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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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Vlachou S. A Brief History and the Significance of the GABA B Receptor. Curr Top Behav Neurosci 2021; 52:1-17. [PMID: 34595739 DOI: 10.1007/7854_2021_264] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
γ-Aminobutyric acid (GABA) is the main inhibitory neurotransmitter in the brain. GABA type B (GABAB) receptors (GABABRs) are the only metabotropic G protein-coupled receptors for GABA and can be found distributed not only in the central nervous system, but also in the periphery. This chapter introduces important, fundamental knowledge related to GABABR function and the various potential therapeutic applications of the development of novel GABABR-active compounds, as documented through extensive studies presented in subsequent chapters of this Current Topic in Behavioral Neurosciences volume on the role of the neurobiology of GABABR function. The compounds that have received increased attention in the last few years compared to GABABR agonists and antagonists - the positive allosteric modulators - exhibit better pharmacological profiles and fewer side effects. As we continue to unveil the mystery of GABABRs at the molecular and cellular levels, we further understand the significance of these receptors. Future directions should aim for developing highly selective GABABR compounds for treating neuropsychiatric disorders and their symptomatology.
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Affiliation(s)
- Styliani Vlachou
- Neuropsychopharmacology Division, Behavioural Neuroscience Laboratory, School of Psychology, Faculty of Science and Health, Dublin City University, Dublin, Ireland.
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3
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Increased Excitatory Synaptic Transmission Associated with Adult Seizure Vulnerability Induced by Early-Life Inflammation in Mice. J Neurosci 2021; 41:4367-4377. [PMID: 33827934 DOI: 10.1523/jneurosci.2667-20.2021] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2020] [Revised: 03/24/2021] [Accepted: 03/28/2021] [Indexed: 12/27/2022] Open
Abstract
Early-life inflammatory stress increases seizure susceptibility later in life. However, possible sex- and age-specific differences and the associated mechanisms are largely unknown. C57BL/6 mice were bred in house, and female and male pups were injected with lipopolysaccharide (LPS; 100 μg/kg, i.p.) or vehicle control (saline solution) at postnatal day 14 (P14). Seizure threshold was assessed in response to pentylenetetrazol (1% solution, i.v.) in adolescence (∼P40) and adulthood (∼P60). We found that adult, but not adolescent, mice treated with LPS displayed ∼34% lower seizure threshold compared with controls. Females and males showed similar increased seizure susceptibility, suggesting that altered brain excitability was age dependent, but not sex dependent. Whole-cell recordings revealed no differences in excitatory synaptic activity onto CA1 pyramidal neurons from control or neonatally inflamed adolescent mice of either sex. However, adult mice of both sexes previously exposed to LPS displayed spontaneous EPSC frequency approximately twice that of controls, but amplitude was unchanged. Although these changes were not associated with alterations in dendritic spines or in the NMDA/AMPA receptor ratio, they were linked to an increased glutamate release probability from Schaffer collateral, but not temporoammonic pathway. This glutamate increase was associated with reduced activity of presynaptic GABAB receptors and was independent of the endocannabinoid-mediated suppression of excitation. Our new findings demonstrate that early-life inflammation leads to long-term increased hippocampal excitability in adult female and male mice associated with changes in glutamatergic synaptic transmission. These alterations may contribute to enhanced vulnerability of the brain to subsequent pathologic challenges such as epileptic seizures.SIGNIFICANCE STATEMENT Adult physiology has been shown to be affected by early-life inflammation. Our data reveal that early-life inflammation increases excitatory synaptic transmission onto hippocampal CA1 pyramidal neurons in an age-dependent manner through disrupted presynaptic GABAB receptor activity on Schaffer collaterals. This hyperexcitability was seen only in adult, and not in adolescent, animals of either sex. The data suggest a maturation process, independent of sex, in the priming action of early-life inflammation and highlight the importance of studying mature brains to reveal cellular changes associated with early-life interventions.
