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Colmers PLW, Arshad MN, Mukherjee J, Lin S, Ng SFJ, Sarmiere P, Davies PA, Moss SJ. Sustained Inhibition of GABA-AT by OV329 Enhances Neuronal Inhibition and Prevents Development of Benzodiazepine Refractory Seizures. eNeuro 2024; 11:ENEURO.0137-24.2024. [PMID: 38937107 PMCID: PMC11236575 DOI: 10.1523/eneuro.0137-24.2024] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2024] [Revised: 06/18/2024] [Accepted: 06/24/2024] [Indexed: 06/29/2024] Open
Abstract
γ-Aminobutyric acid (GABA) is the principal inhibitory neurotransmitter in the adult brain which mediates its rapid effects on neuronal excitability via ionotropic GABAA receptors. GABA levels in the brain are critically dependent upon GABA-aminotransferase (GABA-AT) which promotes its degradation. Vigabatrin, a low-affinity GABA-AT inhibitor, exhibits anticonvulsant efficacy, but its use is limited due to cumulative ocular toxicity. OV329 is a rationally designed, next-generation GABA-AT inhibitor with enhanced potency. We demonstrate that sustained exposure to OV329 in mice reduces GABA-AT activity and subsequently elevates GABA levels in the brain. Parallel increases in the efficacy of GABAergic inhibition were evident, together with elevations in electroencephalographic delta power. Consistent with this, OV329 exposure reduced the severity of status epilepticus and the development of benzodiazepine refractory seizures. Thus, OV329 may be of utility in treating seizure disorders and associated pathologies that result from neuronal hyperexcitability.
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Affiliation(s)
- Phillip L W Colmers
- Department of Neuroscience, Tufts University School of Medicine, Boston, Massachusetts 02111
| | - Muhammad Nauman Arshad
- Department of Neuroscience, Tufts University School of Medicine, Boston, Massachusetts 02111
| | | | | | - Shu Fun Josephine Ng
- Department of Neuroscience, Tufts University School of Medicine, Boston, Massachusetts 02111
| | | | - Paul A Davies
- Department of Neuroscience, Tufts University School of Medicine, Boston, Massachusetts 02111
| | - Stephen J Moss
- Department of Neuroscience, Tufts University School of Medicine, Boston, Massachusetts 02111
- Department of Neuroscience, Physiology and Pharmacology, University College London, London WC1 6BT, United Kingdom
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2
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Portugal CC. Ascorbate and its transporter SVCT2: The dynamic duo's integrated roles in CNS neurobiology and pathophysiology. Free Radic Biol Med 2024; 212:448-462. [PMID: 38182073 DOI: 10.1016/j.freeradbiomed.2023.12.040] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/11/2023] [Revised: 12/11/2023] [Accepted: 12/27/2023] [Indexed: 01/07/2024]
Abstract
Ascorbate is a small antioxidant molecule essential for the proper development and function of the brain. Ascorbate is transported into the brain and between brain cells via the Sodium vitamin C co-transporter 2 (SVCT2). This review provides an in-depth analysis of ascorbate's physiology, including how ascorbate is absorbed from food into the CNS, emphasizing cellular mechanisms of ascorbate recycling and release in different CNS compartments. Additionally, the review delves into the various functions of ascorbate in the CNS, including its impact on epigenetic modulation, synaptic plasticity, and neurotransmission. It also emphasizes ascorbate's role on neuromodulation and its involvement in neurodevelopmental processes and disorders. Furthermore, it analyzes the relationship between the duo ascorbate/SVCT2 in neuroinflammation, particularly its effects on microglial activation, cytokine release, and oxidative stress responses, highlighting its association with neurodegenerative diseases, such as Alzheimer's disease (AD). Overall, this review emphasizes the crucial role of the dynamic duo ascorbate/SVCT2 in CNS physiology and pathology and the need for further research to fully comprehend its significance in a neurobiological context and its potential therapeutic applications.
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Affiliation(s)
- Camila C Portugal
- I3s - Instituto de Investigação e Inovação em Saúde da Universidade do Porto and IBMC - Instituto de Biologia Molecular e Celular, Rua Alfredo Allen 208, 4200-135, Porto, Portugal.
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3
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Suryavanshi P, Sawant-Pokam P, Clair S, Brennan KC. Increased presynaptic excitability in a migraine with aura mutation. Brain 2024; 147:680-697. [PMID: 37831655 PMCID: PMC10834252 DOI: 10.1093/brain/awad326] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2023] [Revised: 08/24/2023] [Accepted: 09/04/2023] [Indexed: 10/15/2023] Open
Abstract
Migraine is a common and disabling neurological disorder. The headache and sensory amplifications of migraine are attributed to hyperexcitable sensory circuits, but a detailed understanding remains elusive. A mutation in casein kinase 1 delta (CK1δ) was identified in non-hemiplegic familial migraine with aura and advanced sleep phase syndrome. Mice carrying the CK1δT44A mutation were more susceptible to spreading depolarization (the phenomenon that underlies migraine aura), but mechanisms underlying this migraine-relevant phenotype were not known. We used a combination of whole-cell electrophysiology and multiphoton imaging, in vivo and in brain slices, to compare CK1δT44A mice (adult males) to their wild-type littermates. We found that despite comparable synaptic activity at rest, CK1δT44A neurons were more excitable upon repetitive stimulation than wild-type, with a reduction in presynaptic adaptation at excitatory but not inhibitory synapses. The mechanism of this adaptation deficit was a calcium-dependent enhancement of the size of the readily releasable pool of synaptic vesicles, and a resultant increase in glutamate release, in CK1δT44A compared to wild-type synapses. Consistent with this mechanism, CK1δT44A neurons showed an increase in the cumulative amplitude of excitatory post-synaptic currents, and a higher excitation-to-inhibition ratio during sustained activity compared to wild-type. At a local circuit level, action potential bursts elicited in CK1δT44A neurons triggered an increase in recurrent excitation compared to wild-type, and at a network level, CK1δT44A mice showed a longer duration of 'up state' activity, which is dependent on recurrent excitation. Finally, we demonstrated that the spreading depolarization susceptibility of CK1δT44A mice could be returned to wild-type levels with the same intervention (reduced extracellular calcium) that normalized presynaptic adaptation. Taken together, these findings show a stimulus-dependent presynaptic gain of function at glutamatergic synapses in a genetic model of migraine, that accounts for the increased spreading depolarization susceptibility and may also explain the sensory amplifications that are associated with the disease.
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Affiliation(s)
- Pratyush Suryavanshi
- Department of Neurology, University of Utah School of Medicine, Salt Lake City, UT 84132, USA
- Interdepartmental Neuroscience Program, University of Utah School of Medicine, Salt Lake City, UT 84132, USA
- Department of Pediatrics, University of Iowa, Iowa City, IA 52242, USA
| | - Punam Sawant-Pokam
- Department of Neurology, University of Utah School of Medicine, Salt Lake City, UT 84132, USA
| | - Sarah Clair
- Department of Neurology, University of Utah School of Medicine, Salt Lake City, UT 84132, USA
| | - K C Brennan
- Department of Neurology, University of Utah School of Medicine, Salt Lake City, UT 84132, USA
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4
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Koh W, Kwak H, Cheong E, Lee CJ. GABA tone regulation and its cognitive functions in the brain. Nat Rev Neurosci 2023; 24:523-539. [PMID: 37495761 DOI: 10.1038/s41583-023-00724-7] [Citation(s) in RCA: 24] [Impact Index Per Article: 24.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 06/26/2023] [Indexed: 07/28/2023]
Abstract
γ-Aminobutyric acid (GABA) is the major inhibitory neurotransmitter released at GABAergic synapses, mediating fast-acting phasic inhibition. Emerging lines of evidence unequivocally indicate that a small amount of extracellular GABA - GABA tone - exists in the brain and induces a tonic GABA current that controls neuronal activity on a slow timescale relative to that of phasic inhibition. Surprisingly, studies indicate that glial cells that synthesize GABA, such as astrocytes, release GABA through non-vesicular mechanisms, such as channel-mediated release, and thereby act as the source of GABA tone in the brain. In this Review, we first provide an overview of major advances in our understanding of the cell-specific molecular and cellular mechanisms of GABA synthesis, release and clearance that regulate GABA tone in various brain regions. We next examine the diverse ways in which the tonic GABA current regulates synaptic transmission and synaptic plasticity through extrasynaptic GABAA-receptor-mediated mechanisms. Last, we discuss the physiological mechanisms through which tonic inhibition modulates cognitive function on a slow timescale. In this Review, we emphasize that the cognitive functions of tonic GABA current extend beyond mere inhibition, laying a foundation for future research on the physiological and pathophysiological roles of GABA tone regulation in normal and abnormal psychiatric conditions.
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Affiliation(s)
- Wuhyun Koh
- Center for Cognition and Sociality, Institute for Basic Science, Daejeon, South Korea
| | - Hankyul Kwak
- Department of Biotechnology, College of Life Science and Biotechnology, Yonsei University, Seoul, South Korea
| | - Eunji Cheong
- Department of Biotechnology, College of Life Science and Biotechnology, Yonsei University, Seoul, South Korea.
| | - C Justin Lee
- Center for Cognition and Sociality, Institute for Basic Science, Daejeon, South Korea.
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5
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Magloire V, Savtchenko LP, Jensen TP, Sylantyev S, Kopach O, Cole N, Tyurikova O, Kullmann DM, Walker MC, Marvin JS, Looger LL, Hasseman JP, Kolb I, Pavlov I, Rusakov DA. Volume-transmitted GABA waves pace epileptiform rhythms in the hippocampal network. Curr Biol 2023; 33:1249-1264.e7. [PMID: 36921605 PMCID: PMC10615848 DOI: 10.1016/j.cub.2023.02.051] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2022] [Revised: 01/05/2023] [Accepted: 02/15/2023] [Indexed: 03/17/2023]
Abstract
Mechanisms that entrain and pace rhythmic epileptiform discharges remain debated. Traditionally, the quest to understand them has focused on interneuronal networks driven by synaptic GABAergic connections. However, synchronized interneuronal discharges could also trigger the transient elevations of extracellular GABA across the tissue volume, thus raising tonic conductance (Gtonic) of synaptic and extrasynaptic GABA receptors in multiple cells. Here, we monitor extracellular GABA in hippocampal slices using patch-clamp GABA "sniffer" and a novel optical GABA sensor, showing that periodic epileptiform discharges are preceded by transient, region-wide waves of extracellular GABA. Neural network simulations that incorporate volume-transmitted GABA signals point to a cycle of GABA-driven network inhibition and disinhibition underpinning this relationship. We test and validate this hypothesis using simultaneous patch-clamp recordings from multiple neurons and selective optogenetic stimulation of fast-spiking interneurons. Critically, reducing GABA uptake in order to decelerate extracellular GABA fluctuations-without affecting synaptic GABAergic transmission or resting GABA levels-slows down rhythmic activity. Our findings thus unveil a key role of extrasynaptic, volume-transmitted GABA in pacing regenerative rhythmic activity in brain networks.
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Affiliation(s)
- Vincent Magloire
- UCL Queen Square Institute of Neurology, University College London, Queen Square, London WC1N 3BG, UK.
| | - Leonid P Savtchenko
- UCL Queen Square Institute of Neurology, University College London, Queen Square, London WC1N 3BG, UK.
| | - Thomas P Jensen
- UCL Queen Square Institute of Neurology, University College London, Queen Square, London WC1N 3BG, UK
| | - Sergyi Sylantyev
- UCL Queen Square Institute of Neurology, University College London, Queen Square, London WC1N 3BG, UK; Rowett Institute, University of Aberdeen, Ashgrove Road West, Aberdeen AB25 2ZD, UK
| | - Olga Kopach
- UCL Queen Square Institute of Neurology, University College London, Queen Square, London WC1N 3BG, UK
| | - Nicholas Cole
- UCL Queen Square Institute of Neurology, University College London, Queen Square, London WC1N 3BG, UK
| | - Olga Tyurikova
- UCL Queen Square Institute of Neurology, University College London, Queen Square, London WC1N 3BG, UK
| | - Dimitri M Kullmann
- UCL Queen Square Institute of Neurology, University College London, Queen Square, London WC1N 3BG, UK
| | - Matthew C Walker
- UCL Queen Square Institute of Neurology, University College London, Queen Square, London WC1N 3BG, UK
| | - Jonathan S Marvin
- Janelia Research Campus, Howard Hughes Medical Institute, Ashburn, VA, USA
| | - Loren L Looger
- Janelia Research Campus, Howard Hughes Medical Institute, Ashburn, VA, USA; Howard Hughes Medical Institute, University of California, San Diego, La Jolla, CA 92093, USA; GENIE Project Team, Janelia Research Campus, Howard Hughes Medical Institute, Ashburn, VA, USA
| | - Jeremy P Hasseman
- Janelia Research Campus, Howard Hughes Medical Institute, Ashburn, VA, USA; GENIE Project Team, Janelia Research Campus, Howard Hughes Medical Institute, Ashburn, VA, USA
| | - Ilya Kolb
- Janelia Research Campus, Howard Hughes Medical Institute, Ashburn, VA, USA; GENIE Project Team, Janelia Research Campus, Howard Hughes Medical Institute, Ashburn, VA, USA
| | - Ivan Pavlov
- UCL Queen Square Institute of Neurology, University College London, Queen Square, London WC1N 3BG, UK
| | - Dmitri A Rusakov
- UCL Queen Square Institute of Neurology, University College London, Queen Square, London WC1N 3BG, UK.
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6
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Bhatt M, Gauthier-Manuel L, Lazzarin E, Zerlotti R, Ziegler C, Bazzone A, Stockner T, Bossi E. A comparative review on the well-studied GAT1 and the understudied BGT-1 in the brain. Front Physiol 2023; 14:1145973. [PMID: 37123280 PMCID: PMC10137170 DOI: 10.3389/fphys.2023.1145973] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2023] [Accepted: 03/30/2023] [Indexed: 05/02/2023] Open
Abstract
γ-aminobutyric acid (GABA) is the primary inhibitory neurotransmitter in the central nervous system (CNS). Its homeostasis is maintained by neuronal and glial GABA transporters (GATs). The four GATs identified in humans are GAT1 (SLC6A1), GAT2 (SLC6A13), GAT3 (SLC6A11), and betaine/GABA transporter-1 BGT-1 (SLC6A12) which are all members of the solute carrier 6 (SLC6) family of sodium-dependent transporters. While GAT1 has been investigated extensively, the other GABA transporters are less studied and their role in CNS is not clearly defined. Altered GABAergic neurotransmission is involved in different diseases, but the importance of the different transporters remained understudied and limits drug targeting. In this review, the well-studied GABA transporter GAT1 is compared with the less-studied BGT-1 with the aim to leverage the knowledge on GAT1 to shed new light on the open questions concerning BGT-1. The most recent knowledge on transporter structure, functions, expression, and localization is discussed along with their specific role as drug targets for neurological and neurodegenerative disorders. We review and discuss data on the binding sites for Na+, Cl-, substrates, and inhibitors by building on the recent cryo-EM structure of GAT1 to highlight specific molecular determinants of transporter functions. The role of the two proteins in GABA homeostasis is investigated by looking at the transport coupling mechanism, as well as structural and kinetic transport models. Furthermore, we review information on selective inhibitors together with the pharmacophore hypothesis of transporter substrates.
