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Abstract
GABA is the main inhibitory neurotransmitter in the mammalian central nervous system (CNS) and acts via metabotropic GABAB receptors. Neurodegenerative diseases are a major burden and affect an ever increasing number of humans. The actual therapeutic drugs available are partially effective to slow down the progression of the diseases, but there is a clear need to improve pharmacological treatment thus find alternative drug targets and develop newer pharmaco-treatments. This chapter is dedicated to reviewing the latest evidence about GABAB receptors and their inhibitory mechanisms and pathways involved in the neurodegenerative pathologies.
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Affiliation(s)
- Alessandra P Princivalle
- Department of Bioscience and Chemistry, Biomolecular Research Centre, College of Health, Wellbeing and Life Sciences at Sheffield Hallam University, Sheffield, UK.
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2
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Cieślik P, Wierońska JM. Regulation of Glutamatergic Activity via Bidirectional Activation of Two Select Receptors as a Novel Approach in Antipsychotic Drug Discovery. Int J Mol Sci 2020; 21:ijms21228811. [PMID: 33233865 PMCID: PMC7699963 DOI: 10.3390/ijms21228811] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2020] [Revised: 11/10/2020] [Accepted: 11/16/2020] [Indexed: 12/14/2022] Open
Abstract
Schizophrenia is a mental disorder that affects approximately 1-2% of the population and develops in early adulthood. The disease is characterized by positive, negative, and cognitive symptoms. A large percentage of patients with schizophrenia have a treatment-resistant disease, and the risk of developing adverse effects is high. Many researchers have attempted to introduce new antipsychotic drugs to the clinic, but most of these treatments failed, and the diversity of schizophrenic symptoms is one of the causes of disappointing results. The present review summarizes the results of our latest papers, showing that the simultaneous activation of two receptors with sub-effective doses of their ligands induces similar effects as the highest dose of each compound alone. The treatments were focused on inhibiting the increased glutamate release responsible for schizophrenia arousal, without interacting with dopamine (D2) receptors. Ligands activating metabotropic receptors for glutamate, GABAB or muscarinic receptors were used, and the compounds were administered in several different combinations. Some combinations reversed all schizophrenia-related deficits in animal models, but others were active only in select models of schizophrenia symptoms (i.e., cognitive or negative symptoms).
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3
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Ammari R, Broberger C. Pre- and post-synaptic modulation by GABA B receptors of rat neuroendocrine dopamine neurones. J Neuroendocrinol 2020; 32:e12881. [PMID: 32803906 DOI: 10.1111/jne.12881] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/03/2019] [Revised: 05/22/2020] [Accepted: 06/05/2020] [Indexed: 12/17/2022]
Abstract
The secretion of prolactin from the pituitary is negatively controlled by tuberoinfundibular dopamine (TIDA) neurones. The electrical properties of TIDA cells have recently been identified as a modulatory target of neurotransmitters and hormones in the lactotrophic axis. The role of the GABAB receptor in this control has received little attention, yet is of particular interest because it may act as a TIDA neurone autoreceptor. Here, this issue was explored in a spontaneously active rat TIDA in vitro slice preparation using whole-cell recordings. Application of the GABAB receptor agonist, baclofen, dose-dependently slowed down or abolished the network oscillations typical of this preparation. Pharmacological manipulations identify the underlying mechanism as an outward current mediated by G-protein-coupled inwardly rectifying K+ -like channels. In addition to this postsynaptic modulation, we describe a presynaptic modulation where GABAB receptors restrain the release of glutamate and GABA onto TIDA neurones. Our data identify both pre- and postsynaptic modulation of TIDA neurones by GABAB receptors that may play a role in the neuronal network control of pituitary prolactin secretion and lactation.
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Affiliation(s)
- Rachida Ammari
- Department of Neuroscience, Karolinska Institutet, Stockholm, Sweden
| | - Christian Broberger
- Department of Neuroscience, Karolinska Institutet, Stockholm, Sweden
- Department of Biochemistry and Biophysics, Stockholm University, Stockholm, Sweden
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Sheilabi MA, Battacharyya D, Caetano L, Thom M, Reuber M, Duncan JS, Princivalle AP. Quantitative expression and localization of GABA B receptor protein subunits in hippocampi from patients with refractory temporal lobe epilepsy. Neuropharmacology 2017; 136:117-128. [PMID: 28782512 DOI: 10.1016/j.neuropharm.2017.08.001] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2017] [Revised: 08/01/2017] [Accepted: 08/02/2017] [Indexed: 01/03/2023]
Abstract
This study investigates GABAB protein expression and mRNA levels in three types of specimens. Two types of specimens from patients with temporal lobe epilepsy (TLE), secondary to hippocampal sclerosis, sclerotic hippocampal samples (TLE-HS), and tissue from the structurally preserved non-spiking ipsilateral superior temporal gyrus (TLE-STG) removed from the same patient during epilepsy surgery; and third specimen is hippocampal tissue from individuals with no history of epilepsy (post-mortem controls, PMC). mRNA expression of GABAB subunits was quantified in TLE-HS, TLE-STG and PMC specimens by qRT-PCR. Qualitative and quantitative Western blot (WB) and immunohistochemistry techniques were employed to quantify and localize GABAB proteins subunits. qRT-PCR data demonstrated an overall decrease of both GABAB1 isoforms in TLE-HS compared to TLE-STG. These results were mirrored by the WB findings. GABAB2 mRNA and protein were significantly reduced in TLE-HS samples compared to TLE-STG; however they appeared to be upregulated in TLE-HS compared to the PMC samples. Immunohistochemistry (IHC) showed that GABAB proteins were widely distributed in PMC and TLE-HS hippocampal sections with regional differences in the intensity of the signal. The higher expression of mature GABAB protein in TLE-HS than PMC is in agreement with previous studies. However, these findings could be due to post-mortem changes in PMC specimens. The TLE-STG samples examined here represent a better 'control' tissue compared to TLE-HS samples characterised by lower than expected GABAB expression. This interpretation provides a better explanation for previous functional studies suggesting reduced inhibition in TLE-HS tissue due to attenuated GABAB currents. This article is part of the "Special Issue Dedicated to Norman G. Bowery".
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Affiliation(s)
- Mariam A Sheilabi
- Biomolecular Sciences Research Centre, Sheffield Hallam University, Howard Street, Sheffield, S1 1WB, UK
| | - Dev Battacharyya
- Neurosurgery, Sheffield Hallamshire Hospital, Glossop Road, Sheffield, S10 2JF, UK
| | - Laura Caetano
- Biomolecular Sciences Research Centre, Sheffield Hallam University, Howard Street, Sheffield, S1 1WB, UK
| | - Maria Thom
- Department of Neuropathology, Institute of Neurology, UCL, Queen Square, London, UK
| | - Markus Reuber
- Academic Neurology Unit, University of Sheffield, Royal Hallamshire Hospital, Glossop Road, Sheffield, S10 2JF, UK
| | - John S Duncan
- Department of Clinical and Experimental Epilepsy, Institute of Neurology, UCL, Queen Square, London, UK
| | - Alessandra P Princivalle
- Biomolecular Sciences Research Centre, Sheffield Hallam University, Howard Street, Sheffield, S1 1WB, UK; Division of Neuroscience, Department of Pharmacology, Medical School, University of Birmingham, Birmingham, B15 2TT, UK.
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5
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Romaus-Sanjurjo D, Fernández-López B, Sobrido-Cameán D, Barreiro-Iglesias A, Rodicio MC. Cloning of the GABA B Receptor Subunits B1 and B2 and their Expression in the Central Nervous System of the Adult Sea Lamprey. Front Neuroanat 2016; 10:118. [PMID: 28008311 PMCID: PMC5143684 DOI: 10.3389/fnana.2016.00118] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2016] [Accepted: 11/22/2016] [Indexed: 11/25/2022] Open
Abstract
In vertebrates, γ-aminobutyric acid (GABA) is the main inhibitory transmitter in the central nervous system (CNS) acting through ionotropic (GABAA) and metabotropic (GABAB) receptors. The GABAB receptor produces a slow inhibition since it activates second messenger systems through the binding and activation of guanine nucleotide-binding proteins [G-protein-coupled receptors (GPCRs)]. Lampreys are a key reference to understand molecular evolution in vertebrates. The importance of the GABAB receptor for the modulation of the circuits controlling locomotion and other behaviors has been shown in pharmacological/physiological studies in lampreys. However, there is no data about the sequence of the GABAB subunits or their expression in the CNS of lampreys. Our aim was to identify the sea lamprey GABAB1 and GABAB2 transcripts and study their expression in the CNS of adults. We cloned two partial sequences corresponding to the GABAB1 and GABAB2 cDNAs of the sea lamprey as confirmed by sequence analysis and comparison with known GABAB sequences of other vertebrates. In phylogenetic analyses, the sea lamprey GABAB sequences clustered together with GABABs sequences of vertebrates and emerged as an outgroup to all gnathostome sequences. We observed a broad and overlapping expression of both transcripts in the entire CNS. Expression was mainly observed in neuronal somas of the periventricular regions including the identified reticulospinal cells. No expression was observed in identifiable fibers. Comparison of our results with those reported in other vertebrates indicates that a broad and overlapping expression of the GABAB subunits in the CNS is a conserved character shared by agnathans and gnathostomes.
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Affiliation(s)
- Daniel Romaus-Sanjurjo
- Department of Functional Biology, CIBUS, Faculty of Biology, Universidade de Santiago de Compostela Santiago de Compostela, Spain
| | - Blanca Fernández-López
- Department of Functional Biology, CIBUS, Faculty of Biology, Universidade de Santiago de Compostela Santiago de Compostela, Spain
| | - Daniel Sobrido-Cameán
- Department of Functional Biology, CIBUS, Faculty of Biology, Universidade de Santiago de Compostela Santiago de Compostela, Spain
| | - Antón Barreiro-Iglesias
- Department of Functional Biology, CIBUS, Faculty of Biology, Universidade de Santiago de Compostela Santiago de Compostela, Spain
| | - María Celina Rodicio
- Department of Functional Biology, CIBUS, Faculty of Biology, Universidade de Santiago de Compostela Santiago de Compostela, Spain
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Cifuentes-Diaz C, Marullo S, Doly S. Anatomical and ultrastructural study of PRAF2 expression in the mouse central nervous system. Brain Struct Funct 2015; 221:4169-4185. [PMID: 26645984 DOI: 10.1007/s00429-015-1159-8] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2015] [Accepted: 11/24/2015] [Indexed: 02/01/2023]
Abstract
Prenylated Rab acceptor family, member 2 (PRAF2) is a four transmembrane domain protein of 19 kDa that is highly expressed in particular areas of mammalian brains. PRAF2 is mostly found in the endoplasmic reticulum (ER) of neurons where it plays the role of gatekeeper for the GB1 subunit of the GABAB receptor, preventing its progression in the biosynthetic pathway in the absence of hetero-dimerization with the GB2 subunit. However, PRAF2 can interact with several receptors and immunofluorescence studies indicate that PRAF2 distribution is larger than the ER, suggesting additional biological functions. Here, we conducted an immuno-cytochemical study of PRAF2 distribution in mouse central nervous system (CNS) at anatomical, cellular and ultra-structural levels. PRAF2 appears widely expressed in various regions of mature CNS, such as the olfactory bulbs, cerebral cortex, amygdala, hippocampus, ventral tegmental area and spinal cord. Consistent with its regulatory role of GABAB receptors, PRAF2 was particularly abundant in brain regions known to express GB1 subunits. However, other brain areas where GB1 is expressed, such as basal ganglia, thalamus and hypothalamus, contain little or no PRAF2. In these areas, GB1 subunits might reach the cell surface of neurons independently of GB2 to exert biological functions distinct from those of GABAB receptors, or be regulated by other gatekeepers. Electron microscopy studies confirmed the localization of PRAF2 in the ER, but identified previously unappreciated localizations, in mitochondria, primary cilia and sub-synaptic region. These data indicate additional modes of GABAB regulation in specific brain areas and new biological functions of PRAF2.
