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Haustein MD, Kracun S, Lu XH, Shih T, Jackson-Weaver O, Tong X, Xu J, Yang XW, O'Dell TJ, Marvin JS, Ellisman MH, Bushong EA, Looger LL, Khakh BS. Conditions and constraints for astrocyte calcium signaling in the hippocampal mossy fiber pathway. Neuron 2014; 82:413-29. [PMID: 24742463 DOI: 10.1016/j.neuron.2014.02.041] [Citation(s) in RCA: 185] [Impact Index Per Article: 16.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 02/13/2014] [Indexed: 02/04/2023]
Abstract
The spatiotemporal activities of astrocyte Ca²⁺ signaling in mature neuronal circuits remain unclear. We used genetically encoded Ca²⁺ and glutamate indicators as well as pharmacogenetic and electrical control of neurotransmitter release to explore astrocyte activity in the hippocampal mossy fiber pathway. Our data revealed numerous localized, spontaneous Ca²⁺ signals in astrocyte branches and territories, but these were not driven by neuronal activity or glutamate. Moreover, evoked astrocyte Ca²⁺ signaling changed linearly with the number of mossy fiber action potentials. Under these settings, astrocyte responses were global, suppressed by neurotransmitter clearance, and mediated by glutamate and GABA. Thus, astrocyte engagement in the fully developed mossy fiber pathway was slow and territorial, contrary to that frequently proposed for astrocytes within microcircuits. We show that astrocyte Ca²⁺ signaling functionally segregates large volumes of neuropil and that these transients are not suited for responding to, or regulating, single synapses in the mossy fiber pathway.
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Affiliation(s)
- Martin D Haustein
- Department of Physiology, David Geffen School of Medicine, University of California Los Angeles, Los Angeles, CA 90095-1751, USA
| | - Sebastian Kracun
- Department of Physiology, David Geffen School of Medicine, University of California Los Angeles, Los Angeles, CA 90095-1751, USA
| | - Xiao-Hong Lu
- Center for Neurobehavioral Genetics, Semel Institute for Neuroscience and Human Behavior, David Geffen School of Medicine, University of California Los Angeles, Los Angeles, CA 90095-1751, USA
| | - Tiffany Shih
- National Center for Microscopy and Imaging Research and Department of Neurosciences, University of California San Diego, La Jolla, CA 92093, USA
| | - Olan Jackson-Weaver
- Department of Physiology, David Geffen School of Medicine, University of California Los Angeles, Los Angeles, CA 90095-1751, USA
| | - Xiaoping Tong
- Department of Physiology, David Geffen School of Medicine, University of California Los Angeles, Los Angeles, CA 90095-1751, USA
| | - Ji Xu
- Department of Physiology, David Geffen School of Medicine, University of California Los Angeles, Los Angeles, CA 90095-1751, USA
| | - X William Yang
- Center for Neurobehavioral Genetics, Semel Institute for Neuroscience and Human Behavior, David Geffen School of Medicine, University of California Los Angeles, Los Angeles, CA 90095-1751, USA
| | - Thomas J O'Dell
- Department of Physiology, David Geffen School of Medicine, University of California Los Angeles, Los Angeles, CA 90095-1751, USA
| | - Jonathan S Marvin
- Janelia Farm Research Campus, Howard Hughes Medical Institute, Ashburn, VA 20147, USA
| | - Mark H Ellisman
- National Center for Microscopy and Imaging Research and Department of Neurosciences, University of California San Diego, La Jolla, CA 92093, USA
| | - Eric A Bushong
- National Center for Microscopy and Imaging Research and Department of Neurosciences, University of California San Diego, La Jolla, CA 92093, USA
| | - Loren L Looger
- Janelia Farm Research Campus, Howard Hughes Medical Institute, Ashburn, VA 20147, USA
| | - Baljit S Khakh
- Department of Physiology, David Geffen School of Medicine, University of California Los Angeles, Los Angeles, CA 90095-1751, USA; Department of Neurobiology, David Geffen School of Medicine, University of California Los Angeles, Los Angeles, CA 90095-1751, USA.
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102
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Araque A, Carmignoto G, Haydon PG, Oliet SHR, Robitaille R, Volterra A. Gliotransmitters travel in time and space. Neuron 2014; 81:728-39. [PMID: 24559669 DOI: 10.1016/j.neuron.2014.02.007] [Citation(s) in RCA: 921] [Impact Index Per Article: 83.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 02/03/2014] [Indexed: 12/12/2022]
Abstract
The identification of the presence of active signaling between astrocytes and neurons in a process termed gliotransmission has caused a paradigm shift in our thinking about brain function. However, we are still in the early days of the conceptualization of how astrocytes influence synapses, neurons, networks, and ultimately behavior. In this Perspective, our goal is to identify emerging principles governing gliotransmission and consider the specific properties of this process that endow the astrocyte with unique functions in brain signal integration. We develop and present hypotheses aimed at reconciling confounding reports and define open questions to provide a conceptual framework for future studies. We propose that astrocytes mainly signal through high-affinity slowly desensitizing receptors to modulate neurons and perform integration in spatiotemporal domains complementary to those of neurons.
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Affiliation(s)
- Alfonso Araque
- Instituto Cajal, Consejo Superior de Investigaciones Científicas, 28002 Madrid, Spain; Department of Neuroscience, University of Minnesota, Minneapolis, MN 55455, USA
| | - Giorgio Carmignoto
- Istituto di Neuroscienze, Consiglio Nazionale delle Ricerche and Dipartimento Scienze Biomediche, Università di Padova, 35121 Padova, Italy.
| | - Philip G Haydon
- Department of Neuroscience, Tufts University School of Medicine, Boston, MA 02111, USA
| | - Stéphane H R Oliet
- Inserm U862, Neurocentre Magendie, 33077 Bordeaux, France; Université de Bordeaux, 33077 Bordeaux, France
| | - Richard Robitaille
- Département de Neurosciences, Université de Montréal, Montréal, QC H3C 3J7, Canada; Groupe de Recherche sur le Système Nerveux Central, Université de Montréal, Montréal, QC H3C 3J7, Canada
| | - Andrea Volterra
- Département de Neurosciences Fondamentales (DNF), Faculté de Biologie et de Médecine, Université de Lausanne, 1005 Lausanne, Switzerland
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103
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104
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Xie AX, Lauderdale K, Murphy T, Myers TL, Fiacco TA. Inducing plasticity of astrocytic receptors by manipulation of neuronal firing rates. J Vis Exp 2014. [PMID: 24686723 PMCID: PMC4155624 DOI: 10.3791/51458] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Close to two decades of research has established that astrocytes in situ and in vivo express numerous G protein-coupled receptors (GPCRs) that can be stimulated by neuronally-released transmitter. However, the ability of astrocytic receptors to exhibit plasticity in response to changes in neuronal activity has received little attention. Here we describe a model system that can be used to globally scale up or down astrocytic group I metabotropic glutamate receptors (mGluRs) in acute brain slices. Included are methods on how to prepare parasagittal hippocampal slices, construct chambers suitable for long-term slice incubation, bidirectionally manipulate neuronal action potential frequency, load astrocytes and astrocyte processes with fluorescent Ca(2+) indicator, and measure changes in astrocytic Gq GPCR activity by recording spontaneous and evoked astrocyte Ca(2+) events using confocal microscopy. In essence, a "calcium roadmap" is provided for how to measure plasticity of astrocytic Gq GPCRs. Applications of the technique for study of astrocytes are discussed. Having an understanding of how astrocytic receptor signaling is affected by changes in neuronal activity has important implications for both normal synaptic function as well as processes underlying neurological disorders and neurodegenerative disease.
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Affiliation(s)
- Alison X Xie
- Graduate Program in Neuroscience, University of California Riverside
| | - Kelli Lauderdale
- Graduate Program in Neuroscience, University of California Riverside
| | - Thomas Murphy
- Graduate Program in Neuroscience, University of California Riverside
| | - Timothy L Myers
- Graduate Program in Neuroscience, University of California Riverside
| | - Todd A Fiacco
- Department of Cell Biology and Neuroscience, University of California Riverside; Center for Glial-Neuronal Interactions, University of California Riverside;
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105
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Diversity of astroglial functions alludes to subcellular specialisation. Trends Neurosci 2014; 37:228-42. [PMID: 24631033 DOI: 10.1016/j.tins.2014.02.008] [Citation(s) in RCA: 69] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2013] [Revised: 02/12/2014] [Accepted: 02/13/2014] [Indexed: 01/23/2023]
Abstract
Rapid signal exchange between astroglia and neurons has emerged as an essential element of neural circuits of the brain. However, the increasing variety of mechanisms contributing to this signalling appears to be facing a conceptual stalemate. The communication medium of astroglia involves intracellular [Ca(2+)] waves, which until recently have been associated with slow, global [Ca(2+)] rises. How such a uniform trigger could handle fast and diverse molecular messages remains unexplained. Recent studies have, however, revealed a variety of apparently independent Ca(2+) activities within individual astrocytic compartments, also indicating the prevalence of subcellular segregation for some signalling mechanisms. These signs of intracellular compartmentalisation might provide the key to the multitude of adaptive roles played by astroglia.