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Naik R, Valentine H, Dannals RF, Wong DF, Horti AG. Synthesis and Evaluation of a New 18F-Labeled Radiotracer for Studying the GABA B Receptor in the Mouse Brain. ACS Chem Neurosci 2018; 9:1453-1461. [PMID: 29498831 DOI: 10.1021/acschemneuro.8b00038] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
New GABAB agonists, fluoropyridyl ether analogues of baclofen, have been synthesized as potential PET radiotracers. The compound with highest inhibition binding affinity as well as greatest agonist response, ( R)-4-amino-3-(4-chloro-3-((2-fluoropyridin-4-yl)methoxy)phenyl)butanoic acid (1b), was radiolabeled with 18F with good radiochemical yield, high radiochemical purity, and high molar radioactivity. The regional brain distribution of the radiolabeled ( R)-4-amino-3-(4-chloro-3-((2-[18F]fluoropyridin-4-yl)methoxy)phenyl)butanoic acid, [18F]1b, was studied in CD-1 male mice. The study demonstrated that [18F]1b enters the mouse brain (1% ID/g tissue). The accumulation of [18F]1b in the mouse brain was inhibited (35%) by preinjection of GABAB agonist 1a, suggesting that the radiotracer brain uptake is partially mediated by GABAB receptors. The presented data demonstrate a feasibility of imaging of GABAB receptors in rodents and justify further development of GABAB PET tracers with improved specific binding and greater blood-brain barrier permeability.
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Affiliation(s)
- Ravi Naik
- Department of Radiology, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21287 United States
| | - Heather Valentine
- Department of Radiology, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21287 United States
| | - Robert F. Dannals
- Department of Radiology, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21287 United States
| | - Dean F. Wong
- Department of Radiology, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21287 United States
| | - Andrew G. Horti
- Department of Radiology, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21287 United States
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TERUNUMA M. Diversity of structure and function of GABA B receptors: a complexity of GABA B-mediated signaling. PROCEEDINGS OF THE JAPAN ACADEMY. SERIES B, PHYSICAL AND BIOLOGICAL SCIENCES 2018; 94:390-411. [PMID: 30541966 PMCID: PMC6374141 DOI: 10.2183/pjab.94.026] [Citation(s) in RCA: 71] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/01/2018] [Accepted: 10/09/2018] [Indexed: 05/24/2023]
Abstract
γ-aminobutyric acid type B (GABAB) receptors are broadly expressed in the nervous system and play an important role in neuronal excitability. GABAB receptors are G protein-coupled receptors that mediate slow and prolonged inhibitory action, via activation of Gαi/o-type proteins. GABAB receptors mediate their inhibitory action through activating inwardly rectifying K+ channels, inactivating voltage-gated Ca2+ channels, and inhibiting adenylate cyclase. Functional GABAB receptors are obligate heterodimers formed by the co-assembly of R1 and R2 subunits. It is well established that GABAB receptors interact not only with G proteins and effectors but also with various proteins. This review summarizes the structure, subunit isoforms, and function of GABAB receptors, and discusses the complexity of GABAB receptors, including how receptors are localized in specific subcellular compartments, the mechanism regulating cell surface expression and mobility of the receptors, and the diversity of receptor signaling through receptor crosstalk and interacting proteins.
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Affiliation(s)
- Miho TERUNUMA
- Division of Oral Biochemistry, Graduate School of Medical and Dental Sciences, Niigata University, Niigata, Japan
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6
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Trist DG, Kenakin TP, Blackburn TP. In memory of Norman Bowery (1944-2016). Curr Opin Pharmacol 2017; 35:89-93. [PMID: 28864032 DOI: 10.1016/j.coph.2017.05.008] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2017] [Revised: 05/25/2017] [Accepted: 05/25/2017] [Indexed: 11/25/2022]
Abstract
This article is in memory of Professor Norman Bowery (1944-2016). Norman was a pharmacologist who spent most of his career researching the pharmacology of γ-aminobutyric acid (GABA). He discovered a novel metabotropic receptor subtype, GABAB, that is pharmacologically, and structurally different from the original ionotropic receptor now designated as GABAA. In his research he also studied the neurotransmitters glutamate and substance P, two molecules whose release in parts of the spinal cord is inhibited by baclofen a GABAB receptor agonist. Norman was interested in the therapeutic potential of interacting with the GABAB receptor, in particular spasticity, pain and absence epilepsy.
