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Carricaburu E, Benner O, Burlingham SR, Dos Santos Passos C, Hobaugh N, Karr CH, Chanda S. Gephyrin promotes autonomous assembly and synaptic localization of GABAergic postsynaptic components without presynaptic GABA release. Proc Natl Acad Sci U S A 2024; 121:e2315100121. [PMID: 38889143 PMCID: PMC11214061 DOI: 10.1073/pnas.2315100121] [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: 08/30/2023] [Accepted: 05/17/2024] [Indexed: 06/20/2024] Open
Abstract
Synapses containing γ-aminobutyric acid (GABA) constitute the primary centers for inhibitory neurotransmission in our nervous system. It is unclear how these synaptic structures form and align their postsynaptic machineries with presynaptic terminals. Here, we monitored the cellular distribution of several GABAergic postsynaptic proteins in a purely glutamatergic neuronal culture derived from human stem cells, which virtually lacks any vesicular GABA release. We found that several GABAA receptor (GABAAR) subunits, postsynaptic scaffolds, and major cell-adhesion molecules can reliably coaggregate and colocalize at even GABA-deficient subsynaptic domains, but remain physically segregated from glutamatergic counterparts. Genetic deletions of both Gephyrin and a Gephyrin-associated guanosine di- or triphosphate (GDP/GTP) exchange factor Collybistin severely disrupted the coassembly of these postsynaptic compositions and their proper apposition with presynaptic inputs. Gephyrin-GABAAR clusters, developed in the absence of GABA transmission, could be subsequently activated and even potentiated by delayed supply of vesicular GABA. Thus, molecular organization of GABAergic postsynapses can initiate via a GABA-independent but Gephyrin-dependent intrinsic mechanism.
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Affiliation(s)
- Etta Carricaburu
- Department of Biochemistry and Molecular Biology, Colorado State University, Fort Collins, CO80523
| | - Orion Benner
- Department of Biochemistry and Molecular Biology, Colorado State University, Fort Collins, CO80523
| | - Scott R. Burlingham
- Department of Biochemistry and Molecular Biology, Colorado State University, Fort Collins, CO80523
| | | | - Natalia Hobaugh
- Biological Sciences Division, University of Chicago, Chicago, IL60637
| | - Charles H. Karr
- Department of Biochemistry and Molecular Biology, Colorado State University, Fort Collins, CO80523
| | - Soham Chanda
- Department of Biochemistry and Molecular Biology, Colorado State University, Fort Collins, CO80523
- Molecular, Cellular and Integrated Neurosciences Program, Colorado State University, Fort Collins, CO80523
- Cell and Molecular Biology Program, Colorado State University, Fort Collins, CO80523
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2
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Lu MH, Uematsu A, Kiyokawa Y, Emoto K, Takeuchi Y. Glutamatergic Projections from the Posterior Complex of the Anterior Olfactory Nucleus to the Amygdala Complexes. Neuroscience 2023; 521:102-109. [PMID: 37142179 DOI: 10.1016/j.neuroscience.2023.04.024] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2023] [Revised: 04/17/2023] [Accepted: 04/25/2023] [Indexed: 05/06/2023]
Abstract
Social buffering is a phenomenon where stress responses are ameliorated by an affiliative conspecific. Our previous findings suggest that the posterior complex of the anterior olfactory nucleus (AOP) is well positioned to participate in the neural mechanisms underlying social buffering. However, the lack of anatomical information prevents us from further estimating the role of the AOP. Here, we obtained anatomical information regarding the AOP in male rats. In Experiment 1 (n = 5), among 4',6-diamidino-2-phenylindole-positive cells in the AOP, the proportion of glutamic acid decarboxylase 67 (GAD67)-positive cells was 13.8% ± 1.2%. In Experiment 2 (n = 5), among the cells that were labeled by a retrograde tracer injected into the basolateral complex of the amygdala (BLA), the proportion of GAD67-positive cells was 18.6% ± 0.8%. In Experiment 3 (n = 5), we demonstrated the existence of cells that were labeled by the retrograde tracer injected into the posterior part of the medial amygdala (MeP), mostly into the ventral part of the MeP. In addition, the proportion of GAD67-positive cells among the tracer-labeled cells was 21.7% ± 1.7%. In Experiment 4 (n = 3), the retrograde tracers were injected into the BLA and MeP, mostly into the ventral part of the MeP. The proportion of double-labeled cells among the tracer-labeled cells was 2.1% ± 1.2%. Taken together, these results suggest that the AOP is predominantly composed of glutamatergic neurons. In addition, the AOP sends mutually independent glutamatergic-predominant projections to the BLA and MeP.
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Affiliation(s)
- Ming-Hsuan Lu
- Laboratory of Veterinary Ethology, The University of Tokyo, Japan
| | - Akira Uematsu
- International Research Center for Neurointelligence, The University of Tokyo, Japan; Graduate School of Science, The University of Tokyo, Japan; Present Adress: Human Informatics and Interaction Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Japan
| | - Yasushi Kiyokawa
- Laboratory of Veterinary Ethology, The University of Tokyo, Japan.
| | - Kazuo Emoto
- International Research Center for Neurointelligence, The University of Tokyo, Japan; Graduate School of Science, The University of Tokyo, Japan
| | - Yukari Takeuchi
- Laboratory of Veterinary Ethology, The University of Tokyo, Japan
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Logiacco F, Xia P, Georgiev SV, Franconi C, Chang YJ, Ugursu B, Sporbert A, Kühn R, Kettenmann H, Semtner M. Microglia sense neuronal activity via GABA in the early postnatal hippocampus. Cell Rep 2021; 37:110128. [PMID: 34965412 DOI: 10.1016/j.celrep.2021.110128] [Citation(s) in RCA: 24] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2021] [Revised: 09/14/2021] [Accepted: 11/22/2021] [Indexed: 01/05/2023] Open
Abstract
Microglia, the resident macrophages in the central nervous system, express receptors for classical neurotransmitters, such as γ-aminobutyric acid (GABA) and glutamate, suggesting that they sense synaptic activity. To detect microglial Ca2+ responses to neuronal activity, we generate transgenic mouse lines expressing the fluorescent Ca2+ indicator GCaMP6m, specifically in microglia and demonstrate that electrical stimulation of the Schaffer collateral pathway results in microglial Ca2+ responses in early postnatal but not adult hippocampus. Preceding the microglial responses, we also observe similar Ca2+ responses in astrocytes, and both are sensitive to tetrodotoxin. Blocking astrocytic glutamate uptake or GABA transport abolishes stimulation-induced microglial responses as well as antagonizing the microglial GABAB receptor. Our data, therefore, suggest that the neuronal activity-induced glutamate uptake and the release of GABA by astrocytes trigger the activation of GABAB receptors in microglia. This neuron, astrocyte, and microglia communication pathway might modulate microglial activity in developing neuronal networks.
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Affiliation(s)
- Francesca Logiacco
- Cellular Neurosciences, Max-Delbrück-Center for Molecular Medicine in the Helmholtz Association, 13125 Berlin, Germany; Department of Biology, Chemistry, and Pharmacy, Freie Universität Berlin, 12169 Berlin, Germany
| | - Pengfei Xia
- Cellular Neurosciences, Max-Delbrück-Center for Molecular Medicine in the Helmholtz Association, 13125 Berlin, Germany
| | - Svilen Veselinov Georgiev
- Cellular Neurosciences, Max-Delbrück-Center for Molecular Medicine in the Helmholtz Association, 13125 Berlin, Germany
| | - Celeste Franconi
- Cellular Neurosciences, Max-Delbrück-Center for Molecular Medicine in the Helmholtz Association, 13125 Berlin, Germany
| | - Yi-Jen Chang
- Cellular Neurosciences, Max-Delbrück-Center for Molecular Medicine in the Helmholtz Association, 13125 Berlin, Germany
| | - Bilge Ugursu
- Cellular Neurosciences, Max-Delbrück-Center for Molecular Medicine in the Helmholtz Association, 13125 Berlin, Germany; Experimental Ophthalmology, Charité Universitätsmedizin Berlin, Augustenburger Platz 1, 13353 Berlin, Germany
| | - Anje Sporbert
- Advanced Light Microscopy, Max-Delbrück-Center for Molecular Medicine in the Helmholtz Association, 13125 Berlin, Germany
| | - Ralf Kühn
- Transgenic Core Facility, Max-Delbrück-Center for Molecular Medicine in the Helmholtz Association, 13125 Berlin, Germany
| | - Helmut Kettenmann
- Cellular Neurosciences, Max-Delbrück-Center for Molecular Medicine in the Helmholtz Association, 13125 Berlin, Germany; Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, Shenzhen, China
| | - Marcus Semtner
- Cellular Neurosciences, Max-Delbrück-Center for Molecular Medicine in the Helmholtz Association, 13125 Berlin, Germany.