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106
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McClain J, Grubišić V, Fried D, Gomez-Suarez RA, Leinninger GM, Sévigny J, Parpura V, Gulbransen BD. Ca2+ responses in enteric glia are mediated by connexin-43 hemichannels and modulate colonic transit in mice. Gastroenterology 2014; 146:497-507.e1. [PMID: 24211490 PMCID: PMC3935238 DOI: 10.1053/j.gastro.2013.10.061] [Citation(s) in RCA: 160] [Impact Index Per Article: 14.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/15/2013] [Revised: 10/18/2013] [Accepted: 10/30/2013] [Indexed: 12/17/2022]
Abstract
BACKGROUND & AIMS In the enteric nervous system, neurotransmitters initiate changes in calcium (Ca(2+) responses) in glia, but it is not clear how this process affects intestinal function. We investigated whether Ca(2+)-mediated responses in enteric glia are required to maintain gastrointestinal function. METHODS We used in situ Ca(2+) imaging to monitor glial Ca(2+) responses, which were manipulated with pharmacologic agents or via glia-specific disruption of the gene encoding connexin-43 (Cx43) (hGFAP::CreER(T2+/-)/Cx43(f/f) mice). Gastrointestinal function was assessed based on pellet output, total gut transit, colonic bead expulsion, and muscle tension recordings. Proteins were localized and quantified by immunohistochemistry, immunoblot, and reverse transcription polymerase chain reaction analyses. RESULTS Ca(2+) responses in enteric glia of mice were mediated by Cx43 hemichannels. Cx43 immunoreactivity was confined to enteric glia within the myenteric plexus of the mouse colon; the Cx43 inhibitors carbenoxolone and 43Gap26 inhibited the ability of enteric glia to propagate Ca(2+) responses. In vivo attenuation of Ca(2+) responses in the enteric glial network slowed gut transit overall and delayed colonic transit--these changes are also observed during normal aging. Altered motility with increasing age was associated with reduced glial Ca(2+)-mediated responses and changes in glial expression of Cx43 messenger RNA and protein. CONCLUSIONS Ca(2+)-mediated responses in enteric glia regulate gastrointestinal function in mice. Altered intercellular signaling between enteric glia and neurons might contribute to motility disorders.
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Affiliation(s)
- Jonathon McClain
- Neuroscience Program and Department of Physiology, Michigan State University, 567 Wilson Road, East Lansing, MI, 48824 USA
| | - Vladimir Grubišić
- Department of Neurobiology, Center for Glial Biology in Medicine, Atomic Force Microscopy and Nanotechnology Laboratories, Civitan International Research Center, Evelyn F. McKnight Brain Institute, University of Alabama, Birmingham, AL 35294, USA
| | - David Fried
- Department of Pharmacology and Toxicology, Michigan State University, East Lansing, MI 48824
| | - Roberto A Gomez-Suarez
- Department of Neurobiology, Center for Glial Biology in Medicine, Atomic Force Microscopy and Nanotechnology Laboratories, Civitan International Research Center, Evelyn F. McKnight Brain Institute, University of Alabama, Birmingham, AL 35294, USA.,Department of Pediatrics Division of Pediatric Gastroenterology Hepatology And Nutrition at Nemours Chlidren's Hospital. Orlando, FL 32827, USA
| | - Gina M Leinninger
- Neuroscience Program and Department of Physiology, Michigan State University, 567 Wilson Road, East Lansing, MI, 48824 USA
| | - Jean Sévigny
- Département de microbiologie-infectiologie et d'immunologie, Faculté de Médecine, Université Laval, Québec, QC, Canada.,Centre de recherche du CHU de Québec, Québec, QC, G1V 4G2 Canada
| | - Vladimir Parpura
- Department of Neurobiology, Center for Glial Biology in Medicine, Atomic Force Microscopy and Nanotechnology Laboratories, Civitan International Research Center, Evelyn F. McKnight Brain Institute, University of Alabama, Birmingham, AL 35294, USA.,Department of Biotechnology, University of Rijeka, 51000 Rijeka, Croatia
| | - Brian D Gulbransen
- Neuroscience Program and Department of Physiology, Michigan State University, 567 Wilson Road, East Lansing, MI, 48824 USA
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107
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López-Hidalgo M, Schummers J. Cortical maps: a role for astrocytes? Curr Opin Neurobiol 2014; 24:176-89. [DOI: 10.1016/j.conb.2013.11.001] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2013] [Revised: 10/31/2013] [Accepted: 11/01/2013] [Indexed: 12/21/2022]
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108
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Young SZ, Lafourcade CA, Platel JC, Lin TV, Bordey A. GABAergic striatal neurons project dendrites and axons into the postnatal subventricular zone leading to calcium activity. Front Cell Neurosci 2014; 8:10. [PMID: 24478632 PMCID: PMC3904109 DOI: 10.3389/fncel.2014.00010] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2013] [Accepted: 01/07/2014] [Indexed: 01/01/2023] Open
Abstract
GABA regulates the behavior of neuroblasts and neural progenitor cells in the postnatal neurogenic subventricular zone (SVZ) through GABAA receptor (GABAAR)-mediated calcium increases. However, the source of GABA necessary for sufficient GABAAR-mediated depolarization and calcium increase has remained speculative. Here, we explored whether GABAergic striatal neurons functionally connect with SVZ cells. Using patch clamp recordings or single cell electroporation, striatal neurons along the SVZ were filled with a fluorescent dye revealing that they send both dendrites and axons into the SVZ. About 93% of the recorded neurons were medium spiny or aspiny GABAergic neurons and each neuron sent 3-4 processes into the SVZ covering ~56 μm. Using calcium imaging, we found that depolarization of striatal neurons led to increased calcium activity in SVZ cells that were mediated by GABAAR activation. Collectively, these findings undercover a novel mode of signaling in the SVZ providing a mechanism of brain activity-mediated regulation of postnatal neurogenesis through GABAergic striatal activity.
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Affiliation(s)
- Stephanie Z Young
- Departments of Neurosurgery and Cellular and Molecular Physiology, Yale University School of Medicine New Haven, CT, USA
| | - Carlos A Lafourcade
- Departments of Neurosurgery and Cellular and Molecular Physiology, Yale University School of Medicine New Haven, CT, USA
| | - Jean-Claude Platel
- Developmental Biology, Aix-Marseille University, IBDML, CNRS, UMR7288 Marseille, France
| | - Tiffany V Lin
- Departments of Neurosurgery and Cellular and Molecular Physiology, Yale University School of Medicine New Haven, CT, USA
| | - Angélique Bordey
- Departments of Neurosurgery and Cellular and Molecular Physiology, Yale University School of Medicine New Haven, CT, USA
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109
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Abstract
The function and efficacy of synaptic transmission are determined not only by the composition and activity of pre- and postsynaptic components but also by the environment in which a synapse is embedded. Glial cells constitute an important part of this environment and participate in several aspects of synaptic functions. Among the glial cell family, the roles played by astrocytes at the synaptic level are particularly important, ranging from the trophic support to the fine-tuning of transmission. Astrocytic structures are frequently observed in close association with glutamatergic synapses, providing a morphological entity for bidirectional interactions with synapses. Experimental evidence indicates that astrocytes sense neuronal activity by elevating their intracellular calcium in response to neurotransmitters and may communicate with neurons. The precise role of astrocytes in regulating synaptic properties, function, and plasticity remains however a subject of intense debate and many aspects of their interactions with neurons remain to be investigated. A particularly intriguing aspect is their ability to rapidly restructure their processes and modify their coverage of the synaptic elements. The present review summarizes some of these findings with a particular focus on the mechanisms driving this form of structural plasticity and its possible impact on synaptic structure and function.
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110
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Astrocyte calcium microdomains are inhibited by Bafilomycin A1 and cannot be replicated by low-level Schaffer collateral stimulation in situ. Cell Calcium 2014; 55:1-16. [DOI: 10.1016/j.ceca.2013.10.004] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2013] [Accepted: 10/09/2013] [Indexed: 11/20/2022]
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111
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Davila D, Thibault K, Fiacco TA, Agulhon C. Recent molecular approaches to understanding astrocyte function in vivo. Front Cell Neurosci 2013; 7:272. [PMID: 24399932 PMCID: PMC3871966 DOI: 10.3389/fncel.2013.00272] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2013] [Accepted: 12/06/2013] [Indexed: 12/11/2022] Open
Abstract
Astrocytes are a predominant glial cell type in the nervous systems, and are becoming recognized as important mediators of normal brain function as well as neurodevelopmental, neurological, and neurodegenerative brain diseases. Although numerous potential mechanisms have been proposed to explain the role of astrocytes in the normal and diseased brain, research into the physiological relevance of these mechanisms in vivo is just beginning. In this review, we will summarize recent developments in innovative and powerful molecular approaches, including knockout mouse models, transgenic mouse models, and astrocyte-targeted gene transfer/expression, which have led to advances in understanding astrocyte biology in vivo that were heretofore inaccessible to experimentation. We will examine the recently improved understanding of the roles of astrocytes – with an emphasis on astrocyte signaling – in the context of both the healthy and diseased brain, discuss areas where the role of astrocytes remains debated, and suggest new research directions.