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Affiliation(s)
- Manan Bhatt
- Department of Biotechnology and Life Sciences, University of Insubria, Varese, Italy
- Centre for Neuroscience—University of Insubria, Varese, Italy
| | - Laure Gauthier-Manuel
- Department of Biophysics II/Structural Biology, University of Regensburg, Regensburg, Germany
| | - Erika Lazzarin
- Center for Physiology and Pharmacology, Institute of Pharmacology, Medical University of Vienna, Waehringerstr, Vienna
| | - Rocco Zerlotti
- Department of Biophysics II/Structural Biology, University of Regensburg, Regensburg, Germany
- Nanion Technologies GmbH, Munich, Germany
| | - Christine Ziegler
- Department of Biophysics II/Structural Biology, University of Regensburg, Regensburg, Germany
| | | | - Thomas Stockner
- Center for Physiology and Pharmacology, Institute of Pharmacology, Medical University of Vienna, Waehringerstr, Vienna
- *Correspondence: Thomas Stockner, ; Elena Bossi,
| | - Elena Bossi
- Department of Biotechnology and Life Sciences, University of Insubria, Varese, Italy
- Centre for Neuroscience—University of Insubria, Varese, Italy
- *Correspondence: Thomas Stockner, ; Elena Bossi,
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7
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Kuanyshbek A, Wang M, Andersson Å, Tuifua M, Palmer EE, Sachdev RK, Mu TW, Vetter I, Keramidas A. Anti-seizure mechanisms of midazolam and valproate at the β2(L51M) variant of the GABA A receptor. Neuropharmacology 2022; 221:109295. [PMID: 36257447 PMCID: PMC9981329 DOI: 10.1016/j.neuropharm.2022.109295] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2022] [Revised: 10/07/2022] [Accepted: 10/11/2022] [Indexed: 11/05/2022]
Abstract
Genetic sequencing is identifying an expanding number of variants of GABAA receptors associated with human epilepsies. We identified a new de novo variant of the β2 subunit (β2L51M) of the inhibitory GABAA receptor associated with seizures. Our analysis determined the pathogenicity of the variant and the effects of anti-seizure medications. Our data demonstrates that the variant reduced cell surface trafficking and peak GABA-gated currents. Synaptic currents mediated by variant-containing receptors decayed faster than wild-type and single receptor currents showed that the variant shortened the duration of receptor activity by decreasing receptor open times. We tested the effects of the anti-seizure medications, midazolam, carbamazepine and valproate and found that all three enhance variant receptor surface expression. Additionally, midazolam restored receptor function by increasing single receptor active periods and synaptic current decay times towards wild-type levels. By contrast, valproate increased synaptic peak currents, event frequency and promoted synaptic bursting. Our study identifies a new disease-causing variant to the GABAA receptor, profiles its pathogenic effects and demonstrates how anti-seizure drugs correct its functional deficits.
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Affiliation(s)
- Alibek Kuanyshbek
- Institute for Molecular Bioscience, The University of Queensland, Brisbane, Australia
| | - Meng Wang
- Department of Physiology and Biophysics, Case Western Reserve University School of Medicine, Cleveland, OH, 44106, USA
| | - Åsa Andersson
- Institute for Molecular Bioscience, The University of Queensland, Brisbane, Australia
| | - Marie Tuifua
- Institute for Molecular Bioscience, The University of Queensland, Brisbane, Australia
| | - Elizabeth E Palmer
- Sydney Children's Hospital Network, Randwick Sydney Australia and School of Women's and Children's Health, UNSW Medicine, The University of New South Wales, Sydney, NSW, Australia
| | - Rani K Sachdev
- Sydney Children's Hospital Network, Randwick Sydney Australia and School of Women's and Children's Health, UNSW Medicine, The University of New South Wales, Sydney, NSW, Australia
| | - Ting-Wei Mu
- Department of Physiology and Biophysics, Case Western Reserve University School of Medicine, Cleveland, OH, 44106, USA
| | - Irina Vetter
- Institute for Molecular Bioscience, The University of Queensland, Brisbane, Australia; School of Pharmacy, The University of Queensland, Woolloongabba, Queensland, 4102, Australia
| | - Angelo Keramidas
- Institute for Molecular Bioscience, The University of Queensland, Brisbane, Australia.
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8
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Evrard MR, Li M, Shen H, Smith SS. Preventing adolescent synaptic pruning in mouse prelimbic cortex via local knockdown of α4βδ GABA A receptors increases anxiety response in adulthood. Sci Rep 2021; 11:21059. [PMID: 34702942 PMCID: PMC8548505 DOI: 10.1038/s41598-021-99965-8] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2021] [Accepted: 09/29/2021] [Indexed: 01/25/2023] Open
Abstract
Anxiety is increasingly reported, especially in adolescent females. The etiology is largely unknown, which limits effective treatment. Layer 5 prelimbic cortex (L5PL) increases anxiety responses but undergoes adolescent synaptic pruning, raising the question of the impact of pruning on anxiety. Here we show that preventing L5PL pruning increases anxiety in response to an aversive event in adolescent and adult female mice. Spine density of Golgi-stained neurons decreased ~ 63% from puberty (~ PND35, vaginal opening) to post-puberty (PND56, P < 0.0001). Expression of α4βδ GABAA receptors (GABARs) transiently increased tenfold in L5PL at puberty (P < 0.00001), but decreased post-pubertally. Both global and local knockdown of these receptors during puberty prevented pruning, increasing spine density post-pubertally (P < 0.0001), an effect reversed by blocking NMDA receptors (NMDARs). Pubertal expression of the NMDAR-dependent spine protein kalirin7 decreased (50%, P < 0.0001), an effect prevented by α4 knock-out, suggesting that α4βδ-induced reductions in kalirin7 underlie pruning. Increased spine density due to local α4 knockdown at puberty decreased open arm time on the elevated plus maze post-pubertally (62%, P < 0.0001) in response to an aversive stimulus, suggesting that increases in L5PL synapses increase anxiety responses. These findings suggest that prelimbic synaptic pruning is necessary to limit anxiety in adulthood and may suggest novel therapies.
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Affiliation(s)
- Matthew R Evrard
- Department of Physiology and Pharmacology, SUNY Downstate Medical Center, 450 Clarkson Ave., Brooklyn, NY, 11203, USA.,Graduate Program in Neural and Behavioral Science, SUNY Downstate Medical Center, 450 Clarkson Ave., Brooklyn, NY, 11203, USA
| | - Michael Li
- Department of Physiology and Pharmacology, SUNY Downstate Medical Center, 450 Clarkson Ave., Brooklyn, NY, 11203, USA.,College of Arts and Sciences, Hunter College, New York, NY, 10065, USA
| | - Hui Shen
- Department of Physiology and Pharmacology, SUNY Downstate Medical Center, 450 Clarkson Ave., Brooklyn, NY, 11203, USA.,School of Biomedical Engineering, Tianjin Medical University, No. 22 Qixiangtai Road, Heping District, Tianjin, 300070, China
| | - Sheryl S Smith
- Department of Physiology and Pharmacology, SUNY Downstate Medical Center, 450 Clarkson Ave., Brooklyn, NY, 11203, USA.
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Bai X, Kirchhoff F, Scheller A. Oligodendroglial GABAergic Signaling: More Than Inhibition! Neurosci Bull 2021; 37:1039-1050. [PMID: 33928492 PMCID: PMC8275815 DOI: 10.1007/s12264-021-00693-w] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2020] [Accepted: 11/22/2020] [Indexed: 12/12/2022] Open
Abstract
GABA is the main inhibitory neurotransmitter in the CNS acting at two distinct types of receptor: ligand-gated ionotropic GABAA receptors and G protein-coupled metabotropic GABAB receptors, thus mediating fast and slow inhibition of excitability at central synapses. GABAergic signal transmission has been intensively studied in neurons in contrast to oligodendrocytes and their precursors (OPCs), although the latter express both types of GABA receptor. Recent studies focusing on interneuron myelination and interneuron-OPC synapses have shed light on the importance of GABA signaling in the oligodendrocyte lineage. In this review, we start with a short summary on GABA itself and neuronal GABAergic signaling. Then, we elaborate on the physiological role of GABA receptors within the oligodendrocyte lineage and conclude with a description of these receptors as putative targets in treatments of CNS diseases.
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Affiliation(s)
- Xianshu Bai
- Molecular Physiology, Center for Integrative Physiology and Molecular Medicine (CIPMM), University of Saarland, 66421, Homburg, Germany
| | - Frank Kirchhoff
- Molecular Physiology, Center for Integrative Physiology and Molecular Medicine (CIPMM), University of Saarland, 66421, Homburg, Germany.
| | - Anja Scheller
- Molecular Physiology, Center for Integrative Physiology and Molecular Medicine (CIPMM), University of Saarland, 66421, Homburg, Germany
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10
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Sears SM, Hewett SJ. Influence of glutamate and GABA transport on brain excitatory/inhibitory balance. Exp Biol Med (Maywood) 2021; 246:1069-1083. [PMID: 33554649 DOI: 10.1177/1535370221989263] [Citation(s) in RCA: 64] [Impact Index Per Article: 21.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
An optimally functional brain requires both excitatory and inhibitory inputs that are regulated and balanced. A perturbation in the excitatory/inhibitory balance-as is the case in some neurological disorders/diseases (e.g. traumatic brain injury Alzheimer's disease, stroke, epilepsy and substance abuse) and disorders of development (e.g. schizophrenia, Rhett syndrome and autism spectrum disorder)-leads to dysfunctional signaling, which can result in impaired cognitive and motor function, if not frank neuronal injury. At the cellular level, transmission of glutamate and GABA, the principle excitatory and inhibitory neurotransmitters in the central nervous system control excitatory/inhibitory balance. Herein, we review the synthesis, release, and signaling of GABA and glutamate followed by a focused discussion on the importance of their transport systems to the maintenance of excitatory/inhibitory balance.
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Affiliation(s)
- Sheila Ms Sears
- Department of Biology, Program in Neuroscience, 2029Syracuse University, Syracuse, NY 13244, USA
| | - Sandra J Hewett
- Department of Biology, Program in Neuroscience, 2029Syracuse University, Syracuse, NY 13244, USA
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11
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Zajic DE, Podrabsky JE. GABA metabolism is crucial for long-term survival of anoxia in annual killifish embryos. J Exp Biol 2020; 223:jeb229716. [PMID: 32859669 DOI: 10.1242/jeb.229716] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2020] [Accepted: 08/24/2020] [Indexed: 08/25/2023]
Abstract
In most vertebrates, a lack of oxygen quickly leads to irreparable damages to vital organs, such as the brain and heart. However, there are some vertebrates that have evolved mechanisms to survive periods of no oxygen (anoxia). The annual killifish (Austrofundulus limnaeus) survives in ephemeral ponds in the coastal deserts of Venezuela and their embryos have the remarkable ability to tolerate anoxia for months. When exposed to anoxia, embryos of A. limnaeus respond by producing significant amounts of γ-aminobutyric acid (GABA). This study aims to understand the role of GABA in supporting the metabolic response to anoxia. To explore this, we investigated four developmentally distinct stages of A. limnaeus embryos that vary in their anoxia tolerance. We measured GABA and lactate concentrations across development in response to anoxia and aerobic recovery. We then inhibited enzymes responsible for the production and degradation of GABA and observed GABA and lactate concentrations, as well as embryo mortality. Here, we show for the first time that GABA metabolism affects anoxia tolerance in A. limnaeus embryos. Inhibition of enzymes responsible for GABA production (glutamate decarboxylase) and degradation (GABA-transaminase and succinic acid semialdehyde dehydrogenase) led to increased mortality, supporting a role for GABA as an intermediate product and not a metabolic end-product. We propose multiple roles for GABA during anoxia and aerobic recovery in A. limnaeus embryos, serving as a neurotransmitter, an energy source, and an anti-oxidant.
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Affiliation(s)
- Daniel E Zajic
- Department of Biology, Portland State University, PO Box 751, Portland, OR 97207, USA
- Health, Human Performance, and Athletics Department, Linfield University, 900 SE Baker, McMinnville, OR 97128, USA
| | - Jason E Podrabsky
- Department of Biology, Portland State University, PO Box 751, Portland, OR 97207, USA
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12
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Absalom NL, Liao VWY, Kothur K, Indurthi DC, Bennetts B, Troedson C, Mohammad SS, Gupta S, McGregor IS, Bowen MT, Lederer D, Mary S, De Waele L, Jansen K, Gill D, Kurian MA, McTague A, Møller RS, Ahring PK, Dale RC, Chebib M. Gain-of-function GABRB3 variants identified in vigabatrin-hypersensitive epileptic encephalopathies. Brain Commun 2020; 2:fcaa162. [PMID: 33585817 PMCID: PMC7869430 DOI: 10.1093/braincomms/fcaa162] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2020] [Revised: 07/31/2020] [Accepted: 08/28/2020] [Indexed: 01/06/2023] Open
Abstract
Variants in the GABRB3 gene encoding the β3-subunit of the γ-aminobutyric acid type A ( receptor are associated with various developmental and epileptic encephalopathies. Typically, these variants cause a loss-of-function molecular phenotype whereby γ-aminobutyric acid has reduced inhibitory effectiveness leading to seizures. Drugs that potentiate inhibitory GABAergic activity, such as nitrazepam, phenobarbital or vigabatrin, are expected to compensate for this and thereby reduce seizure frequency. However, vigabatrin, a drug that inhibits γ-aminobutyric acid transaminase to increase tonic γ-aminobutyric acid currents, has mixed success in treating seizures in patients with GABRB3 variants: some patients experience seizure cessation, but there is hypersensitivity in some patients associated with hypotonia, sedation and respiratory suppression. A GABRB3 variant that responds well to vigabatrin involves a truncation variant (p.Arg194*) resulting in a clear loss-of-function. We hypothesized that patients with a hypersensitive response to vigabatrin may exhibit a different γ-aminobutyric acid A receptor phenotype. To test this hypothesis, we evaluated the phenotype of de novo variants in GABRB3 (p.Glu77Lys and p.Thr287Ile) associated with patients who are clinically hypersensitive to vigabatrin. We introduced the GABRB3 p.Glu77Lys and p.Thr287Ile variants into a concatenated synaptic and extrasynaptic γ-aminobutyric acid A receptor construct, to resemble the γ-aminobutyric acid A receptor expression by a patient heterozygous for the GABRB3 variant. The mRNA of these constructs was injected into Xenopus oocytes and activation properties of each receptor measured by two-electrode voltage clamp electrophysiology. Results showed an atypical gain-of-function molecular phenotype in the GABRB3 p.Glu77Lys and p.Thr287Ile variants characterized by increased potency of γ-aminobutyric acid A without change to the estimated maximum open channel probability, deactivation kinetics or absolute currents. Modelling of the activation properties of the receptors indicated that either variant caused increased chloride flux in response to low concentrations of γ-aminobutyric acid that mediate tonic currents. We therefore propose that the hypersensitivity reaction to vigabatrin is a result of GABRB3 variants that exacerbate GABAergic tonic currents and caution is required when prescribing vigabatrin. In contrast, drug strategies increasing tonic currents in loss-of-function variants are likely to be a safe and effective therapy. This study demonstrates that functional genomics can explain beneficial and adverse anti-epileptic drug effects, and propose that vigabatrin should be considered in patients with clear loss-of-function GABRB3 variants.
