151
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Guo Y, Liu Y, Xu L, Wu S, Yang C, Wu D, Wu H, Li C. Astrocytic pathology in the immune-mediated motor neuron injury. ACTA ACUST UNITED AC 2007; 8:230-4. [PMID: 17653921 DOI: 10.1080/17482960701278612] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Abstract
Reactive astrogliosis has been found in the cerebral cortex and spinal cord in amyotrophic lateral sclerosis, whereas astrocytic pathology in immune-mediated motor neuron injury has not been reported. On the basis of the establishment of an immune-mediated motor neuron injury model, histological, immunohistochemical and ultrastructural studies on astrocytes were carried out. Reactive astrogliosis in spinal cord anterior horn was observed, and the increase of GFAP-positive astrocytes may occur prior to the clinical manifestations. Reactive astrocytes could show pathological changes similar to those of motor neurons, such as swollen mitochondria and dilated endoplasmic reticulum. Of special interest are crystallized inclusions that were frequently observed in the reactive astrocytes in the bovine ventral horn homogenate-immunized anterior horn. The precise nature and origin of these inclusions deserve to be elucidated.
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Affiliation(s)
- Yansu Guo
- Department of Neurology, The Second Hospital of Hebei Medical University, China
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152
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Castro MA, Pozo M, Cortés C, García MDLA, Concha II, Nualart F. Intracellular ascorbic acid inhibits transport of glucose by neurons, but not by astrocytes. J Neurochem 2007; 102:773-82. [PMID: 17630983 DOI: 10.1111/j.1471-4159.2007.04631.x] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
It has been demonstrated that glutamatergic activity induces ascorbic acid (AA) depletion in astrocytes. Additionally, different data indicate that AA may inhibit glucose accumulation in primary cultures of rat hippocampal neurons. Thus, our hypothesis postulates that AA released from the astrocytes during glutamatergic synaptic activity may inhibit glucose uptake by neurons. We observed that cultured neurons express the sodium-vitamin C cotransporter 2 and the facilitative glucose transporters (GLUT) 1 and 3, however, in hippocampal brain slices GLUT3 was the main transporter detected. Functional activity of GLUTs was confirmed by means of kinetic analysis using 2-deoxy-d-glucose. Therefore, we showed that AA, once accumulated inside the cell, inhibits glucose transport in both cortical and hippocampal neurons in culture. Additionally, we showed that astrocytes are not affected by AA. Using hippocampal slices, we observed that upon blockade of monocarboxylate utilization by alpha-cyano-4-hydroxycinnamate and after glucose deprivation, glucose could rescue neuronal response to electrical stimulation only if AA uptake is prevented. Finally, using a transwell system of separated neuronal and astrocytic cultures, we observed that glutamate can reduce glucose transport in neurons only in presence of AA-loaded astrocytes, suggesting the essential role of astrocyte-released AA in this effect.
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Affiliation(s)
- Maite A Castro
- Instituto de Bioquímica, Facultad de Ciencias Biológicas, Universidad Austral de Chile, Valdivia, Chile
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153
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Patti L, Raiteri L, Grilli M, Zappettini S, Bonanno G, Marchi M. Evidence that α7 nicotinic receptor modulates glutamate release from mouse neocortical gliosomes. Neurochem Int 2007; 51:1-7. [PMID: 17462791 DOI: 10.1016/j.neuint.2007.03.003] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2007] [Revised: 03/05/2007] [Accepted: 03/07/2007] [Indexed: 11/23/2022]
Abstract
The presence of nicotinic receptors on astrocytes in human and rat brain has been previously demonstrated however their possible functional role is still poorly understood. In this study we investigated on the presence of nicotinic receptors on gliosomes, purified from mouse cortex, and on their role in eliciting glutamate release. Epibatidine significantly increased basal release of [3H]D-aspartate and of endogenous glutamate from mouse gliosomes but not from synaptosomes. This effect was prevented by methyllycaconitine, alpha-bungarotoxin and mecamylamine but not by dihydro-beta-erythroidine. Epibatidine provoked also a significant increase of calcium concentration in gliosomes but not in synaptosomes; the increase in [Ca2+]i induced by epibatidine and KCl in gliosomes was very similar to each other. The present results indicate that alpha7 nicotinic receptors exist on mouse cortical glial particles and stimulate glutamate release.
