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Sharma D, Tripathi M, Doddamani R, Sharma MC, Lalwani S, Sarat Chandra P, Banerjee Dixit A, Banerjee J. Correlation of age at seizure onset with GABA A receptor subunit and chloride Co-transporter configuration in Focal cortical dysplasia (FCD). Neurosci Lett 2023; 796:137065. [PMID: 36638954 DOI: 10.1016/j.neulet.2023.137065] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2022] [Revised: 12/23/2022] [Accepted: 01/09/2023] [Indexed: 01/12/2023]
Abstract
Focal cortical dysplasia (FCD) represents a group of malformations of cortical development, which are speculated to be related to early developmental defects in the cerebral cortex. According to dysmature cerebral development hypothesis of FCD altered GABAA receptor function is known to contribute to abnormal neuronal network. Here, we studied the possible association between age at seizure onset in FCD with the subunit configuration of GABAA receptors in resected brain specimens obtained from patients with FCD. We observed a significantly higher ratio of α4/α1 subunit-containing GABAA receptors in patients with early onset (EO) FCD as compared to those with late onset (LO) FCD as is seen during the course of development where α4-containing GABAA receptors expression is high as compared to α1-containing GABAA receptors expression. Likewise, the influx to efflux chloride co-transporter expression of NKCC1/KCC2 was also increased in patients with EO FCD as seen during brain development. In addition, we observed that the ratio of GABA/Glutamate neurotransmitters was lower in patients with EO FCD as compared to that in patients with LO FCD. Our findings suggest altered configuration of GABAA receptors in FCD which could be contributing to aberrant depolarizing GABAergic activity. In particular, we observed a correlation of age at seizure onset in FCD with subunit configuration of GABAA receptors, levels of NKCC1/KCC2 and the ratio of GABA/Glutamate neurotransmitters such that the patients with EO FCD exhibited a more critically modulated GABAergic network.
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Affiliation(s)
- Devina Sharma
- Department of Neurosurgery, All India Institute of Medical Sciences, New Delhi, India
| | - Manjari Tripathi
- Department of Neurology, All India Institute of Medical Sciences, New Delhi, India
| | - Ramesh Doddamani
- Department of Neurosurgery, All India Institute of Medical Sciences, New Delhi, India
| | - M C Sharma
- Department of Pathology, All India Institute of Medical Sciences, New Delhi, India
| | - Sanjeev Lalwani
- Department of Forensic Medicine and Toxicology, All India Institute of Medical Sciences, New Delhi, India
| | - P Sarat Chandra
- Department of Neurosurgery, All India Institute of Medical Sciences, New Delhi, India
| | - Aparna Banerjee Dixit
- Dr. B.R Ambedkar Center for Biomedical Research, University of Delhi, New Delhi, India
| | - Jyotirmoy Banerjee
- Department of Biophysics, All India Institute of Medical Sciences, New Delhi, India.
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2
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Electrophysiology of ionotropic GABA receptors. Cell Mol Life Sci 2021; 78:5341-5370. [PMID: 34061215 PMCID: PMC8257536 DOI: 10.1007/s00018-021-03846-2] [Citation(s) in RCA: 41] [Impact Index Per Article: 13.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2020] [Revised: 04/02/2021] [Accepted: 04/23/2021] [Indexed: 10/30/2022]
Abstract
GABAA receptors are ligand-gated chloride channels and ionotropic receptors of GABA, the main inhibitory neurotransmitter in vertebrates. In this review, we discuss the major and diverse roles GABAA receptors play in the regulation of neuronal communication and the functioning of the brain. GABAA receptors have complex electrophysiological properties that enable them to mediate different types of currents such as phasic and tonic inhibitory currents. Their activity is finely regulated by membrane voltage, phosphorylation and several ions. GABAA receptors are pentameric and are assembled from a diverse set of subunits. They are subdivided into numerous subtypes, which differ widely in expression patterns, distribution and electrical activity. Substantial variations in macroscopic neural behavior can emerge from minor differences in structure and molecular activity between subtypes. Therefore, the diversity of GABAA receptors widens the neuronal repertoire of responses to external signals and contributes to shaping the electrical activity of neurons and other cell types.
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3
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Manville RW, Papanikolaou M, Abbott GW. M-Channel Activation Contributes to the Anticonvulsant Action of the Ketone Body β-Hydroxybutyrate. J Pharmacol Exp Ther 2019; 372:148-156. [PMID: 31757819 DOI: 10.1124/jpet.119.263350] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2019] [Accepted: 11/20/2019] [Indexed: 12/26/2022] Open
Abstract
Ketogenic diets are effective therapies for refractory epilepsy, yet the underlying mechanisms are incompletely understood. The anticonvulsant efficacy of ketogenic diets correlates positively to the serum concentration of β-hydroxybutyrate (BHB), the primary ketone body generated by ketosis. Voltage-gated potassium channels generated by KCNQ2-5 subunits, especially KCNQ2/3 heteromers, generate the M-current, a therapeutic target for synthetic anticonvulsants. Here, we report that BHB directly activates KCNQ2/3 channels (EC50 = 0.7 µM), via a highly conserved S5 tryptophan (W265) on KCNQ3. BHB was also acutely effective as an anticonvulsant in the pentylene tetrazole (PTZ) seizure assay in mice. Strikingly, coadministration of γ-amino-β-hydroxybutyric acid, a high-affinity KCNQ2/3 partial agonist that also acts via KCNQ3-W265, similarly reduced the efficacy of BHB in KCNQ2/3 channel activation in vitro and in the PTZ seizure assay in vivo. Our results uncover a novel, unexpected molecular basis for anticonvulsant effects of the major ketone body induced by ketosis. SIGNIFICANCE STATEMENT: Ketogenic diets are used to treat refractory epilepsy but the therapeutic mechanism is not fully understood. Here, we show that clinically relevant concentrations of β-hydroxybutyrate, the primary ketone body generated during ketogenesis, activates KCNQ2/3 potassium channels by binding to a specific site on KCNQ3, an effect known to reduce neuronal excitability. We provide evidence using a mouse chemoconvulsant model that KCNQ2/3 activation contributes to the antiepileptic action of β-hydroxybutyrate.
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Affiliation(s)
- Rían W Manville
- Bioelectricity Laboratory, Department of Physiology and Biophysics, School of Medicine, University of California, Irvine, California
| | - Maria Papanikolaou
- Bioelectricity Laboratory, Department of Physiology and Biophysics, School of Medicine, University of California, Irvine, California
| | - Geoffrey W Abbott
- Bioelectricity Laboratory, Department of Physiology and Biophysics, School of Medicine, University of California, Irvine, California
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Maniezzi C, Talpo F, Spaiardi P, Toselli M, Biella G. Oxytocin Increases Phasic and Tonic GABAergic Transmission in CA1 Region of Mouse Hippocampus. Front Cell Neurosci 2019; 13:178. [PMID: 31133808 PMCID: PMC6516053 DOI: 10.3389/fncel.2019.00178] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2019] [Accepted: 04/12/2019] [Indexed: 11/17/2022] Open
Abstract
Oxytocin is a neuropeptide that plays important peripheral and central neuromodulatory functions. Our data show that, following activation of oxytocin receptors (OtRs) with the selective agonist TGOT (Thr4,Gly7-oxytocin), a significant increase in frequency and amplitude of spontaneous inhibitory postsynaptic currents (sIPSC) occurred in hippocampal CA1 pyramidal neurons (PYR) in mice. TGOT affected also sIPSC deactivation kinetics, suggesting the involvement of perisynaptic GABAA receptors (GABAARs) as well. By contrast, TGOT did not cause significant changes in frequency, amplitude or deactivation kinetics of miniature IPSC, suggesting that the effects elicited by the agonist are strictly dependent on the firing activity of presynaptic neurons. Moreover, TGOT was able to modulate tonic GABAergic current mediated by extrasynaptic GABAARs expressed by PYRs. Consistently, at spike threshold TGOT induced in most PYRs a significant membrane hyperpolarization and a decrease in firing rate. The source of increased inhibition onto PYRs was represented by stuttering fast-spiking GABAergic interneurons (INs) that directly respond to TGOT with a depolarization and an increase in their firing rate. One putative ionic mechanism underlying this effect could be represented by OtR activation-induced up-modulation of L-type Ca2+ channels. In conclusion, our results indicate that oxytocin can influence the activity of a subclass of hippocampal GABAergic INs and therefore regulate the operational modes of the downstream PYRs by increasing phasic and tonic GABAergic transmission in CA1 region of mouse hippocampus.
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Affiliation(s)
- Claudia Maniezzi
- Laboratory of Physiology, Department of Biology and Biotechnology "Lazzaro Spallanzani", University of Pavia, Pavia, Italy
| | - Francesca Talpo
- Laboratory of Physiology, Department of Biology and Biotechnology "Lazzaro Spallanzani", University of Pavia, Pavia, Italy
| | - Paolo Spaiardi
- Neurophysiology Unit, Department of Brain and Behavioral Sciences, University of Pavia, Pavia, Italy
| | - Mauro Toselli
- Laboratory of Physiology, Department of Biology and Biotechnology "Lazzaro Spallanzani", University of Pavia, Pavia, Italy
| | - Gerardo Biella
- Laboratory of Physiology, Department of Biology and Biotechnology "Lazzaro Spallanzani", University of Pavia, Pavia, Italy
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5
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Berggaard N, Witter MP, van der Want JJL. GABA A Receptor Subunit α3 in Network Dynamics in the Medial Entorhinal Cortex. Front Syst Neurosci 2019; 13:10. [PMID: 30930755 PMCID: PMC6428777 DOI: 10.3389/fnsys.2019.00010] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2018] [Accepted: 02/25/2019] [Indexed: 12/11/2022] Open
Abstract
Layer II of the medial entorhinal cortex (MEC LII) contains the largest number of spatially modulated grid cells and is one of the first regions in the brain to express Alzheimer's disease (AD)-related pathology. The most common principal cell type in MEC LII, reelin-expressing stellate cells, are grid cell candidates. Recently we found evidence that γ-aminobutyric acid (GABA)A receptor subunits show a specific distribution in MEC LII, in which GABAA α3 is selectively associated with reelin-positive neurons, with limited association with the other principal cell type, calbindin (CB)-positive pyramidal neurons. Furthermore, the expression of α3 subunit decreases in mice between P15 and P25, which coincides with the emergence of stable grid cell activity. It has been shown that the α3 subunit undergoes specific developmental changes and that it may exert pro-inflammatory actions if improperly regulated. In this review article, we evaluate the changing kinetics of α3-GABAA receptors (GABAARs). during development in relation to α3-subunit expression pattern in MEC LII and conclude that α3 could be closely related to the stabilization of grid cell activity and theta oscillations. We further conclude that dysregulated α3 may be a driving factor in early AD pathology.
