51
|
Abstract
Neuroglia, the "glue" that fills the space between neurons in the central nervous system, takes active part in nerve cell signaling. Neuroglial cells, astroglia, oligodendroglia, and microglia, are together about as numerous as neurons in the brain as a whole, and in the cerebral cortex grey matter, but the proportion varies widely among brain regions. Glial volume, however, is less than one-fifth of the tissue volume in grey matter. When stimulated by neurons or other cells, neuroglial cells release gliotransmitters by exocytosis, similar to neurotransmitter release from nerve endings, or by carrier-mediated transport or channel flux through the plasma membrane. Gliotransmitters include the common neurotransmitters glutamate and GABA, the nonstandard amino acid d-serine, the high-energy phosphate ATP, and l-lactate. The latter molecule is a "buffer" between glycolytic and oxidative metabolism as well as a signaling substance recently shown to act on specific lactate receptors in the brain. Complementing neurotransmission at a synapse, neuroglial transmission often implies diffusion of the transmitter over a longer distance and concurs with the concept of volume transmission. Transmission from glia modulates synaptic neurotransmission based on energetic and other local conditions in a volume of tissue surrounding the individual synapse. Neuroglial transmission appears to contribute significantly to brain functions such as memory, as well as to prevalent neuropathologies.
Collapse
Affiliation(s)
- Vidar Gundersen
- SN-Lab, Division of Anatomy, Department of Molecular Medicine, Institute of Basic Medical Sciences, and CMBN/SERTA/Healthy Brain Ageing Centre, University of Oslo, Oslo, Norway; Department of Neurology, Oslo University Hospital-Rikshospitalet, Oslo, Norway; Center for Healthy Aging, Department of Neuroscience and Pharmacology, Faculty of Health Sciences, University of Copenhagen, Copenhagen, Denmark; and Brain and Muscle Energy Group, Department of Oral Biology and Division of Anatomy, Department of Molecular Medicine, University of Oslo, Oslo, Norway
| | - Jon Storm-Mathisen
- SN-Lab, Division of Anatomy, Department of Molecular Medicine, Institute of Basic Medical Sciences, and CMBN/SERTA/Healthy Brain Ageing Centre, University of Oslo, Oslo, Norway; Department of Neurology, Oslo University Hospital-Rikshospitalet, Oslo, Norway; Center for Healthy Aging, Department of Neuroscience and Pharmacology, Faculty of Health Sciences, University of Copenhagen, Copenhagen, Denmark; and Brain and Muscle Energy Group, Department of Oral Biology and Division of Anatomy, Department of Molecular Medicine, University of Oslo, Oslo, Norway
| | - Linda Hildegard Bergersen
- SN-Lab, Division of Anatomy, Department of Molecular Medicine, Institute of Basic Medical Sciences, and CMBN/SERTA/Healthy Brain Ageing Centre, University of Oslo, Oslo, Norway; Department of Neurology, Oslo University Hospital-Rikshospitalet, Oslo, Norway; Center for Healthy Aging, Department of Neuroscience and Pharmacology, Faculty of Health Sciences, University of Copenhagen, Copenhagen, Denmark; and Brain and Muscle Energy Group, Department of Oral Biology and Division of Anatomy, Department of Molecular Medicine, University of Oslo, Oslo, Norway
| |
Collapse
|
52
|
Kim J, Waldvogel HJ, Faull RLM, Curtis MA, Nicholson LFB. The RAGE receptor and its ligands are highly expressed in astrocytes in a grade-dependant manner in the striatum and subependymal layer in Huntington's disease. J Neurochem 2015; 134:927-42. [DOI: 10.1111/jnc.13178] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2015] [Revised: 05/04/2015] [Accepted: 05/13/2015] [Indexed: 11/30/2022]
Affiliation(s)
- Joanne Kim
- Department of Anatomy with Radiology; Faculty of Medical and Health Science (FMHS); University of Auckland; Auckland New Zealand
- Centre for Brain Research; Faculty of Medical and Health Science (FMHS); University of Auckland; Auckland New Zealand
| | - Henry J. Waldvogel
- Department of Anatomy with Radiology; Faculty of Medical and Health Science (FMHS); University of Auckland; Auckland New Zealand
- Centre for Brain Research; Faculty of Medical and Health Science (FMHS); University of Auckland; Auckland New Zealand
| | - Richard L. M. Faull
- Department of Anatomy with Radiology; Faculty of Medical and Health Science (FMHS); University of Auckland; Auckland New Zealand
- Centre for Brain Research; Faculty of Medical and Health Science (FMHS); University of Auckland; Auckland New Zealand
| | - Maurice A. Curtis
- Department of Anatomy with Radiology; Faculty of Medical and Health Science (FMHS); University of Auckland; Auckland New Zealand
- Centre for Brain Research; Faculty of Medical and Health Science (FMHS); University of Auckland; Auckland New Zealand
| | - Louise F. B. Nicholson
- Department of Anatomy with Radiology; Faculty of Medical and Health Science (FMHS); University of Auckland; Auckland New Zealand
- Centre for Brain Research; Faculty of Medical and Health Science (FMHS); University of Auckland; Auckland New Zealand
| |
Collapse
|
53
|
Li D, Hérault K, Zylbersztejn K, Lauterbach MA, Guillon M, Oheim M, Ropert N. Astrocyte VAMP3 vesicles undergo Ca2+ -independent cycling and modulate glutamate transporter trafficking. J Physiol 2015; 593:2807-32. [PMID: 25864578 DOI: 10.1113/jp270362] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2015] [Accepted: 04/07/2015] [Indexed: 01/26/2023] Open
Abstract
KEY POINTS Mouse cortical astrocytes express VAMP3 but not VAMP2. VAMP3 vesicles undergo Ca(2+) -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 Ca(2+) -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 Ca(2+) -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.
Collapse
Affiliation(s)
- Dongdong Li
- CNRS UMR 8118, Paris, F-75006 France; Brain Physiology Laboratory, Saints-Pères Research in Neurosciences Federation, Université Paris Descartes, Sorbonne Paris Cité, 45 rue des Saints Pères, Paris, F-75006, France.,INSERM U603, Paris, F-75006 France; CNRS UMR 8154, Paris, F-75006 France, Neurophysiology and New Microscopies Laboratory, 45 rue des Saints Pères, Paris, F-75006, France
| | - Karine Hérault
- CNRS UMR 8118, Paris, F-75006 France; Brain Physiology Laboratory, Saints-Pères Research in Neurosciences Federation, Université Paris Descartes, Sorbonne Paris Cité, 45 rue des Saints Pères, Paris, F-75006, France
| | - Kathleen Zylbersztejn
- INSERM ERL U950, Paris, F-75013, France.,Université Paris Diderot, Sorbonne Paris Cité, Paris, F-75013, France.,CNRS, UMR 7592, Institut Jacques Monod, Paris, F-75013, France
| | - Marcel A Lauterbach
- Neurophotonics Laboratory, CNRS UMR 8250, Université Paris Descartes, Sorbonne Paris Cité, 45 rue des Saints Pères, Paris, F-75006, France
| | - Marc Guillon
- Neurophotonics Laboratory, CNRS UMR 8250, Université Paris Descartes, Sorbonne Paris Cité, 45 rue des Saints Pères, Paris, F-75006, France
| | - Martin Oheim
- CNRS UMR 8118, Paris, F-75006 France; Brain Physiology Laboratory, Saints-Pères Research in Neurosciences Federation, Université Paris Descartes, Sorbonne Paris Cité, 45 rue des Saints Pères, Paris, F-75006, France.,INSERM U603, Paris, F-75006 France; CNRS UMR 8154, Paris, F-75006 France, Neurophysiology and New Microscopies Laboratory, 45 rue des Saints Pères, Paris, F-75006, France
| | - Nicole Ropert
- CNRS UMR 8118, Paris, F-75006 France; Brain Physiology Laboratory, Saints-Pères Research in Neurosciences Federation, Université Paris Descartes, Sorbonne Paris Cité, 45 rue des Saints Pères, Paris, F-75006, France.,INSERM U603, Paris, F-75006 France; CNRS UMR 8154, Paris, F-75006 France, Neurophysiology and New Microscopies Laboratory, 45 rue des Saints Pères, Paris, F-75006, France
| |
Collapse
|
54
|
Fleischer W, Theiss S, Slotta J, Holland C, Schnitzler A. High-frequency voltage oscillations in cultured astrocytes. Physiol Rep 2015; 3:3/5/e12400. [PMID: 25969464 PMCID: PMC4463829 DOI: 10.14814/phy2.12400] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
Because of their close interaction with neuronal physiology, astrocytes can modulate brain function in multiple ways. Here, we demonstrate a yet unknown astrocytic phenomenon: Astrocytes cultured on microelectrode arrays (MEAs) exhibited extracellular voltage fluctuations in a broad frequency spectrum (100–600 Hz) after electrical stimulation. These aperiodic high-frequency oscillations (HFOs) could last several seconds and did not spread across the MEA. The voltage-gated calcium channel antagonist cilnidipine dose-dependently decreased the power of the oscillations. While intracellular calcium was pivotal, incubation with bafilomycin A1 showed that vesicular release of transmitters played only a minor role in the emergence of HFOs. Gap junctions and volume-regulated anionic channels had just as little functional impact, which was demonstrated by the addition of carbenoxolone (100 μmol/L) and NPPB (100 μmol/L). Hyperpolarization with low potassium in the extracellular solution (2 mmol/L) dramatically raised oscillation power. A similar effect was seen when we added extra sodium (+50 mmol/L) or if we replaced it with NMDG+ (50 mmol/L). The purinergic receptor antagonist PPADS suppressed the oscillation power, while the agonist ATP (100 μmol/L) had only an increasing effect when the bath solution pH was slightly lowered to pH 7.2. From these observations, we conclude that astrocytic voltage oscillations are triggered by activation of voltage-gated calcium channels and driven by a downstream influx of cations through channels that are permeable for large ions such as NMDG+. Most likely candidates are subtypes of pore-forming P2X channels with a low affinity for ATP.