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Affiliation(s)
- David Davila
- Glia-Glia and Glia-Neuron Interactions Group, National Center for Scientific Research, UFR Biomedicale, Paris Descartes University Paris, France
| | - Karine Thibault
- Glia-Glia and Glia-Neuron Interactions Group, National Center for Scientific Research, UFR Biomedicale, Paris Descartes University Paris, France
| | - Todd A Fiacco
- Department of Cell Biology and Neuroscience, and Center for Glial-Neuronal Interactions and Program in Cellular, Molecular and Developmental Biology, University of California at Riverside Riverside, CA, USA
| | - Cendra Agulhon
- Glia-Glia and Glia-Neuron Interactions Group, National Center for Scientific Research, UFR Biomedicale, Paris Descartes University Paris, France
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112
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The role of astrocytes in the regulation of synaptic plasticity and memory formation. Neural Plast 2013; 2013:185463. [PMID: 24369508 PMCID: PMC3867861 DOI: 10.1155/2013/185463] [Citation(s) in RCA: 135] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2013] [Revised: 10/07/2013] [Accepted: 11/05/2013] [Indexed: 12/22/2022] Open
Abstract
Astrocytes regulate synaptic transmission and play a role in the formation of new memories, long-term potentiation (LTP), and functional synaptic plasticity. Specifically, astroglial release of glutamate, ATP, and cytokines likely alters the survivability and functioning of newly formed connections. Among these pathways, regulation of glutamate appears to be most directly related to the promotion of LTP, which is highly dependent on the synchronization of synaptic receptors through the regulation of excitatory postsynaptic potentials. Moreover, regulation of postsynaptic glutamate receptors, particularly AMPA receptors, is dependent on signaling by ATP synthesized in astrocytes. Finally, cytokine signaling is also implicated in regulating LTP, but is likely most important in plasticity following tissue damage. Despite the role of these signaling factors in regulating LTP and functional plasticity, an integrative model of these factors has not yet been elucidated. In this review, we seek to summarize the current body of evidence on astrocytic mechanisms for regulation of LTP and functional plasticity, and provide an integrative model of the processes.
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113
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Hubbard JA, Hsu MS, Fiacco TA, Binder DK. Glial cell changes in epilepsy: Overview of the clinical problem and therapeutic opportunities. Neurochem Int 2013; 63:638-51. [DOI: 10.1016/j.neuint.2013.01.017] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2012] [Revised: 01/14/2013] [Accepted: 01/18/2013] [Indexed: 12/20/2022]
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114
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Li D, Agulhon C, Schmidt E, Oheim M, Ropert N. New tools for investigating astrocyte-to-neuron communication. Front Cell Neurosci 2013; 7:193. [PMID: 24194698 PMCID: PMC3810613 DOI: 10.3389/fncel.2013.00193] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2013] [Accepted: 10/07/2013] [Indexed: 12/24/2022] Open
Abstract
Gray matter protoplasmic astrocytes extend very thin processes and establish close contacts with synapses. It has been suggested that the release of neuroactive gliotransmitters at the tripartite synapse contributes to information processing. However, the concept of calcium (Ca2+)-dependent gliotransmitter release from astrocytes, and the release mechanisms are being debated. Studying astrocytes in their natural environment is challenging because: (i) astrocytes are electrically silent; (ii) astrocytes and neurons express an overlapping repertoire of transmembrane receptors; (iii) the size of astrocyte processes in contact with synapses are below the resolution of confocal and two-photon microscopes (iv) bulk-loading techniques using fluorescent Ca2+ indicators lack cellular specificity. In this review, we will discuss some limitations of conventional methodologies and highlight the interest of novel tools and approaches for studying gliotransmission. Genetically encoded Ca2+ indicators (GECIs), light-gated channels, and exogenous receptors are being developed to selectively read out and stimulate astrocyte activity. Our review discusses emerging perspectives on: (i) the complexity of astrocyte Ca2+ signaling revealed by GECIs; (ii) new pharmacogenetic and optogenetic approaches to activate specific Ca2+ signaling pathways in astrocytes; (iii) classical and new techniques to monitor vesicle fusion in cultured astrocytes; (iv) possible strategies to express specifically reporter genes in astrocytes.
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Affiliation(s)
- Dongdong Li
- Biophysics of Gliotransmitter Release Team, Laboratory of Neurophysiology and New Microscopies, INSERM U603, CNRS UMR 8154, University Paris Descartes Paris, France
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115
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Pirttimaki TM, Parri HR. Astrocyte plasticity: implications for synaptic and neuronal activity. Neuroscientist 2013; 19:604-15. [PMID: 24122819 DOI: 10.1177/1073858413504999] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Astrocytes are increasingly implicated in a range of functions in the brain, many of which were previously ascribed to neurons. Much of the prevailing interest centers on the role of astrocytes in the modulation of synaptic transmission and their involvement in the induction of forms of plasticity such as long-term potentiation and long-term depression. However, there is also an increasing realization that astrocytes themselves can undergo plasticity. This plasticity may be manifest as changes in protein expression which may modify calcium activity within the cells, changes in morphology that affect the environment of the synapse and the extracellular space, or changes in gap junction astrocyte coupling that modify the transfer of ions and metabolites through astrocyte networks. Plasticity in the way that astrocytes release gliotransmitters can also have direct effects on synaptic activity and neuronal excitability. Astrocyte plasticity can potentially have profound effects on neuronal network activity and be recruited in pathological conditions. An emerging principle of astrocyte plasticity is that it is often induced by neuronal activity, reinforcing our emerging understanding of the working brain as a constant interaction between neurons and glial cells.
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Affiliation(s)
- Tiina M Pirttimaki
- 1A.I. Virtanen Institute for Molecular Sciences, University of Eastern Finland, Kuopio, Finland
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116
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Platel JC, Kelsch W. Role of NMDA receptors in adult neurogenesis: an ontogenetic (re)view on activity-dependent development. Cell Mol Life Sci 2013; 70:3591-601. [PMID: 23397131 PMCID: PMC11113726 DOI: 10.1007/s00018-013-1262-z] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2012] [Revised: 12/18/2012] [Accepted: 01/03/2013] [Indexed: 12/27/2022]
Abstract
It is now widely accepted that neurogenesis continues throughout life. Accumulating evidence suggests that neurotransmitters are essential signaling molecules that control the different steps of neurogenesis. Nevertheless, we are only beginning to understand the precise role of neurotransmitter receptors and in particular excitatory glutamatergic transmission in the differentiation of adult-born neurons. Recent technical advances allow single-cell gene deletion to study cell-autonomous effects during the maturation of adult-born neurons. Single-cell gene deletion overcomes some of the difficulties in interpreting global gene deletion effects on entire brain areas or systemic pharmacological approaches that might result in compensatory circuit effects. The aim of this review is to summarize recent advances in the understanding of the role of NMDA receptors (NMDARs) during the differentiation of adult-born neurons and put them in perspective with previous findings on cortical development.
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Affiliation(s)
- Jean-Claude Platel
- Grenoble Institut des Neurosciences U836, Université Joseph Fourier, Site Santé La Tronche BP 170, 38042 Grenoble Cedex 9, France
| | - Wolfgang Kelsch
- Central Institute of Mental Health, Medical Faculty Mannheim, Heidelberg University, J5, 68159 Mannheim, Germany
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117
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Dallérac G, Chever O, Rouach N. How do astrocytes shape synaptic transmission? Insights from electrophysiology. Front Cell Neurosci 2013; 7:159. [PMID: 24101894 PMCID: PMC3787198 DOI: 10.3389/fncel.2013.00159] [Citation(s) in RCA: 120] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2013] [Accepted: 09/02/2013] [Indexed: 02/01/2023] Open
Abstract
A major breakthrough in neuroscience has been the realization in the last decades that the dogmatic view of astroglial cells as being merely fostering and buffering elements of the nervous system is simplistic. A wealth of investigations now shows that astrocytes actually participate in the control of synaptic transmission in an active manner. This was first hinted by the intimate contacts glial processes make with neurons, particularly at the synaptic level, and evidenced using electrophysiological and calcium imaging techniques. Calcium imaging has provided critical evidence demonstrating that astrocytic regulation of synaptic efficacy is not a passive phenomenon. However, given that cellular activation is not only represented by calcium signaling, it is also crucial to assess concomitant mechanisms. We and others have used electrophysiological techniques to simultaneously record neuronal and astrocytic activity, thus enabling the study of multiple ionic currents and in depth investigation of neuro-glial dialogues. In the current review, we focus on the input such approach has provided in the understanding of astrocyte-neuron interactions underlying control of synaptic efficacy.
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Affiliation(s)
- Glenn Dallérac
- Neuroglial Interactions in Cerebral Physiopathology, Center for Interdisciplinary Research in Biology, CNRS UMR 7241, INSERM U1050, Collège de France Paris, France
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118
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Abstract
There is no question about the fact that astrocytes and other glial cells release neurotransmitters that activate receptors on neurons, glia and vascular cells, and that calcium is an important second messenger regulating the release. This occurs in cell culture, tissue slice and in vivo. Negative results from informative experiments designed to test the mechanism of calcium-dependent neurotransmitter release from astrocytes and the ensuing effects on synaptic transmission, have been cited as evidence calling into question whether astrocytes release neurotransmitters under normal circumstances with effects on synaptic transmission. The special feature section in this issue of Neuron Glia Biology addresses these issues and other aspects of neurotransmitter release from astrocytes in communicating with neurons and glial cells. Together these studies suggest that application of vocabulary and concepts developed for synaptic communication between neurons can lead to confusion and apparent paradoxes with respect to communication by extracellular signaling molecules released from glia in response to functional activity.
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119
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Abstract
Astrocytes are the predominant glial cell type in the CNS. Although astrocytes are electrically nonexcitable, their excitability is manifested by their Ca2+ signaling, which serves as a mediator of neuron-glia bidirectional interactions via tripartite synapses. Studies from in vivo two-photon imaging indicate that in healthy animals, the properties of spontaneous astrocytic Ca2+ signaling are affected by animal species, age, wakefulness and the location of astrocytes in the brain. Intercellular Ca2+ waves in astrocytes can be evoked by a variety of stimulations. In animal models of some brain disorders, astrocytes can exhibit enhanced Ca2+ excitability featured as regenerative intercellular Ca2+ waves. This review first briefly summarizes the astrocytic Ca2+ signaling pathway and the procedure of in vivo two-photon Ca2+ imaging of astrocytes. It subsequently summarizes in vivo astrocytic Ca2+ signaling in health and brain disorders from experimental studies of animal models, and discusses the possible mechanisms and therapeutic implications underlying the enhanced Ca2+ excitability in astrocytes in brain disorders. Finally, this review summarizes molecular genetic approaches used to selectively manipulate astrocyte function in vivo and their applications to study the role of astrocytes in synaptic plasticity and brain disorders.