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Affiliation(s)
- Nina Berggaard
- Department of Clinical and Molecular Medicine, Faculty of Medicine and Health Sciences, Norwegian University of Science and Technology, Trondheim, Norway
| | - Menno P Witter
- Center for Computational Neuroscience, Egil and Pauline Braathen and Fred Kavli Center for Cortical Microcircuits, Kavli Institute for Systems Neuroscience, NTNU Norwegian University of Science and Technology, Trondheim, Norway
| | - Johannes J L van der Want
- Department of Clinical and Molecular Medicine, Faculty of Medicine and Health Sciences, Norwegian University of Science and Technology, Trondheim, Norway
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6
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Direct neurotransmitter activation of voltage-gated potassium channels. Nat Commun 2018; 9:1847. [PMID: 29748663 PMCID: PMC5945843 DOI: 10.1038/s41467-018-04266-w] [Citation(s) in RCA: 44] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2017] [Accepted: 04/16/2018] [Indexed: 11/25/2022] Open
Abstract
Voltage-gated potassium channels KCNQ2–5 generate the M-current, which controls neuronal excitability. KCNQ2–5 subunits each harbor a high-affinity anticonvulsant drug-binding pocket containing an essential tryptophan (W265 in human KCNQ3) conserved for >500 million years, yet lacking a known physiological function. Here, phylogenetic analysis, electrostatic potential mapping, in silico docking, electrophysiology, and radioligand binding assays reveal that the anticonvulsant binding pocket evolved to accommodate endogenous neurotransmitters including γ-aminobutyric acid (GABA), which directly activates KCNQ5 and KCNQ3 via W265. GABA, and endogenous metabolites β-hydroxybutyric acid (BHB) and γ-amino-β-hydroxybutyric acid (GABOB), competitively and differentially shift the voltage dependence of KCNQ3 activation. Our results uncover a novel paradigm: direct neurotransmitter activation of voltage-gated ion channels, enabling chemosensing of the neurotransmitter/metabolite landscape to regulate channel activity and cellular excitability. M-current is conveyed by voltage-sensitive KCNQ channels, which are enriched in GABAergic neurons and are activated by anticonvulsants such as retigabine. Here the authors show that GABA directly activates KCNQ3, at the residue required for its anticonvulsant activity.
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7
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Vidal V, García-Cerro S, Martínez P, Corrales A, Lantigua S, Vidal R, Rueda N, Ozmen L, Hernández MC, Martínez-Cué C. Decreasing the Expression of GABA A α5 Subunit-Containing Receptors Partially Improves Cognitive, Electrophysiological, and Morphological Hippocampal Defects in the Ts65Dn Model of Down Syndrome. Mol Neurobiol 2017; 55:4745-4762. [PMID: 28717969 DOI: 10.1007/s12035-017-0675-3] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2017] [Accepted: 06/27/2017] [Indexed: 12/31/2022]
Abstract
Trisomy 21 or Down syndrome (DS) is the most common cause of intellectual disability of a genetic origin. The Ts65Dn (TS) mouse, which is the most commonly used and best-characterized mouse model of DS, displays many of the cognitive, neuromorphological, and biochemical anomalies that are found in the human condition. One of the mechanisms that have been proposed to be responsible for the cognitive deficits in this mouse model is impaired GABA-mediated inhibition. Because of the well-known modulatory role of GABAA α5 subunit-containing receptors in cognitive processes, these receptors are considered to be potential targets for improving the intellectual disability in DS. The chronic administration of GABAA α5-negative allosteric modulators has been shown to be procognitive without anxiogenic or proconvulsant side effects. In the present study, we use a genetic approach to evaluate the contribution of GABAA α5 subunit-containing receptors to the cognitive, electrophysiological, and neuromorphological deficits in TS mice. We show that reducing the expression of GABAA α5 receptors by deleting one or two copies of the Gabra5 gene in TS mice partially ameliorated the cognitive impairments, improved long-term potentiation, enhanced neural differentiation and maturation, and normalized the density of the GABAergic synapse markers. Reducing the gene dosage of Gabra5 in TS mice did not induce motor alterations and anxiety or affect the viability of the mice. Our results provide further evidence of the role of GABAA α5 receptor-mediated inhibition in cognitive impairment in the TS mouse model of DS.
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Affiliation(s)
- Verónica Vidal
- Departamento de Fisiología y Farmacología, Facultad de Medicina, Universidad deCantabria, Santander, Spain
| | - Susana García-Cerro
- Departamento de Fundamentos Clínicos, Unidad de Farmacología, Universitat de Barcelona, Barcelona, Spain
| | - Paula Martínez
- Departamento de Fisiología y Farmacología, Facultad de Medicina, Universidad deCantabria, Santander, Spain
| | - Andrea Corrales
- Departamento de Fisiología y Farmacología, Facultad de Medicina, Universidad deCantabria, Santander, Spain
| | - Sara Lantigua
- Departamento de Fisiología y Farmacología, Facultad de Medicina, Universidad deCantabria, Santander, Spain
| | - Rebeca Vidal
- Departamento de Fisiología y Farmacología, Facultad de Medicina, Universidad deCantabria, Santander, Spain.,Instituto de Biomedicina y Biotecnología de Cantabria, IBBTEC (Universidad de Cantabria, CSIC, SODERCAN), Santander, Spain.,Centro de Investigacion Biomédica en Red de Salud Mental (CIBERSAM), Instituto de Salud Carlos III, Madrid, Spain
| | - Noemí Rueda
- Departamento de Fisiología y Farmacología, Facultad de Medicina, Universidad deCantabria, Santander, Spain
| | - Laurence Ozmen
- Pharma Research and Early Development, Hoffman-La Roche Ltd., Basel, Switzerland
| | | | - Carmen Martínez-Cué
- Departamento de Fisiología y Farmacología, Facultad de Medicina, Universidad deCantabria, Santander, Spain.
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Contestabile A, Magara S, Cancedda L. The GABAergic Hypothesis for Cognitive Disabilities in Down Syndrome. Front Cell Neurosci 2017; 11:54. [PMID: 28326014 PMCID: PMC5339239 DOI: 10.3389/fncel.2017.00054] [Citation(s) in RCA: 82] [Impact Index Per Article: 11.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2016] [Accepted: 02/14/2017] [Indexed: 12/04/2022] Open
Abstract
Down syndrome (DS) is a genetic disorder caused by the presence of a third copy of chromosome 21. DS affects multiple organs, but it invariably results in altered brain development and diverse degrees of intellectual disability. A large body of evidence has shown that synaptic deficits and memory impairment are largely determined by altered GABAergic signaling in trisomic mouse models of DS. These alterations arise during brain development while extending into adulthood, and include genesis of GABAergic neurons, variation of the inhibitory drive and modifications in the control of neural-network excitability. Accordingly, different pharmacological interventions targeting GABAergic signaling have proven promising preclinical approaches to rescue cognitive impairment in DS mouse models. In this review, we will discuss recent data regarding the complex scenario of GABAergic dysfunctions in the trisomic brain of DS mice and patients, and we will evaluate the state of current clinical research targeting GABAergic signaling in individuals with DS.
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Affiliation(s)
- Andrea Contestabile
- Department of Neuroscience and Brain Technologies, Istituto Italiano di Tecnologia (IIT) Genova, Italy
| | - Salvatore Magara
- Department of Neuroscience and Brain Technologies, Istituto Italiano di Tecnologia (IIT) Genova, Italy
| | - Laura Cancedda
- Department of Neuroscience and Brain Technologies, Istituto Italiano di Tecnologia (IIT)Genova, Italy; Dulbecco Telethon InstituteGenova, Italy
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9
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Chaiworakul V, Kosonsiriluk S, Mauro LJ, El Halawani ME. Ovarian steroid withdrawal results in GABA A receptor upregulation in the photoperiodic neuroendocrine pathways of the turkey hen. Gen Comp Endocrinol 2017; 240:84-90. [PMID: 27717718 DOI: 10.1016/j.ygcen.2016.10.002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/04/2016] [Revised: 09/10/2016] [Accepted: 10/01/2016] [Indexed: 11/21/2022]
Abstract
The mechanism(s) underlying photorefractoriness in temperate zone seasonally breeding birds remains undetermined. Our recent findings reveal a link between the upregulation of GABAA receptors (GABAARs) in the premammillary nucleus (PMM) and the state of photorefractoriness. Gonadal steroid levels fluctuate during the breeding season; increasing after gonadal recrudescence and declining sharply once gonadal regression begins. Here, we examined the effect of gonadal steroid withdrawal on the expression of GABAARs in the turkey PMM. Exogenous ovarian steroids were administered and then withdrawn from turkey hens to mimic the decline of ovarian steroids levels at the end of a breeding season. The upregulation of GABAAR α3, α4, δ, π, and γ2-subunits was observed in the PMM of the steroid withdrawal group when compared to the non-steroid treatment group. The level of tyrosine hydroxylase, photopigment melanopsin, and circadian clock genes in the PMM of the steroid withdrawal group resembled the levels observed in the natural photorefractory hens and were significantly lower than those of the short-day light stimulated group. A reduction in gonadotropin-releasing hormone-I mRNA expressed within the nucleus commissurae pallii was also observed in hens undergoing steroid withdrawal. These results suggest that the natural decline in circulating ovarian steroid levels may modulate the GABAergic system in the PMM through the upregulation of GABAA receptors. This, in turn, could diminish the reproductive neuroendocrine responses to light and favor a condition resembling the state of photorefractoriness.
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Affiliation(s)
- Voravasa Chaiworakul
- Department of Animal Science, University of Minnesota, Saint Paul, MN 55108, USA
| | | | - Laura J Mauro
- Department of Animal Science, University of Minnesota, Saint Paul, MN 55108, USA
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10
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Lai F, Fagernes CE, Jutfelt F, Nilsson GE. Expression of genes involved in brain GABAergic neurotransmission in three-spined stickleback exposed to near-future CO 2. CONSERVATION PHYSIOLOGY 2016; 4:cow068. [PMID: 28066553 PMCID: PMC5196030 DOI: 10.1093/conphys/cow068] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/05/2016] [Revised: 11/02/2016] [Accepted: 11/16/2016] [Indexed: 05/28/2023]
Abstract
Change in the activity of the main inhibitory receptor, GABAA, has been suggested to be a general mechanism behind the behavioural alterations reported in ocean acidification studies on fish. It has been proposed that regulatory acid-base mechanisms in response to high CO2 alter the neuronal Cl- and HCO3- gradients that are important for GABAA receptor function. Here, we report a comprehensive analysis of gene expression of GABAA receptor subunits and of genes involved in GABAergic transmission in the brain of fish exposed to near-future CO2. Altogether, 56 mRNA transcripts were quantified in brains of three-spined stickleback (Gasterosteus aculeatus) kept in control pCO2 (333 ± 30 μatm CO2) or at high pCO2 levels (991 ± 57 μatm) for 43 days. The gene expression analysis included GABAA receptor subunits (α1-6, β1-3, γ1-3, δ, π and ρ1-3), enzymes and transporters involved in GABA metabolism (GAD1-2, GABAT and GAT1-3), GABAA receptor-associated proteins (GABARAP and GABARAPL), ion cotransporters (KCC1-4, NKCC1, ClC21-3, AE3 and NDAE) and carbonic anhydrase (CAII). Exposure to high CO2 had only minor effects on the expression of genes involved in GABAergic neurotransmission. There were significant increases in the mRNA levels of α family subunits of the GABAA receptor, with a more pronounced expression of α12, α3, α4 and α6b. No changes were detected in the expression of other GABAA subunits or in genes related to receptor turnover, GABA metabolism or ion transport. Although the minor changes seen for mRNA levels might reflect compensatory mechanisms in the high-CO2 conditions, these were apparently insufficient to restore normal neural function, because the behavioural changes persisted within the time frame studied.