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Affiliation(s)
- Carmen Cifuentes-Diaz
- Institut du Fer à Moulin, INSERM UMR-S839, Université Pierre et Marie Curie, 75005, Paris, France
| | - Stefano Marullo
- Institut Cochin, INSERM U1016, CNRS UMR8104, Université Paris Descartes, Sorbonne Paris Cité, 27 rue du Faubourg St-Jacques, 75014, Paris, France
| | - Stéphane Doly
- Institut Cochin, INSERM U1016, CNRS UMR8104, Université Paris Descartes, Sorbonne Paris Cité, 27 rue du Faubourg St-Jacques, 75014, Paris, France.
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Prager EM, Bergstrom HC, Wynn GH, Braga MFM. The basolateral amygdala γ-aminobutyric acidergic system in health and disease. J Neurosci Res 2015; 94:548-67. [PMID: 26586374 DOI: 10.1002/jnr.23690] [Citation(s) in RCA: 112] [Impact Index Per Article: 12.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2015] [Revised: 10/01/2015] [Accepted: 10/18/2015] [Indexed: 01/13/2023]
Abstract
The brain comprises an excitatory/inhibitory neuronal network that maintains a finely tuned balance of activity critical for normal functioning. Excitatory activity in the basolateral amygdala (BLA), a brain region that plays a central role in emotion and motivational processing, is tightly regulated by a relatively small population of γ-aminobutyric acid (GABA) inhibitory neurons. Disruption in GABAergic inhibition in the BLA can occur when there is a loss of local GABAergic interneurons, an alteration in GABAA receptor activation, or a dysregulation of mechanisms that modulate BLA GABAergic inhibition. Disruptions in GABAergic control of the BLA emerge during development, in aging populations, or after trauma, ultimately resulting in hyperexcitability. BLA hyperexcitability manifests behaviorally as an increase in anxiety, emotional dysregulation, or development of seizure activity. This Review discusses the anatomy, development, and physiology of the GABAergic system in the BLA and circuits that modulate GABAergic inhibition, including the dopaminergic, serotonergic, noradrenergic, and cholinergic systems. We highlight how alterations in various neurotransmitter receptors, including the acid-sensing ion channel 1a, cannabinoid receptor 1, and glutamate receptor subtypes, expressed on BLA interneurons, modulate GABAergic transmission and how defects of these systems affect inhibitory tonus within the BLA. Finally, we discuss alterations in the BLA GABAergic system in neurodevelopmental (autism/fragile X syndrome) and neurodegenerative (Alzheimer's disease) diseases and after the development of epilepsy, anxiety, and traumatic brain injury. A more complete understanding of the intrinsic excitatory/inhibitory circuit balance of the amygdala and how imbalances in inhibitory control contribute to excessive BLA excitability will guide the development of novel therapeutic approaches in neuropsychiatric diseases.
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Affiliation(s)
- Eric M Prager
- Department of Anatomy, Physiology, and Genetics, F. Edward Hébert School of Medicine, Uniformed Services, University of the Health Sciences, Bethesda, Maryland
| | | | - Gary H Wynn
- Center for the Study of Traumatic Stress, F. Edward Hébert School of Medicine, Uniformed Services University of the Health Sciences, Bethesda, Maryland.,Department of Psychiatry, F. Edward Hébert School of Medicine, Uniformed Services University of the Health Sciences, Bethesda, Maryland.,Program in Neuroscience, F. Edward Hébert School of Medicine, Uniformed Services University of the Health Sciences, Bethesda, Maryland
| | - Maria F M Braga
- Department of Anatomy, Physiology, and Genetics, F. Edward Hébert School of Medicine, Uniformed Services, University of the Health Sciences, Bethesda, Maryland.,Center for the Study of Traumatic Stress, F. Edward Hébert School of Medicine, Uniformed Services University of the Health Sciences, Bethesda, Maryland.,Department of Psychiatry, F. Edward Hébert School of Medicine, Uniformed Services University of the Health Sciences, Bethesda, Maryland.,Program in Neuroscience, F. Edward Hébert School of Medicine, Uniformed Services University of the Health Sciences, Bethesda, Maryland
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8
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Baloucoune GA, Chun L, Zhang W, Xu C, Huang S, Sun Q, Wang Y, Tu H, Liu J. GABAB receptor subunit GB1 at the cell surface independently activates ERK1/2 through IGF-1R transactivation. PLoS One 2012; 7:e39698. [PMID: 22761875 PMCID: PMC3386256 DOI: 10.1371/journal.pone.0039698] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2012] [Accepted: 05/29/2012] [Indexed: 12/24/2022] Open
Abstract
Background Functional GABAB receptor is believed to require hetero-dimerization between GABAB1 (GB1) and GABAB2 (GB2) subunits. The GB1 extracellular domain is required for ligand binding, and the GB2 trans-membrane domain is responsible for coupling to G proteins. Atypical GABAB receptor responses observed in GB2-deficient mice suggested that GB1 may have activity in the absence of GB2. However the underlying mechanisms remain poorly characterized. Methodology/Principal Findings Here, by using cells overexpressing a GB1 mutant (GB1asa) with the ability to translocate to the cell surface in the absence of GB2, we show that GABAB receptor agonists, such as GABA and Baclofen, can induce ERK1/2 phosphorylation in the absence of GB2. Furthermore, we demonstrate that GB1asa induces ERK1/2 phosphorylation through Gi/o proteins and PLC dependent IGF-1R transactivation. Conclusions/Significance Our data suggest that GB1 may form a functional receptor at the cell surface in the absence of GB2.
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Affiliation(s)
- Guillaume A. Baloucoune
- Sino-France Laboratory for Drug Screening, Key Laboratory of Molecular Biophysics of Ministry of Education, College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, Hubei, China
| | - Lei Chun
- Sino-France Laboratory for Drug Screening, Key Laboratory of Molecular Biophysics of Ministry of Education, College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, Hubei, China
| | - Wenhua Zhang
- Sino-France Laboratory for Drug Screening, Key Laboratory of Molecular Biophysics of Ministry of Education, College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, Hubei, China
| | - Chanjuan Xu
- Sino-France Laboratory for Drug Screening, Key Laboratory of Molecular Biophysics of Ministry of Education, College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, Hubei, China
| | - Siluo Huang
- Sino-France Laboratory for Drug Screening, Key Laboratory of Molecular Biophysics of Ministry of Education, College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, Hubei, China
| | - Qian Sun
- Sino-France Laboratory for Drug Screening, Key Laboratory of Molecular Biophysics of Ministry of Education, College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, Hubei, China
| | - Yunyun Wang
- Sino-France Laboratory for Drug Screening, Key Laboratory of Molecular Biophysics of Ministry of Education, College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, Hubei, China
| | - Haijun Tu
- Sino-France Laboratory for Drug Screening, Key Laboratory of Molecular Biophysics of Ministry of Education, College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, Hubei, China
| | - Jianfeng Liu
- Sino-France Laboratory for Drug Screening, Key Laboratory of Molecular Biophysics of Ministry of Education, College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, Hubei, China
- * E-mail:
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Ribeiro AF, Correia D, Torres AA, Boas GRV, Rueda AVL, Camarini R, Chiavegatto S, Boerngen-Lacerda R, Brunialti-Godard AL. A transcriptional study in mice with different ethanol-drinking profiles: possible involvement of the GABA(B) receptor. Pharmacol Biochem Behav 2012; 102:224-32. [PMID: 22579910 DOI: 10.1016/j.pbb.2012.04.010] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/22/2011] [Revised: 04/24/2012] [Accepted: 04/29/2012] [Indexed: 12/15/2022]
Abstract
Previous studies have suggested that γ-aminobutyric acid-B (GABA(B)) receptor agonists effectively reduce ethanol intake. The quantification using real-time polymerase chain reaction of Gabbr1 and Gabbr2 mRNA from the prefrontal cortex, hypothalamus, hippocampus, and striatum in mice exposed to an animal model of the addiction developed in our laboratory was performed to evaluate the involvement of the GABA(B) receptor in ethanol consumption. We used outbred, Swiss mice exposed to a three-bottle free-choice model (water, 5% v/v ethanol, and 10% v/v ethanol) that consisted of four phases: acquisition (AC), withdrawal (W), reexposure (RE), and quinine-adulteration (AD). Based on individual ethanol intake, the mice were classified into three groups: "addicted" (A group; preference for ethanol and persistent consumption during all phases), "heavy" (H group; preference for ethanol and a reduction in ethanol intake in the AD phase compared to AC phase), and "light" (L group; preference for water during all phases). In the prefrontal cortex in the A group, we found high Gabbr1 and Gabbr2 transcription levels, with significantly higher Gabbr1 transcription levels compared with the C (ethanol-naive control mice), L, and H groups. In the hippocampus in the A group, Gabbr2 mRNA levels were significantly lower compared with the C, L, and H groups. In the striatum, we found a significant increase in Gabbr1 transcription levels compared with the C, L, and H groups. No differences in Gabbr1 or Gabbr2 transcription levels were observed in the hypothalamus among groups. In summary, Gabbr1 and Gabbr2 transcription levels were altered in cerebral areas related to drug taking only in mice behaviorally classified as "addicted" drinkers, suggesting that these genes may contribute to high and persistent ethanol consumption.
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Affiliation(s)
- Andrea Frozino Ribeiro
- Department of General Biology, Universidade Federal de Minas Gerais, Pampulha, Belo Horizonte, MG, CEP 31270-901, Brazil
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Paris-Robidas S, Brochu E, Sintes M, Emond V, Bousquet M, Vandal M, Pilote M, Tremblay C, Di Paolo T, Rajput AH, Rajput A, Calon F. Defective dentate nucleus GABA receptors in essential tremor. ACTA ACUST UNITED AC 2011; 135:105-16. [PMID: 22120148 DOI: 10.1093/brain/awr301] [Citation(s) in RCA: 139] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
The development of new treatments for essential tremor, the most frequent movement disorder, is limited by a poor understanding of its pathophysiology and the relative paucity of clinicopathological studies. Here, we report a post-mortem decrease in GABA(A) (35% reduction) and GABA(B) (22-31% reduction) receptors in the dentate nucleus of the cerebellum from individuals with essential tremor, compared with controls or individuals with Parkinson's disease, as assessed by receptor-binding autoradiography. Concentrations of GABA(B) receptors in the dentate nucleus were inversely correlated with the duration of essential tremor symptoms (r(2) = 0.44, P < 0.05), suggesting that the loss of GABA(B) receptors follows the progression of the disease. In situ hybridization experiments also revealed a diminution of GABA(B(1a+b)) receptor messenger RNA in essential tremor (↓27%). In contrast, no significant changes of GABA(A) and GABA(B) receptors (protein and messenger RNA), GluN2B receptors, cytochrome oxidase-1 or GABA concentrations were detected in molecular or granular layers of the cerebellar cortex. It is proposed that a decrease in GABA receptors in the dentate nucleus results in disinhibition of cerebellar pacemaker output activity, propagating along the cerebello-thalamo-cortical pathways to generate tremors. Correction of such defective cerebellar GABAergic drive could have a therapeutic effect in essential tremor.
