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Kardos J, Héja L, Jemnitz K, Kovács R, Palkovits M. The nature of early astroglial protection-Fast activation and signaling. Prog Neurobiol 2017; 153:86-99. [PMID: 28342942 DOI: 10.1016/j.pneurobio.2017.03.005] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2016] [Revised: 09/22/2016] [Accepted: 03/05/2017] [Indexed: 12/14/2022]
Abstract
Our present review is focusing on the uniqueness of balanced astroglial signaling. The balance of excitatory and inhibitory signaling within the CNS is mainly determined by sharp synaptic transients of excitatory glutamate (Glu) and inhibitory γ-aminobutyrate (GABA) acting on the sub-second timescale. Astroglia is involved in excitatory chemical transmission by taking up i) Glu through neurotransmitter-sodium transporters, ii) K+ released due to presynaptic action potential generation, and iii) water keeping osmotic pressure. Glu uptake-coupled Na+ influx may either ignite long-range astroglial Ca2+ transients or locally counteract over-excitation via astroglial GABA release and increased tonic inhibition. Imbalance of excitatory and inhibitory drives is associated with a number of disease conditions, including prevalent traumatic and ischaemic injuries or the emergence of epilepsy. Therefore, when addressing the potential of early therapeutic intervention, astroglial signaling functions combating progress of Glu excitotoxicity is of critical importance. We suggest, that excitotoxicity is linked primarily to over-excitation induced by the impairment of astroglial Glu uptake and/or GABA release. Within this framework, we discuss the acute alterations of Glu-cycling and metabolism and conjecture the therapeutic promise of regulation. We also confer the role played by key carrier proteins and enzymes as well as their interplay at the molecular, cellular, and organ levels. Moreover, based on our former studies, we offer potential prospect on the emerging theme of astroglial succinate sensing in course of Glu excitotoxicity.
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Affiliation(s)
- Julianna Kardos
- Functional Pharmacology Research Group, Institute of Organic Chemistry, Research Centre for Natural Sciences, Hungarian Academy of Sciences, Hungary.
| | - László Héja
- Functional Pharmacology Research Group, Institute of Organic Chemistry, Research Centre for Natural Sciences, Hungarian Academy of Sciences, Hungary
| | - Katalin Jemnitz
- Functional Pharmacology Research Group, Institute of Organic Chemistry, Research Centre for Natural Sciences, Hungarian Academy of Sciences, Hungary
| | - Richárd Kovács
- Institute of Neurophysiology, Charité - Universitätsmedizin, Berlin, Germany
| | - Miklós Palkovits
- Human Brain Tissue Bank and Laboratory, Semmelweis University, Budapest, Hungary
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Agusti A, Hernández-Rabaza V, Balzano T, Taoro-Gonzalez L, Ibañez-Grau A, Cabrera-Pastor A, Fustero S, Llansola M, Montoliu C, Felipo V. Sildenafil reduces neuroinflammation in cerebellum, restores GABAergic tone, and improves motor in-coordination in rats with hepatic encephalopathy. CNS Neurosci Ther 2017; 23:386-394. [PMID: 28296282 DOI: 10.1111/cns.12688] [Citation(s) in RCA: 36] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2016] [Revised: 01/23/2017] [Accepted: 02/09/2017] [Indexed: 12/31/2022] Open
Abstract
AIMS Patients with liver disease may develop hepatic encephalopathy (HE), with cognitive impairment and motor in-coordination. Rats with HE due to portacaval shunts (PCS) show motor in-coordination. We hypothesized that in PCS rats: (i) Motor in-coordination would be due to enhanced GABAergic tone in cerebellum; (ii) increased GABAergic tone would be due to neuroinflammation; (iii) increasing cGMP would reduce neuroinflammation and GABAergic tone and restore motor coordination. To assess these hypotheses, we assessed if (i) treatment with sildenafil reduces neuroinflammation; (ii) reduced neuroinflammation is associated with reduced GABAergic tone and restored motor coordination. METHODS Rats were treated with sildenafil to increase cGMP. Microglia and astrocytes activation were analyzed by immunohistochemistry, extracellular GABA by microdialysis, and motor coordination in the beam walking. RESULTS PCS rats show neuroinflammation in cerebellum, with microglia and astrocytes activation, increased IL-1b and TNF-a and reduced YM-1 and IL-4. Membrane expression of the GABA transporter GAT1 is reduced, while GAT3 is increased. Extracellular GABA and motor in-coordination are increased. Sildenafil treatment eliminates neuroinflammation, microglia and astrocytes activation; changes in membrane expression of GABA transporters; and restores motor coordination. CONCLUSIONS This study supports an interplay between cGMP-neuroinflammation and GABAergic neurotransmission in impairing motor coordination in PCS rats.
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Affiliation(s)
- Ana Agusti
- Laboratory of Neurobiology, Centro de Investigación Príncipe Felipe, Valencia, Spain
| | | | - Tiziano Balzano
- Laboratory of Neurobiology, Centro de Investigación Príncipe Felipe, Valencia, Spain
| | - Lucas Taoro-Gonzalez
- Laboratory of Neurobiology, Centro de Investigación Príncipe Felipe, Valencia, Spain
| | - Andrea Ibañez-Grau
- Laboratory of Neurobiology, Centro de Investigación Príncipe Felipe, Valencia, Spain
| | - Andrea Cabrera-Pastor
- Laboratory of Neurobiology, Centro de Investigación Príncipe Felipe, Valencia, Spain
| | - Santos Fustero
- Laboratory of Neurobiology, Centro de Investigación Príncipe Felipe, Valencia, Spain
| | - Marta Llansola
- Laboratory of Neurobiology, Centro de Investigación Príncipe Felipe, Valencia, Spain
| | - Carmina Montoliu
- Laboratory of Neurobiology, Centro de Investigación Príncipe Felipe, Valencia, Spain
| | - Vicente Felipo
- Laboratory of Neurobiology, Centro de Investigación Príncipe Felipe, Valencia, Spain
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Todd AC, Marx MC, Hulme SR, Bröer S, Billups B. SNAT3-mediated glutamine transport in perisynaptic astrocytesin situis regulated by intracellular sodium. Glia 2017; 65:900-916. [DOI: 10.1002/glia.23133] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2016] [Revised: 01/12/2017] [Accepted: 02/08/2017] [Indexed: 01/16/2023]
Affiliation(s)
- Alison C. Todd
- Eccles Institute of Neuroscience, The John Curtin School of Medical Research; The Australian National University; 131 Garran Road Canberra ACT 2601 Australia
- Centre for Integrative Physiology, School of Biomedical Sciences; University of Edinburgh; Edinburgh EH8 9XD United Kingdom
| | - Mari-Carmen Marx
- Department of Pharmacology; University of Cambridge; Tennis Court Road Cambridge CB2 1BT United Kingdom
| | - Sarah R. Hulme
- Eccles Institute of Neuroscience, The John Curtin School of Medical Research; The Australian National University; 131 Garran Road Canberra ACT 2601 Australia
| | - Stefan Bröer
- Research School of Biology; The Australian National University; Linnaeus Way 134 Canberra ACT 2601 Australia
| | - Brian Billups
- Eccles Institute of Neuroscience, The John Curtin School of Medical Research; The Australian National University; 131 Garran Road Canberra ACT 2601 Australia
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Wellendorph P, Jacobsen J, Skovgaard-Petersen J, Jurik A, Vogensen SB, Ecker G, Schousboe A, Krogsgaard-Larsen P, Clausen RP. γ-Aminobutyric Acid and Glycine Neurotransmitter Transporters. METHODS AND PRINCIPLES IN MEDICINAL CHEMISTRY 2017. [DOI: 10.1002/9783527679430.ch4] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Affiliation(s)
- Petrine Wellendorph
- University of Copenhagen; Faculty of Health and Medical Sciences, Department of Drug Design and Pharmacology; Universitetsparken 2, DK-2100 Copenhagen Denmark
| | - Julie Jacobsen
- University of Copenhagen; Faculty of Health and Medical Sciences, Department of Drug Design and Pharmacology; Universitetsparken 2, DK-2100 Copenhagen Denmark
| | - Jonas Skovgaard-Petersen
- University of Copenhagen; Faculty of Health and Medical Sciences, Department of Drug Design and Pharmacology; Universitetsparken 2, DK-2100 Copenhagen Denmark
| | - Andreas Jurik
- University of Vienna; Department of Pharmaceutical Chemistry; Althanstrasse 14, A-1090 Vienna Austria
| | - Stine B. Vogensen
- University of Copenhagen; Faculty of Health and Medical Sciences, Department of Drug Design and Pharmacology; Universitetsparken 2, DK-2100 Copenhagen Denmark
| | - Gerhard Ecker
- University of Vienna; Department of Pharmaceutical Chemistry; Althanstrasse 14, A-1090 Vienna Austria
| | - Arne Schousboe
- University of Copenhagen; Faculty of Health and Medical Sciences, Department of Drug Design and Pharmacology; Universitetsparken 2, DK-2100 Copenhagen Denmark
| | - Povl Krogsgaard-Larsen
- University of Copenhagen; Faculty of Health and Medical Sciences, Department of Drug Design and Pharmacology; Universitetsparken 2, DK-2100 Copenhagen Denmark
| | - Rasmus P. Clausen
- University of Copenhagen; Faculty of Health and Medical Sciences, Department of Drug Design and Pharmacology; Universitetsparken 2, DK-2100 Copenhagen Denmark
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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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Glial GABA Transporters as Modulators of Inhibitory Signalling in Epilepsy and Stroke. ADVANCES IN NEUROBIOLOGY 2017; 16:137-167. [PMID: 28828609 DOI: 10.1007/978-3-319-55769-4_7] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Imbalances in GABA-mediated tonic inhibition are involved in several pathophysiological conditions. A classical way of controlling tonic inhibition is through pharmacological intervention with extrasynaptic GABAA receptors that sense ambient GABA and mediate a persistent GABAergic conductance. An increase in tonic inhibition may, however, also be obtained indirectly by inhibiting glial GABA transporters (GATs). These are sodium-coupled membrane transport proteins that normally act to terminate GABA neurotransmitter action by taking up GABA into surrounding astrocytes. The aim of the review is to provide an overview of glial GATs in regulating tonic inhibition, especially in epilepsy and stroke. This entails a comprehensive summary of changes known to occur in GAT expression levels and signalling following epileptic and ischemic insults. Further, we discuss the accumulating pharmacological evidence for targeting GATs in these diseases.
