The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Martin Oheim - One of the best experts on this subject based on the ideXlab platform.
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astrocyte vamp3 vesicles undergo ca2 independent cycling and modulate glutamate transporter trafficking
The Journal of Physiology, 2015Co-Authors: Karine Herault, Kathleen Zylbersztejn, Martin Oheim, Marcel A. Lauterbach, Marc Guillon, Dongdong LiAbstract:Key points Mouse cortical astrocytes express VAMP3 but not VAMP2. VAMP3 vesicles undergo Ca2+-independent exo- and endocytotic cycling at the plasma membrane. VAMP3 vesicle traffic regulates the recycling of plasma membrane glutamate transporters. cAMP modulates VAMP3 vesicle cycling and glutamate uptake. Abstract Previous studies suggest that small synaptic-like vesicles in astrocytes carry vesicle-associated vSNARE proteins, VAMP3 (cellubrevin) and VAMP2 (synaptobrevin 2), both contributing to the Ca2+-regulated exocytosis of Gliotransmitters, thereby modulating brain information processing. Here, using cortical astrocytes taken from VAMP2 and VAMP3 knock-out mice, we find that astrocytes express only VAMP3. The morphology and function of VAMP3 vesicles were studied in cultured astrocytes at single vesicle level with stimulated emission depletion (STED) and total internal reflection fluorescence (TIRF) microscopies. We show that VAMP3 antibodies label small diameter (∼80 nm) vesicles and that VAMP3 vesicles undergo Ca2+-independent exo-endocytosis. We also show that this pathway modulates the surface expression of plasma membrane glutamate transporters and the glutamate uptake by astrocytes. Finally, using pharmacological and optogenetic tools, we provide evidence suggesting that the cytosolic cAMP level influences astrocytic VAMP3 vesicle trafficking and glutamate transport. Our results suggest a new role for VAMP3 vesicles in astrocytes.
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Lack of Evidence for Vesicular Glutamate Transporter Expression in Mouse Astrocytes
Journal of Neuroscience, 2013Co-Authors: Karine Herault, Martin Oheim, Kaetlin Silm, Alexis Evrard, Sonja Wojcik, Etienne Herzog, Nicole RopertAbstract:The concept of a tripartite synapse including a presynaptic terminal, a postsynaptic spine, and an astrocytic process that responds to neuronal activity by fast Gliotransmitter release, confers to the electrically silent astrocytes an active role in information processing. However, the mechanisms of Gliotransmitter release are still highly controversial. The reported expression of all three vesicular glutamatetransporters(VGLUT1-3) by astrocytes suggests that astrocytes, like neurons, may release glutamate by exocytosis. However, the demonstration of astrocytic VGLUT expression is largely based on immunostaining, and the possibility of nonspecific labeling needs to be systematically addressed. We therefore examined the expression of VGLUT1-3 in astrocytes, both in culture and in situ. We used Western blots and single-vesicle imaging by total internal reflection fluorescence microscopy in live cultured astrocytes, and confocal microscopy, at the cellular level in cortical, hippocampal, and cerebellar brain slices, combined with quantitative image analysis. Control experiments were systematically performed in cultured astrocytes using wild-type, VGLUT1-3 knock-out, VGLUT1(Venus) knock-in, and VGLUT2-EGFP transgenic mice. In fixed brain slices, we quantified the degree of overlap between VGLUT1-3 and neuronal or astrocytic markers, both in an object-based manner using fluorescence line profiles, and in a pixel-based manner using dual-color scatter plots followed by the calculation of Pearson's correlation coefficient over all pixels with intensities significantly different from background. Our data provide no evidence in favor of the expression of any of the three VGLUTs by gray matter protoplasmic astrocytes of the primary somatosensory cortex, the thalamic ventrobasal nucleus, the hippocampus, and the cerebellum.