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Affiliation(s)
- Nathan L Absalom
- Faculty of Medicine and Health, School of Pharmacy, Brain and Mind Centre, The University of Sydney, Sydney, New South Wales 2006, Australia
| | - Vivian W Y Liao
- Faculty of Medicine and Health, School of Pharmacy, Brain and Mind Centre, The University of Sydney, Sydney, New South Wales 2006, Australia
| | - Kavitha Kothur
- Kids Neuroscience Centre at The Children’s Hospital at Westmead, Westmead, New South Wales 2145, Australia
| | - Dinesh C Indurthi
- Faculty of Medicine and Health, School of Pharmacy, Brain and Mind Centre, The University of Sydney, Sydney, New South Wales 2006, Australia
| | - Bruce Bennetts
- Department of Molecular Genetics, The Children’s Hospital at Westmead, Westmead, New South Wales 2145, Australia
- Discipline of Paediatrics and Adolescent Health, The Children's Hospital at Westmead Clinical School, The University of Sydney, 2145, Australia
| | - Christopher Troedson
- T.Y. Nelson Department of Neurology and Neurosurgery, The Children's Hospital at Westmead, Westmead, New South Wales 2145, Australia
| | - Shekeeb S Mohammad
- Kids Neuroscience Centre at The Children’s Hospital at Westmead, Westmead, New South Wales 2145, Australia
| | - Sachin Gupta
- T.Y. Nelson Department of Neurology and Neurosurgery, The Children's Hospital at Westmead, Westmead, New South Wales 2145, Australia
| | - Iain S McGregor
- Faculty of Science, Lambert Initiative for Cannabinoid Therapeutics, Brain and Mind Centre, The University of Sydney, Sydney, New South Wales 2006, Australia
| | - Michael T Bowen
- Faculty of Science, Lambert Initiative for Cannabinoid Therapeutics, Brain and Mind Centre, The University of Sydney, Sydney, New South Wales 2006, Australia
| | - Damien Lederer
- Institute of Pathology and Genetics, Center for Human Genetics, Gosselies 6041, Belgium
| | - Sandrine Mary
- Institute of Pathology and Genetics, Center for Human Genetics, Gosselies 6041, Belgium
| | - Liesbeth De Waele
- Department of Development and Regeneration, KULeuven, Leuven 3000, Belgium
| | - Katrien Jansen
- Department of Development and Regeneration, KULeuven, Leuven 3000, Belgium
| | - Deepak Gill
- Kids Neuroscience Centre at The Children’s Hospital at Westmead, Westmead, New South Wales 2145, Australia
| | - Manju A Kurian
- Molecular Neurosciences, UCL Great Ormond Street Institute of Child Health, London WC1E 6BT, UK
- Department of Neurology, Great Ormond Street Hospital for Children, London WC1N 3JH, UK
| | - Amy McTague
- Molecular Neurosciences, UCL Great Ormond Street Institute of Child Health, London WC1E 6BT, UK
- Department of Neurology, Great Ormond Street Hospital for Children, London WC1N 3JH, UK
| | - Rikke S Møller
- Department of Epilepsy Genetics and Personalized Medicine, Danish Epilepsy Centre, Dianalund 4293, Denmark
- Department of Regional Health Research, University of Southern Denmark, Odense 5230, Denmark
| | - Philip K Ahring
- Faculty of Medicine and Health, School of Pharmacy, Brain and Mind Centre, The University of Sydney, Sydney, New South Wales 2006, Australia
| | - Russell C Dale
- Kids Neuroscience Centre at The Children’s Hospital at Westmead, Westmead, New South Wales 2145, Australia
| | - Mary Chebib
- Faculty of Medicine and Health, School of Pharmacy, Brain and Mind Centre, The University of Sydney, Sydney, New South Wales 2006, Australia
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GABAB receptor-mediated tonic inhibition of locus coeruleus neurons plays a role in deep anesthesia induced by isoflurane. Neuroreport 2020; 31:557-564. [PMID: 32282581 DOI: 10.1097/wnr.0000000000001450] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Noradrenergic neurons in the locus coeruleus referred to as locus coeruleus neurons, provide the major supply of norepinephrine to the forebrain and play important roles in behavior through regulation of wakefulness and arousal. In a previous study using brain slice preparations, we reported that locus coeruleus neurons are subject to tonic inhibition mediated by γ-aminobutyric acid B receptors (GABABRs) and that the extent of tonic inhibition varies with ambient GABA levels. Since ambient GABA in the locus coeruleus was reported to fluctuate during the sleep-wakefulness cycle, here we tested whether GABABR-mediated tonic inhibition of locus coeruleus neurons could be a mechanism underlying changes in brain arousal. We first demonstrated that GABABR-mediated tonic inhibition of locus coeruleus neurons also exists in vivo by showing that local infusion of CGP35348, a GABABR antagonist, into the locus coeruleus increased the firing rate of locus coeruleus neurons in anesthetized rats. We then showed that this manipulation accelerated the behavioral emergence of rats from deep anesthesia induced by isoflurane. Together, these observations show that GABABR-mediated tonic inhibition of locus coeruleus neurons occurs in vivo and support the idea that this effect may be important in regulating the functional state of the brain.
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Si W, Li H, Kang T, Ye J, Yao Z, Liu Y, Yu T, Zhang Y, Ling Y, Cao H, Wang J, Li Y, Fang F. Effect of GABA-T on Reproductive Function in Female Rats. Animals (Basel) 2020; 10:ani10040567. [PMID: 32230949 PMCID: PMC7222393 DOI: 10.3390/ani10040567] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2020] [Revised: 03/16/2020] [Accepted: 03/25/2020] [Indexed: 12/29/2022] Open
Abstract
This study explored the role of γ-aminobutyric acid transaminase (GABA-T) in the puberty and reproductive performance of female rats. Immunofluorescence technique, quantitative real-time PCR (RT-qPCR) and enzyme-linked immunosorbent assay (ELISA) were used to detect the distribution of GABA-T and the expression of genes and hormones in female rats, respectively. The results showed that GABA-T was mainly distributed in the arcuate nucleus (ARC), paraventricular nucleus (PVN) and periventricular nucleus (PeN) of the hypothalamus, and in the adenohypophysis, ovarian granulosa cells and oocytes. Abat mRNA level at 28 d was lowest in the hypothalamus and the pituitary; at puberty, it was lowest in the ovary. Abat mRNA level was highest in adults in the hypothalamus; at infancy and puberty, it was highest in the pituitary; and at 21 d it was highest in the ovary. After vigabatrin (GABA-T irreversible inhibitor) was added to hypothalamus cells, the levels of Abat mRNA and Rfrp-3 mRNA were significantly reduced, but Gnrh mRNA increased at the dose of 25 and 50 μg/mL; Kiss1 mRNA was significantly increased but Gabbr1 mRNA was reduced at the 50 μg/mL dose. In prepubertal rats injected with vigabatrin, puberty onset was delayed. Abat mRNA, Kiss1 mRNA and Gnrh mRNA levels were significantly reduced, but Rfrp-3 mRNA level increased in the hypothalamus. Vigabatrin reduced the concentrations of GABA-T, luteinizing hormone (LH) and progesterone (P4), and the ovarian index. Lactation performance was reduced in adult rats with vigabatrin treatment. Four hours after vigabatrin injection, the concentrations of GABA-T and LH were significantly reduced in adult and 25 d rats, but follicle-stimulating hormone (FSH) increased in 25 d rats. In conclusion, GABA-T affects the reproductive function of female rats by regulating the levels of Gnrh, Kiss1 and Rfrp-3 in the hypothalamus as well as the concentrations of LH and P4.
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Affiliation(s)
- Wenyu Si
- Anhui Provincial Laboratory of Animal Genetic Resources Protection and Breeding, College of Animal Science and Technology, Anhui Agricultural University, 130 Changjiang West Road, Hefei 230036, China; (W.S.); (H.L.); (T.K.); (J.Y.); (Z.Y.); (Y.L.); (T.Y.); (Y.Z.); (Y.L.); (H.C.); (J.W.); (Y.L.)
- Anhui Provincial Laboratory for Local Livestock and Poultry Genetic Resource Conservation and Bio-Breeding, 130 Changjiang West Road, Hefei 230036, China
- Department of Animal Veterinary Science, College of Animal Science and Technology, Anhui Agricultural University, 130 Changjiang West Road, Hefei 230036, China
| | - Hailing Li
- Anhui Provincial Laboratory of Animal Genetic Resources Protection and Breeding, College of Animal Science and Technology, Anhui Agricultural University, 130 Changjiang West Road, Hefei 230036, China; (W.S.); (H.L.); (T.K.); (J.Y.); (Z.Y.); (Y.L.); (T.Y.); (Y.Z.); (Y.L.); (H.C.); (J.W.); (Y.L.)
- Department of Animal Veterinary Science, College of Animal Science and Technology, Anhui Agricultural University, 130 Changjiang West Road, Hefei 230036, China
| | - Tiezhu Kang
- Anhui Provincial Laboratory of Animal Genetic Resources Protection and Breeding, College of Animal Science and Technology, Anhui Agricultural University, 130 Changjiang West Road, Hefei 230036, China; (W.S.); (H.L.); (T.K.); (J.Y.); (Z.Y.); (Y.L.); (T.Y.); (Y.Z.); (Y.L.); (H.C.); (J.W.); (Y.L.)
- Department of Animal Veterinary Science, College of Animal Science and Technology, Anhui Agricultural University, 130 Changjiang West Road, Hefei 230036, China
| | - Jing Ye
- Anhui Provincial Laboratory of Animal Genetic Resources Protection and Breeding, College of Animal Science and Technology, Anhui Agricultural University, 130 Changjiang West Road, Hefei 230036, China; (W.S.); (H.L.); (T.K.); (J.Y.); (Z.Y.); (Y.L.); (T.Y.); (Y.Z.); (Y.L.); (H.C.); (J.W.); (Y.L.)
- Department of Animal Veterinary Science, College of Animal Science and Technology, Anhui Agricultural University, 130 Changjiang West Road, Hefei 230036, China
| | - Zhiqiu Yao
- Anhui Provincial Laboratory of Animal Genetic Resources Protection and Breeding, College of Animal Science and Technology, Anhui Agricultural University, 130 Changjiang West Road, Hefei 230036, China; (W.S.); (H.L.); (T.K.); (J.Y.); (Z.Y.); (Y.L.); (T.Y.); (Y.Z.); (Y.L.); (H.C.); (J.W.); (Y.L.)
- Department of Animal Veterinary Science, College of Animal Science and Technology, Anhui Agricultural University, 130 Changjiang West Road, Hefei 230036, China
| | - Ya Liu
- Anhui Provincial Laboratory of Animal Genetic Resources Protection and Breeding, College of Animal Science and Technology, Anhui Agricultural University, 130 Changjiang West Road, Hefei 230036, China; (W.S.); (H.L.); (T.K.); (J.Y.); (Z.Y.); (Y.L.); (T.Y.); (Y.Z.); (Y.L.); (H.C.); (J.W.); (Y.L.)
- Anhui Provincial Laboratory for Local Livestock and Poultry Genetic Resource Conservation and Bio-Breeding, 130 Changjiang West Road, Hefei 230036, China
- Department of Animal Veterinary Science, College of Animal Science and Technology, Anhui Agricultural University, 130 Changjiang West Road, Hefei 230036, China
| | - Tong Yu
- Anhui Provincial Laboratory of Animal Genetic Resources Protection and Breeding, College of Animal Science and Technology, Anhui Agricultural University, 130 Changjiang West Road, Hefei 230036, China; (W.S.); (H.L.); (T.K.); (J.Y.); (Z.Y.); (Y.L.); (T.Y.); (Y.Z.); (Y.L.); (H.C.); (J.W.); (Y.L.)
- Anhui Provincial Laboratory for Local Livestock and Poultry Genetic Resource Conservation and Bio-Breeding, 130 Changjiang West Road, Hefei 230036, China
- Department of Animal Veterinary Science, College of Animal Science and Technology, Anhui Agricultural University, 130 Changjiang West Road, Hefei 230036, China
| | - Yunhai Zhang
- Anhui Provincial Laboratory of Animal Genetic Resources Protection and Breeding, College of Animal Science and Technology, Anhui Agricultural University, 130 Changjiang West Road, Hefei 230036, China; (W.S.); (H.L.); (T.K.); (J.Y.); (Z.Y.); (Y.L.); (T.Y.); (Y.Z.); (Y.L.); (H.C.); (J.W.); (Y.L.)
- Anhui Provincial Laboratory for Local Livestock and Poultry Genetic Resource Conservation and Bio-Breeding, 130 Changjiang West Road, Hefei 230036, China
- Department of Animal Veterinary Science, College of Animal Science and Technology, Anhui Agricultural University, 130 Changjiang West Road, Hefei 230036, China
| | - Yinghui Ling
- Anhui Provincial Laboratory of Animal Genetic Resources Protection and Breeding, College of Animal Science and Technology, Anhui Agricultural University, 130 Changjiang West Road, Hefei 230036, China; (W.S.); (H.L.); (T.K.); (J.Y.); (Z.Y.); (Y.L.); (T.Y.); (Y.Z.); (Y.L.); (H.C.); (J.W.); (Y.L.)