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Affiliation(s)
| | - Terry P Kenakin
- Department of Pharmacology, 120 Mason Farm Road, 4009 Genetic Medicine Bldg, Campus Box 7365, UNC-Chapel Hill, Chapel Hill, NC 27599-7365, United States
| | - Thomas P Blackburn
- TPBioventures Ltd., Turnpike House, 1208/1210 London Road, Leigh on Sea, Essex, England SS9 2UA, UK
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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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Neuroprotective role of GABAB receptor modulation against streptozotocin-induced behavioral and biochemical abnormalities in rats. Neuroscience 2017; 357:67-74. [DOI: 10.1016/j.neuroscience.2017.05.054] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2016] [Revised: 05/22/2017] [Accepted: 05/30/2017] [Indexed: 11/18/2022]
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9
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Rocha L, Alonso-Vanegas M, Martínez-Juárez IE, Orozco-Suárez S, Escalante-Santiago D, Feria-Romero IA, Zavala-Tecuapetla C, Cisneros-Franco JM, Buentello-García RM, Cienfuegos J. GABAergic alterations in neocortex of patients with pharmacoresistant temporal lobe epilepsy can explain the comorbidity of anxiety and depression: the potential impact of clinical factors. Front Cell Neurosci 2015; 8:442. [PMID: 25601827 PMCID: PMC4283637 DOI: 10.3389/fncel.2014.00442] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2014] [Accepted: 12/08/2014] [Indexed: 01/12/2023] Open
Abstract
Temporal lobe epilepsy (TLE) is a chronic neurodegenerative disease with a high prevalence of psychiatric disorders. Temporal neocortex contributes to either seizure propagation or generation in TLE, a situation that has been associated with alterations of the γ-amino-butyric acid (GABA) system. On the other hand, an impaired neurotransmission mediated by GABA in temporal neocortex has also been involved with the pathophysiology of psychiatric disorders. In spite of these situations, the role of the necortical GABA system in the comorbidity of TLE and mood disorders has not been investigated. The present study was designed to identify alterations in the GABA system such as binding to GABAA and GABAB receptors and benzodiazepine site, the tissue content of GABA and the expression of the mRNA encoding the α1–6, β1–3, and γ GABAA subunits, in the temporal neocortex of surgically treated patients with TLE with and without anxiety, and/or depression. Neocortex of patients with TLE and comorbid anxiety and/or depression showed increased expression of the mRNA encoding the γ2-subunit, reduced GABAB-induced G-protein activation in spite of elevated GABAB binding, and lower tissue content of GABA when compared to autopsy controls. Some of these changes significantly correlated with seizure frequency and duration of epilepsy. The results obtained suggest a dysfunction of the GABAergic neurotransmission in temporal neocortex of patients with TLE and comorbid anxiety and/or depression that could be also influenced by clinical factors such as seizure frequency and duration of illness.
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Affiliation(s)
- Luisa Rocha
- Department of Pharmacobiology, Center for Research and Advanced Studies of the National Polytechnic Institute (CINVESTAV) , Mexico City , Mexico
| | - Mario Alonso-Vanegas
- National Institute of Neurology and Neurosurgery "Manuel Velasco Suarez" , Mexico City , Mexico
| | - Iris E Martínez-Juárez
- National Institute of Neurology and Neurosurgery "Manuel Velasco Suarez" , Mexico City , Mexico
| | - Sandra Orozco-Suárez
- Unit for Medical Research in Neurological Diseases, National Medical Center , Mexico City , Mexico
| | - David Escalante-Santiago
- Unit for Medical Research in Neurological Diseases, National Medical Center , Mexico City , Mexico
| | | | - Cecilia Zavala-Tecuapetla
- Department of Pharmacobiology, Center for Research and Advanced Studies of the National Polytechnic Institute (CINVESTAV) , Mexico City , Mexico
| | | | | | - Jesús Cienfuegos
- National Institute of Neurology and Neurosurgery "Manuel Velasco Suarez" , Mexico City , Mexico
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10