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Mohammadi M, Zare Z, Allah-Moradi E, Vaezi N, Valadan R, Tehrani M. Alterations in mRNA and protein expression of glutamate transporters in rat hippocampus after paraoxon exposure. Neurotoxicology 2016; 57:251-257. [PMID: 27769869 DOI: 10.1016/j.neuro.2016.10.009] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2016] [Revised: 10/15/2016] [Accepted: 10/15/2016] [Indexed: 01/30/2023]
Abstract
Organophosphates affect brain function through a variety of mechanisms beyond their shared role as cholinesterase inhibitors. The aim of the current study was to investigate the changes in the expression of glial (GLAST and GLT-1) and neuronal (EAAC1) glutamate transporters at mRNA and protein levels in paraoxon-treated rat hippocampus. Adult male Wistar rats were intraperitoneally treated with either vehicle (corn oil) or one of three dosages of paraoxon (0.3, 0.7 or 1mg/kg). After 4 or 18h, both hippocampi of each rat were collected to detect mRNA and protein expression of glutamate transporters using the quantitative reverse transcriptase polymerase chain reaction (qRT-PCR) and western blotting, respectively. Animals treated with 0.3mg/kg paraoxon showed no difference in mRNA and protein levels of the glutamate transporters when compared with control group. At 4h after exposure with 0.7 and 1mg/kg paraoxon, the expression of GLAST and GLT-1 increased at mRNA and protein levels and remained elevated after 18h. No difference in the expression of EAAC1 at mRNA and protein levels was observed in any paraoxon-treated groups compared with the control group. This study showed an increased expression of glial (GLAST and GLT-1), but not neuronal (EAAC1) glutamate transporters, in adult rat hippocampus following administration of convulsive dosages of paraoxon. These suggest a protective and compensatory adaptation for effective uptake of glutamate in hippocampus induced by paraoxon and thus attenuating seizure activity.
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Affiliation(s)
- Moslem Mohammadi
- Department of Physiology & Pharmacology, School of Medicine, Mazandaran University of Medical Sciences, Sari, Iran
| | - Zohreh Zare
- Department of Anatomical Sciences, School of Medicine, Mazandaran University of Medical Sciences, Sari, Iran
| | - Esmaeil Allah-Moradi
- Department of Immunology, School of Medicine, Mazandaran University of Medical Sciences, Sari, Iran
| | - Narges Vaezi
- Department of Toxicology and Pharmacology, School of Pharmacy, Mazandaran University of Medical Sciences, Sari, Iran
| | - Reza Valadan
- Department of Immunology, School of Medicine, Mazandaran University of Medical Sciences, Sari, Iran; Molecular and Cell Biology Research Center, Mazandaran University of Medical Sciences, Sari, Iran
| | - Mohsen Tehrani
- Department of Immunology, School of Medicine, Mazandaran University of Medical Sciences, Sari, Iran; Molecular and Cell Biology Research Center, Mazandaran University of Medical Sciences, Sari, Iran.
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58
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Advances in understanding the functions of native GlyT1 and GlyT2 neuronal glycine transporters. Neurochem Int 2016; 99:169-177. [DOI: 10.1016/j.neuint.2016.07.001] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2016] [Revised: 07/05/2016] [Accepted: 07/05/2016] [Indexed: 11/20/2022]
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A New Computational Model for Neuro-Glio-Vascular Coupling: Astrocyte Activation Can Explain Cerebral Blood Flow Nonlinear Response to Interictal Events. PLoS One 2016; 11:e0147292. [PMID: 26849643 PMCID: PMC4743967 DOI: 10.1371/journal.pone.0147292] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2015] [Accepted: 01/01/2016] [Indexed: 12/31/2022] Open
Abstract
Developing a clear understanding of the relationship between cerebral blood flow (CBF) response and neuronal activity is of significant importance because CBF increase is essential to the health of neurons, for instance through oxygen supply. This relationship can be investigated by analyzing multimodal (fMRI, PET, laser Doppler…) recordings. However, the important number of intermediate (non-observable) variables involved in the underlying neurovascular coupling makes the discovery of mechanisms all the more difficult from the sole multimodal data. We present a new computational model developed at the population scale (voxel) with physiologically relevant but simple equations to facilitate the interpretation of regional multimodal recordings. This model links neuronal activity to regional CBF dynamics through neuro-glio-vascular coupling. This coupling involves a population of glial cells called astrocytes via their role in neurotransmitter (glutamate and GABA) recycling and their impact on neighboring vessels. In epilepsy, neuronal networks generate epileptiform discharges, leading to variations in astrocytic and CBF dynamics. In this study, we took advantage of these large variations in neuronal activity magnitude to test the capacity of our model to reproduce experimental data. We compared simulations from our model with isolated epileptiform events, which were obtained in vivo by simultaneous local field potential and laser Doppler recordings in rats after local bicuculline injection. We showed a predominant neuronal contribution for low level discharges and a significant astrocytic contribution for higher level discharges. Besides, neuronal contribution to CBF was linear while astrocytic contribution was nonlinear. Results thus indicate that the relationship between neuronal activity and CBF magnitudes can be nonlinear for isolated events and that this nonlinearity is due to astrocytic activity, highlighting the importance of astrocytes in the interpretation of regional recordings.
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Fonteles AA, de Souza CM, de Sousa Neves JC, Menezes APF, Santos do Carmo MR, Fernandes FDP, de Araújo PR, de Andrade GM. Rosmarinic acid prevents against memory deficits in ischemic mice. Behav Brain Res 2016; 297:91-103. [PMID: 26456521 DOI: 10.1016/j.bbr.2015.09.029] [Citation(s) in RCA: 55] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2015] [Revised: 09/17/2015] [Accepted: 09/23/2015] [Indexed: 01/21/2023]
Abstract
Polyphenols have neuroprotective effects after brain ischemia. It has been demonstrated that rosmarinic acid (RA), a natural phenolic compound, possesses antioxidant and anti-inflammatory properties. To evaluate the effectiveness of RA against memory deficits induced by permanent middle cerebral artery occlusion (pMCAO) mice were treated with RA (0.1, 1, and 20mg/kg/day, i.p. before ischemia and during 5 days). Animals were evaluated for locomotor activity and working memory 72 h after pMCAO, and spatial and recognition memories 96 h after pMCAO. In addition, in another set of experiments brain infarction, neurological deficit score and myeloperoxidase (MPO) activity were evaluates 24h after the pMCAO. Finally, immunohistochemistry, and western blot, and ELISA assay were used to analyze glial fibrillary acidic protein (GFAP), and synaptophysin (SYP) expression, and BDNF level, respectively. The working, spatial, and recognition memory deficits were significantly improved with RA treatment (20mg/kg). RA reduced infarct size and neurological deficits caused by acute ischemia. The mechanism for RA neuroprotection involved, neuronal loss suppression, and increase of synaptophysin expression, and increase of BDNF. Furthermore, the increase of MPO activity and GFAP immunireactivity were prevented in MCAO group treated with RA. These results suggest that RA exerts memory protective effects probably due to synaptogenic activity and anti-inflammatory action.
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Affiliation(s)
- Analu Aragão Fonteles
- Post-Graduate Programme in Pharmacology, Department of Physiology and Pharmacology, Fortaleza, Brazil; Institute of Biomedicine of Brazilian Semi-Arid, Fortaleza, Brazil
| | - Carolina Melo de Souza
- Post-Graduate Programme in Medical Sciences, Department of Medicine, Faculty of Medicine, Federal University of Ceará, Fortaleza, Brazil
| | | | - Ana Paula Fontenele Menezes
- Post-Graduate Programme in Medical Sciences, Department of Medicine, Faculty of Medicine, Federal University of Ceará, Fortaleza, Brazil
| | | | - Francisco Diego Pinheiro Fernandes
- Post-Graduate Programme in Medical Sciences, Department of Medicine, Faculty of Medicine, Federal University of Ceará, Fortaleza, Brazil
| | - Patrícia Rodrigues de Araújo
- Post-Graduate Programme in Medical Sciences, Department of Medicine, Faculty of Medicine, Federal University of Ceará, Fortaleza, Brazil
| | - Geanne Matos de Andrade
- Post-Graduate Programme in Pharmacology, Department of Physiology and Pharmacology, Fortaleza, Brazil; Post-Graduate Programme in Medical Sciences, Department of Medicine, Faculty of Medicine, Federal University of Ceará, Fortaleza, Brazil; Institute of Biomedicine of Brazilian Semi-Arid, Fortaleza, Brazil.
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Verkhratsky A, Matteoli M, Parpura V, Mothet JP, Zorec R. Astrocytes as secretory cells of the central nervous system: idiosyncrasies of vesicular secretion. EMBO J 2016; 35:239-57. [PMID: 26758544 DOI: 10.15252/embj.201592705] [Citation(s) in RCA: 282] [Impact Index Per Article: 35.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2015] [Accepted: 12/01/2015] [Indexed: 11/09/2022] Open
Abstract
Astrocytes are housekeepers of the central nervous system (CNS) and are important for CNS development, homeostasis and defence. They communicate with neurones and other glial cells through the release of signalling molecules. Astrocytes secrete a wide array of classic neurotransmitters, neuromodulators and hormones, as well as metabolic, trophic and plastic factors, all of which contribute to the gliocrine system. The release of neuroactive substances from astrocytes occurs through several distinct pathways that include diffusion through plasmalemmal channels, translocation by multiple transporters and regulated exocytosis. As in other eukaryotic cells, exocytotic secretion from astrocytes involves divergent secretory organelles (synaptic-like microvesicles, dense-core vesicles, lysosomes, exosomes and ectosomes), which differ in size, origin, cargo, membrane composition, dynamics and functions. In this review, we summarize the features and functions of secretory organelles in astrocytes. We focus on the biogenesis and trafficking of secretory organelles and on the regulation of the exocytotic secretory system in the context of healthy and diseased astrocytes.