- Anhui Provincial Laboratory for Local Livestock and Poultry Genetic Resource Conservation and Bio-Breeding, 130 Changjiang West Road, Hefei 230036, China
- Department of Animal Veterinary Science, College of Animal Science and Technology, Anhui Agricultural University, 130 Changjiang West Road, Hefei 230036, China
| | - Hongguo Cao
- Anhui Provincial Laboratory of Animal Genetic Resources Protection and Breeding, College of Animal Science and Technology, Anhui Agricultural University, 130 Changjiang West Road, Hefei 230036, China; (W.S.); (H.L.); (T.K.); (J.Y.); (Z.Y.); (Y.L.); (T.Y.); (Y.Z.); (Y.L.); (H.C.); (J.W.); (Y.L.)
- Anhui Provincial Laboratory for Local Livestock and Poultry Genetic Resource Conservation and Bio-Breeding, 130 Changjiang West Road, Hefei 230036, China
- Department of Animal Veterinary Science, College of Animal Science and Technology, Anhui Agricultural University, 130 Changjiang West Road, Hefei 230036, China
| | - Juhua Wang
- Anhui Provincial Laboratory of Animal Genetic Resources Protection and Breeding, College of Animal Science and Technology, Anhui Agricultural University, 130 Changjiang West Road, Hefei 230036, China; (W.S.); (H.L.); (T.K.); (J.Y.); (Z.Y.); (Y.L.); (T.Y.); (Y.Z.); (Y.L.); (H.C.); (J.W.); (Y.L.)
- Anhui Provincial Laboratory for Local Livestock and Poultry Genetic Resource Conservation and Bio-Breeding, 130 Changjiang West Road, Hefei 230036, China
- Department of Animal Veterinary Science, College of Animal Science and Technology, Anhui Agricultural University, 130 Changjiang West Road, Hefei 230036, China
| | - Yunsheng Li
- Anhui Provincial Laboratory of Animal Genetic Resources Protection and Breeding, College of Animal Science and Technology, Anhui Agricultural University, 130 Changjiang West Road, Hefei 230036, China; (W.S.); (H.L.); (T.K.); (J.Y.); (Z.Y.); (Y.L.); (T.Y.); (Y.Z.); (Y.L.); (H.C.); (J.W.); (Y.L.)
- Anhui Provincial Laboratory for Local Livestock and Poultry Genetic Resource Conservation and Bio-Breeding, 130 Changjiang West Road, Hefei 230036, China
- Department of Animal Veterinary Science, College of Animal Science and Technology, Anhui Agricultural University, 130 Changjiang West Road, Hefei 230036, China
| | - Fugui Fang
- Anhui Provincial Laboratory of Animal Genetic Resources Protection and Breeding, College of Animal Science and Technology, Anhui Agricultural University, 130 Changjiang West Road, Hefei 230036, China; (W.S.); (H.L.); (T.K.); (J.Y.); (Z.Y.); (Y.L.); (T.Y.); (Y.Z.); (Y.L.); (H.C.); (J.W.); (Y.L.)
- Anhui Provincial Laboratory for Local Livestock and Poultry Genetic Resource Conservation and Bio-Breeding, 130 Changjiang West Road, Hefei 230036, China
- Department of Animal Veterinary Science, College of Animal Science and Technology, Anhui Agricultural University, 130 Changjiang West Road, Hefei 230036, China
- Correspondence:
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Shen J, Shenkar D, An L, Tomar JS. Local and Interregional Neurochemical Associations Measured by Magnetic Resonance Spectroscopy for Studying Brain Functions and Psychiatric Disorders. Front Psychiatry 2020; 11:802. [PMID: 32848957 PMCID: PMC7432119 DOI: 10.3389/fpsyt.2020.00802] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/08/2020] [Accepted: 07/27/2020] [Indexed: 12/11/2022] Open
Abstract
Magnetic resonance spectroscopy (MRS) studies have found significant correlations among neurometabolites (e.g., between glutamate and GABA) across individual subjects and altered correlations in neuropsychiatric disorders. In this article, we discuss neurochemical associations among several major neurometabolites which underpin these observations by MRS. We also illustrate the role of spectral editing in eliminating unwanted correlations caused by spectral overlapping. Finally, we describe the prospects of mapping macroscopic neurochemical associations across the brain and characterizing excitation-inhibition balance of neural networks using glutamate- and GABA-editing MRS imaging.
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Affiliation(s)
- Jun Shen
- Molecular Imaging Branch, National Institute of Mental Health, Bethesda, MD, United States
| | - Dina Shenkar
- Molecular Imaging Branch, National Institute of Mental Health, Bethesda, MD, United States
| | - Li An
- Molecular Imaging Branch, National Institute of Mental Health, Bethesda, MD, United States
| | - Jyoti Singh Tomar
- Molecular Imaging Branch, National Institute of Mental Health, Bethesda, MD, United States
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Wu Y, Proch KL, Teran FA, Lechtenberg RJ, Kothari H, Richerson GB. Chemosensitivity of Phox2b-expressing retrotrapezoid neurons is mediated in part by input from 5-HT neurons. J Physiol 2019; 597:2741-2766. [PMID: 30866045 PMCID: PMC6826216 DOI: 10.1113/jp277052] [Citation(s) in RCA: 31] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2018] [Accepted: 03/07/2019] [Indexed: 01/18/2023] Open
Abstract
KEY POINTS Neurons of the retrotrapezoid nucleus (RTN) and medullary serotonin (5-HT) neurons are both candidates for central CO2 /pH chemoreceptors, but it is not known how interactions between them influence their responses to pH. We found that RTN neurons in brain slices were stimulated by exogenous 5-HT and by heteroexchange release of endogenous 5-HT, and these responses were blocked by antagonists of 5-HT7 receptors. The pH response of RTN neurons in brain slices was markedly reduced by the same antagonists of 5-HT7 receptors. Similar results were obtained in dissociated, primary cell cultures prepared from the ventral medulla, where it was also found that the pH response of RTN neurons was blocked by preventing 5-HT synthesis and enhanced by blocking 5-HT reuptake. Exogenous 5-HT did not enable latent intrinsic RTN chemosensitivity. RTN neurons may play more of a role as relays from other central and peripheral chemoreceptors than as CO2 sensors. ABSTRACT Phox2b-expressing neurons in the retrotrapezoid nucleus (RTN) and serotonin (5-HT) neurons in the medullary raphe have both been proposed to be central respiratory chemoreceptors. How interactions between these two sets of neurons influence their responses to acidosis is not known. Here we recorded from mouse Phox2b+ RTN neurons in brain slices, and found that their response to moderate hypercapnic acidosis (pH 7.4 to ∼7.2) was markedly reduced by antagonists of 5-HT7 receptors. RTN neurons were stimulated in response to heteroexchange release of 5-HT, indicating that RTN neurons are sensitive to endogenous 5-HT. This electrophysiological behaviour was replicated in primary, dissociated cell cultures containing 5-HT and RTN neurons grown together. In addition, pharmacological inhibition of 5-HT synthesis in culture reduced RTN neuron chemosensitivity, and blocking 5-HT reuptake enhanced chemosensitivity. The effect of 5-HT on RTN neuron chemosensitivity was not explained by a mechanism whereby activation of 5-HT7 receptors enables or potentiates intrinsic chemosensitivity of RTN neurons, as exogenous 5-HT did not enhance the pH response. The ventilatory response to inhaled CO2 of mice was markedly decreased in vivo after systemic treatment with ketanserin, an antagonist of 5-HT2 and 5-HT7 receptors. These data indicate that 5-HT and RTN neurons may interact synergistically in a way that enhances the respiratory chemoreceptor response. The primary role of RTN neurons may be as relays and amplifiers of the pH response from 5-HT neurons and other chemoreceptors rather than as pH sensors themselves.
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Affiliation(s)
- Yuanming Wu
- Department of NeurologyUniversity of IowaIowa CityIA52242USA
| | - Katherine L. Proch
- Department of NeurologyUniversity of IowaIowa CityIA52242USA
- Graduate Program in NeuroscienceUniversity of IowaIowa CityIA52242USA
| | - Frida A. Teran
- Department of NeurologyUniversity of IowaIowa CityIA52242USA
- Graduate Program in NeuroscienceUniversity of IowaIowa CityIA52242USA
- Iowa Neuroscience InstituteUniversity of IowaIowa CityIA52242USA
| | | | - Harsh Kothari
- Department of PediatricsUniversity of IowaIowa CityIA52242USA
| | - George B. Richerson
- Department of NeurologyUniversity of IowaIowa CityIA52242USA
- Graduate Program in NeuroscienceUniversity of IowaIowa CityIA52242USA
- Department of Molecular Physiology & BiophysicsUniversity of IowaIowa CityIA52242USA
- Neurology ServiceVeterans Affairs Medical CenterIowa CityIA52242USA
- Iowa Neuroscience InstituteUniversity of IowaIowa CityIA52242USA
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Role of gamma-amino-butyric acid in the dorsal anterior cingulate in age-associated changes in cognition. Neuropsychopharmacology 2018; 43:2285-2291. [PMID: 30050047 PMCID: PMC6135795 DOI: 10.1038/s41386-018-0134-5] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/29/2018] [Revised: 05/13/2018] [Accepted: 06/18/2018] [Indexed: 11/08/2022]
Abstract
GABAergic mechanisms have been shown to contribute to cognitive aging in animal models, but there is currently limited in vivo evidence to support this relationship in humans. It is also unclear whether aging is associated with changes in GABA levels measured with proton magnetic resonance spectroscopy (MRS). Spectral-editing MRS at 3 T was used to measure GABA in the dorsal anterior cingulate cortex (dACC) for a large sample of healthy volunteers (N = 229) aged 18-55. In a subset of 171 participants, age effects on several cognitive tasks were studied. We formally tested whether the MRS measures mediated the relationship between age and cognition. Robust associations of age with performance were found for the Wisconsin Card Sorting Test ([WCST], p < 0.0001). Age was also significantly associated with declining levels of GABA in the dACC (p < 0.001), and GABA levels significantly predicted WCST performance (p < 0.0004). Mediation analysis revealed that GABA in the dACC mediated the effect of age on WCST performance (p < 0.01). Other metabolites were similarly associated with age, but only GABA and creatine levels were significantly associated with WCST performance. No association with age or cognitive performance was found in a frontal white matter control region in a subset of participants. The association of GABA with WCST performance was not related to the amount of brain atrophy associated with aging as measured by the proportion of CSF, gray, and white matter in the MRS voxel. These results implicate GABAergic and possibly energetic metabolism in the dACC as mechanisms of age effects in executive function.
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Lin YH, Liang HY, Xu K, Ni HY, Dong J, Xiao H, Chang L, Wu HY, Li F, Zhu DY, Luo CX. Dissociation of nNOS from PSD-95 promotes functional recovery after cerebral ischaemia in mice through reducing excessive tonic GABA release from reactive astrocytes. J Pathol 2017; 244:176-188. [DOI: 10.1002/path.4999] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2017] [Revised: 09/12/2017] [Accepted: 10/12/2017] [Indexed: 12/22/2022]
Affiliation(s)
- Yu-Hui Lin
- Department of Pharmacology, School of Pharmacy; Nanjing Medical University; Nanjing PR China
| | - Hai-Ying Liang
- Department of Pharmacology, School of Pharmacy; Nanjing Medical University; Nanjing PR China
| | - Ke Xu
- Department of Pharmacology, School of Pharmacy; Nanjing Medical University; Nanjing PR China
| | - Huan-Yu Ni
- Department of Pharmacology, School of Pharmacy; Nanjing Medical University; Nanjing PR China
| | - Jian Dong
- Department of Pharmacology, School of Pharmacy; Nanjing Medical University; Nanjing PR China
| | - Hui Xiao
- Department of Pharmacology, School of Pharmacy; Nanjing Medical University; Nanjing PR China
| | - Lei Chang
- Department of Pharmacology, School of Pharmacy; Nanjing Medical University; Nanjing PR China
- Laboratory of Cerebrovascular Disease; Nanjing Medical University; Nanjing PR China
| | - Hai-Yin Wu
- Department of Pharmacology, School of Pharmacy; Nanjing Medical University; Nanjing PR China
- Laboratory of Cerebrovascular Disease; Nanjing Medical University; Nanjing PR China
| | - Fei Li
- Department of Medicinal Chemistry, School of Pharmacy; Nanjing Medical University; Nanjing PR China
| | - Dong-Ya Zhu
- Department of Pharmacology, School of Pharmacy; Nanjing Medical University; Nanjing PR China
- Laboratory of Cerebrovascular Disease; Nanjing Medical University; Nanjing PR China
| | - Chun-Xia Luo
- Department of Pharmacology, School of Pharmacy; Nanjing Medical University; Nanjing PR China
- Laboratory of Cerebrovascular Disease; Nanjing Medical University; Nanjing PR China
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Afroz S, Shen H, Smith SS. α4βδ GABA A receptors reduce dendritic spine density in CA1 hippocampus and impair relearning ability of adolescent female mice: Effects of a GABA agonist and a stress steroid. Neuroscience 2017; 347:22-35. [PMID: 28189613 DOI: 10.1016/j.neuroscience.2017.01.051] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2016] [Revised: 01/22/2017] [Accepted: 01/31/2017] [Indexed: 01/10/2023]
Abstract
Synaptic pruning underlies the transition from an immature to an adult CNS through refinements of neuronal circuits. Our recent study indicates that pubertal synaptic pruning is triggered by the inhibition generated by extrasynaptic α4βδ GABAA receptors (GABARs) which are increased for 10 d on dendritic spines of CA1 pyramidal cells at the onset of puberty (PND 35-44) in the female mouse, suggesting α4βδ GABARs as a novel target for the regulation of adolescent synaptic pruning. In the present study we used a pharmacological approach to further examine the role of these receptors in altering spine density during puberty of female mice and the impact of these changes on spatial learning, assessed in adulthood. Two drugs were chronically administered during the pubertal period (PND 35-44): the GABA agonist gaboxadol (GBX, 0.1mg/kg, i.p.), to enhance current gated by α4βδ GABARs and the neurosteroid/stress steroid THP (3α-OH-5β-pregnan-20-one, 10mg/kg, i.p.) to decrease expression of α4βδ. Spine density was determined on PND 56 with Golgi staining. Spatial learning and relearning were assessed using the multiple object relocation task and an active place avoidance task on PND 56. Pubertal GBX decreased spine density post-pubertally by 70% (P<0.05), while decreasing α4βδ expression with THP increased spine density by twofold (P<0.05), in both cases, with greatest effects on the mushroom spines. Adult relearning ability was compromised in both hippocampus-dependent tasks after pubertal administration of either drug. These findings suggest that an optimal spine density produced by α4βδ GABARs is necessary for optimal cognition in adults.
