951
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Astrocytes impose postburst depression of release probability at hippocampal glutamate synapses. J Neurosci 2010; 30:5776-80. [PMID: 20410129 DOI: 10.1523/jneurosci.3957-09.2010] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Many neurons typically fire action potentials in brief, high-frequency bursts with specific consequences for their synaptic output. Here we have examined short-term plasticity engaged during burst activation using electrophysiological recordings in acute rat hippocampal slices. We show that CA3-CA1 glutamate synapses exhibit a prominent depression of presynaptic release probability for approximately 1 s after such a burst. This postburst depression exhibits a distinct cooperativity threshold, is abolished by inhibiting astrocyte metabolism and astrocyte calcium signaling, and is not operational in the developing hippocampus. Our results suggest that astrocytes are actively involved in short-term synaptic depression, shaping synaptic activity during behaviorally relevant neural activity.
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952
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Abstract
In December 2009, Glenn Hatton died, and neuroendocrinology lost a pioneer who had done much to forge our present understanding of the hypothalamus and whose productivity had not faded with the passing years. Glenn, an expert in both functional morphology and electrophysiology, was driven by a will to understand the significance of his observations in the context of the living, behaving organism. He also had the wit to generate bold and challenging hypotheses, the wherewithal to expose them to critical and elegant experimental testing, and a way with words that gave his papers and lectures clarity and eloquence. The hypothalamo-neurohypophysial system offered a host of opportunities for understanding how physiological functions are fulfilled by the electrical activity of neurones, how neuronal behaviour changes with changing physiological states, and how morphological changes contribute to the physiological response. In the vision that Glenn developed over 35 years, the neuroendocrine brain is as dynamic in structure as it is adaptable in function. Its adaptability is reflected not only by mere synaptic plasticity, but also by changes in neuronal morphology and in the morphology of the glial cells. Astrocytes, in Glenn's view, were intimate partners of the neurones, partners with an essential role in adaptation to changing physiological demands.
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Affiliation(s)
- G Leng
- Centre for Integrative Physiology, University of Edinburgh, Edinburgh EH8 9XD, UK.
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954
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Gómez-Gonzalo M, Losi G, Chiavegato A, Zonta M, Cammarota M, Brondi M, Vetri F, Uva L, Pozzan T, de Curtis M, Ratto GM, Carmignoto G. An excitatory loop with astrocytes contributes to drive neurons to seizure threshold. PLoS Biol 2010; 8:e1000352. [PMID: 20405049 PMCID: PMC2854117 DOI: 10.1371/journal.pbio.1000352] [Citation(s) in RCA: 168] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2009] [Accepted: 03/02/2010] [Indexed: 11/24/2022] Open
Abstract
Studies in rodent brain slices suggest that seizures in focal epilepsies are sustained and propagated by the reciprocal interaction between neurons and astroglial cells Seizures in focal epilepsies are sustained by a highly synchronous neuronal discharge that arises at restricted brain sites and subsequently spreads to large portions of the brain. Despite intense experimental research in this field, the earlier cellular events that initiate and sustain a focal seizure are still not well defined. Their identification is central to understand the pathophysiology of focal epilepsies and to develop new pharmacological therapies for drug-resistant forms of epilepsy. The prominent involvement of astrocytes in ictogenesis was recently proposed. We test here whether a cooperation between astrocytes and neurons is a prerequisite to support ictal (seizure-like) and interictal epileptiform events. Simultaneous patch-clamp recording and Ca2+ imaging techniques were performed in a new in vitro model of focal seizures induced by local applications of N-methyl-D-aspartic acid (NMDA) in rat entorhinal cortex slices. We found that a Ca2+ elevation in astrocytes correlates with both the initial development and the maintenance of a focal, seizure-like discharge. A delayed astrocyte activation during ictal discharges was also observed in other models (including the whole in vitro isolated guinea pig brain) in which the site of generation of seizure activity cannot be precisely monitored. In contrast, interictal discharges were not associated with Ca2+ changes in astrocytes. Selective inhibition or stimulation of astrocyte Ca2+ signalling blocked or enhanced, respectively, ictal discharges, but did not affect interictal discharge generation. Our data reveal that neurons engage astrocytes in a recurrent excitatory loop (possibly involving gliotransmission) that promotes seizure ignition and sustains the ictal discharge. This neuron–astrocyte interaction may represent a novel target to develop effective therapeutic strategies to control seizures. In focal epilepsy, seizures are generated by a localized, synchronous neuronal electrical discharge that may spread to large portions of the brain. Despite intense experimental research in this field, a key question relevant to the human epilepsy condition remains completely unanswered: what are the cellular events that lead to the onset of a seizure in the first place? In various in vitro models of seizures using rodent brain slices, we simultaneously recorded neuronal firing and Ca2+ signals both from neurons and from astrocytes, the principal population of glial cells in the brain. We found that activation of astrocytes by neuronal activity and signalling from astrocytes back to neurons contribute to the initiation of a focal seizure. This reciprocal excitatory loop between neurons and astrocytes represents a new mechanism in the pathophysiology of epilepsy that should be considered by those aiming to develop more effective therapies for epilepsies that are not controlled by currently available treatments.