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Affiliation(s)
- Floriana Lai
- Section for Physiology and Cell Biology, Department of Biosciences, University of Oslo, Norway
| | - Cathrine E Fagernes
- Section for Physiology and Cell Biology, Department of Biosciences, University of Oslo, Norway
| | - Fredrik Jutfelt
- Department of Biology, Norwegian University of Science and Technology, Trondheim, Norway
| | - Göran E Nilsson
- Section for Physiology and Cell Biology, Department of Biosciences, University of Oslo, Norway
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11
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Sabanov V, Braat S, D'Andrea L, Willemsen R, Zeidler S, Rooms L, Bagni C, Kooy RF, Balschun D. Impaired GABAergic inhibition in the hippocampus of Fmr1 knockout mice. Neuropharmacology 2016; 116:71-81. [PMID: 28012946 DOI: 10.1016/j.neuropharm.2016.12.010] [Citation(s) in RCA: 45] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2016] [Revised: 11/30/2016] [Accepted: 12/12/2016] [Indexed: 01/24/2023]
Abstract
Many clinical and molecular features of the fragile X syndrome, a common form of intellectual disability and autism, can be modeled by deletion of the Fmr1 protein (Fmrp) in mice. Previous studies showed a decreased expression of several components of the GABAergic system in Fmr1 knockout mice. Here, we used this mouse model to investigate the functional consequences of Fmrp deletion on hippocampal GABAergic inhibition in the CA1-region of the hippocampus. Whole-cell patch-clamp recordings demonstrated a significantly reduced amplitude of evoked inhibitory postsynaptic currents (eIPSCs) and a decrease in the amplitude and frequency of spontaneous IPSCs. In addition, miniature IPSCs were reduced in amplitude and frequency and decayed significantly slower than mIPSCs in controls. Quantitative real-time PCR revealed a significantly lower expression of α2, β1 and δ GABAA receptor subunits in the hippocampus of the juvenile mice (P22) compared to wild-type littermates. Correspondingly, we found also at the protein level reduced amounts of α2, β1 and δ subunits in Fmr1 knockout mice. Overall, these results demonstrate that the reduction in several components of the GABAergic system is already present at young age and that this reduction results in measurable abnormalities on GABAA receptor-mediated phasic inhibition. These abnormalities might contribute to the behavioral and cognitive deficits of this fragile X mouse model.
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Affiliation(s)
- Victor Sabanov
- Laboratory of Biological Psychology, KU Leuven, Leuven, Belgium.
| | - Sien Braat
- Department of Medical Genetics, University of Antwerp, Antwerp, Belgium.
| | - Laura D'Andrea
- Center for Human Genetics-VIB Center for the Biology of Disease, KULeuven, Leuven, Belgium; Department of Biomedicine and Prevention, University of Rome Tor Vergata, Italy.
| | - Rob Willemsen
- Department of Clinical Genetics, Erasmus MC, Rotterdam, The Netherlands.
| | - Shimriet Zeidler
- Department of Clinical Genetics, Erasmus MC, Rotterdam, The Netherlands.
| | - Liesbeth Rooms
- Laboratory of Biological Psychology, KU Leuven, Leuven, Belgium.
| | - Claudia Bagni
- Center for Human Genetics-VIB Center for the Biology of Disease, KULeuven, Leuven, Belgium; Department of Biomedicine and Prevention, University of Rome Tor Vergata, Italy; Department of Fundamental Neuroscience, University of Lausanne, Switzerland.
| | - R Frank Kooy
- Department of Medical Genetics, University of Antwerp, Antwerp, Belgium.
| | - Detlef Balschun
- Laboratory of Biological Psychology, KU Leuven, Leuven, Belgium.
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12
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Mir FR, Carrer HF, Cambiasso MJ. Sex differences in depolarizing actions of GABA A receptor activation in rat embryonic hypothalamic neurons. Eur J Neurosci 2016; 45:521-527. [PMID: 27888546 DOI: 10.1111/ejn.13467] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2016] [Revised: 10/27/2016] [Accepted: 11/02/2016] [Indexed: 11/28/2022]
Abstract
GABAA receptor activation exerts trophic actions in immature neurons through depolarization of resting membrane potential. The switch to its classical hyperpolarizing role is developmentally regulated. Previous results suggest that a hormonally biased sex difference exists at the onset of the switch in hypothalamic neurons. The aim of this work was to evaluate sex differences in GABAA receptor function of hypothalamic neurons before brain masculinization by gonadal hormones. Hypothalamic cells were obtained from embryonic day 16 male and female rat foetuses, 2 days before the peak of testosterone production by the foetal testis, and grown in vitro for 9 days. Whole-cell and perforated patch-clamp recordings were carried out in order to measure several electrophysiological parameters. Our results show that there are more male than female neurons responding with depolarization to muscimol. Additionally, among cells with depolarizing responses, males have higher and longer lasting responses than females. These results highlight the relevance of differences in neural cell sex irrespective of exposure to sex hormones.
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Affiliation(s)
- Franco R Mir
- Laboratory of Neurophysiology, Instituto de Investigación Médica Mercedes y Martín Ferreyra, INIMEC-CONICET-Universidad Nacional de Córdoba, Friuli 2434, 5016, Córdoba, Argentina
| | - Hugo F Carrer
- Laboratory of Neurophysiology, Instituto de Investigación Médica Mercedes y Martín Ferreyra, INIMEC-CONICET-Universidad Nacional de Córdoba, Friuli 2434, 5016, Córdoba, Argentina
| | - María J Cambiasso
- Laboratory of Neurophysiology, Instituto de Investigación Médica Mercedes y Martín Ferreyra, INIMEC-CONICET-Universidad Nacional de Córdoba, Friuli 2434, 5016, Córdoba, Argentina.,Departamento de Biología Bucal, Facultad de Odontología, Universidad Nacional de Córdoba, Córdoba, Argentina
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13
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Immunochemical Localization of GABA A Receptor Subunits in the Freshwater Polyp Hydra vulgaris (Cnidaria, Hydrozoa). Neurochem Res 2016; 41:2914-2922. [PMID: 27450241 DOI: 10.1007/s11064-016-2010-1] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2016] [Revised: 07/14/2016] [Accepted: 07/16/2016] [Indexed: 10/21/2022]
Abstract
γ-aminobutyric acid (GABA) receptors, responding to GABA positive allosteric modulators, are present in the freshwater polyp Hydra vulgaris (Cnidaria, Hydrozoa), one of the most primitive metazoans to develop a nervous system. We examined the occurrence and distribution of GABAA receptor subunits in Hydra tissues by western blot and immunohistochemistry. Antibodies against different GABAA receptor subunits were used in Hydra membrane preparations. Unique protein bands, inhibited by the specific peptide, appeared at 35, 60, ∼50 and ∼52 kDa in membranes incubated with α3, β1, γ3 or δ antibodies, respectively. Immunohistochemical screening of whole mount Hydra preparations revealed diffuse immunoreactivity to α3, β1 or γ3 antibodies in tentacles, hypostome, and upper part of the gastric region; immunoreactive fibers were also present in the lower peduncle. By contrast, δ antibodies revealed a strong labeling in the lower gastric region and peduncle, as well as in tentacles. Double labeling showed colocalization of α3/β1, α3/γ3 and α3/δ immunoreactivity in granules or cells in tentacles and gastric region. In the peduncle, colocalization of both α3/β1 and α3/γ3 immunoreactivity was found in fibers running horizontally above the foot. These data indicate that specific GABAA receptor subunits are present and differentially distributed in Hydra body regions. Subunit colocalization suggests that Hydra GABA receptors are heterologous multimers, possibly sub-serving different physiological activities.
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Abstract
In this issue of Neuron,Lin et al. (2015) report an optical method to precisely manipulate the activity of GABAA receptors by designing a mutant receptor that binds photosensitive compounds. This allows for studying GABAA receptors in situ and represents a valuable tool to investigate how inhibition affects brain physiology.
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Affiliation(s)
- Martin Mortensen
- Department of Neuroscience, Physiology & Pharmacology, UCL, Gower Street, London, WC1E 6BT, UK
| | - Trevor G Smart
- Department of Neuroscience, Physiology & Pharmacology, UCL, Gower Street, London, WC1E 6BT, UK.
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RNA Editing: A Contributor to Neuronal Dynamics in the Mammalian Brain. Trends Genet 2016; 32:165-175. [PMID: 26803450 DOI: 10.1016/j.tig.2015.12.005] [Citation(s) in RCA: 97] [Impact Index Per Article: 12.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2015] [Revised: 12/21/2015] [Accepted: 12/22/2015] [Indexed: 01/10/2023]
Abstract
Post-transcriptional RNA modification by adenosine to inosine (A-to-I) editing expands the functional output of many important neuronally expressed genes. The mechanism provides flexibility in the proteome by expanding the variety of isoforms, and is a requisite for neuronal function. Indeed, targets for editing include key mediators of synaptic transmission with an overall significant effect on neuronal signaling. In addition, editing influences splice-site choice and miRNA targeting capacity, and thereby regulates neuronal gene expression. Editing efficiency at most of these sites increases during neuronal differentiation and brain maturation in a spatiotemporal manner. This editing-induced dynamics in the transcriptome is essential for normal brain development, and we are only beginning to understand its role in neuronal function. In this review we discuss the impact of RNA editing in the brain, with special emphasis on the physiological consequences for neuronal development and plasticity.