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Affiliation(s)
- Alexei Verkhratsky
- Faculty of Life Sciences, The University of Manchester, Manchester, UK Achucarro Center for Neuroscience, IKERBASQUE Basque Foundation for Science, Bilbao, Spain Department of Neurosciences, University of the Basque Country UPV/EHU and CIBERNED, Leioa, Spain University of Nizhny Novgorod, Nizhny Novgorod, Russia Laboratory of Neuroendocrinology-Molecular Cell Physiology, Faculty of Medicine, Institute of Pathophysiology University of Ljubljana, Ljubljana, Slovenia Celica BIOMEDICAL, Ljubljana, Slovenia
| | - Michela Matteoli
- CNR Institute of Neuroscience, Milano, Italy Humanitas Research Hospital, Rozzano, Italy
| | - Vladimir Parpura
- Department of Neurobiology, Civitan International Research Center and Center for Glial Biology in Medicine, Evelyn F. McKnight Brain Institute, Atomic Force Microscopy & Nanotechnology Laboratories University of Alabama at Birmingham, Birmingham, AL, USA
| | - Jean-Pierre Mothet
- Team Gliotransmission & Synaptopathies, Aix-Marseille University CNRS, CRN2M UMR7286, Marseille, France
| | - Robert Zorec
- Laboratory of Neuroendocrinology-Molecular Cell Physiology, Faculty of Medicine, Institute of Pathophysiology University of Ljubljana, Ljubljana, Slovenia Celica BIOMEDICAL, Ljubljana, Slovenia
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Kirischuk S, Héja L, Kardos J, Billups B. Astrocyte sodium signaling and the regulation of neurotransmission. Glia 2015; 64:1655-66. [DOI: 10.1002/glia.22943] [Citation(s) in RCA: 47] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2015] [Accepted: 10/28/2015] [Indexed: 02/01/2023]
Affiliation(s)
- Sergei Kirischuk
- University Medical Center of the Johannes Gutenberg University Mainz, Institute of Physiology; Mainz Germany
| | - László Héja
- Institute of Organic Chemistry, Research Centre for Natural Sciences, Hungarian Academy of Sciences; Budapest Hungary
| | - Julianna Kardos
- Institute of Organic Chemistry, Research Centre for Natural Sciences, Hungarian Academy of Sciences; Budapest Hungary
| | - Brian Billups
- Eccles Institute of Neuroscience, John Curtin School of Medical Research, The Australian National University; Acton ACT Australia
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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: 41] [Impact Index Per Article: 4.6] [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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Abstract
We delineate perspectives for the design and discovery of antiepileptic drugs (AEDs) with fewer side effects by focusing on astroglial modulation of spatiotemporal seizure dynamics. It is now recognized that the major inhibitory neurotransmitter of the brain, γ-aminobutyric acid (GABA), can be released through the reversal of astroglial GABA transporters. Synaptic spillover and subsequent glutamate (Glu) uptake in neighboring astrocytes evoke replacement of extracellular Glu for GABA, driving neurons away from the seizure threshold. Attenuation of synaptic signaling by this negative feedback through the interplay of Glu and GABA transporters of adjacent astroglia can result in shortened seizures. By contrast, long-range activation of astroglia through gap junctions may promote recurrent seizures on the model of pharmacoresistant temporal lobe epilepsy. From their first detection to our current understanding, we identify various targets that shape both short- and long-range neuro-astroglia coupling, as these are manifest in epilepsy phenomena and in the associated research promotions of AED.
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Affiliation(s)
- Julianna Kardos
- Functional Pharmacology Research Group, Institute of Organic Chemistry, Research Centre for Natural Sciences, Hungarian Academy of Sciences, 1117 Budapest, Hungary
| | - Zsolt Szabó
- Functional Pharmacology Research Group, Institute of Organic Chemistry, Research Centre for Natural Sciences, Hungarian Academy of Sciences, 1117 Budapest, Hungary
| | - László Héja
- Functional Pharmacology Research Group, Institute of Organic Chemistry, Research Centre for Natural Sciences, Hungarian Academy of Sciences, 1117 Budapest, Hungary
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65
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Bragina L, Bonifacino T, Bassi S, Milanese M, Bonanno G, Conti F. Differential expression of metabotropic glutamate and GABA receptors at neocortical glutamatergic and GABAergic axon terminals. Front Cell Neurosci 2015; 9:345. [PMID: 26388733 PMCID: PMC4559644 DOI: 10.3389/fncel.2015.00345] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2015] [Accepted: 08/18/2015] [Indexed: 12/04/2022] Open
Abstract
Metabotropic glutamate (Glu) receptors (mGluRs) and GABAB receptors are highly expressed at presynaptic sites. To verify the possibility that the two classes of metabotropic receptors contribute to axon terminals heterogeneity, we studied the localization of mGluR1α, mGluR5, mGluR2/3, mGluR7, and GABAB1 in VGLUT1-, VGLUT2-, and VGAT- positive terminals in the cerebral cortex of adult rats. VGLUT1-positive puncta expressed mGluR1α (∼5%), mGluR5 (∼6%), mGluR2/3 (∼22%), mGluR7 (∼17%), and GABAB1 (∼40%); VGLUT2-positive terminals expressed mGluR1α (∼10%), mGluR5 (∼11%), mGluR2/3 (∼20%), mGluR7 (∼28%), and GABAB1 (∼25%); whereas VGAT-positive puncta expressed mGluR1α (∼27%), mGluR5 (∼24%), mGluR2/3 (∼38%), mGluR7 (∼31%), and GABAB1 (∼19%). Control experiments ruled out the possibility that postsynaptic mGluRs and GABAB1 might have significantly biased our results. We also performed functional assays in synaptosomal preparations, and showed that all agonists modify Glu and GABA levels, which return to baseline upon exposure to antagonists. Overall, these findings indicate that mGluR1α, mGluR5, mGluR2/3, mGluR7, and GABAB1 expression differ significantly between glutamatergic and GABAergic axon terminals, and that the robust expression of heteroreceptors may contribute to the homeostatic regulation of the balance between excitation and inhibition.
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Affiliation(s)
- Luca Bragina
- Section of Neuroscience and Cell Biology, Department of Experimental and Clinical Medicine, Università Politecnica delle MarcheAncona, Italy
- Center for Neurobiology of Aging, Istituto Nazionale di Riposo e Cura per Anziani – Istituto di Ricovero e Cura a Carattere ScientificoAncona, Italy
| | - Tiziana Bonifacino
- Department of Pharmacy, Unit of Pharmacology and Toxicology, University of GenoaGenoa, Italy
| | - Silvia Bassi
- Section of Neuroscience and Cell Biology, Department of Experimental and Clinical Medicine, Università Politecnica delle MarcheAncona, Italy
| | - Marco Milanese
- Department of Pharmacy, Unit of Pharmacology and Toxicology, University of GenoaGenoa, Italy
| | - Giambattista Bonanno
- Department of Pharmacy, Unit of Pharmacology and Toxicology, University of GenoaGenoa, Italy
- Center of Excellence for Biomedical Research, University of GenoaGenoa, Italy
| | - Fiorenzo Conti
- Section of Neuroscience and Cell Biology, Department of Experimental and Clinical Medicine, Università Politecnica delle MarcheAncona, Italy
- Center for Neurobiology of Aging, Istituto Nazionale di Riposo e Cura per Anziani – Istituto di Ricovero e Cura a Carattere ScientificoAncona, Italy
- Fondazione di Medicina Molecolare, Università Politecnica delle MarcheAncona, Italy
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66
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Kékesi O, Ioja E, Szabó Z, Kardos J, Héja L. Recurrent seizure-like events are associated with coupled astroglial synchronization. Front Cell Neurosci 2015; 9:215. [PMID: 26150770 PMCID: PMC4471369 DOI: 10.3389/fncel.2015.00215] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2014] [Accepted: 05/20/2015] [Indexed: 01/22/2023] Open
Abstract
Increasing evidence suggest that astrocytes significantly modulate neuronal function at the level of the tripartite synapse both in physiological and pathophysiological conditions. The global control of the astrocytic syncytium over neuronal networks, however, is still less recognized. Here we examined astrocytic signaling during epileptiform activity which is generally attributed to large-scale neuronal synchronization. We show that seizure-like events in the low-[Mg(2+)] in vitro epilepsy model initiate massive, long-range astrocytic synchronization which is spatiotemporally coupled to the synchronized neuronal activity reaching its maximum at the electrographic tonic/clonic transition. Cross-correlation analysis of neuronal and astrocytic Ca(2+) signaling demonstrates that high degree of synchronization arises not only among astrocytes, but also between neuronal and astrocyte populations, manifesting in astrocytic seizure-like events. We further show that astrocytic gap junction proteins contribute to astrocytic synchronization since their inhibition by carbenoxolone (CBX) or Cx43 antibody increased the interictal interval and in 41% of slices completely prevented recurrent seizure-like activity. In addition, CBX also induced unsynchronized Ca(2+) transients associated with decreasing incidence of epileptiform discharges afterwards. We propose therefore that local, unsynchronized astrocytic Ca(2+) transients inhibit, while long-range, synchronized Ca(2+) signaling contributes to the propagation of recurrent seizure-like events.
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Affiliation(s)
- Orsolya Kékesi
- Research Centre for Natural Sciences, Hungarian Academy of Sciences, Institute of Organic Chemistry, Functional Pharmacology Group Budapest, Hungary
| | - Enikö Ioja
- Research Centre for Natural Sciences, Hungarian Academy of Sciences, Institute of Organic Chemistry, Functional Pharmacology Group Budapest, Hungary
| | - Zsolt Szabó
- Research Centre for Natural Sciences, Hungarian Academy of Sciences, Institute of Organic Chemistry, Functional Pharmacology Group Budapest, Hungary
| | - Julianna Kardos
- Research Centre for Natural Sciences, Hungarian Academy of Sciences, Institute of Organic Chemistry, Functional Pharmacology Group Budapest, Hungary
| | - László Héja
- Research Centre for Natural Sciences, Hungarian Academy of Sciences, Institute of Organic Chemistry, Functional Pharmacology Group Budapest, Hungary
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67
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Pál I, Kardos J, Dobolyi Á, Héja L. Appearance of fast astrocytic component in voltage-sensitive dye imaging of neural activity. Mol Brain 2015; 8:35. [PMID: 26043770 PMCID: PMC4455916 DOI: 10.1186/s13041-015-0127-9] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2014] [Accepted: 05/24/2015] [Indexed: 12/21/2022] Open
Abstract
Background Voltage-sensitive dye (VSD) imaging and intrinsic optical signals (IOS) are widely used methods for monitoring spatiotemporal neural activity in extensive networks. In spite of that, identification of their major cellular and molecular components has not been concluded so far. Results We addressed these issues by imaging spatiotemporal spreading of IOS and VSD transients initiated by Schaffer collateral stimulation in rat hippocampal slices with temporal resolution comparable to standard field potential recordings using a 464-element photodiode array. By exploring the potential neuronal and astroglial molecular players in VSD and IOS generation, we identified multiple astrocytic mechanisms that significantly contribute to the VSD signal, in addition to the expected neuronal targets. Glutamate clearance through the astroglial glutamate transporter EAAT2 has been shown to be a significant player in VSD generation within a very short (<5 ms) time-scale, indicating that astrocytes do contribute to the development of spatiotemporal VSD transients previously thought to be essentially neuronal. In addition, non-specific anion channels, astroglial K+ clearance through Kir4.1 channel and astroglial Na+/K+ ATPase also contribute to IOS and VSD transients. Conclusion VSD imaging cannot be considered as a spatially extended field potential measurement with predominantly neuronal origin, instead it also reflects a fast communication between neurons and astrocytes.