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Affiliation(s)
- Shinghua Ding
- Dalton Cardiovascular Research Center, Department of Biological Engineering, University of Missouri, Columbia, MO 65211, USA
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120
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Abstract
What is the biological basis for human cognition? Our understanding why human brains make us smarter than other animals is still in its infancy. In recent years, astrocytes have been shown to be indispensable for neuronal survival, growth, synapse formation, and synapse function. Now, in a new study from Maiken Nedergaard and Steven Goldman's groups (Han et al., 2013), human glia progenitor cells have been transplanted into mouse forebrains. These progenitors survived, migrated widely, and gave rise to astrocytes that displayed the characteristics of human astrocytes in the rodent host brains. Strikingly, the mice with transplanted human cells displayed improved long term potentiation (LTP) and learning, suggesting the potential importance of human astrocytes in the unique cognitive abilities of human brains. This landmark paper is an important first step toward future investigations of whether and how human astrocytes play a role in distinguishing the cognitive abilities of humans from those of other animals.
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Affiliation(s)
- Ye Zhang
- Department of Neurobiology, Stanford University, Stanford, CA, USA
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121
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Pannasch U, Rouach N. Emerging role for astroglial networks in information processing: from synapse to behavior. Trends Neurosci 2013; 36:405-17. [PMID: 23659852 DOI: 10.1016/j.tins.2013.04.004] [Citation(s) in RCA: 179] [Impact Index Per Article: 14.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2012] [Revised: 04/01/2013] [Accepted: 04/01/2013] [Indexed: 01/05/2023]
Abstract
Astrocytes contribute to neurotransmission through a variety of mechanisms ranging from synapse isolation to active signaling. Astroglial involvement in neurophysiology has been mostly investigated at the single-cell level. However, a unique feature of astrocytes is their high level of intercellular connectivity mediated by connexins, the proteins forming gap junction (GJ) channels. These astroglial GJ circuits enable the rapid intercellular exchange of ions, metabolites, and neuroactive substances. Recent findings have suggested that, despite their extensity, astroglial networks are also selective, preferential as well as plastic, and can regulate synapses, neuronal circuits, and behavior. The present review critically discusses the impact of astroglial networks on normal and pathological neuronal information processing as well as the underlying mechanisms.
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Affiliation(s)
- Ulrike Pannasch
- Neuroglial Interactions in Cerebral Physiopathology, Center for Interdisciplinary Research in Biology, Centre Nationale de la Recherche Scientifique (CNRS) Unité Mixte de Recherche 7241, Institut National de la Santé et de la Recherche Médicale (INSERM) Unité 1050, Collège de France, 75005 Paris, France
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122
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Cao X, Li LP, Wang Q, Wu Q, Hu HH, Zhang M, Fang YY, Zhang J, Li SJ, Xiong WC, Yan HC, Gao YB, Liu JH, Li XW, Sun LR, Zeng YN, Zhu XH, Gao TM. Astrocyte-derived ATP modulates depressive-like behaviors. Nat Med 2013; 19:773-7. [PMID: 23644515 DOI: 10.1038/nm.3162] [Citation(s) in RCA: 437] [Impact Index Per Article: 36.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2012] [Accepted: 03/15/2013] [Indexed: 12/15/2022]
Abstract
Major depressive disorder (MDD) is a cause of disability that affects approximately 16% of the world's population; however, little is known regarding the underlying biology of this disorder. Animal studies, postmortem brain analyses and imaging studies of patients with depression have implicated glial dysfunction in MDD pathophysiology. However, the molecular mechanisms through which astrocytes modulate depressive behaviors are largely uncharacterized. Here, we identified ATP as a key factor involved in astrocytic modulation of depressive-like behavior in adult mice. We observed low ATP abundance in the brains of mice that were susceptible to chronic social defeat. Furthermore, we found that the administration of ATP induced a rapid antidepressant-like effect in these mice. Both a lack of inositol 1,4,5-trisphosphate receptor type 2 and transgenic blockage of vesicular gliotransmission induced deficiencies in astrocytic ATP release, causing depressive-like behaviors that could be rescued via the administration of ATP. Using transgenic mice that express a Gq G protein-coupled receptor only in astrocytes to enable selective activation of astrocytic Ca(2+) signaling, we found that stimulating endogenous ATP release from astrocytes induced antidepressant-like effects in mouse models of depression. Moreover, we found that P2X2 receptors in the medial prefrontal cortex mediated the antidepressant-like effects of ATP. These results highlight astrocytic ATP release as a biological mechanism of MDD.
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Affiliation(s)
- Xiong Cao
- Department of Neurobiology, School of Basic Medical Sciences, Southern Medical University, Guangzhou, China
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123
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Peng H, Kang N, Xu J, Stanton PK, Kang J. Two distinct modes of exocytotic fusion pore expansion in large astrocytic vesicles. J Biol Chem 2013; 288:16872-16881. [PMID: 23620588 DOI: 10.1074/jbc.m113.468231] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
Formation of the fusion pore is a central question for regulated exocytosis by which secretory cells release neurotransmitters or hormones. Here, by dynamically monitoring exocytosis of large vesicles (2-7 μM) in astrocytes with two-photon microscopy imaging, we found that the exocytotic fusion pore was generated from the SNARE-dependent fusion at a ring shape of the docked plasma-vesicular membrane and the movement of a fusion-produced membrane fragment. We observed two modes of fragment movements, 1) a shift fragment that shifted to expand the fusion pore and 2) a fall-in fragment that fell into the collapsed vesicle to expand the fusion pore. Shift and fall-in modes are associated with full and partial collapses of large vesicles, respectively. The astrocytic marker, sulforhodamine 101, stained the fusion-produced membrane fragment more brightly than FM 1-43. Sulforhodamine 101 imaging showed that double fusion pores could simultaneously occur in a single vesicle (16% of large vesicles) to accelerate discharge of vesicular contents. Electron microscopy of large astrocytic vesicles showed shift and fall-in membrane fragments. Two modes of fusion pore formation demonstrate a novel mechanism underlying fusion pore expansion and provide a new explanation for full and partial collapses of large secretory vesicles.
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Affiliation(s)
- Hong Peng
- Department of Cell Biology and Anatomy, New York Medical College, Valhalla, New York 10595
| | - Ning Kang
- Department of Cell Biology and Anatomy, New York Medical College, Valhalla, New York 10595
| | - Jun Xu
- East Hospital, Tongji University School of Medicine, Shanghai 200120, China.
| | - Patric K Stanton
- Department of Cell Biology and Anatomy, New York Medical College, Valhalla, New York 10595
| | - Jian Kang
- Department of Cell Biology and Anatomy, New York Medical College, Valhalla, New York 10595.
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124
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Mutation of a NCKX eliminates glial microdomain calcium oscillations and enhances seizure susceptibility. J Neurosci 2013; 33:1169-78. [PMID: 23325253 DOI: 10.1523/jneurosci.3920-12.2013] [Citation(s) in RCA: 79] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Glia exhibit spontaneous and activity-dependent fluctuations in intracellular Ca(2+), yet it is unclear whether glial Ca(2+) oscillations are required during neuronal signaling. Somatic glial Ca(2+) waves are primarily mediated by the release of intracellular Ca(2+) stores, and their relative importance in normal brain physiology has been disputed. Recently, near-membrane microdomain Ca(2+) transients were identified in fine astrocytic processes and found to arise via an intracellular store-independent process. Here, we describe the identification of rapid, near-membrane Ca(2+) oscillations in Drosophila cortex glia of the CNS. In a screen for temperature-sensitive conditional seizure mutants, we identified a glial-specific Na(+)/Ca(2+), K(+) exchanger (zydeco) that is required for microdomain Ca(2+) oscillatory activity. We found that zydeco mutant animals exhibit increased susceptibility to seizures in response to a variety of environmental stimuli, and that zydeco is required acutely in cortex glia to regulate seizure susceptibility. We also found that glial expression of calmodulin is required for stress-induced seizures in zydeco mutants, suggesting a Ca(2+)/calmodulin-dependent glial signaling pathway underlies glial-neuronal communication. These studies demonstrate that microdomain glial Ca(2+) oscillations require NCKX-mediated plasma membrane Ca(2+) flux, and that acute dysregulation of glial Ca(2+) signaling triggers seizures.
