract
Interactions between the intracellular domain of ligand-gated membrane receptors and cytoplasmic proteins play important roles in their assembly, clustering, and function. In addition, protein-protein interactions may provide an alternative mechanism by which neurotransmitters activate intracellular pathways. In this study, we report a novel interaction between the GABA rho1 subunit and cellular retinoic acid binding protein in mammalian retina that could serve as a link between the GABA signaling pathway and the control of gene expression in neurons. The interaction between the intracellular loop of the human GABA rho subunit and cellular retinoic acid binding protein was identified using a CytoTrap XR yeast two-hybrid system, and was further confirmed by co-precipitation of the human GABA rho subunit and cellular retinoic acid binding protein from baboon retinal samples. The cellular retinoic acid binding protein binding domain on the human rho1 subunit was located to the C-terminal region of human GABA rho subunit, and the interaction of the human GABA rho subunit with cellular retinoic acid binding protein could be antagonized by a peptide derived from within the binding domain of the rho1 subunit. Since cellular retinoic acid binding protein is a carrier protein for retinoic acid, we investigated the effect of GABA on retinoic acid activity in neuroblastoma cells containing endogenously expressed cellular retinoic acid binding protein. In the absence of the rho1 receptor, these cells showed enhanced neurite outgrowth when exposed to retinoic acid and GABA had no effect on their response to retinoic acid. In contrast, cells stably transfected with the human rho1 subunit showed a significantly reduced sensitivity to retinoic acid when exposed to GABA. These results suggest that the GABA receptor subunit effectively altered gene expression through its interaction with the cellular retinoic acid binding protein pathway.
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Affiliation(s)
- X-Q Song
- Department of Ophthalmology and Visual Sciences, University of Illinois at Chicago, 1855 West Taylor Street, Chicago, IL 60612, USA
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