Collapse
Affiliation(s)
- Wiebke Fleischer
- Institute of Clinical Neuroscience and Medical Psychology, Medical Faculty, Heinrich Heine University, Düsseldorf, Germany
| | - Stephan Theiss
- Institute of Clinical Neuroscience and Medical Psychology, Medical Faculty, Heinrich Heine University, Düsseldorf, Germany RESULT Medical GmbH, Düsseldorf, Germany
| | - Johannes Slotta
- Institute of Clinical Neuroscience and Medical Psychology, Medical Faculty, Heinrich Heine University, Düsseldorf, Germany
| | - Christine Holland
- Institute of Clinical Neuroscience and Medical Psychology, Medical Faculty, Heinrich Heine University, Düsseldorf, Germany
| | - Alfons Schnitzler
- Institute of Clinical Neuroscience and Medical Psychology, Medical Faculty, Heinrich Heine University, Düsseldorf, Germany
| |
Collapse
|
55
|
Astrocyte physiopathology: At the crossroads of intercellular networking, inflammation and cell death. Prog Neurobiol 2015; 130:86-120. [PMID: 25930681 DOI: 10.1016/j.pneurobio.2015.04.003] [Citation(s) in RCA: 139] [Impact Index Per Article: 15.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/24/2014] [Revised: 04/15/2015] [Accepted: 04/20/2015] [Indexed: 12/11/2022]
Abstract
Recent breakthroughs in neuroscience have led to the awareness that we should revise our traditional mode of thinking and studying the CNS, i.e. by isolating the privileged network of "intelligent" synaptic contacts. We may instead need to contemplate all the variegate communications occurring between the different neural cell types, and centrally involving the astrocytes. Basically, it appears that a single astrocyte should be considered as a core that receives and integrates information from thousands of synapses, other glial cells and the blood vessels. In turn, it generates complex outputs that control the neural circuitry and coordinate it with the local microcirculation. Astrocytes thus emerge as the possible fulcrum of the functional homeostasis of the healthy CNS. Yet, evidence indicates that the bridging properties of the astrocytes can change in parallel with, or as a result of, the morphological, biochemical and functional alterations these cells undergo upon injury or disease. As a consequence, they have the potential to transform from supportive friends and interactive partners for neurons into noxious foes. In this review, we summarize the currently available knowledge on the contribution of astrocytes to the functioning of the CNS and what goes wrong in various pathological conditions, with a particular focus on Amyotrophic Lateral Sclerosis, Alzheimer's Disease and ischemia. The observations described convincingly demonstrate that the development and progression of several neurological disorders involve the de-regulation of a finely tuned interplay between multiple cell populations. Thus, it seems that a better understanding of the mechanisms governing the integrated communication and detrimental responses of the astrocytes as well as their impact towards the homeostasis and performance of the CNS is fundamental to open novel therapeutic perspectives.
Collapse
|
56
|
Vardjan N, Verkhratsky A, Zorec R. Pathologic Potential of Astrocytic Vesicle Traffic: New Targets to Treat Neurologic Diseases? Cell Transplant 2015; 24:599-612. [DOI: 10.3727/096368915x687750] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Vesicles are small intracellular organelles that are fundamental for constitutive housekeeping of the plasmalemma, intercellular transport, and cell-to-cell communications. In astroglial cells, traffic of vesicles is associated with cell morphology, which determines the signaling potential and metabolic support for neighboring cells, including when these cells are considered to be used for cell transplantations or for regulating neurogenesis. Moreover, vesicles are used in astrocytes for the release of vesicle-laden chemical messengers. Here we review the properties of membrane-bound vesicles that store gliotransmitters, endolysosomes that are involved in the traffic of plasma membrane receptors, and membrane transporters. These vesicles are all linked to pathological states, including amyotrophic lateral sclerosis, multiple sclerosis, neuroinflammation, trauma, edema, and states in which astrocytes contribute to developmental disorders. In multiple sclerosis, for example, fingolimod, a recently introduced drug, apparently affects vesicle traffic and gliotransmitter release from astrocytes, indicating that this process may well be used as a new pathophysiologic target for the development of new therapies.
Collapse
Affiliation(s)
- Nina Vardjan
- Celica Biomedical, Ljubljana, Slovenia
- Laboratory of Neuroendocrinology-Molecular Cell Physiology, Institute of Pathophysiology, Faculty of Medicine, University of Ljubljana, Ljubljana, Slovenia
| | - Alexei Verkhratsky
- Celica Biomedical, Ljubljana, Slovenia
- Laboratory of Neuroendocrinology-Molecular Cell Physiology, Institute of Pathophysiology, Faculty of Medicine, University of Ljubljana, Ljubljana, Slovenia
- Achucarro Center for Neuroscience, Ikerbasque, Basque Foundation for Science, Bilbao, Spain
- Faculty of Life Sciences, The University of Manchester, Manchester, UK
| | - Robert Zorec
- Celica Biomedical, Ljubljana, Slovenia
- Laboratory of Neuroendocrinology-Molecular Cell Physiology, Institute of Pathophysiology, Faculty of Medicine, University of Ljubljana, Ljubljana, Slovenia
| |
Collapse
|
57
|
Park H, Han KS, Seo J, Lee J, Dravid SM, Woo J, Chun H, Cho S, Bae JY, An H, Koh W, Yoon BE, Berlinguer-Palmini R, Mannaioni G, Traynelis SF, Bae YC, Choi SY, Lee CJ. Channel-mediated astrocytic glutamate modulates hippocampal synaptic plasticity by activating postsynaptic NMDA receptors. Mol Brain 2015; 8:7. [PMID: 25645137 PMCID: PMC4320468 DOI: 10.1186/s13041-015-0097-y] [Citation(s) in RCA: 62] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2014] [Accepted: 01/15/2015] [Indexed: 11/10/2022] Open
Abstract
Background Activation of G protein coupled receptor (GPCR) in astrocytes leads to Ca2+-dependent glutamate release via Bestrophin 1 (Best1) channel. Whether receptor-mediated glutamate release from astrocytes can regulate synaptic plasticity remains to be fully understood. Results We show here that Best1-mediated astrocytic glutamate activates the synaptic N-methyl-D-aspartate receptor (NMDAR) and modulates NMDAR-dependent synaptic plasticity. Our data show that activation of the protease-activated receptor 1 (PAR1) in hippocampal CA1 astrocytes elevates the glutamate concentration at Schaffer collateral-CA1 (SC-CA1) synapses, resulting in activation of GluN2A-containing NMDARs and NMDAR-dependent potentiation of synaptic responses. Furthermore, the threshold for inducing NMDAR-dependent long-term potentiation (LTP) is lowered when astrocytic glutamate release accompanied LTP induction, suggesting that astrocytic glutamate is significant in modulating synaptic plasticity. Conclusions Our results provide direct evidence for the physiological importance of channel-mediated astrocytic glutamate in modulating neural circuit functions.
Collapse
|
58
|
Crunelli V, Carmignoto G, Steinhäuser C. Novel astrocyte targets: new avenues for the therapeutic treatment of epilepsy. Neuroscientist 2015; 21:62-83. [PMID: 24609207 PMCID: PMC4361461 DOI: 10.1177/1073858414523320] [Citation(s) in RCA: 41] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
During the last 20 years, it has been well established that a finely tuned, continuous crosstalk between neurons and astrocytes not only critically modulates physiological brain functions but also underlies many neurological diseases. In particular, this novel way of interpreting brain activity is markedly influencing our current knowledge of epilepsy, prompting a re-evaluation of old findings and guiding novel experimentation. Here, we review recent studies that have unraveled novel and unique contributions of astrocytes to the generation and spread of convulsive and nonconvulsive seizures and epileptiform activity. The emerging scenario advocates an overall framework in which a dynamic and reciprocal interplay among astrocytic and neuronal ensembles is fundamental for a fuller understanding of epilepsy. In turn, this offers novel astrocytic targets for the development of those really novel chemical entities for the control of convulsive and nonconvulsive seizures that have been acknowledged as a key priority in the management of epilepsy.
Collapse
Affiliation(s)
- Vincenzo Crunelli
- Neuroscience Division, School of Biosciences, Cardiff University, Cardiff, UK
| | - Giorgio Carmignoto
- Centro Nazionale della Ricerca, Neuroscience Institute and Department of Biomedical Sciences, University of Padova, Padova, Italy
| | - Christian Steinhäuser
- Institute of Cellular Neurosciences, Medical Faculty, University of Bonn, Bonn, Germany
| |
Collapse
|
59
|
Minieri L, Pivonkova H, Harantova L, Anderova M, Ferroni S. Intracellular Na+
inhibits volume-regulated anion channel in rat cortical astrocytes. J Neurochem 2015; 132:286-300. [DOI: 10.1111/jnc.12962] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2014] [Revised: 09/04/2014] [Accepted: 09/25/2014] [Indexed: 01/08/2023]
Affiliation(s)
- Laura Minieri
- Department of Pharmacy and Biotechnology; University of Bologna; Bologna Italy
| | - Helena Pivonkova
- Department of Cellular Neurophysiology; Institute of Experimental Medicine; Academy of Sciences of the Czech Republic; Prague Czech Republic
| | - Lenka Harantova
- Department of Cellular Neurophysiology; Institute of Experimental Medicine; Academy of Sciences of the Czech Republic; Prague Czech Republic
| | - Miroslava Anderova
- Department of Cellular Neurophysiology; Institute of Experimental Medicine; Academy of Sciences of the Czech Republic; Prague Czech Republic
| | - Stefano Ferroni
- Department of Pharmacy and Biotechnology; University of Bologna; Bologna Italy
| |
Collapse
|
60
|
Montero TD, Orellana JA. Hemichannels: new pathways for gliotransmitter release. Neuroscience 2014; 286:45-59. [PMID: 25475761 DOI: 10.1016/j.neuroscience.2014.11.048] [Citation(s) in RCA: 76] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2014] [Revised: 10/14/2014] [Accepted: 11/20/2014] [Indexed: 01/16/2023]
Abstract
Growing evidence suggests that glial cells express virtually all known types of neurotransmitter receptors, enabling them to sense neuronal activity and microenvironment changes by responding locally via the Ca(2+)-dependent release of bioactive molecules, known as "gliotransmitters". Several mechanisms of gliotransmitter release have been documented. One of these mechanisms involves the opening of plasma membrane channels, known as hemichannels. These channels are composed of six protein subunits consisting of connexins or pannexins, two highly conserved protein families encoded by 21 or 3 genes, respectively, in humans. Most data indicate that under physiological conditions, glial cell hemichannels have low activity, but this activity is sufficient to ensure the release of relevant quantities of gliotransmitters to the extracellular milieu, including ATP, glutamate, adenosine and glutathione. Nevertheless, it has been suggested that dysregulations of hemichannel properties could be critical in the beginning and during the maintenance of homeostatic imbalances observed in several brain diseases. In this study, we review the current knowledge on the hemichannel-dependent release of gliotransmitters in the physiology and pathophysiology of the CNS.