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4
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Diverse Actions of Astrocytes in GABAergic Signaling. Int J Mol Sci 2019; 20:ijms20122964. [PMID: 31216630 PMCID: PMC6628243 DOI: 10.3390/ijms20122964] [Citation(s) in RCA: 42] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2019] [Revised: 06/10/2019] [Accepted: 06/14/2019] [Indexed: 01/06/2023] Open
Abstract
An imbalance of excitatory and inhibitory neurotransmission leading to over excitation plays a crucial role in generating seizures, while enhancing GABAergic mechanisms are critical in terminating seizures. In recent years, it has been reported in many studies that astrocytes are deeply involved in synaptic transmission. Astrocytes form a critical component of the “tripartite” synapses by wrapping around the pre- and post-synaptic elements. From this location, astrocytes are known to greatly influence the dynamics of ions and transmitters in the synaptic cleft. Despite recent extensive research on excitatory tripartite synapses, inhibitory tripartite synapses have received less attention, even though they influence inhibitory synaptic transmission by affecting chloride and GABA concentration dynamics. In this review, we will discuss the diverse actions of astrocytic chloride and GABA homeostasis at GABAergic tripartite synapses. We will then consider the pathophysiological impacts of disturbed GABA homeostasis at the tripartite synapse.
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Abstract
Astrocytes are neural cells of ectodermal, neuroepithelial origin that provide for homeostasis and defense of the central nervous system (CNS). Astrocytes are highly heterogeneous in morphological appearance; they express a multitude of receptors, channels, and membrane transporters. This complement underlies their remarkable adaptive plasticity that defines the functional maintenance of the CNS in development and aging. Astrocytes are tightly integrated into neural networks and act within the context of neural tissue; astrocytes control homeostasis of the CNS at all levels of organization from molecular to the whole organ.
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Affiliation(s)
- Alexei Verkhratsky
- The University of Manchester , Manchester , United Kingdom ; Achúcarro Basque Center for Neuroscience, IKERBASQUE, Basque Foundation for Science , Bilbao , Spain ; Department of Neuroscience, University of the Basque Country UPV/EHU and CIBERNED, Leioa, Spain ; Center for Basic and Translational Neuroscience, Faculty of Health and Medical Sciences, University of Copenhagen , Copenhagen , Denmark ; and Center for Translational Neuromedicine, University of Rochester Medical Center , Rochester, New York
| | - Maiken Nedergaard
- The University of Manchester , Manchester , United Kingdom ; Achúcarro Basque Center for Neuroscience, IKERBASQUE, Basque Foundation for Science , Bilbao , Spain ; Department of Neuroscience, University of the Basque Country UPV/EHU and CIBERNED, Leioa, Spain ; Center for Basic and Translational Neuroscience, Faculty of Health and Medical Sciences, University of Copenhagen , Copenhagen , Denmark ; and Center for Translational Neuromedicine, University of Rochester Medical Center , Rochester, New York
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Verkhratsky A, Nedergaard M. Physiology of Astroglia. Physiol Rev 2018; 98:239-389. [PMID: 29351512 PMCID: PMC6050349 DOI: 10.1152/physrev.00042.2016] [Citation(s) in RCA: 945] [Impact Index Per Article: 157.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2016] [Revised: 03/22/2017] [Accepted: 04/27/2017] [Indexed: 02/07/2023] Open
Abstract
Astrocytes are neural cells of ectodermal, neuroepithelial origin that provide for homeostasis and defense of the central nervous system (CNS). Astrocytes are highly heterogeneous in morphological appearance; they express a multitude of receptors, channels, and membrane transporters. This complement underlies their remarkable adaptive plasticity that defines the functional maintenance of the CNS in development and aging. Astrocytes are tightly integrated into neural networks and act within the context of neural tissue; astrocytes control homeostasis of the CNS at all levels of organization from molecular to the whole organ.
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Affiliation(s)
- Alexei Verkhratsky
- The University of Manchester , Manchester , United Kingdom ; Achúcarro Basque Center for Neuroscience, IKERBASQUE, Basque Foundation for Science , Bilbao , Spain ; Department of Neuroscience, University of the Basque Country UPV/EHU and CIBERNED, Leioa, Spain ; Center for Basic and Translational Neuroscience, Faculty of Health and Medical Sciences, University of Copenhagen , Copenhagen , Denmark ; and Center for Translational Neuromedicine, University of Rochester Medical Center , Rochester, New York
| | - Maiken Nedergaard
- The University of Manchester , Manchester , United Kingdom ; Achúcarro Basque Center for Neuroscience, IKERBASQUE, Basque Foundation for Science , Bilbao , Spain ; Department of Neuroscience, University of the Basque Country UPV/EHU and CIBERNED, Leioa, Spain ; Center for Basic and Translational Neuroscience, Faculty of Health and Medical Sciences, University of Copenhagen , Copenhagen , Denmark ; and Center for Translational Neuromedicine, University of Rochester Medical Center , Rochester, New York
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7
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Losi G, Mariotti L, Carmignoto G. GABAergic interneuron to astrocyte signalling: a neglected form of cell communication in the brain. Philos Trans R Soc Lond B Biol Sci 2015; 369:20130609. [PMID: 25225102 DOI: 10.1098/rstb.2013.0609] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
GABAergic interneurons represent a minority of all cortical neurons and yet they efficiently control neural network activities in all brain areas. In parallel, glial cell astrocytes exert a broad control of brain tissue homeostasis and metabolism, modulate synaptic transmission and contribute to brain information processing in a dynamic interaction with neurons that is finely regulated in time and space. As most studies have focused on glutamatergic neurons and excitatory transmission, our knowledge of functional interactions between GABAergic interneurons and astrocytes is largely defective. Here, we critically discuss the currently available literature that hints at a potential relevance of this specific signalling in brain function. Astrocytes can respond to GABA through different mechanisms that include GABA receptors and transporters. GABA-activated astrocytes can, in turn, modulate local neuronal activity by releasing gliotransmitters including glutamate and ATP. In addition, astrocyte activation by different signals can modulate GABAergic neurotransmission. Full clarification of the reciprocal signalling between different GABAergic interneurons and astrocytes will improve our understanding of brain network complexity and has the potential to unveil novel therapeutic strategies for brain disorders.
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Affiliation(s)
- Gabriele Losi
- Department of Biomedical Science, Consiglio Nazionale delle Ricerche, Neuroscience Institute and University of Padova, Padova, Italy
| | - Letizia Mariotti
- Department of Biomedical Science, Consiglio Nazionale delle Ricerche, Neuroscience Institute and University of Padova, Padova, Italy
| | - Giorgio Carmignoto
- Department of Biomedical Science, Consiglio Nazionale delle Ricerche, Neuroscience Institute and University of Padova, Padova, Italy
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Rusanescu G, Mao J. Immature spinal cord neurons are dynamic regulators of adult nociceptive sensitivity. J Cell Mol Med 2015. [PMID: 26223362 PMCID: PMC4594677 DOI: 10.1111/jcmm.12648] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Chronic pain is a debilitating condition with unknown mechanism. Nociceptive sensitivity may be regulated by genetic factors, some of which have been separately linked to neuronal progenitor cells and neuronal differentiation. This suggests that genetic factors that interfere with neuronal differentiation may contribute to a chronic increase in nociceptive sensitivity, by extending the immature, hyperexcitable stage of spinal cord neurons. Although adult rodent spinal cord neurogenesis was previously demonstrated, the fate of these progenitor cells is unknown. Here, we show that peripheral nerve injury in adult rats induces extensive spinal cord neurogenesis and a long-term increase in the number of spinal cord laminae I–II neurons ipsilateral to injury. The production and maturation of these new neurons correlates with the time course and modulation of nociceptive behaviour, and transiently mimics the cellular and behavioural conditions present in genetically modified animal models of chronic pain. This suggests that the number of immature neurons present at any time in the spinal cord dorsal horns contributes to the regulation of nociceptive sensitivity. The continuous turnover of these neurons, which can fluctuate between normal and injured states, is a dynamic regulator of nociceptive sensitivity. In support of this hypothesis, we find that promoters of neuronal differentiation inhibit, while promoters of neurogenesis increase long-term nociception. TrkB agonists, well-known promoters of nociception in the short-term, significantly inhibit long-term nociception by promoting the differentiation of newly produced immature neurons. These findings suggest that promoters of neuronal differentiation may be used to alleviate chronic pain.