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Arellano RO, Sánchez-Gómez MV, Alberdi E, Canedo-Antelo M, Chara JC, Palomino A, Pérez-Samartín A, Matute C. Axon-to-Glia Interaction Regulates GABAA Receptor Expression in Oligodendrocytes. Mol Pharmacol 2015; 89:63-74. [PMID: 26538574 DOI: 10.1124/mol.115.100594] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2015] [Accepted: 11/03/2015] [Indexed: 01/02/2023] Open
Abstract
Myelination requires oligodendrocyte-neuron communication, and both neurotransmitters and contact interactions are essential for this process. Oligodendrocytes are endowed with neurotransmitter receptors whose expression levels and properties may change during myelination. However, only scant information is available about the extent and timing of these changes or how they are regulated by oligodendrocyte-neuron interactions. Here, we used electrophysiology to study the expression of ionotropic GABA, glutamate, and ATP receptors in oligodendrocytes derived from the optic nerve and forebrain cultured either alone or in the presence of dorsal root ganglion neurons. We observed that oligodendrocytes from both regions responded to these transmitters at 1 day in culture. After the first day in culture, however, GABA sensitivity diminished drastically to less than 10%, while that of glutamate and ATP remained constant. In contrast, the GABA response amplitude was sustained and remained stable in oligodendrocytes cocultured with dorsal root ganglion neurons. Immunochemistry and pharmacological properties of the responses indicated that they were mediated by distinctive GABAA receptors and that in coculture with neurons, the oligodendrocytes bearing the receptors were those in direct contact with axons. These results reveal that GABAA receptor regulation in oligodendrocytes is driven by axonal cues and that GABA signaling may play a role in myelination and/or during axon-glia recognition.
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Affiliation(s)
- Rogelio O Arellano
- Achucarro Basque Center for Neuroscience, Centro de Investigación Biomédica en Red en Enfermedades Neurodegenerativas, and Departamento de Neurociencias, Universidad del País Vasco, Leioa, Spain (R.O.A., M.V.S.-G., E.A., M.C.-A., J.C.C., A.P., A.P.-S., C.M.); and Instituto de Neurobiología, Laboratorio de Neurofisiología Celular, Universidad Nacional Autónoma de México, Juriquilla, Querétaro, México (R.O.A.)
| | - María Victoria Sánchez-Gómez
- Achucarro Basque Center for Neuroscience, Centro de Investigación Biomédica en Red en Enfermedades Neurodegenerativas, and Departamento de Neurociencias, Universidad del País Vasco, Leioa, Spain (R.O.A., M.V.S.-G., E.A., M.C.-A., J.C.C., A.P., A.P.-S., C.M.); and Instituto de Neurobiología, Laboratorio de Neurofisiología Celular, Universidad Nacional Autónoma de México, Juriquilla, Querétaro, México (R.O.A.)
| | - Elena Alberdi
- Achucarro Basque Center for Neuroscience, Centro de Investigación Biomédica en Red en Enfermedades Neurodegenerativas, and Departamento de Neurociencias, Universidad del País Vasco, Leioa, Spain (R.O.A., M.V.S.-G., E.A., M.C.-A., J.C.C., A.P., A.P.-S., C.M.); and Instituto de Neurobiología, Laboratorio de Neurofisiología Celular, Universidad Nacional Autónoma de México, Juriquilla, Querétaro, México (R.O.A.)
| | - Manuel Canedo-Antelo
- Achucarro Basque Center for Neuroscience, Centro de Investigación Biomédica en Red en Enfermedades Neurodegenerativas, and Departamento de Neurociencias, Universidad del País Vasco, Leioa, Spain (R.O.A., M.V.S.-G., E.A., M.C.-A., J.C.C., A.P., A.P.-S., C.M.); and Instituto de Neurobiología, Laboratorio de Neurofisiología Celular, Universidad Nacional Autónoma de México, Juriquilla, Querétaro, México (R.O.A.)
| | - Juan Carlos Chara
- Achucarro Basque Center for Neuroscience, Centro de Investigación Biomédica en Red en Enfermedades Neurodegenerativas, and Departamento de Neurociencias, Universidad del País Vasco, Leioa, Spain (R.O.A., M.V.S.-G., E.A., M.C.-A., J.C.C., A.P., A.P.-S., C.M.); and Instituto de Neurobiología, Laboratorio de Neurofisiología Celular, Universidad Nacional Autónoma de México, Juriquilla, Querétaro, México (R.O.A.)
| | - Aitor Palomino
- Achucarro Basque Center for Neuroscience, Centro de Investigación Biomédica en Red en Enfermedades Neurodegenerativas, and Departamento de Neurociencias, Universidad del País Vasco, Leioa, Spain (R.O.A., M.V.S.-G., E.A., M.C.-A., J.C.C., A.P., A.P.-S., C.M.); and Instituto de Neurobiología, Laboratorio de Neurofisiología Celular, Universidad Nacional Autónoma de México, Juriquilla, Querétaro, México (R.O.A.)
| | - Alberto Pérez-Samartín
- Achucarro Basque Center for Neuroscience, Centro de Investigación Biomédica en Red en Enfermedades Neurodegenerativas, and Departamento de Neurociencias, Universidad del País Vasco, Leioa, Spain (R.O.A., M.V.S.-G., E.A., M.C.-A., J.C.C., A.P., A.P.-S., C.M.); and Instituto de Neurobiología, Laboratorio de Neurofisiología Celular, Universidad Nacional Autónoma de México, Juriquilla, Querétaro, México (R.O.A.)
| | - Carlos Matute
- Achucarro Basque Center for Neuroscience, Centro de Investigación Biomédica en Red en Enfermedades Neurodegenerativas, and Departamento de Neurociencias, Universidad del País Vasco, Leioa, Spain (R.O.A., M.V.S.-G., E.A., M.C.-A., J.C.C., A.P., A.P.-S., C.M.); and Instituto de Neurobiología, Laboratorio de Neurofisiología Celular, Universidad Nacional Autónoma de México, Juriquilla, Querétaro, México (R.O.A.)
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17
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Schipper S, Aalbers MW, Rijkers K, Swijsen A, Rigo JM, Hoogland G, Vles JSH. Tonic GABAA Receptors as Potential Target for the Treatment of Temporal Lobe Epilepsy. Mol Neurobiol 2015; 53:5252-65. [PMID: 26409480 PMCID: PMC5012145 DOI: 10.1007/s12035-015-9423-8] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2015] [Accepted: 09/03/2015] [Indexed: 12/11/2022]
Abstract
Tonic GABAA receptors are a subpopulation of receptors that generate long-lasting inhibition and thereby control network excitability. In recent years, these receptors have been implicated in various neurological and psychiatric disorders, including Parkinson’s disease, schizophrenia, and epilepsy. Their distinct subunit composition and function, compared to phasic GABAA receptors, opens the possibility to specifically modulate network properties. In this review, the role of tonic GABAA receptors in epilepsy and as potential antiepileptic target will be discussed.
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Affiliation(s)
- S Schipper
- Department of Neurology, Maastricht University Medical Center, Maastricht, The Netherlands.
- Faculty of Health Medicine and Life Sciences, School of Mental Health and Neuroscience, Maastricht University Medical Center, Maastricht, The Netherlands.
| | - M W Aalbers
- Faculty of Health Medicine and Life Sciences, School of Mental Health and Neuroscience, Maastricht University Medical Center, Maastricht, The Netherlands
| | - K Rijkers
- Faculty of Health Medicine and Life Sciences, School of Mental Health and Neuroscience, Maastricht University Medical Center, Maastricht, The Netherlands
- Department of Neurosurgery and Orthopedic Surgery, Atrium Hospital Heerlen, Heerlen, The Netherlands
| | - A Swijsen
- BIOMED Research Institute, Hasselt University/Transnational University Limburg, Martelarenlaan 42, 3500, Hasselt, Belgium
| | - J M Rigo
- BIOMED Research Institute, Hasselt University/Transnational University Limburg, Martelarenlaan 42, 3500, Hasselt, Belgium
| | - G Hoogland
- Faculty of Health Medicine and Life Sciences, School of Mental Health and Neuroscience, Maastricht University Medical Center, Maastricht, The Netherlands
- Department of Neurosurgery, Maastricht University Medical Center, Maastricht, The Netherlands
| | - J S H Vles
- Department of Neurology, Maastricht University Medical Center, Maastricht, The Netherlands
- Faculty of Health Medicine and Life Sciences, School of Mental Health and Neuroscience, Maastricht University Medical Center, Maastricht, The Netherlands
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18
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Abstract
Rapid activation of postsynaptic GABAA receptors (GABAARs) is crucial in many neuronal functions, including the synchronization of neuronal ensembles and controlling the precise timing of action potentials. Although the γ2 subunit is believed to be essential for the postsynaptic clustering of GABAARs, synaptic currents have been detected in neurons obtained from γ2(-/-) mice. To determine the role of the γ2 subunit in synaptic GABAAR enrichment, we performed a spatially and temporally controlled γ2 subunit deletion by injecting Cre-expressing viral vectors into the neocortex of GABAARγ2(77I)lox mice. Whole-cell recordings revealed the presence of miniature IPSCs in Cre(+) layer 2/3 pyramidal cells (PCs) with unchanged amplitudes and rise times, but significantly prolonged decays. Such slowly decaying currents could be evoked in PCs by action potentials in presynaptic fast-spiking interneurons. Freeze-fracture replica immunogold labeling revealed the presence of the α1 and β3 subunits in perisomatic synapses of cells that lack the γ2 subunit. Miniature IPSCs in Cre(+) PCs were insensitive to low concentrations of flurazepam, providing a pharmacological confirmation of the lack of the γ2 subunit. Receptors assembled from only αβ subunits were unlikely because Zn(2+) did not block the synaptic currents. Pharmacological experiments indicated that the αβγ3 receptor, rather than the αβδ, αβε, or αβγ1 receptors, was responsible for the slowly decaying IPSCs. Our data demonstrate the presence of IPSCs and the synaptic enrichment of the α1 and β3 subunits and suggest that the γ3 subunit is the most likely candidate for clustering GABAARs at synapses in the absence of the γ2 subunit.
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Swijsen A, Avila A, Brône B, Janssen D, Hoogland G, Rigo JM. Experimental early-life febrile seizures induce changes in GABA(A) R-mediated neurotransmission in the dentate gyrus. Epilepsia 2012; 53:1968-77. [PMID: 23030508 DOI: 10.1111/j.1528-1167.2012.03694.x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
PURPOSE Febrile seizures (FS), the most frequent seizure type during childhood, have been linked to temporal lobe epilepsy (TLE) in adulthood. Yet, underlying mechanisms are still largely unknown. Altered γ-aminobutyric acid (GABA)ergic neurotransmission in the dentate gyrus (DG) circuit has been hypothesized to be involved. This study aims at analyzing whether experimental FS change inhibitory synaptic input and postsynaptic GABA(A) R function in dentate granule cells. METHODS We applied an immature rat model of hyperthermia (HT)-induced FS. GABA(A) R-mediated neurotransmission was studied using whole-cell patch-clamp recordings from dentate granule neurons in hippocampal slices within 6-9 days post-HT. KEY FINDINGS Frequencies of spontaneous inhibitory postsynaptic currents (sIPSCs) were reduced in HT rats that had experienced seizures, whereas sIPSC amplitudes were enhanced. Whole-cell GABA responses revealed a doubled GABA(A) R sensitivity in dentate granule cells from HT animals, compared to that of normothermic (NT) controls. Analysis of sIPSCs and whole-cell GABA responses showed similar kinetics in postsynaptic GABA(A) Rs of HT and NT rats. quantitative real-time polymerase chain reaction (qPCR) experiments indicated changes in DG GABA(A) R subunit expression, which was most pronounced for the α3 subunit. SIGNIFICANCE The data support the hypothesis that FS persistently alter neuronal excitability.