Collapse
Affiliation(s)
- T D Montero
- Departamento de Neurología, Escuela de Medicina, Pontificia Universidad Católica de Chile, Santiago, Chile
| | - J A Orellana
- Departamento de Neurología, Escuela de Medicina, Pontificia Universidad Católica de Chile, Santiago, Chile.
| |
Collapse
|
61
|
Montana V, Verkhratsky A, Parpura V. Pathological role for exocytotic glutamate release from astrocytes in hepatic encephalopathy. Curr Neuropharmacol 2014; 12:324-33. [PMID: 25342940 PMCID: PMC4207072 DOI: 10.2174/1570159x12666140903094700] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2014] [Revised: 05/18/2014] [Accepted: 05/25/2014] [Indexed: 12/30/2022] Open
Abstract
Liver failure can lead to generalized hyperammonemia, which is thought to be the underlying cause of hepatic encephalopathy. This neuropsychiatric syndrome is accompanied by functional changes of astrocytes. These glial cells enter ammonia-induced self-amplifying cycle characterized by brain oedema, oxidative and osmotic stress that causes modification of proteins and RNA. Consequently, protein expression and function are affected, including that of glutamine synthetase and plasmalemmal glutamate transporters, leading to glutamate excitotoxicity; Ca2+-dependent exocytotic glutamate release from astrocytes contributes to this extracellular glutamate overload.
Collapse
Affiliation(s)
- Vedrana Montana
- Department of Neurobiology, Center for Glial Biology in Medicine, Atomic Force Microscopy & 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
| | - Alexei Verkhratsky
- Faculty of Life Sciences, The University of Manchester, Manchester, M13 9PT, UK ; Achucarro Center for Neuroscience, IKERBASQUE, Basque Foundation for Science, 48011 Bilbao, Spain ; University of Nizhny Novgorod, Nizhny Novgorod 603022, Russia
| | - Vladimir Parpura
- Department of Neurobiology, Center for Glial Biology in Medicine, Atomic Force Microscopy & 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
| |
Collapse
|
62
|
Amhaoul H, Staelens S, Dedeurwaerdere S. Imaging brain inflammation in epilepsy. Neuroscience 2014; 279:238-52. [DOI: 10.1016/j.neuroscience.2014.08.044] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2014] [Revised: 08/27/2014] [Accepted: 08/27/2014] [Indexed: 01/15/2023]
|
63
|
Falnikar A, Li K, Lepore AC. Therapeutically targeting astrocytes with stem and progenitor cell transplantation following traumatic spinal cord injury. Brain Res 2014; 1619:91-103. [PMID: 25251595 DOI: 10.1016/j.brainres.2014.09.037] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2014] [Revised: 09/10/2014] [Accepted: 09/15/2014] [Indexed: 12/12/2022]
Abstract
Replacement of lost and/or dysfunctional astrocytes via multipotent neural stem cell (NSC) and lineage-restricted neural progenitor cell (NPC) transplantation is a promising therapeutic approach for traumatic spinal cord injury (SCI). Cell transplantation in general offers the potential to replace central nervous system (CNS) cell types, achieve remyelination, deliver missing gene products, promote and guide axonal growth, modulate the host immune response, deliver neuroprotective factors, and provide a cellular substrate for bridging the lesion site, amongst other possible benefits. A host of cell types that differ in their developmental stage, CNS region and species of derivation, as well as in their phenotypic potential, have been tested in a variety of SCI animal models. Historically in the SCI field, most pre-clinical NSC and NPC transplantation studies have focused on neuronal and oligodendrocyte replacement. However, much less attention has been geared towards targeting astroglial dysfunction in the inured spinal cord, despite the integral roles played by astrocytes in both normal CNS function and in the diseased nervous system. Despite the relative lack of studies, cell transplantation-based targeting of astrocytes dates back to some of the earliest transplant studies in SCI animal models. In this review, we will describe the history of work involving cell transplantation for targeting astrocytes in models of SCI. We will also touch on the current state of affairs in the field, as well as on important future directions as we move forward in trying to develop this approach into a viable strategy for SCI patients. Practical issues such as timing of delivery, route of transplantation and immunesuppression needs are beyond the scope of this review. This article is part of a Special Issue entitled SI: Spinal cord injury.
Collapse
Affiliation(s)
- Aditi Falnikar
- Department of Neuroscience, Farber Institute for Neurosciences, Thomas Jefferson University Medical College, 900 Walnut Street, JHN 469, Philadelphia, PA 19107, United States
| | - Ke Li
- Department of Neuroscience, Farber Institute for Neurosciences, Thomas Jefferson University Medical College, 900 Walnut Street, JHN 469, Philadelphia, PA 19107, United States
| | - Angelo C Lepore
- Department of Neuroscience, Farber Institute for Neurosciences, Thomas Jefferson University Medical College, 900 Walnut Street, JHN 469, Philadelphia, PA 19107, United States.
| |
Collapse
|
64
|
Jiang S, Wang YQ, Xu CF, Li YN, Guo R, Li L. Involvement of connexin43 in the acute hyperosmotic stimulus‑induced synthesis and release of vasopressin in the supraoptic nucleus of rats. Mol Med Rep 2014; 10:2165-71. [PMID: 25050982 DOI: 10.3892/mmr.2014.2400] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2013] [Accepted: 05/02/2014] [Indexed: 11/05/2022] Open
Abstract
There is evidence that astroglial connexin43 (Cx43) in the supraoptic nucleus (SON) is required for the hyperosmolarity‑induced increase in Fos protein expression in magnocellular neurosecretory cells (MNCs). In the present study, the role of astroglial Cx43 in the synthesis and release of vasopressin (VP) by MNCs in the SON subjected to hyperosmotic stimulus was examined. The results revealed that the VP levels in the SON and plasma were increased following acute hyperosmotic stimulus. Treatment of MNCs with Cx43‑specific antisense oligodeoxynucleotides (ASODN), which temporarily reduced Cx43 protein production, limited the VP synthesis and release induced by a hyperosmotic stimulus. Similarly, the addition of gap junction and Cx43 hemichannel blockers also attenuated the VP synthesis and release induced by an acute hyperosmotic stimulus. A high extracellular [Ca2+]([Ca2+]o) has been demonstrated to reduce the gap junction activity or opening probability of Cx54 hemichannels. Notably, it was identified that high [Ca2+]o attenuated the VP synthesis and release induced by acute hyperosmotic stimulus, while low [Ca2+]o had a weak or no effect. These results suggested that Cx43 participates in the VP synthesis and release induced by hyperosmotic stimulation in the SON.
Collapse
Affiliation(s)
- Shan Jiang
- Department of Physical Medicine and Rehabilitation, The First Affiliated Hospital, Chinese PLA General Hospital, Beijing 100048, P.R. China
| | - Yong-Qiang Wang
- Department of Opthalmology, Jinan Military General Hospital, Jinan, Shandong 250031, P.R. China
| | - Cheng-Feng Xu
- Department of Physical Medicine and Rehabilitation, The First Affiliated Hospital, Chinese PLA General Hospital, Beijing 100048, P.R. China
| | - Ya-Na Li
- Department of Physical Medicine and Rehabilitation, The First Affiliated Hospital, Chinese PLA General Hospital, Beijing 100048, P.R. China
| | - Rong Guo
- Department of Physical Medicine and Rehabilitation, The First Affiliated Hospital, Chinese PLA General Hospital, Beijing 100048, P.R. China
| | - Ling Li
- Department of Physical Medicine and Rehabilitation, The First Affiliated Hospital, Chinese PLA General Hospital, Beijing 100048, P.R. China
| |
Collapse
|
65
|
Liu FT, Xu SM, Xiang ZH, Li XN, Li J, Yuan HB, Sun XJ. Molecular hydrogen suppresses reactive astrogliosis related to oxidative injury during spinal cord injury in rats. CNS Neurosci Ther 2014; 20:778-86. [PMID: 24685114 DOI: 10.1111/cns.12258] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2013] [Revised: 02/28/2014] [Accepted: 03/02/2014] [Indexed: 12/16/2022] Open
Abstract
AIMS Spinal cord injury (SCI) can induce excessive astrocyte activation. Hydrogen has been deemed as a novel antioxidant. We investigated whether molecular hydrogen could act as an antiastrogliosis agent during SCI and oxidative injury in experimental rats and cultured astrocytes. METHODS Hydrogen-rich saline (HS, 8 mL/kg, i.p.) was injected every 12 h after SCI in rats. The expression of STAT3, p-STAT3, and glial fibrillary acidic protein (GFAP); the release of IL-1β, IL-6, and TNF-α; and astrogliosis, along with the BBB score, were evaluated. Culturing astrocytes with hydrogen-rich medium, the intracellular reactive oxygen species (ROS), astrogliosis, and the release of proinflammatory cytokines were assessed after H2O2-induced injury. RESULTS In the HS group, the expression of STAT3, p-STAT3, and GFAP and the proinflammatory cytokines were decreased in local spinal cord on postoperation day (POD) 3; on PODs 7 and 14, reactive astrogliosis was suppressed, and the locomotor function was also improved. Furthermore, hydrogen-rich medium attenuated the intracellular production of ROS (especially HO•), astrogliosis, and the secretion of proinflammatory cytokines in astrocytes 12 h after H2O2-induced injury. CONCLUSIONS Molecular hydrogen could suppress reactive astrogliosis after contusive SCI and reduce the release of proinflammatory cytokines produced by active astrocytes related to oxidative injury. Thus, molecular hydrogen is potential to be a neuroprotective agent.
Collapse
Affiliation(s)
- Fang-Ting Liu
- Department of Anesthesiology, Neuroscience Research Centre, Changzheng Hospital, Second Military Medical University, Shanghai, China
| | | | | | | | | | | | | |
Collapse
|
66
|
Li Z, DU J, Sun H, Mang J, He J, Wang J, Liu H, Xu Z. Effects of the combination of methylprednisolone with aminoguanidine on functional recovery in rats following spinal cord injury. Exp Ther Med 2014; 7:1605-1610. [PMID: 24926352 PMCID: PMC4043599 DOI: 10.3892/etm.2014.1613] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2013] [Accepted: 02/12/2014] [Indexed: 12/18/2022] Open
Abstract
Methylprednisolone (MP), a synthetic glucocorticoid, has been widely used as a standard therapeutic agent for the treatment of spinal cord injury (SCI). The combination of MP and other pharmacological agents aimed at enhancing functional recovery is desirable as the beneficial effects of MP are controversial, due to a variety of side-effects. Aminoguanidine (AG), a small water-soluble compound, is potentially useful in the treatment of acute SCI. The aim of the present study was to determine the effects of MP and AG, administered in combination, following SCI in adult rats. In rats with SCI, the combination therapy group treated with AG (75 mg/kg) and MP (0.75 mg/kg) exhibited significantly reduced levels of cytokine expression and cell apoptosis compared with those in the control group. In addition, the data demonstrated that the combination therapy significantly enhanced the recovery of limb function. These data clearly suggest that treatment with a combination of MP and AG represents a promising strategy of clinically applicable pharmacological therapy for the rapid initiation of neuroprotection following SCI.