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125
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Differential sensitivity of brainstem versus cortical astrocytes to changes in pH reveals functional regional specialization of astroglia. J Neurosci 2013; 33:435-41. [PMID: 23303924 DOI: 10.1523/jneurosci.2813-12.2013] [Citation(s) in RCA: 90] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Astrocytes might function as brain interoceptors capable of detecting different (chemo)sensory modalities and transmitting sensory information to the relevant neural networks controlling vital functions. For example, astrocytes that reside near the ventral surface of the brainstem (central respiratory chemosensitive area) respond to physiological decreases in pH with vigorous elevations in intracellular Ca(2+) and release of ATP. ATP transmits astroglial excitation to the brainstem respiratory network and contributes to adaptive changes in lung ventilation. Here we show that in terms of pH-sensitivity, ventral brainstem astrocytes are clearly distinct from astrocytes residing in the cerebral cortex. We monitored vesicular fusion in cultured rat brainstem astrocytes using total internal reflection fluorescence microscopy and found that ∼35% of them respond to acidification with an increased rate of exocytosis of ATP-containing vesicular compartments. These fusion events require intracellular Ca(2+) signaling and are independent of autocrine ATP actions. In contrast, the rate of vesicular fusion in cultured cortical astrocytes is not affected by changes in pH. Compared to cortical astrocytes, ventral brainstem astrocytes display higher levels of expression of genes encoding proteins associated with ATP vesicular transport and fusion, including vesicle-associated membrane protein-3 and vesicular nucleotide transporter. These results suggest that astrocytes residing in different parts of the rat brain are functionally specialized. In contrast to cortical astrocytes, astrocytes of the brainstem chemosensitive area(s) possess signaling properties that are functionally relevant-they are able to sense changes in pH and respond to acidification with enhanced vesicular release of ATP.
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126
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Kang N, Peng H, Yu Y, Stanton PK, Guilarte TR, Kang J. Astrocytes release D-serine by a large vesicle. Neuroscience 2013; 240:243-57. [PMID: 23485803 DOI: 10.1016/j.neuroscience.2013.02.029] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2012] [Revised: 01/14/2013] [Accepted: 02/13/2013] [Indexed: 11/30/2022]
Abstract
Long-term potentiation (LTP) of synaptic transmission in the CA1 region of the hippocampus depends on the activation of N-methyl-D-aspartate receptors (NMDARs), which can be regulated by Ca²⁺-dependent release of D-serine from astrocytes. The detailed mechanism underlying astrocytic d-serine release is still unknown. In hippocampal slices prepared from Sprague-Dawley rats, we found that clamping astrocytic [Ca²⁺] at 100-150 nM or puffing artificial cerebrospinal fluid (ACSF) into the extracellular space (weak mechanical stimulation) enhanced the synaptic activation of NMDARs. The enhancement was blocked by the NMDAR glycine site antagonist 5,7-dichlorokynurenic acid, glycine saturation, and infusion of astrocytes with D-amino acid oxidase and the serine racemase inhibitor L-erythro-3-hydroxyaspartate, suggesting the involvement of astrocytic D-serine release. Intracellular 100-150 nM [Ca²⁺] or puffing ACSF stimulated astrocytes to generate D-serine-containing large vesicles (1-3 μm), exocytotic fusion of which released D-serine. The formation of astrocytic large vesicles involved the intracellular fusion of small vesicles and/or other organelles. Spontaneous fusion of large vesicles occurred occasionally in astrocytes at rest, contributing to baseline D-serine levels, which increased the rising slope of NMDAR post-burst potentiation (PBP) without altering the PBP peak amplitude. Thus, under physiological conditions, astrocytic D-serine release by large vesicles facilitated weak theta-burst (TBS consisting of five bursts), but not strong TBS (TBS consisting of 10 bursts) stimulation-induced LTP.
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Affiliation(s)
- N Kang
- Department of Cell Biology and Anatomy, New York Medical College, Basic Science Building, Room 220, Valhalla, NY 10595, USA
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127
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Devaraju P, Sun MY, Myers TL, Lauderdale K, Fiacco TA. Astrocytic group I mGluR-dependent potentiation of astrocytic glutamate and potassium uptake. J Neurophysiol 2013; 109:2404-14. [PMID: 23427307 DOI: 10.1152/jn.00517.2012] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
One of the most important functions of astrocytes is removal of glutamate released during synaptic transmission. Surprisingly, the mechanisms by which astrocyte glutamate uptake is acutely modulated remain to be clarified. Astrocytes express metabotropic glutamate receptors (mGluRs) and other G protein-coupled receptors (GPCRs), which are activated during neuronal activity. Here, we test the hypothesis that astrocytic group I mGluRs acutely regulate glutamate uptake by astrocytes in situ. This hypothesis was tested in acute mouse hippocampal slices. Activation of astrocytic mGluRs, using a tetanic high-frequency stimulus (HFS) applied to Schaffer collaterals, led to potentiation of the amplitude of the synaptically evoked glutamate transporter currents (STCs) and associated charge transfer without changes in kinetics. Similar potentiation of STCs was not observed in the presence of group I mGluR antagonists or the PKC inhibitor, PKC 19-36, suggesting that HFS-induced potentiation of astrocyte glutamate uptake is astrocytic group I mGluR and PKC dependent. Pharmacological stimulation of a transgenic GPCR (MrgA1R), expressed exclusively in astrocytes, also potentiated STC amplitude and charge transfer, albeit quicker and shorter lasting compared with HFS-induced potentiation. The amplitude of the slow, inward astrocytic current due to potassium (K(+)) influx was also enhanced following activation of the endogenous mGluRs or the astrocyte-specific MrgA1 Gq GPCRs. Taken together, these findings suggest that astrocytic group I mGluR activation has a synergistic, modulatory effect on the uptake of glutamate and K(+).
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Affiliation(s)
- Prakash Devaraju
- Department of Cell Biology and Neuroscience, University of California, Riverside, CA, USA
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128
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Neural progenitor cells regulate capillary blood flow in the postnatal subventricular zone. J Neurosci 2013; 32:16435-48. [PMID: 23152626 DOI: 10.1523/jneurosci.1457-12.2012] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
In the postnatal subventricular zone (SVZ), S phase entry of neural progenitor cells (NPCs) correlates with a local increase in blood flow. However, the cellular mechanism controlling this hemodynamic response remains unknown. We show that a subpopulation of SVZ cells, astrocyte-like cells or B-cells, sends projections ensheathing pericytes on SVZ capillaries in young mice. We examined whether calcium increases in pericytes or B-cells led to a vascular response in acute slices using the P2Y(2/4) receptor (P2Y(2/4)R) agonist UTP, electrical stimulation, or transgenic mice expressing exogenous Gq-coupled receptors (MrgA1) in B-cells. UTP increased calcium in pericytes leading to capillary constrictions. Electrical stimulation induced calcium propagation in SVZ cells followed by capillary constrictions involving purinergic receptors. In transgenic mice, selective calcium increases in B-cells induced P2Y(2/4)R-dependent capillary constrictions, suggesting that B-cells release ATP activating purinergic receptors on pericytes. Interestingly, in the presence of a P2Y(2/4)R blocker, dilation was observed. Intraventricular UTP injection transiently decreased blood flow monitored in vivo using laser Doppler flowmetry. Using neonatal electroporation, we expressed MrgA1 in slow cycling radial glia-derived B1 cells, i.e., NPCs. Intraventricular injection of an MrgA1 ligand increased blood flow in the SVZ. Thus, upon intracellular calcium increases B-cells/NPCs release ATP and vasodilating factors that activate purinergic receptors on pericytes triggering a vascular response and blood flow increase in vivo. Considering that NPCs receive signals from other SVZ cells, these findings further suggest that NPCs act as transducers of neurometabolic coupling in the SVZ.
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129
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Sasaki T. The axon as a unique computational unit in neurons. Neurosci Res 2013; 75:83-8. [PMID: 23298528 DOI: 10.1016/j.neures.2012.12.004] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2012] [Revised: 12/11/2012] [Accepted: 12/17/2012] [Indexed: 11/25/2022]
Abstract
In the mammalian cortex, axons are highly ramified and link an enormous number of neurons over large distances. The conventional view assumes that action potentials (APs) are initiated at the axon initial segment in an all-or-none fashion and are then self-propagated orthodromically along axon collaterals without distortion of the AP waveform. By contrast, recent experimental results suggest that the axonal AP waveform can be modified depending on the activation states of the ion channels and receptors on axonal cell membranes. This AP modulation can regulate neurotransmission to postsynaptic neurons. In addition, the latest studies have provided evidence that cortical axons can integrate somatic burst firings and promote activity-dependent ectopic AP generation, which may underlie the oscillogenesis of fast rhythmic network activity. These seminal observations indicate that axons can perform diverse functional operations that extend beyond the prevailing model of axon physiology.
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Affiliation(s)
- Takuya Sasaki
- Division of Cerebral Structure, National Institute for Physiological Sciences, Okazaki 444-8787, Japan.
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130
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De Pittà M, Volman V, Berry H, Parpura V, Volterra A, Ben-Jacob E. Computational quest for understanding the role of astrocyte signaling in synaptic transmission and plasticity. Front Comput Neurosci 2012; 6:98. [PMID: 23267326 PMCID: PMC3528083 DOI: 10.3389/fncom.2012.00098] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2012] [Accepted: 12/06/2012] [Indexed: 01/08/2023] Open
Abstract
The complexity of the signaling network that underlies astrocyte-synapse interactions may seem discouraging when tackled from a theoretical perspective. Computational modeling is challenged by the fact that many details remain hitherto unknown and conventional approaches to describe synaptic function are unsuitable to explain experimental observations when astrocytic signaling is taken into account. Supported by experimental evidence is the possibility that astrocytes perform genuine information processing by means of their calcium signaling and are players in the physiological setting of the basal tone of synaptic transmission. Here we consider the plausibility of this scenario from a theoretical perspective, focusing on the modulation of synaptic release probability by the astrocyte and its implications on synaptic plasticity. The analysis of the signaling pathways underlying such modulation refines our notion of tripartite synapse and has profound implications on our understanding of brain function.