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Affiliation(s)
- Laura Patti
- Sezione di Farmacologia e Tossicologia, Dipartimento di Medicina Sperimentale, Università degli Studi di Genova, Viale Cembrano 4, 16148 Genoa, Italy
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154
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Ho WSC, van den Pol AN. Bystander attenuation of neuronal and astrocyte intercellular communication by murine cytomegalovirus infection of glia. J Virol 2007; 81:7286-92. [PMID: 17459923 PMCID: PMC1933277 DOI: 10.1128/jvi.02501-06] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2006] [Accepted: 04/18/2007] [Indexed: 11/20/2022] Open
Abstract
Astrocytes are the first cells infected by murine cytomegalovirus (MCMV) in primary cultures of brain. These cells play key roles in intercellular signaling and neuronal development, and they modulate synaptic activity within the nervous system. Using ratiometric fura-2 digital calcium imaging of >8,000 neurons and glia, we found that MCMV-infected astrocytes showed an increase in intracellular basal calcium levels and an enhanced response to neuroactive substances, including glutamate and ATP, and to high potassium levels. Cultured neurons with no sign of MCMV infection showed attenuated synaptic signaling after infection of the underlying astrocyte substrate, and intercellular communication between astrocytes with no sign of infection was reduced by the presence of infected glia. These bystander effects would tend to cause further deterioration of cellular communication in the brain in addition to the problems caused by the loss of directly infected cells.
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Affiliation(s)
- Winson S C Ho
- Department of Neurosurgery, Yale University School of Medicine, 333 Cedar St., New Haven, CT 06520, USA
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155
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Chen J, Zhang J, Zhao Y, Yuan L, Nie X, Li J, Ma Z, Zhang Y, Wang Q, Chen Y, Jin Y, Rao Z. Hyperalgesia in response to traumatic occlusion and GFAP expression in rat parabranchial nucleus: modulation with fluorocitrate. Cell Tissue Res 2007; 329:231-7. [PMID: 17443351 DOI: 10.1007/s00441-007-0409-3] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2006] [Accepted: 02/28/2007] [Indexed: 11/24/2022]
Abstract
We have examined, by immunocytochemical methods and nociceptive behavior assessment in rats, whether astrocytes in the parabrachial nucleus (PBN) are involved in the regulation of traumatic occlusion. The expression of glial fibrillary acidic protein (GFAP) in PBN of ipsilateral and contralateral sides was up-regulated 4 h after occlusal changes in molars, reached peak levels at 24 h, and was then gradually down-regulated. PBN astrocytes activated by traumatic occlusion were found to have enlarged cell bodies and thickened processes within 8 h. An inhibitor of glia metabolism (FCA, fluorocitrate) reduced astrocyte activation and significantly attenuated the development of pain hypersensitivity in this model. The results suggested that the GFAP-immunoreactive astrocytes in PBN within the bridge of Varolius were activated by traumatic occlusion, and that they were involved in the transmission and modulation of nociceptive information in the central nervous system. However, although astrocytes in PBN are thus probably involved in causing post-occlusal hyperalgesia, we have not been able to exclude that astrocytes at other locations also contribute to this effect.
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Affiliation(s)
- Jinwu Chen
- Department of Oral Radiology and General Dentistry, School of Stomatology, Fourth Military Medical University, Xi'an, 710032, People's Republic of China.
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156
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Gipson KE, Yeckel MF. Coincident glutamatergic and cholinergic inputs transiently depress glutamate release at rat schaffer collateral synapses. J Neurophysiol 2007; 97:4108-19. [PMID: 17303811 PMCID: PMC2878610 DOI: 10.1152/jn.01051.2006] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The mammalian hippocampus, together with subcortical and cortical areas, is responsible for some forms of learning and memory. Proper hippocampal function depends on the highly dynamic nature of its circuitry, including the ability of synapses to change their strength for brief to long periods of time. In this study, we focused on a transient depression of glutamatergic synaptic transmission at Schaffer collateral synapses in acute hippocampal slices. The depression of evoked excitatory postsynaptic current (EPSC) amplitudes, herein called transient depression, follows brief trains of synaptic stimulation in stratum radiatum of CA1 and lasts for 2-3 min. Depression results from a decrease in presynaptic glutamate release, as NMDA-receptor-mediated EPSCs and composite EPSCs are depressed similarly and depression is accompanied by an increase in the paired-pulse ratio. Transient depression is prevented by blockade of metabotropic glutamate and acetylcholine receptors, presumably located presynaptically. These two receptor types--acting together--cause depression. Blockade of a single receptor type necessitates significantly stronger conditioning trains for triggering depression. Addition of an acetylcholinesterase inhibitor enables depression from previously insufficient conditioning trains. Furthermore, a strong coincident, but not causal, relationship existed between presynaptic depression and postsynaptic internal Ca(2+) release, emphasizing the potential importance of functional interactions between presynaptic and postsynaptic effects of convergent cholinergic and glutamatergic inputs to CA1. These convergent afferents, one intrinsic to the hippocampus and the other likely originating in the medial septum, may regulate CA1 network activity, the induction of long-term synaptic plasticity, and ultimately hippocampal function.