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Affiliation(s)
- Ildikó Pál
- Group of Functional Pharmacology, Institute of Cognitive Neuroscience and Psychology, Research Centre for Natural Sciences, Hungarian Academy of Sciences, Magyar tudósok körútja 2, H-1117, Budapest, Hungary.
| | - Julianna Kardos
- Group of Functional Pharmacology, Institute of Cognitive Neuroscience and Psychology, Research Centre for Natural Sciences, Hungarian Academy of Sciences, Magyar tudósok körútja 2, H-1117, Budapest, Hungary.
| | - Árpád Dobolyi
- MTA-ELTE-NAP B Laboratory of Molecular and Systems Neurobiology, H-1117, Budapest, Hungary. .,Department of Anatomy, Human Brain Tissue Bank, Semmelweis University, H-1450, Budapest, Hungary.
| | - László Héja
- Group of Functional Pharmacology, Institute of Cognitive Neuroscience and Psychology, Research Centre for Natural Sciences, Hungarian Academy of Sciences, Magyar tudósok körútja 2, H-1117, Budapest, Hungary.
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68
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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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Liu L, Mao D, Liu L, Huang Y, Bo T. Effects of progesterone on glutamate transporter 2 and gamma-aminobutyric acid transporter 1 expression in the developing rat brain after recurrent seizures. Neural Regen Res 2015; 7:2036-42. [PMID: 25624835 PMCID: PMC4296423 DOI: 10.3969/j.issn.1673-5374.2012.26.005] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2012] [Accepted: 06/15/2012] [Indexed: 12/21/2022] Open
Abstract
Seizures were induced by flurothyl inhalation. Rats were intramuscularly treated with progesterone after each seizure. Results demonstrated that glutamate transporter 2 and γ-aminobutyric acid transporter 1 expression levels were significantly increased in the cerebral cortex and hippocampus of the developing rat brain following recurrent seizures. After progesterone treatment, glutamate transporter 2 protein expression was upregulated, but γ-aminobutyric acid transporter 1 levels decreased. These results suggest that glutamate transporter 2 and γ-aminobutyric acid transporter 1 are involved in the pathological processes of epilepsy. Progesterone can help maintain a balance between excitatory and inhibitory systems by modulating the amino acid transporter system, and protect the developing brain after recurrent seizures.
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Affiliation(s)
- Lingjuan Liu
- Department of Pediatrics, Second Xiangya Hospital, Central South University, Changsha 410011, Hunan Province, China
| | - Dingan Mao
- Department of Pediatrics, Second Xiangya Hospital, Central South University, Changsha 410011, Hunan Province, China
| | - Liqun Liu
- Department of Pediatrics, Second Xiangya Hospital, Central South University, Changsha 410011, Hunan Province, China
| | - Yu Huang
- Department of Pediatrics, Second Xiangya Hospital, Central South University, Changsha 410011, Hunan Province, China
| | - Tao Bo
- Department of Pediatrics, Second Xiangya Hospital, Central South University, Changsha 410011, Hunan Province, China
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70
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Stephan J, Friauf E. Functional analysis of the inhibitory neurotransmitter transporters GlyT1, GAT-1, and GAT-3 in astrocytes of the lateral superior olive. Glia 2014; 62:1992-2003. [PMID: 25103283 DOI: 10.1002/glia.22720] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2014] [Revised: 06/26/2014] [Accepted: 06/27/2014] [Indexed: 01/03/2023]
Abstract
Neurotransmitter clearance from the synaptic cleft is a major function of astrocytes and requires neurotransmitter transporters. In the rodent lateral superior olive (LSO), a conspicuous auditory brainstem center, both glycine and GABA mediate synaptic inhibition. However, the main inhibitory input from the medial nucleus of the trapezoid body (MNTB) appears to be glycinergic by postnatal day (P) 14, when circuit maturation is almost accomplished. Using whole-cell patch-clamp recordings at P3-20, we analyzed glycine transporters (GlyT1) and GABA transporters (GAT-1, GAT-3) in mouse LSO astrocytes, emphasizing on their developmental regulation. Application of glycine or GABA induced a dose- and age-dependent inward current and a respective depolarization. The GlyT1-specific inhibitor sarcosine reduced the maximal glycine-induced current (IGly (max) ) by about 60%. The GAT-1 and GAT-3 antagonists NO711 and SNAP5114, respectively, reduced the maximal GABA-induced current (IGABA (max) ) by about 35%. Furthermore, [Cl(-) ]o reduction decreased IGly (max) and IGABA (max) by about 85 to 95%, showing the Cl(-) dependence of GlyT and GAT. IGABA (max) was stronger than IGly (max) , and the ratio increased developmentally from 1.6-fold to 3.7-fold. Together, our results demonstrate the functional presence of the three inhibitory neurotransmitter transporters GlyT1, GAT-1, and GAT-3 in LSO astrocytes. Furthermore, the uptake capability for GABA was higher than for glycine, pointing toward eminent GABAergic signaling in the LSO. GABA may originate from another source than the MNTB-LSO synapses, namely from another projection or from reversal of astrocytic GATs. Thus, neuronal signaling in the LSO appears to be more versatile than previously thought. GLIA 2014;62:1992-2003.
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Affiliation(s)
- Jonathan Stephan
- Department of Biology, Animal Physiology Group, University of Kaiserslautern, Kaiserslautern, Germany
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71
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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: 192] [Impact Index Per Article: 19.2] [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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72
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Jacob PF, Vaz SH, Ribeiro JA, Sebastião AM. P2Y1 receptor inhibits GABA transport through a calcium signalling-dependent mechanism in rat cortical astrocytes. Glia 2014; 62:1211-26. [PMID: 24733747 DOI: 10.1002/glia.22673] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2013] [Revised: 03/29/2014] [Accepted: 03/31/2014] [Indexed: 12/16/2022]
Abstract
Astrocytes express a variety of purinergic (P2) receptors, involved in astrocytic communication through fast increases in [Ca(2+) ]i . Of these, the metabotropic ATP receptors (P2Y) regulate cytoplasmic Ca(2+) levels through the PLC-PKC pathway. GABA transporters are a substrate for a number of Ca(2+) -related kinases, raising the possibility that calcium signalling in astrocytes impact the control of extracellular levels of the major inhibitory transmitter in the brain. To access this possibility we tested the influence of P2Y receptors upon GABA transport into astrocytes. Mature primary cortical astroglial-enriched cultures expressed functional P2Y receptors, as evaluated through Ca(2+) imaging, being P2Y1 the predominant P2Y receptor subtype. ATP (100 μM, for 1 min) caused an inhibition of GABA transport through either GAT-1 or GAT-3 transporters, decreasing the Vmax kinetic constant. ATP-induced inhibition of GATs activity was still evident in the presence of adenosine deaminase, precluding an adenosine-mediated effect. This, was mimicked by a specific agonist for the P2Y1,12,13 receptor (2-MeSADP). The effect of 2-MeSADP on GABA transport was blocked by the P2 (PPADS) and P2Y1 selective (MRS2179) receptor antagonists, as well as by the PLC inhibitor (U73122). 2-MeSADP failed to inhibit GABA transport in astrocytes where intracellular calcium had been chelated (BAPTA-AM) or where calcium stores were depleted (α-cyclopiazonic acid, CPA). In conclusion, P2Y1 receptors in astrocytes inhibit GABA transport through a mechanism dependent of P2Y1 -mediated calcium signalling, suggesting that astrocytic calcium signalling, which occurs as a consequence of neuronal firing, may operate a negative feedback loop to enhance extracellular levels of GABA.
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Affiliation(s)
- Pedro F Jacob
- Institute of Pharmacology and Neurosciences, Faculty of Medicine, University of Lisbon, Lisbon, Portugal; Neurosciences Unit, Institute of Molecular Medicine University of Lisbon, Lisbon, Portugal
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Wlodarczyk AI, Xu C, Song I, Doronin M, Wu YW, Walker MC, Semyanov A. Tonic GABAA conductance decreases membrane time constant and increases EPSP-spike precision in hippocampal pyramidal neurons. Front Neural Circuits 2013; 7:205. [PMID: 24399937 PMCID: PMC3872325 DOI: 10.3389/fncir.2013.00205] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2013] [Accepted: 12/11/2013] [Indexed: 11/21/2022] Open
Abstract
Because of a complex dendritic structure, pyramidal neurons have a large membrane surface relative to other cells and so a large electrical capacitance and a large membrane time constant (τm). This results in slow depolarizations in response to excitatory synaptic inputs, and consequently increased and variable action potential latencies, which may be computationally undesirable. Tonic activation of GABAA receptors increases membrane conductance and thus regulates neuronal excitability by shunting inhibition. In addition, tonic increases in membrane conductance decrease the membrane time constant (τm), and improve the temporal fidelity of neuronal firing. Here we performed whole-cell current clamp recordings from hippocampal CA1 pyramidal neurons and found that bath application of 10μM GABA indeed decreases τm in these cells. GABA also decreased first spike latency and jitter (standard deviation of the latency) produced by current injection of 2 rheobases (500 ms). However, when larger current injections (3–6 rheobases) were used, GABA produced no significant effect on spike jitter, which was low. Using mathematical modeling we demonstrate that the tonic GABAA conductance decreases rise time, decay time and half-width of EPSPs in pyramidal neurons. A similar effect was observed on EPSP/IPSP pairs produced by stimulation of Schaffer collaterals: the EPSP part of the response became shorter after application of GABA. Consistent with the current injection data, a significant decrease in spike latency and jitter was obtained in cell attached recordings only at near-threshold stimulation (50% success rate, S50). When stimulation was increased to 2- or 3- times S50, GABA significantly affected neither spike latency nor spike jitter. Our results suggest that a decrease in τm associated with elevations in ambient GABA can improve EPSP-spike precision at near-threshold synaptic inputs.