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11
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Tian Y, Gunther JR, Liao IH, Liu D, Ander BP, Stamova BS, Lit L, Jickling GC, Xu H, Zhan X, Sharp FR. GABA- and acetylcholine-related gene expression in blood correlate with tic severity and microarray evidence for alternative splicing in Tourette syndrome: a pilot study. Brain Res 2011; 1381:228-36. [PMID: 21241679 DOI: 10.1016/j.brainres.2011.01.026] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2010] [Revised: 12/08/2010] [Accepted: 01/10/2011] [Indexed: 10/18/2022]
Abstract
Tourette syndrome (TS) is a complex childhood neurodevelopmental disorder characterized by motor and vocal tics. Recently, altered numbers of GABAergic-parvalbumin (PV) and cholinergic interneurons were observed in the basal ganglia of individuals with TS. Thus, we postulated that gamma-amino butyric acid (GABA)- and acetylcholine (ACh)-related genes might be associated with the pathophysiology of TS. Total RNA isolated from whole blood of 26 un-medicated TS subjects and 23 healthy controls (HC) was processed on Affymetrix Human Exon 1.0 ST arrays. Data were analyzed to identify genes whose expression correlated with tic severity in TS, and to identify genes differentially spliced in TS compared to HC subjects. Many genes (3627) correlated with tic severity in TS (p < 0.05) among which GABA- (p = 2.1 × 10⁻³) and ACh- (p = 4.25 × 10⁻⁸) related genes were significantly over-represented. Moreover, several GABA and ACh-related genes were predicted to be alternatively spliced in TS compared to HC including GABA receptors GABRA4 and GABRG1, the nicotinic ACh receptor CHRNA4 and cholinergic differentiation factor (CDF). This pilot study suggests that at least some of these GABA- and ACh-related genes observed in blood that correlate with tics or are alternatively spliced are involved in the pathophysiology of TS and tics.
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Affiliation(s)
- Yingfang Tian
- University of California at Davis, M.I.N.D., Institute and Department of Neurology, USA
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12
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Hyland NP, Cryan JF. A Gut Feeling about GABA: Focus on GABA(B) Receptors. Front Pharmacol 2010; 1:124. [PMID: 21833169 PMCID: PMC3153004 DOI: 10.3389/fphar.2010.00124] [Citation(s) in RCA: 118] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2010] [Accepted: 09/07/2010] [Indexed: 12/15/2022] Open
Abstract
γ-Aminobutyric acid (GABA) is the main inhibitory neurotransmitter in the body and hence GABA-mediated neurotransmission regulates many physiological functions, including those in the gastrointestinal (GI) tract. GABA is located throughout the GI tract and is found in enteric nerves as well as in endocrine-like cells, implicating GABA as both a neurotransmitter and an endocrine mediator influencing GI function. GABA mediates its effects via GABA receptors which are either ionotropic GABA(A) or metabotropic GABA(B). The latter which respond to the agonist baclofen have been least characterized, however accumulating data suggest that they play a key role in GI function in health and disease. Like GABA, GABA(B) receptors have been detected throughout the gut of several species in the enteric nervous system, muscle, epithelial layers as well as on endocrine-like cells. Such widespread distribution of this metabotropic GABA receptor is consistent with its significant modulatory role over intestinal motility, gastric emptying, gastric acid secretion, transient lower esophageal sphincter relaxation and visceral sensation of painful colonic stimuli. More intriguing findings, the mechanisms underlying which have yet to be determined, suggest GABA(B) receptors inhibit GI carcinogenesis and tumor growth. Therefore, the diversity of GI functions regulated by GABA(B) receptors makes it a potentially useful target in the treatment of several GI disorders. In light of the development of novel compounds such as peripherally acting GABA(B) receptor agonists, positive allosteric modulators of the GABA(B) receptor and GABA producing enteric bacteria, we review and summarize current knowledge on the function of GABA(B) receptors within the GI tract.
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Affiliation(s)
- Niall P Hyland
- Alimentary Pharmabiotic Centre and Department of Pharmacology and Therapeutics, University College Cork Cork, Ireland
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13
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Magnaghi V. GABA and neuroactive steroid interactions in glia: new roles for old players? Curr Neuropharmacol 2010; 5:47-64. [PMID: 18615153 DOI: 10.2174/157015907780077132] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2006] [Revised: 04/24/2006] [Accepted: 07/27/2006] [Indexed: 02/06/2023] Open
Abstract
In recent years it has becoming clear that glial cells of the central and peripheral nervous system play a crucial role from the earliest stages of development throughout adult life. Glial cells are important for neuronal plasticity, axonal conduction and synaptic transmission. In this respect, glial cells are able to produce, uptake and metabolize many factors that are essential for neuronal physiology, including classic neurotransmitters and neuroactive steroids. In particular, neuroactive steroids, which are mainly synthesized by glial cells, are able to modulate some neurotransmitter receptors affecting both glia and neurons. Among the signaling systems that are specialized for neuron-glial communication, we can include neurotransmitter GABA.The main focus of this review is to illustrate the cross-talk between neurons and glial cells in terms of GABA neurotransmission and actions of neuroactive steroids. To this purpose, we will review the presence of the different GABA receptors in the glial cells of the central and peripheral nervous system. Then, we will discuss their modulation by some neuroactive steroids.
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Affiliation(s)
- Valerio Magnaghi
- Department of Endocrinology and Center of Excellence on Neurodegenerative Disease, University of Milan, Italy.
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GABAB receptors: physiological functions and mechanisms of diversity. ADVANCES IN PHARMACOLOGY (SAN DIEGO, CALIF.) 2010; 58:231-55. [PMID: 20655485 DOI: 10.1016/s1054-3589(10)58010-4] [Citation(s) in RCA: 119] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
GABA(B) receptors are the G-protein-coupled receptors (GPCRs) for gamma-aminobutyric acid (GABA), the main inhibitory neurotransmitter in the central nervous system. GABA(B) receptors are implicated in the etiology of a variety of psychiatric disorders and are considered attractive drug targets. With the cloning of GABA(B) receptor subunits 13 years ago, substantial progress was made in the understanding of the molecular structure, physiology, and pharmacology of these receptors. However, it remained puzzling that native studies demonstrated a heterogeneity of GABA(B) responses that contrasted with a very limited diversity of cloned GABA(B) receptor subunits. Until recently, the only firmly established molecular diversity consisted of two GABA(B1) subunit isoforms, GABA(B1a) and GABA(B1b), which assemble with GABA(B2) subunits to generate heterodimeric GABA(B(1a,2)) and GABA(B(1b,2)) receptors. Using genetic, ultrastructural, biochemical, and electrophysiological approaches, it has been possible to identify functional properties that segregate with these two receptors. Moreover, receptor modifications and factors that can alter the receptor response have been identified. Most importantly, recent data reveal the existence of a family of auxiliary GABA(B) receptor subunits that assemble as tetramers with the C-terminal domain of GABA(B2) subunits and drastically alter pharmacology and kinetics of the receptor response. The data are most consistent with native GABA(B) receptors minimally forming dimeric assemblies of units composed of GABA(B1), GABA(B2), and a tetramer of auxiliary subunits. This represents a substantial departure from current structural concepts for GPCRs.
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15
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Richer M, David M, Villeneuve LR, Trieu P, Ethier N, Pétrin D, Mamarbachi AM, Hébert TE. GABA-B(1) receptors are coupled to the ERK1/2 MAP kinase pathway in the absence of GABA-B(2) subunits. J Mol Neurosci 2008; 38:67-79. [PMID: 19052921 DOI: 10.1007/s12031-008-9163-6] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2008] [Accepted: 11/06/2008] [Indexed: 01/22/2023]
Abstract
In the current model of gamma-aminobutyric acid (GABA) B receptor function, there is a requirement for GABA-B(1/2) heterodimerisation for targetting to the cell surface. However, different lines of evidence suggest that the GABA-B(1) subunit can form a functional receptor in the absence of GABA-B(2). We observed coupling of endogenous GABA-B(1) receptors in the DI-TNC1 glial cell line to the ERK pathway in response to baclofen even though these cells do not express GABA-B(2). GABA-B(1A) receptors were also able to mediate a rapid, transient, and dose-dependent activation of the ERK1/2 MAP kinase pathway when transfected alone into HEK 293 cells. The response was abolished by G(i/o) and MEK inhibition, potentiated by inhibitors of phospholipase C and protein kinase C and did not involve PI-3-kinase activity. Finally, using bioluminescence resonance energy transfer and co-immunoprecipitation, we show the existence of homodimeric GABA-B(1A) receptors in transfected HEK293 cells. Altogether, our observations show that GABA-B(1A) receptors are able to activate the ERK1/2 pathway despite the absence of surface targetting partner GABA-B(2) in both HEK 293 cells and the DI-TNC1 cell line.
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Affiliation(s)
- Maxime Richer
- Département de biochimie and Groupe de recherche universitaire sur le médicament (GRUM), Université de Montréal, Montréal, Québec, Canada
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16
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Cinar R, Freund TF, Katona I, Mackie K, Szucs M. Reciprocal inhibition of G-protein signaling is induced by CB(1) cannabinoid and GABA(B) receptor interactions in rat hippocampal membranes. Neurochem Int 2008; 52:1402-9. [PMID: 18407377 DOI: 10.1016/j.neuint.2008.02.005] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2008] [Accepted: 02/21/2008] [Indexed: 11/27/2022]
Abstract
Cannabinoid CB(1) and the metabotropic GABA(B) receptors have been shown to display similar pharmacological effects and co-localization in certain brain regions. Previous studies have reported a functional link between the two systems. As a first step to investigate the underlying molecular mechanism, here we show cross-inhibition of G-protein signaling between GABA(B) and CB(1) receptors in rat hippocampal membranes. The CB(1) agonist R-Win55,212-2 displayed high potency and efficacy in stimulating guanosine-5'-O-(3-[(35)S]thio)triphosphate, [(35)S]GTPgammaS binding. Its effect was completely blocked by the specific CB(1) antagonist AM251 suggesting that the signaling was via CB(1) receptors. The GABA(B) agonists baclofen and SKF97541 also elevated [(35)S]GTPgammaS binding by about 60%, with potency values in the micromolar range. Phaclofen behaved as a low potency antagonist with an ED(50) approximately 1mM. However, phaclofen at low doses (1 and 10nM) slightly but significantly attenuated maximal stimulation of [(35)S]GTPgammaS binding by the CB(1) agonist R-Win55,212-2. The observation that higher concentrations of phaclofen had no such effect rule out the possibility of its direct action on CB(1) receptors. The pharmacologically inactive stereoisomer S-Win55,212-3 had no effect either alone or in combination with phaclofen establishing that the interaction is stereospecific in hippocampus. The specific CB(1) antagonist AM251 at a low dose (1 nM) also inhibited the efficacy of G-protein signaling of the GABA(B) receptor agonist SKF97541. Cross-talk of the two receptor systems was not detected in either spinal cord or cerebral cortex membranes. It is speculated that the interaction might occur via an allosteric interaction between a subset of GABA(B) and CB(1) receptors in rat hippocampal membranes. Although the exact molecular mechanism of the reciprocal inhibition between CB(1) and GABA(B) receptors will have to be explored by future studies it is intriguing that the cross-talk might be involved in balance tuning the endocannabinoid and GABAergic signaling in hippocampus.
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Affiliation(s)
- Resat Cinar
- Institute of Biochemistry, Biological Research Center, Hungarian Academy of Sciences, Szeged, Hungary
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17
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Marshall FH. The role of GABA(B) receptors in the regulation of excitatory neurotransmission. Results Probl Cell Differ 2007; 44:87-98. [PMID: 17549439 DOI: 10.1007/400_2007_038] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
GABA(B) receptors are the metabotrophic receptors for GABA. They are members of the G-protein coupled superfamily of receptors but are highly unusual as they are made up of a dimer of 7-transmembrane spanning subunits. The receptors are widely distributed throughout the central nervous system where they act post-synaptically to cause a long-lasting hyperpolarisation through the activation of a potassium conductance. They are also present pre-synaptically where they act as auto and heteroreceptors to inhibit neurotransmitter release. GABA(B) receptors play a complex role in the regulation of excitatory transmission and their activation can have both inhibitory and dis-inhibitory effects. This has profound physiological and behavioural consequences including modification of LTP and memory, regulation of seizure activity and nociception.