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Affiliation(s)
- Keith E Gipson
- Department of Neurobiology, Yale University School of Medicine, 333 Cedar Street, New Haven, CT 06510, USA
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157
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Straub SV, Bonev AD, Wilkerson MK, Nelson MT. Dynamic inositol trisphosphate-mediated calcium signals within astrocytic endfeet underlie vasodilation of cerebral arterioles. ACTA ACUST UNITED AC 2007; 128:659-69. [PMID: 17130519 PMCID: PMC2151598 DOI: 10.1085/jgp.200609650] [Citation(s) in RCA: 78] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
Active neurons communicate to intracerebral arterioles in part through an elevation of cytosolic Ca2+ concentration ([Ca2+]i) in astrocytes, leading to the generation of vasoactive signals involved in neurovascular coupling. In particular, [Ca2+]i increases in astrocytic processes (“endfeet”), which encase cerebral arterioles, have been shown to result in vasodilation of arterioles in vivo. However, the spatial and temporal properties of endfoot [Ca2+]i signals have not been characterized, and information regarding the mechanism by which these signals arise is lacking. [Ca2+]i signaling in astrocytic endfeet was measured with high spatiotemporal resolution in cortical brain slices, using a fluorescent Ca2+ indicator and confocal microscopy. Increases in endfoot [Ca2+]i preceded vasodilation of arterioles within cortical slices, as detected by simultaneous measurement of endfoot [Ca2+]i and vascular diameter. Neuronal activity–evoked elevation of endfoot [Ca2+]i was reduced by inhibition of inositol 1,4,5-trisphosphate (InsP3) receptor Ca2+ release channels and almost completely abolished by inhibition of endoplasmic reticulum Ca2+ uptake. To probe the Ca2+ release mechanisms present within endfeet, spatially restricted flash photolysis of caged InsP3 was utilized to liberate InsP3 directly within endfeet. This maneuver generated large amplitude [Ca2+]i increases within endfeet that were spatially restricted to this region of the astrocyte. These InsP3-induced [Ca2+]i increases were sensitive to depletion of the intracellular Ca2+ store, but not to ryanodine, suggesting that Ca2+-induced Ca2+ release from ryanodine receptors does not contribute to the generation of endfoot [Ca2+]i signals. Neuronally evoked increases in astrocytic [Ca2+]i propagated through perivascular astrocytic processes and endfeet as multiple, distinct [Ca2+]i waves and exhibited a high degree of spatial heterogeneity. Regenerative Ca2+ release processes within the endfeet were evident, as were localized regions of Ca2+ release, and treatment of slices with the vasoactive neuropeptides somatostatin and vasoactive intestinal peptide was capable of inducing endfoot [Ca2+]i increases, suggesting the potential for signaling between local interneurons and astrocytic endfeet in the cortex. Furthermore, photorelease of InsP3 within individual endfeet resulted in a local vasodilation of adjacent arterioles, supporting the concept that astrocytic endfeet function as local “vasoregulatory units” by translating information from active neurons into complex InsP3-mediated Ca2+ release signals that modulate arteriolar diameter.
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Affiliation(s)
- Stephen V Straub
- Department of Pharmacology, University of Vermont, Burlington, VT 05405, USA
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158
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Montana V, Malarkey EB, Verderio C, Matteoli M, Parpura V. Vesicular transmitter release from astrocytes. Glia 2006; 54:700-715. [PMID: 17006898 DOI: 10.1002/glia.20367] [Citation(s) in RCA: 230] [Impact Index Per Article: 12.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
Astrocytes can release a variety of transmitters, including glutamate and ATP, in response to stimuli that induce increases in intracellular Ca(2+) levels. This release occurs via a regulated, exocytotic pathway. As evidence of this, astrocytes express protein components of the vesicular secretory apparatus, including synaptobrevin 2, syntaxin, and SNAP-23. Additionally, astrocytes possess vesicular organelles, the essential morphological elements required for regulated Ca(2+)-dependent transmitter release. The location of specific exocytotic sites on these cells, however, remains to be unequivocally determined.