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Affiliation(s)
- Maurizio De Pittà
- School of Physics and Astronomy, Tel Aviv University Ramat Aviv, Israel
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131
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Tong X, Shigetomi E, Looger LL, Khakh BS. Genetically Encoded Calcium Indicators and Astrocyte Calcium Microdomains. Neuroscientist 2012; 19:274-91. [DOI: 10.1177/1073858412468794] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
The discovery of intracellular Ca2+ signals within astrocytes has changed our view of how these ubiquitous cells contribute to brain function. Classically thought merely to serve supportive functions, astrocytes are increasingly thought to respond to, and regulate, neurons. The use of organic Ca2+ indicator dyes such as Fluo-4 and Fura-2 has proved instrumental in the study of astrocyte physiology. However, progress has recently been accelerated by the use of cytosolic and membrane targeted genetically encoded calcium indicators (GECIs). Herein, we review these recent findings, discuss why studying astrocyte Ca2+ signals is important to understand brain function, and summarize work that led to the discovery of TRPA1 channel-mediated near-membrane Ca2+ signals in astrocytes and their indirect neuromodulatory roles at inhibitory synapses in the CA1 stratum radiatum region of the hippocampus. We suggest that the use of membrane-targeted and cytosolic GECIs holds great promise to explore the diversity of Ca2+ signals within single astrocytes and also to study diversity of function for astrocytes in different parts of the brain.
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Affiliation(s)
- Xiaoping Tong
- Department of Physiology, David Geffen School of Medicine, University of California Los Angeles, Los Angeles, CA, USA
| | - Eiji Shigetomi
- Department of Physiology, David Geffen School of Medicine, University of California Los Angeles, Los Angeles, CA, USA
- Department of Pharmacology, Faculty of Medicine, University of Yamanashi Chuo, Yamanashi, Japan
| | - Loren L. Looger
- Janelia Farm Research Campus, Howard Hughes Medical Institute, Ashburn, VA, USA
| | - Baljit S. Khakh
- Department of Physiology, David Geffen School of Medicine, University of California Los Angeles, Los Angeles, CA, USA
- Department of Neurobiology, David Geffen School of Medicine, University of California Los Angeles, Los Angeles, CA, USA
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132
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Xie AX, Sun MY, Murphy T, Lauderdale K, Tiglao E, Fiacco TA. Bidirectional scaling of astrocytic metabotropic glutamate receptor signaling following long-term changes in neuronal firing rates. PLoS One 2012; 7:e49637. [PMID: 23166735 PMCID: PMC3499417 DOI: 10.1371/journal.pone.0049637] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2012] [Accepted: 10/16/2012] [Indexed: 11/19/2022] Open
Abstract
Very little is known about the ability of astrocytic receptors to exhibit plasticity as a result of changes in neuronal activity. Here we provide evidence for bidirectional scaling of astrocytic group I metabotropic glutamate receptor signaling in acute mouse hippocampal slices following long-term changes in neuronal firing rates. Plasticity of astrocytic mGluRs was measured by recording spontaneous and evoked Ca2+ elevations in both astrocytic somata and processes. An exogenous astrocytic Gq G protein-coupled receptor was resistant to scaling, suggesting that the alterations in astrocyte Ca2+ signaling result from changes in activity of the surface mGluRs rather than a change in intracellular G protein signaling molecules. These findings suggest that astrocytes actively detect shifts in neuronal firing rates and adjust their receptor signaling accordingly. This type of long-term plasticity in astrocytes resembles neuronal homeostatic plasticity and might be important to ensure an optimal or expected level of input from neurons.
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Affiliation(s)
- Alison X. Xie
- Graduate Program in Neuroscience, University of California Riverside, Riverside, California, United States of America
| | - Min-Yu Sun
- Graduate Program in Cellular, Molecular, and Developmental Biology, University of California Riverside, Riverside, California, United States of America
| | - Thomas Murphy
- Graduate Program in Neuroscience, University of California Riverside, Riverside, California, United States of America
| | - Kelli Lauderdale
- Graduate Program in Neuroscience, University of California Riverside, Riverside, California, United States of America
| | - Elizabeth Tiglao
- Undergraduate Neuroscience Major, University of California Riverside, Riverside, California, United States of America
| | - Todd A. Fiacco
- Department of Cell Biology and Neuroscience and Center for Glial-Neuronal Interactions, University of California Riverside, Riverside, California, United States of America
- * E-mail:
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133
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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: 4.5] [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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134
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Astrocyte- neuron interaction as a mechanism responsible for generation of neural synchrony: a study based on modeling and experiments. J Comput Neurosci 2012; 34:489-504. [DOI: 10.1007/s10827-012-0432-6] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2012] [Revised: 09/29/2012] [Accepted: 10/11/2012] [Indexed: 10/27/2022]
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135
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Chen J, Tan Z, Zeng L, Zhang X, He Y, Gao W, Wu X, Li Y, Bu B, Wang W, Duan S. Heterosynaptic long-term depression mediated by ATP released from astrocytes. Glia 2012; 61:178-91. [PMID: 23044720 DOI: 10.1002/glia.22425] [Citation(s) in RCA: 123] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2012] [Accepted: 08/30/2012] [Indexed: 01/01/2023]
Abstract
Heterosynaptic long-term depression (hLTD) at untetanized synapses accompanying the induction of long-term potentiation (LTP) spatially sharpens the activity-induced synaptic potentiation; however, the underlying mechanism remains unclear. We found that hLTD in the hippocampal CA1 region is caused by stimulation-induced ATP release from astrocytes that suppresses transmitter release from untetanized synaptic terminals via activation of P2Y receptors. Selective stimulation of astrocytes expressing channelrhodopsin-2, a light-gated cation channel permeable to Ca(2+) , resulted in LTD of synapses on neighboring neurons. This synaptic modification required Ca(2+) elevation in astrocytes and activation of P2Y receptors, but not N-methyl-D-aspartate receptors. Furthermore, blocking P2Y receptors or buffering astrocyte intracellular Ca(2+) at a low level prevented hLTD without affecting LTP induced by SC stimulation. Thus, astrocyte activation is both necessary and sufficient for mediating hLTD accompanying LTP induction, strongly supporting the notion that astrocytes actively participate in activity-dependent synaptic plasticity of neural circuits.
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Affiliation(s)
- Jiadong Chen
- Institute of Neuroscience and Key Laboratory of Neuroscience, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, China
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136
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Agulhon C, Sun MY, Murphy T, Myers T, Lauderdale K, Fiacco TA. Calcium Signaling and Gliotransmission in Normal vs. Reactive Astrocytes. Front Pharmacol 2012; 3:139. [PMID: 22811669 PMCID: PMC3395812 DOI: 10.3389/fphar.2012.00139] [Citation(s) in RCA: 115] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2012] [Accepted: 06/26/2012] [Indexed: 01/07/2023] Open
Abstract
A prominent area of neuroscience research over the past 20 years has been the acute modulation of neuronal synaptic activity by Ca2+-dependent release of the transmitters ATP, D-serine, and glutamate (called gliotransmitters) by astrocytes. Although the physiological relevance of this mechanism is under debate, emerging evidence suggests that there are critical factors in addition to Ca2+ that are required for gliotransmitters to be released from astrocytes. Interestingly, these factors include activated microglia and the proinflammatory cytokine Tumor Necrosis Factor α (TNFα), chemotactic cytokine Stromal cell-Derived Factor-1α (SDF-1α), and inflammatory mediator prostaglandin E2 (PGE2). Of note, microglial activation and release of inflammatory molecules from activated microglia and reactive astrocytes can occur within minutes of a triggering stimulus. Therefore, activation of astrocytes by inflammatory molecules combined with Ca2+ elevations may lead to gliotransmitter release, and be an important step in the early sequence of events contributing to hyperexcitability, excitotoxicity, and neurodegeneration in the damaged or diseased brain. In this review, we will first examine evidence questioning Ca2+-dependent gliotransmitter release from astrocytes in healthy brain tissue, followed by a close examination of recent work suggesting that Ca2+-dependent gliotransmitter release occurs as an early event in the development of neurological disorders and neuroinflammatory and neurodegenerative diseases.
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Affiliation(s)
- Cendra Agulhon
- UFR Biomédicale, CNRS UMR 8154, Université Paris Descartes Paris, France
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137
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Shih AY, Driscoll JD, Drew PJ, Nishimura N, Schaffer CB, Kleinfeld D. Two-photon microscopy as a tool to study blood flow and neurovascular coupling in the rodent brain. J Cereb Blood Flow Metab 2012; 32:1277-309. [PMID: 22293983 PMCID: PMC3390800 DOI: 10.1038/jcbfm.2011.196] [Citation(s) in RCA: 327] [Impact Index Per Article: 25.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/23/2011] [Revised: 10/18/2011] [Accepted: 11/13/2011] [Indexed: 01/09/2023]
Abstract
The cerebral vascular system services the constant demand for energy during neuronal activity in the brain. Attempts to delineate the logic of neurovascular coupling have been greatly aided by the advent of two-photon laser scanning microscopy to image both blood flow and the activity of individual cells below the surface of the brain. Here we provide a technical guide to imaging cerebral blood flow in rodents. We describe in detail the surgical procedures required to generate cranial windows for optical access to the cortex of both rats and mice and the use of two-photon microscopy to accurately measure blood flow in individual cortical vessels concurrent with local cellular activity. We further provide examples on how these techniques can be applied to the study of local blood flow regulation and vascular pathologies such as small-scale stroke.