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optogenetic activation of liglur expressing astrocytes evokes anion channel mediated glutamate release
The Journal of Physiology, 2012Co-Authors: Karine Herault, Martin Oheim, Ehud Y Isacoff, Nicole RopertAbstract:Non-technical summary Ca2+ increases in astrocytes have been suggested to trigger the release of neuroactive compounds called Gliotransmitters. To study the mechanism of Gliotransmitter release, it is desirable to have a method able to selectively and reproducibly evoke Ca2+ increases in astrocytes. Here, we show that the optogenetic tool the light-gated glutamate receptor 6 (LiGluR) reproducibly evokes Ca2+ rises in cultured astrocytes. Combining LiGluR photoactivation and evanescent-field Ca2+ imaging, we explored the cellular mechanism of Gliotransmitter release from astrocytes in an all-optical manner. The results suggest that high Ca2+ in astrocytes triggers the release of glutamate via anion channels rather than vesicular exocytosis. Abstract Increases in astrocyte Ca2+ 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 Ca2+-permeable ionotropic GluR6 glutamate receptor (LiGluR), and to a lesser extent the new Ca2+-translocating channelrhodopsin CatCh, evokes more reliable Ca2+ elevation than the mutant channelrhodopsin 2, ChR2(H134R) in cultured cortical astrocytes. We used evanescent-field excitation for near-membrane Ca2+ imaging, and epifluorescence to activate and inactivate LiGluR. By alternating activation and inactivation light pulses, the LiGluR-evoked Ca2+ 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.
Kathleen Zylbersztejn - One of the best experts on this subject based on the ideXlab platform.
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astrocyte vamp3 vesicles undergo ca2 independent cycling and modulate glutamate transporter trafficking
The Journal of Physiology, 2015Co-Authors: Karine Herault, Kathleen Zylbersztejn, Martin Oheim, Marcel A. Lauterbach, Marc Guillon, Dongdong LiAbstract:Key points Mouse cortical astrocytes express VAMP3 but not VAMP2. VAMP3 vesicles undergo Ca2+-independent exo- and endocytotic cycling at the plasma membrane. VAMP3 vesicle traffic regulates the recycling of plasma membrane glutamate transporters. cAMP modulates VAMP3 vesicle cycling and glutamate uptake. Abstract Previous studies suggest that small synaptic-like vesicles in astrocytes carry vesicle-associated vSNARE proteins, VAMP3 (cellubrevin) and VAMP2 (synaptobrevin 2), both contributing to the Ca2+-regulated exocytosis of Gliotransmitters, thereby modulating brain information processing. Here, using cortical astrocytes taken from VAMP2 and VAMP3 knock-out mice, we find that astrocytes express only VAMP3. The morphology and function of VAMP3 vesicles were studied in cultured astrocytes at single vesicle level with stimulated emission depletion (STED) and total internal reflection fluorescence (TIRF) microscopies. We show that VAMP3 antibodies label small diameter (∼80 nm) vesicles and that VAMP3 vesicles undergo Ca2+-independent exo-endocytosis. We also show that this pathway modulates the surface expression of plasma membrane glutamate transporters and the glutamate uptake by astrocytes. Finally, using pharmacological and optogenetic tools, we provide evidence suggesting that the cytosolic cAMP level influences astrocytic VAMP3 vesicle trafficking and glutamate transport. Our results suggest a new role for VAMP3 vesicles in astrocytes.
Dongdong Li - One of the best experts on this subject based on the ideXlab platform.