Collapse
Affiliation(s)
- Zongshu Li
- Department of Neurology, China-Japan Union Hospital of Jilin University, Changchun, Jilin 130033, P.R. China ; Department of Neurology, Jilin Province People's Hospital, Changchun, Jilin 130021, P.R. China
| | - Juan DU
- Department of Rheumatology and Immunology, China-Japan Union Hospital of Jilin University, Changchun, Jilin 130033, P.R. China
| | - Hongxia Sun
- Department of Neurology, Jilin Province People's Hospital, Changchun, Jilin 130021, P.R. China
| | - Jing Mang
- Department of Neurology, China-Japan Union Hospital of Jilin University, Changchun, Jilin 130033, P.R. China
| | - Jinting He
- Department of Neurology, China-Japan Union Hospital of Jilin University, Changchun, Jilin 130033, P.R. China
| | - Jiaoqi Wang
- Department of Neurology, China-Japan Union Hospital of Jilin University, Changchun, Jilin 130033, P.R. China
| | - Hongyu Liu
- Department of Neurology, China-Japan Union Hospital of Jilin University, Changchun, Jilin 130033, P.R. China
| | - Zhongxin Xu
- Department of Neurology, China-Japan Union Hospital of Jilin University, Changchun, Jilin 130033, P.R. China
| |
Collapse
|
67
|
Photolysis of caged Ca2+ but not receptor-mediated Ca2+ signaling triggers astrocytic glutamate release. J Neurosci 2013; 33:17404-12. [PMID: 24174673 DOI: 10.1523/jneurosci.2178-13.2013] [Citation(s) in RCA: 50] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Astrocytes in hippocampal slices can dynamically regulate synaptic transmission in a process mediated by increases in intracellular Ca(2+). However, it is debated whether astrocytic Ca(2+) signals result in release of glutamate. We here compared astrocytic Ca(2+) signaling triggered by agonist exposure versus photolysis side by side. Using transgenic mice in which astrocytes selectively express the MrgA1 receptor, we found that receptor-mediated astrocytic Ca(2+) signaling consistently triggered neuronal hyperpolarization and decreased the frequency of miniature excitatory postsynaptic currents (EPSCs). In contrast, photolysis of caged Ca(2+) (o-nitrophenyl-EGTA) in astrocytes led to neuronal depolarization and increased the frequency of mEPSCs through a metabotropic glutamate receptor-mediated pathway. Analysis of transgenic mice in which astrocytic vesicular release is suppressed (dominant-negative SNARE mice) and pharmacological manipulations suggested that glutamate is primarily released by opening of anion channels rather than exocytosis. Combined, these studies show that photolysis but not by agonists induced astrocytic Ca(2+) signaling triggers glutamate release.
Collapse
|
68
|
Park H, Han KS, Oh SJ, Jo S, Woo J, Yoon BE, Lee CJ. High glutamate permeability and distal localization of Best1 channel in CA1 hippocampal astrocyte. Mol Brain 2013; 6:54. [PMID: 24321245 PMCID: PMC4029177 DOI: 10.1186/1756-6606-6-54] [Citation(s) in RCA: 51] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2013] [Accepted: 12/04/2013] [Indexed: 11/11/2022] Open
Abstract
Background Glutamate is the major neurotransmitter that mediates a principal form of excitatory synaptic transmission in the brain. From the presynaptic terminals of neurons, glutamate is released upon exocytosis of the glutamate-packaged vesicles. In recent years, astrocytes are also known to release glutamate via various routes to modulate synaptic transmission. In particular, we have characterized a glutamate-permeable Ca2+-activated anion channel encoded by Bestrophin 1 gene (Best1) that is responsible for Ca2+-dependent, channel-mediated glutamate release in astrocyte. Best1 channel contains a large pore that is readily permeable to large molecules such as glutamate and GABA. In those studies we obtained permeability ratio of glutamate to Cl- in heterologously expressed mouse Best1 in HEK293T cells and in endogenously expressed mouse Best1 in cultured astrocytes. However, up to now, glutamate permeability of the native Best1 channel in vivo has not been reported. Findings In whole-cell recordings of CA1 hippocampal astrocytes, we found that opening of Best1 channel upon activation of a Gq-coupled GPCR, protease-activated receptor 1 (PAR1) generated the anion current carried by glutamate via Ca2+ increase. This Ca2+-evoked glutamate-mediated anion current was unaffected by pretreatment of the inhibitors for a gap junction hemi-channel or Ca2+-activated K+ conductance. This astrocytic anion conductance carried by glutamate was mediated by Best1 channel expression in CA1 hippocampal astrocytes, because Best1 knock-down by shRNA expression eliminated astrocytic glutamate conductance by PAR-1 activation. However, we found that these astrocytes showed a deviation in reversal potential of Best1-mediated current from the predicted value. By performing dual patch recording, we concluded that the deviation of reversal potential is due to incomplete space clamping arising from extremely leaky membrane (input resistance ranging 1–3 MΩ), very low length constant of astrocytic processes, and the localization of Best1 channel in distal microdomains near synapses. Based on the relative shift of reversal potentials by ion substitutions, we estimated the permeability ratio of glutamate and Cl- (Pglutamate/PCl) as 0.53. Conclusions Our study shows that Best1, located at the microdomains near the synaptic junctions, has a significantly high permeability to glutamate in vivo, serving as the prominent glutamate-releasing channel in astrocytes, mediating the release of various gliotransmitters in the brain, and playing an important role in modulating synaptic transmission.
Collapse
Affiliation(s)
| | | | | | | | | | | | - C Justin Lee
- Center for Neural Science and WCI Center for Functional Connectomics, Korea Institute of Science and Technology (KIST), Seoul, Korea.
| |
Collapse
|
69
|
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: 2.4] [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]
|
70
|
Astrocytes use a novel transporter to fill gliotransmitter vesicles with D-serine: evidence for vesicular synergy. J Neurosci 2013; 33:10193-4. [PMID: 23785135 DOI: 10.1523/jneurosci.1665-13.2013] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023] Open
|
71
|
Yang J, Li MX, Luo Y, Chen T, Liu J, Fang P, Jiang B, Hu ZL, Jin Y, Chen JG, Wang F. Chronic ceftriaxone treatment rescues hippocampal memory deficit in AQP4 knockout mice via activation of GLT-1. Neuropharmacology 2013; 75:213-22. [PMID: 23973312 DOI: 10.1016/j.neuropharm.2013.08.009] [Citation(s) in RCA: 50] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2013] [Revised: 07/03/2013] [Accepted: 08/08/2013] [Indexed: 10/26/2022]
Abstract
Aquaporin-4 (AQP4) is the predominant water channel protein in the mammalian brain, and is mainly expressed in astrocytes. Besides its important role in water transport across the blood-brain barrier, our present study demonstrated that AQP4 deficiency impaired hippocampal long-term potentiation (LTP) and hippocampus-dependent memory formation, accompanied by the increase in extracellular glutamate concentration and N-methyl-d-aspartate (NMDA) receptor-mediated currents in hippocampal dentate gyrus (DG) region. The impairment of LTP and memory formation of AQP4 knockout (KO) mice was mediated by the downregulation of glutamate transporter-1 (GLT-1) expression/function, since it can be rescued by β-lactam antibiotic ceftriaxone (Cef), a potent GLT-1 stimulator. These results suggest that AQP4 functions as the modulator of synaptic plasticity and memory, and chronic Cef treatment rescues hippocampal memory deficit induced by AQP4 knockout.
Collapse
Affiliation(s)
- Jun Yang
- Department of Pharmacology, Tongji Medical College, Huazhong University of Science and Technology, Wuhan 430030, China.
| | - Ming-Xing Li
- Department of Pharmacology, Tongji Medical College, Huazhong University of Science and Technology, Wuhan 430030, China.
| | - Yi Luo
- Department of Pharmacology, Tongji Medical College, Huazhong University of Science and Technology, Wuhan 430030, China.
| | - Tao Chen
- Department of Pharmacology, Tongji Medical College, Huazhong University of Science and Technology, Wuhan 430030, China.
| | - Jing Liu
- Department of Pharmacology, Tongji Medical College, Huazhong University of Science and Technology, Wuhan 430030, China.
| | - Peng Fang
- Department of Pharmacology, Tongji Medical College, Huazhong University of Science and Technology, Wuhan 430030, China.
| | - Bo Jiang
- Department of Pharmacology, Tongji Medical College, Huazhong University of Science and Technology, Wuhan 430030, China.
| | - Zhuang-Li Hu
- Department of Pharmacology, Tongji Medical College, Huazhong University of Science and Technology, Wuhan 430030, China; Key Laboratory of Neurological Diseases (HUST), Ministry of Education of China, Wuhan 430030, China; The Key Laboratory for Drug Target Researches and Pharmacodynamic Evaluation of Hubei Province, Wuhan 430030, China.
| | - You Jin
- Department of Pharmacology, Tongji Medical College, Huazhong University of Science and Technology, Wuhan 430030, China; Key Laboratory of Neurological Diseases (HUST), Ministry of Education of China, Wuhan 430030, China; The Key Laboratory for Drug Target Researches and Pharmacodynamic Evaluation of Hubei Province, Wuhan 430030, China.
| | - Jian-Guo Chen
- Department of Pharmacology, Tongji Medical College, Huazhong University of Science and Technology, Wuhan 430030, China; Key Laboratory of Neurological Diseases (HUST), Ministry of Education of China, Wuhan 430030, China; The Key Laboratory for Drug Target Researches and Pharmacodynamic Evaluation of Hubei Province, Wuhan 430030, China.
| | - Fang Wang
- Department of Pharmacology, Tongji Medical College, Huazhong University of Science and Technology, Wuhan 430030, China; Key Laboratory of Neurological Diseases (HUST), Ministry of Education of China, Wuhan 430030, China; The Key Laboratory for Drug Target Researches and Pharmacodynamic Evaluation of Hubei Province, Wuhan 430030, China.
| |
Collapse
|
72
|
Potokar M, Vardjan N, Stenovec M, Gabrijel M, Trkov S, Jorgačevski J, Kreft M, Zorec R. Astrocytic vesicle mobility in health and disease. Int J Mol Sci 2013; 14:11238-58. [PMID: 23712361 PMCID: PMC3709730 DOI: 10.3390/ijms140611238] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2013] [Revised: 04/26/2013] [Accepted: 05/08/2013] [Indexed: 12/14/2022] Open
Abstract
Astrocytes are no longer considered subservient to neurons, and are, instead, now understood to play an active role in brain signaling. The intercellular communication of astrocytes with neurons and other non-neuronal cells involves the exchange of molecules by exocytotic and endocytotic processes through the trafficking of intracellular vesicles. Recent studies of single vesicle mobility in astrocytes have prompted new views of how astrocytes contribute to information processing in nervous tissue. Here, we review the trafficking of several types of membrane-bound vesicles that are specifically involved in the processes of (i) intercellular communication by gliotransmitters (glutamate, adenosine 5′-triphosphate, atrial natriuretic peptide), (ii) plasma membrane exchange of transporters and receptors (EAAT2, MHC-II), and (iii) the involvement of vesicle mobility carrying aquaporins (AQP4) in water homeostasis. The properties of vesicle traffic in astrocytes are discussed in respect to networking with neighboring cells in physiologic and pathologic conditions, such as amyotrophic lateral sclerosis, multiple sclerosis, and states in which astrocytes contribute to neuroinflammatory conditions.