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Affiliation(s)
- Ann Swijsen
- BIOMED Research Institute, Hasselt University/Transnational University Limburg, Diepenbeek, Belgium
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20
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Pavlov I, Walker MC. Tonic GABA(A) receptor-mediated signalling in temporal lobe epilepsy. Neuropharmacology 2012; 69:55-61. [PMID: 22538087 DOI: 10.1016/j.neuropharm.2012.04.003] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2012] [Revised: 03/27/2012] [Accepted: 04/02/2012] [Indexed: 11/25/2022]
Abstract
The tonic activation of extrasynaptic GABAA receptors by extracellular GABA provides a powerful means of regulating neuronal excitability. A consistent finding from studies that have used various models of temporal lobe epilepsy is that tonic GABAA receptor-mediated conductances are largely preserved in epileptic brain (in contrast to synaptic inhibition which is often reduced). Tonic inhibition is therefore an attractive target for antiepileptic drugs. However, the network consequences of a commonly used approach to augment tonic GABAA receptor-mediated conductances by global manipulation of extracellular GABA are difficult to predict without understanding how epileptogenesis alters the pharmacology and GABA sensitivity of tonic inhibition, and how manipulation of tonic conductances modulates the output of individual neurons. Here we review the current literature on epilepsy-associated changes in tonic GABAA receptor-mediated signalling, and speculate about possible effects they have at the network level. This article is part of the Special Issue entitled 'New Targets and Approaches to the Treatment of Epilepsy'.
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Affiliation(s)
- Ivan Pavlov
- Department of Clinical and Experimental Epilepsy, UCL Institute of Neurology, London WC1N3BG, UK.
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21
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Abstract
Since the discovery of the major excitatory and inhibitory neurotransmitters and their receptors in the brain, many have deliberated over their likely structures and how these may relate to function. This was initially satisfied by the determination of the first amino acid sequences of the Cys-loop receptors that recognized acetylcholine, serotonin, GABA, and glycine, followed later by similar determinations for the glutamate receptors, comprising non-NMDA and NMDA subtypes. The last decade has seen a rapid advance resulting in the first structures of Cys-loop receptors, related bacterial and molluscan homologs, and glutamate receptors, determined down to atomic resolution. This now provides a basis for determining not just the complete structures of these important receptor classes, but also for understanding how various domains and residues interact during agonist binding, receptor activation, and channel opening, including allosteric modulation. This article reviews our current understanding of these mechanisms for the Cys-loop and glutamate receptor families.
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Affiliation(s)
- Trevor G Smart
- Department of Neuroscience, Physiology & Pharmacology, University College London, London, United Kingdom.
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22
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In vitro neuropharmacological evaluation of penitrem-induced tremorgenic syndromes: importance of the GABAergic system. Neurochem Int 2011; 59:1074-81. [PMID: 21924313 DOI: 10.1016/j.neuint.2011.08.014] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2011] [Revised: 08/10/2011] [Accepted: 08/22/2011] [Indexed: 10/17/2022]
Abstract
The effects of the fungal neurotoxin penitrem A on the GABAergic and glutamatergic systems in rat brain were evaluated. Penitrem A inhibited binding of the GABA(A)-receptor ligand [³H]TBOB to rat forebrain and cerebellar membrane preparations with IC₅₀ (half maximal inhibitory concentration) values of 11 and 9 μM, respectively. Furthermore, penitrem A caused a concentration-dependent increase of [³H]flunitrazepam and [³H]muscimol binding in rat forebrain, but not in cerebellar preparations. The stimulation of [³H]flunitrazepam binding by penitrem A was abolished by the addition of GABA. In cerebellar preparations, a different pharmacological profile was found, with penitrem A allosterically inhibiting [³H]TBOB binding by interacting with a bicuculline-sensitive site. Moreover, penitrem A inhibited the high affinity uptake of GABA and glutamate into cerebellar synaptosomes with IC₅₀ values of 20 and 47 μM, respectively. The toxin showed no effect on NMDA or AMPA glutamate receptor binding. In conclusion, our results suggest that penitrem A exerts region-specific effects in the brain, leading to positive modulation of GABA(A)-receptor function in forebrain. Conversely, penitrem A may act as a bicuculline-like convulsant in cerebellum.
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Vithlani M, Terunuma M, Moss SJ. The dynamic modulation of GABA(A) receptor trafficking and its role in regulating the plasticity of inhibitory synapses. Physiol Rev 2011; 91:1009-22. [PMID: 21742794 DOI: 10.1152/physrev.00015.2010] [Citation(s) in RCA: 148] [Impact Index Per Article: 11.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Inhibition in the adult mammalian central nervous system (CNS) is mediated by γ-aminobutyric acid (GABA). The fast inhibitory actions of GABA are mediated by GABA type A receptors (GABA(A)Rs); they mediate both phasic and tonic inhibition in the brain and are the principle sites of action for anticonvulsant, anxiolytic, and sedative-hypnotic agents that include benzodiazepines, barbiturates, neurosteroids, and some general anesthetics. GABA(A)Rs are heteropentameric ligand-gated ion channels that are found concentrated at inhibitory postsynaptic sites where they mediate phasic inhibition and at extrasynaptic sites where they mediate tonic inhibition. The efficacy of inhibition and thus neuronal excitability is critically dependent on the accumulation of specific GABA(A)R subtypes at inhibitory synapses. Here we evaluate how neurons control the number of GABA(A)Rs on the neuronal plasma membrane together with their selective stabilization at synaptic sites. We then go on to examine the impact that these processes have on the strength of synaptic inhibition and behavior.
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Affiliation(s)
- Mansi Vithlani
- Department of Neuroscience, Tufts University School of Medicine, Boston, Massachusetts, USA
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Daniel C, Wahlstedt H, Ohlson J, Björk P, Ohman M. Adenosine-to-inosine RNA editing affects trafficking of the gamma-aminobutyric acid type A (GABA(A)) receptor. J Biol Chem 2010; 286:2031-40. [PMID: 21030585 DOI: 10.1074/jbc.m110.130096] [Citation(s) in RCA: 60] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
Recoding by adenosine-to-inosine RNA editing plays an important role in diversifying proteins involved in neurotransmission. We have previously shown that the Gabra-3 transcript, coding for the α3 subunit of the GABA(A) receptor is edited in mouse, causing an isoleucine to methionine (I/M) change. Here we show that this editing event is evolutionarily conserved from human to chicken. Analyzing recombinant GABA(A) receptor subunits expressed in HEK293 cells, our results suggest that editing at the I/M site in α3 has functional consequences on receptor expression. We demonstrate that I/M editing reduces the cell surface and the total number of α3 subunits. The reduction in cell surface levels is independent of the subunit combination as it is observed for α3 in combination with either the β2 or the β3 subunit. Further, an amino acid substitution at the corresponding I/M site in the α1 subunit has a similar effect on cell surface presentation, indicating the importance of this site for receptor trafficking. We show that the I/M editing during brain development is inversely related to the α3 protein abundance. Our results suggest that editing controls trafficking of α3-containing receptors and may therefore facilitate the switch of subunit compositions during development as well as the subcellular distribution of α subunits in the adult brain.
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Affiliation(s)
- Chammiran Daniel
- Department of Molecular Biology and Functional Genomics, Stockholm University, SE-10691 Stockholm, Sweden
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25
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Prototypic GABA(A) receptor agonist muscimol acts preferentially through forebrain high-affinity binding sites. Neuropsychopharmacology 2010; 35:999-1007. [PMID: 20032968 PMCID: PMC2823376 DOI: 10.1038/npp.2009.203] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Muscimol has been regarded as a universal agonist for all gamma-aminobutyric acid type A receptor (GABA(A)-R) subtypes. However, brain regional distribution of muscimol's high-affinity binding sites greatly differs from those of other binding sites of the GABA(A)-R. To test whether behavioral effects of muscimol correlated with the density of high-affinity [(3)H]muscimol binding, we examined several GABA(A)-R subunit gene-modified mouse lines: alpha1, alpha4, or delta-knockouts (KO), alpha4+delta-double KO, and Thy1.2 promoter-driven alpha6 transgenic mice (Thy1alpha6). We determined the high-affinity [(3)H]muscimol binding in brain sections by quantitative autoradiography and sedative/ataxic effects induced in vivo by muscimol using a constant speed rotarod. alpha4-KO mice had reduced [(3)H]muscimol binding in the caudate-putamen, thalamus, and hippocampus, and were less sensitive to the behavioral impairment by muscimol. Similarly, delta-KO mice also had reduced binding to forebrain regions and a lower behavioral sensitivity to muscimol than their wild-type controls. In contrast, alpha1-KO mice had unaltered behavioral sensitivity to muscimol and unaltered [(3)H]muscimol binding, even though previous studies have demonstrated dramatically reduced binding to various other GABA(A)-R sites in these mice. Finally, Thy1alpha6 mice exhibited increased behavioral sensitivity to muscimol, and to another direct GABA-site agonist gaboxadol, and increased [(3)H]muscimol binding in the cerebral cortex and hippocampus. Thus, the differences in sedative and motor-impairing actions of muscimol in various mouse models correlated with the level of forebrain high-affinity [(3)H]muscimol binding. These data suggest that a small special population of GABA(A)-Rs, most likely extrasynaptic non-alpha1-containing receptors, strongly contributes to the in vivo pharmacological effects of muscimol.