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Affiliation(s)
- Sonia Afroz
- Department of Physiology and Pharmacology, SUNY Downstate Medical Center, 450 Clarkson Ave., Brooklyn, NY 11203, USA
| | - Hui Shen
- Department of Physiology and Pharmacology, SUNY Downstate Medical Center, 450 Clarkson Ave., Brooklyn, NY 11203, USA; School of Biomedical Engineering, Tianjin Medical University, No. 22 Qixiangtai Road, Heping District, Tianjin 300070, China
| | - Sheryl S Smith
- Department of Physiology and Pharmacology, SUNY Downstate Medical Center, 450 Clarkson Ave., Brooklyn, NY 11203, USA.
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Eskandari S, Willford SL, Anderson CM. Revised Ion/Substrate Coupling Stoichiometry of GABA Transporters. ADVANCES IN NEUROBIOLOGY 2017; 16:85-116. [PMID: 28828607 DOI: 10.1007/978-3-319-55769-4_5] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
The purpose of this review is to highlight recent evidence in support of a 3 Na+: 1 Cl-: 1 GABA coupling stoichiometry for plasma membrane GABA transporters (SLC6A1 , SLC6A11 , SLC6A12 , SLC6A13 ) and how the revised stoichiometry impacts our understanding of the contribution of GABA transporters to GABA homeostasis in synaptic and extrasynaptic regions in the brain under physiological and pathophysiological states. Recently, our laboratory probed the GABA transporter stoichiometry by analyzing the results of six independent measurements, which included the shifts in the thermodynamic transporter reversal potential caused by changes in the extracellular Na+, Cl-, and GABA concentrations, as well as the ratio of charge flux to substrate flux for Na+, Cl-, and GABA under voltage-clamp conditions. The shifts in the transporter reversal potential for a tenfold change in the external concentration of Na+, Cl-, and GABA were 84 ± 4, 30 ± 1, and 29 ± 1 mV, respectively. Charge flux to substrate flux ratios were 0.7 ± 0.1 charges/Na+, 2.0 ± 0.2 charges/Cl-, and 2.1 ± 0.1 charges/GABA. We then compared these experimental results with the predictions of 150 different transporter stoichiometry models, which included 1-5 Na+, 0-5 Cl-, and 1-5 GABA per transport cycle. Only the 3 Na+: 1 Cl-: 1 GABA stoichiometry model correctly predicts the results of all six experimental measurements. Using the revised 3 Na+: 1 Cl-: 1 GABA stoichiometry, we propose that the GABA transporters mediate GABA uptake under most physiological conditions. Transporter-mediated GABA release likely takes place under pathophysiological or extreme physiological conditions.
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Affiliation(s)
- Sepehr Eskandari
- Biological Sciences Department, California State Polytechnic University, Pomona, CA, 91768, USA.
| | - Samantha L Willford
- Biological Sciences Department, California State Polytechnic University, Pomona, CA, 91768, USA
| | - Cynthia M Anderson
- Biological Sciences Department, California State Polytechnic University, Pomona, CA, 91768, USA
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Salameh AI, Hübner CA, Boron WF. Role of Cl - -HCO 3- exchanger AE3 in intracellular pH homeostasis in cultured murine hippocampal neurons, and in crosstalk to adjacent astrocytes. J Physiol 2016; 595:93-124. [PMID: 27353306 DOI: 10.1113/jp272470] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2016] [Accepted: 06/20/2016] [Indexed: 12/11/2022] Open
Abstract
KEY POINTS A polymorphism of human AE3 is associated with idiopathic generalized epilepsy. Knockout of AE3 in mice lowers the threshold for triggering epileptic seizures. The explanations for these effects are elusive. Comparisons of cells from wild-type vs. AE3-/- mice show that AE3 (present in hippocampal neurons, not astrocytes; mediates HCO3- efflux) enhances intracellular pH (pHi ) recovery (decrease) from alkali loads in neurons and, surprisingly, adjacent astrocytes. During metabolic acidosis (MAc), AE3 speeds initial acidification, but limits the extent of pHi decrease in neurons and astrocytes. AE3 speeds re-alkalization after removal of MAc in neurons and astrocytes, and speeds neuronal pHi recovery from an ammonium prepulse-induced acid load. We propose that neuronal AE3 indirectly increases acid extrusion in (a) neurons via Cl- loading, and (b) astrocytes by somehow enhancing NBCe1 (major acid extruder). The latter would enhance depolarization-induced alkalinization of astrocytes, and extracellular acidification, and thereby reduce susceptibility to epileptic seizures. ABSTRACT The anion exchanger AE3, expressed in hippocampal (HC) neurons but not astrocytes, contributes to intracellular pH (pHi ) regulation by facilitating the exchange of extracellular Cl- for intracellular HCO3- . The human AE3 polymorphism A867D is associated with idiopathic generalized epilepsy. Moreover, AE3 knockout (AE3-/- ) mice are more susceptible to epileptic seizure. The mechanism of these effects has been unclear because the starting pHi in AE3-/- and wild-type neurons is indistinguishable. The purpose of the present study was to use AE3-/- mice to investigate the role of AE3 in pHi homeostasis in HC neurons, co-cultured with astrocytes. We find that the presence of AE3 increases the acidification rate constant during pHi recovery from intracellular alkaline loads imposed by reducing [CO2 ]. The presence of AE3 also speeds intracellular acidification during the early phase of metabolic acidosis (MAc), not just in neurons but, surprisingly, in adjacent astrocytes. Additionally, AE3 contributes to braking the decrease in pHi later during MAc in both neurons and astrocytes. Paradoxically, AE3 enhances intracellular re-alkalization after MAc removal in neurons and astrocytes, and pHi recovery from an ammonium prepulse-induced acid load in neurons. The effects of AE3 knockout on astrocytic pHi homeostasis in MAc-related assays require the presence of neurons, and are consistent with the hypothesis that the AE3 knockout reduces functional expression of astrocytic NBCe1. These findings suggest a new type of neuron-astrocyte communication, based on the expression of AE3 in neurons, which could explain how AE3 reduces seizure susceptibility.
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Affiliation(s)
- Ahlam I Salameh
- Department of Physiology and Biophysics, Case Western Reserve University School of Medicine, Cleveland, OH, 44106, USA
| | | | - Walter F Boron
- Department of Physiology and Biophysics, Case Western Reserve University School of Medicine, Cleveland, OH, 44106, USA
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Danielsson J, Zaidi S, Kim B, Funayama H, Yim PD, Xu D, Worgall TS, Gallos G, Emala CW. Airway Epithelial Cell Release of GABA is Regulated by Protein Kinase A. Lung 2016; 194:401-8. [PMID: 26989055 DOI: 10.1007/s00408-016-9867-2] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2015] [Accepted: 03/09/2016] [Indexed: 01/05/2023]
Abstract
INTRODUCTION γ-amino butyric acid (GABA) is not only the major inhibitory neurotransmitter in the central nervous system (CNS), but it also plays an important role in the lung, mediating airway smooth muscle relaxation and mucus production. As kinases such as protein kinase A (PKA) are known to regulate the release and reuptake of GABA in the CNS by GABA transporters, we hypothesized that β-agonists would affect GABA release from airway epithelial cells through activation of PKA. METHODS C57/BL6 mice received a pretreatment of a β-agonist or vehicle (PBS), followed by methacholine or PBS. Bronchoalveolar lavage (BAL) was collected and the amount of GABA was quantified using HPLC mass spectrometry. For in vitro studies, cultured BEAS-2B human airway epithelial cells were loaded with (3)H-GABA. (3)H-GABA released was measured during activation and inhibition of PKA and tyrosine kinase signaling pathways. RESULTS β-agonist pretreatment prior to methacholine challenge attenuated in vivo GABA release in mouse BAL and (3)H-GABA release from depolarized BEAS-2B cells. GABA release was also decreased in BEAS-2B cells by increases in cAMP but not by Epac or tyrosine kinase activation. CONCLUSION β-agonists decrease GABA release from airway epithelium through the activation of cAMP and PKA. This has important therapeutic implications as β-agonists and GABA are important mediators of both mucus production and airway smooth muscle tone.
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Affiliation(s)
- Jennifer Danielsson
- Department of Anesthesiology, Columbia University, 630 W 168th St., P&S Box 46, New York, NY, 10032, USA.
| | - Sarah Zaidi
- Department of Pediatrics, Columbia University, New York, NY, 10032, USA
| | - Benjamin Kim
- Department of Pathology and Cell Biology, Columbia University, New York, NY, 10032, USA
| | - Hiromi Funayama
- Department of Anesthesiology, Columbia University, 630 W 168th St., P&S Box 46, New York, NY, 10032, USA
- Department of Pediatric Dentistry, Tsurumi University School of Dental Medicine, Yokohama, Japan
| | - Peter D Yim
- Department of Anesthesiology, Columbia University, 630 W 168th St., P&S Box 46, New York, NY, 10032, USA
| | - Dingbang Xu
- Department of Anesthesiology, Columbia University, 630 W 168th St., P&S Box 46, New York, NY, 10032, USA
| | - Tilla S Worgall
- Department of Pathology and Cell Biology, Columbia University, New York, NY, 10032, USA
| | - George Gallos
- Department of Anesthesiology, Columbia University, 630 W 168th St., P&S Box 46, New York, NY, 10032, USA
| | - Charles W Emala
- Department of Anesthesiology, Columbia University, 630 W 168th St., P&S Box 46, New York, NY, 10032, USA
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Raiteri L, Raiteri M. Multiple functions of neuronal plasma membrane neurotransmitter transporters. Prog Neurobiol 2015; 134:1-16. [PMID: 26300320 DOI: 10.1016/j.pneurobio.2015.08.002] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2015] [Revised: 07/09/2015] [Accepted: 08/18/2015] [Indexed: 12/11/2022]
Abstract
Removal from receptors of neurotransmitters just released into synapses is one of the major steps in neurotransmission. Transporters situated on the plasma membrane of nerve endings and glial cells perform the process of neurotransmitter (re)uptake. Because the density of transporters in the membranes can fluctuate, transporters can determine the transmitter concentrations at receptors, thus modulating indirectly the excitability of neighboring neurons. Evidence is accumulating that neurotransmitter transporters can exhibit multiple functions. Being bidirectional, neurotransmitter transporters can mediate transmitter release by working in reverse, most often under pathological conditions that cause ionic gradient dysregulations. Some transporters reverse to release transmitters, like dopamine or serotonin, when activated by 'indirectly acting' substrates, like the amphetamines. Some transporters exhibit as one major function the ability to capture transmitters into nerve terminals that perform insufficient synthesis. Transporter activation can generate conductances that regulate directly neuronal excitability. Synaptic and non-synaptic transporters play different roles. Cytosolic Na(+) elevations accompanying transport can interact with plasmalemmal or/and mitochondrial Na(+)/Ca(2+) exchangers thus generating calcium signals. Finally, neurotransmitter transporters can behave as receptors mediating releasing stimuli able to cause transmitter efflux through multiple mechanisms. Neurotransmitter transporters are therefore likely to play hitherto unknown roles in multiple therapeutic treatments.
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Affiliation(s)
- Luca Raiteri
- Department of Pharmacy, Pharmacology and Toxicology Section, University of Genoa, Genoa, Italy; Center of Excellence for Biomedical Research, University of Genoa, Genoa, Italy; National Institute of Neuroscience, Genoa, Italy
| | - Maurizio Raiteri
- Department of Pharmacy, Pharmacology and Toxicology Section, University of Genoa, Genoa, Italy; Center of Excellence for Biomedical Research, University of Genoa, Genoa, Italy; National Institute of Neuroscience, Genoa, Italy.
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Wang P, Eshaq RS, Meshul CK, Moore C, Hood RL, Leidenheimer NJ. Neuronal gamma-aminobutyric acid (GABA) type A receptors undergo cognate ligand chaperoning in the endoplasmic reticulum by endogenous GABA. Front Cell Neurosci 2015; 9:188. [PMID: 26041994 PMCID: PMC4435044 DOI: 10.3389/fncel.2015.00188] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2015] [Accepted: 04/28/2015] [Indexed: 01/01/2023] Open
Abstract
GABAA receptors mediate fast inhibitory neurotransmission in the brain. Dysfunction of these receptors is associated with various psychiatric/neurological disorders and drugs targeting this receptor are widely used therapeutic agents. Both the efficacy and plasticity of GABAA receptor-mediated neurotransmission depends on the number of surface GABAA receptors. An understudied aspect of receptor cell surface expression is the post-translational regulation of receptor biogenesis within the endoplasmic reticulum (ER). We have previously shown that exogenous GABA can act as a ligand chaperone of recombinant GABAA receptors in the early secretory pathway leading us to now investigate whether endogenous GABA facilitates the biogenesis of GABAA receptors in primary cerebral cortical cultures. In immunofluorescence labeling experiments, we have determined that neurons expressing surface GABAA receptors contain both GABA and its degradative enzyme GABA transaminase (GABA-T). Treatment of neurons with GABA-T inhibitors, a treatment known to increase intracellular GABA levels, decreases the interaction of the receptor with the ER quality control protein calnexin, concomittantly increasing receptor forward-trafficking and plasma membrane insertion. The effect of GABA-T inhibition on the receptor/calnexin interaction is not due to the activation of surface GABAA or GABAB receptors. Consistent with our hypothesis that GABA acts as a cognate ligand chaperone in the ER, immunogold-labeling of rodent brain slices reveals the presence of GABA within the rough ER. The density of this labeling is similar to that present in mitochondria, the organelle in which GABA is degraded. Lastly, the effect of GABA-T inhibition on the receptor/calnexin interaction was prevented by pretreatment with a GABA transporter inhibitor. Together, these data indicate that endogenous GABA acts in the rough ER as a cognate ligand chaperone to facilitate the biogenesis of neuronal GABAA receptors.