Collapse
Affiliation(s)
- Maja Potokar
- Laboratory of Neuroendocrinology-Molecular Cell Physiology, Institute of Pathophysiology, Faculty of Medicine, University of Ljubljana, Zaloška 4, 1000 Ljubljana, Slovenia; E-Mails: (M.P.); (N.V.); (M.S.); (M.G.); (S.T.); (J.J.); (M.K.)
- Celica Biomedical Center, Tehnološki park 24, 1000 Ljubljana, Slovenia
| | - Nina Vardjan
- Laboratory of Neuroendocrinology-Molecular Cell Physiology, Institute of Pathophysiology, Faculty of Medicine, University of Ljubljana, Zaloška 4, 1000 Ljubljana, Slovenia; E-Mails: (M.P.); (N.V.); (M.S.); (M.G.); (S.T.); (J.J.); (M.K.)
- Celica Biomedical Center, Tehnološki park 24, 1000 Ljubljana, Slovenia
| | - Matjaž Stenovec
- Laboratory of Neuroendocrinology-Molecular Cell Physiology, Institute of Pathophysiology, Faculty of Medicine, University of Ljubljana, Zaloška 4, 1000 Ljubljana, Slovenia; E-Mails: (M.P.); (N.V.); (M.S.); (M.G.); (S.T.); (J.J.); (M.K.)
- Celica Biomedical Center, Tehnološki park 24, 1000 Ljubljana, Slovenia
| | - Mateja Gabrijel
- Laboratory of Neuroendocrinology-Molecular Cell Physiology, Institute of Pathophysiology, Faculty of Medicine, University of Ljubljana, Zaloška 4, 1000 Ljubljana, Slovenia; E-Mails: (M.P.); (N.V.); (M.S.); (M.G.); (S.T.); (J.J.); (M.K.)
- Celica Biomedical Center, Tehnološki park 24, 1000 Ljubljana, Slovenia
| | - Saša Trkov
- Laboratory of Neuroendocrinology-Molecular Cell Physiology, Institute of Pathophysiology, Faculty of Medicine, University of Ljubljana, Zaloška 4, 1000 Ljubljana, Slovenia; E-Mails: (M.P.); (N.V.); (M.S.); (M.G.); (S.T.); (J.J.); (M.K.)
- Celica Biomedical Center, Tehnološki park 24, 1000 Ljubljana, Slovenia
| | - Jernej Jorgačevski
- Laboratory of Neuroendocrinology-Molecular Cell Physiology, Institute of Pathophysiology, Faculty of Medicine, University of Ljubljana, Zaloška 4, 1000 Ljubljana, Slovenia; E-Mails: (M.P.); (N.V.); (M.S.); (M.G.); (S.T.); (J.J.); (M.K.)
- Celica Biomedical Center, Tehnološki park 24, 1000 Ljubljana, Slovenia
| | - Marko Kreft
- Laboratory of Neuroendocrinology-Molecular Cell Physiology, Institute of Pathophysiology, Faculty of Medicine, University of Ljubljana, Zaloška 4, 1000 Ljubljana, Slovenia; E-Mails: (M.P.); (N.V.); (M.S.); (M.G.); (S.T.); (J.J.); (M.K.)
- Celica Biomedical Center, Tehnološki park 24, 1000 Ljubljana, Slovenia
- Biotechnical Faculty, University of Ljubljana, Večna pot 111, 1000 Ljubljana, Slovenia
| | - Robert Zorec
- Laboratory of Neuroendocrinology-Molecular Cell Physiology, Institute of Pathophysiology, Faculty of Medicine, University of Ljubljana, Zaloška 4, 1000 Ljubljana, Slovenia; E-Mails: (M.P.); (N.V.); (M.S.); (M.G.); (S.T.); (J.J.); (M.K.)
- Celica Biomedical Center, Tehnološki park 24, 1000 Ljubljana, Slovenia
- Author to whom correspondence should be addressed; E-Mail: ; Tel.: +386-1543-7020; Fax: +386-1543-7036
| |
Collapse
|
73
|
Sun D, Qu J, Jakobs TC. Reversible reactivity by optic nerve astrocytes. Glia 2013; 61:1218-35. [PMID: 23650091 DOI: 10.1002/glia.22507] [Citation(s) in RCA: 73] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2012] [Accepted: 03/14/2013] [Indexed: 12/25/2022]
Abstract
Reactive astrocytes are typically studied in models that cause irreversible mechanical damage to axons, neuronal cell bodies, and glia. Here, we evaluated the response of astrocytes in the optic nerve head to a subtle injury induced by a brief, mild elevation of the intraocular pressure. Astrocytes demonstrated reactive remodeling that peaked at three days, showing hypertrophy, process retraction, and simplification of their shape. This was not accompanied by any significant changes in the gene expression profile. At no time was there discernible damage to the optic axons, as evidenced by electron microscopy and normal anterograde and retrograde transport. Remarkably, the morphological remodeling was reversible. These findings underscore the plastic nature of reactivity. They show that reactivity can resolve fully if the insult is removed, and suggest that reactivity per se is not necessarily deleterious to axons. This reaction may represent very early events in the sequence that eventually leads to glial scarring.
Collapse
Affiliation(s)
- Daniel Sun
- Massachusetts Eye and Ear Infirmary, Harvard Medical School, Boston, MA 02114, USA
| | | | | |
Collapse
|
74
|
Abstract
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 glutamate transporters (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.
Collapse
|
75
|
Neuronal D-serine and glycine release via the Asc-1 transporter regulates NMDA receptor-dependent synaptic activity. J Neurosci 2013; 33:3533-44. [PMID: 23426681 DOI: 10.1523/jneurosci.3836-12.2013] [Citation(s) in RCA: 165] [Impact Index Per Article: 15.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
D-Serine and glycine are coagonists of NMDA receptors (NMDARs), but their relative contributions for several NMDAR-dependent processes are unclear. We now report that the alanine-serine-cysteine transporter-1 (Asc-1) mediates release of both D-serine and glycine from neurons, and, in turn, this modulates NMDAR synaptic activity. Asc-1 antiporter activity is enhanced by D-isoleucine (D-Ile), which releases D-serine and glycine from Asc-1-transfected cells, primary neuronal cultures, and hippocampal slices. D-Ile has no effect on astrocytes, which do not express Asc-1. We show that D-Ile enhances the long-term potentiation (LTP) in rat and mouse hippocampal CA1 by stimulating Asc-1-mediated endogenous D-serine release. D-Ile effects on synaptic plasticity are abolished by enzymatically depleting D-serine or by using serine racemase knock-out (SR-KO) mice, confirming its specificity and supporting the notion that LTP depends mostly on D-serine release. Conversely, our data also disclose a role of glycine in activating synaptic NMDARs. Although acute enzymatic depletion of D-serine also drastically decreases the isolated NMDAR synaptic potentials, these responses are still enhanced by D-Ile. Furthermore, NMDAR synaptic potentials are preserved in SR-KO mice and are also enhanced by D-Ile, indicating that glycine overlaps with D-serine binding at synaptic NMDARs. Altogether, our results disclose a novel role of Asc-1 in regulating NMDAR-dependent synaptic activity by mediating concurrent non-vesicular release of D-serine and glycine. Our data also highlight an important role of neuron-derived D-serine and glycine, indicating that astrocytic D-serine is not solely responsible for activating synaptic NMDARs.
Collapse
|
76
|
Potokar M, Stenovec M, Jorgačevski J, Holen T, Kreft M, Ottersen OP, Zorec R. Regulation of AQP4 surface expression via vesicle mobility in astrocytes. Glia 2013; 61:917-28. [DOI: 10.1002/glia.22485] [Citation(s) in RCA: 55] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2012] [Accepted: 01/28/2013] [Indexed: 11/05/2022]
Affiliation(s)
| | | | | | - Torgeir Holen
- Center for Molecular Biology and Neuroscience; University of Oslo; Oslo; Norway
| | | | - Ole Petter Ottersen
- Center for Molecular Biology and Neuroscience; University of Oslo; Oslo; Norway
| | | |
Collapse
|
77
|
Yin Y, Sun W, Li Z, Zhang B, Cui H, Deng L, Xie P, Xiang J, Zou J. Effects of combining methylprednisolone with rolipram on functional recovery in adult rats following spinal cord injury. Neurochem Int 2013; 62:903-12. [PMID: 23499793 DOI: 10.1016/j.neuint.2013.03.005] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2012] [Revised: 02/05/2013] [Accepted: 03/05/2013] [Indexed: 12/20/2022]
Abstract
Methylprednisolone (MP) has been widely used as a standard therapeutic agent for the treatment of spinal cord injury (SCI). Because of its controversial beneficial effects, the combination of MP and other pharmacological agents aimed at enhancing functional recovery is desirable. The phosphodiesterase 4 (PDE4) inhibitor rolipram has been implicated in promotion of regeneration due to elevating cAMP. In the present study, we sought to determine the effects of MP and rolipram, administered in combination, after spinal cord injury (SCI) in adult rats. Here we show that in vitro administration of rolipram and MP significantly increased neuron survival and promoted neurite outgrowth of neurons on the inhibitory substrate CSPGs by upregulation of MMP-2 expression; in vivo administration of rolipram and MP inhibited CSPG expression and increase CSPG digestion after rat SCI. Rolipram and MP combining treatment promoted significant neuroprotection through reduced motoneuron death, minimized lesion cavity, and increased regeneration of lesioned corticospinal tract (CST) axons beyond the lesion site after SCI. Enhanced functional recovery was also observed. Overall, our study strongly suggested that the combination treatment of MP and rolipram may represent a promising strategy for clinically applicable pharmacological therapy for rapid initiation of neuroprotection after SCI.