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Affiliation(s)
- Fiona H Marshall
- Department of Pharmacology, University of Cambridge, Tennis Court Road, Cambridge, UK.
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18
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Kantamneni S, Corrêa SAL, Hodgkinson GK, Meyer G, Vinh NN, Henley JM, Nishimune A. GISP: a novel brain-specific protein that promotes surface expression and function of GABA(B) receptors. J Neurochem 2007; 100:1003-17. [PMID: 17241134 PMCID: PMC3315443 DOI: 10.1111/j.1471-4159.2006.04271.x] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Synaptic transmission depends on the regulated surface expression of neurotransmitter receptors, but many of the cellular processes required to achieve this remain poorly understood. To better define specific mechanisms for the GABA(B) receptor (GABA(B)R) trafficking, we screened for proteins that bind to the carboxy-terminus of the GABA(B1) subunit. We report the identification and characterization of a novel 130-kDa protein, GPCR interacting scaffolding protein (GISP), that interacts directly with the GABA(B1) subunit via a coiled-coil domain. GISP co-fractionates with GABA(B)R and with the postsynaptic density and co-immunoprecipitates with GABA(B1) and GABA(B2) from rat brain. In cultured hippocampal neurons, GISP displays a punctate dendritic distribution and has an overlapping localization with GABA(B)Rs. When co-expressed with GABA(B)Rs in human embryonic kidney cells, GISP promotes GABA(B)R surface expression and enhances both baclofen-evoked extracellular signal-regulated kinase (ERK) phosphorylation and G-protein inwardly rectifying potassium channel (GIRK) currents. These results suggest that GISP is involved in the forward trafficking and stabilization of functional GABA(B)Rs.
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19
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Abstract
In the basal ganglia the effects of gamma-aminobutyrate (GABA) are mediated by both ionotropic (GABA(A)) and metabotropic (GABA(B)) receptors. Although the existence and widespread distribution in the CNS of the GABA(B) receptor had been established in the 1980s the field of GABA(B) research was revolutionized with the discovery that two related G-protein-coupled receptors (GPCRs) needed to dimerize to form the functional GABA(B) receptor at the cell surface. This finding lead to a number of studies of oligomerization in GPCRs and detailed pharmacological studies of the cloned receptors and their splice variants. Particular interest has focused on the proteins interacting with the receptor which may be important in mediating the longer term signalling effects of the receptor and modifying its cellular localization or physiology. The cloning of the GABA(B) receptors also lead to the identification of the first compounds interacting in an allosteric fashion with the receptor some of which may have therapeutic value. Most recently "knockouts" of both the GABA(B) subunits have been produced where in general as expected there is a loss of the majority of the inhibitory effects of the GABA(B) receptor.
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Affiliation(s)
- Piers C Emson
- The Babraham Institute, Babraham Research Campus, Cambridge CB2 4AT, UK.
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20
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Barbaresi P. Cellular and subcellular localization of the GABAB receptor 1a/b subunit in the rat periaqueductal gray matter. J Comp Neurol 2007; 505:478-92. [DOI: 10.1002/cne.21509] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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21
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David M, Richer M, Mamarbachi AM, Villeneuve LR, Dupré DJ, Hebert TE. Interactions between GABA-B1 receptors and Kir 3 inwardly rectifying potassium channels. Cell Signal 2006; 18:2172-81. [PMID: 16809021 DOI: 10.1016/j.cellsig.2006.05.014] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2006] [Accepted: 05/11/2006] [Indexed: 12/01/2022]
Abstract
gamma-aminobutyric acid (GABA) is the principal inhibitory neurotransmitter in the mammalian brain. It acts via both ionotropic GABA-A and metabotropic GABA-B receptors. We evaluated the interaction of receptors with members of the inwardly rectifying potassium (Kir 3) channel family, which also play an important role in neuronal transmission and membrane excitability. These channels are functionally regulated by GABA-B receptors. Possible physical interactions between GABA-B receptor and Kir 3 channels expressed in HEK cells were evaluated using Bioluminescence Resonance Energy Transfer (BRET) experiments, co-immunoprecipitation and confocal microscopy. Our data indicate that Kir 3 channels and Gbetagamma subunits can interact with the GABA-B(1) subunits independently of the GABA-B(2) subunit or Kir 3.4 which are ultimately responsible for their targetting to the cell surface. Thus signalling complexes containing GABA-B receptors, G proteins and Kir channels are formed shortly after biosynthesis most likely in the endoplasmic reticulum.
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Affiliation(s)
- Martin David
- Département de biochimie, Université de Montréal, Canada
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22
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Dupré DJ, Robitaille M, Ethier N, Villeneuve LR, Mamarbachi AM, Hébert TE. Seven Transmembrane Receptor Core Signaling Complexes Are Assembled Prior to Plasma Membrane Trafficking. J Biol Chem 2006; 281:34561-73. [PMID: 16959776 DOI: 10.1074/jbc.m605012200] [Citation(s) in RCA: 137] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Much is known about beta2-adrenergic receptor trafficking and internalization following prolonged agonist stimulation. However, less is known about outward trafficking of the beta2-adrenergic receptor to the plasma membrane or the role that trafficking might play in the assembly of receptor signaling complexes, important for targeting, specificity, and rapidity of subsequent signaling events. Here, by using a combination of bioluminescence resonance energy transfer, bimolecular fluorescence complementation, and confocal microscopy, we evaluated the steps in the formation of the core receptor-G protein heterotrimer complex. By using dominant negative Rab and Sar GTPase constructs, we demonstrate that receptor dimers and receptor-G betagamma complexes initially associate in the endoplasmic reticulum, whereas G alpha subunits are added to the complex during endoplasmic reticulum-Golgi transit. We also observed that G protein heterotrimers adopt different trafficking itineraries when expressed alone or with stoichiometric co-expression with receptor. Furthermore, deliberate mistargeting of specific components of these complexes leads to diversion of other members from their normal subcellular localization, confirming the role of these early interactions in targeting and formation of specific signaling complexes.
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Affiliation(s)
- Denis J Dupré
- Department of Pharmacology and Therapeutics, McGill University, Montréal, Quebec H3G 1Y6, Canada
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23
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Ferreira-Gomes J, Neto FL, Castro-Lopes JM. GABA(B2) receptor subunit mRNA decreases in the thalamus of monoarthritic animals. Brain Res Bull 2006; 71:252-8. [PMID: 17113954 DOI: 10.1016/j.brainresbull.2006.09.010] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2006] [Revised: 08/01/2006] [Accepted: 09/08/2006] [Indexed: 10/24/2022]
Abstract
Many studies have implicated GABA(B) receptors in pain transmission mechanisms, especially in the spinal cord. In the thalamus, mRNA expression of the GABA(B(1b)) isoform was shown to be regulated in relay nuclei in response to chronic noxious input arising from experimental monoarthritis. GABA(B(1a)) and GABA(B2) mRNA expression was here determined by in situ hybridisation in the brain of control, 2, 4, 7 and 14 days monoarthritic rats, to evaluate whether this expression was regulated by chronic noxious input in thalamic nuclei. mRNA labelling was analysed quantitatively in the ventrobasal complex, posterior, central medial/central lateral and reticular thalamic nuclei; the thalamic visual relay and dentate gyrus were examined for control. No mRNA expression was detected for GABA(B(1a)) in control and monoarthritic animals. Similarly, GABA(B2) mRNA was not found in the reticular nucleus. However, GABA(B2) mRNA expression was observed in the ventrobasal complex, posterior and central medial/central lateral nuclei of control animals. A significant decrease of 42% at 2 days and 27% at 4 days of monoarthritis was observed in the ventrobasal complex contralaterally, when compared with controls, returning to basal levels at 7 days of monoarthritis. In the ipsilateral posterior nucleus, there was a significant decrease of 38% at 2 days of monoarthritis. No significant changes were observed in central medial/central lateral nuclei. The data suggest that GABA(B2) mRNA expression in the ventrobasal complex and posterior nucleus is regulated by noxious input and that GABA(B) receptors might play a role in the plasticity of these relay nuclei during chronic inflammatory pain.
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Affiliation(s)
- Joana Ferreira-Gomes
- Institute of Histology and Embryology, Faculty of Medicine and IBMC, 4200-319 Porto, University of Porto, Portugal
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24
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Magnaghi V, Ballabio M, Consoli A, Lambert JJ, Roglio I, Melcangi RC. GABA receptor-mediated effects in the peripheral nervous system: A cross-interaction with neuroactive steroids. J Mol Neurosci 2006; 28:89-102. [PMID: 16632878 DOI: 10.1385/jmn:28:1:89] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2005] [Revised: 11/30/1999] [Accepted: 08/18/2005] [Indexed: 12/18/2022]
Abstract
Gamma-aminobutyric acid (GABA), the major inhibitory neurotransmitter in the adult mammalian central nervous system (CNS), exerts its action via an interaction with specific receptors (e.g., GABAA and GABAB). These receptors are expressed not only in neurons but also on glial cells of the CNS, which might represent a target for the allosteric action of neuroactive steroids. Herein, we have demonstrated first that in the peripheral nervous system (PNS), the sciatic nerve and myelin-producing Schwann cells express both GABAA and GABAB receptors. Specific ligands, muscimol and baclofen, respectively, control Schwann-cell proliferation and expression of some specific myelin proteins (i.e., glycoprotein P0 and peripheral myelin protein 22 [PMP22]). Moreover, the progesterone (P) metabolite allopregnanolone, acting via the GABAA receptor, can influence PMP22 synthesis. In addition, we demonstrate that P, dihydroprogesterone, and allopregnanolone influence the expression of GABAB subunits in Schwann cells. The results suggest, at least in the myelinating cells of the PNS, a cross-interaction within the GABAergic receptor system, via GABAA and GABAB receptors and neuroactive steroids.
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Affiliation(s)
- Valerio Magnaghi
- Department of Endocrinology and Center of Excellence on Neurodegenerative Diseases, University of Milan, 20133 Milan, Italy.
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25
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Villalba RM, Raju DV, Hall RA, Smith Y. GABA(B) receptors in the centromedian/parafascicular thalamic nuclear complex: an ultrastructural analysis of GABA(B)R1 and GABA(B)R2 in the monkey thalamus. J Comp Neurol 2006; 496:269-87. [PMID: 16538684 DOI: 10.1002/cne.20950] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Strong gamma-aminobutyric acid type B (GABA(B)) receptor binding has been shown throughout the thalamus, but the distribution of the two GABA(B) receptor subunits, GABA(B) receptor subunit 1 (GABA(B)R1) and GABA(B) receptor subunit 2 (GABA(B)R2), remains poorly characterized. In primates, the caudal intralaminar nuclei, centromedian and parafascicular (CM/PF), are an integral part of basal ganglia circuits and a main source of inputs to the striatum. In this study, we analyzed the subcellular and subsynaptic distribution of GABA(B) receptor subunits by using light and electron microscopic immunocytochemical techniques. Quantitative immunoperoxidase and immunogold analysis showed that both subunits display a similar pattern of distribution in CM/PF, being expressed largely at extrasynaptic and perisynaptic sites in neuronal cell bodies, dendrites, and axon-like processes and less abundantly in axon terminals. Postsynaptic GABA(B)R1 labeling was found mostly on the plasma membrane (70-80%), whereas GABA(B)R2 was more evenly distributed between the plasma membrane and intracellular compartments of CM/PF neurons. A few axon terminals forming symmetric and asymmetric synapses were also labeled for GABA(B)R1 and GABA(B)R2, but the bulk of presynaptic labeling was expressed in small axon-like processes. About 20% of presynaptic vesicle-containing dendrites of local circuit neurons displayed GABA(B)R1/R2 immunoreactivity. Vesicular glutamate transporters (vGluT1)-containing terminals forming asymmetric synapses expressed GABA(B)R1 and/or displayed postsynaptic GABA(B)R1 at the edges of their asymmetric specialization. Overall, these findings provide evidence for multiple sites where GABA(B) receptors could modulate GABAergic and glutamatergic transmission in the primate CM/PF complex.