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Affiliation(s)
- Gabriel Rusanescu
- MGH Center for Translational Pain Research, Department of Anesthesia, Critical Care and Pain Medicine, Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA
| | - Jianren Mao
- MGH Center for Translational Pain Research, Department of Anesthesia, Critical Care and Pain Medicine, Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA
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9
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Abstract
Gamma-amino butyric acid (GABA) is the major inhibitory neurotransmitter that is known to be synthesized and released from GABAergic neurons in the brain. However, recent studies have shown that not only neurons but also astrocytes contain a considerable amount of GABA that can be released and activate GABA receptors in neighboring neurons. These exciting new findings for glial GABA raise further interesting questions about the source of GABA, its mechanism of release and regulation and the functional role of glial GABA. In this review, we highlight recent studies that identify the presence and release of GABA in glial cells, we show several proposed potential pathways for accumulation and modulation of glial intracellular and extracellular GABA content, and finally we discuss functional roles for glial GABA in the brain.
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Affiliation(s)
- Bo-Eun Yoon
- Department of Nanobiomedical Science, Dankook University Chungnam, South Korea
| | - C Justin Lee
- WCI Center for Functional Connectomics, Korea Institute of Science and Technology (KIST) Seoul, South Korea ; Center for Neural Science and Center for Functional Connectomics, Korea Institute of Science and Technology (KIST) Seoul, South Korea
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10
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Tonic inhibition in dentate gyrus impairs long-term potentiation and memory in an Alzheimer's [corrected] disease model. Nat Commun 2014; 5:4159. [PMID: 24923909 PMCID: PMC4159602 DOI: 10.1038/ncomms5159] [Citation(s) in RCA: 193] [Impact Index Per Article: 19.3] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2014] [Accepted: 05/19/2014] [Indexed: 01/07/2023] Open
Abstract
Amyloid plaques and tau tangles are common pathological hallmarks for Alzheimer’s disease (AD), however reducing Aβ production failed to relieve the symptoms of AD patients. Here we report a high GABA (γ-aminobutyric acid) content in reactive astrocytes in the dentate gyrus (DG) of a mouse model for AD (5xFAD) that results in increased tonic inhibition and memory deficit. We also confirm in human AD patient brains that dentate astrocytes have a high GABA content, suggesting that high astrocytic GABA level may be a novel biomarker and a potential diagnostic tool for AD. The excessive GABA in 5xFAD astrocytes is released through an astrocyte-specific GABA transporter GAT3/4, and significantly enhanced tonic GABA inhibition in dentate granule cells. Importantly, reducing tonic inhibition in 5xFAD mice rescues the impairment of long-term potentiation (LTP) and memory deficit. Thus, reducing tonic GABA inhibition in the DG may lead to a novel therapy for Alzheimer’s disease.
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11
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Butt AM, Fern RF, Matute C. Neurotransmitter signaling in white matter. Glia 2014; 62:1762-79. [PMID: 24753049 DOI: 10.1002/glia.22674] [Citation(s) in RCA: 87] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2013] [Revised: 03/04/2014] [Accepted: 03/31/2014] [Indexed: 12/16/2022]
Abstract
White matter (WM) tracts are bundles of myelinated axons that provide for rapid communication throughout the CNS and integration in grey matter (GM). The main cells in myelinated tracts are oligodendrocytes and astrocytes, with small populations of microglia and oligodendrocyte precursor cells. The prominence of neurotransmitter signaling in WM, which largely exclude neuronal cell bodies, indicates it must have physiological functions other than neuron-to-neuron communication. A surprising aspect is the diversity of neurotransmitter signaling in WM, with evidence for glutamatergic, purinergic (ATP and adenosine), GABAergic, glycinergic, adrenergic, cholinergic, dopaminergic and serotonergic signaling, acting via a wide range of ionotropic and metabotropic receptors. Both axons and glia are potential sources of neurotransmitters and may express the respective receptors. The physiological functions of neurotransmitter signaling in WM are subject to debate, but glutamate and ATP-mediated signaling have been shown to evoke Ca(2+) signals in glia and modulate axonal conduction. Experimental findings support a model of neurotransmitters being released from axons during action potential propagation acting on glial receptors to regulate the homeostatic functions of astrocytes and myelination by oligodendrocytes. Astrocytes also release neurotransmitters, which act on axonal receptors to strengthen action potential propagation, maintaining signaling along potentially long axon tracts. The co-existence of multiple neurotransmitters in WM tracts suggests they may have diverse functions that are important for information processing. Furthermore, the neurotransmitter signaling phenomena described in WM most likely apply to myelinated axons of the cerebral cortex and GM areas, where they are doubtless important for higher cognitive function.
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Affiliation(s)
- Arthur M Butt
- Institute of Biomedical and Biomolecular Sciences, School of Pharmacy and Biomedical Sciences, University of Portsmouth, United Kingdom
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12
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Abstract
White matter neurons in multiple sclerosis brains are destroyed during demyelination and then replaced in some chronic multiple sclerosis lesions that exhibit a morphologically distinct population of activated microglia [Chang A, et al. (2008) Brain 131(Pt 9):2366-2375]. Here we investigated whether activated microglia secrete factors that promote the generation of neurons from white matter cells. Adult rat brain microglia (resting or activated with lipopolysaccharide) were isolated by flow cytometry and cocultured with neonatal rat optic nerve cells in separate but media-connected chambers. Optic nerve cells cocultured with activated microglia showed a significant increase in the number of cells of neuronal phenotype, identified by neuron-specific class III beta-tubulin (TUJ-1) labeling, compared with cultures with resting microglia. To investigate the possible source of the TUJ-1-positive cells, A2B5-positive oligodendrocyte progenitor cells and A2B5-negative cells were isolated and cocultured with resting and activated microglia. Significantly more TUJ-1-positive cells were generated from A2B5-negative cells (∼70%) than from A2B5-positive cells (~30%). Mass spectrometry analysis of microglia culture media identified protease serine 2 (PRSS2) as a factor secreted by activated, but not resting, microglia. When added to optic nerve cultures, PRSS2 significantly increased neurogenesis, whereas the serine protease inhibitor, secretory leukocyte protease inhibitor, decreased activated microglia-induced neurogenesis. Collectively our data provide evidence that activated microglia increase neurogenesis through secretion of PRSS2.