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Rocha L, Alonso-Vanegas M, Martínez-Juárez IE, Orozco-Suárez S, Escalante-Santiago D, Feria-Romero IA, Zavala-Tecuapetla C, Cisneros-Franco JM, Buentello-García RM, Cienfuegos J. GABAergic alterations in neocortex of patients with pharmacoresistant temporal lobe epilepsy can explain the comorbidity of anxiety and depression: the potential impact of clinical factors. Front Cell Neurosci 2015. [PMID: 25601827 DOI: 10.3389/fnce1.2014.00442] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Temporal lobe epilepsy (TLE) is a chronic neurodegenerative disease with a high prevalence of psychiatric disorders. Temporal neocortex contributes to either seizure propagation or generation in TLE, a situation that has been associated with alterations of the γ-amino-butyric acid (GABA) system. On the other hand, an impaired neurotransmission mediated by GABA in temporal neocortex has also been involved with the pathophysiology of psychiatric disorders. In spite of these situations, the role of the necortical GABA system in the comorbidity of TLE and mood disorders has not been investigated. The present study was designed to identify alterations in the GABA system such as binding to GABAA and GABAB receptors and benzodiazepine site, the tissue content of GABA and the expression of the mRNA encoding the α1-6, β1-3, and γ GABAA subunits, in the temporal neocortex of surgically treated patients with TLE with and without anxiety, and/or depression. Neocortex of patients with TLE and comorbid anxiety and/or depression showed increased expression of the mRNA encoding the γ2-subunit, reduced GABAB-induced G-protein activation in spite of elevated GABAB binding, and lower tissue content of GABA when compared to autopsy controls. Some of these changes significantly correlated with seizure frequency and duration of epilepsy. The results obtained suggest a dysfunction of the GABAergic neurotransmission in temporal neocortex of patients with TLE and comorbid anxiety and/or depression that could be also influenced by clinical factors such as seizure frequency and duration of illness.
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Affiliation(s)
- Luisa Rocha
- Department of Pharmacobiology, Center for Research and Advanced Studies of the National Polytechnic Institute (CINVESTAV) , Mexico City , Mexico
| | - Mario Alonso-Vanegas
- National Institute of Neurology and Neurosurgery "Manuel Velasco Suarez" , Mexico City , Mexico
| | - Iris E Martínez-Juárez
- National Institute of Neurology and Neurosurgery "Manuel Velasco Suarez" , Mexico City , Mexico
| | - Sandra Orozco-Suárez
- Unit for Medical Research in Neurological Diseases, National Medical Center , Mexico City , Mexico
| | - David Escalante-Santiago
- Unit for Medical Research in Neurological Diseases, National Medical Center , Mexico City , Mexico
| | | | - Cecilia Zavala-Tecuapetla
- Department of Pharmacobiology, Center for Research and Advanced Studies of the National Polytechnic Institute (CINVESTAV) , Mexico City , Mexico
| | | | | | - Jesús Cienfuegos
- National Institute of Neurology and Neurosurgery "Manuel Velasco Suarez" , Mexico City , Mexico
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Therapeutic potential of GABA(B) receptor ligands in drug addiction, anxiety, depression and other CNS disorders. Pharmacol Biochem Behav 2013; 110:174-84. [PMID: 23872369 DOI: 10.1016/j.pbb.2013.07.003] [Citation(s) in RCA: 71] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/28/2013] [Revised: 06/27/2013] [Accepted: 07/05/2013] [Indexed: 01/06/2023]
Abstract
Glutamate and γ-aminobutyric acid (GABA) are the major excitatory and inhibitory neurotransmitter systems, respectively in the central nervous system (CNS). Dysregulation, in any of these or both, has been implicated in various CNS disorders. GABA acts via ionotropic (GABA(A) and GABA(C) receptor) and metabotropic (GABA(B)) receptor. Dysregulation of GABAergic signaling and alteration in GABA(B) receptor expression has been implicated in various CNS disorders. Clinically, baclofen-a GABA(B) receptor agonist is available for the treatment of spasticity, dystonia etc., associated with various neurological disorders. Moreover, GABAB receptor ligands has also been suggested to be beneficial in various neuropsychiatric and neurodegenerative disorders. The present review is aimed to discuss the role of GABA(B) receptors and the possible outcomes of GABA(B) receptor modulation in CNS disorders.