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Affiliation(s)
- Andy Y Shih
- Department of Physics, University of California at San Diego, La Jolla, California, USA
| | - Jonathan D Driscoll
- Department of Physics, University of California at San Diego, La Jolla, California, USA
| | - Patrick J Drew
- Department of Engineering Science and Mechanics, Pennsylvania State University, University Park, Pennsylvania, USA
- Department of Neurosurgery, Pennsylvania State University, University Park, Pennsylvania, USA
| | - Nozomi Nishimura
- Department of Biomedical Engineering, Cornell University, Ithaca, New York, USA
| | - Chris B Schaffer
- Department of Biomedical Engineering, Cornell University, Ithaca, New York, USA
| | - David Kleinfeld
- Department of Physics, University of California at San Diego, La Jolla, California, USA
- Section of Neurobiology, University of California at San Diego, La Jolla, California, USA
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138
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Santello M, Calì C, Bezzi P. Gliotransmission and the tripartite synapse. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2012; 970:307-31. [PMID: 22351062 DOI: 10.1007/978-3-7091-0932-8_14] [Citation(s) in RCA: 148] [Impact Index Per Article: 11.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
In the last years, the classical view of glial cells (in particular of astrocytes) as a simple supportive cell for neurons has been replaced by a new vision in which glial cells are active elements of the brain. Such a new vision is based on the existence of a bidirectional communication between astrocytes and neurons at synaptic level. Indeed, perisynaptic processes of astrocytes express active G-protein-coupled receptors that are able (1) to sense neurotransmitters released from the synapse during synaptic activity, (2) to increase cytosolic levels of calcium, and (3) to stimulate the release of gliotransmitters that in turn can interact with the synaptic elements. The mechanism(s) by which astrocytes can release gliotransmitter has been extensively studied during the last years. Many evidences have suggested that a fraction of astrocytes in situ release neuroactive substances both with calcium-dependent and calcium-independent mechanism(s); whether these mechanisms coexist and under what physiological or pathological conditions they occur, it remains unclear. However, the calcium-dependent exocytotic vesicular release has received considerable attention due to its potential to occur under physiological conditions via a finely regulated way. By releasing gliotransmitters in millisecond time scale with a specific vesicular apparatus, astrocytes can integrate and process synaptic information and control or modulate synaptic transmission and plasticity.
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Affiliation(s)
- Mirko Santello
- DBCM, Department of Physiology, University of Bern, Bühlplatz 5, 3012 Bern, Switzerland
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139
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Ormel L, Stensrud MJ, Chaudhry FA, Gundersen V. A distinct set of synaptic-like microvesicles in atroglial cells contain VGLUT3. Glia 2012; 60:1289-300. [DOI: 10.1002/glia.22348] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2012] [Accepted: 04/13/2012] [Indexed: 11/09/2022]
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140
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Slezak M, Grosche A, Niemiec A, Tanimoto N, Pannicke T, Münch T, Crocker B, Isope P, Härtig W, Beck S, Huber G, Ferracci G, Perraut M, Reber M, Miehe M, Demais V, Lévêque C, Metzger D, Szklarczyk K, Przewlocki R, Seeliger M, Sage-Ciocca D, Hirrlinger J, Reichenbach A, Reibel S, Pfrieger F. Relevance of Exocytotic Glutamate Release from Retinal Glia. Neuron 2012; 74:504-16. [DOI: 10.1016/j.neuron.2012.03.027] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 03/07/2012] [Indexed: 10/28/2022]
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141
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Verkhratsky A, Rodríguez JJ, Parpura V. Calcium signalling in astroglia. Mol Cell Endocrinol 2012; 353:45-56. [PMID: 21945602 DOI: 10.1016/j.mce.2011.08.039] [Citation(s) in RCA: 171] [Impact Index Per Article: 13.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/30/2011] [Revised: 08/28/2011] [Accepted: 08/31/2011] [Indexed: 12/15/2022]
Abstract
Astroglia possess excitability based on movements of Ca(2+) ions between intracellular compartments and plasmalemmal Ca(2+) fluxes. This "Ca(2+) excitability" is controlled by several families of proteins located in the plasma membrane, within the cytosol and in the intracellular organelles, most notably in the endoplasmic reticulum (ER) and mitochondria. Accumulation of cytosolic Ca(2+) can be caused by the entry of Ca(2+) from the extracellular space through ionotropic receptors and store-operated channels expressed in astrocytes. Plasmalemmal Ca(2+) ATP-ase and sodium-calcium exchanger extrude cytosolic Ca(2+) to the extracellular space; the exchanger can also operate in reverse, depending of the intercellular Na(+) concentration, to deliver Ca(2+) to the cytosol. The ER internal store possesses inositol 1,4,5-trisphosphate receptors which can be activated upon stimulation of astrocytes through a multiple plasma membrane metabotropic G-protein coupled receptors. This leads to release of Ca(2+) from the ER and its elevation in the cytosol, the level of which can be modulated by mitochondria. The mitochondrial uniporter takes up Ca(2+) into the matrix, while free Ca(2+) exits the matrix through the mitochondrial Na(+)/Ca(2+) exchanger as well as via transient openings of the mitochondrial permeability transition pore. One of the prominent consequences of astroglial Ca(2+) excitability is gliotransmission, a release of transmitters from astroglia which can lead to signalling to adjacent neurones.
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142
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Binder DK, Nagelhus EA, Ottersen OP. Aquaporin-4 and epilepsy. Glia 2012; 60:1203-14. [DOI: 10.1002/glia.22317] [Citation(s) in RCA: 115] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2011] [Accepted: 02/09/2012] [Indexed: 12/17/2022]
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143
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Lee DJ, Hsu MS, Seldin MM, Arellano JL, Binder DK. Decreased expression of the glial water channel aquaporin-4 in the intrahippocampal kainic acid model of epileptogenesis. Exp Neurol 2012; 235:246-55. [PMID: 22361023 DOI: 10.1016/j.expneurol.2012.02.002] [Citation(s) in RCA: 88] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2011] [Revised: 12/24/2011] [Accepted: 02/06/2012] [Indexed: 01/28/2023]
Abstract
Recent evidence suggests that astrocytes may be a potential new target for the treatment of epilepsy. The glial water channel aquaporin-4 (AQP4) is expressed in astrocytes, and along with the inwardly-rectifying K(+) channel K(ir)4.1 is thought to underlie the reuptake of H(2)O and K(+) into glial cells during neural activity. Previous studies have demonstrated increased seizure duration and slowed potassium kinetics in AQP4(-/-) mice, and redistribution of AQP4 in hippocampal specimens from patients with chronic epilepsy. However, the regulation and role of AQP4 during epileptogenesis remain to be defined. In this study, we examined the expression of AQP4 and other glial molecules (GFAP, K(ir)4.1, glutamine synthetase) in the intrahippocampal kainic acid (KA) model of epilepsy and compared behavioral and histologic outcomes in wild-type mice vs. AQP4(-/-) mice. Marked and prolonged reduction in AQP4 immunoreactivity on both astrocytic fine processes and endfeet was observed following KA status epilepticus in multiple hippocampal layers. In addition, AQP4(-/-) mice had more spontaneous recurrent seizures than wild-type mice during the first week after KA SE as assessed by chronic video-EEG monitoring and blinded EEG analysis. While both genotypes exhibited similar reactive astrocytic changes, granule cell dispersion and CA1 pyramidal neuron loss, there were an increased number of fluorojade-positive cells early after KA SE in AQP4(-/-) mice. These results indicate a marked reduction of AQP4 following KA SE and suggest that dysregulation of water and potassium homeostasis occurs during early epileptogenesis. Restoration of astrocytic water and ion homeostasis may represent a novel therapeutic strategy.
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Affiliation(s)
- Darrin J Lee
- Department of Neurological Surgery, University of California, Davis, CA, USA
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144
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Arias A, Lamé MW, Santarelli L, Hen R, Greene LA, Angelastro JM. Regulated ATF5 loss-of-function in adult mice blocks formation and causes regression/eradication of gliomas. Oncogene 2012; 31:739-51. [PMID: 21725368 PMCID: PMC3277917 DOI: 10.1038/onc.2011.276] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2011] [Revised: 04/29/2011] [Accepted: 05/26/2011] [Indexed: 12/03/2022]
Abstract
Glioblastomas are among the most incurable cancers. Our past findings indicated that glioblastoma cells, but not neurons or glia, require the transcription factor ATF5 (activating transcription factor 5) for survival. However, it was unknown whether interference with ATF5 function can prevent or promote regression/eradication of malignant gliomas in vivo. To address this issue, we created a mouse model by crossing a human glial fibrillary acidic protein (GFAP) promoter-tetracycline transactivator mouse line with tetracycline operon-dominant negative-ATF5 (d/n-ATF5) mice to establish bi-transgenic mice. In this model, d/n-ATF5 expression is controlled by doxycycline and the promoter for GFAP, a marker for stem/progenitor cells as well as gliomas. Endogenous gliomas were produced with high efficiency by retroviral delivery of platelet-derived growth factor (PDGF)-B and p53-short hairpin RNA (shRNA) in adult bi-transgenic mice in which expression of d/n-ATF5 was spatially and temporally regulated. Induction of d/n-ATF5 before delivery of PDGF-B/p53-shRNA virus greatly reduced the proportion of mice that formed tumors. Moreover, d/n-ATF5 induction after tumor formation led to regression/eradication of detectable gliomas without evident damage to normal brain cells in all 24 mice assessed.