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Le Meur K, Mendizabal-Zubiaga J, Grandes P, Audinat E. GABA release by hippocampal astrocytes. Front Comput Neurosci 2012; 6:59. [PMID: 22912614 PMCID: PMC3421239 DOI: 10.3389/fncom.2012.00059] [Citation(s) in RCA: 61] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2012] [Accepted: 07/25/2012] [Indexed: 01/10/2023] Open
Abstract
Astrocytes can directly influence neuronal activity through the release of various transmitters acting on membrane receptors expressed by neurons. However, in contrast to glutamate and ATP for instance, the release of GABA (γ-amino-butyric acid) by astrocytes is still poorly documented. Here, we used whole-cell recordings in rat acute brain slices and electron microscopy to test whether hippocampal astrocytes release the inhibitory transmitter GABA. We observed that slow transient inhibitory currents due to the activation of GABAA receptors occur spontaneously in principal neurons of the three main hippocampal fields (CA1, CA3, and dentate gyrus). These currents share characteristics with the slow NMDA receptor-mediated currents previously shown to result from astrocytic glutamate release: they occur in the absence of synaptic transmission and have variable kinetics and amplitudes as well as low frequencies. Osmotic pressure reduction, known to enhance transmitter release from astrocytes, similarly increased the frequency of non-synaptic GABA and glutamate currents. Simultaneous occurrence of slow inhibitory and excitatory currents was extremely rare. Yet, electron microscopy examination of immunostained hippocampal sections shows that about 80% of hippocampal astrocytes [positive for glial fibrillary acidic protein (GFAP)] were immunostained for GABA. Our results provide quantitative characteristics of the astrocyte-to-neuron GABAergic signaling. They also suggest that all principal neurons of the hippocampal network are under a dual, excitatory and inhibitory, influence of astrocytes. The relevance of the astrocytic release of GABA, and glutamate, on the physiopathology of the hippocampus remains to be established.
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14
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Yoon BE, Woo J, Lee CJ. Astrocytes as GABA-ergic and GABA-ceptive cells. Neurochem Res 2012; 37:2474-9. [PMID: 22700085 DOI: 10.1007/s11064-012-0808-z] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2012] [Revised: 05/21/2012] [Accepted: 05/23/2012] [Indexed: 10/28/2022]
Abstract
GABA (gamma-aminobutyric acid) is considered to be the major inhibitory neurotransmitter that is synthesized in and released from GABA-ergic neurons in the brain. However, recent studies have shown that not only neurons but astrocytes contain a considerable amount of GABA, which can be released and activate the receptors responsive to GABA. In addition, astrocytes are themselves responsive to GABA by expressing GABA receptors. These exciting new findings raise more questions about the origin of GABA, whether it is synthesized or taken up, and about the role of astrocytic GABA and GABA receptors. In this review, we propose several potential pathways for astrocytes to accumulate GABA and discuss the evidence for functional expression of GABA receptors in astrocytes.
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Affiliation(s)
- Bo-Eun Yoon
- WCI Center for Functional Connectomics, Korea Institute of Science and Technology (KIST), Seoul 136-791, Korea
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15
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Héja L, Nyitrai G, Kékesi O, Dobolyi A, Szabó P, Fiáth R, Ulbert I, Pál-Szenthe B, Palkovits M, Kardos J. Astrocytes convert network excitation to tonic inhibition of neurons. BMC Biol 2012; 10:26. [PMID: 22420899 PMCID: PMC3342137 DOI: 10.1186/1741-7007-10-26] [Citation(s) in RCA: 126] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2011] [Accepted: 03/15/2012] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Glutamate and γ-aminobutyric acid (GABA) transporters play important roles in balancing excitatory and inhibitory signals in the brain. Increasing evidence suggest that they may act concertedly to regulate extracellular levels of the neurotransmitters. RESULTS Here we present evidence that glutamate uptake-induced release of GABA from astrocytes has a direct impact on the excitability of pyramidal neurons in the hippocampus. We demonstrate that GABA, synthesized from the polyamine putrescine, is released from astrocytes by the reverse action of glial GABA transporter (GAT) subtypes GAT-2 or GAT-3. GABA release can be prevented by blocking glutamate uptake with the non-transportable inhibitor DHK, confirming that it is the glutamate transporter activity that triggers the reversal of GABA transporters, conceivably by elevating the intracellular Na+ concentration in astrocytes. The released GABA significantly contributes to the tonic inhibition of neurons in a network activity-dependent manner. Blockade of the Glu/GABA exchange mechanism increases the duration of seizure-like events in the low-[Mg2+] in vitro model of epilepsy. Under in vivo conditions the increased GABA release modulates the power of gamma range oscillation in the CA1 region, suggesting that the Glu/GABA exchange mechanism is also functioning in the intact hippocampus under physiological conditions. CONCLUSIONS The results suggest the existence of a novel molecular mechanism by which astrocytes transform glutamatergic excitation into GABAergic inhibition providing an adjustable, in situ negative feedback on the excitability of neurons.
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Affiliation(s)
- László Héja
- Department of Functional Pharmacology, Institute of Molecular Pharmacology, Research Centre for Natural Sciences, Hungarian Academy of Sciences, Pusztaszeri 59-67, 1025 Budapest, Hungary.
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Vélez-Fort M, Audinat E, Angulo MC. Central Role of GABA in Neuron–Glia Interactions. Neuroscientist 2011; 18:237-50. [PMID: 21609943 DOI: 10.1177/1073858411403317] [Citation(s) in RCA: 73] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
The major types of glial cells—astrocytes, microglia, and cells of the oligodendroglial lineage—are known to express functional metabotropic and ionotropic GABA receptors. Neuronal signaling mechanisms allowing for the activation of these receptors in glia are probably as complex as those described among neurons and involve synaptic and extrasynaptic transmission modes. In addition, astrocytes can signal back to neurons by releasing GABA, probably through unconventional nonvesicular mechanisms. The decryption of the roles played by GABAergic signaling in neuron–glia interactions is only beginning, but it has been suggested that activation of glial cells by GABA influences important functions of the brain such as neuronal activity, differentiation, myelination, and neuroprotection. This review discusses the cellular mechanisms allowing the major types of glial cells to sense and transmit GABAergic signals and gives an overview of potential roles of this signaling pathway in developing and mature brains.
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Affiliation(s)
- Mateo Vélez-Fort
- Inserm U603, Paris, France
- CNRS UMR 8154, Paris, France
- Université Paris Descartes, Paris, France
- Division of Neurophysiology, The National Institute for Medical Research, Mill Hill, UK
| | - Etienne Audinat
- Inserm U603, Paris, France
- CNRS UMR 8154, Paris, France
- Université Paris Descartes, Paris, France
| | - María Cecilia Angulo
- Inserm U603, Paris, France
- CNRS UMR 8154, Paris, France
- Université Paris Descartes, Paris, France
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17
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Le-Corronc H, Rigo JM, Branchereau P, Legendre P. GABA(A) receptor and glycine receptor activation by paracrine/autocrine release of endogenous agonists: more than a simple communication pathway. Mol Neurobiol 2011; 44:28-52. [PMID: 21547557 DOI: 10.1007/s12035-011-8185-1] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2011] [Accepted: 04/14/2011] [Indexed: 02/04/2023]
Abstract
It is a common and widely accepted assumption that glycine and GABA are the main inhibitory transmitters in the central nervous system (CNS). But, in the past 20 years, several studies have clearly demonstrated that these amino acids can also be excitatory in the immature central nervous system. In addition, it is now established that both GABA receptors (GABARs) and glycine receptors (GlyRs) can be located extrasynaptically and can be activated by paracrine release of endogenous agonists, such as GABA, glycine, and taurine. Recently, non-synaptic release of GABA, glycine, and taurine gained further attention with increasing evidence suggesting a developmental role of these neurotransmitters in neuronal network formation before and during synaptogenesis. This review summarizes recent knowledge about the non-synaptic activation of GABA(A)Rs and GlyRs, both in developing and adult CNS. We first present studies that reveal the functional specialization of both non-synaptic GABA(A)Rs and GlyRs and we discuss the neuronal versus non-neuronal origin of the paracrine release of GABA(A)R and GlyR agonists. We then discuss the proposed non-synaptic release mechanisms and/or pathways for GABA, glycine, and taurine. Finally, we summarize recent data about the various roles of non-synaptic GABAergic and glycinergic systems during the development of neuronal networks and in the adult.