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Froestl W. Chemistry and Pharmacology of GABAB Receptor Ligands. GABABRECEPTOR PHARMACOLOGY - A TRIBUTE TO NORMAN BOWERY 2010; 58:19-62. [DOI: 10.1016/s1054-3589(10)58002-5] [Citation(s) in RCA: 102] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
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Hüttmann K, Yilmazer-Hanke D, Seifert G, Schramm J, Pape HC, Steinhäuser C. Molecular and functional properties of neurons in the human lateral amygdala. Mol Cell Neurosci 2006; 31:210-7. [PMID: 16214367 DOI: 10.1016/j.mcn.2005.09.011] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2005] [Revised: 08/30/2005] [Accepted: 09/09/2005] [Indexed: 11/25/2022] Open
Abstract
Neuronal properties were investigated through patch-clamp recording in situ in surgical specimens of the human lateral amygdala (LA) obtained from patients with intractable temporal lobe epilepsy. Projection neurons displayed spiny dendrites, action potentials with varying degree of frequency adaptation, and an inwardly rectifying K+ (Kir) conductance coupled to GABA(B) receptors. In interneurons, dendrites were spineless or sparsely spiny, action potentials were shorter than those in projection neurons and often occurred spontaneously, and GABA(B) receptor-mediated responses were lacking. Single-cell RT-PCR demonstrated expression of Kir channel subunits Kir3.1 and Kir3.2 and of vesicular glutamate transporters VGLUT1 and VGLUT2 in projection neurons. It is concluded that projection neurons and interneurons of the human LA can be distinguished based upon morphological, electrophysiological, and molecular biological criteria. The most striking difference relates to the expression of postsynaptic GABA(B) receptors coupled to Kir3 channels in projection neurons and the lack of functional GABA(B) receptors in interneurons.
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Affiliation(s)
- Kerstin Hüttmann
- Experimental Neurobiology, Neurosurgery, University of Bonn, Sigmund Freud Str. 25, D-53105 Bonn, Germany
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Enna SJ, Bowery NG. GABA(B) receptor alterations as indicators of physiological and pharmacological function. Biochem Pharmacol 2005; 68:1541-8. [PMID: 15451397 DOI: 10.1016/j.bcp.2004.06.037] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2004] [Accepted: 06/21/2004] [Indexed: 11/15/2022]
Abstract
Given the widespread distribution of GABA(B) receptors throughout the central nervous system, and within certain peripheral organs, it is likely their selective pharmacological manipulation could be of benefit in the treatment of a variety of disorders. Studies aimed at defining the clinical potential of GABA(B) receptor agonists and antagonists have included gene deletion experiments, examination of changes in receptor binding, subunit expression and function in diseased tissue, as well as after the chronic administration of drugs. The results indicate that a functional GABA(B) receptor requires the combination of GABA(B(1)) and GABA(B(2)) subunits, that receptor function does not always correlate with subunit expression and receptor binding, and that GABA(B) receptor modifications may be associated with the clinical response to antidepressants, mood stabilizers, and GABA(B) receptor agonists and antagonists. Moreover, changes in GABA(B) binding or expression suggest this receptor may be involved in mediating symptoms associated with chronic pain, epilepsy and schizophrenia. This, together with results from other types of studies, indicates the potential therapeutic value of developing drugs capable of selectively activating, inhibiting, or modulating GABA(B) receptor function.
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Affiliation(s)
- S J Enna
- Department of Pharmacology, Toxicology and Therapeutics, University of Kansas Medical School, 3901 Rainbow Boulevard, Mail Stop 1018, Kansas City, Kansas 66160-0227, USA.