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astrocyte vamp3 vesicles undergo ca2 independent cycling and modulate glutamate transporter trafficking
The Journal of Physiology, 2015Co-Authors: Karine Herault, Kathleen Zylbersztejn, Martin Oheim, Marcel A. Lauterbach, Marc Guillon, Dongdong LiAbstract:Key points Mouse cortical astrocytes express VAMP3 but not VAMP2. VAMP3 vesicles undergo Ca2+-independent exo- and endocytotic cycling at the plasma membrane. VAMP3 vesicle traffic regulates the recycling of plasma membrane glutamate transporters. cAMP modulates VAMP3 vesicle cycling and glutamate uptake. Abstract Previous studies suggest that small synaptic-like vesicles in astrocytes carry vesicle-associated vSNARE proteins, VAMP3 (cellubrevin) and VAMP2 (synaptobrevin 2), both contributing to the Ca2+-regulated exocytosis of Gliotransmitters, thereby modulating brain information processing. Here, using cortical astrocytes taken from VAMP2 and VAMP3 knock-out mice, we find that astrocytes express only VAMP3. The morphology and function of VAMP3 vesicles were studied in cultured astrocytes at single vesicle level with stimulated emission depletion (STED) and total internal reflection fluorescence (TIRF) microscopies. We show that VAMP3 antibodies label small diameter (∼80 nm) vesicles and that VAMP3 vesicles undergo Ca2+-independent exo-endocytosis. We also show that this pathway modulates the surface expression of plasma membrane glutamate transporters and the glutamate uptake by astrocytes. Finally, using pharmacological and optogenetic tools, we provide evidence suggesting that the cytosolic cAMP level influences astrocytic VAMP3 vesicle trafficking and glutamate transport. Our results suggest a new role for VAMP3 vesicles in astrocytes.
Karine Herault - One of the best experts on this subject based on the ideXlab platform.
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astrocyte vamp3 vesicles undergo ca2 independent cycling and modulate glutamate transporter trafficking
The Journal of Physiology, 2015Co-Authors: Karine Herault, Kathleen Zylbersztejn, Martin Oheim, Marcel A. Lauterbach, Marc Guillon, Dongdong LiAbstract:Key points Mouse cortical astrocytes express VAMP3 but not VAMP2. VAMP3 vesicles undergo Ca2+-independent exo- and endocytotic cycling at the plasma membrane. VAMP3 vesicle traffic regulates the recycling of plasma membrane glutamate transporters. cAMP modulates VAMP3 vesicle cycling and glutamate uptake. Abstract Previous studies suggest that small synaptic-like vesicles in astrocytes carry vesicle-associated vSNARE proteins, VAMP3 (cellubrevin) and VAMP2 (synaptobrevin 2), both contributing to the Ca2+-regulated exocytosis of Gliotransmitters, thereby modulating brain information processing. Here, using cortical astrocytes taken from VAMP2 and VAMP3 knock-out mice, we find that astrocytes express only VAMP3. The morphology and function of VAMP3 vesicles were studied in cultured astrocytes at single vesicle level with stimulated emission depletion (STED) and total internal reflection fluorescence (TIRF) microscopies. We show that VAMP3 antibodies label small diameter (∼80 nm) vesicles and that VAMP3 vesicles undergo Ca2+-independent exo-endocytosis. We also show that this pathway modulates the surface expression of plasma membrane glutamate transporters and the glutamate uptake by astrocytes. Finally, using pharmacological and optogenetic tools, we provide evidence suggesting that the cytosolic cAMP level influences astrocytic VAMP3 vesicle trafficking and glutamate transport. Our results suggest a new role for VAMP3 vesicles in astrocytes.