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Affiliation(s)
- Herve Le-Corronc
- Institut National de la Santé et de la Recherche Médicale, U952, Centre National de la Recherche Scientifique, UMR 7224, Université Pierre et Marie Curie, 9 quai Saint Bernard, Paris, Ile de France, France
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18
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Lee M, Schwab C, McGeer PL. Astrocytes are GABAergic cells that modulate microglial activity. Glia 2011; 59:152-65. [PMID: 21046567 DOI: 10.1002/glia.21087] [Citation(s) in RCA: 233] [Impact Index Per Article: 17.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
GABA is assumed to function in brain only as an inhibitory neurotransmitter. Here we report a much broader CNS role. We show that human astrocytes are GABAergic cells, and that human microglia are GABAceptive cells. We show that in adult human brain tissue, astrocytes immunostain for the GABA synthesizing enzyme GAD 67, the GABA metabolizing enzyme GABA-T and the GABA(A) and GABA(B) receptors. The intensity of staining is comparable or greater to that observed for known inhibitory neurons. We show that cultured human astrocytes strongly express the mRNA and protein for GAD 67, as well as GABA-T, and the GABA(A) and GABA(B) receptors. We further show that cultured human microglia express the mRNA and protein for GABA-T, in addition to the GABA(A) and GABA(B) receptors characterizing them as GABAceptive cells. We demonstrate that GABA suppresses the reactive response of both astrocytes and microglia to the inflammatory stimulants lipopolysaccharide (LPS) and interferon-γ by inhibiting induction of inflammatory pathways mediated by NFκB and P38 MAP kinase. This results in a reduced release of the inflammatory cytokines TNFα and IL-6 and an attenuation of conditioned medium neurotoxicity toward neuroblastoma SH-SY5Y cells. These inhibitory reactions are partially mimicked by the GABA(A) receptor agonist muscimol and the GABA(B) receptor agonist baclofen, indicating that GABA can stimulate both types of receptors in astrocytes as well as microglia. We conclude that the antiinflammatory actions of GABA offer new therapeutic opportunities since agonists should enhance the effectiveness of other antiinflammatory agents that operate through non-GABA pathways.
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Affiliation(s)
- Moonhee Lee
- Kinsmen Laboratory of Neurological Research, University of British Columbia, Vancouver, BC, Canada
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19
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Lee S, Yoon BE, Berglund K, Oh SJ, Park H, Shin HS, Augustine GJ, Lee CJ. Channel-Mediated Tonic GABA Release from Glia. Science 2010; 330:790-6. [DOI: 10.1126/science.1184334] [Citation(s) in RCA: 383] [Impact Index Per Article: 27.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
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20
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Constantinou S, Fern R. Conduction block and glial injury induced in developing central white matter by glycine, GABA, noradrenalin, or nicotine, studied in isolated neonatal rat optic nerve. Glia 2009; 57:1168-77. [DOI: 10.1002/glia.20839] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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21
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Angulo MC, Le Meur K, Kozlov AS, Charpak S, Audinat E. GABA, a forgotten gliotransmitter. Prog Neurobiol 2008; 86:297-303. [PMID: 18786601 DOI: 10.1016/j.pneurobio.2008.08.002] [Citation(s) in RCA: 85] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2008] [Revised: 05/30/2008] [Accepted: 08/12/2008] [Indexed: 01/27/2023]
Abstract
The amino acid gamma-aminobutiric acid (GABA) is a major inhibitory transmitter in the vertebrate central nervous system (CNS) where it can be released by neurons and by glial cells. Neuronal GABAergic signaling is well characterized: the mechanisms of GABA release, the receptors it targets and the functional consequences of their activation have been extensively studied. In contrast, the corresponding features of glial GABAergic signaling have attracted less attention. In this review, we first discuss evidence from the literature for GABA accumulation, production and release by glial cells. We then review the results of recent experiments that point toward functional roles of GABA as a "gliotransmitter".
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Affiliation(s)
- María Cecilia Angulo
- Inserm U603, Paris, France; CNRS UMR 8154, Paris, France; Université Paris Descartes, Paris, France
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22
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Ferreiro-Galve S, Candal E, Carrera I, Anadón R, Rodríguez-Moldes I. Early development of GABAergic cells of the retina in sharks: an immunohistochemical study with GABA and GAD antibodies. J Chem Neuroanat 2008; 36:6-16. [PMID: 18524536 DOI: 10.1016/j.jchemneu.2008.04.004] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2007] [Revised: 03/17/2008] [Accepted: 04/18/2008] [Indexed: 11/24/2022]
Abstract
We studied the ontogeny and organization of GABAergic cells in the retina of two elasmobranches, the lesser-spotted dogfish (Scyliorhinus canicula) and the brown shyshark (Haploblepharus fuscus) by using immunohistochemistry for gamma-aminobutyric acid (GABA) and glutamic acid decarboxylase (GAD). Both antibodies revealed the same pattern of immunoreactivity and both species showed similar organization of GABAergic cells. GABAergic cells were first detected in neural retina of embryos at stage 26, which showed a neuroepithelial appearance without any layering. In stages 27-29 the retina showed similar organization but the number of neuroblastic GABAergic cells increased. When layering became apparent in the central retina (stage-30 embryos), GABAergic cells mainly appeared organized in the outer and inner retina, and GABAergic processes and fibres were seen in the primordial inner plexiform layer (IPL), optic fibre layer and optic nerve stalk. In stage-32 embryos, layering was completed in the central retina, where immunoreactivity appeared in perikarya of the horizontal cell layer, inner nuclear layer and ganglion cell layer, and in numerous processes coursing in the IPL, optic fibre layer and optic nerve. From stage 32 to hatching (stage 34), the layered retina extends from centre-to-periphery, recapitulating that observed in the central retina at earlier stages. In adults, GABA/GAD immunoreactivity disappears from the horizontal cell layer except in the marginal retina. Our results indicate that the source of GABA in the shark retina can be explained by its synthesis by GAD. Such synthesis precedes layering and synaptogenesis, thus supporting a developmental role for GABA in addition to act as neurotransmitter and neuromodulator.
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Affiliation(s)
- Susana Ferreiro-Galve
- Department of Cell Biology and Ecology, University of Santiago de Compostela, 15782 Santiago de Compostela, Spain
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23
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Some gamma-motoneurons contain gamma-aminobutyric acid in the rat cervical spinal cord. Brain Res 2008; 1201:78-87. [PMID: 18294622 DOI: 10.1016/j.brainres.2008.01.056] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2007] [Revised: 01/10/2008] [Accepted: 01/10/2008] [Indexed: 11/21/2022]
Abstract
Gamma-aminobutyric acid (GABA) is utilized in the peripheral as well as central nervous system. In this study, fibers immunoreactive for 67 kDa isoform of glutamic acid decarboxylase (GAD67), an enzyme which synthesizes GABA, were found to terminate in the intercapsular region of muscle spindles of the upper limb. GABA-containing fibers were also found in the ventral roots of C5 to T5 spinal segments, brachial plexus, and radial nerve. These fibers were thin and immunoreactive for choline-acetyl transferase (ChAT). After transection of the brachial plexus, GABA immunoreactivity disappeared completely in the ipsilateral triceps brachii muscle (TBM). After the injection of fluorogold into the TBM, some retrogradely labeled medium-sized neurons were positive for GAD67, but not VGAT mRNA. All these observations clearly indicate that GABA-containing gamma-motoneurons in the lower cervical spinal cord send their fibers to muscle spindles in the upper extremities. Since we detected neither GABAA nor GABAB receptors in the TBM by RT-PCR, the function of the GABA-containing gamma-motoneurons remains unclear.
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24
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Seidenfaden R, Desoeuvre A, Bosio A, Virard I, Cremer H. Glial conversion of SVZ-derived committed neuronal precursors after ectopic grafting into the adult brain. Mol Cell Neurosci 2006; 32:187-98. [PMID: 16730456 DOI: 10.1016/j.mcn.2006.04.003] [Citation(s) in RCA: 115] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2006] [Revised: 03/27/2006] [Accepted: 04/06/2006] [Indexed: 12/23/2022] Open
Abstract
In the adult mouse forebrain, large numbers of neuronal precursors, destined to become GABA- and dopamine-producing interneurons of the olfactory bulb (OB), are generated in the subventricular zone (SVZ). Although this neurogenic system represents a potential reservoir of stem and progenitor cells for brain repair approaches, information about the survival and differentiation of SVZ-derived cells in ectopic brain regions is still fragmentary. We show here that ectopic grafting of SVZ tissue gave rise to two morphologically distinguishable cell types displaying oligodendrocytic or astrocytic characteristics. Since SVZ tissue contains neuronal and glial progenitors, we used magnetic cell sorting to deplete A2B5+ glial progenitors from the dissociated SVZ and to positively select cells that express PSA-NCAM. This procedure allowed the purification of neuronal precursors expressing TUJ1, DCX and GAD65/67. Transplantation of these cells led again to the generation of the same two glial cell types, showing that committed interneuron precursors undergo glial differentiation outside their normal environment.