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Affiliation(s)
- Rosa M Villalba
- Yerkes National Primate Research Center, Emory University, Atlanta, Georgia 30322, USA.
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26
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Millan MJ. Multi-target strategies for the improved treatment of depressive states: Conceptual foundations and neuronal substrates, drug discovery and therapeutic application. Pharmacol Ther 2006; 110:135-370. [PMID: 16522330 DOI: 10.1016/j.pharmthera.2005.11.006] [Citation(s) in RCA: 389] [Impact Index Per Article: 21.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2005] [Accepted: 11/28/2005] [Indexed: 12/20/2022]
Abstract
Major depression is a debilitating and recurrent disorder with a substantial lifetime risk and a high social cost. Depressed patients generally display co-morbid symptoms, and depression frequently accompanies other serious disorders. Currently available drugs display limited efficacy and a pronounced delay to onset of action, and all provoke distressing side effects. Cloning of the human genome has fuelled expectations that symptomatic treatment may soon become more rapid and effective, and that depressive states may ultimately be "prevented" or "cured". In pursuing these objectives, in particular for genome-derived, non-monoaminergic targets, "specificity" of drug actions is often emphasized. That is, priority is afforded to agents that interact exclusively with a single site hypothesized as critically involved in the pathogenesis and/or control of depression. Certain highly selective drugs may prove effective, and they remain indispensable in the experimental (and clinical) evaluation of the significance of novel mechanisms. However, by analogy to other multifactorial disorders, "multi-target" agents may be better adapted to the improved treatment of depressive states. Support for this contention is garnered from a broad palette of observations, ranging from mechanisms of action of adjunctive drug combinations and electroconvulsive therapy to "network theory" analysis of the etiology and management of depressive states. The review also outlines opportunities to be exploited, and challenges to be addressed, in the discovery and characterization of drugs recognizing multiple targets. Finally, a diversity of multi-target strategies is proposed for the more efficacious and rapid control of core and co-morbid symptoms of depression, together with improved tolerance relative to currently available agents.
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Affiliation(s)
- Mark J Millan
- Institut de Recherches Servier, Centre de Recherches de Croissy, Psychopharmacology Department, 125, Chemin de Ronde, 78290-Croissy/Seine, France.
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27
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Bianchi MS, Lux-Lantos VA, Bettler B, Libertun C. Expression of gamma-aminobutyric acid B receptor subunits in hypothalamus of male and female developing rats. BRAIN RESEARCH. DEVELOPMENTAL BRAIN RESEARCH 2005; 160:124-9. [PMID: 16297450 DOI: 10.1016/j.devbrainres.2005.06.017] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/01/2005] [Revised: 06/28/2005] [Accepted: 06/30/2005] [Indexed: 11/26/2022]
Abstract
GABA and its receptors show particular ontogenic distributions in different rat brain areas. Recently, GABAB receptors (GBR) have been described to assemble as heterodimers formed by a GBR1a/b and a GBR2 subunit. Here, the ontogeny of rat GBRs and the pattern of subunit expression in both sexes were determined in the hypothalamus, a critical area for homeostatic regulation. Male and female rats were sacrificed at 1, 4, 12, 20, 28, 38 days of life and at adulthood and hypothalami were removed and frozen. Western blots analysis for GBR1 and GBR2 subunits showed that both were expressed in male and female hypothalamic membranes from day 1 to adulthood. In females, both GBR1a and GBR1b were maximally expressed in newborns and decreased towards adulthood. At birth, expression of GBR1a was significantly higher than GBR1b, while at 38 days, GBR1b was more abundant. In males, GBR1a and GBR1b expression was higher in young animals and decreased gradually showing adult levels between the second and third weeks of age without differences between isoforms. Comparing GBR1 variants levels in hypothalamus between sexes, GBR1a was significantly more abundant in females at birth while at 38 days its expression was higher in males; GBR1b showed no sex differences along development. GBR2 was detected in hypothalami of females and males at all ages; maximum levels were observed at 12 days and adult levels were attained at 38 days, without sex differences. This is the first report on the ontogeny of hypothalamic GABAB receptors in male and female rats, with a particular developmental pattern of subunit and isoform expression and presenting some sex differences.
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Affiliation(s)
- María S Bianchi
- Instituto de Biología y Medicina Experimental-CONICET, V. de Obligado 2490, (C1428ADN) Buenos Aires, Argentina
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28
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Lacey CJ, Boyes J, Gerlach O, Chen L, Magill PJ, Bolam JP. GABA(B) receptors at glutamatergic synapses in the rat striatum. Neuroscience 2005; 136:1083-95. [PMID: 16226840 DOI: 10.1016/j.neuroscience.2005.07.013] [Citation(s) in RCA: 74] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2005] [Revised: 06/06/2005] [Accepted: 07/01/2005] [Indexed: 12/12/2022]
Abstract
Although multiple effects of GABA(B) receptor activation on synaptic transmission in the striatum have been described, the precise locations of the receptors mediating these effects have not been determined. To address this issue, we carried out pre-embedding immunogold electron microscopy in the rat using antibodies against the GABA(B) receptor subunits, GABA(B1) and GABA(B2). In addition, to investigate the relationship between GABA(B) receptors and glutamatergic striatal afferents, we used antibodies against the vesicular glutamate transporters, vesicular glutamate transporter 1 and vesicular glutamate transporter 2, as markers for glutamatergic terminals. Immunolabeling for GABA(B1) and GABA(B2) was widely and similarly distributed in the striatum, with immunogold particles localized at both presynaptic and postsynaptic sites. The most commonly labeled structures were dendritic shafts and spines, as well as terminals forming asymmetric and symmetric synapses. In postsynaptic structures, the majority of labeling associated with the plasma membrane was localized at extrasynaptic sites, although immunogold particles were also found at the postsynaptic specialization of some symmetric, putative GABAergic synapses. Labeling in axon terminals was located within, or at the edge of, the presynaptic active zone, as well as at extrasynaptic sites. Double labeling for GABA(B) receptor subunits and vesicular glutamate transporters revealed that labeling for both GABA(B1) and GABA(B2) was localized on glutamatergic axon terminals that expressed either vesicular glutamate transporter 1 or vesicular glutamate transporter 2. The patterns of innervation of striatal neurons by the vesicular glutamate transporter 1- and vesicular glutamate transporter 2-positive terminals suggest that they are selective markers of corticostriatal and thalamostriatal afferents, respectively. These results thus provide evidence that presynaptic GABA(B) heteroreceptors are in a position to modulate the two major excitatory inputs to striatal spiny projection neurons arising in the cortex and thalamus. In addition, presynaptic GABA(B) autoreceptors are present on the terminals of spiny projection neurons and/or striatal GABAergic interneurons. Furthermore, the data indicate that GABA may also affect the excitability of striatal neurons via postsynaptic GABA(B) receptors.
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Affiliation(s)
- C J Lacey
- Medical Research Council Anatomical Neuropharmacology Unit, Department of Pharmacology, University of Oxford, Oxford OX1 3TH, UK
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29
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Prinster SC, Hague C, Hall RA. Heterodimerization of G Protein-Coupled Receptors: Specificity and Functional Significance. Pharmacol Rev 2005; 57:289-98. [PMID: 16109836 DOI: 10.1124/pr.57.3.1] [Citation(s) in RCA: 302] [Impact Index Per Article: 15.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
G protein-coupled receptors (GPCRs) are cell surface receptors that mediate physiological responses to a diverse array of stimuli. GPCRs have traditionally been thought to act as monomers, but recent evidence suggests that GPCRs may form dimers (or higher-order oligomers) as part of their normal trafficking and function. In fact, certain GPCRs seem to have a strict requirement for heterodimerization to attain proper surface expression and functional activity. Even those GPCRs that do not absolutely require heterodimerization may still specifically associate with other GPCR subtypes, sometimes resulting in dramatic effects on receptor pharmacology, signaling, and/or internalization. Understanding the specificity and functional significance of GPCR heterodimerization is of tremendous clinical importance since GPCRs are the molecular targets for numerous therapeutic drugs.
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Affiliation(s)
- Steven C Prinster
- Department of Pharmacology, Emory University School of Medicine, Atlanta, GA 30322, USA
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30
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Cryan JF, Kaupmann K. Don't worry 'B' happy!: a role for GABA(B) receptors in anxiety and depression. Trends Pharmacol Sci 2005; 26:36-43. [PMID: 15629203 DOI: 10.1016/j.tips.2004.11.004] [Citation(s) in RCA: 255] [Impact Index Per Article: 13.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
GABA, the main inhibitory neurotransmitter in the brain, regulates many physiological and psychological processes. Thus, dysfunction of the GABA system is implicated in the pathophysiology of several neuropsychiatric disorders, including anxiety and depression. However, the role of GABA(B) receptors in behavioural processes related to these disorders has not been resolved. GABA(B) receptors are G-protein-coupled receptors that function as heterodimers of GABA(B(1)) and GABA(B(2)) subunits. In addition to highly selective agonists and antagonists, novel GABA(B) receptor tools have been developed recently to further assist elucidation of the role of GABA(B) receptors in CNS function. These include mice that lack functional GABA(B) receptors, and novel positive modulators of the GABA(B) receptor. In this review, we discuss evidence that points to a role of GABA(B) receptors in anxiety and depression.
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Affiliation(s)
- John F Cryan
- Neuroscience Research, Novartis Institutes for BioMedical Research, Novartis Pharma AG, Basel, Switzerland.
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31
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Gassmann M, Shaban H, Vigot R, Sansig G, Haller C, Barbieri S, Humeau Y, Schuler V, Müller M, Kinzel B, Klebs K, Schmutz M, Froestl W, Heid J, Kelly PH, Gentry C, Jaton AL, Van der Putten H, Mombereau C, Lecourtier L, Mosbacher J, Cryan JF, Fritschy JM, Lüthi A, Kaupmann K, Bettler B. Redistribution of GABAB(1) protein and atypical GABAB responses in GABAB(2)-deficient mice. J Neurosci 2005; 24:6086-97. [PMID: 15240800 PMCID: PMC6729668 DOI: 10.1523/jneurosci.5635-03.2004] [Citation(s) in RCA: 186] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
GABAB receptors mediate slow synaptic inhibition in the nervous system. In transfected cells, functional GABAB receptors are usually only observed after coexpression of GABAB(1) and GABAB(2) subunits, which established the concept of heteromerization for G-protein-coupled receptors. In the heteromeric receptor, GABAB(1) is responsible for binding of GABA, whereas GABAB(2) is necessary for surface trafficking and G-protein coupling. Consistent with these in vitro observations, the GABAB(1) subunit is also essential for all GABAB signaling in vivo. Mice lacking the GABAB(1) subunit do not exhibit detectable electrophysiological, biochemical, or behavioral responses to GABAB agonists. However, GABAB(1) exhibits a broader cellular expression pattern than GABAB(2), suggesting that GABAB(1) could be functional in the absence of GABAB(2). We now generated GABAB(2)-deficient mice to analyze whether GABAB(1) has the potential to signal without GABAB(2) in neurons. We show that GABAB(2)-/- mice suffer from spontaneous seizures, hyperalgesia, hyperlocomotor activity, and severe memory impairment, analogous to GABAB(1)-/- mice. This clearly demonstrates that the lack of heteromeric GABAB(1,2) receptors underlies these phenotypes. To our surprise and in contrast to GABAB(1)-/- mice, we still detect atypical electrophysiological GABAB responses in hippocampal slices of GABAB(2)-/- mice. Furthermore, in the absence of GABAB(2), the GABAB(1) protein relocates from distal neuronal sites to the soma and proximal dendrites. Our data suggest that association of GABAB(2) with GABAB(1) is essential for receptor localization in distal processes but is not absolutely necessary for signaling. It is therefore possible that functional GABAB receptors exist in neurons that naturally lack GABAB(2) subunits.