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Steiger JL, Bandyopadhyay S, Farb DH, Russek SJ. cAMP response element-binding protein, activating transcription factor-4, and upstream stimulatory factor differentially control hippocampal GABABR1a and GABABR1b subunit gene expression through alternative promoters. J Neurosci 2005; 24:6115-26. [PMID: 15240803 PMCID: PMC6729677 DOI: 10.1523/jneurosci.1200-04.2004] [Citation(s) in RCA: 76] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Expression of metabotropic GABA(B) receptors is essential for slow inhibitory synaptic transmission in the CNS, and disruption of GABA(B) receptor-mediated responses has been associated with several disorders, including neuropathic pain and epilepsy. The location of GABA(B) receptors in neurons determines their specific role in synaptic transmission, and it is believed that sorting of subunit isoforms, GABA(B)R1a and GABA(B)R1b, to presynaptic or postsynaptic membranes helps to determine this role. GABA(B)R1a and GABA(B)R1b are thought to arise by alternative splicing of heteronuclear RNA. We now demonstrate that alternative promoters, rather than alternative splicing, produce GABA(B)R1a and GABA(B)R1b isoforms. Our data further show that subunit gene expression in hippocampal neurons is mediated by the cAMP response element-binding protein (CREB) by binding to unique cAMP response elements in the alternative promoter regions. Double-stranded oligonucleotide decoys selectively alter levels of endogenous GABA(B)R1a and GABA(B)R1b in primary hippocampal neurons, and CREB knock-out mice show changes in levels of GABA(B)R1a and GABA(B)R1b transcripts, consistent with decoy competition experiments. These results demonstrate a critical role of CREB in transcriptional mechanisms that control GABA(B)R1 subunit levels in vivo. In addition, the CREB-related factor activating transcription factor-4 (ATF4) has been shown to interact directly with GABA(B)R1 in neurons, and we show that ATF4 differentially regulates GABA(B)R1a and GABA(B)R1b promoter activity. These results, together with our finding that the depolarization-sensitive upstream stimulatory factor (USF) binds to a composite CREB/ATF4/USF regulatory element only in the absence of CREB binding, indicate that selective control of alternative GABA(B)R1 promoters by CREB, ATF4, and USF may dynamically regulate expression of their gene products in the nervous system.
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Affiliation(s)
- Janine L Steiger
- Laboratory of Molecular Neurobiology, Department of Pharmacology, Boston University School of Medicine, Boston, Massachusetts 02118, USA
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Avoli M, Benini R, de Guzman P, Omar A. GABA(B) receptor activation and limbic network ictogenesis. Neuropharmacology 2004; 46:43-51. [PMID: 14654096 DOI: 10.1016/s0028-3908(03)00307-1] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Rat brain slices containing interconnected hippocampus and entorhinal cortex (EC) responded to 4-aminopyridine (50 microM) application by generating: (i) CA3-driven interictal discharges that propagated to the EC; and (ii) N-methyl-D-aspartic (NMDA) acid receptor-dependent ictal events originating in EC (cf. J. Neurosci. 17 (1997) 9308 for experiments made in brain slices). Ictal discharges disappeared within 1-2 h, but were re-established by cutting the Schaffer collaterals, which abolished CA3-driven interictal discharge propagation to EC. In intact slices, GABA(B) receptor activation by baclofen (5-40 microM): (i) depressed CA3-driven interictal activity; and (ii) disclosed non-NMDA glutamatergic receptor-dependent ictal discharges originating in CA3 and propagating to EC. These effects were reversed by the GABA(B) receptor antagonist CGP 35348 (0.5 mM). Application of increasing baclofen doses to slices in which hippocampus and EC networks were surgically isolated decreased epileptiform events with an IC50 that was lower in EC (0.6 microM; n = 12) than in CA3 (2.5 microM; n = 12). Hence, under control conditions, EC ictogenesis depends on NMDA receptor function and is controlled by CA3-driven output activity; in contrast, following GABA(B) receptor activation EC excitability is depressed to a greater extent than CA3, which leads to non-NMDA glutamatergic receptor-mediated ictogenesis in CA3. We propose that GABA(B) receptor modulation may represent an important mechanism for setting the site of initiation, the modalities of propagation and the glutamatergic receptor properties of ictogenesis in the limbic system and, perhaps, in mesial temporal lobe epilepsy patients.
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Affiliation(s)
- Massimo Avoli
- Departments of Neurology and Neurosurgery, and of Physiology, Montreal Neurological Institute, McGill University, Montreal, QC, Canada H3A 2B4.