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Affiliation(s)
- Ralph Seidenfaden
- Institut de Biologie du Développement de Marseille, CNRS, Université de la Méditeranée, Campus de Luminy-case 907, 13288 Marseille cedex 9, France.
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25
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Abstract
In the immature brain, GABA (gamma-aminobutyric acid) is excitatory, and GABA-releasing synapses are formed before glutamatergic contacts in a wide range of species and structures. GABA becomes inhibitory by the delayed expression of a chloride exporter, leading to a negative shift in the reversal potential for choride ions. I propose that this mechanism provides a solution to the problem of how to excite developing neurons to promote growth and synapse formation while avoiding the potentially toxic effects of a mismatch between GABA-mediated inhibition and glutamatergic excitation. As key elements of this cascade are activity dependent, the formation of inhibition adds an element of nurture to the construction of cortical networks.
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Affiliation(s)
- Yehezkel Ben-Ari
- Institut de Neurobiologie de la Méditerranée (INMED), INSERM Unit 29, Parc Scientifique de Luminy, 13273 Marseille Cedex 09, France.
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26
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Affiliation(s)
- J D Plautz
- Department of Cell Biology, Scripps Research Institute, La Jolla, California 92037, USA
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27
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Abstract
The major pathological correlate of cerebral palsy is ischemic injury of CNS white matter. Histological studies show early injury of glial cells and axons. To investigate glial cell injury, I monitored intracellular Ca2+ and cell viability in fura-2-loaded neonatal rat white matter glial cells during ischemia. Fura-2 fixation combined with immunohistochemistry revealed that fura-2-loaded cells were GFAP+/O4(-) and were therefore a population of neonatal white matter astrocytes. Significant ischemic Ca2+ influx was found, mediated by both L- and T-type voltage-gated Ca2+ channels. Ca2+ influx via T-type channels was the most important factor during the initial stage of ischemia and was associated with significant cell death within 10-20 min of the onset of ischemia. The Na+-Ca2+ exchanger acted to remove cytoplasmic Ca2+ throughout the ischemic and recovery periods. Neither the release of Ca2+ from intracellular stores nor influx via glutamate-gated channels contributed to the rise in intracellular Ca2+ during ischemia. Ischemic cell death was reduced significantly by removing extracellular Ca2+ or by blocking voltage-gated Ca2+ channels. The exclusively voltage-gated Ca2+ channel nature of the Ca2+ influx, the role played by T-type Ca2+ channels, the protective effect of the Na+-Ca2+ exchanger, and the lack of significant Ca2+ release from intracellular stores are features of ischemia that have not been reported in other CNS cell types.
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28
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Upregulation of L-type Ca2+ channels in reactive astrocytes after brain injury, hypomyelination, and ischemia. J Neurosci 1998. [PMID: 9502793 DOI: 10.1523/jneurosci.18-07-02321.1998] [Citation(s) in RCA: 110] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Anti-peptide antibodies that specifically recognize the alpha1 subunit of class A-D voltage-gated Ca2+ channels and a monoclonal antibody (MANC-1) to the alpha2 subunit of L-type Ca2+ channels were used to investigate the distribution of these Ca2+ channel subtypes in neurons and glia in models of brain injury, including kainic acid-induced epilepsy in the hippocampus, mechanical and thermal lesions in the forebrain, hypomyelination in white matter, and ischemia. Immunostaining of the alpha2 subunit of L-type Ca2+ channels by the MANC-1 antibody was increased in reactive astrocytes in each of these forms of brain injury. The alpha1C subunits of class C L-type Ca2+ channels were upregulated in reactive astrocytes located in the affected regions in each of these models of brain injury, although staining for the alpha1 subunits of class D L-type, class A P/Q-type, and class B N-type Ca2+ channels did not change from patterns normally observed in control animals. In all of these models of brain injury, there was no apparent redistribution or upregulation of the voltage-gated Ca2+ channels in neurons. The upregulation of L-type Ca2+ channels in reactive astrocytes may contribute to the maintenance of ionic homeostasis in injured brain regions, enhance the release of neurotrophic agents to promote neuronal survival and differentiation, and/or enhance signaling in astrocytic networks in response to injury.
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29
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Abstract
Considering the mechanisms responsible for age- and Alzheimer's disease (AD)-related neuronal degeneration, little attention was paid to the opposing relationships between the energy-rich phosphates, mainly the availability of the adenosine triphosphate (ATP), and the activity of the glutamic acid decarboxylase (GAD), the rate-limiting enzyme synthesizing the gamma-amino butyric acid (GABA). Here, it is postulated that in all neuronal phenotypes the declining ATP-mediated negative control of GABA synthesis gradually declines and results in age- and AD-related increases of GABA synthesis. The Ca2+-independent carrier-mediated GABA release interferes with Ca2+-dependent exocytotic release of all transmitter-modulators, because the interstitial (ambient) GABA acts on axonal preterminal and terminal varicosities endowed with depolarizing GABA(A)-benzodiazepine receptors; this makes GABA the "executor" of virtually all age- and AD-related neurodegenerative processes. Such a role of GABA is diametrically opposite to that in the perinatal phase, when the carrier-mediated GABA release, acting on GABA(A)/chloride ionophore receptors, positively controls chemotactic migration of neuronal precursor cells, has trophic actions and initiates synaptogenesis, thereby enabling retrograde axonal transport of target produced factors that trigger differentiation of neuronal phenotypes. However, with advancing age, and prematurely in AD, the declining mitochondrial ATP synthesis unleashes GABA synthesis, and its carrier-mediated release blocks Ca2+-dependent exocytotic release of all transmitter-modulators, leading to dystrophy of chronically depolarized axon terminals and block of retrograde transport of target-produced trophins, causing "starvation" and death of neuronal somata. The above scenario is consistent with the following observations: 1) a 10-month daily administration to aging rats of the GABA-chloride ionophore antagonist, pentylenetetrazol, or of the BDZ antagonist, flumazenil (FL), each forestalls the age-related decline in cognitive functions and losses of hippocampal neurons; 2) the brains of aging rats, relative to young animals, and the postmortem brains of AD patients, relative to age-matched controls, show up to two-fold increases in GABA synthesis; 3) the aging humans and those showing symptoms of AD, as well as the aging nonhuman primates and rodents--all show in the forebrain dystrophic axonal varicosities, losses of transmitter vesicles, and swollen mitochondria. These markers, currently regarded as the earliest signs of aging and AD, can be reproduced in vitro cell cultures by 1 microM GABA; the development of these markers can be prevented by substituting Cl- with SO4(2-); 4) the extrasynaptic GABA suppresses the membrane Na+, K+-ATPase and ion pumping, while the resulting depolarization of soma-dendrites relieves the "protective" voltage-dependent Mg2+ control of the N-methyl-D-aspartate (NMDA) channels, thereby enabling Ca2+-dependent persistent toxic actions of the excitatory amino acids (EAA); and 5) in whole-cell patch-clamp recording from neurons of aging rats, relative to young rats, the application of 3 microM GABA, causes twofold increases in the whole-cell membrane Cl- conductances and a loss of the physiologically important neuronal ability to desensitize to repeated GABA applications. These age-related alterations in neuronal membrane functions are amplified by 150% in the presence of agonists of BDZ recognition sites located on GABA receptor. The GABA deafferentation hypothesis also accounts for the age- and AD-related degeneration in the forebrain ascending cholinergic, glutamatergic, and the ascending mesencephalic monoaminergic system, despite that the latter, to foster the distribution-utilization of locally produced trophins, evolved syncytium-like connectivities among neuronal somata, axon collaterals, and dendrites, to bidirectionally transport trophins. (ABSTRACT TRUNCATED)
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Affiliation(s)
- T J Marczynski
- Department of Pharmacology, College of Medicine, University of Illinois, Chicago 60612, USA.