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26
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Miller PS, Smart TG. Binding, activation and modulation of Cys-loop receptors. Trends Pharmacol Sci 2010; 31:161-74. [PMID: 20096941 DOI: 10.1016/j.tips.2009.12.005] [Citation(s) in RCA: 233] [Impact Index Per Article: 16.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2009] [Revised: 12/17/2009] [Accepted: 12/18/2009] [Indexed: 11/19/2022]
Abstract
It is over forty years since the major neurotransmitters and their protein receptors were identified, and over twenty years since determination of the first amino-acid sequences of the Cys-loop receptors that recognize acetylcholine, serotonin, GABA and glycine. The last decade has seen the first structures of these proteins (and related bacterial and molluscan homologues) determined to atomic resolution. Hopefully over the next decade, more detailed molecular structures of entire Cys-loop receptors in drug-bound and drug-free conformations will become available. These, together with functional studies, will provide a clear picture of how these receptors participate in neurotransmission and how structural variations between receptor subtypes impart their unique characteristics. This insight should facilitate the design of novel and improved therapeutics to treat neurological disorders. This review considers our current understanding about the processes of agonist binding, receptor activation and channel opening, as well as allosteric modulation of the Cys-loop receptor family.
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Affiliation(s)
- Paul S Miller
- Department of Neuroscience, Physiology & Pharmacology, University College London, Gower Street, London WC1E 6BT, UK
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27
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Abstract
A-to-I (adenosine-to-inosine) RNA editing catalysed by the ADARs (adenosine deaminases that act on RNA) is a post-transcriptional event that contributes to protein diversity in metazoans. In mammalian neuronal ion channels, editing alters functionally important amino acids and creates receptor subtypes important for the development of the nervous system. The excitatory AMPA (alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid) and kainate glutamate receptors, as well as the inhibitory GABA(A) [GABA (gamma-aminobutyric acid) type A] receptor, are subject to A-to-I RNA editing. Editing affects several features of the receptors, including kinetics, subunit assembly and cell-surface expression. Here, we discuss the regulation of editing during brain maturation and the impact of RNA editing on the expression of different receptor subtypes.
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28
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Nimmich ML, Heidelberg LS, Fisher JL. RNA editing of the GABA(A) receptor alpha3 subunit alters the functional properties of recombinant receptors. Neurosci Res 2009; 63:288-93. [PMID: 19367790 DOI: 10.1016/j.neures.2009.01.003] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
RNA editing provides a post-transcriptional mechanism to increase structural heterogeneity of gene products. Recently, the alpha3 subunit of the GABAA receptors has been shown to undergo RNA editing. As a result, a highly conserved isoleucine residue in the third transmembrane domain is replaced with a methionine. To determine the effect of this structural change on receptor function, we compared the GABA sensitivity, pharmacological properties and macroscopic kinetics of recombinant receptors containing either the edited or unedited forms of the alpha3 subunit along with beta3 and gamma2L. Editing substantially altered the GABA sensitivity and deactivation rate of the receptors, with the unedited form showing a lower GABA EC50 and slower decay. Comparable effects were observed with a mutation at the homologous location in the alpha1 subunit, suggesting a common role for this site in regulation of channel gating. Except for the response to GABA, the pharmacological properties of the receptor were unaffected by editing, with similar enhancement by a variety of modulators. Since RNA editing of the alpha3 subunit increases through development, our findings suggest that GABAergic neurotransmission may be more effective early in development, with greater GABA sensitivity and slower decay rates conferred by the unedited alpha3 subunit.
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Affiliation(s)
- Mitchell L Nimmich
- Department of Pharmacology, Physiology and Neuroscience, University of South Carolina School of Medicine, Columbia 29208, USA
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Matsuoka H, Harada K, Endo Y, Warashina A, Doi Y, Nakamura J, Inoue M. Molecular mechanisms supporting a paracrine role of GABA in rat adrenal medullary cells. J Physiol 2008; 586:4825-42. [PMID: 18755746 DOI: 10.1113/jphysiol.2008.158709] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
GABA is known to produce membrane depolarization and secretion in adrenal medullary (AM) cells in various species. However, whether the GABAergic system is intrinsic or extrinsic or both in the adrenal medulla and the role that GABA plays are controversial. Therefore, these issues were addressed by combining a biochemical and functional analysis. Glutamic acid decarboxylase (GAD), a GABA synthesizing enzyme, and vesicular GABA transporter (VGAT) were expressed in rat AM cells at the mRNA and protein levels, and the adrenal medulla had no nerve fibre-like structures immunoreactive to an anti-GAD Ab. The double staining for VGAT and chromogranin A indicates that GABA was stored in chromaffin granules. The alpha1, alpha3, beta2/3, gamma2 and delta subunits of GABA(A) receptors were identified in AM cells at the mRNA and protein levels. Pharmacological properties of GABA-induced Cl(-) currents, immunoprecipitation experiments and immunocytochemistry indicated the expression of not only gamma2-, but also delta-containing GABA(A) receptors, which have higher affinities for GABA and neurosteroids. Expression of GATs, which are involved in the clearance of GABA at GABAergic synapses, were conspicuously suppressed in the adrenal medulla, compared with expression levels of GABA(A) receptors. Increases in Ca(2+) signal in AM cells evoked trans-synaptically by nerve stimulation were suppressed during the response to GABA, and this suppression was attributed to the shunt effect of the GABA-induced increase in conductance. Overall Ca(2+) responses to electrical stimulation and GABA in AM cells were larger or smaller than those to electrical stimulation alone, depending on the frequency of stimulation. The results indicate that GABA functions as a paracrine in rat AM cells and this function may be supported by the suppression of GAT expression and the expression of not only gamma2-, but also delta-GABA(A) receptors.
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Affiliation(s)
- Hidetada Matsuoka
- Department of Cell and Systems Physiology, University of Occupational and Environmental Health School of Medicine, Kitakyushu 807-8555, Japan
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Jansen M, Rabe H, Strehle A, Dieler S, Debus F, Dannhardt G, Akabas MH, Lüddens H. Synthesis of GABAA receptor agonists and evaluation of their alpha-subunit selectivity and orientation in the GABA binding site. J Med Chem 2008; 51:4430-48. [PMID: 18651727 DOI: 10.1021/jm701562x] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Drugs used to treat various disorders target GABA A receptors. To develop alpha subunit selective compounds, we synthesized 5-(4-piperidyl)-3-isoxazolol (4-PIOL) derivatives. The 3-isoxazolol moiety was substituted by 1,3,5-oxadiazol-2-one, 1,3,5-oxadiazol-2-thione, and substituted 1,2,4-triazol-3-ol heterocycles with modifications to the basic piperidine substituent as well as substituents without basic nitrogen. Compounds were screened by [(3)H]muscimol binding and in patch-clamp experiments with heterologously expressed GABA A alpha ibeta 3gamma 2 receptors (i = 1-6). The effects of 5-aminomethyl-3 H-[1,3,4]oxadiazol-2-one 5d were comparable to GABA for all alpha subunit isoforms. 5-piperidin-4-yl-3 H-[1,3,4]oxadiazol-2-one 5a and 5-piperidin-4-yl-3 H-[1,3,4]oxadiazol-2-thione 6a were weak agonists at alpha 2-, alpha 3-, and alpha 5-containing receptors. When coapplied with GABA, they were antagonistic in alpha 2-, alpha 4-, and alpha 6-containing receptors and potentiated alpha 3-containing receptors. 6a protected GABA binding site cysteine-substitution mutants alpha 1F64C and alpha 1S68C from reacting with methanethiosulfonate-ethylsulfonate. 6a specifically covalently modified the alpha 1R66C thiol, in the GABA binding site, through its oxadiazolethione sulfur. These results demonstrate the feasibility of synthesizing alpha subtype selective GABA mimetic drugs.
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Affiliation(s)
- Michaela Jansen
- Department of Medicinal Chemistry, Johannes Gutenberg-UniVersity, Mainz, Germany
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31
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Wegner F, Deuther-Conrad W, Scheunemann M, Brust P, Fischer S, Hiller A, Diekers M, Strecker K, Wohlfarth K, Allgaier C, Steinbach J, Hoepping A. GABAA receptor pharmacology of fluorinated derivatives of the novel sedative-hypnotic pyrazolopyrimidine indiplon. Eur J Pharmacol 2008; 580:1-11. [DOI: 10.1016/j.ejphar.2007.10.016] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2007] [Revised: 10/08/2007] [Accepted: 10/15/2007] [Indexed: 10/22/2022]
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Abstract
Precise neural inhibition in thalamocortical circuits is required for the generation of sleep spindles and suppression of hypersynchrony associated with epileptiform activity. Accordingly, the time course of GABA(A) receptor-mediated IPSC events is an important parameter influencing the strength of inhibitory signaling. In the thalamus, two distinct types of IPSC kinetics are observed: thalamocortical relay neurons in the ventrobasal nucleus (VB) exhibit a fast decaying IPSC, whereas neurons in the adjacent reticular nucleus (RTN) display a long-lasting, slowly decaying IPSC. Here, we used patch-clamp electrophysiology and computational modeling to elucidate the basis for IPSC kinetic heterogeneity in the thalamus. Rapid application of GABA to excised membrane patches revealed that decay kinetics were attributable to intrinsic differences in GABA(A) receptor deactivation. Examination of desensitization and gating properties revealed these to be similar in VB and RTN, with the notable lack of fast and long-lasting desensitized states in both cell types. Computational simulations demonstrate that slow GABA binding and unbinding rates could reproduce the characteristic long-lasting IPSCs in RTN cells. These results indicate that within thalamic circuits, a powerful diversity of inhibitory function can result from simple differences in underlying GABA(A) receptor affinity.
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Affiliation(s)
- Claude M Schofield
- Department of Neurology and Neurological Sciences, Stanford University, Stanford, California 94305, USA.
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You H, Dunn SMJ. Identification of a domain in the delta subunit (S238-V264) of the alpha4beta3delta GABAA receptor that confers high agonist sensitivity. J Neurochem 2007; 103:1092-101. [PMID: 17711419 DOI: 10.1111/j.1471-4159.2007.04817.x] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
We have expressed the alpha4beta3delta and alpha4beta3gamma2L subtypes of the rat GABAA receptor in Xenopus oocytes and have investigated their agonist activation properties. GABA was a more potent agonist of the alpha4beta3delta receptor (EC50 approximately 1.4 micromol/L) than of the alpha4beta3gamma2L subtype (EC50 approximately 27.6 micromol/L). Other GABAA receptor agonists (muscimol, 4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridin-3-ol, imidazole-4-amino acid) displayed similar subtype selectivity. The structural determinants underlying these differences have been investigated by co-expressing chimeric delta/gamma2L subunits with alpha4 and beta3 subunits. A stretch of amino acids in the delta subunit, S238-V264, is shown to play an important role in determining both agonist potency and the efficacies of full or partial agonists. This segment includes transmembrane domain 1 and the short intracellular loop that leads to the second transmembrane domain. The effects of the competitive antagonists, bicuculline and SR95531, and the channel blocker, picrotoxin, were not significantly affected by the incorporation of chimeric subunits. As the delta and gamma2L subunits have not been previously implicated directly in agonist binding, we suggest that the effects are likely to arise from changes in the transduction mechanisms that link agonist binding to channel activation.