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Affiliation(s)
| | - Chun Xu
- RIKEN Brain Science Institute Wako-shi, Japan
| | - Inseon Song
- RIKEN Brain Science Institute Wako-shi, Japan
| | - Maxim Doronin
- RIKEN Brain Science Institute Wako-shi, Japan ; Department of Neurodynamics and Neurobiology, University of Nizhny Novgorod Nizhny Novgorod, Russia
| | - Yu-Wei Wu
- RIKEN Brain Science Institute Wako-shi, Japan
| | - Matthew C Walker
- Department of Clinical and Experimental Epilepsy, UCL Institute of Neurology London, UK
| | - Alexey Semyanov
- RIKEN Brain Science Institute Wako-shi, Japan ; Department of Neurodynamics and Neurobiology, University of Nizhny Novgorod Nizhny Novgorod, Russia
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Melone M, Ciappelloni S, Conti F. A quantitative analysis of cellular and synaptic localization of GAT-1 and GAT-3 in rat neocortex. Brain Struct Funct 2013; 220:885-97. [PMID: 24368619 DOI: 10.1007/s00429-013-0690-8] [Citation(s) in RCA: 47] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2013] [Accepted: 12/10/2013] [Indexed: 11/24/2022]
Abstract
High-affinity plasma membrane GABA transporters GAT-1 and GAT-3 contribute to the modulation of GABA-mediated inhibition in adult mammalian cerebral cortex. How GATs regulate inhibition in neocortical circuits remains however poorly understood for the lack of information on key localizational features. In this study, we used quantitative pre- and post-embedding electron microscopy to define the distribution of GAT-1 and GAT-3 in elements contributing to synapses and to unveil their ultrastructural organization at adult cortical GABAergic synapses. GAT-1 and GAT-3 were found in both neuronal and astrocytic processes: GAT-1 was prevalently segregated in neuronal elements and in profiles contributing to synapses, whereas GAT-3 was mostly expressed in astrocytes and did not exhibit a preferential distribution in elements contributing to synapses. Analysis of the ultrastructural distribution of GAT-1 and GAT-3 in the plasma membrane of axon terminals and perisynaptic astrocytic processes of symmetric synapses in relation to the active zone revealed that GAT-1 was more concentrated in restricted perisynaptic and extrasynaptic regions, whereas GAT-3 was prominent in extrasynaptic areas. These studies provide a basis for understanding the role GAT-1 and GAT-3 play in the modulation of GABA-mediated phasic and tonic inhibition in cerebral cortex.
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Affiliation(s)
- Marcello Melone
- Department of Experimental and Clinical Medicine, Section of Neuroscience and Cell Biology, Università Politecnica delle Marche, 60026, Ancona, Italy,
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75
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Wójtowicz AM, Dvorzhak A, Semtner M, Grantyn R. Reduced tonic inhibition in striatal output neurons from Huntington mice due to loss of astrocytic GABA release through GAT-3. Front Neural Circuits 2013; 7:188. [PMID: 24324407 PMCID: PMC3840359 DOI: 10.3389/fncir.2013.00188] [Citation(s) in RCA: 69] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2013] [Accepted: 11/04/2013] [Indexed: 01/17/2023] Open
Abstract
The extracellular concentration of the two main neurotransmitters glutamate and GABA is low but not negligible which enables a number of tonic actions. The effects of ambient GABA vary in a region-, cell-type, and age-dependent manner and can serve as indicators of disease-related alterations. Here we explored the tonic inhibitory actions of GABA in Huntington's disease (HD). HD is a devastating neurodegenerative disorder caused by a mutation in the huntingtin gene. Whole cell patch clamp recordings from striatal output neurons (SONs) in slices from adult wild type mice and two mouse models of HD (Z_Q175_KI homozygotes or R6/2 heterozygotes) revealed an HD-related reduction of the GABA(A) receptor-mediated tonic chloride current (ITonic(GABA)) along with signs of reduced GABA(B) receptor-mediated presynaptic depression of synaptic GABA release. About half of ITonic(GABA) depended on tetrodotoxin-sensitive synaptic GABA release, but the remaining current was still lower in HD. Both in WT and HD, ITonic(GABA) was more prominent during the first 4 h after preparing the slices, when astrocytes but not neurons exhibited a transient depolarization. All further tests were performed within 1–4 h in vitro. Experiments with SNAP5114, a blocker of the astrocytic GABA transporter GAT-3, suggest that in WT but not HD GAT-3 operated in the releasing mode. Application of a transportable substrate for glutamate transporters (D-aspartate 0.1–1 mM) restored the non-synaptic GABA release in slices from HD mice. ITonic(GABA) was also rescued by applying the hyperagonist gaboxadol (0.33 μM). The results lead to the hypothesis that lesion-induced astrocyte depolarization facilitates non-synaptic release of GABA through GAT-3. However, the capacity of depolarized astrocytes to provide GABA for tonic inhibition is strongly reduced in HD.
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Affiliation(s)
- Anna M Wójtowicz
- Cluster of Excellence NeuroCure, University Medicine Charité Berlin, Germany ; Department of Experimental Neurology, University Medicine Charité Berlin, Germany
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76
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Creevy KE, Gagnepain JF, Platt SR, Edwards GL, Kent M. Comparison of concentrations of γ-aminobutyric acid and glutamate in cerebrospinal fluid of dogs with idiopathic epilepsy with and without seizure-related magnetic resonance imaging hyperintense areas in the limbic system. Am J Vet Res 2013; 74:1118-25. [PMID: 23879850 DOI: 10.2460/ajvr.74.8.1118] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
OBJECTIVE To investigate differences in CSF concentrations of excitatory and inhibitory neurotransmitters in dogs with and without T2-weighted (T2W) MRI hyperintense areas in the limbic system. SAMPLE Archived CSF samples and stored brain MRI images of 5 healthy research dogs (group 1), 8 dogs with idiopathic epilepsy (IE) with no abnormal MRI findings (group 2), and 4 dogs with IE with hyperintense areas in the limbic system detected by means of T2W MRI (group 3). PROCEDURES Archived CSF samples and stored MRI images obtained from all dogs were evaluated. Dogs in groups 2 and 3 were matched on the basis of age and breed. High-performance liquid chromatography was used to evaluate glutamate and γ-aminobutyric acid (GABA) concentrations in CSF samples. RESULTS Glutamate concentrations were higher in CSF of both groups of dogs with IE than in healthy dogs. However, glutamate concentrations in CSF were not significantly higher in dogs with IE and with hyperintense areas than in dogs with IE but no abnormal MRI findings. Concentrations of GABA in CSF were higher in group 3 than in group 2 and in group 2 than in group 1. CONCLUSIONS AND CLINICAL RELEVANCE No significant difference was evident between glutamate concentrations in CSF of dogs with IE and with and without hyperintense areas detected by means of T2W MRI. However, glutamate concentrations typically were higher in CSF of dogs with IE and MRI hyperintense areas. Future studies with larger sample sizes should be conducted to confirm this finding and to determine the clinical importance of high glutamate concentrations in CSF of dogs with IE.
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Affiliation(s)
- Kate E Creevy
- Department of Small Animal Medicine and Surgery, University of Georgia, Athens, GA 30602, USA.
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77
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Unichenko P, Dvorzhak A, Kirischuk S. Transporter-mediated replacement of extracellular glutamate for GABA in the developing murine neocortex. Eur J Neurosci 2013; 38:3580-8. [DOI: 10.1111/ejn.12380] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2013] [Revised: 08/21/2013] [Accepted: 09/03/2013] [Indexed: 11/29/2022]
Affiliation(s)
- Petr Unichenko
- Institute of Physiology; University Medical Center of the Johannes Gutenberg University Mainz; Duesbergweg 6 55128 Mainz Germany
| | - Anton Dvorzhak
- Department of Experimental Neurology; Cluster of Excellence Neurocure; University Medicine Charitè; Berlin Germany
| | - Sergei Kirischuk
- Institute of Physiology; University Medical Center of the Johannes Gutenberg University Mainz; Duesbergweg 6 55128 Mainz Germany
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Evolution of neurotransmitter gamma-aminobutyric acid, glutamate and their receptors. DONG WU XUE YAN JIU = ZOOLOGICAL RESEARCH 2013; 33:E75-81. [PMID: 23266985 DOI: 10.3724/sp.j.1141.2012.e05-06e75] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Gamma-aminobutyric acid (GABA) and glutamate are two important amino acid neurotransmitters widely present in the nervous systems of mammals, insects, round worm, and platyhelminths, while their receptors are quite diversified across different animal phyla. However, the evolutionary mechanisms between the two conserved neurotransmitters and their diversified receptors remain elusive, and antagonistic interactions between GABA and glutamate signal transduction systems, in particular, have begun to attract significant attention. In this review, we summarize the extant results on the origin and evolution of GABA and glutamate, as well as their receptors, and analyze possible evolutionary processes and phylogenetic relationships of various GABAs and glutamate receptors. We further discuss the evolutionary history of Excitatory/Neutral Amino Acid Transporter (EAAT), a transport protein, which plays an important role in the GABA-glutamate "yin and yang" balanced regulation. Finally, based on current advances, we propose several potential directions of future research.
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Egawa K, Yamada J, Furukawa T, Yanagawa Y, Fukuda A. Cl⁻ homeodynamics in gap junction-coupled astrocytic networks on activation of GABAergic synapses. J Physiol 2013; 591:3901-17. [PMID: 23732644 PMCID: PMC3764636 DOI: 10.1113/jphysiol.2013.257162] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
The electrophysiological properties and functional role of GABAergic signal transmission from neurons to the gap junction-coupled astrocytic network are still unclear. GABA-induced astrocytic Cl− flux has been hypothesized to affect the driving force for GABAergic transmission by modulating [Cl−]o. Thus, revealing the properties of GABA-mediated astrocytic responses will deepen our understanding of GABAergic signal transmission. Here, we analysed the Cl− dynamics of neurons and astrocytes in CA1 hippocampal GABAergic tripartite synapses, using Cl− imaging during GABA application, and whole cell recordings from interneuron–astrocyte pairs in the stratum lacunosum-moleculare. Astrocytic [Cl−]i was adjusted to physiological conditions (40 mm). Although GABA application evoked bidirectional Cl− flux via GABAA receptors and mouse GABA transporter 4 (mGAT4) in CA1 astrocytes, a train of interneuron firing induced only GABAA receptor-mediated inward currents in an adjacent astrocyte. A GAT1 inhibitor increased the interneuron firing-induced currents and induced bicuculline-insensitive, mGAT4 inhibitor-sensitive currents, suggesting that synaptic spillover of GABA predominantly induced the astrocytic Cl− efflux because GABAA receptors are localized near the synaptic clefts. This GABA-induced Cl− efflux was accompanied by Cl− siphoning via the gap junctions of the astrocytic network because gap junction inhibitors significantly reduced the interneuron firing-induced currents. Thus, Cl− efflux from astrocytes is homeostatically maintained within astrocytic networks. A gap junction inhibitor enhanced the activity-dependent depolarizing shifts of reversal potential of neuronal IPSCs evoked by repetitive stimulation to GABAergic synapses. These results suggest that Cl− conductance within the astrocytic network may contribute to maintaining GABAergic synaptic transmission by regulating [Cl−]o.