Collapse
Affiliation(s)
- Ying Yin
- Department of Clinical Laboratory Science, Wuxi People's Hospital of Nanjing Medical University, Wuxi, PR China
| | | | | | | | | | | | | | | | | |
Collapse
|
78
|
Perederiy JV, Westbrook GL. Structural plasticity in the dentate gyrus- revisiting a classic injury model. Front Neural Circuits 2013; 7:17. [PMID: 23423628 PMCID: PMC3575076 DOI: 10.3389/fncir.2013.00017] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2012] [Accepted: 01/27/2013] [Indexed: 12/12/2022] Open
Abstract
The adult brain is in a continuous state of remodeling. This is nowhere more true than in the dentate gyrus, where competing forces such as neurodegeneration and neurogenesis dynamically modify neuronal connectivity, and can occur simultaneously. This plasticity of the adult nervous system is particularly important in the context of traumatic brain injury or deafferentation. In this review, we summarize a classic injury model, lesioning of the perforant path, which removes the main extrahippocampal input to the dentate gyrus. Early studies revealed that in response to deafferentation, axons of remaining fiber systems and dendrites of mature granule cells undergo lamina-specific changes, providing one of the first examples of structural plasticity in the adult brain. Given the increasing role of adult-generated new neurons in the function of the dentate gyrus, we also compare the response of newborn and mature granule cells following lesioning of the perforant path. These studies provide insights not only to plasticity in the dentate gyrus, but also to the response of neural circuits to brain injury.
Collapse
Affiliation(s)
- Julia V Perederiy
- Vollum Institute, Oregon Health and Science University Portland, OR, USA
| | | |
Collapse
|
79
|
Wang YF, Sun MY, Hou Q, Parpura V. Hyposmolality differentially and spatiotemporally modulates levels of glutamine synthetase and serine racemase in rat supraoptic nucleus. Glia 2013; 61:529-38. [PMID: 23361961 DOI: 10.1002/glia.22453] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2012] [Accepted: 11/09/2012] [Indexed: 01/22/2023]
Abstract
Prolonged hyposmotic challenge (HOC) has a dual effect on vasopressin (VP) secretion [Yagil and Sladek (1990) Am J Physiol 258(2 Pt 2):R492-R500]. We describe an electrophysiological correlate of this phenomenon, whereby in vitro HOC transiently reduced the firing activity of VP neurons within the supraoptic nucleus of brain slices, which was followed by a rebound increase of their activity; this was paralleled by changes in the level of proteins relevant to astroglia-neuronal interactions. Hence, in vitro HOC transiently (at 5 min) increased the level of astrocyte-specific glial fibrillary acidic protein (GFAP), which then declined to control or base level (at 20 min); this was blocked by the gliotoxin L-aminoadipic acid, but not by tetanus toxin, which was used to inhibit neurotransmission. Similarly, in vivo HOC led to changes in GFAP level, which after an early increase (10 min) returned to normal (30 min). Immunoassays revealed that neuronal, but not astrocytic, expression of serine racemase (SR) was increased at the late stage of HOC in vivo, whereas at an early stage there was a transient increase in level of the astrocyte-specific glutamine synthetase (GS). Furthermore, there was an increased molecular association between GFAP and GS at 10 min, whereas SR increased its association with the neuronal nuclear antigen NeuN at 30 min. These results suggest that the dual effect of HOC on VP neuronal secretion/activity could be related to metabolic/signaling changes in astrocytes (glutamate-glutamine conversion) and neurons (D-serine synthesis/ammonia production), which may account for the rebound in VP neuronal activity, presumably by promoting the activation of neuronal glutamate receptors.
Collapse
Affiliation(s)
- Yu-Feng Wang
- Department of Cell Biology and Neuroscience, University of California, Riverside, California, USA.
| | | | | | | |
Collapse
|
80
|
Woo DH, Han KS, Shim JW, Yoon BE, Kim E, Bae JY, Oh SJ, Hwang EM, Marmorstein AD, Bae YC, Park JY, Lee CJ. TREK-1 and Best1 channels mediate fast and slow glutamate release in astrocytes upon GPCR activation. Cell 2012; 151:25-40. [PMID: 23021213 DOI: 10.1016/j.cell.2012.09.005] [Citation(s) in RCA: 253] [Impact Index Per Article: 21.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2012] [Revised: 06/18/2012] [Accepted: 09/05/2012] [Indexed: 11/28/2022]
Abstract
Astrocytes release glutamate upon activation of various GPCRs to exert important roles in synaptic functions. However, the molecular mechanism of release has been controversial. Here, we report two kinetically distinct modes of nonvesicular, channel-mediated glutamate release. The fast mode requires activation of G(αi), dissociation of G(βγ), and subsequent opening of glutamate-permeable, two-pore domain potassium channel TREK-1 through direct interaction between G(βγ) and N terminus of TREK-1. The slow mode is Ca(2+) dependent and requires G(αq) activation and opening of glutamate-permeable, Ca(2+)-activated anion channel Best1. Ultrastructural analyses demonstrate that TREK-1 is preferentially localized at cell body and processes, whereas Best1 is mostly found in microdomains of astrocytes near synapses. Diffusion modeling predicts that the fast mode can target neuronal mGluR with peak glutamate concentration of 100 μM, whereas slow mode targets neuronal NMDA receptors at around 1 μM. Our results reveal two distinct sources of astrocytic glutamate that can differentially influence neighboring neurons.
Collapse
Affiliation(s)
- Dong Ho Woo
- Center for Neural Science, Korea Institute of Science and Technology, Seoul, Republic of Korea
| | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
81
|
Bertollini C, Murana E, Mosca L, D'Erme M, Scala F, Francioso A, Catalano M, Limatola C, Bregestovski P, Di Angelantonio S, Ragozzino D. Transient increase in neuronal chloride concentration by neuroactive aminoacids released from glioma cells. Front Mol Neurosci 2012. [PMID: 23189038 PMCID: PMC3505843 DOI: 10.3389/fnmol.2012.00100] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
Neuronal chloride concentration ([Cl−]i) is known to be dynamically modulated and alterations in Cl− homeostasis may occur in the brain at physiological and pathological conditions, being also likely involved in glioma-related seizures. However, the mechanism leading to changes in neuronal [Cl−]i during glioma invasion are still unclear. To characterize the potential effect of glioma released soluble factors on neuronal [Cl−]i, we used genetically encoded CFP/YFP-based ratiometric Cl-(apical) Sensor transiently expressed in cultured hippocampal neurons. Exposition of neurons to glioma conditioned medium (GCM) caused rapid and transient elevation of [Cl−]i, resulting in the increase of fluorescence ratio, which was strongly reduced by blockers of ionotropic glutamate receptors APV and NBQX. Furthermore, in HEK cells expressing GluR1-AMPA receptors, GCM activated ionic currents with efficacy similar to those caused by glutamate, supporting the notion that GCM contains glutamate or glutamatergic agonists, which cause neuronal depolarization, activation of NMDA and AMPA/KA receptors leading to elevation of [Cl−]i. Chromatographic analysis of the GCM showed that it contained several aminoacids, including glutamate, whose release from glioma cells did not occur via the most common glial mechanisms of transport, or in response to hypoosmotic stress. GCM also contained glycine, whose action contrasted the glutamate effect. Indeed, strychnine application significantly increased GCM-induced depolarization and [Cl−]i rise. GCM-evoked [Cl−]i elevation was not inhibited by antagonists of Cl− transporters and significantly reduced in the presence of anion channels blocker NPPB, suggesting that Cl− selective channels are a major route for GCM-induced Cl− influx. Altogether, these data show that glioma released aminoacids may dynamically alter Cl− equilibrium in surrounding neurons, deeply interfering with their inhibitory balance, likely leading to physiological and pathological consequences.
Collapse
Affiliation(s)
- Cristina Bertollini
- Department of Physiology and Pharmacology, Istituto Pasteur-Fondazione Cenci Bolognetti, Sapienza University of Rome Rome, Italy
| | | | | | | | | | | | | | | | | | | | | |
Collapse
|
82
|
Brambilla L, Martorana F, Rossi D. Astrocyte signaling and neurodegeneration: new insights into CNS disorders. Prion 2012; 7:28-36. [PMID: 23093800 DOI: 10.4161/pri.22512] [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: 12/11/2022] Open
Abstract
Growing evidence indicates that astrocytes cannot be just considered as passive supportive cells deputed to preserve neuronal activity and survival, but rather they are involved in a striking number of active functions that are critical to the performance of the central nervous system (CNS). As a consequence, it is becoming more and more evident that the peculiar properties of these cells can actively contribute to the extraordinary functional complexity of the brain and spinal cord. This new perception of the functioning of the CNS opens up a wide range of new possibilities to interpret various physiological and pathological events, and moves the focus beyond the neuronal compartment toward astrocyte-neuron interactions. With this in mind, here we provide a synopsis of the activities astrocytes perform in normal conditions, and we try to discuss what goes wrong with these cells in specific pathological conditions, such as Alzheimer Disease, prion diseases and amyotrophic lateral sclerosis.
Collapse
Affiliation(s)
- Liliana Brambilla
- Laboratory for Research on Neurodegenerative Disorders, IRCCS Fondazione Salvatore Maugeri, Pavia, Italy
| | | | | |
Collapse
|
83
|
Oh SJ, Han KS, Park H, Woo DH, Kim HY, Traynelis SF, Lee CJ. Protease activated receptor 1-induced glutamate release in cultured astrocytes is mediated by Bestrophin-1 channel but not by vesicular exocytosis. Mol Brain 2012; 5:38. [PMID: 23062602 PMCID: PMC3539998 DOI: 10.1186/1756-6606-5-38] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2012] [Accepted: 10/09/2012] [Indexed: 11/27/2022] Open
Abstract
Background Glutamate is the major transmitter that mediates the principal form of excitatory synaptic transmission in the brain. It has been well established that glutamate is released via Ca2+-dependent exocytosis of glutamate-containing vesicles in neurons. However, whether astrocytes exocytose to release glutamate under physiological condition is still unclear. Findings We report a novel form of glutamate release in astrocytes via the recently characterized Ca2+-activated anion channel, Bestrophin-1 (Best1) by Ca2+ dependent mechanism through the channel pore. We demonstrate that upon activation of protease activated receptor 1 (PAR1), an increase in intracellular Ca2+ concentration leads to an opening of Best1 channels and subsequent release of glutamate in cultured astrocytes. Conclusions These results provide strong molecular evidence for potential astrocyte-neuron interaction via Best1-mediated glutamate release.