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Lack of Evidence for Vesicular Glutamate Transporter Expression in Mouse Astrocytes
Journal of Neuroscience, 2013Co-Authors: Karine Herault, Martin Oheim, Kaetlin Silm, Alexis Evrard, Sonja Wojcik, Etienne Herzog, Nicole RopertAbstract:The concept of a tripartite synapse including a presynaptic terminal, a postsynaptic spine, and an astrocytic process that responds to neuronal activity by fast Gliotransmitter release, confers to the electrically silent astrocytes an active role in information processing. However, the mechanisms of Gliotransmitter release are still highly controversial. The reported expression of all three vesicular glutamatetransporters(VGLUT1-3) by astrocytes suggests that astrocytes, like neurons, may release glutamate by exocytosis. However, the demonstration of astrocytic VGLUT expression is largely based on immunostaining, and the possibility of nonspecific labeling needs to be systematically addressed. We therefore examined the expression of VGLUT1-3 in astrocytes, both in culture and in situ. We used Western blots and single-vesicle imaging by total internal reflection fluorescence microscopy in live cultured astrocytes, and confocal microscopy, at the cellular level in cortical, hippocampal, and cerebellar brain slices, combined with quantitative image analysis. Control experiments were systematically performed in cultured astrocytes using wild-type, VGLUT1-3 knock-out, VGLUT1(Venus) knock-in, and VGLUT2-EGFP transgenic mice. In fixed brain slices, we quantified the degree of overlap between VGLUT1-3 and neuronal or astrocytic markers, both in an object-based manner using fluorescence line profiles, and in a pixel-based manner using dual-color scatter plots followed by the calculation of Pearson's correlation coefficient over all pixels with intensities significantly different from background. Our data provide no evidence in favor of the expression of any of the three VGLUTs by gray matter protoplasmic astrocytes of the primary somatosensory cortex, the thalamic ventrobasal nucleus, the hippocampus, and the cerebellum.
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optogenetic activation of liglur expressing astrocytes evokes anion channel mediated glutamate release
The Journal of Physiology, 2012Co-Authors: Karine Herault, Martin Oheim, Ehud Y Isacoff, Nicole RopertAbstract:Non-technical summary Ca2+ increases in astrocytes have been suggested to trigger the release of neuroactive compounds called Gliotransmitters. To study the mechanism of Gliotransmitter release, it is desirable to have a method able to selectively and reproducibly evoke Ca2+ increases in astrocytes. Here, we show that the optogenetic tool the light-gated glutamate receptor 6 (LiGluR) reproducibly evokes Ca2+ rises in cultured astrocytes. Combining LiGluR photoactivation and evanescent-field Ca2+ imaging, we explored the cellular mechanism of Gliotransmitter release from astrocytes in an all-optical manner. The results suggest that high Ca2+ in astrocytes triggers the release of glutamate via anion channels rather than vesicular exocytosis. Abstract Increases in astrocyte Ca2+ 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 Ca2+-permeable ionotropic GluR6 glutamate receptor (LiGluR), and to a lesser extent the new Ca2+-translocating channelrhodopsin CatCh, evokes more reliable Ca2+ elevation than the mutant channelrhodopsin 2, ChR2(H134R) in cultured cortical astrocytes. We used evanescent-field excitation for near-membrane Ca2+ imaging, and epifluorescence to activate and inactivate LiGluR. By alternating activation and inactivation light pulses, the LiGluR-evoked Ca2+ 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.
Philip G Haydon - One of the best experts on this subject based on the ideXlab platform.
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septal cholinergic neuromodulation tunes the astrocyte dependent gating of hippocampal nmda receptors to wakefulness
Neuron, 2017Co-Authors: Thomas Papouin, Jaclyn M Dunphy, Michaela Tolman, Kelly T Dineley, Philip G HaydonAbstract:Summary The activation of the N-methyl D-aspartate receptor (NMDAR) is controlled by a glutamate-binding site and a distinct, independently regulated, co-agonist-binding site. In most brain regions, the NMDAR co-agonist is the astrocyte-derived Gliotransmitter D-serine. We found that D-serine levels oscillate in mouse hippocampus as a function of wakefulness, in vitro and in vivo. This causes a full saturation of the NMDAR co-agonist site in the dark (active) phase that dissipates to sub-saturating levels during the light (sleep) phase, and influences learning performance throughout the day. We demonstrate that hippocampal astrocytes sense the wakefulness-dependent activity of septal cholinergic fibers through the α7-nicotinic acetylcholine receptor (α7nAChR), whose activation drives D-serine release. We conclude that astrocytes tune the gating of synaptic NMDARs to the vigilance state and demonstrate that this is directly relevant to schizophrenia, a disorder characterized by NMDAR and cholinergic hypofunctions. Indeed, bypassing cholinergic activity with a clinically tested α7nAChR agonist successfully enhances NMDAR activation. Video Abstract