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Affiliation(s)
- A Arias
- Department of Molecular Biosciences, University of California, Davis School of Veterinary Medicine, Davis, CA, USA
| | - M W Lamé
- Department of Molecular Biosciences, University of California, Davis School of Veterinary Medicine, Davis, CA, USA
| | - L Santarelli
- Department of Neuroscience, Columbia University, New York, NY, USA
| | - R Hen
- Department of Neuroscience, Columbia University, New York, NY, USA
| | - L A Greene
- Department of Pathology and Cell Biology, Columbia University, New York, NY, USA
| | - J M Angelastro
- Department of Molecular Biosciences, University of California, Davis School of Veterinary Medicine, Davis, CA, USA
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145
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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: 416] [Impact Index Per Article: 32.0] [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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146
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Requardt RP, Hirrlinger PG, Wilhelm F, Winkler U, Besser S, Hirrlinger J. Ca²⁺ signals of astrocytes are modulated by the NAD⁺/NADH redox state. J Neurochem 2012; 120:1014-25. [PMID: 22299833 DOI: 10.1111/j.1471-4159.2012.07645.x] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Astrocytes are important glial cells in the brain providing metabolic support to neurons as well as contributing to brain signaling. These different functional levels have to be highly coordinated to allow for proper cell and brain function. In this study, we show that in astrocytes the NAD(+) /NADH redox state modulates dopamine-induced Ca(2+) signals thereby connecting metabolism and Ca(2+) signaling. Application of dopamine induced a dose-dependent increase in Ca(2+) signal frequency in these cells, which was dependent on D(1) -receptor signaling, glycolytic activity, an increase in cytosolic NADH and inositol 1,4,5-triphosphate receptor operated intracellular Ca(2+) stores. Application of dopamine at a low concentration (1 μM) did not induce an increase in Ca(2+) signal frequency by itself. However, simultaneously increasing cytosolic NADH content either by direct application of NADH or by application of lactate resulted in a pronounced increase in Ca(2+) signal frequency. This increase could be blocked by co-application of pyruvate, suggesting that indeed the NAD(+) /NADH redox state is regulating Ca(2+) signals. We conclude that at the NAD(+) /NADH redox state metabolic and signaling information is integrated in astrocytes, thereby most likely contributing to precisely coordinate these different tasks of astrocytes.
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Affiliation(s)
- Robert P Requardt
- Carl-Ludwig-Institute for Physiology, Faculty of Medicine, University of Leipzig, Leipzig, Germany
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147
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Filosa JA, Naskar K, Perfume G, Iddings JA, Biancardi VC, Vatta MS, Stern JE. Endothelin-mediated calcium responses in supraoptic nucleus astrocytes influence magnocellular neurosecretory firing activity. J Neuroendocrinol 2012; 24:378-92. [PMID: 22007724 DOI: 10.1111/j.1365-2826.2011.02243.x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
In addition to their peripheral vasoactive effects, accumulating evidence supports an important role for endothelins (ETs) in the regulation of the hypothalamic magnocellular neurosecretory system, which produces and releases the neurohormones vasopressin (VP) and oxytocin (OT). Still, the precise cellular substrates, loci and mechanisms underlying the actions of ETs on the magnocellular system are poorly understood. In the present study, we combined patch-clamp electrophysiology, confocal Ca(2+) imaging and immunohistochemistry to study the actions of ETs on supraoptic nucleus (SON) magnocellular neurosecretory neurones and astrocytes. Our studies show that ET-1 evoked rises in [Ca(2+) ](i) levels in SON astrocytes (but not neurones), an effect largely mediated by the activation of ET(B) receptors and mobilisation of thapsigargin-sensitive Ca(2+) stores. The presence of ET(B) receptors in SON astrocytes was also verified immunohistochemically. ET(B) receptor activation either increased (75%) or decreased (25%) SON firing activity, both in VP and putative OT neurones, and these effects were prevented when slices were preincubated in glutamate receptor blockers or nitric oxide synthase blockers, respectively. Moreover, ET(B) -mediated effects in SON neurones were also prevented by a gliotoxin compound, and when changes in [Ca(2+) ](i) were prevented with bath-applied BAPTA-AM or thapsigargin. Conversely, intracellular Ca(2+) chelation in the recorded SON neurones failed to block ET(B) -mediated effects. In summary, our results indicate that ET(B) receptor activation in SON astrocytes induces the mobilisation of [Ca(2+) ](i) , likely resulting in the activation of glutamate and nitric oxide signalling pathways, evoking in turn excitatory and inhibitory SON neuronal responses, respectively. Taken together, our study supports an important role for astrocytes in mediating the actions of ETs on the magnocellular neurosecretory system.
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Affiliation(s)
- J A Filosa
- Department of Physiology, Georgia Health Sciences University, Augusta, GA 30912, USA
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148
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Nedergaard M, Verkhratsky A. Artifact versus reality--how astrocytes contribute to synaptic events. Glia 2012; 60:1013-23. [PMID: 22228580 DOI: 10.1002/glia.22288] [Citation(s) in RCA: 222] [Impact Index Per Article: 17.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2011] [Accepted: 12/05/2011] [Indexed: 11/11/2022]
Abstract
The neuronal doctrine, developed a century ago regards neuronal networks as the sole substrate of higher brain function. Recent advances in glial physiology have promoted an alternative hypothesis, which places information processing in the brain into integrated neuronal-glial networks utilizing both binary (neuronal action potentials) and analogue (diffusional propagation of second messengers/metabolites through gap junctions or transmitters through the interstitial space) signal encoding. It has been proposed that the feed-forward and feed-back communication between these two types of neural cells, which underlies information transfer and processing, is accomplished by the release of neurotransmitters from neuronal terminals as well as from astroglial processes. Understanding of this subject, however, remains incomplete and important questions and controversies require resolution. Here we propose that the primary function of perisynaptic glial processes is to create an "astroglial cradle" that shields the synapse from a multitude of extrasynaptic signaling events and provides for multifaceted support and long-term plasticity of synaptic contacts through variety of mechanisms, which may not necessarily involve the release of "glio" transmitters.
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Affiliation(s)
- Maiken Nedergaard
- Division of Glia Disease and Therapeutics, Department of Neurosurgery, Center for Translational Neuromedicine, University of Rochester Medical School, Rochester, NY 14580, USA.
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149
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Li D, Hérault K, Isacoff EY, Oheim M, Ropert N. Optogenetic activation of LiGluR-expressing astrocytes evokes anion channel-mediated glutamate release. J Physiol 2012; 590:855-73. [PMID: 22219341 DOI: 10.1113/jphysiol.2011.219345] [Citation(s) in RCA: 60] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Increases in astrocyte Ca(2+) have been suggested to evoke gliotransmitter release, however, the mechanism of release, the identity of such transmitter(s), and even whether and when such release occurs, are controversial, largely due to the lack of a method for selective and reproducible stimulation of electrically silent astrocytes. Here we show that photoactivation of the light-gated Ca(2+)-permeable ionotropic GluR6 glutamate receptor (LiGluR), and to a lesser extent the new Ca(2+)-translocating channelrhodopsin CatCh, evokes more reliable Ca(2+) elevation than the mutant channelrhodopsin 2, ChR2(H134R) in cultured cortical astrocytes. We used evanescent-field excitation for near-membrane Ca(2+) imaging, and epifluorescence to activate and inactivate LiGluR. By alternating activation and inactivation light pulses, the LiGluR-evoked Ca(2+) rises could be graded in amplitude and duration. The optical stimulation of LiGluR-expressing astrocytes evoked probabilistic glutamate-mediated signalling to adjacent LiGluR-non-expressing astrocytes. This astrocyte-to-astrocyte signalling was insensitive to the inactivation of vesicular release, hemichannels and glutamate-transporters, and sensitive to anion channel blockers. Our results show that LiGluR is a powerful tool to selectively and reproducibly activate astrocytes.
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Affiliation(s)
- Dongdong Li
- INSERM U603, CNRS UMR 8154, Laboratoire de Neurophysiologie et Nouvelles Microscopies, 45 rue des Saints Pères, Paris, F-75006 France.
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150
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Pirttimaki TM, Parri HR. Glutamatergic input-output properties of thalamic astrocytes. Neuroscience 2012; 205:18-28. [PMID: 22233780 PMCID: PMC3314995 DOI: 10.1016/j.neuroscience.2011.12.049] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2011] [Revised: 12/02/2011] [Accepted: 12/22/2011] [Indexed: 11/10/2022]
Abstract
Astrocytes in the somatosensory ventrobasal (VB) thalamus of rats respond to glutamatergic synaptic input with metabotropic glutamate receptor (mGluR) mediated intracellular calcium ([Ca2+]i) elevations. Astrocytes in the VB thalamus also release the gliotransmitter (GT) glutamate in a Ca2+-dependent manner. The tripartite synapse hypothesis posits that astrocytic [Ca2+]i elevations resulting from synaptic input releases gliotransmitters that then feedback to modify the synapse. Understanding the dynamics of this process and the conditions under which it occurs are therefore important steps in elucidating the potential roles and impact of GT release in particular brain activities. In this study, we investigated the relationship between VB thalamus afferent synaptic input and astrocytic glutamate release by recording N-methyl-d-aspartate (NMDA) receptor-mediated slow inward currents (SICs) elicited in neighboring neurons. We found that Lemniscal or cortical afferent stimulation, which can elicit astrocytic [Ca2+]i elevations, do not typically result in the generation of SICs in thalamocortical (TC) neurons. Rather, we find that the spontaneous emergence of SICs is largely resistant to acute afferent input. The frequency of SICs, however, is correlated to long-lasting afferent activity. In contrast to short-term stimulus-evoked GT release effects reported in other brain areas, astrocytes in the VB thalamus do not express a straightforward input–output relationship for SIC generation but exhibit integrative characteristics.
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Affiliation(s)
- T M Pirttimaki
- School of Life and Health Sciences, Aston University, Birmingham B4 7ET, UK
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