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Affiliation(s)
- Martin Gassmann
- Pharmazentrum, Department of Clinical-Biological Sciences, University of Basel, CH-4056 Basel, Switzerland
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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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33
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Kawakami S, Uezono Y, Makimoto N, Enjoji A, Kaibara M, Kanematsu T, Taniyama K. Characterization of GABA(B) receptors involved in inhibition of motility associated with acetylcholine release in the dog small intestine: possible existence of a heterodimer of GABA(B1) and GABA(B2) subunits. J Pharmacol Sci 2004; 94:368-75. [PMID: 15107576 DOI: 10.1254/jphs.94.368] [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] [Indexed: 10/26/2022] Open
Abstract
Characterization of the gamma-aminobutyric acid (GABA)(B) receptor involved in the motility of dog small intestine was analyzed by application of the microdialysis method to the small intestine of the whole body of the dog. The reverse transcription-polymerase chain reaction (RT-PCR) was used. Intraarterial administration of muscimol induced acceleration of motility associated with acetylcholine (ACh) release, these responses being antagonized by bicuculline. Intraarterial administration of baclofen induced inhibition of motility associated with ACh release, these responses being antagonized by CGP62349. GABA induced inhibition of motility associated with decrease in ACh release. CGP62349 alone induced acceleration of motility associated with increase in ACh release. RT-PCR revealed the presence of mRNAs for both subunits of GABA(B) receptor, GABA(B1) and GABA(B2), in the dog small intestine, although GABA(B1) subunits were 6 isoforms of GABA(B1) (GABA(B1(a)) - GABA(B1(g))), except GABA(B1(d)). Thus, the GABA(B) receptor located at cholinergic neurons as a heterodimer with subunits of GABA(B1) and GABA(B2) in the dog small intestine operates predominantly relative to the GABA(A) receptor in physiological motility.
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Affiliation(s)
- Shunsuke Kawakami
- Department of Translational Medical Sciences, Nagasaki University Graduate School of Biomedical Sciences, Nagasaki, Japan
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34
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Tamura T, Nozaki A, Abe KI, Dansako H, Naka K, Ikeda M, Tanaka K, Kato N. cDNA microarray analysis of lactoferrin expression in non-neoplastic human hepatocyte PH5CH8 cells. Biochim Biophys Acta Gen Subj 2004; 1721:73-80. [PMID: 15652181 DOI: 10.1016/j.bbagen.2004.10.003] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2004] [Revised: 09/08/2004] [Accepted: 10/06/2004] [Indexed: 12/24/2022]
Abstract
Lactoferrin (LF), a milk protein belonging to the iron transporter transferrin family, is known as a primary defense protein against pathogenic microorganisms. Previously, we found that bovine and human LFs prevented hepatitis C virus infection in cultured human hepatocytes by a direct interaction with the virus. Since LF is proposed to have transcriptional regulatory activity in addition to its antimicrobial function, we sought to identify the target genes that these two types of LF have in common. To this end, we were the first to perform microarray analysis (9970 genes) using human hepatocytes that expressed bovine or human LF by retrovirus-mediated gene transfer. In the results, LF could give a variety of expression profiles in the human hepatocytes, and showed that 9 and 19 genes were commonly up-regulated (more than 2.0-fold) and down-regulated (less than 0.50-fold), respectively, in both bovine and human LF-expressing cells compared with control cells. Among these genes, we found that gamma-aminobutyric acid (GABA)-B receptor 2 was transcriptionally down-regulated by bovine and human LFs, but not by human transferrin. Furthermore, we obtained the suggestive result that LF may modulate the level of intracellular cAMP. This modulation is one of the cellular responses that the GABA-B receptor modifies. This is the first report of microarray analysis applied to search inclusively for the target genes of LF.
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Affiliation(s)
- Takahiko Tamura
- Department of Molecular Biology, Okayama University Graduate School of Medicine and Dentistry, 2-5-1 Shikata-cho, Okayama 700-8558, Japan
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McDonald AJ, Mascagni F, Muller JF. Immunocytochemical localization of GABABR1 receptor subunits in the basolateral amygdala. Brain Res 2004; 1018:147-58. [PMID: 15276873 DOI: 10.1016/j.brainres.2004.05.053] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 05/13/2004] [Indexed: 10/26/2022]
Abstract
Gamma-aminobutyric acid B (GABAB) receptors (GBRs) are G-protein-coupled receptors that mediate a slow, prolonged form of inhibition in the basolateral amygdala (ABL) and other brain areas. Recent studies indicate that this receptor is a heterodimer consisting of GABABR1 (GBR1) and GABABR2 subunits. In the present investigation, antibodies to the GABABR1 subunit were used to study the neuronal localization of GBRs in the rat ABL. GBR immunoreactivity was mainly found in spine-sparse interneurons and astrocytes at the light microscopic level. Very few pyramidal neurons exhibited perikaryal staining. Dual-labeling immunofluorescence analysis indicated that each of the four main subpopulations of interneurons exhibited GBR immunoreactivity. Virtually 100% of large CCK+ neurons in the basolateral and lateral nuclei were GBR+. In the basolateral nucleus 72% of somatostatin (SOM), 73% of parvalbumin (PV) and 25% of VIP positive interneurons were GBR+. In the lateral nucleus 50% of somatostatin, 30% of parvalbumin and 27% of VIP positive interneurons were GBR+. Electron microscopic (EM) analysis revealed that most of the light neuropil staining seen at the light microscopic level was due to the staining of dendritic shafts and spines, most of which probably belonged to spiny pyramidal cells. Very few axon terminals (Ats) were GBR+. In summary, this investigation demonstrates that the distal dendrites of pyramidal cells, and varying percentages of each of the four main subpopulations of interneurons in the ABL, express GBRs. Because previous studies suggest that GBR-mediated inhibition modulates NMDA-dependent EPSPs in the ABL, these receptors may play an important role in neuronal plasticity related to emotional learning.
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Affiliation(s)
- Alexander J McDonald
- Department of Pharmacology, Physiology, and Neuroscience, University of South Carolina School of Medicine, Columbia, SC 29208, USA.
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36
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Thuault SJ, Brown JT, Sheardown SA, Jourdain S, Fairfax B, Spencer JP, Restituito S, Nation JHL, Topps S, Medhurst AD, Randall AD, Couve A, Moss SJ, Collingridge GL, Pangalos MN, Davies CH, Calver AR. The GABAB2 subunit is critical for the trafficking and function of native GABAB receptors. Biochem Pharmacol 2004; 68:1655-66. [PMID: 15451409 DOI: 10.1016/j.bcp.2004.07.032] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2004] [Accepted: 07/12/2004] [Indexed: 11/25/2022]
Abstract
Studies in heterologous systems have demonstrated that heterodimerisation of the two GABA(B) receptor subunits appears to be crucial for the trafficking and signalling of the receptor. Gene targeting of the GABA(B1) gene has demonstrated that the expression of GABA(B1) is essential for GABA(B) receptor function in the central nervous system (CNS). However, the contribution of the GABA(B2) subunit in the formation of native GABA(B) receptors is still unclear, in particular whether other proteins can substitute for this subunit. We have created a transgenic mouse in which the endogenous GABA(B2) gene has been mutated in order to express a C-terminally truncated version of the protein. As a result, the GABA(B1) subunit does not reach the cell surface and concomitantly both pre- and post-synaptic GABA(B) receptor functions are abolished. Taken together with previous gene deletion studies for the GABA(B1) subunit, this suggests that classical GABA(B) function in the brain is exclusively mediated by GABA(B1/2) heteromers.
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Affiliation(s)
- Seb J Thuault
- Neurology and GI CEDD, GlaxoSmithKline, New Frontiers Science Park, Third Avenue, Harlow, Essex CM19 5AW, UK
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Charara A, Galvan A, Kuwajima M, Hall RA, Smith Y. An electron microscope immunocytochemical study of GABA(B) R2 receptors in the monkey basal ganglia: a comparative analysis with GABA(B) R1 receptor distribution. J Comp Neurol 2004; 476:65-79. [PMID: 15236467 DOI: 10.1002/cne.20210] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
Functional gamma-aminobutyric acid (GABA)(B) receptors are heterodimers made up of GABA(B) R1 and GABA(B) R2 subunits. The subcellular localization of GABA(B) R2 receptors remains poorly known in the central nervous system. Therefore, we performed an ultrastructural analysis of the localization of GABA(B) R2 receptor immunoreactivity in the monkey basal ganglia. Furthermore, to characterize better the neuronal sites at which GABA(B) R1 and GABA(B) R2 may interact to form functional receptors, we compared the relative distribution of immunoreactivity of the two GABA(B) receptors in various basal ganglia nuclei. Light to moderate GABA(B) R2 immunoreactivity was found in cell bodies and neuropil elements in all basal ganglia nuclei. At the electron microscope level, GABA(B) R2 immunoreactivity was commonly expressed postsynaptically, although immunoreactive preterminal axonal segments were also frequently encountered, particularly in the globus pallidus and substantia nigra, where they accounted for the third of the total number of GABA(B) R2-containing elements. A few labeled terminals that displayed the ultrastructural features of glutamatergic boutons were occasionally found in most basal ganglia nuclei, except for the subthalamic nucleus, which was devoid of GABA(B) R2-immunoreactive boutons. The relative distribution of GABA(B) R2 immunoreactivity in the monkey basal ganglia was largely consistent with that of GABA(B) R1, but some exceptions were found, most noticeably in the globus pallidus and substantia nigra, which contained a significantly larger proportion of presynaptic elements labeled for GABA(B) R1 than GABA(B) R2. These findings suggest the possible coexistence and heterodimerization of GABA(B) R1 and GABA(B) R2 at various pre- and postsynaptic sites, but also raise the possibility that the formation of functional GABA(B) receptors in specific compartments of basal ganglia neurons relies on mechanisms other than GABA(B) R1/R2 heterodimerization.