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Affiliation(s)
- Kiyoshi Egawa
- Department of Neurophysiology, Hamamatsu University School of Medicine, Hamamatsu 431-3192, Japan
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80
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Song I, Volynski K, Brenner T, Ushkaryov Y, Walker M, Semyanov A. Different transporter systems regulate extracellular GABA from vesicular and non-vesicular sources. Front Cell Neurosci 2013; 7:23. [PMID: 23494150 PMCID: PMC3595500 DOI: 10.3389/fncel.2013.00023] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2012] [Accepted: 02/25/2013] [Indexed: 11/25/2022] Open
Abstract
Tonic GABA type A (GABAA) conductance is a key factor regulating neuronal excitability and computation in neuronal networks. The magnitude of the tonic GABAA conductance depends on the concentration of ambient GABA originating from vesicular and non-vesicular sources and is tightly regulated by GABA uptake. Here we show that the transport system regulating ambient GABA responsible for tonic GABAA conductances in hippocampal CA1 interneurons depends on its source. In mice, GABA from vesicular sources is regulated by mouse GABA transporter 1 (mGAT1), while that from non-vesicular sources by mouse GABA transporters 3/4 (mGAT3/4). This finding suggests that the two transporter systems do not just provide backup for each other, but regulate distinct signaling pathways. This allows individual tuning of the two signaling systems and indicates that drugs designed to act at specific transporters will have distinct therapeutic actions.
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Affiliation(s)
- Inseon Song
- RIKEN Brain Science Institute Wako-shi, Saitama, Japan
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81
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The astrocytic contribution to neurovascular coupling – Still more questions than answers? Neurosci Res 2013; 75:171-83. [DOI: 10.1016/j.neures.2013.01.014] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2012] [Revised: 12/15/2012] [Accepted: 12/30/2012] [Indexed: 01/03/2023]
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82
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Kersanté F, Rowley SCS, Pavlov I, Gutièrrez-Mecinas M, Semyanov A, Reul JMHM, Walker MC, Linthorst ACE. A functional role for both -aminobutyric acid (GABA) transporter-1 and GABA transporter-3 in the modulation of extracellular GABA and GABAergic tonic conductances in the rat hippocampus. J Physiol 2013; 591:2429-41. [PMID: 23381899 PMCID: PMC3678035 DOI: 10.1113/jphysiol.2012.246298] [Citation(s) in RCA: 102] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
Tonic γ-aminobutyric acid (GABA)A receptor-mediated signalling controls neuronal network excitability in the hippocampus. Although the extracellular concentration of GABA (e[GABA]) is critical in determining tonic conductances, knowledge on how e[GABA] is regulated by different GABA transporters (GATs) in vivo is limited. Therefore, we studied the role of GATs in the regulation of hippocampal e[GABA] using in vivo microdialysis in freely moving rats. Here we show that GAT-1, which is predominantly presynaptically located, is the major GABA transporter under baseline, quiescent conditions. Furthermore, a significant contribution of GAT-3 in regulating e[GABA] was revealed by administration of the GAT-3 inhibitor SNAP-5114 during simultaneous blockade of GAT-1 by NNC-711. Thus, the GABA transporting activity of GAT-3 (the expression of which is confined to astrocytes) is apparent under conditions in which GAT-1 is blocked. However, sustained neuronal activation by K+-induced depolarization caused a profound spillover of GABA into the extrasynaptic space and this increase in e[GABA] was significantly potentiated by sole blockade of GAT-3 (i.e. even when uptake of GAT-1 is intact). Furthermore, experiments using tetrodotoxin to block action potentials revealed that GAT-3 regulates extrasynaptic GABA levels from action potential-independent sources when GAT-1 is blocked. Importantly, changes in e[GABA] resulting from both GAT-1 and GAT-3 inhibition directly precipitate changes in tonic conductances in dentate granule cells as measured by whole-cell patch-clamp recording. Thus, astrocytic GAT-3 contributes to the regulation of e[GABA] in the hippocampus in vivo and may play an important role in controlling the excitability of hippocampal cells when network activity is increased.
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Affiliation(s)
- Flavie Kersanté
- Neurobiology of Stress and Behaviour Research Group, Henry Wellcome Laboratories for Integrative Neuroscience and Endocrinology, School of Clinical Sciences, University of Bristol, Dorothy Hodgkin Building, Whitson Street, Bristol BS1 3NY, UK
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83
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Abstract
Astrocytes exhibit their excitability based on variations in cytosolic Ca(2+) levels, which leads to variety of signalling events. Only recently, however, intracellular fluctuations of more abundant cation Na(+) are brought in the limelight of glial signalling. Indeed, astrocytes possess several plasmalemmal molecular entities that allow rapid transport of Na(+) across the plasma membrane: (1) ionotropic receptors, (2) canonical transient receptor potential cation channels, (3) neurotransmitter transporters and (4) sodium-calcium exchanger. Concerted action of these molecules in controlling cytosolic Na(+) may complement Ca(2+) signalling to provide basis for complex bidirectional astrocyte-neurone communication at the tripartite synapse.
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84
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Kim SY, Jones TA. The effects of ceftriaxone on skill learning and motor functional outcome after ischemic cortical damage in rats. Restor Neurol Neurosci 2013; 31:87-97. [PMID: 23047495 PMCID: PMC4433287 DOI: 10.3233/rnn-2012-120245] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
PURPOSE Ceftriaxone, a β-lactam antibiotic, can selectively enhance the expression of glutamate transporter 1 (GLT1), the most abundant astrocytic glutamate transporter expressed in the cortex. It has been found to have neuroprotective effects when administered prior to brain ischemic damage or during the acute phase post-stroke, but its effects in chronic period have not been examined. METHODS We examined the effects of ceftriaxone on the acquisition of motor skill and the functional outcome after focal ischemic cortical lesions. In adult male rats, ceftriaxone (200 mg/kg) or vehicle was intraperitoneally injected daily for 5 days, a treatment regime previously established to upregulate GLT-1. This preceded 28 days of skilled reach training in intact animals or began 3 days following lesions, followed by 5 weeks of rehabilitative reach training. RESULTS In intact rats, ceftriaxone did not affect skill learning rate or final performance. Following ischemic lesions, though there was no significant difference in lesion sizes between groups, ceftriaxone exacerbated initial deficits in reaching performance. CONCLUSION These findings of detrimental effects on motor functional outcome suggest that ceftriaxone may be more useful for neuroprotection during the acute phase of ischemia than for functional recovery in the post-acute period after ischemic damage.
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Affiliation(s)
- Soo Young Kim
- Institute for Neuroscience, University of Texas at Austin, TX, USA.
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85
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Cai K, Nanga RPR, Lamprou L, Schinstine C, Elliott M, Hariharan H, Reddy R, Epperson CN. The impact of gabapentin administration on brain GABA and glutamate concentrations: a 7T ¹H-MRS study. Neuropsychopharmacology 2012; 37:2764-71. [PMID: 22871916 PMCID: PMC3499716 DOI: 10.1038/npp.2012.142] [Citation(s) in RCA: 91] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
Gamma-aminobutyric acid (GABA) and glutamate are implicated in numerous neuropsychiatric and substance abuse conditions, but their spectral overlap with other resonances makes them a challenge to quantify in humans. Gabapentin, marketed for the treatment of seizures and neuropathic pain, has been shown to increase in vivo GABA concentration in the brain of both rodents and humans. Gabapentin effects on glutamate are not known. We conducted a gabapentin (900 mg) challenge in healthy human subjects to confirm and explore its effects on GABA and glutamate concentrations, respectively, and to test the ability of single voxel localized proton magnetic resonance spectroscopy (¹H-MRS) to reliably measure GABA and glutamate in the visual cortex at the ultra-high magnetic field of 7 Tesla. Reproducibility of GABA and glutamate measurements was determined in a comparison group without drug twice within day and 2 weeks apart. Although GABA concentration changes were small both within day (average 5.6%) and between day (average 4.8%), gabapentin administration was associated with an average increase in GABA concentration of 55.7% (6.9-91.0%). Importantly, drug-induced change in GABA levels was inversely correlated to the individual's baseline GABA level (R²=0.72). Mean glutamate concentrations did not change significantly with or without drug administration. In conclusion, localized ¹H-MRS at 7 Tesla can be successfully applied to the measurement of GABA concentration and is sensitive to acute drug-induced changes in cortical GABA. Whether baseline GABA concentrations predict clinical efficacy of gabapentin is an area worthy of exploration.