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Affiliation(s)
- Marta Gómez-Gonzalo
- Institute of Neuroscience – Consiglio Nazionale delle Ricerche (CNR), University of Padova, Padova, Italy
- Department of Experimental Biomedical Sciences, University of Padova, Padova, Italy
| | - Gabriele Losi
- Institute of Neuroscience – Consiglio Nazionale delle Ricerche (CNR), University of Padova, Padova, Italy
- Department of Experimental Biomedical Sciences, University of Padova, Padova, Italy
| | - Angela Chiavegato
- Institute of Neuroscience – Consiglio Nazionale delle Ricerche (CNR), University of Padova, Padova, Italy
- Department of Experimental Biomedical Sciences, University of Padova, Padova, Italy
| | - Micaela Zonta
- Institute of Neuroscience – Consiglio Nazionale delle Ricerche (CNR), University of Padova, Padova, Italy
- Department of Experimental Biomedical Sciences, University of Padova, Padova, Italy
| | - Mario Cammarota
- Institute of Neuroscience – Consiglio Nazionale delle Ricerche (CNR), University of Padova, Padova, Italy
- Department of Experimental Biomedical Sciences, University of Padova, Padova, Italy
| | - Marco Brondi
- National Enterprise for nanoScience and nanoTechnology (NEST), Instituto Nanoscienze CNR, Scuola Normale Superiore, Pisa, Italy
- Institute of Neuroscience – CNR, Pisa, Italy
| | | | - Laura Uva
- Fondazione Istituto Neurologico Carlo Besta, Milano, Italy
| | - Tullio Pozzan
- Institute of Neuroscience – Consiglio Nazionale delle Ricerche (CNR), University of Padova, Padova, Italy
- Department of Experimental Biomedical Sciences, University of Padova, Padova, Italy
- Venetian Institute of Molecular Medicine, Padova, Italy
| | | | - Gian Michele Ratto
- National Enterprise for nanoScience and nanoTechnology (NEST), Instituto Nanoscienze CNR, Scuola Normale Superiore, Pisa, Italy
- Institute of Neuroscience – CNR, Pisa, Italy
| | - Giorgio Carmignoto
- Institute of Neuroscience – Consiglio Nazionale delle Ricerche (CNR), University of Padova, Padova, Italy
- Department of Experimental Biomedical Sciences, University of Padova, Padova, Italy
- * E-mail:
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955
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Abstract
In the past 20 years, an extra layer of information processing, in addition to that provided by neurons, has been proposed for the CNS. Neuronally evoked increases of the intracellular calcium concentration in astrocytes have been suggested to trigger exocytotic release of the 'gliotransmitters' glutamate, ATP and D-serine. These are proposed to modulate neuronal excitability and transmitter release, and to have a role in diseases as diverse as stroke, epilepsy, schizophrenia, Alzheimer's disease and HIV infection. However, there is intense controversy about whether astrocytes can exocytose transmitters in vivo. Resolving this issue would considerably advance our understanding of brain function.