Collapse
Affiliation(s)
- Soo-Jin Oh
- Korea Institute of Science and Technology, Seoul, South Korea
| | | | | | | | | | | | | |
Collapse
|
84
|
Le Meur K, Mendizabal-Zubiaga J, Grandes P, Audinat E. GABA release by hippocampal astrocytes. Front Comput Neurosci 2012; 6:59. [PMID: 22912614 PMCID: PMC3421239 DOI: 10.3389/fncom.2012.00059] [Citation(s) in RCA: 61] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2012] [Accepted: 07/25/2012] [Indexed: 01/10/2023] Open
Abstract
Astrocytes can directly influence neuronal activity through the release of various transmitters acting on membrane receptors expressed by neurons. However, in contrast to glutamate and ATP for instance, the release of GABA (γ-amino-butyric acid) by astrocytes is still poorly documented. Here, we used whole-cell recordings in rat acute brain slices and electron microscopy to test whether hippocampal astrocytes release the inhibitory transmitter GABA. We observed that slow transient inhibitory currents due to the activation of GABAA receptors occur spontaneously in principal neurons of the three main hippocampal fields (CA1, CA3, and dentate gyrus). These currents share characteristics with the slow NMDA receptor-mediated currents previously shown to result from astrocytic glutamate release: they occur in the absence of synaptic transmission and have variable kinetics and amplitudes as well as low frequencies. Osmotic pressure reduction, known to enhance transmitter release from astrocytes, similarly increased the frequency of non-synaptic GABA and glutamate currents. Simultaneous occurrence of slow inhibitory and excitatory currents was extremely rare. Yet, electron microscopy examination of immunostained hippocampal sections shows that about 80% of hippocampal astrocytes [positive for glial fibrillary acidic protein (GFAP)] were immunostained for GABA. Our results provide quantitative characteristics of the astrocyte-to-neuron GABAergic signaling. They also suggest that all principal neurons of the hippocampal network are under a dual, excitatory and inhibitory, influence of astrocytes. The relevance of the astrocytic release of GABA, and glutamate, on the physiopathology of the hippocampus remains to be established.
Collapse
|
85
|
Aquaporin-4 deficiency impairs synaptic plasticity and associative fear memory in the lateral amygdala: involvement of downregulation of glutamate transporter-1 expression. Neuropsychopharmacology 2012; 37:1867-78. [PMID: 22473056 PMCID: PMC3376319 DOI: 10.1038/npp.2012.34] [Citation(s) in RCA: 87] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Astrocytes are implicated in information processing, signal transmission, and regulation of synaptic plasticity. Aquaporin-4 (AQP4) is the major water channel in adult brain and is primarily expressed in astrocytes. A growing body of evidence indicates that AQP4 is a potential molecular target for the regulation of astrocytic function. However, little is known about the role of AQP4 in synaptic plasticity in the amygdala. Therefore, we evaluated long-term potentiation (LTP) in the lateral amygdala (LA) and associative fear memory of AQP4 knockout (KO) and wild-type mice. We found that AQP4 deficiency impaired LTP in the thalamo-LA pathway and associative fear memory. Furthermore, AQP4 deficiency significantly downregulated glutamate transporter-1 (GLT-1) expression and selectively increased NMDA receptor (NMDAR)-mediated EPSCs in the LA. However, low concentration of NMDAR antagonist reversed the impairment of LTP in KO mice. Upregulating GLT-1 expression by chronic treatment with ceftriaxone also reversed the impairment of LTP and fear memory in KO mice. These findings imply a role for AQP4 in synaptic plasticity and associative fear memory in the amygdala by regulating GLT-1 expression.
Collapse
|
86
|
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: 221] [Impact Index Per Article: 18.4] [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.
Collapse
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.
| | | |
Collapse
|
87
|
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: 59] [Impact Index Per Article: 4.9] [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.
Collapse
Affiliation(s)
- Dongdong Li
- INSERM U603, CNRS UMR 8154, Laboratoire de Neurophysiologie et Nouvelles Microscopies, 45 rue des Saints Pères, Paris, F-75006 France.
| | | | | | | | | |
Collapse
|
88
|
Abstract
Astrocytes participate in all essential CNS functions, including blood flow regulation, energy metabolism, ion and water homeostasis, immune defence, neurotransmission, and adult neurogenesis. It is thus not surprising that astrocytic morphology and function differ between regions, and that different subclasses of astrocytes exist within the same brain region. Recent lines of work also show that the complexity of protoplasmic astrocytes increases during evolution. Human astrocytes are structurally more complex, larger, and propagate calcium signals significantly faster than rodent astrocytes. In this chapter, we review the diversity of astrocytic form and function, while considering the markedly expanded roles of astrocytes with phylogenetic evolution. We also define major challenges for the future, which include determining how astrocytic functions are locally specified, defining the molecular controls upon astrocytic fate and physiology and establishing how evolutionary changes in astrocytes contribute to higher cognitive functions.
Collapse
Affiliation(s)
- Nancy Ann Oberheim
- Center for Translational Neuromedicine, Department of Neurology, University of Rochester Medical Center, Rochester, NY, USA
| | | | | |
Collapse
|
89
|
Depolarization-Induced Release of Amino Acids From the Vestibular Nuclear Complex. Neurochem Res 2011; 37:732-9. [DOI: 10.1007/s11064-011-0666-0] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2011] [Revised: 11/17/2011] [Accepted: 11/28/2011] [Indexed: 10/14/2022]
|
90
|
Abstract
The seminal discovery that glial cells, particularly astrocytes, can release a number of gliotransmitters that serve as signalling molecules for the cross-talk with neighbouring cellular populations has recently changed our perception of brain functioning, as well as our view of the pathogenesis of several disorders of the CNS. Since glutamate was one of the first gliotransmitters to be identified and characterized, we tackle the mechanisms that underlie its release from astrocytes, including the Ca2+ signals underlying its efflux from astroglia, and we discuss the involvement of these events in a number of relevant physiological processes, from the modulatory control of neighbouring synapses to the regulation of blood supply to cerebral tissues. The relevance of these mechanisms strongly indicates that the contribution of glial cells and gliotransmission to the activities of the brain cannot be overlooked, and any study of CNS physiopathology needs to consider glial biology to have a comprehensive overview of brain function and dysfunction. Abnormalites in the signalling that controls the astrocytic release of glutamate are described in several experimental models of neurological disorders, for example, AIDS dementia complex, Alzheimer's disease and cerebral ischaemia. While the modalities of glutamate release from astrocytes remain poorly understood, and this represents a major impediment to the definition of novel therapeutic strategies targeting this process at the molecular level, some key mediators deputed to the control of the glial release of this excitatory amino acid have been identified. Among these, we can mention, for instance, proinflammatory cytokines, such as tumour necrosis factor-α, and prostaglandins. Agents that are able to block the major steps of tumour necrosis factor-α and prostaglandin production and/or signalling can be proposed as novel therapeutic targets for the treatment of these disorders.
Collapse
Affiliation(s)
- Daniela Rossi
- Laboratory for Research on Neurodegenerative Disorders, IRCCS Fondazione Salvatore Maugeri, Pavia, Italy.
| | | | | |
Collapse
|
91
|
Xu X, Warrington AE, Bieber AJ, Rodriguez M. Enhancing CNS repair in neurological disease: challenges arising from neurodegeneration and rewiring of the network. CNS Drugs 2011; 25:555-73. [PMID: 21699269 PMCID: PMC3140701 DOI: 10.2165/11587830-000000000-00000] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Repair of the central nervous system (CNS) constitutes an integral part of treating neurological disease and plays a crucial role in restoring CNS architecture and function. Distinct strategies have been developed to reconstruct the damaged neural tissue, with many tested preclinically in animal models. We review cell replacement-based repair strategies. By taking spinal cord injury, cerebral ischaemia and degenerative CNS disorders as examples for CNS repair, we discuss progress and potential problems in utilizing embryonic stem cells and adult neural/non-neural stem cells to repair cell loss in the CNS. Nevertheless, CNS repair is not simply a matter of cell transplantation. The major challenge is to induce regenerating neural cells to integrate into the neural network and compensate for damaged neural function. The neural cells confront an environment very different from that of the developmental stage in which these cells differentiate to form interwoven networks. During the repair process, one of the challenges is neurodegeneration, which can develop from interrupted innervations to/from the targets, chronic inflammation, ischaemia, aging or idiopathic neural toxicity. Neurodegeneration, which occurs on the basis of a characteristic vascular and neural web, usually presents as a chronically progressive process with unknown aetiology. Currently, there is no effective treatment to stop or slow down neurodegeneration. Pathological changes from patients with Alzheimer's disease, Parkinson's disease and amyotrophic lateral sclerosis indicate a broken homeostasis in the CNS. We discuss how the blood-brain barrier and neural networks are formed to maintain CNS homeostasis and their contribution to neurodegeneration in diseased conditions. Another challenge is that some inhibitors produced by CNS injury do not facilitate the regenerating neural cells to incorporate into a pre-existing network. We review glial responses to CNS injury. Of note, the reactive astrocytes not only encompass the lesions/pathogens but may also form glial scars to impede regenerating axons from traversing the lesions. In addition, myelin debris can prevent axon growth. Myelination enables saltatory transduction of electrical impulses along axonal calibers and actually provides trophic support to stabilize the axons. Therefore, repair strategies should be designed to promote axonal growth, myelination and modulate astrocytic responses. Finally, we discuss recent progress in developing human monoclonal IgMs that regulate CNS homeostasis and promote neural regeneration.
Collapse
Affiliation(s)
- Xiaohua Xu
- Department of Neurology, Mayo Clinic and Foundation, Rochester, MN 55905
| | | | - Allan J. Bieber
- Department of Neurology, Mayo Clinic and Foundation, Rochester, MN 55905
| | - Moses Rodriguez
- Department of Neurology, Mayo Clinic and Foundation, Rochester, MN 55905, Department of Immunology, Mayo Clinic and Foundation, Rochester, MN 55905
| |
Collapse
|
92
|
Fields RD. Imaging single photons and intrinsic optical signals for studies of vesicular and non-vesicular ATP release from axons. Front Neuroanat 2011; 5:32. [PMID: 21852965 PMCID: PMC3151621 DOI: 10.3389/fnana.2011.00032] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2011] [Accepted: 05/26/2011] [Indexed: 12/12/2022] Open
Abstract
The temporal and spatial dynamics of neurotransmitter release are fundamental to understanding activity-dependent signaling between axons and other cells, including neurons, glia, and vascular cells. A microscopic imaging technique is described that enables studying release of the neurotransmitter ATP from axons in response to action potentials. The method combines imaging single-photons, intrinsic optical signal imaging, and high magnification time-lapse microcopy to enable investigations of action potential-induced ATP release together with cell morphology and activity-dependent axon swelling. ATP released from axons catalyzes a chemiluminescent reaction between luciferin and luciferase that generates single photons that can be imaged individually. In addition to vesicular release, ATP release through membrane channels activated by axon swelling was monitored simultaneously with intrinsic optical signals. Repeated emissions of photons were observed from localized 15 μm regions of axons, with a frequency distribution that differed from a normal distribution and from the frequency of emissions outside these localized regions.