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Affiliation(s)
- Ping Wang
- Department of Biochemistry and Molecular Biology, Louisiana State University, Health Sciences Center-Shreveport Shreveport, LA, USA
| | - Randa S Eshaq
- Department of Biochemistry and Molecular Biology, Louisiana State University, Health Sciences Center-Shreveport Shreveport, LA, USA
| | - Charles K Meshul
- Veterans Hospital Portland/Research Services/Neurocytology Laboratory and Department of Behavioral Neuroscience, Oregon Health & Science University Portland, OR, USA
| | - Cynthia Moore
- Veterans Hospital Portland/Research Services/Neurocytology Laboratory and Department of Behavioral Neuroscience, Oregon Health & Science University Portland, OR, USA
| | - Rebecca L Hood
- Veterans Hospital Portland/Research Services/Neurocytology Laboratory and Department of Behavioral Neuroscience, Oregon Health & Science University Portland, OR, USA
| | - Nancy J Leidenheimer
- Department of Biochemistry and Molecular Biology, Louisiana State University, Health Sciences Center-Shreveport Shreveport, LA, USA
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Evidence for a Revised Ion/Substrate Coupling Stoichiometry of GABA Transporters. J Membr Biol 2015; 248:795-810. [DOI: 10.1007/s00232-015-9797-6] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2015] [Accepted: 03/19/2015] [Indexed: 10/23/2022]
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Synaptic GABA release prevents GABA transporter type-1 reversal during excessive network activity. Nat Commun 2015; 6:6597. [PMID: 25798861 PMCID: PMC4374149 DOI: 10.1038/ncomms7597] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2014] [Accepted: 02/10/2015] [Indexed: 12/15/2022] Open
Abstract
GABA transporters control extracellular GABA, which regulates the key aspects of neuronal and network behaviour. A prevailing view is that modest neuronal depolarization results in GABA transporter type-1 (GAT-1) reversal causing non-vesicular GABA release into the extracellular space during intense network activity. This has important implications for GABA uptake-targeting therapies. Here we combined a realistic kinetic model of GAT-1 with experimental measurements of tonic GABAA receptor currents in ex vivo hippocampal slices to examine GAT-1 operation under varying network conditions. Our simulations predict that synaptic GABA release during network activity robustly prevents GAT-1 reversal. We test this in the 0 Mg2+ model of epileptiform discharges using slices from healthy and chronically epileptic rats and find that epileptiform activity is associated with increased synaptic GABA release and is not accompanied by GAT-1 reversal. We conclude that sustained efflux of GABA through GAT-1 is unlikely to occur during physiological or pathological network activity. Membrane depolarization during increased neuronal activity as seen during epilepsy has been suggested to easily reverse neuronal GABA transporters. Here the authors use modelling and experimental data and challenge this view by showing that synaptic GABA release during excessive neuronal firing averts reversal of GABA uptake.
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The modulatory action of harmane on serotonergic neurotransmission in rat brain. Brain Res 2015; 1597:57-64. [DOI: 10.1016/j.brainres.2014.11.056] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2014] [Revised: 10/27/2014] [Accepted: 11/27/2014] [Indexed: 02/06/2023]
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Romei C, Sabolla C, Raiteri L. High-affinity GABA uptake by neuronal GAT1 transporters provokes release of [3H]GABA by homoexchange and through GAT1-independent Ca2+-mediated mechanisms. Neuropharmacology 2015; 88:164-70. [DOI: 10.1016/j.neuropharm.2014.08.007] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2014] [Revised: 07/23/2014] [Accepted: 08/10/2014] [Indexed: 12/19/2022]
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Zheng M, Matsuo T, Miyamoto A, Hoshino O. Tonically balancing intracortical excitation and inhibition by GABAergic gliotransmission. Neural Comput 2014; 26:1690-716. [PMID: 24877734 DOI: 10.1162/neco_a_00612] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/04/2022]
Abstract
For sensory cortices to respond reliably to feature stimuli, the balancing of neuronal excitation and inhibition is crucial. A typical example might be the balancing of phasic excitation within cell assemblies and phasic inhibition between cell assemblies. The former controls the gain of and the latter the tuning of neuronal responses. A change in ambient GABA concentration might affect the dynamic behavior of neurons in a tonic manner. For instance, an increase in ambient GABA concentration enhances the activation of extrasynaptic receptors, augments an inhibitory current, and thus inhibits neurons. When a decrease in ambient GABA concentration occurs, the tonic inhibitory current is reduced, and thus the neurons are relatively excited. We simulated a neural network model in order to examine whether and how such a tonic excitatory-inhibitory mechanism could work for sensory information processing. The network consists of cell assemblies. Each cell assembly, comprising principal cells (P), GABAergic interneurons (Ia, Ib), and glial cells (glia), responds to one particular feature stimulus. GABA transporters, embedded in glial plasma membranes, regulate ambient GABA levels. Hypothetical neuron-glia signaling via inhibitory (Ia-to-glia) and excitatory (P-to-glia) synaptic contacts was assumed. The former let transporters import (remove) GABA from the extracellular space and excited stimulus-relevant P cells. The latter let them export GABA into the extracellular space and inhibited stimulus-irrelevant P cells. The main finding was that the glial membrane transporter gave a combinatorial excitatory-inhibitory effect on P cells in a tonic manner, thereby improving the gain and tuning of neuronal responses. Interestingly, it worked cooperatively with the conventional, phasic excitatory-inhibitory mechanism. We suggest that the GABAergic gliotransmission mechanism may provide balanced intracortical excitation and inhibition so that the best perceptual performance of the cortex can be achieved.
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Affiliation(s)
- Meihong Zheng
- Department of Psychology, Tsinghua University, Beijing, 100084, China
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Tarasenko A, Krupko O, Himmelreich N. New insights into molecular mechanism(s) underlying the presynaptic action of nitric oxide on GABA release. Biochim Biophys Acta Gen Subj 2014; 1840:1923-32. [PMID: 24480299 DOI: 10.1016/j.bbagen.2014.01.030] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2013] [Revised: 01/17/2014] [Accepted: 01/21/2014] [Indexed: 12/31/2022]
Abstract
BACKGROUND Nitric oxide (NO) is an important presynaptic modulator of synaptic transmission. Here, we aimed to correlate the release of the major inhibitory neurotransmitter GABA with intracellular events occurring in rat brain axon terminals during their exposure to NO in the range of nanomolar-low micromolar concentrations. METHODS Using [(3)H]GABA and fluorescent dyes (Fluo 4-AM, acridine orange and rhodamine 6G), the following parameters were evaluated: vesicular and cytosolic GABA pools, intracellular calcium concentration, synaptic vesicle acidification, and mitochondrial membrane potential. Diethylamine NONOate (DEA/NO) and S-nitroso-N-acetylpenicillamine (SNAP) were used as NO donors. RESULTS DEA/NO and SNAP (in the presence of dithiothreitol (DTT)) stimulated external Ca(2+)-independent [(3)H]GABA release, which was not attributed to a rise in intracellular calcium concentration. [(3)H]GABA release coincided with increasing GABA level in cytosol and decreasing the vesicular GABA content available for exocytotic release. There was a strong temporal correlation between NO-induced increase in cytosolic [GABA] and dissipation of both synaptic vesicle proton gradient and mitochondrial membrane potential. Dissipation was reversible, and recovery of both parameters correlated in time with re-accumulation of [(3)H]GABA into synaptic vesicles. The molar ratio of DTT to SNAP determined the rate and duration of the recovery processes. CONCLUSIONS We suggest that NO can stimulate GABA release via GABA transporter reversal resulting from increased GABA levels in cytosol. The latter is reversible and appears to be due to S-nitrosylation of key proteins, which affect the energy status of the pre-synapse. GENERAL SIGNIFICANCE Our findings provide new insight into molecular mechanism(s) underlying the presynaptic action of nitric oxide on inhibitory neurotransmission.
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Affiliation(s)
- Alla Tarasenko
- Department of Neurochemistry, Palladin Institute of Biochemistry, National Academy of Sciences of Ukraine, Leontovich Str. 9, Kyiv 01601, Ukraine.
| | - Olga Krupko
- Department of Neurochemistry, Palladin Institute of Biochemistry, National Academy of Sciences of Ukraine, Leontovich Str. 9, Kyiv 01601, Ukraine.
| | - Nina Himmelreich
- Department of Neurochemistry, Palladin Institute of Biochemistry, National Academy of Sciences of Ukraine, Leontovich Str. 9, Kyiv 01601, Ukraine.
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Milanese M, Romei C, Usai C, Oliveri M, Raiteri L. A new function for glycine GlyT2 transporters: Stimulation of γ-aminobutyric acid release from cerebellar nerve terminals through GAT1 transporter reversal and Ca2+-dependent anion channels. J Neurosci Res 2013; 92:398-408. [DOI: 10.1002/jnr.23321] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2013] [Accepted: 10/08/2013] [Indexed: 11/06/2022]
Affiliation(s)
- Marco Milanese
- Department of Pharmacy; Pharmacology and Toxicology Section, University of Genoa; Genoa Italy
- Center of Excellence for Biomedical Research; University of Genoa; Genoa Italy
| | - Cristina Romei
- Department of Pharmacy; Pharmacology and Toxicology Section, University of Genoa; Genoa Italy
| | - Cesare Usai
- Institute of Biophysics; National Research Council; Genoa Italy
| | - Martina Oliveri
- Department of Pharmacy; Pharmacology and Toxicology Section, University of Genoa; Genoa Italy
| | - Luca Raiteri
- Department of Pharmacy; Pharmacology and Toxicology Section, University of Genoa; Genoa Italy
- Center of Excellence for Biomedical Research; University of Genoa; Genoa Italy
- National Institute of Neuroscience; Genoa Italy
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Li ZX, Yu HM, Jiang KW. Tonic GABA inhibition in hippocampal dentate granule cells: its regulation and function in temporal lobe epilepsies. Acta Physiol (Oxf) 2013; 209:199-211. [PMID: 23865761 DOI: 10.1111/apha.12148] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2013] [Revised: 05/06/2013] [Accepted: 07/12/2013] [Indexed: 01/06/2023]
Abstract
Both human and experimental evidence strongly supports the view of brain region- and cell-specific changes in tonic GABA inhibition in temporal lobe epilepsies (TLE). This 'tonic' form of signalling is not time-locked to presynaptic action potentials, which depends upon detection of ambient GABA by extrasynaptic GABAA receptors (GABAA Rs). Extrasynaptic GABAA Rs have distinct physiological and pharmacological features, including high GABA-binding affinity and low desensitization and a variety of the specific subunit combinations (α4δ-,α6δ-,α5γ-,ε-containing receptors). These features closely contribute to the function of tonic GABA current, which is preserved properly or increased in dentate gyrus in models of TLE, even in the face of a loss of synaptic inhibition and inhibitory interneurones. Markedly reduced tonic GABA inhibition may facilitate an episode of epilepsy, while persistent elevated tonic inhibition may contribute to the onset of spontaneous recurrent seizures. In dentate granule cells, tonic GABA inhibition is positively modulated by endogenous neurosteroids and other factors, which undergo changes related to hormonal status after TLE. Tonic inhibition regulates neuronal excitability through its effects on membrane potential by both offsetting the threshold and reducing the frequency of action potentials and input resistance. Therefore, extrasynaptic GABAA Rs are expected to be the most important pharmacological targets in TLE. It is likely that both elevate the ambient GABA concentration and potentiate the tonic currents, contributing to the antiepileptic effects.
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Affiliation(s)
- Z.-X. Li
- Department of Neurology; The Children's Hospital Zhejiang University School of Medicine; Hangzhou; China
| | - H.-M. Yu
- Department of Neonatology; The Children's Hospital Zhejiang University School of Medicine; Hangzhou; China
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Shahrokhi A, Hassanzadeh G, Vousooghi N, Joghataei MT, Eftekhari S, Zarrindast MR. The effect of tiagabine on physical development and neurological reflexes and their relationship with the γ-aminobutyric acid switch in the rat cerebral cortex during developmental stages. Behav Pharmacol 2013; 24:561-8. [PMID: 26057770 DOI: 10.1097/fbp.0b013e328365422f] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
In the present study, we focused on γ-aminobutyric acid (GABA) signaling through the γ-aminobutyric acid transporter (GAT) in the developing rat cerebral cortex. Tiagabine was used as a GAT inhibitor. The offspring received injections from birth until postnatal day 21 intraperitoneally. Physical development and neurological reflexes were assessed daily. Tiagabine did not influence body weight, the onset and completion of incisor eruption, or the time to appearance of cliff avoidance. However, the onset and completion of eye opening, ear unfolding, and fur growth occurred earlier in treated pups. Further, the slanted board test and righting reflex showed accelerated development (i.e. decreased time to criterion) when compared with the control group. To determine whether the obtained effects are related to the GABA switch, we examined the protein and mRNA expression of the K(+)-Cl(-) cotransporter KCC2 using western blotting and RT-PCR, respectively. Downregulation of KCC2 mRNA and protein levels was observed when GAT was inhibited. The results may indicate a role of GAT in the neurobehavioral changes that accompany the developmental switch in GABA function.
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Affiliation(s)
- Amene Shahrokhi
- Department of Neuroscience, School of Advanced Technologies in Medicine, Tehran University of Medical Sciences, Tehran, Iran
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The effects of volatile anesthetics on the extracellular accumulation of [(3)H]GABA in rat brain cortical slices. Cell Mol Neurobiol 2013; 34:71-81. [PMID: 24081560 DOI: 10.1007/s10571-013-9988-6] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2013] [Accepted: 09/14/2013] [Indexed: 12/13/2022]
Abstract
GABA is an inhibitory neurotransmitter that appears to be associated with the action of volatile anesthetics. These anesthetics potentiate GABA-induced postsynaptic currents by synaptic GABAA receptors, although recent evidence suggests that these agents also significantly affect extrasynaptic GABA receptors. However, the effect of volatile anesthetics on the extracellular concentration of GABA in the central nervous system has not been fully established. In the present study, rat brain cortical slices loaded with [(3)H]GABA were used to investigate the effect of halothane and sevoflurane on the extracellular accumulation of this neurotransmitter. The accumulation of [(3)H]GABA was significantly increased by sevoflurane (0.058, 0.11, 0.23, 0.46, and 0.93 mM) and halothane (0.006, 0.012, 0.024, 0.048, 0072, and 0.096 mM) with an EC50 of 0.26 mM and 35 μM, respectively. TTX (blocker of voltage-dependent Na(+) channels), EGTA (an extracellular Ca(2+) chelator) and BAPTA-AM (an intracellular Ca(2+) chelator) did not interfere with the accumulation of [(3)H]GABA induced by 0.23 mM sevoflurane and 0.048 mM halothane. SKF 89976A, a GABA transporter type 1 (GAT-1) inhibitor, reduced the sevoflurane- and halothane-induced increase in the accumulation of GABA by 57 and 63 %, respectively. Incubation of brain cortical slices at low temperature (17 °C), a condition that inhibits GAT function and reduces GABA release through reverse transport, reduced the sevoflurane- and halothane-induced increase in the accumulation of [(3)H]GABA by 82 and 75 %, respectively, relative to that at normal temperature (37 °C). Ouabain, a Na(+)/K(+) ATPase pump inhibitor, which is known to induce GABA release through reverse transport, abolished the sevoflurane and halothane effects on the accumulation of [(3)H]GABA. The effect of sevoflurane and halothane did not involve glial transporters because β-alanine, a blocker of GAT-2 and GAT-3, did not inhibit the effect of the anesthetics. In conclusion, the present study suggests that sevoflurane and halothane increase the accumulation of GABA by inducing the reverse transport of this neurotransmitter. Therefore, volatile anesthetics could interfere with neuronal excitability by increasing the action of GABA on synaptic and extrasynaptic GABA receptors.