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Affiliation(s)
- Ali Charara
- Yerkes National Primate Research Center, Emory University, Atlanta, Georgia 30322, USA
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Bettler B, Kaupmann K, Mosbacher J, Gassmann M. Molecular structure and physiological functions of GABA(B) receptors. Physiol Rev 2004; 84:835-67. [PMID: 15269338 DOI: 10.1152/physrev.00036.2003] [Citation(s) in RCA: 640] [Impact Index Per Article: 32.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
GABA(B) receptors are broadly expressed in the nervous system and have been implicated in a wide variety of neurological and psychiatric disorders. The cloning of the first GABA(B) receptor cDNAs in 1997 revived interest in these receptors and their potential as therapeutic targets. With the availability of molecular tools, rapid progress was made in our understanding of the GABA(B) system. This led to the surprising discovery that GABA(B) receptors need to assemble from distinct subunits to function and provided exciting new insights into the structure of G protein-coupled receptors (GPCRs) in general. As a consequence of this discovery, it is now widely accepted that GPCRs can exist as heterodimers. The cloning of GABA(B) receptors allowed some important questions in the field to be answered. It is now clear that molecular studies do not support the existence of pharmacologically distinct GABA(B) receptors, as predicted by work on native receptors. Advances were also made in clarifying the relationship between GABA(B) receptors and the receptors for gamma-hydroxybutyrate, an emerging drug of abuse. There are now the first indications linking GABA(B) receptor polymorphisms to epilepsy. Significantly, the cloning of GABA(B) receptors enabled identification of the first allosteric GABA(B) receptor compounds, which is expected to broaden the spectrum of therapeutic applications. Here we review current concepts on the molecular composition and function of GABA(B) receptors and discuss ongoing drug-discovery efforts.
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Affiliation(s)
- Bernhard Bettler
- Pharmazentrum, Dept. of Clinical-Biological Sciences, Institute of Physiology, Univ. of Basel, Klingelbergstr. 50, CH-4056 Basel, Switzerland.
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Magnaghi V, Ballabio M, Cavarretta ITR, Froestl W, Lambert JJ, Zucchi I, Melcangi RC. GABAB receptors in Schwann cells influence proliferation and myelin protein expression. Eur J Neurosci 2004; 19:2641-9. [PMID: 15147298 DOI: 10.1111/j.0953-816x.2004.03368.x] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
The location and the role of gamma-aminobutyric acid type B (GABA(B)) receptors in the central nervous system have recently received considerable attention, whilst relatively little is known regarding the peripheral nervous system. In this regard, here we demonstrate for the first time that GABA(B) receptor isoforms [i.e. GABA(B(1)) and GABA(B(2))] are specifically localized in the rat Schwann cell population of the sciatic nerve. Using the selective GABA(B) agonist [i.e. (-)-baclofen] and the antagonists (i.e. CGP 62349, CGP 56999 A, CGP 55845 A), such receptors are shown to be functionally active and negatively coupled to the adenylate cyclase system. Furthermore, exposure of cultured Schwann cells to (-)-baclofen inhibits their proliferation and reduces the synthesis of specific myelin proteins (i.e. glycoprotein Po, peripheral myelin protein 22, myelin-associated glycoprotein, connexin 32), providing evidence for a physiological role of GABA(B) receptors in the glial cells of the peripheral nervous system.
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Affiliation(s)
- Valerio Magnaghi
- Department of Endocrinology and Center of Excellence on Neurodegenerative Diseases, University of Milan, Via Balzaretti 9, 20133 Milan, Italy.
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Waldvogel HJ, Billinton A, White JH, Emson PC, Faull RLM. Comparative cellular distribution of GABAA and GABAB receptors in the human basal ganglia: immunohistochemical colocalization of the alpha 1 subunit of the GABAA receptor, and the GABABR1 and GABABR2 receptor subunits. J Comp Neurol 2004; 470:339-56. [PMID: 14961561 DOI: 10.1002/cne.20005] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
The GABA(B) receptor is a G-protein linked metabotropic receptor that is comprised of two major subunits, GABA(B)R1 and GABA(B)R2. In this study, the cellular distribution of the GABA(B)R1 and GABA(B)R2 subunits was investigated in the normal human basal ganglia using single and double immunohistochemical labeling techniques on fixed human brain tissue. The results showed that the GABA(B) receptor subunits GABA(B)R1 and GABA(B)R2 were both found on the same neurons and followed the same distribution patterns. In the striatum, these subunits were found on the five major types of interneurons based on morphology and neurochemical labeling (types 1, 2, 3, 5, 6) and showed weak labeling on the projection neurons (type 4). In the globus pallidus, intense GABA(B)R1 and GABA(B)R2 subunit labeling was found in large pallidal neurons, and in the substantia nigra, both pars compacta and pars reticulata neurons were labeled for both receptor subunits. Studies investigating the colocalization of the GABA(A) alpha(1) subunit and GABA(B) receptor subunits showed that the GABA(A) receptor alpha(1) subunit and the GABA(B)R1 subunit were found together on GABAergic striatal interneurons (type 1 parvalbumin, type 2 calretinin, and type 3 GAD neurons) and on neurons in the globus pallidus and substantia nigra pars reticulata. GABA(B)R1 and GABA(B)R2 were found on substantia nigra pars compacta neurons but the GABA(A) receptor alpha(1) subunit was absent from these neurons. The results of this study provide the morphological basis for GABAergic transmission within the human basal ganglia and provides evidence that GABA acts through both GABA(A) and GABA(B) receptors. That is, GABA acts through GABA(B) receptors, which are located on most of the cell types of the striatum, globus pallidus, and substantia nigra. GABA also acts through GABA(A) receptors containing the alpha(1) subunit on specific striatal GABAergic interneurons and on output neurons of the globus pallidus and substantia nigra pars reticulata.
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Affiliation(s)
- Henry J Waldvogel
- Department of Anatomy with Radiology, Faculty of Medical and Health Sciences, University of Auckland, Private Bag 92019, Auckland, New Zealand.
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Boyes J, Bolam JP. The subcellular localization of GABA(B) receptor subunits in the rat substantia nigra. Eur J Neurosci 2004; 18:3279-93. [PMID: 14686901 DOI: 10.1111/j.1460-9568.2003.03076.x] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The inhibitory effects of GABA within the substantia nigra (SN) are mediated in part by metabotropic GABA(B) receptors. To better understand the mechanisms underlying these effects, we have examined the subcellular localization of the GABA(B) receptor subunits, GABA(B1) and GABA(B2), in SN neurons and afferents using pre-embedding immunocytochemistry combined with anterograde or retrograde labelling. In both the SN pars compacta (SNc) and pars reticulata (SNr), GABA(B1) and GABA(B2) showed overlapping, but distinct, patterns of immunolabelling. GABA(B1) was more strongly expressed by putative dopaminergic neurons in the SNc than by SNr projection neurons, whereas GABA(B2) was mainly expressed in the neuropil of both regions. Immunogold labelling for GABA(B1) and GABA(B2) was localized in presynaptic and postsynaptic elements throughout the SN. The majority of labelling was intracellular or was associated with extrasynaptic sites on the plasma membrane. In addition, labelling for both subunits was found on the presynaptic and postsynaptic membranes at symmetric, putative GABAergic synapses, including those formed by anterogradely labelled striatonigral and pallidonigral terminals. Labelling was also observed on the presynaptic membrane and at the edge of the postsynaptic density at asymmetric, putative excitatory synapses. Double immunolabelling, using the vesicular glutamate transporter 2, revealed the glutamatergic nature of many of the immunogold-labelled asymmetric synapses. The widespread distribution of GABA(B) subunits in the SNc and SNr suggests that GABA(B)-mediated effects in these regions are likely to be more complex than previously described, involving presynaptic autoreceptors and heteroreceptors, and postsynaptic receptors on different populations of SN neurons.
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Affiliation(s)
- Justin Boyes
- MRC Anatomical Neuropharmacology Unit, University of Oxford, Oxford OX1 3TH, UK
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Martin SC, Steiger JL, Gravielle MC, Lyons HR, Russek SJ, Farb DH. Differential expression of ?-aminobutyric acid type B receptor subunit mRNAs in the developing nervous system and receptor coupling to adenylyl cyclase in embryonic neurons. J Comp Neurol 2004; 473:16-29. [PMID: 15067715 DOI: 10.1002/cne.20094] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
gamma-Aminobutyric acid type B receptors (GABA(B)Rs) mediate both slow inhibitory synaptic activity in the adult nervous system and motility signals for migrating embryonic cortical cells. Previous papers have described the expression of GABA(B)Rs in the adult brain, but the expression and functional significance of these gene products in the embryo are largely unknown. Here we examine GABA(B)R expression from rat embryonic day 10 (E10) to E18 compared with adult and ask whether embryonic cortical neurons contain functional GABA(B)R. GABA(B)R1 transcript levels greatly exceed GABA(B)R2 levels in the developing neural tube at E11, and olfactory bulb and striatum at E17 but equalize in most regions of adult nervous tissue, except for the glomerular and granule cell layers of the main olfactory bulb and the striatum. Consistent with expression differences, the binding affinity of GABA for GABA(B)Rs is significantly lower in adult striatum compared with cerebellum. Multiple lines of evidence from in situ hybridization, RNase protection, and real-time PCR demonstrate that GABA(B)R1a, GABA(B)R1b, GABA(B)R1h (a subunit subtype, lacking a sushi domain, that we have identified in embryonic rat brain), GABA(B)R2, and GABA(B)L transcript levels are not coordinately regulated. Despite the functional requirement for a heterodimer of GABA(B)R subunits, the expression of each subunit mRNA is under independent control during embryonic development, and, by E18, GABA(B)Rs are negatively coupled to adenylyl cyclase in neocortical neurons. The presence of embryonic GABA(B)R transcripts and protein and functional receptor coupling indicates potentially important roles for GABA(B)Rs in modulation of synaptic transmission in the developing embryonic nervous system.
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Affiliation(s)
- Stella C Martin
- Laboratory of Molecular Neurobiology, Department of Pharmacology, Boston University School of Medicine, Boston, Massachusetts 02118-2394, USA
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43
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Uezono Y, Kaibara M, Hayashi H, Kawakami S, Enjoji A, Kanematsu T, Taniyama K. Characterization of GABAB Receptor in the Human Colon. J Pharmacol Sci 2004; 94:211-3. [PMID: 14978362 DOI: 10.1254/jphs.94.211] [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] [Indexed: 10/26/2022] Open
Abstract
Characterization of the GABA(B) receptor in the human colon was performed by the reverse transcription-polymerase chain reaction (RT-PCR). mRNAs for both subunits of the GABA(B) receptor, GABA(B1) and GABA(B2), were detected in the human colon. The GABA(B1(e)) isoform was detected in the human colon, but not in the brain, and the other isoforms, except GABA(B1(d)), were detected in both tissues. Thus, the GABA(B) receptor may be present as a heterodimer with subunits of GABA(B1) and GABA(B2) in the human colon.
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Affiliation(s)
- Yasuhito Uezono
- Division of Pharmacology, Department of Translational Medical Sciences, Nagasaki University Graduate School of Biomedical Sciences, Japan
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44
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López-Bendito G, Shigemoto R, Kulik A, Vida I, Fairén A, Luján R. Distribution of metabotropic GABA receptor subunits GABAB1a/b and GABAB2 in the rat hippocampus during prenatal and postnatal development. Hippocampus 2004; 14:836-48. [PMID: 15382254 DOI: 10.1002/hipo.10221] [Citation(s) in RCA: 67] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Metabotropic gamma-aminobutyric acid receptors (GABAB) play modulatory roles in central synaptic transmission and are involved in controlling neuronal migration during development. We used immunohistochemical methods to elucidate the expression pattern as well as the cellular and the precise subcellular localization of the GABA(B1a/b) and GABAB2 subunits in the rat hippocampus during prenatal and postnatal development. At the light microscopic level, both GABA(B1a/b) and GABAB2 were expressed in the hippocampal primordium from embryonic day E14. During postnatal development, immunoreactivity for GABA(B1a/b) and GABAB2 was distributed mainly in pyramidal cells, with discrete GABA(B1a/b)-immunopositive cell bodies of interneurons present throughout the hippocampus. Using double immunofluorescence, we demonstrated that during the second week of postnatal development, GABA(B1a/b) but not GABAB2 was expressed in glial cells throughout the hippocampal formation. At the electron microscopic level, GABA(B1a/b) and GABAB2 showed a similar distribution pattern during postnatal development. Thus, at all ages the two receptor subunits were located postsynaptically in dendritic spines and shafts at extrasynaptic and perisynaptic sites in both pyramidal and nonpyramidal cells. We further demonstrated that the two subunits were localized presynaptically along the extrasynaptic plasma membrane of axon terminals and along the presynaptic active zone in both asymmetrical and, to a lesser extent, symmetrical synapses. These results suggest that GABAB receptors are widely expressed in the hippocampus throughout development and that GABA(B1a/b) and GABAB2 form both pre- and postsynaptic receptors.