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956
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Greenwood SM, Bushell TJ. Astrocytic activation and an inhibition of MAP kinases are required for proteinase-activated receptor-2-mediated protection from neurotoxicity. J Neurochem 2010; 113:1471-80. [PMID: 20402964 DOI: 10.1111/j.1471-4159.2010.06737.x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Proteinase-activated receptor-2 (PAR-2) expression levels are altered in several CNS disorders with these changes being proposed to either exacerbate or diminish the disease state depending on the cell type in which this occurs. Here we present data investigating the consequence of PAR-2 activation on kainate (KA)-induced neurotoxicity in organotypic hippocampal slices cultures (OHSC). Exposure of OHSC to the PAR-2 activators trypsin or Ser-Leu-Ile-Gly-Arg-Leu (SLIGRL) induced no neurotoxicity when applied alone but was neuroprotective against KA-induced neurotoxicity. SLIGRL-mediated neuroprotection involved astrocytic activation as the neuroprotective effect was abolished following OHSC pre-treatment with fluoroacetate. Moreover, co-application of either reparixin or LY341495, antagonists of the CXCR2 chemokine receptor and metabotropic glutamate receptors respectively, inhibited the SLIGRL-mediated neuroprotection. SLIGRL application inhibited both p38 MAPK and ERK activity in OHSC, but not the JNK 1/2 signalling pathway. Accordingly, the co-application of the p38 MAPK and ERK inhibitors SB203580 and UO126 reduced KA-induced cell death, mimicking PAR-2-mediated neuroprotection. These data indicate that PAR-2 activation is neuroprotective and involves astrocytic activation, gliotransmitter release, and the subsequent inhibition of MAPK signalling cascades, providing further evidence for PAR-2 as an interesting therapeutic target in certain CNS disorders.
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Affiliation(s)
- Sam M Greenwood
- Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, Glasgow, UK
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957
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Rosenberg D, Kartvelishvily E, Shleper M, Klinker CMC, Bowser MT, Wolosker H. Neuronal release of D-serine: a physiological pathway controlling extracellular D-serine concentration. FASEB J 2010; 24:2951-61. [PMID: 20371631 DOI: 10.1096/fj.09-147967] [Citation(s) in RCA: 100] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
D-serine is thought to be a glia-derived transmitter that activates N-methyl D-aspartate receptors (NMDARs) in the brain. Here, we investigate the pathways for D-serine release using primary cultures, brain slices, and in vivo microdialysis. In contrast with the notion that D-serine is exclusively released from astrocytes, we found that D-serine is released by neuronal depolarization both in vitro and in vivo. Veratridine (50 microM) or depolarization by 40 mM KCl elicits a significant release of endogenous D-serine from primary neuronal cultures. Controls with astrocyte cultures indicate that glial cells are insensitive to veratridine, but release D-serine mainly by the opening of volume-regulated anion channels. In cortical slices perfused with veratridine, endogenous D-serine release is 10-fold higher than glutamate receptor-evoked release. Release of D-serine from slices does not require internal or external Ca(2+), suggesting a nonvesicular release mechanism. To confirm the neuronal origin of D-serine, we selectively loaded neurons in cortical slices with D-[(3)H]serine or applied D-alanine, which specifically releases D-serine from neurons. Depolarization with veratridine promotes D-serine release in vivo monitored by high temporal resolution microdialysis of the striatum. Our data indicate that the neuronal pool of D-serine plays a major role in D-serine dynamics, with implications for the regulation of NMDAR transmission.
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Affiliation(s)
- Dina Rosenberg
- Department of Biochemistry, B. Rappaport Faculty of Medicine, Technion-Israel Institute of Technology, Haifa 31096, Israel
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959
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Glia: the many ways to modulate synaptic plasticity. Neurochem Int 2010; 57:440-5. [PMID: 20193723 DOI: 10.1016/j.neuint.2010.02.013] [Citation(s) in RCA: 165] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2009] [Revised: 02/15/2010] [Accepted: 02/19/2010] [Indexed: 11/21/2022]
Abstract
Synaptic plasticity consists in a change in synaptic strength that is believed to be the basis of learning and memory. Synaptic plasticity has been for a very long period of time a hallmark of neurons. Recent advances in physiology of glial cells indicate that astrocyte and microglia possess all the features to participate and modulate the various form of synaptic plasticity. Indeed beside their respective supportive and immune functions an increasing number of study demonstrate that astrocytes and microglia express receptors for most neurotransmitters and release neuroactive substances that have been shown to modulate neuronal activity and synaptic plasticity. Because glial cells are all around synapses and release a wide variety of neuroactive molecule during physiological and pathological conditions, glial cells have been reported to modulate synaptic plasticity in many different ways. From change in synaptic coverage, to release of chemokines and cytokines up to dedicated "glio" transmitters release, glia were reported to affect synaptic scaling, homeostatic plasticity, metaplasticity, long-term potentiation and long-term depression.
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