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30
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Yee JM, Agulian S, Kocsis JD. Vigabatrin enhances promoted release of GABA in neonatal rat optic nerve. Epilepsy Res 1998; 29:195-200. [PMID: 9551781 DOI: 10.1016/s0920-1211(97)00086-7] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Vigabatrin (gamma-vinyl GABA) is an antiepileptic drug and blocks GABA transaminase activity resulting in elevations in cellular GABA levels in the brain. Nipecotic acid (NPA) promotes release of GABA from neonatal optic nerve astrocytes, resulting in a bicuculline-sensitive depolarization of the optic nerve axons. The NPA-induced depolarization of vigabatrin-treated rats (100 mg/kg, i.p.) more than doubled, suggesting an elevation in free GABA levels; the GABA transporter inhibitor, NO-711 reduced the depolarization. These results are consistent with the known ability of vigabatrin to block the GABA degradation enzyme GABA-transaminase, suggesting that vigabatrin elevates astrocytic GABA levels, thereby favoring greater release of GABA through the GABA transporter.
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Affiliation(s)
- J M Yee
- Department of Neurology, Yale University School of Medicine and Neuroscience Research Center, VA Medical Center, West Haven, CT 06516, USA
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31
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Taylor CP, Gee NS, Su TZ, Kocsis JD, Welty DF, Brown JP, Dooley DJ, Boden P, Singh L. A summary of mechanistic hypotheses of gabapentin pharmacology. Epilepsy Res 1998; 29:233-49. [PMID: 9551785 DOI: 10.1016/s0920-1211(97)00084-3] [Citation(s) in RCA: 464] [Impact Index Per Article: 17.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Although the cellular mechanisms of pharmacological actions of gabapentin (Neurontin) remain incompletely described, several hypotheses have been proposed. It is possible that different mechanisms account for anticonvulsant, antinociceptive, anxiolytic and neuroprotective activity in animal models. Gabapentin is an amino acid, with a mechanism that differs from those of other anticonvulsant drugs such as phenytoin, carbamazepine or valproate. Radiotracer studies with [14C]gabapentin suggest that gabapentin is rapidly accessible to brain cell cytosol. Several hypotheses of cellular mechanisms have been proposed to explain the pharmacology of gabapentin: 1. Gabapentin crosses several membrane barriers in the body via a specific amino acid transporter (system L) and competes with leucine, isoleucine, valine and phenylalanine for transport. 2. Gabapentin increases the concentration and probably the rate of synthesis of GABA in brain, which may enhance non-vesicular GABA release during seizures. 3. Gabapentin binds with high affinity to a novel binding site in brain tissues that is associated with an auxiliary subunit of voltage-sensitive Ca2+ channels. Recent electrophysiology results suggest that gabapentin may modulate certain types of Ca2+ current. 4. Gabapentin reduces the release of several monoamine neurotransmitters. 5. Electrophysiology suggests that gabapentin inhibits voltage-activated Na+ channels, but other results contradict these findings. 6. Gabapentin increases serotonin concentrations in human whole blood, which may be relevant to neurobehavioral actions. 7. Gabapentin prevents neuronal death in several models including those designed to mimic amyotrophic lateral sclerosis (ALS). This may occur by inhibition of glutamate synthesis by branched-chain amino acid aminotransferase (BCAA-t).
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Affiliation(s)
- C P Taylor
- Department of Neuroscience Therapeutics, Parke-Davis Pharmaceutical Research, Division of Warner-Lambert Co., Ann Arbor, MI 48105, USA
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32
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Howd AG, Rattray M, Butt AM. Expression of GABA transporter mRNAs in the developing and adult rat optic nerve. Neurosci Lett 1997; 235:98-100. [PMID: 9389605 DOI: 10.1016/s0304-3940(97)00699-x] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
There is electrophysiological evidence of a functional role for gamma-aminobutyric acid (GABA) and GABA transporters (GATs) in the neonatal rat optic nerve, and that they are down-regulated during development. The results of the present study demonstrate directly by reverse transcription-polymerase chain reaction (RT-PCR) that the mRNAs encoding for GAT-1, -2 and -3 are expressed in the optic nerves of both neonatal (5 day old) and adult rats. The results support a role for GABA in the developing rat optic nerve, a typical white matter tract which contains axons and glia, but neither neuronal cell bodies nor synapses. Significantly, the persistence of GAT mRNAs suggests an enduring function for both GABA and glial uptake mechanisms in the adult optic nerve.
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Affiliation(s)
- A G Howd
- Division of Physiology, UMDS, Guys' and St. Thomas' Hospital, London, UK
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33
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White HS. Clinical significance of animal seizure models and mechanism of action studies of potential antiepileptic drugs. Epilepsia 1997; 38 Suppl 1:S9-17. [PMID: 9092952 DOI: 10.1111/j.1528-1157.1997.tb04523.x] [Citation(s) in RCA: 157] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
More than 50 million persons worldwide suffer from epilepsy, many of whom are refractory to treatment with standard antiepileptic drugs (AEDs). Fortunately, new AEDs commercialized since 1990 are improving the clinical outlook for many patients. Our growing understanding of anticonvulsant mechanisms and the relevance of preclinical animal studies to clinical antiepileptic activity have already contributed to the design of several new AEDs and should be increasingly beneficial to further efforts at drug development. Mechanisms have been identified for older AEDs [phenytoin (PHT), carbamazepine (CBZ), valproate (VPA), barbiturates, benzodiazepines (BZDs), ethosuximide (ESM)] and newer AEDs [vigabatrin (VGB), lamotrigine (LTG), gabapentin (GBP) tiagabine (TGB), felbamate (FBM), topiramate (TPM)]. Several novel anticonvulsant mechanisms have recently been discovered. FBM appears to be active at the strychnine-insensitive glycine binding site of the NMDA receptor. TPM is active on the kainate/AMPA subtype of glutamate receptor and at a potentially novel site on the GABA(A) receptor. For several reasons, availability of a single AED with multiple mechanisms of action may be preferred over availability of multiple AEDs with single mechanisms of action. These reasons include ease of titration, lack of drug-drug interactions, and reduced potential for pharmacodynamic tolerance.
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Affiliation(s)
- H S White
- Department of Pharmacology and Toxicology, University of Utah, Salt Lake City 84112, U.S.A
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34
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Abstract
A basic strategy for the pharmacological treatment of epilepsy is to develop drugs that reduce the excitability of CNS neurons at times preceding or during the onset of seizure discharge with minimal effects on normal electrical activity. Several antiepileptic drugs currently in use exert their action by modulating sodium channels or receptors of the abundant inhibitory neurotransmitter, GABA. These approaches, which are often successful in reducing the number or severity of seizures, have some effects that limit their clinical use. More recently, a new class of antiepileptic drugs such as vigabatrin, which blocks GABA degradation enzymes, have been developed as effective antiepileptics and are associated with minimal side effects. Although these drugs do not display agonist or antagonist properties at GABA receptor sites, they do appear to interact with brain GABA systems because NMR spectroscopy studies indicate that subjects given these drugs have elevated brain GABA levels, and in vitro electrophysiological studies on CNS tissue reveal elevated GABA release. The precise cellular mechanisms of antiepileptic action of these GABA metabolic modulators are not clear, but current work on the cellular effects of these drugs suggests a model that may explain their action.