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Vigabatrin inhibits seizures and mTOR pathway activation in a mouse model of tuberous sclerosis complex. PLoS One 2013; 8:e57445. [PMID: 23437388 PMCID: PMC3577710 DOI: 10.1371/journal.pone.0057445] [Citation(s) in RCA: 70] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2012] [Accepted: 01/24/2013] [Indexed: 11/25/2022] Open
Abstract
Epilepsy is a common neurological disorder and cause of significant morbidity and mortality. Although antiseizure medication is the first-line treatment for epilepsy, currently available medications are ineffective in a significant percentage of patients and have not clearly been demonstrated to have disease-specific effects for epilepsy. While seizures are usually intractable to medication in tuberous sclerosis complex (TSC), a common genetic cause of epilepsy, vigabatrin appears to have unique efficacy for epilepsy in TSC. While vigabatrin increases gamma-aminobutyric acid (GABA) levels, the precise mechanism of action of vigabatrin in TSC is not known. In this study, we investigated the effects of vigabatrin on epilepsy in a knock-out mouse model of TSC and tested the novel hypothesis that vigabatrin inhibits the mammalian target of rapamycin (mTOR) pathway, a key signaling pathway that is dysregulated in TSC. We found that vigabatrin caused a modest increase in brain GABA levels and inhibited seizures in the mouse model of TSC. Furthermore, vigabatrin partially inhibited mTOR pathway activity and glial proliferation in the knock-out mice in vivo, as well as reduced mTOR pathway activation in cultured astrocytes from both knock-out and control mice. This study identifies a potential novel mechanism of action of an antiseizure medication involving the mTOR pathway, which may account for the unique efficacy of this drug for a genetic epilepsy.
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Ransom CB, Tao W, Wu Y, Spain WJ, Richerson GB. Rapid regulation of tonic GABA currents in cultured rat hippocampal neurons. J Neurophysiol 2012; 109:803-12. [PMID: 23114210 DOI: 10.1152/jn.00460.2012] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
Subacute and chronic changes in tonic GABAergic inhibition occur in human and experimental epilepsy. Less is known about how tonic inhibition is modulated over shorter time frames (seconds). We measured endogenous tonic GABA currents from cultured rat hippocampal neurons to evaluate how they are affected by 1) transient increases in extracellular GABA concentration ([GABA]), 2) transient postsynaptic depolarization, and 3) depolarization of presynaptic cells. Transient increases in [GABA] (1 μM) reduced tonic currents; this reduction resulted from GABA-induced shifts in the reversal potential for GABA currents (E(GABA)). Transient depolarization of postsynaptic neurons reversed the effects of exogenous GABA and potentiated tonic currents. The voltage-dependent potentiation of tonic GABA currents was independent of E(GABA) shifts and represented postdepolarization potentiation (PDP), an intrinsic GABA(A) receptor property (Ransom CB, Wu Y, Richerson GB. J Neurosci 30: 7672-7684, 2010). Inhibition of vesicular GABA release with concanamycin A (ConA) did not affect tonic currents. In ConA-treated cells, transient application of 12 mM K(+) to depolarize presynaptic neurons and glia produced a persistent increase in tonic current amplitude. The K(+)-induced increase in tonic current was reversibly inhibited by SKF89976a (40 μM), indicating that this was caused by nonvesicular GABA release from GABA transporter type 1 (GAT1). Nonvesicular GABA release due to GAT1 reversal also occurred in acute hippocampal brain slices. Our results indicate that tonic GABA currents are rapidly regulated by GABA-induced changes in intracellular Cl(-) concentration, PDP of extrasynaptic GABA(A) receptors, and nonvesicular GABA release. These mechanisms may influence tonic inhibition during seizures when neurons are robustly depolarized and extracellular GABA and K(+) concentrations are elevated.
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Affiliation(s)
- Christopher B Ransom
- Epilepsy Center of Excellence, Veterans Affairs Puget Sound Health Care System, Seattle, WA, USA.
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Kuver A, Shen H, Smith SS. Regulation of the surface expression of α4β2δ GABAA receptors by high efficacy states. Brain Res 2012; 1463:1-20. [PMID: 22609410 PMCID: PMC3371167 DOI: 10.1016/j.brainres.2012.04.047] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2011] [Revised: 04/20/2012] [Accepted: 04/25/2012] [Indexed: 01/10/2023]
Abstract
α4βδ GABA(A) receptors (GABARs) have low CNS expression, but their expression is increased by 48h exposure to the neurosteroid THP (3α-OH-5α[β]-pregnan-20-one). THP also increases the efficacy of δ-containing GABARs acutely, where GABA is a partial agonist. Thus, we examined effects of THP (100 nM) and full GABA agonists at α4β2δ (gaboxadol, 10 μM, and β-alanine, 10 μM-1mM), on surface expression of α4β2δ. To this end, we used an α4 construct tagged with a 3XFLAG (F) epitope or measured expression of native α4 and δ. HEK-293 cells or cultured hippocampal neurons were transfected with α4Fβ2δ and treated 24h later with GABA agonists, THP, GABA plus THP or vehicle (0.01% DMSO) for 0.5 h-48 h. Immunocytochemistry was performed under both non-permeabilized and permeabilized conditions to detect surface and intracellular labeling, respectively, using confocal microscopy. The high efficacy agonists and GABA (1 or 10 μM) plus THP increased α4β2δ surface expression up to 3-fold after 48h, an effect first seen by 0.5h. This effect was not dependent upon the polarity of GABAergic current, although expression was increased by KCC2. Intracellular labeling was decreased while functional expression was confirmed by whole cell patch clamp recordings of responses to GABA agonists. GABA plus THP treatment did not alter the rate of receptor removal from the surface membrane, suggesting that THP-induced α4β2δ expression is likely via receptor insertion. Surface expression of α4β2δ was decreased by rottlerin (10 μM), suggesting a role for PKC-δ. These results suggest that trafficking of α4β2δ GABARs is regulated by high efficacy states.
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Affiliation(s)
- Aarti Kuver
- Dept. of Physiology and Pharmacology, SUNY Downstate Medical Center, 450 Clarkson Ave., Brooklyn, NY 11203 U.S.A
| | - Hui Shen
- Dept. of Physiology and Pharmacology, SUNY Downstate Medical Center, 450 Clarkson Ave., Brooklyn, NY 11203 U.S.A
| | - Sheryl S. Smith
- Dept. of Physiology and Pharmacology, SUNY Downstate Medical Center, 450 Clarkson Ave., Brooklyn, NY 11203 U.S.A
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Hoshino O. Subthreshold Membrane Depolarization as Memory Trace for Perceptual Learning. Neural Comput 2011; 23:3205-31. [DOI: 10.1162/neco_a_00211] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/04/2022]
Abstract
Experience-dependent synaptic plasticity characterizes the adaptable brain and is believed to be the cellular substrate for perceptual learning. A chemical agent such as gamma-aminobutyric acid (GABA) is known to affect synaptic alteration, perhaps gating perceptual learning. We examined whether and how ambient (extrasynaptic) GABA affects experience-dependent synaptic alteration. A cortical neural network model was simulated. Transporters on GABAergic interneurons regulate ambient GABA levels around their axonal target neurons by removing GABA from (forward transport) or releasing it into (reverse transport) the extracellular space. The ambient GABA provides neurons with tonic inhibitory currents by activating extrasynaptic GABAa receptors. During repeated exposures to the same stimulus, we modified the synaptic connection strength between principal cells in a spike-timing-dependent manner. This modulated the activity of GABAergic interneurons, and reduced or augmented ambient GABA concentration. Reduction in ambient GABA concentration led to slight depolarization (less than several millivolts) in ongoing-spontaneous membrane potential. This was a subthreshold neuronal behavior because ongoing-spontaneous spiking activity remained almost unchanged. The ongoing-spontaneous subthreshold depolarization improved a suprathreshold neuronal response. If the stimulus was long absent for perceptual learning, augmentation of ambient GABA concentration took place and the ongoing-spontaneous subthreshold depolarization was depressed. We suggest that a perceptual memory trace could be left in neuronal circuitry as an ongoing-spontaneous subthreshold membrane depolarization, which would allow that memory to be accessed easily afterward, whereas a trace of a memory that has not recently been retrieved fades away when the ongoing-spontaneous subthreshold membrane depolarization built by previous perceptual learning is depressed. This would lead that memory to be accessed with some difficulty. In the brain, ambient GABA, whose level could be regulated by transporter may have an important role in leaving memory trace for perceptual learning.
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Affiliation(s)
- Osamu Hoshino
- Department of Intelligent Systems Engineering, Ibaraki University, Hitachi, Ibaraki, 316-8511, Japan
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JEDLICKA SABRINAS, DADARLAT MARIA, HASSELL TRAVIS, LIN YANZHU, YOUNG AARON, ZHANG MIN, IRAZOQUI PEDRO, RICKUS JENNAL. CALIBRATION OF NEUROTRANSMITTER RELEASE FROM NEURAL CELLS FOR THERAPEUTIC IMPLANTS. Int J Neural Syst 2011; 19:197-212. [DOI: 10.1142/s0129065709001963] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
In this work we quantified the in vitro calibration relationships between high frequency electrical stimulation and GABA and glutamate release in both mature retinoic acid differentiated P19 neurons and immortalized embryonic cortical cells engineered to express glutamic acid decarboxylase, GAD65. Extracellular glutamate and GABA was quantified by 2D gas chromatography and time of flight mass spectrometry after stimulation at varying amplitudes and frequencies. Amplitude sweeps resulted in a linear calibration for P19 neurons; the level of neurotransmitter varied over one order of magnitude from ~ 200 pg/neuron to ~ 1.2 ng/neuron for glutamate and ~ 1 ng/neuron to ~ 2 ng/neuron for GABA, depending on the stimulation amplitude. Frequency sweeps resulted in a peak release at 250 Hz for glutamate and 400 Hz for GABA in P19 cells. The GABA transporter inhibitor, nipecotic acid, increased extracellular GABA levels and decrease glutamate. In contrast the embryonic cortical cells had a strongly nonlinear dependency of release on stimulation amplitude, and a weak dependence on frequency. These cells had roughly equal extracellular glutamate and GABA levels after stimulation despite the expression of GAD65. In addition glutamate and GABA levels were insensitive to nipecotic acid. These results demonstrate an ability to calibrate and tune neurotransmitter release from neural cells using high frequency stimulation parameters.
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Affiliation(s)
- SABRINA S. JEDLICKA
- Department of Agricultural and Biological Engineering, USA
- Physiological Sensing Facility at the Bindley Bioscience Center, USA
| | | | - TRAVIS HASSELL
- Weldon School of Biomedical Engineering, USA
- Indiana University School of Medicine, Indiana University, Indianapolis, IN 46202, USA
| | - YANZHU LIN
- Department of Statistics, Purdue University, West Lafayette, IN 47907, USA
| | - AARON YOUNG
- Weldon School of Biomedical Engineering, USA
| | - MIN ZHANG
- Department of Statistics, Purdue University, West Lafayette, IN 47907, USA
| | | | - JENNA L. RICKUS
- Department of Agricultural and Biological Engineering, USA
- Physiological Sensing Facility at the Bindley Bioscience Center, USA
- Weldon School of Biomedical Engineering, USA
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Nasrallah FA, Balcar VJ, Rae CD. Activity-dependent γ-aminobutyric acid release controls brain cortical tissue slice metabolism. J Neurosci Res 2011; 89:1935-45. [DOI: 10.1002/jnr.22649] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2010] [Revised: 02/15/2011] [Accepted: 03/01/2011] [Indexed: 12/16/2022]
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Sperk G, Wieselthaler-Hölzl A, Pirker S, Tasan R, Strasser SS, Drexel M, Pifl C, Marschalek J, Ortler M, Trinka E, Heitmair-Wietzorrek K, Ciofi P, Feucht M, Baumgartner C, Czech T. Glutamate decarboxylase 67 is expressed in hippocampal mossy fibers of temporal lobe epilepsy patients. Hippocampus 2011; 22:590-603. [PMID: 21509853 DOI: 10.1002/hipo.20923] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 12/05/2010] [Indexed: 11/12/2022]
Abstract
Recently, expression of glutamate decarboxylase-67 (GAD67), a key enzyme of GABA synthesis, was detected in the otherwise glutamatergic mossy fibers of the rat hippocampus. Synthesis of the enzyme was markedly enhanced after experimentally induced status epilepticus. Here, we investigated the expression of GAD67 protein and mRNA in 44 hippocampal specimens from patients with mesial temporal lobe epilepsy (TLE) using double immunofluorescence histochemistry, immunoblotting, and in situ hybridization. Both in specimens with (n = 37) and without (n = 7) hippocampal sclerosis, GAD67 was highly coexpressed with dynorphin in terminal areas of mossy fibers, including the dentate hilus and the stratum lucidum of sector CA3. In the cases with Ammon's horn sclerosis, also the inner molecular layer of the dentate gyrus contained strong staining for GAD67 immunoreactivity, indicating labeling of mossy fiber terminals that specifically sprout into this area. Double immunofluorescence revealed the colocalization of GAD67 immunoreactivity with the mossy fiber marker dynorphin. The extent of colabeling correlated with the number of seizures experienced by the patients. Furthermore, GAD67 mRNA was found in granule cells of the dentate gyrus. Levels, both of GAD67 mRNA and of GAD67 immunoreactivity were similar in sclerotic and nonsclerotic specimens and appeared to be increased compared to post mortem controls. Provided that the strong expression of GAD67 results in synthesis of GABA in hippocampal mossy fibers this may represent a self-protecting mechanism in TLE. In addition GAD67 expression also may result in conversion of excessive intracellular glutamate to nontoxic GABA within mossy fiber terminals.
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Affiliation(s)
- Günther Sperk
- Department of Pharmacology, Medical University Innsbruck, Austria.
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Jiménez-González C, Pirttimaki T, Cope DW, Parri HR. Non-neuronal, slow GABA signalling in the ventrobasal thalamus targets δ-subunit-containing GABA(A) receptors. Eur J Neurosci 2011; 33:1471-82. [PMID: 21395866 PMCID: PMC3110310 DOI: 10.1111/j.1460-9568.2011.07645.x] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
The rodent ventrobasal (VB) thalamus contains a relatively uniform population of thalamocortical (TC) neurons that receive glutamatergic input from the vibrissae and the somatosensory cortex, and inhibitory input from the nucleus reticularis thalami (nRT). In this study we describe γ-aminobutyric acid (GABA)(A) receptor-dependent slow outward currents (SOCs) in TC neurons that are distinct from fast inhibitory postsynaptic currents (IPSCs) and tonic currents. SOCs occurred spontaneously or could be evoked by hypo-osmotic stimulus, and were not blocked by tetrodotoxin, removal of extracellular Ca(2+) or bafilomycin A1, indicating a non-synaptic, non-vesicular GABA origin. SOCs were more common in TC neurons of the VB compared with the dorsal lateral geniculate nucleus, and were rarely observed in nRT neurons, whilst SOC frequency in the VB increased with age. Application of THIP, a selective agonist at δ-subunit-containing GABA(A) receptors, occluded SOCs, whereas the benzodiazepine site inverse agonist β-CCB had no effect, but did inhibit spontaneous and evoked IPSCs. In addition, the occurrence of SOCs was reduced in mice lacking the δ-subunit, and their kinetics were also altered. The anti-epileptic drug vigabatrin increased SOC frequency in a time-dependent manner, but this effect was not due to reversal of GABA transporters. Together, these data indicate that SOCs in TC neurons arise from astrocytic GABA release, and are mediated by δ-subunit-containing GABA(A) receptors. Furthermore, these findings suggest that the therapeutic action of vigabatrin may occur through the augmentation of this astrocyte-neuron interaction, and highlight the importance of glial cells in CNS (patho) physiology.