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Furtinger S, Pirker S, Czech T, Baumgartner C, Sperk G. Increased expression of gamma-aminobutyric acid type B receptors in the hippocampus of patients with temporal lobe epilepsy. Neurosci Lett 2004; 352:141-5. [PMID: 14625043 DOI: 10.1016/j.neulet.2003.08.046] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
Malfunctioning of the GABA-ergic system has been postulated as a possible cause of epilepsy. We investigated changes in the mRNA expression of the GABA(B) receptor subtypes GABA(B)-R1 and GABA(B)-R2 and of GABA(B) receptor binding in the hippocampus of patients with temporal lobe epilepsy (TLE) compared with post-mortem controls. In patients with Ammon's horn sclerosis, significant decreases in [3H]CG54626A binding were observed in subfields CA1 and CA3 of the hippocampus proper and the dentate hilus. On the other hand, both GABA(B) receptor mRNAs and receptor binding were enhanced after correction for neuronal loss in dentate granule cells and in the molecular layer, respectively, and the subiculum of patients with and without hippocampal sclerosis. These increases were even more pronounced when correcting the values for cell losses in the respective areas and indicated also increased expression of GABA(B)-R in the dentate hilus. Increased expression of both subtypes of GABA(B) receptors indicates augmented presynaptic inhibition of glutamate release as a possible protective mechanism in TLE.
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Affiliation(s)
- Sabine Furtinger
- Department of Pharmacology, University of Innsbruck, 6020 Innsbruck, Austria
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18
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Plasticity of GABA(B) receptor-mediated heterosynaptic interactions at mossy fibers after status epilepticus. J Neurosci 2004. [PMID: 14673002 DOI: 10.1523/jneurosci.23-36-11382.2003] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Several neurotransmitters, including GABA acting at presynaptic GABA(B) receptors, modulate glutamate release at synapses between hippocampal mossy fibers and CA3 pyramidal neurons. This phenomenon gates excitation of the hippocampus and may therefore prevent limbic seizure propagation. Here we report that status epilepticus, triggered by either perforant path stimulation or pilocarpine administration, was followed 24 hr later by a loss of GABA(B) receptor-mediated heterosynaptic depression among populations of mossy fibers. This was accompanied by a decrease in the sensitivity of mossy fiber transmission to the exogenous GABA(B) receptor agonist baclofen. Autoradiography revealed a reduction in GABA(B) receptor binding in the stratum lucidum after status epilepticus. Failure of GABA(B) receptor-mediated modulation of mossy fiber transmission at mossy fibers may contribute to the development of spontaneous seizures after status epilepticus.
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19
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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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20
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Chandler KE, Princivalle AP, Fabian-Fine R, Bowery NG, Kullmann DM, Walker MC. Plasticity of GABA(B) receptor-mediated heterosynaptic interactions at mossy fibers after status epilepticus. J Neurosci 2003; 23:11382-91. [PMID: 14673002 PMCID: PMC6740526] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/27/2023] Open
Abstract
Several neurotransmitters, including GABA acting at presynaptic GABA(B) receptors, modulate glutamate release at synapses between hippocampal mossy fibers and CA3 pyramidal neurons. This phenomenon gates excitation of the hippocampus and may therefore prevent limbic seizure propagation. Here we report that status epilepticus, triggered by either perforant path stimulation or pilocarpine administration, was followed 24 hr later by a loss of GABA(B) receptor-mediated heterosynaptic depression among populations of mossy fibers. This was accompanied by a decrease in the sensitivity of mossy fiber transmission to the exogenous GABA(B) receptor agonist baclofen. Autoradiography revealed a reduction in GABA(B) receptor binding in the stratum lucidum after status epilepticus. Failure of GABA(B) receptor-mediated modulation of mossy fiber transmission at mossy fibers may contribute to the development of spontaneous seizures after status epilepticus.