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Affiliation(s)
- Jeffery D. Kocsis
- Department of Neurology Yale University School of Medicine New Haven, Connecticut Neuroscience Research Center VA Medical Center West Haven, Connecticut
| | - Richard H. Mattson
- Department of Neurology Yale University School of Medicine New Haven, Connecticut Neuroscience Research Center VA Medical Center West Haven, Connecticut
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35
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Fern R, Ransom BR, Waxman SG. Autoprotective mechanisms in the CNS: some new lessons from white matter. MOLECULAR AND CHEMICAL NEUROPATHOLOGY 1996; 27:107-29. [PMID: 8962597 DOI: 10.1007/bf02815088] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Anoxia/ischemia in the CNS is a common and devastating phenomenon. It is possible that the best hopes for protection against anoxic/ischemic injury may involve recruiting and/or augmenting any autoprotective systems that evolution has provided for the CNS. We describe here the existence of such an autoprotective system present in CNS white matter. White matter is both well suited to studying extrasynaptic systems, such as the system we describe here, and is a highly appropriate target for research into anoxic-ischemic injury in its own right. We show that white matter contains functional GABAB and adenosine receptors that respond to an anoxic efflux of GABA and adenosine by recruiting a convergent intracellular mechanism involving protein kinase C (PKC). The net result of this receptor-mediated cascade is an increase in resistance to anoxia, which presumably allows CNS white matter to tolerate better a common class of ischemic events that are located solely in white matter and that comprises approximately 25% of all strokes seen clinically.
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Affiliation(s)
- R Fern
- Department of Neurology, Yale University School of Medicine, New Haven, CT 06510, USA
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36
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Guillemin G, Boussin FD, Le Grand R, Croitoru J, Coffigny H, Dormont D. Granulocyte macrophage colony stimulating factor stimulates in vitro proliferation of astrocytes derived from simian mature brains. Glia 1996; 16:71-80. [PMID: 8787775 DOI: 10.1002/(sici)1098-1136(199601)16:1<71::aid-glia8>3.0.co;2-e] [Citation(s) in RCA: 53] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
In the brain, granulocyte-macrophage colony stimulating factor (GM-CSF) may be released by infiltrated cells of the immune system including T and B lymphocytes and mononuclear phagocytes, but also by nervous system resident cells such as microglia and astrocytes. Astrocyte-secreted GM-CSF may play an important role in enhancing the local inflammatory response to central nervous system (CNS) injury and in recruting microglia and activated macrophages. In this study, we demonstrated that GM-CSF, as TNF alpha and IL 6, stimulates in vitro proliferation of simian astrocytes in primary cultures. Results were confirmed by blocking experiments performed with a specific neutralizing mAb directed against GM-CSF. Furthermore, we demonstrated that GM-CSF mediates its effect on these cells through the alpha subunit of the GM-CSF receptor which is constitutively expressed at the membrane of the cultured simian astrocytes as assessed by immunofluorescence. GM-CSF effects on astrocytes could be involved in astrocytosis, a hallmark of various neurological injuries and in inflammatory processes in an autocrine manner.
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Affiliation(s)
- G Guillemin
- Service de Neurovirologie, CEA, DSV/DRM/SSA/IPSC, Fontenay-aux-Roses, France
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Pastor A, Chvátal A, Syková E, Kettenmann H. Glycine- and GABA-activated currents in identified glial cells of the developing rat spinal cord slice. Eur J Neurosci 1995; 7:1188-98. [PMID: 7582092 DOI: 10.1111/j.1460-9568.1995.tb01109.x] [Citation(s) in RCA: 73] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
In the neonatal rat spinal cord, four types of glial cells, namely astrocytes, oligodendrocytes and two types of precursor cells, can be distinguished based on their membrane current patterns and distinct morphological features. In the present study, we demonstrate that these cells respond to the inhibitory neurotransmitters glycine and GABA, as revealed with the whole-cell recording configuration of the patch-clamp technique. All astrocytes and glial precursor cells and a subpopulation of oligodendrocytes responded to glycine. The involvement of glycine receptors was inferred from the observation that the response was blocked by strychnine and that the induced current reversed close to the Cl- equilibrium potential. GABA induced large membrane currents in astrocytes and precursor cells while oligodendrocytes showed only small responses. The GABA-activated current was due to the activation of GABAA receptors since muscimol mimicked and bicuculline blocked the response; moreover, the reversal potential was close to the Cl- equilibrium potential. Besides the increase in a Cl- conductance, GABAA receptor activation also induced a block of the resting K+ conductance, as observed previously in Bergmann glial cells. Our experiments show that while glial GABAA receptors are found in many brain regions and the spinal cord, glial glycine receptors have so far been detected only in the spinal cord. The restricted coexpression of glial and neuronal glycine receptors in a defined central nervous system grey matter area implies that such glial receptors may be involved in synaptic transmission.
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Affiliation(s)
- A Pastor
- Institute of Neurobiology, University of Heidelberg, Germany
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Butt AM, Jennings J. The astrocyte response to gamma-aminobutyric acid attenuates with age in the rat optic nerve. Proc Biol Sci 1994; 258:9-15. [PMID: 7997461 DOI: 10.1098/rspb.1994.0134] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
There is increasing evidence that glial cells respond to the inhibitory neurotransmitter gamma-aminobutyric acid (GABA), and astrocytes have been shown to possess GABAA receptors both in vivo and in vitro. A recent study by Sakatani et al. (Proc. R. Soc. Lond. B247, 155 (1992)) demonstrated the transient expression of functional GABAA receptors in the developing rat optic nerve, but axonal and glial components of the response were not distinguished. To help address this problem, we have determined the electrophysiological response to GABA in astrocytes of the isolated intact optic nerves from neonatal rats, identified morphologically following intracellular injection of horseradish peroxidase. Astrocytes responded to GABA by a GABAA receptor-mediated depolarization which attenuated gradually during post-natal development; astrocytes in 21-day-old nerves were not observed to respond to GABA. The results indicate the transient presence of functional GABAA receptors in developing rat optic nerve astrocytes in situ, and we speculate upon a role for GABA in glial signalling and the organization of axonglial interrelations during development.
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Affiliation(s)
- A M Butt
- Division of Physiology, UMDS, St Thomas's Hospital, London, U.K
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Abstract
Membrane potential changes of rat neonatal optic nerves were studied in a sucrose-gap chamber. Nipecotic acid (NPA), which blocks uptake and promotes release of GABA, resulted in a bicuculline-sensitive depolarization (3.08 +/- 0.3 mV, n = 5). Pretreatment of the nerves with the anticonvulsant gabapentin (100 microM for 1 h) resulted in a near doubling of the NPA-induced depolarization (6.64 +/- 0.54 mV, n = 5). Gabapentin itself did not alter membrane potential, nor did brief applications of gabapentin enhance the NPA- or GABA-induced depolarization. Thus, gabapentin appears to enhance the releasable pool of GABA in this CNS neural system. These results have implications for the mechanism of the anticonvulsant properties of gabapentin.
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Affiliation(s)
- J D Kocsis
- Department of Neurology, Yale University School of Medicine, New Haven, CT 06516
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Butt AM, Jennings J. Response of astrocytes to gamma-aminobutyric acid in the neonatal rat optic nerve. Neurosci Lett 1994; 168:53-6. [PMID: 8028793 DOI: 10.1016/0304-3940(94)90414-6] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
The electrophysiological response to gamma-aminobutyric acid (GABA) was determined in astrocytes of the isolated intact optic nerves of rats aged 8 to 12 days old, identified morphologically following intracellular injection of horseradish peroxidase. At this age, astrocytes had a mean (+/- S.E.M.) resting membrane potential of -62.25 +/- 1.9 mV (n = 32), and responded to GABA by a depolarization characterized by an initial peak of mean 9.1 +/- 0.6 mV, which was not sustained and fell to a plateau level. The effect of GABA was mimicked by the GABAA-receptor agonist muscimol, but not by the GABAB-receptor agonist baclofen, and was reduced in the presence of the GABAA-receptor antagonist bicuculline. Astrocytes responded to 10 mM [K+]o by a single phase depolarization of 16 +/- 2 mV (n = 5). It is concluded that GABA acts directly on astrocytes and its effect is not mediated by K+ released by axons. This study indicates the presence of functional GABAA receptors in neonatal rat optic nerve astrocytes in situ. The results suggest immature astrocytes may be the source of the GABA response described in two recent studies on the rat whole optic nerve preparation. The astrocyte response to GABA may be important in axon-glial signalling during development.
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Affiliation(s)
- A M Butt
- Sherrington School of Physiology, U.M.D.S., St. Thomas's Hospital, London, UK
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