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Zaidi S, Gallos G, Yim PD, Xu D, Sonett JR, Panettieri RA, Gerthoffer W, Emala CW. Functional expression of γ-amino butyric acid transporter 2 in human and guinea pig airway epithelium and smooth muscle. Am J Respir Cell Mol Biol 2010; 45:332-9. [PMID: 21057105 DOI: 10.1165/rcmb.2010-0177oc] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
γ-Amino butyric acid (GABA) is a primary inhibitory neurotransmitter in the central nervous system, and is classically released by fusion of synaptic vesicles with the plasma membrane or by egress via GABA transporters (GATs). Recently, a GABAergic system comprised of GABA(A) and GABA(B) receptors has been identified on airway epithelial and smooth muscle cells that regulate mucus secretion and contractile tone of airway smooth muscle (ASM). In addition, the enzyme that synthesizes GABA, glutamic acid decarboxylase, has been identified in airway epithelial cells; however, the mechanism(s) by which this synthesized GABA is released from epithelial intracellular stores is unknown. We questioned whether any of the four known isoforms of GATs are functionally expressed in ASM or epithelial cells. We detected mRNA and protein expression of GAT2 and -4, and isoforms of glutamic acid decarboxylase in native and cultured human ASM and epithelial cells. In contrast, mRNA encoding vesicular GAT (VGAT), the neuronal GABA transporter, was not detected. Functional inhibition of (3)H-GABA uptake was demonstrated using GAT2 and GAT4/betaine-GABA transporter 1 (BGT1) inhibitors in both human ASM and epithelial cells. These results demonstrate that two isoforms of GATs, but not VGAT, are expressed in both airway epithelial and smooth muscle cells. They also provide a mechanism by which locally synthesized GABA can be released from these cells into the airway to activate GABA(A) channels and GABA(B) receptors, with subsequent autocrine and/or paracrine signaling effects on airway epithelium and ASM.
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Affiliation(s)
- Sarah Zaidi
- Department of Pediatrics, College of Physicians and Surgeons of Columbia University, New York, New York 10032, USA
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Dósa Z, Nieto-Gonzalez JL, Korshoej AR, Gibson KM, Jensen K. Effect of gene dosage on single-cell hippocampal electrophysiology in a murine model of SSADH deficiency (gamma-hydroxybutyric aciduria). Epilepsy Res 2010; 90:39-46. [PMID: 20363598 DOI: 10.1016/j.eplepsyres.2010.03.005] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2009] [Revised: 03/02/2010] [Accepted: 03/07/2010] [Indexed: 12/20/2022]
Abstract
Human and murine succinic semialdehyde dehydrogenase (SSADH; gamma-hydroxybutyric (GHB) aciduria) deficiency represents an epileptic disorder associated with hyperGABA- and hyperGHB-ergic states. Despite significant neurotransmitters alterations, well-defined single-cell electrophysiological studies, aimed to provide insight into regional neuropathology, have been lacking. In this study, we characterized the effect of residual SSADH enzyme function/increased GABA levels on single-cell hippocampal electrophysiology in SSADH+/+ (wild-type; WT), SSADH+/- (heterozygous; HET), and SSADH-/- (knock-out; KO) mice. Tonic extrasynaptic GABAA receptor (GABAAR)-mediated currents were elevated in HET and KO mice, whereas phasic synaptic GABAAR currents were unaltered in dentate gyrus granule cells. Similarly, tonic GABAAR-mediated currents were increased in dentate gyrus interneurons of KO animals, while phasic GABAergic neurotransmission was unaffected in the same cells. Our results indicate global disruption of cortical networks in SSADH KO mice, affecting both excitatory and inhibitory neurons. Our findings provide new clues concerning seizure evolution in the murine model (absence-->tonic-clonic-->status epilepticus), and extend pathophysiological insight into human SSADH deficiency.
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Affiliation(s)
- Zita Dósa
- Synaptic Physiology Laboratory, Department of Physiology and Biophysics, Aarhus University, Aarhus, Denmark
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Peng XQ, Gardner EL, Xi ZX. Gamma-vinyl GABA increases nonvesicular release of GABA and glutamate in the nucleus accumbens in rats via action on anion channels and GABA transporters. Psychopharmacology (Berl) 2010; 208:511-9. [PMID: 20033132 PMCID: PMC3713230 DOI: 10.1007/s00213-009-1753-7] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/28/2009] [Accepted: 12/01/2009] [Indexed: 02/06/2023]
Abstract
RATIONALE gamma-Amino butyric acid (GABA) is a well-characterized inhibitory neurotransmitter in the central nervous system, which may also stimulate nonvesicular release of other neurotransmitters under certain conditions. We have recently reported that gamma-vinyl GABA (GVG), an irreversible GABA transaminase inhibitor, elevates extracellular GABA but fails to alter dopamine release in the nucleus accumbens (NAc). OBJECTIVES Here, we investigated the mechanism(s) by which GVG elevates extracellular GABA levels and whether GVG also alters glutamate release in the NAc. MATERIALS AND METHODS In vivo microdialysis was used to simultaneously measure extracellular NAc GABA and glutamate before and after GVG administration in freely moving rats. RESULTS Systemic administration of GVG or intra-NAc local perfusion of GVG significantly increased extracellular NAc GABA and glutamate. GVG-enhanced GABA was completely blocked by intra-NAc local perfusion of 5-nitro-2, 3-(phenylpropylamino)-benzoic acid (NPPB), a selective anion channel blocker and partially blocked by SKF89976A, a type 1 GABA transporter inhibitor. GVG-enhanced glutamate was completely blocked by NPPB or SKF89976A. Tetrodotoxin, a voltage-dependent Na(+)-channel blocker, failed to alter GVG-enhanced GABA and glutamate. CONCLUSIONS These data suggest that GVG-enhanced extracellular GABA and glutamate are mediated predominantly by the opening of anion channels and partially by the reversal of GABA transporters. Enhanced extracellular glutamate may functionally attenuate the pharmacological action of GABA and prevent enhanced GABA-induced excess inhibition.
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Affiliation(s)
- Xiao-Qing Peng
- Intramural Research Program, National Institute on Drug Abuse, Baltimore, MD 21224, USA
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Vizi ES, Fekete A, Karoly R, Mike A. Non-synaptic receptors and transporters involved in brain functions and targets of drug treatment. Br J Pharmacol 2010; 160:785-809. [PMID: 20136842 DOI: 10.1111/j.1476-5381.2009.00624.x] [Citation(s) in RCA: 126] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
Beyond direct synaptic communication, neurons are able to talk to each other without making synapses. They are able to send chemical messages by means of diffusion to target cells via the extracellular space, provided that the target neurons are equipped with high-affinity receptors. While synaptic transmission is responsible for the 'what' of brain function, the 'how' of brain function (mood, attention, level of arousal, general excitability, etc.) is mainly controlled non-synaptically using the extracellular space as communication channel. It is principally the 'how' that can be modulated by medicine. In this paper, we discuss different forms of non-synaptic transmission, localized spillover of synaptic transmitters, local presynaptic modulation and tonic influence of ambient transmitter levels on the activity of vast neuronal populations. We consider different aspects of non-synaptic transmission, such as synaptic-extrasynaptic receptor trafficking, neuron-glia communication and retrograde signalling. We review structural and functional aspects of non-synaptic transmission, including (i) anatomical arrangement of non-synaptic release sites, receptors and transporters, (ii) intravesicular, intra- and extracellular concentrations of neurotransmitters, as well as the spatiotemporal pattern of transmitter diffusion. We propose that an effective general strategy for efficient pharmacological intervention could include the identification of specific non-synaptic targets and the subsequent development of selective pharmacological tools to influence them.
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Affiliation(s)
- E S Vizi
- Department of Pharmacology, Institute of Experimental Medicine, Hungarian Academy of Sciences, Budapest, Hungary.
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Abstract
The GABAR [GABA(A) (gamma-aminobutyric acid type A) receptor], which mediates most inhibition in the brain, is regulated homoeostatically to maintain an optimal level of neuronal excitability. In particular, the alpha(4)betadelta subtype of the GABAR plays a pivotal role in this regulation. This receptor, which is expressed extrasynaptically on the dendrites, normally has low expression in the brain, but displays a remarkable degree of plasticity. It can also be a sensitive target for endogenous neurosteroids such as THP (3alpha-hydroxy-5[alpha]beta-pregnan-20-one (allo-pregnanolone); a neurosteroid and positive modulator of the GABAR), which is released during stress, although the effect of the steroid is polarity-dependent, such that it increases inward current, but decreases outward current, at alpha(4)beta(2)delta GABAR. Expression of alpha(4)beta(2)delta GABAR in CA1 hippocampus is also tightly regulated by fluctuating levels of neurosteroids, as seen at the onset of puberty. Declining levels of inhibition resulting from the decrease in THP at puberty are compensated for by an increase in alpha(4)betadelta GABAR along the apical dendrites of CA1 hippocampal pyramidal cells, which reduces neuronal excitability by decreasing the input resistance. However, excessive decrease of neuronal function is averted when THP levels rise, as would occur during stress, because this steroid decreases the outward GABAergic tonic current via inhibition of alpha(4)beta(2)delta GABAR, thereby restoring measures of neuronal excitability to pre-pubertal levels. Thus the homoeostatic regulation of alpha(4)betadelta GABAR expression plays an important role in maintaining ambient levels of neuronal excitability at puberty.
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Smith SS, Aoki C, Shen H. Puberty, steroids and GABA(A) receptor plasticity. Psychoneuroendocrinology 2009; 34 Suppl 1:S91-S103. [PMID: 19523771 PMCID: PMC2794901 DOI: 10.1016/j.psyneuen.2009.05.011] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/29/2009] [Revised: 04/27/2009] [Accepted: 05/19/2009] [Indexed: 11/17/2022]
Abstract
GABA(A) receptors (GABAR) mediate most inhibition in the CNS and are also a target for neuroactive steroids such as 3alpha,5[alpha]beta-THP (3alphaOH-5[alpha]beta-OH-pregnan-20-one or [allo]pregnanolone). Although these steroids robustly enhance current gated by alpha1beta2delta GABAR, we have shown that 3alpha,5[alpha]beta-THP effects at recombinant alpha4beta2delta GABAR depend on the direction of Cl(-) flux, where the steroid increases outward flux, but decreases inward flux through the receptor. This polarity-dependent inhibition of alpha4beta2delta GABAR resulted from an increase in the rate and extent of rapid desensitization of the receptor, recorded from recombinant receptors expressed in HEK-293 cells with whole cell voltage clamp techniques. This inhibitory effect of 3alpha,5[alpha]beta-THP was not observed at other receptor subtypes, suggesting it was selective for alpha4beta2delta GABAR. Furthermore, it was prevented by a selective mutation of basic residue arginine 353 in the intracellular loop of the receptor, suggesting that this might be a putative chloride modulatory site. Expression of alpha4betadelta GABAR increases markedly at extrasynaptic sites at the onset of puberty in female mice. At this time, 3alpha,5[alpha]beta-THP decreased the inhibitory tonic current, recorded with perforated patch techniques to maintain the physiological Cl(-) gradient. By decreasing this shunting inhibition, 3alpha,5[alpha]beta-THP increased the excitability of CA1 hippocampal pyramidal cells at puberty. These effects of the steroid were opposite to those observed before puberty when 3alpha,5[alpha]beta-THP reduced neuronal excitability as a pre-synaptic effect. Behaviorally, the excitatory effect of 3alpha,5[alpha]beta-THP was reflected as an increase in anxiety at the onset of puberty in female mice. Taken together, these findings suggest that the emergence of alpha4beta2delta GABAR at the onset of puberty reverses the effect of a stress steroid. These findings may be relevant for the mood swings and increased response to stressful events reported in adolescence.
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Affiliation(s)
- Sheryl S Smith
- Department of Physiology and Pharmacology, SUNY Downstate Medical Center, 450 Clarkson Ave., Brooklyn, NY 11203, USA.
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Hoshino O. GABA transporter preserving ongoing spontaneous neuronal activity at firing subthreshold. Neural Comput 2009; 21:1683-713. [PMID: 19191601 DOI: 10.1162/neco.2009.05-08-778] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/04/2022]
Abstract
There has been compelling evidence that the GABA transporter is crucial not only for removing gamma-aminobutyric acid (GABA) from but also releasing it into extracellular space, thereby clamping ambient GABA (GABA in extracellular space) at a certain level. The ambient GABA is known to activate extrasynaptic GABA receptors and provide tonic inhibitory current into neurons. We investigated how the transporter regulates the level of ambient GABA, mediates tonic neuronal inhibition, and influences ongoing spontaneous neuronal activity. A cortical neural network model is proposed in which GABA transporters on lateral (L) and feedback (F) inhibitory (GABAergic) interneurons are functionally made. Principal (P) cell assemblies participate in expressing information about elemental sensory features. At membrane potentials below the reversal potential, there is net influx of GABA, whereas at membrane potentials above the reversal potential, there is net efflux of GABA. Through this transport mechanism, ambient GABA concentration is kept within a submicromolar range during an ongoing spontaneous neuronal activity time period. Here we show that the GABA transporter on L cells regulates the overall level of ambient GABA across cell assemblies, and that on F cells it does so within individual cell assemblies. This combinatorial regulation of ambient GABA allows P cells to oscillate near firing threshold during the ongoing time period, thereby reducing their reaction time to externally applied stimuli. We suggest that the GABA transporter, with its forward and reverse transport mechanism, could regulate the ambient GABA. This transporter-mediated ambient GABA regulation may contribute to establishing an ongoing subthreshold neuronal state by which the network can respond rapidly to subsequent sensory input.
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Affiliation(s)
- Osamu Hoshino
- Department of Intelligent Systems Engineering, Ibaraki University, Hitachi, Ibaraki, 316-8511 Japan.
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