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glial cells in patho physiology
Journal of Neurochemistry, 2012Co-Authors: Vladimir Parpura, Philip G Haydon, Stéphane H. R. Oliet, Andreas Reichenbach, Michael T Heneka, Vedrana Montana, Arne Schousboe, Randy F Stout, David C Spray, Thomas PannickeAbstract: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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integrated brain circuits astrocytic networks modulate neuronal activity and behavior
Annual Review of Physiology, 2010Co-Authors: Michael M Halassa, Philip G HaydonAbstract:The past decade has seen an explosion of research on roles of neuron-astrocyte interactions in the control of brain function. We highlight recent studies performed on the tripartite synapse, the structure consisting of pre- and postsynaptic elements of the synapse and an associated astrocytic process. Astrocytes respond to neuronal activity and neurotransmitters, through the activation of metabotropic receptors, and can release the Gliotransmitters ATP, d-serine, and glutamate, which act on neurons. Astrocyte-derived ATP modulates synaptic transmission, either directly or through its metabolic product adenosine. d-serine modulates NMDA receptor function, whereas glia-derived glutamate can play important roles in relapse following withdrawal from drugs of abuse. Cell type–specific molecular genetics has allowed a new level of examination of the function of astrocytes in brain function and has revealed an important role of these glial cells that is mediated by adenosine accumulation in the control of sleep ...
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synaptic islands defined by the territory of a single astrocyte
The Journal of Neuroscience, 2007Co-Authors: Michael M Halassa, Hajime Takano, Tommaso Fellin, Jinghui Dong, Philip G HaydonAbstract:In the mammalian brain, astrocytes modulate neuronal function, in part, by synchronizing neuronal firing and coordinating synaptic networks. Little, however, is known about how this is accomplished from a structural standpoint. To investigate the structural basis of astrocyte-mediated neuronal synchrony and synaptic coordination, the three-dimensional relationships between cortical astrocytes and neurons was investigated. Using a transgenic and viral approach to label astrocytes with enhanced green fluorescent protein, we performed a three-dimensional reconstruction of astrocytes from tissue sections or live animals in vivo. We found that cortical astrocytes occupy nonoverlapping territories similar to those described in the hippocampus. Using immunofluorescence labeling of neuronal somata, a single astrocyte enwraps on average four neuronal somata with an upper limit of eight. Single-neuron dye-fills allowed us to estimate that one astrocyte contacts 300–600 neuronal dendrites. Together with the recent findings showing that glial Ca2+ signaling is restricted to individual astrocytes in vivo, and that Ca2+ signaling leads to gliotransmission, we propose the concept of functional islands of synapses in which groups of synapses confined within the boundaries of an individual astrocyte are modulated by the Gliotransmitter environment controlled by that astrocyte. Our description offers a new structurally based conceptual framework to evaluate functional data involving interactions between neurons and astrocytes in the mammalian brain.
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the tripartite synapse roles for gliotransmission in health and disease
Trends in Molecular Medicine, 2007Co-Authors: Michael M Halassa, Tommaso Fellin, Philip G HaydonAbstract:In addition to being essential supporters of neuronal function, astrocytes are now recognized as active elements in the brain. Astrocytes sense and integrate synaptic activity and, depending on intracellular Ca 2+ levels, release Gliotransmitters (e.g. glutamate, d-serine and ATP) that have feedback actions on neurons. Recent experimental results have raised the possibility that quantitative variations in gliotransmission might contribute to disorders of the nervous system. Here, we discuss targeted molecular genetic approaches that have demonstrated that alterations in protein expression in astrocytes can lead to serious changes in neuronal function. We also introduce the concept of ‘astrocyte activation spectrum' in which enhanced and reduced gliotransmission might contribute to epilepsy and schizophrenia, respectively. The results of future experimental tests of the astrocyte activation spectrum, which relates gliotransmission to neurological and psychiatric disorders, might point to a new therapeutic target in the brain.