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Affiliation(s)
- Guillermina López-Bendito
- Centro Regional de Investigaciones Biomédicas, Facultad de Medicina, Universidad de Castilla-La Mancha, Albacete, Spain
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Wong CGT, Bottiglieri T, Snead OC. GABA, gamma-hydroxybutyric acid, and neurological disease. Ann Neurol 2003; 54 Suppl 6:S3-12. [PMID: 12891648 DOI: 10.1002/ana.10696] [Citation(s) in RCA: 339] [Impact Index Per Article: 16.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
gamma-Aminobutyric acid (GABA) is the primary inhibitory neurotransmitter in the central nervous system. GABA is converted from glutamic acid by the action of glutamic acid decarboxylase (GAD) of which two isoforms exist GAD65 and GAD67. GABA then is broken down, both within the cell and in the synaptic cleft by GABA transaminase to form succinic semialdehyde. In turn, succinic semialdehyde is converted either to succinic acid by succinic semialdehyde dehydrogenase or into gamma-hydroxybutyric acid (GHB) by succinic semialdehyde reductase. Because GABA modulates the majority of inhibition that is ongoing in the brain, perturbations in GABAergic inhibition have the potential to result in seizures. Therefore, the most common disorder in which GABA is targeted as a treatment is epilepsy. However, other disorders such as psychiatric disease, spasticity, and stiff-person syndrome all have been related to disorders of GABAergic function in the brain. This review covers the roles of GABAergic neurotransmission in epilepsy, anxiety disorders, schizophrenia, stiff-person syndrome, and premenstrual dysphoric disorder. In the final section of this review, the GABA metabolite GHB is discussed in terms of its physiological significance and its role in epilepsy, sleep disorders, drug and alcohol addiction, and an inborn error of GABA metabolism, succinic semialdehyde dehydrogenase deficiency.
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Affiliation(s)
- C Guin Ting Wong
- Institute of Medical Sciences, University of Toronto, Faculty of Medicine and Brain and Behavior Research Program, Hospital for Sick Children, Ontario, Canada
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Subcellular localization of metabotropic GABA(B) receptor subunits GABA(B1a/b) and GABA(B2) in the rat hippocampus. J Neurosci 2003. [PMID: 14657159 DOI: 10.1523/jneurosci.23-35-11026.2003] [Citation(s) in RCA: 166] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Metabotropic GABA(B) receptors mediate slow inhibitory effects presynaptically and postsynaptically. Using preembedding immunohistochemical methods combined with quantitative analysis of GABA(B) receptor subunit immunoreactivity, this study provides a detailed description of the cellular and subcellular localization of GABA(B1a/b) and GABA(B2) in the rat hippocampus. At the light microscopic level, an overlapping distribution of GABA(B1a/b) and GABA(B2) was revealed in the dendritic layers of the hippocampus. In addition, expression of the GABA(B1a/b) subunit was found in somata of CA1 pyramidal cells and of a subset of GABAergic interneurons. At the electron microscopic level, immunoreactivity for both subunits was observed on presynaptic and, more abundantly, on postsynaptic elements. Presynaptically, subunits were mainly detected in the extrasynaptic membrane and occasionally over the presynaptic membrane specialization of putative glutamatergic and, to a lesser extent, GABAergic axon terminals. Postsynaptically, the majority of GABA(B) receptor subunits were localized to the extrasynaptic plasma membrane of spines and dendritic shafts of principal cells and shafts of interneuron dendrites. Quantitative analysis revealed enrichment of GABA(B1a/b) around putative glutamatergic synapses on spines and an even distribution on dendritic shafts of pyramidal cells contacted by GABAergic boutons. The association of GABA(B) receptors with glutamatergic synapses at both presynaptic and postsynaptic sides indicates their intimate involvement in the modulation of glutamatergic neurotransmission. The dominant extrasynaptic localization of GABA(B) receptor subunits suggests that their activation is dependent on spillover of GABA requiring simultaneous activity of populations of GABAergic cells as it occurs during population oscillations or epileptic seizures.
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Johnston T, Duty S. Changes in GABA(B) receptor mRNA expression in the rodent basal ganglia and thalamus following lesion of the nigrostriatal pathway. Neuroscience 2003; 120:1027-35. [PMID: 12927208 DOI: 10.1016/s0306-4522(03)00418-4] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Loss of striatal dopaminergic innervation in Parkinson's disease (PD) is accompanied by widespread alterations in GABAergic activity within the basal ganglia and thalamus. Accompanying changes in GABA(B) receptor binding have been noted in some basal ganglia regions in parkinsonian primates, suggesting that plasticity of this receptor may also occur in PD. However, the molecular mechanisms underlying the changes in receptor binding and the manner and extent to which different GABA(B) receptor mRNA subunits and splice-variants are affected remain unknown. This study used in situ hybridisation to examine the full profile of changes in expression of the known rat GABA(B) receptor genes and gene variants in the basal ganglia and thalamus of rats, brought about by degeneration of the nigrostriatal tract. All of the GABA(B) mRNA species examined showed unique expression patterns throughout the basal ganglia and thalamus. In addition, all exhibited a marked loss of expression (between 46 and 80%) in the substantia nigra pars compacta of animals bearing a complete 6-hydroxydopamine-induced lesion of the nigrostriatal tract, confirming the presence of these variants in dopaminergic neurones in this region. Further analysis of autoradioagrams revealed additional changes only in GABA(B(1a)) mRNA in discrete anatomical regions. Expression of the GABA(B(1a)) variant was significantly increased in the substantia nigra pars reticulata (33+/-2%), entopeduncular nucleus (26+/-1%) and the subthalamic nucleus (16+/-1%). Since these regions all receive reduced GABAergic innervation following nigrostriatal tract lesioning, it is possible that the increased expression occurs as a compensatory measure. In conclusion, these data demonstrate that GABA(B) receptor genes exhibit regional- and subunit/variant-specific plasticity at the molecular level under parkinsonian conditions.
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Affiliation(s)
- T Johnston
- Neurodegenerative Disease Research Group, Wolfson Centre for Age-Related Diseases, Hodgkin Building, King's College London, Guy's Campus, SE1 1UL, London, UK
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Slugg RM, Zheng SX, Fang Y, Kelly MJ, Rønnekleiv OK. Baclofen inhibits guinea pig magnocellular neurones via activation of an inwardly rectifying K+ conductance. J Physiol 2003; 551:295-308. [PMID: 12813153 PMCID: PMC2343136 DOI: 10.1113/jphysiol.2003.041319] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
The GABAB receptors GABAB-R1 and GABAB-R2 have been cloned in several mammalian species, and the functional receptor has been shown to exist as a heterodimeric complex. We have cloned guinea pig GABAB-R1 and GABAB-R2 receptor sequences and, using in situ hybridization and immunocytochemistry for vasopressin (AVP), we found that GABAB-R1 and -R2 receptors are expressed in vasopressin neurones of the supraoptic (SON) and paraventricular nuclei (PVN). Therefore, we used both sharp electrode and whole-cell patch recording techniques to examine the effects of the selective GABAB agonist baclofen on SON and PVN magnocellular neurones and to determine the coupling of the GABAB receptor to effector pathways. Recordings were made in coronal hypothalamic slices from both female (ovariectomized) and male guinea pigs. In the presence of tetrodotoxin (TTX), baclofen hyperpolarized (DeltaVmax = 5.6 mV, EC50 = 2.3 microM) SON magnocellular neurones (n = 27) under current clamp, or induced an outward current that reversed at EK (DeltaImax = 24.2 pA) in PVN magnocellular neurones (n = 33) under voltage clamp. Seventeen of the 24 biocytin-labelled SON magnocellular neurones were identified as AVP neurones, and ten of the 33 biocytin-labelled PVN neurones were identified as AVP or neurophysin-containing neurones, although all of the cells were clustered in the vasopressin-rich core. In the absence of TTX, baclofen activated an outward K+ current that hyperpolarized SON and PVN neurones and significantly reduced their firing rate. The outward current showed inward rectification and was blocked by the K+ channel blocker barium and the GABAB receptor antagonist CGP 35348. Therefore, GABAB receptors are coupled to inwardly rectifying K+ channels in SON and PVN magnocellular neurones and may play a prominent role in modulating phasic bursting activity in guinea pig vasopressin neurones.
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Affiliation(s)
- Robert M Slugg
- Department of Physiology and Pharmacology, L334, Oregon Health Sciences University, 3181 Sam Jackson Park Road, Portland, OR 97201, USA.
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Lu J, Chen Y, Pan H, Zhang Y, Wu H, Xu K, Liu X, Jiang Y, Bao X, Shen Y, Wu X. The gene encoding GABBR1 is not associated with childhood absence epilepsy in the Chinese Han population. Neurosci Lett 2003; 343:151-4. [PMID: 12770685 DOI: 10.1016/s0304-3940(03)00316-1] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Childhood absence epilepsy (CAE) is considered to be a genetic disease, but the genes responsible for it have not yet been identified. To investigate whether or not the GABBR1 gene is a susceptibility gene for CAE in the Chinese Han population, we systematically screened all the 22 exons and nearby intron regions of the gene and found 12 single nucleotide polymorphisms (SNPs). Using four SNPs as markers, we conducted a case-control study in 96 CAE patients and 96 normal controls. There were no significant discrepancies between the cases and controls in allele and phenotype frequencies of the four SNPs. There were still no significant differences in haplotype distributions between the cases and controls. We postulate that the GABBR1 gene might not be a susceptibility gene for CAE at least in the Chinese population.
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Affiliation(s)
- Jianjun Lu
- Department of Pediatrics, Peking University First Hospital, No. 8 Xishiku Street, Beijing 100034, PR China
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Furtinger S, Bettler B, Sperk G. Altered expression of GABAB receptors in the hippocampus after kainic-acid-induced seizures in rats. BRAIN RESEARCH. MOLECULAR BRAIN RESEARCH 2003; 113:107-15. [PMID: 12750012 DOI: 10.1016/s0169-328x(03)00097-4] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Epilepsy is closely related to an altered transmission of GABA, the major inhibitory transmitter in the brain. GABA acts through two classes of receptors, ionotropic GABA(A) receptors and metabotropic GABA(B) receptors. Using in situ hybridization, receptor autoradiography and immunocytochemistry, we now investigated temporal changes in the expression the GABA(B)-1 and GABA(B)-2 subunits (GABA(B)-1R and GABA(B)-1R, respectively) in the hippocampus following kainic-acid-induced seizures. Significant decreases (by about 40%) in mRNA levels of both splice variants (a and b) of GABA(B)-1R and of GABA(B)-2R were observed in the principal cell layer of the hippocampus 6-12 h after kainic acid injection in the rat. Whereas mRNA levels in the granule cell layer returned to basal after 24 h, the decreases persisted in sectors CA1 and CA3, presumably due to progressing neurodegeneration. In the sector CA3, GABA(B)-R mRNA levels and GABA(B)-R1 immunoreactivity partially recovered 30 days after the initial kainic acid seizures indicating receptor upregulation in surviving neurons.
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Affiliation(s)
- Sabine Furtinger
- Department of Pharmacology, University of Innsbruck, Peter-Mayr-Strasse 1a, Austria
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