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Affiliation(s)
- Haitao You
- Department of Pharmacology, University of Alberta, Edmonton, Alberta, Canada
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Barberis A, Mozrzymas JW, Ortinski PI, Vicini S. Desensitization and binding properties determine distinct alpha1beta2gamma2 and alpha3beta2gamma2 GABA(A) receptor-channel kinetic behavior. Eur J Neurosci 2007; 25:2726-40. [PMID: 17561840 PMCID: PMC1950087 DOI: 10.1111/j.1460-9568.2007.05530.x] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
GABA(A) receptor subtypes comprising the alpha1 and alpha3 subunits change with development and have a specific anatomical localization in the adult brain. These receptor subtypes have been previously demonstrated to greatly differ in deactivation kinetics but the underlying gating mechanisms have not been fully elucidated. Therefore, we expressed rat alpha1beta2gamma2 and alpha3beta2gamma2 receptors in human embryonic kidney 293 cells and recorded current responses to ultrafast GABA applications at macroscopic and single-channel levels. We found that the slow deactivation of alpha3beta2gamma2-mediated currents is associated with a relatively small rate and extent of apparent desensitization. In contrast, responses mediated by alpha1beta2gamma2 receptors had faster deactivation and stronger desensitization. Alpha3beta2gamma2 receptors had faster recovery in the paired-pulse agonist applications than alpha1beta2gamma2 channels. The onset of currents mediated by alpha3beta2gamma2 receptors was slower than that of alpha1beta2gamma2 for a wide range of GABA concentrations. Single-channel analysis did not reveal differences in the opening/closing kinetics of alpha1beta2gamma2 and alpha3beta2gamma2 channels but burst durations were longer in alpha3beta2gamma2 receptors. Simulation with a previously reported kinetic model was used to explore the differences in respective rate constants. Reproduction of major kinetic differences required a smaller desensitization rate as well as smaller binding and unbinding rates in alpha3beta2gamma2 compared with alpha1beta2gamma2 receptors. Our work describes the mechanisms underlying the kinetic differences between two major GABA(A) receptor subtypes and provides a framework to interpret data from native GABA receptors.
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Affiliation(s)
- Andrea Barberis
- Department of Physiology and Biophysics, Georgetown University School of Medicine225 Basic Research Building, 3900 Reservoir Road, NW Washington, DC 20007, USA
| | - Jerzy W Mozrzymas
- Department of Physiology and Biophysics, Georgetown University School of Medicine225 Basic Research Building, 3900 Reservoir Road, NW Washington, DC 20007, USA
- Laboratory of Neuroscience, Department of Biophysics, Wroclaw Medical UniversityWroclaw, Poland
| | - Pavel I Ortinski
- Department of Physiology and Biophysics, Georgetown University School of Medicine225 Basic Research Building, 3900 Reservoir Road, NW Washington, DC 20007, USA
- Interdisciplinary Program in Neuroscience, Georgetown University School of Medicine225 Basic Research Building, 3900 Reservoir Road, NW Washington, DC 20007, USA
| | - Stefano Vicini
- Department of Physiology and Biophysics, Georgetown University School of Medicine225 Basic Research Building, 3900 Reservoir Road, NW Washington, DC 20007, USA
- Interdisciplinary Program in Neuroscience, Georgetown University School of Medicine225 Basic Research Building, 3900 Reservoir Road, NW Washington, DC 20007, USA
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Picton AJ, Fisher JL. Effect of the alpha subunit subtype on the macroscopic kinetic properties of recombinant GABA(A) receptors. Brain Res 2007; 1165:40-9. [PMID: 17658489 PMCID: PMC2084258 DOI: 10.1016/j.brainres.2007.06.050] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2007] [Revised: 06/12/2007] [Accepted: 06/20/2007] [Indexed: 12/26/2022]
Abstract
The GABA(A) receptors (GABARs) are chloride-permeable ligand-gated ion channels responsible for fast inhibitory neurotransmission. These receptors are structurally heterogeneous, and in mammals can be formed from a combination of sixteen different subunit subtypes. Much of this variety comes from the six different alpha subunit subtypes. All neuronal GABARs contain an alpha subunit, and the identity of the alpha subtype affects the pharmacological properties of the receptors. The expression of each of the different alpha subtypes is regulated developmentally and regionally and changes with both normal physiological processes such development and synaptic plasticity, and pathological conditions such as epilepsy. In order to understand the functional significance of this structural heterogeneity, we examined the effect of the alpha subtype on the receptor's response to GABA. Each of the six alpha subtypes was transiently co-expressed with the beta3 and gamma2L subunits in mammalian cells. The sensitivity to GABA was measured with whole-cell recordings. We also determined the activation, deactivation, desensitization, and recovery kinetics for the six isoforms using rapid application recordings from excised macropatches. We found unique characteristics associated with each alpha subunit subtype. These properties would be expected to influence the post-synaptic response to GABA, creating functional diversity among neurons expressing different alpha subunits.
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Affiliation(s)
- Amber J Picton
- Department of Pharmacology, Physiology and Neuroscience, University of South Carolina School of Medicine, South Carolina 29208, USA
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36
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Arancibia-Carcamo IL, Moss SJ. Molecular organization and assembly of the central inhibitory postsynapse. Results Probl Cell Differ 2006; 43:25-47. [PMID: 17068966 DOI: 10.1007/400_017] [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] [Indexed: 05/12/2023]
Abstract
gamma-Amino butyric acid type A (GABAA) receptors are the major sites of fast synaptic inhibition in the brain. GABAA receptors play an important role in regulating neuronal excitability and in addition have been implicated in numerous neurological disorders. In order to understand synaptic inhibition it is important to comprehend the cellular mechanisms, that neurons utilize to regulate the accumulation and regulation of GABAA receptors at postsynaptic inhibitory specializations. Over the past decade a number of GABAA receptor interacting proteins have been identified allowing us to further understand the trafficking, targeting and clustering of these receptors as well as the regulation of receptor stability. In the following review we examine the proteins identified as GABAA receptor binding partners and other components of the inhibitory postsynaptic scaffold, and how they contribute to the construction of inhibitory synapses and the dynamic modulation of synaptic inhibition.
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Mortensen M, Smart TG. Extrasynaptic alphabeta subunit GABAA receptors on rat hippocampal pyramidal neurons. J Physiol 2006; 577:841-56. [PMID: 17023503 PMCID: PMC1890388 DOI: 10.1113/jphysiol.2006.117952] [Citation(s) in RCA: 145] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Extrasynaptic GABA(A) receptors that are tonically activated by ambient GABA are important for controlling neuronal excitability. In hippocampal pyramidal neurons, the subunit composition of these extrasynaptic receptors may include alpha5betagamma and/or alpha4betadelta subunits. Our present studies reveal that a component of the tonic current in the hippocampus is highly sensitive to inhibition by Zn(2+). This component is probably not mediated by either alpha5betagamma or alpha4betadelta receptors, but might be explained by the presence of alphabeta isoforms. Using patch-clamp recording from pyramidal neurons, a small tonic current measured in the absence of exogenous GABA exhibited both high and low sensitivity to Zn(2+) inhibition (IC(50) values, 1.89 and 223 microm, respectively). Using low nanomolar and micromolar GABA concentrations to replicate tonic currents, we identified two components that are mediated by benzodiazepine-sensitive and -insensitive receptors. The latter indicated that extrasynaptic GABA(A) receptors exist that are devoid of gamma2 subunits. To distinguish whether the benzodiazepine-insensitive receptors were alphabeta or alphabetadelta isoforms, we used single-channel recording. Expressing recombinant alpha1beta3gamma2, alpha5beta3gamma2, alpha4beta3delta and alpha1beta3 receptors in human embryonic kidney (HEK) or mouse fibroblast (Ltk) cells, revealed similar openings with high main conductances (approximately 25-28 pS) for gamma2 or delta subunit-containing receptors whereas alphabeta receptors were characterized by a lower main conductance state (approximately 11 pS). Recording from pyramidal cell somata revealed a similar range of channel conductances, indicative of a mixture of GABA(A) receptors in the extrasynaptic membrane. The lowest conductance state (approximately 11 pS) was the most sensitive to Zn(2+) inhibition in accord with the presence of alphabeta receptors. This receptor type is estimated to account for up to 10% of all extrasynaptic GABA(A) receptors on hippocampal pyramidal neurons.
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Affiliation(s)
- Martin Mortensen
- Department of Pharmacology, University College London, Gower Street, London WC1E 6BT, UK
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38
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Drafts BC, Fisher JL. Identification of structures within GABAA receptor alpha subunits that regulate the agonist action of pentobarbital. J Pharmacol Exp Ther 2006; 318:1094-101. [PMID: 16728592 DOI: 10.1124/jpet.106.104844] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Barbiturates act on GABA(A) receptors (GABARs) through three distinct mechanisms, resulting in positive allosteric modulation, direct activation, and inhibition. These effects are observed at different concentrations and are differentially affected by some mutations and by the receptor's subunit composition. Mammalian GABARs can be formed from a combination of 16 different subunit subtypes. Although the effect of barbiturates depends largely on the beta subunit, their agonist activity is substantially influenced by the alpha subunit subtype. Pentobarbital is a more effective agonist than GABA only when receptors contain an alpha6 subunit. Results from chimeric alpha1/alpha6 subunits suggested that structural differences within the extracellular N-terminal domain were responsible for this characteristic. Within this domain, we examined 15 amino acid residues unique to the alpha6 subtype. Each of these sites was individually mutated in the alpha6 subunit to the corresponding residue of the alpha1 subunit. The effect of the mutation on direct activation by pentobarbital was determined with whole-cell electrophysiological recordings. Our results indicate that only one of these mutations, alpha6(T69K), altered pentobarbital efficacy. This single mutation reduced the response to pentobarbital to a level intermediate to the wild-type alpha1beta1gamma2L and alpha6beta1gamma2L isoforms. The mutation did not affect the sensitivity of the receptor to GABA but did reduce the efficacy of etomidate, another i.v. anesthetic with activity similar to pentobarbital. The reverse mutation in the alpha1 subunit (K70T) did not alter the response to pentobarbital. This is the first identification of a structural difference in GABAR alpha subtypes that regulates direct activation by barbiturates.