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Affiliation(s)
- Kate E Chandler
- Institute of Neurology, University College London, London WC1N 3BG, United Kingdom
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21
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Straessle A, Loup F, Arabadzisz D, Ohning GV, Fritschy JM. Rapid and long-term alterations of hippocampal GABAB receptors in a mouse model of temporal lobe epilepsy. Eur J Neurosci 2003; 18:2213-26. [PMID: 14622182 DOI: 10.1046/j.1460-9568.2003.02964.x] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Alterations of gamma-aminobutyric acid (GABA)B receptor expression have been reported in human temporal lobe epilepsy (TLE). Here, changes in regional and cellular expression of the GABAB receptor subunits R1 (GBR1) and R2 (GBR2) were investigated in a mouse model that replicates major functional and histopathological features of TLE. Adult mice received a single, unilateral injection of kainic acid (KA) into the dorsal hippocampus, and GABAB receptor immunoreactivity was analysed between 1 day and 3 months thereafter. In control mice, GBR1 and GBR2 were distributed uniformly across the dendritic layers of CA1-CA3 and dentate gyrus. In addition, some interneurons were labelled selectively for GBR1. At 1 day post-KA, staining for both GBR1 and GBR2 was profoundly reduced in CA1, CA3c and the hilus, and no interneurons were visible anymore. At later stages, the loss of GABAB receptors persisted in CA1 and CA3, whereas staining increased gradually in dentate gyrus granule cells, which become dispersed in this model. Most strikingly, a subpopulation of strongly labelled interneurons reappeared, mainly in the hilus and CA3 starting at 1 week post-KA. In double-staining experiments, these cells were selectively labelled for neuropeptide Y. The number of GBR1-positive interneurons also increased contralaterally in the hilus. The rapid KA-induced loss of GABAB receptors might contribute to epileptogenesis because of a reduction in both presynaptic control of transmitter release and postsynaptic inhibition. In turn, the long-term increase in GABAB receptors in granule cells and specific subtypes of interneurons may represent a compensatory response to recurrent seizures.
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Affiliation(s)
- Andrea Straessle
- Institute of Pharmacology and Toxicology, University of Zurich, Switzerland
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Princivalle AP, Duncan JS, Thom M, Bowery NG. GABA(B1a), GABA(B1b) AND GABA(B2) mRNA variants expression in hippocampus resected from patients with temporal lobe epilepsy. Neuroscience 2003; 122:975-84. [PMID: 14643764 DOI: 10.1016/j.neuroscience.2003.08.044] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
The aim of this study was to investigate the mRNA expression of the two GABA(B1) receptor isoforms and the GABA(B2) subunit, in human postmortem control hippocampal sections and in sections resected from epilepsy patients using quantitative in situ hybridisation autoradiography. Utilising human control hippocampal sections it was shown that the oligonucleotides employed were specific to the receptor. Hippocampal slices from surgical specimens obtained from patients with hippocampal sclerosis and temporal lobe epilepsy were compared with neurologically normal postmortem control subjects for neuropathology and GABA(B) mRNA expression. Neuronal loss was observed in most of the hippocampal subregions, but in the subiculum no significant difference was detected. The localisation of GABA(B1a) and GABA(B1b) isoform mRNAs in human control hippocampal sections supported and extended earlier studies using the GABA(B1) pan probe, which does not distinguish between the two GABA(B1) isoforms. Moreover, the GABA(B2) mRNA location confirmed the heterodimerisation of the receptor. Thus, although there was an apparent correlation between GABA(B1b) and GABA(B2), GABA(B1a) exhibited no such relationship. GABA(B1b) and GABA(B2) showed a similar intensity of expression whilst GABA(B1a) displayed a lower hybridisation signal. Comparison of the expression of the three mRNAs between control and epileptic subjects showed significant decreases or increases in different hippocampal subregions.GABA(B) isoforms and subunit mRNA expression per remaining neuron was significantly increased in the hilus and dentate gyrus. These results demonstrate that altered GABA(B) receptor mRNA expression occurs in human TLE; possibly the observed changes may also serve to counteract ongoing hyperexcitability.
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MESH Headings
- Adult
- Aged
- Aged, 80 and over
- Epilepsy, Temporal Lobe/genetics
- Epilepsy, Temporal Lobe/metabolism
- Epilepsy, Temporal Lobe/pathology
- Female
- Gene Expression Regulation/physiology
- Genetic Variation/physiology
- Hippocampus/metabolism
- Hippocampus/pathology
- Humans
- Male
- Middle Aged
- Protein Isoforms/biosynthesis
- Protein Isoforms/genetics
- RNA, Messenger/biosynthesis
- RNA, Messenger/genetics
- Receptors, GABA/biosynthesis
- Receptors, GABA/genetics
- Receptors, GABA-B/biosynthesis
- Receptors, GABA-B/genetics
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Affiliation(s)
- A P Princivalle
- Department of Pharmacology, Medical School, University of Birmingham, Birmingham B15 2TT, UK.
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