Collapse
Affiliation(s)
- R. Douglas Fields
- Nervous Systems Development and Plasticity Section, National Institute of Child Health and Human Development, National Institutes of HealthBethesda, MD, USA
| |
Collapse
|
93
|
Abstract
Astrocytes were identified about 150 years ago, and, for the longest time, were considered to be supporting cells in the brain providing trophic, metabolic, and structural support for neural networks. Research in the last 2 decades has uncovered many novel molecules in astrocytes and the finding that astrocytes communicate with neurons via Ca2+ signaling, which leads to release of chemical transmitters, termed gliotransmitters, has led to renewed interest in their biology. This chapter will briefly review the unique morphology and molecular properties of astrocytes. The reader will be introduced to the role of astrocytes in blood-brain barrier (BBB) maintenance, in Ca2+ signaling, in synaptic transmission, in CNS synaptogenesis, and as neural progenitor cells. Mention is also made of the diseases in which astrocyte dysfunction has a role.
Collapse
Affiliation(s)
- Sukriti Nag
- Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, ON, Canada
| |
Collapse
|
94
|
Koltsova SV, Platonova A, Maksimov GV, Mongin AA, Grygorczyk R, Orlov SN. Activation of P2Y receptors causes strong and persistent shrinkage of C11-MDCK renal epithelial cells. Am J Physiol Cell Physiol 2011; 301:C403-12. [PMID: 21562307 DOI: 10.1152/ajpcell.00018.2011] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Purinergic receptors activate diverse signaling cascades and regulate the activity of cell volume-sensitive ion transporters. However, the effects of ATP and other agonists of P2 receptors on cell volume dynamics are only scarcely studied. In the present work, we used the recently developed dual-image surface reconstruction technique to explore the influence of purinergic agonists on cell volume in the C11-Madin-Darby canine kidney cell line resembling intercalated cells from kidney collecting ducts. Unexpectedly, we found that ATP and UTP triggered very robust (55-60%) cell shrinkage that lasted up to 2 h after agonist washout. Purinergic regulation of cell volume required increases in intracellular Ca(2+) and could be partially mimicked by the Ca(2+)-ionophore ionomycin or activation of protein kinase C by 4β-phorbol 12-myristate 13-acetate. Cell shrinkage was accompanied by strong reductions in intracellular K(+) and Cl(-) content measured using steady-state (86)Rb(+) and (36)Cl(-) distribution. Both shrinkage and ion efflux in ATP-treated cells were prevented by the anion channel blocker 5-nitro-2-(3-phenylpropylamino)benzoic acid (NPPB) and by the BK(Ca) channel inhibitors charybdotoxin, iberiotoxin, and paxilline. To evaluate the significance of cell-volume changes in purinergic signaling, we measured the impact of ATP on the expression of the immediate-early gene c-Fos. Thirty-minute treatment with ATP increased c-Fos immunoreactivity by approximately fivefold, an effect that was strongly inhibited by charybdotoxin and completely prevented by NPPB. Overall, our findings suggest that ATP-induced cell-volume changes are partially responsible for the physiological actions of purinergic agonists.
Collapse
Affiliation(s)
- Svetlana V Koltsova
- Research Centre, Centre Hospitalier de l’Université de Montréal (CRCHUM), Montreal, Quebec, Canada
| | | | | | | | | | | |
Collapse
|
95
|
Jiang S, Yuan H, Duan L, Cao R, Gao B, Xiong YF, Rao ZR. Glutamate release through connexin 43 by cultured astrocytes in a stimulated hypertonicity model. Brain Res 2011; 1392:8-15. [DOI: 10.1016/j.brainres.2011.03.056] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2010] [Revised: 03/10/2011] [Accepted: 03/23/2011] [Indexed: 11/29/2022]
|
96
|
Katane M, Homma H. D-Aspartate--an important bioactive substance in mammals: a review from an analytical and biological point of view. J Chromatogr B Analyt Technol Biomed Life Sci 2011; 879:3108-21. [PMID: 21524944 DOI: 10.1016/j.jchromb.2011.03.062] [Citation(s) in RCA: 72] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2011] [Revised: 03/23/2011] [Accepted: 03/30/2011] [Indexed: 01/08/2023]
Abstract
It was long believed that D-amino acids were either unnatural isomers or laboratorial artifacts and that the important functions of amino acids were exerted only by l-amino acids. However, recent investigations have shown that a variety of D-amino acids are present in mammals and that they play important roles in physiological functions in the body. Among the free d-amino acids that have been identified in mammals, D-aspartate (D-Asp) has been shown to play a crucial role in the neuroendocrine and endocrine systems as well as in the central nervous system. Here, we present an overview of recent studies of free D-Asp, focusing on the analytical methods in real biological matrices, expression and localization in tissues and cells, biological and physiological activities, biosynthesis, degradation, cellular transport, and possible relevance to disease. In addition to frequently used techniques for the enantiomeric determination of amino acids, including high-performance liquid chromatography and enzymatic methods, the recent development of analytical methods is also described.
Collapse
Affiliation(s)
- Masumi Katane
- Laboratory of Biomolecular Science, Department of Pharmaceutical Life Sciences, Kitasato University, 5-9-1 Shirokane, Tokyo 108-8641, Japan
| | | |
Collapse
|
97
|
Tawfik VL, Chang SY, Hitti FL, Roberts DW, Leiter JC, Jovanovic S, Lee KH. Deep brain stimulation results in local glutamate and adenosine release: investigation into the role of astrocytes. Neurosurgery 2011; 67:367-75. [PMID: 20644423 DOI: 10.1227/01.neu.0000371988.73620.4c] [Citation(s) in RCA: 107] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
BACKGROUND Several neurological disorders are treated with deep brain stimulation; however, the mechanism underlying its ability to abolish oscillatory phenomena associated with diseases as diverse as Parkinson's disease and epilepsy remain largely unknown. OBJECTIVE To investigate the role of specific neurotransmitters in deep brain stimulation and determine the role of non-neuronal cells in its mechanism of action. METHODS We used the ferret thalamic slice preparation in vitro, which exhibits spontaneous spindle oscillations, to determine the effect of high-frequency stimulation on neurotransmitter release. We then performed experiments using an in vitro astrocyte culture to investigate the role of glial transmitter release in high-frequency stimulation-mediated abolishment of spindle oscillations. RESULTS In this series of experiments, we demonstrated that glutamate and adenosine release in ferret slices was able to abolish spontaneous spindle oscillations. The glutamate release was still evoked in the presence of the Na channel blocker tetrodotoxin, but was eliminated with the vesicular H-ATPase inhibitor bafilomycin and the calcium chelator 2-bis(2-aminophenoxy)-ethane-N,N,N',N'-tetraacetic acid tetrakis acetoxymethyl ester. Furthermore, electrical stimulation of purified primary astrocytic cultures was able to evoke intracellular calcium transients and glutamate release, and bath application of 2-bis (2-aminophenoxy)-ethane-N,N,N',N'-tetraacetic acid tetrakis acetoxymethyl ester inhibited glutamate release in this setting. CONCLUSION Vesicular astrocytic neurotransmitter release may be an important mechanism by which deep brain stimulation is able to achieve clinical benefits.
Collapse
Affiliation(s)
- Vivianne L Tawfik
- Department of Pharmacology, Dartmouth Medical School, Hanover, New Hampshire, USA
| | | | | | | | | | | | | |
Collapse
|
98
|
Shah RS, Chang SY, Min HK, Cho ZH, Blaha CD, Lee KH. Deep brain stimulation: technology at the cutting edge. J Clin Neurol 2010; 6:167-82. [PMID: 21264197 PMCID: PMC3024521 DOI: 10.3988/jcn.2010.6.4.167] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2010] [Revised: 09/16/2010] [Accepted: 09/16/2010] [Indexed: 01/15/2023] Open
Abstract
Deep brain stimulation (DBS) surgery has been performed in over 75,000 people worldwide, and has been shown to be an effective treatment for Parkinson's disease, tremor, dystonia, epilepsy, depression, Tourette's syndrome, and obsessive compulsive disorder. We review current and emerging evidence for the role of DBS in the management of a range of neurological and psychiatric conditions, and discuss the technical and practical aspects of performing DBS surgery. In the future, evolution of DBS technology may depend on several key areas, including better scientific understanding of its underlying mechanism of action, advances in high-spatial resolution imaging and development of novel electrophysiological and neurotransmitter microsensor systems. Such developments could form the basis of an intelligent closed-loop DBS system with feedback-guided neuromodulation to optimize both electrode placement and therapeutic efficacy.
Collapse
Affiliation(s)
- Rahul S Shah
- Department of Neurological Surgery, Mayo Clinic, Rochester, MN, USA
| | | | | | | | | | | |
Collapse
|
99
|
Abstract
Astrocytes constitute a major group of glial cells which were long regarded as passive elements, fulfilling nutritive and structural functions for neurons. Calcium rise in astrocytes propagating to neurons was the first demonstration of direct interaction between the two cell types. Since then, calcium has been widely used, not only as an indicator of astrocytic activity but also as a stimulator switch to control astrocyte physiology. As a result, astrocytes have been elevated from auxiliaries to neurons, to cells involved in processing synaptic information. Curiously, while there is evidence that astrocytes play an important role in synaptic plasticity, the data relating to calcium's pivotal role are inconsistent. In this review, we will detail the various mechanisms of calcium flux in astrocytes, then briefly present the calcium-dependent mechanisms of gliotransmitter release. Finally, we will discuss the role of calcium in plasticity and present alternative explanations that could reconcile the conflicting results published recently.
Collapse
|
100
|
Abstract
Reactive astrocytes are a pathological hallmark of many CNS injuries and neurodegenerations. They are characterized by hypertrophy of the soma and processes and an increase in the expression of glial fibrillary acidic protein. Because the cells obscure each other in immunostaining, little is known about the behavior of a single reactive astrocyte, nor how single astrocytes combine to form the glial scar. We have investigated the reaction of fibrous astrocytes to axonal degeneration using a transgenic mouse strain expressing enhanced green fluorescent protein in small subsets of astrocytes. Fibrous astrocytes in the optic nerve and corpus callosum initially react to injury by hypertrophy of the soma and processes. They retract their primary processes, simplifying their shape and dramatically reducing their spatial coverage. At 3 d after crush, quantitative analysis revealed nearly a twofold increase in the thickness of the primary processes, a halving of the number of primary processes leaving the soma and an eightfold reduction in the spatial coverage. In the subsequent week, they partially reextend long processes, returning to a near-normal morphology and an extensive spatial overlap. The resulting glial scar consists of an irregular array of astrocyte processes, contrasting with their original orderly arrangement. These changes are in distinct contrast to those reported for reactive protoplasmic astrocytes of the gray matter, in which the number of processes and branchings increase, but the cells continue to maintain nonoverlapping individual territories throughout their response to injury.
Collapse
|