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Affiliation(s)
- Kejia Cai
- Department of Radiology, Center for Magnetic Resonance and Optical Imaging (CMROI), Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA, USA
| | - Ravi PR Nanga
- Department of Radiology, Center for Magnetic Resonance and Optical Imaging (CMROI), Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA, USA
| | - Lisa Lamprou
- Department of Psychiatry, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA, USA,Department of Psychiatry, Penn Center for Women's Behavioral Wellness, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA, USA
| | - Claudia Schinstine
- Department of Psychiatry, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA, USA,Department of Psychiatry, Penn Center for Women's Behavioral Wellness, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA, USA
| | - Mark Elliott
- Department of Radiology, Center for Magnetic Resonance and Optical Imaging (CMROI), Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA, USA
| | - Hari Hariharan
- Department of Radiology, Center for Magnetic Resonance and Optical Imaging (CMROI), Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA, USA
| | - Ravinder Reddy
- Department of Radiology, Center for Magnetic Resonance and Optical Imaging (CMROI), Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA, USA
| | - C Neill Epperson
- Department of Psychiatry, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA, USA,Department of Psychiatry, Penn Center for Women's Behavioral Wellness, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA, USA,Department of Obstetrics and Gynecology, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA, USA,Penn Center for Women's Behavioral Wellness, 3535 Market Street, Room 3001, Philadelphia, PA 19104, USA, Tel: +1 215 573-8871, Fax: +1 215 573 8881, E-mail:
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86
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Min R, Santello M, Nevian T. The computational power of astrocyte mediated synaptic plasticity. Front Comput Neurosci 2012; 6:93. [PMID: 23125832 PMCID: PMC3485583 DOI: 10.3389/fncom.2012.00093] [Citation(s) in RCA: 59] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2012] [Accepted: 10/15/2012] [Indexed: 12/05/2022] Open
Abstract
Research in the last two decades has made clear that astrocytes play a crucial role in the brain beyond their functions in energy metabolism and homeostasis. Many studies have shown that astrocytes can dynamically modulate neuronal excitability and synaptic plasticity, and might participate in higher brain functions like learning and memory. With the plethora of astrocyte mediated signaling processes described in the literature today, the current challenge is to identify, which of these processes happen under what physiological condition, and how this shapes information processing and, ultimately, behavior. To answer these questions will require a combination of advanced physiological, genetical, and behavioral experiments. Additionally, mathematical modeling will prove crucial for testing predictions on the possible functions of astrocytes in neuronal networks, and to generate novel ideas as to how astrocytes can contribute to the complexity of the brain. Here, we aim to provide an outline of how astrocytes can interact with neurons. We do this by reviewing recent experimental literature on astrocyte-neuron interactions, discussing the dynamic effects of astrocytes on neuronal excitability and short- and long-term synaptic plasticity. Finally, we will outline the potential computational functions that astrocyte-neuron interactions can serve in the brain. We will discuss how astrocytes could govern metaplasticity in the brain, how they might organize the clustering of synaptic inputs, and how they could function as memory elements for neuronal activity. We conclude that astrocytes can enhance the computational power of neuronal networks in previously unexpected ways.
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Affiliation(s)
- Rogier Min
- Department of Physiology, University of Berne Berne, Switzerland
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87
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Kirischuk S, Parpura V, Verkhratsky A. Sodium dynamics: another key to astroglial excitability? Trends Neurosci 2012; 35:497-506. [PMID: 22633141 DOI: 10.1016/j.tins.2012.04.003] [Citation(s) in RCA: 172] [Impact Index Per Article: 14.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2012] [Revised: 04/06/2012] [Accepted: 04/10/2012] [Indexed: 11/19/2022]
Abstract
Astroglial excitability is largely mediated by fluctuations in intracellular ion concentrations. In addition to generally acknowledged Ca²⁺ excitability of astroglia, recent studies have demonstrated that neuronal activity triggers transient increases in the cytosolic Na⁺ concentration ([Na⁺](i)) in perisynaptic astrocytes. These [Na⁺](i) transients are controlled by multiple Na⁺-permeable channels and Na⁺-dependent transporters; spatiotemporally organized [Na⁺](i) dynamics in turn regulate diverse astroglial homeostatic responses such as metabolic/signaling utilization of lactate and glutamate, transmembrane transport of neurotransmitters and K⁺ buffering. In particular, near-membrane [Na⁺](i) transients determine the rate and the direction of the transmembrane transport of GABA and Ca²⁺. We discuss here the role of Na⁺ in the regulation of various systems that mediate fast bidirectional communication between neurones and glia at the single synapse level.
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Affiliation(s)
- Sergei Kirischuk
- Institute of Physiology and Pathophysiology, Universal Medical Center of the Johannes Gutenberg University Mainz, Mainz, Germany
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88
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Pavlov I, Walker MC. Tonic GABA(A) receptor-mediated signalling in temporal lobe epilepsy. Neuropharmacology 2012; 69:55-61. [PMID: 22538087 DOI: 10.1016/j.neuropharm.2012.04.003] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2012] [Revised: 03/27/2012] [Accepted: 04/02/2012] [Indexed: 11/25/2022]
Abstract
The tonic activation of extrasynaptic GABAA receptors by extracellular GABA provides a powerful means of regulating neuronal excitability. A consistent finding from studies that have used various models of temporal lobe epilepsy is that tonic GABAA receptor-mediated conductances are largely preserved in epileptic brain (in contrast to synaptic inhibition which is often reduced). Tonic inhibition is therefore an attractive target for antiepileptic drugs. However, the network consequences of a commonly used approach to augment tonic GABAA receptor-mediated conductances by global manipulation of extracellular GABA are difficult to predict without understanding how epileptogenesis alters the pharmacology and GABA sensitivity of tonic inhibition, and how manipulation of tonic conductances modulates the output of individual neurons. Here we review the current literature on epilepsy-associated changes in tonic GABAA receptor-mediated signalling, and speculate about possible effects they have at the network level. This article is part of the Special Issue entitled 'New Targets and Approaches to the Treatment of Epilepsy'.
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Affiliation(s)
- Ivan Pavlov
- Department of Clinical and Experimental Epilepsy, UCL Institute of Neurology, London WC1N3BG, UK.
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89
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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: 125] [Impact Index Per Article: 10.4] [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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Parpura V, Heneka MT, Montana V, Oliet SHR, Schousboe A, Haydon PG, Stout RF, Spray DC, Reichenbach A, Pannicke T, Pekny M, Pekna M, Zorec R, Verkhratsky A. Glial cells in (patho)physiology. J Neurochem 2012; 121:4-27. [PMID: 22251135 DOI: 10.1111/j.1471-4159.2012.07664.x] [Citation(s) in RCA: 402] [Impact Index Per Article: 33.5] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Neuroglial cells define brain homeostasis and mount defense against pathological insults. Astroglia regulate neurogenesis and development of brain circuits. In the adult brain, astrocytes enter into intimate dynamic relationship with neurons, especially at synaptic sites where they functionally form the tripartite synapse. At these sites, astrocytes regulate ion and neurotransmitter homeostasis, metabolically support neurons and monitor synaptic activity; one of the readouts of the latter manifests in astrocytic intracellular Ca(2+) signals. This form of astrocytic excitability can lead to release of chemical transmitters via Ca(2+) -dependent exocytosis. Once in the extracellular space, gliotransmitters can modulate synaptic plasticity and cause changes in behavior. Besides these physiological tasks, astrocytes are fundamental for progression and outcome of neurological diseases. In Alzheimer's disease, for example, astrocytes may contribute to the etiology of this disorder. Highly lethal glial-derived tumors use signaling trickery to coerce normal brain cells to assist tumor invasiveness. This review not only sheds new light on the brain operation in health and disease, but also points to many unknowns.
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Affiliation(s)
- Vladimir Parpura
- Department of Neurobiology, Center for Glial Biology in Medicine, Civitan International Research Center, Atomic Force Microscopy & Nanotechnology Laboratories, and Evelyn F. McKnight Brain Institute, University of Alabama, Birmingham, Alabama, USA.
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Neurosteroid allopregnanolone regulates EAAC1-mediated glutamate uptake and triggers actin changes in Schwann cells. J Cell Physiol 2012; 227:1740-51. [DOI: 10.1002/jcp.22898] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
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92
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Li D, Li P, He Z, Cen D, Meng Z, Liang L, Luo X. Human Intravenous Immunoglobulins Suppress Seizure Activities and Inhibit the Activation of GFAP-Positive Astrocytes in the Hippocampus of Picrotoxin-Kindled Rats. Int J Neurosci 2011; 122:200-8. [DOI: 10.3109/00207454.2011.639470] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
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93
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Molnár T, Dobolyi A, Nyitrai G, Barabás P, Héja L, Emri Z, Palkovits M, Kardos J. Calcium signals in the nucleus accumbens: activation of astrocytes by ATP and succinate. BMC Neurosci 2011; 12:96. [PMID: 21967230 PMCID: PMC3199278 DOI: 10.1186/1471-2202-12-96] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2011] [Accepted: 10/03/2011] [Indexed: 12/13/2022] Open
Abstract
Background Accumulating evidence suggests that glial signalling is activated by different brain functions. However, knowledge regarding molecular mechanisms of activation or their relation to neuronal activity is limited. The purpose of the present study is to identify the characteristics of ATP-evoked glial signalling in the brain reward area, the nucleus accumbens (NAc), and thereby to explore the action of citric acid cycle intermediate succinate (SUC). Results We described the burst-like propagation of Ca2+ transients evoked by ATP in acute NAc slices from rat brain. Co-localization of the ATP-evoked Ca2+ signalling with immunoreactivities of the astroglia-specific gap junction forming channel protein connexin43 (Cx43) and the glial fibrillary acidic protein (GFAP) indicated that the responsive cells were a subpopulation of Cx43 and GFAP immunoreactive astrocytes. The ATP-evoked Ca2+ transients were present under the blockade of neuronal activity, but were inhibited by Ca2+ store depletion and antagonism of the G protein coupled purinergic P2Y1 receptor subtype-specific antagonist MRS2179. Similarly, Ca2+ transients evoked by the P2Y1 receptor subtype-specific agonist 2-(Methylthio)adenosine 5'-diphosphate were also blocked by MRS2179. These characteristics implied that intercellular Ca2+ signalling originated from the release of Ca2+ from internal stores, triggered by the activation of P2Y1 receptors. Inhibition by the gap junction blockers carbenoxolone and flufenamic acid and by an antibody raised against the gating-associated segment of Cx43 suggested that intercellular Ca2+ signalling proceeded through gap junctions. We demonstrated for the first time that extracellular SUC also evoked Ca2+ transients (EC50 = 50-60 μM) in about 15% of the ATP-responsive NAc astrocytes. By contrast to glial cells, electrophysiologically identified NAc neurons surrounded by ATP-responsive astrocytes were not activated simultaneously. Conclusions We concluded, therefore, that ATP- and SUC-sensitive Ca2+ transients appear to represent a signalling layer independent of NAc neurons. This previously unrecognised glial action of SUC, a major cellular energy metabolite, may play a role in linking metabolism to Ca2+ signalling in astrocytic networks under physiological and pathological conditions such as exercise and metabolic diseases.