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Affiliation(s)
- Brandon C Drafts
- Department of Pharmacology, Physiology, and Neuroscience, University of South Carolina School of Medicine, Columbia, SC 29208, USA
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39
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Ranna M, Sinkkonen ST, Möykkynen T, Uusi-Oukari M, Korpi ER. Impact of epsilon and theta subunits on pharmacological properties of alpha3beta1 GABAA receptors expressed in Xenopus oocytes. BMC Pharmacol 2006; 6:1. [PMID: 16412217 PMCID: PMC1363348 DOI: 10.1186/1471-2210-6-1] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2005] [Accepted: 01/13/2006] [Indexed: 11/29/2022] Open
Abstract
Background γ-Aminobutyric acid type A (GABAA) receptors provide the main inhibitory control in the brain. Their heterogeneity may make it possible to precisely target drug effects to selected neuronal populations. In situ hybridization using rat brain sections has revealed a unique expression of GABAA receptor ε and θ subunit transcripts in the locus coeruleus, where they are accompanied at least by α3, α2, β1 and β3 subunits. Here, we studied the pharmacology of the human α3β1, α3β1ε, α3β1θ and α3β1εθ receptor subtypes expressed in Xenopus oocytes and compared them with the γ2 subunit-containing receptors. Results The GABA sensitivites and effects of several positive modulators of GABAA receptors were studied in the absence and the presence of EC25 GABA using the two-electrode voltage-clamp method. We found 100-fold differences in GABA sensitivity between the receptors, α3β1ε subtype being the most sensitive and α3β1γ2 the least sensitive. Also gaboxadol dose-response curves followed the same sensitivity rank order, with EC50 values being 72 and 411 μM for α3β1ε and α3β1γ2 subtypes, respectively. In the presence of EC25 GABA, introduction of the ε subunit to the receptor complex resulted in diminished modulatory effects by etomidate, propofol, pregnanolone and flurazepam, but not by pentobarbital. Furthermore, the α3β1ε subtype displayed picrotoxin-sensitive spontaneous activity. The θ subunit-containing receptors were efficiently potentiated by the anesthetic etomidate, suggesting that θ subunit could bring the properties of β2 or β3 subunits to the receptor complex. Conclusion The ε and θ subunits bring additional features to α3β1 GABAA receptors. These receptor subtypes may constitute as novel drug targets in selected brain regions, e.g., in the brainstem locus coeruleus nuclei.
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Affiliation(s)
- Martin Ranna
- Institute of Biomedicine, Pharmacology, Biomedicum Helsinki, POB 63 (Haartmaninkatu 8), FI-00014 University of Helsinki, Finland
| | - Saku T Sinkkonen
- Institute of Biomedicine, Pharmacology, Biomedicum Helsinki, POB 63 (Haartmaninkatu 8), FI-00014 University of Helsinki, Finland
| | - Tommi Möykkynen
- Institute of Biomedicine, Pharmacology, Biomedicum Helsinki, POB 63 (Haartmaninkatu 8), FI-00014 University of Helsinki, Finland
| | - Mikko Uusi-Oukari
- Department of Pharmacology and Clinical Pharmacology, University of Turku, Itäinen Pitkäkatu 4, FI-20520 Turku, Finland
| | - Esa R Korpi
- Institute of Biomedicine, Pharmacology, Biomedicum Helsinki, POB 63 (Haartmaninkatu 8), FI-00014 University of Helsinki, Finland
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Petroski RE, Pomeroy JE, Das R, Bowman H, Yang W, Chen AP, Foster AC. Indiplon Is a High-Affinity Positive Allosteric Modulator with Selectivity for α1 Subunit-Containing GABAAReceptors. J Pharmacol Exp Ther 2006; 317:369-77. [PMID: 16399882 DOI: 10.1124/jpet.105.096701] [Citation(s) in RCA: 88] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Indiplon (NBI 34060) is a novel pyrazolopyrimidine currently in development for the treatment of insomnia. We have previously shown that indiplon exhibits high-affinity binding to native GABA(A) receptors from rat brain and acts as a positive allosteric modulator of GABA(A) receptor currents in cultured rat neurons (Sullivan et al., 2004). In this study, we examined the GABA(A) receptor alpha subunit selectivity of indiplon using electrophysiological techniques to record GABA-activated chloride currents from recombinant rodent GABA(A) receptors expressed in human embryonic kidney 293 cells. Indiplon potentiated the GABA-activated chloride current in recombinant GABA(A) receptors in a dose-dependent and reversible manner and was approximately 10-fold selective for alpha1 subunit-containing receptors over GABA(A) receptors containing alpha2, alpha3, or alpha5 subunits. The EC(50) values were 2.6, 24, 60, and 77 nM for alpha1beta2gamma2, alpha2beta2gamma2, alpha3beta3gamma2, and alpha5beta2gamma2 receptors, respectively. Indiplon was approximately 10 times more potent than zolpidem and zopiclone and >100 times more potent than zaleplon. Moreover, indiplon, up to 1 microM, did not potentiate GABA(A) receptors composed of alpha4beta2gamma2 and alpha6beta2gamma2 subunits. This mechanism of action is proposed to underlie the sedative-hypnotic effects of indiplon in animals and humans.
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Affiliation(s)
- Robert E Petroski
- Department of Neuroscience, Neurocrine Biosciences Inc., San Diego, CA 92130, USA.
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41
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Abuhamdah S, Fürstner A, Lees G, Chazot PL. Radioligand binding studies of caloporoside and novel congeners with contrasting effects upon [35S] TBPS binding to the mammalian GABAA receptor. Biochem Pharmacol 2005; 70:1382-8. [PMID: 16168965 DOI: 10.1016/j.bcp.2005.07.026] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2005] [Revised: 07/25/2005] [Accepted: 07/26/2005] [Indexed: 11/21/2022]
Abstract
Caloporoside is a natural active fungal metabolite, which was isolated from Caloporous dichrous and was described to exhibit antibacterial, antifungal and phospholipase C inhibitory activity. We have previously reported evidence that related beta-linked compounds, lactose and octyl-beta-d-mannoside, bind and functionally modulate rodent GABA(A) receptors, respectively. We have characterized the binding pharmacology of synthetic caloporoside and two further congeners, 2-hydroxy-6-([(16R)-(beta-d-mannopyranosyloxy)heptadecyl]) benzoic acid and octyl-beta-d-glucoside on GABA(A) receptors using a [35S]-t-butylbicyclophosphoorothionate (TBPS) radioligand binding assay. Caloporoside and 2-hydroxy-6-([(16R)-(beta-d-mannopyranosyloxy)heptadecyl]) benzoic acid produced concentration-dependent complete inhibition of specific [35S] TBPS binding with overall apparent IC50 values of 14.7+/-0.1 and 14.2+/-0.1 microM, respectively. In contrast, octyl-beta-d-glucoside elicited a concentration-dependent stimulation of specific [35S] TBPS binding (E(max)=144+/-4%; EC50=39.2+/-22.7 nM). The level of stimulation was similar to that elicited by diazepam (E(max)=147+/-6%; EC50=0.8+/-0.1 nM), and was occluded by GABA (0.3 microM). However, the three test compounds failed to elicit any significant effect (positive or negative) upon [3H] flunitrazepam or [3H] muscimol binding, indicating that they did not bind directly, or allosterically couple, to the benzodiazepine or agonist binding site of the GABA(A) receptor, respectively. The constituent monosaccharide, glucose, and both the closely related congeners octyl-beta-d-glucoside or hexyl-beta-d-glucoside have no significant effect upon [35S] TBPS binding. These data, together, provide strong evidence that a beta-glycosidic linkage and chain length are crucial for the positive modulation of [35S] TBPS binding to the GABA(A) receptor by this novel chemical class.
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Affiliation(s)
- S Abuhamdah
- School of Biological and Biomedical Sciences, Science Park, South Road, Durham University, Durham DH1 3LE, UK
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42
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Korpi ER, Sinkkonen ST. GABA(A) receptor subtypes as targets for neuropsychiatric drug development. Pharmacol Ther 2005; 109:12-32. [PMID: 15996746 DOI: 10.1016/j.pharmthera.2005.05.009] [Citation(s) in RCA: 93] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2005] [Accepted: 05/26/2005] [Indexed: 12/30/2022]
Abstract
The main inhibitory neurotransmitter system in the brain, the gamma-aminobutyric acid (GABA) system, is the target for many clinically used drugs to treat, for example, anxiety disorders and epilepsy and to induce sedation and anesthesia. These drugs facilitate the function of pentameric A-type GABA (GABA(A)) receptors that are extremely widespread in the brain and composed from the repertoire of 19 subunit variants. Modern genetic studies have found associations of various subunit gene polymorphisms with neuropsychiatric disorders, including alcoholism, schizophrenia, anxiety, and bipolar affective disorder, but these studies are still at their early phase because they still have failed to lead to validated drug development targets. Recent neurobiological studies on new animal models and receptor subunit mutations have revealed novel aspects of the GABA(A) receptors, which might allow selective targeting of the drug action in receptor subtype-selective fashion, either on the synaptic or extrasynaptic receptor populations. More precisely, the greatest advances have occurred in the clarification of the molecular and behavioral mechanisms of action of the GABA(A) receptor agonists already in the clinical use, such as benzodiazepines and anesthetics, rather than in the introduction of novel compounds to clinical practice. It is likely that these new developments will help to overcome the present problems of the chronic treatment with nonselective GABA(A) agonists, that is, the development of tolerance and dependence, and to focus the drug action on the neurobiologically and neuropathologically relevant substrates.
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Affiliation(s)
- Esa R Korpi
- Institute of Biomedicine, Pharmacology, Biomedicum Helsinki, P.O. Box 63 (Haartmaninkatu 8), FI-00014 University of Helsinki, Finland.
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Farrant M, Nusser Z. Variations on an inhibitory theme: phasic and tonic activation of GABA(A) receptors. Nat Rev Neurosci 2005; 6:215-29. [PMID: 15738957 DOI: 10.1038/nrn1625] [Citation(s) in RCA: 1594] [Impact Index Per Article: 83.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
The proper functioning of the adult mammalian brain relies on the orchestrated regulation of neural activity by a diverse population of GABA (gamma-aminobutyric acid)-releasing neurons. Until recently, our appreciation of GABA-mediated inhibition focused predominantly on the GABA(A) (GABA type A) receptors located at synaptic contacts, which are activated in a transient or 'phasic' manner by GABA that is released from synaptic vesicles. However, there is growing evidence that low concentrations of ambient GABA can persistently activate certain subtypes of GABA(A) receptor, which are often remote from synapses, to generate a 'tonic' conductance. In this review, we consider the distinct roles of synaptic and extrasynaptic GABA receptor subtypes in the control of neuronal excitability.
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Affiliation(s)
- Mark Farrant
- Department of Pharmacology, University College London, Gower Street, London WC1E 6BT, UK.
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Jelitai M, Madarasz E. The role of GABA in the early neuronal development. INTERNATIONAL REVIEW OF NEUROBIOLOGY 2005; 71:27-62. [PMID: 16512345 DOI: 10.1016/s0074-7742(05)71002-3] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Affiliation(s)
- Marta Jelitai
- Laboratory of Neural Cell and Developmental Biology, Institute of Experimental Medicine, Hungarian Academy of Sciences, Budapest
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