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Affiliation(s)
- Tünde Molnár
- Department of Neurochemistry, Institute of Biomolecular Chemistry, Chemical Research Center, Hungarian Academy of Sciences, Pusztaszeriút 59-67, 1025 Budapest, Hungary
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94
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Lee M, McGeer EG, McGeer PL. Mechanisms of GABA release from human astrocytes. Glia 2011; 59:1600-11. [PMID: 21748804 DOI: 10.1002/glia.21202] [Citation(s) in RCA: 81] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2011] [Accepted: 05/25/2011] [Indexed: 11/05/2022]
Abstract
We have previously demonstrated that human astrocytes are GABAergic cells. Throughout the adult human brain, they express the GABA synthesizing enzyme GAD 67, the GABA metabolizing enzyme GABA-T, and the GABA(A) and GABA(B) receptors. GABA modulates the actions of microglia, indicating an important role for astrocytes beyond that of influencing neurotransmitter function. Here we report on the mechanisms by which astrocytes release GABA. Astrocytes were found to express the mRNA and protein for multiple GABA transporters, and multiple receptors for glutamate, GABA, and glycine. In culture, untreated human astrocytes maintained an intracellular GABA level of 2.32 mM. They exported GABA into the culture medium so that an intracellular-extracellular gradient of 3.64 fold was reached. Inhibitors of the GABA transporters GAT1, GAT2, and GAT3, significantly reduced this export in a Ca(2+)-independent fashion. Intracellular GABA levels were enhanced by treatment with the GABA-T inhibitors gabaculine or vigabatrin. Treatment with glutamate increased GABA release in a concentration-dependent fashion. This was partially inhibited by blockers of N-methyl-D-aspartate and kainate receptors. Conversely, glycine and D-serine, co-agonists of NMDA receptors, enhanced the GABA release. GABA release was accompanied by an increase in intracellular Ca(2+) concentration ([Ca(2+)](i)) and was reduced by adding the Ca(2+) chelator, BAPTA-AM to the medium. These data indicate that astrocytes continuously synthesize GABA and that there are multiple mechanisms which can mediate its release. Each of these may play a role in the physiological functioning of astrocytes.
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Affiliation(s)
- Moonhee Lee
- Kinsmen Laboratory of Neurological Research, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z3
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95
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Fleming TM, Scott V, Naskar K, Joe N, Brown CH, Stern JE. State-dependent changes in astrocyte regulation of extrasynaptic NMDA receptor signalling in neurosecretory neurons. J Physiol 2011; 589:3929-41. [PMID: 21690192 DOI: 10.1113/jphysiol.2011.207340] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Despite the long-established presence of glutamate NMDA receptors at extrasynaptic sites (eNMDARs), their functional roles remain poorly understood. Factors influencing the concentration and time course of glutamate in the extrasynaptic space, such as the topography of the neuronal–glial microenvironment, as well as glial glutamate transporters, are expected to affect eNMDAR-mediated signalling strength. In this study, we used in vitro and in vivo electrophysiological recordings to assess the properties, functional relevance and modulation of a persistent excitatory current mediated by activation of eNMDARs in hypothalamic supraoptic nucleus (SON) neurons. We found that ambient glutamate of a non-synaptic origin activates eNMDARs to mediate a persistent excitatory current (termed tonic I(NMDA)), which tonically stimulates neuronal activity. Pharmacological blockade of GLT1 astrocyte glutamate transporters, as well as the gliotoxin α-aminodadipic acid, enhanced tonic I(NMDA) and neuronal activity, supporting an astrocyte regulation of tonic I(NMDA) strength. Dehydration, a physiological challenge known to increase SON firing activity and to induce neuroglial remodelling, including reduced neuronal ensheathment by astrocyte processes, resulted in blunted GLT1 efficacy, enhanced tonic I(NMDA) strength, and increased neuronal activity. Taken together, our studies support the view that glial modulation of tonic I(NMDA) activation contributes to regulation of SON neuronal activity, contributing in turn to neuronal homeostatic responses during a physiological challenge.
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Affiliation(s)
- Tiffany M Fleming
- Department of Physiology, Medical College of Georgia, 1120 15th Street Augusta, GA 30912, USA
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96
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Luna-Munguia H, Orozco-Suarez S, Rocha L. Effects of high frequency electrical stimulation and R-verapamil on seizure susceptibility and glutamate and GABA release in a model of phenytoin-resistant seizures. Neuropharmacology 2011; 61:807-14. [PMID: 21645533 DOI: 10.1016/j.neuropharm.2011.05.027] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2011] [Revised: 05/18/2011] [Accepted: 05/19/2011] [Indexed: 11/30/2022]
Abstract
The present study was focused to characterize the effects of intrahippocampal application of R-verapamil, a P-glycoprotein blocker, and High Frequency Electrical Stimulation (HFS) at 130 Hz, on seizure susceptibility and extracellular concentrations of glutamate and γ-aminobutyric acid (GABA) in hippocampus of kindled rats with drug-resistant seizures. Fully kindled rats classified in responsive and non-responsive to phenytoin were used for this purpose. In contrast with responsive animals, non-responsive rats showed lower afterdischarge threshold (ADT) values in pre-kindling conditions and required less number of kindling trials to achieve the kindled state. Once the animals attained the kindled state, both epileptic groups presented high glutamate and low GABA interictal release, effect more evident in non-responsive rats. In hippocampus of responsive animals, GABA levels demonstrated two increases at 120 and 240 min after the ictal event, a situation no detected for non-responsive rats. Kindled animals receiving hippocampal HFS showed augmented ADT, an effect associated with enhanced GABA release in responsive rats. Intrahippocampal perfusion of R-verapamil (5 mM) decreased the seizure susceptibility (high ADT values), enhanced the interictal GABA release and the postictal levels of glutamate and GABA in responsive and non-responsive rats. It is conclude that alterations of glutamate and GABA release in the epileptic hippocampus of non-responsive animals resemble those found in hippocampus of patients with refractory TLE. In addition, intrahippocampal application of HFS and R-verapamil modifies the amino acid release and reduces the seizure susceptibility of both, responsive and non-responsive rats.
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Affiliation(s)
- Hiram Luna-Munguia
- Department of Pharmacobiology, Center for Research and Advanced Studies, Mexico City, Mexico
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97
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Rowley NM, Smith MD, Lamb JG, Schousboe A, White HS. Hippocampal betaine/GABA transporter mRNA expression is not regulated by inflammation or dehydration post-status epilepticus. J Neurochem 2011; 117:82-90. [PMID: 21219332 DOI: 10.1111/j.1471-4159.2011.07174.x] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Seizure activity can alter GABA transporter and osmoprotective gene expression, which may be involved in the pathogenesis of epilepsy. However, the response of the betaine/GABA transporter (BGT1) is unknown. The goal of the present study was to compare the expression of BGT1 mRNA to that of other osmoprotective genes and GABA transporters following status epilepticus (SE). The possible contributory role of dehydration and inflammation was also investigated because both have been shown to be involved in the regulation of GABA transporter and/or osmoprotective gene expression. BGT1 mRNA was increased 24 h post-SE, as were osmoprotective genes. BGT1 was decreased 72 h and 4 weeks post-SE, as were the GABA transporter mRNAs. The mRNA values for osmoprotective genes following 24-h water withdrawal were significantly lower than the values obtained 24 h post-SE despite similarities in their plasma osmolality values. BGT1 mRNA was not altered by lipopolysaccharide-induced inflammation while the transcription factor tonicity-responsive enhancer binding protein and the GABA transporters 1 and 3 were. These results suggest that neither plasma osmolality nor inflammation fully account for the changes seen in BGT1 mRNA expression post-SE. However, it is evident that BGT1 mRNA expression is altered by SE and displays a temporal pattern with similarities to both GABA and osmolyte transporters. Further investigation of BGT1 regulation in the brain is warranted.
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Affiliation(s)
- Nicole M Rowley
- Anticonvulsant Drug Development Program, Department of Pharmacology Toxicology, University of Utah, Salt Lake City, Utah 84108, USA
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98
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Benedetti B, Matyash V, Kettenmann H. Astrocytes control GABAergic inhibition of neurons in the mouse barrel cortex. J Physiol 2011; 589:1159-72. [PMID: 21224221 DOI: 10.1113/jphysiol.2010.203224] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Astrocytes in the barrel cortex respond with a transient Ca2+ increase to neuronal stimulation and this response is restricted to the stimulated barrel field. In the present study we suppressed the astrocyte response by dialysing these cells with the Ca2+ chelator BAPTA. Electrical stimulation triggered a depolarization in stellate or pyramidal ‘regular spiking' neurons from cortex layer 4 and 2/3 and this response was augmented in amplitude and duration after astrocytes were dialysed with BAPTA. Combined blockade of GABAA and GABAB receptors mimicked the effect of BAPTA dialysis, while glutamate receptor blockers had no effect. Moreover, the frequency of spontaneous postsynaptic currents was increased after BAPTA dialysis. Outside the range of BAPTA dialysis astrocytes responded with a Ca2+ increase, but in contrast to control, the response was no longer restricted to one barrel field. Our findings indicate that astrocytes control neuronal inhibition in the barrel cortex.
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Affiliation(s)
- B Benedetti
- Max-Delbrück-Centre for Molecular Medicine, Cellular Neuroscience, Robert-Rössle-Str. 10, 13092 Berlin-Buch, Berlin, Germany.
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99
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Pereira A, Furlan FA. Astrocytes and human cognition: modeling information integration and modulation of neuronal activity. Prog Neurobiol 2010; 92:405-20. [PMID: 20633599 DOI: 10.1016/j.pneurobio.2010.07.001] [Citation(s) in RCA: 84] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2010] [Revised: 06/18/2010] [Accepted: 07/06/2010] [Indexed: 10/19/2022]
Abstract
Recent research focusing on the participation of astrocytes in glutamatergic tripartite synapses has revealed mechanisms that support cognitive functions common to human and other mammalian species, such as learning, perception, conscious integration, memory formation/retrieval and the control of voluntary behavior. Astrocytes can modulate neuronal activity by means of release of glutamate, d-serine, adenosine triphosphate and other signaling molecules, contributing to sustain, reinforce or depress pre- and post-synaptic membranes. We review molecular mechanisms present in tripartite synapses and model the cognitive role of astrocytes. Single protoplasmic astrocytes operate as a "Local Hub", integrating information patterns from neuronal and glial populations. Two mechanisms, here modeled as the "domino" and "carousel" effects, contribute to the formation of intercellular calcium waves. As waves propagate through gap junctions and reach other types of astrocytes (interlaminar, polarized, fibrous and varicose projection), the active astroglial network functions as a "Master Hub" that integrates results of distributed processing from several brain areas and supports conscious states. Response of this network would define the effect exerted on neuronal plasticity (membrane potentiation or depression), behavior and psychosomatic processes. Theoretical results of our modeling can contribute to the development of new experimental research programs to test cognitive functions of astrocytes.
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Affiliation(s)
- Alfredo Pereira
- Institute of Biosciences, State University of São Paulo (UNESP), Campus Rubião Jr., 18618-000 Botucatu-SP, Brazil.
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100
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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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