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Affiliation(s)
- Vedrana Montana
- Department of Cell Biology and Neuroscience, Center for Glial-Neuronal Interactions, University of California, Riverside, California
| | - Erik B Malarkey
- Department of Cell Biology and Neuroscience, Center for Glial-Neuronal Interactions, University of California, Riverside, California
| | - Claudia Verderio
- Department of Medical Pharmacology, Consiglio Nazionalle delle Ricerche Institute of Neuroscience, University of Milano, Milano, Italy
| | - Michela Matteoli
- Department of Medical Pharmacology, Consiglio Nazionalle delle Ricerche Institute of Neuroscience, University of Milano, Milano, Italy
| | - Vladimir Parpura
- Department of Cell Biology and Neuroscience, Center for Glial-Neuronal Interactions, University of California, Riverside, California
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159
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Abstract
From a structural perspective, the predominant glial cell of the central nervous system, the astrocyte, is positioned to regulate synaptic transmission and neurovascular coupling: the processes of one astrocyte contact tens of thousands of synapses, while other processes of the same cell form endfeet on capillaries and arterioles. The application of subcellular imaging of Ca2+ signaling to astrocytes now provides functional data to support this structural notion. Astrocytes express receptors for many neurotransmitters, and their activation leads to oscillations in internal Ca2+. These oscillations induce the accumulation of arachidonic acid and the release of the chemical transmitters glutamate, d-serine, and ATP. Ca2+ oscillations in astrocytic endfeet can control cerebral microcirculation through the arachidonic acid metabolites prostaglandin E2 and epoxyeicosatrienoic acids that induce arteriole dilation, and 20-HETE that induces arteriole constriction. In addition to actions on the vasculature, the release of chemical transmitters from astrocytes regulates neuronal function. Astrocyte-derived glutamate, which preferentially acts on extrasynaptic receptors, can promote neuronal synchrony, enhance neuronal excitability, and modulate synaptic transmission. Astrocyte-derived d-serine, by acting on the glycine-binding site of the N-methyl-d-aspartate receptor, can modulate synaptic plasticity. Astrocyte-derived ATP, which is hydrolyzed to adenosine in the extracellular space, has inhibitory actions and mediates synaptic cross-talk underlying heterosynaptic depression. Now that we appreciate this range of actions of astrocytic signaling, some of the immediate challenges are to determine how the astrocyte regulates neuronal integration and how both excitatory (glutamate) and inhibitory signals (adenosine) provided by the same glial cell act in concert to regulate neuronal function.
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Affiliation(s)
- Philip G Haydon
- Silvio Conte Center for Integration at the Tripartite Synapse, Department of Neuroscience, University of Pennsylvania School of Medicine, PA 19104, USA.
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160
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Wang TF, Zhou C, Tang AH, Wang SQ, Chai Z. Cellular mechanism for spontaneous calcium oscillations in astrocytes. Acta Pharmacol Sin 2006; 27:861-8. [PMID: 16787570 DOI: 10.1111/j.1745-7254.2006.00397.x] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
Abstract
AIM To determine the Ca2+ source and cellular mechanisms of spontaneous Ca2+ oscillations in hippocampal astrocytes. METHODS The cultured cells were loaded with Fluo-4 AM, the indicator of intracellular Ca2+, and the dynamic Ca2+ transients were visualized with confocal laser-scanning microscopy. RESULTS The spontaneous Ca2+ oscillations in astrocytes were observed first in co-cultured hippocampal neurons and astrocytes. These oscillations were not affected by tetrodotoxin (TTX) treatment and kept up in purity cultured astrocytes. The spontaneous Ca2+ oscillations were not impacted after blocking the voltage-gated Ca2+ channels or ethylenediamine tetraacetic acid (EDTA) bathing, indicating that intracellular Ca2+ elevation was not the result of extracellular Ca2+ influx. Furthermore, the correlation between the spontaneous Ca2+ oscillations and the Ca2+ store in endoplasmic reticulum (ER) were investigated with pharmacological experiments. The oscillations were: 1) enhanced when cells were exposed to both low Na+ (70 mmol/L) and high Ca2+ (5 mmol/L) solution, and eliminated completely by 2 micromol/L thapsigargin, a blocker of sarcoplasmic reticulum Ca2+-ATPase; and 2) still robust after the application with either 50 micromol/L ryanodine or 400 micromol/L tetracaine, two specific antagonists of ryanodine receptors, but depressed in a dose-dependent manner by 2-APB, an InsP3 receptors (InsP3R) blocker. CONCLUSION InsP3R-induced ER Ca2+ release is an important cellular mechanism for the initiation of spontaneous Ca2+ oscillation in hippocampal astrocytes.
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Affiliation(s)
- Tong-fei Wang
- State Key Laboratory of Biomembrane and Membrane Biotechnology, College of Life Sciences, Peking University, Beijing 100871, China
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161
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Rao SP, Sikdar SK. Astrocytes in 17beta-estradiol treated mixed hippocampal cultures show attenuated calcium response to neuronal activity. Glia 2006; 53:817-26. [PMID: 16565986 DOI: 10.1002/glia.20341] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Glial cells in the brain are capable of responding to hormonal signals. The ovarian steroid hormone 17beta-estradiol, in addition to its actions on neurons, can directly affect glial cells. Estrogen receptors have been described on both neurons and astrocytes, suggesting a complex interplay between these two in mediating the effects of the hormone. Astrocytes sense and respond to neuronal activity with a rise in intracellular calcium concentration ([Ca(2+)](i)). Using simultaneous electrophysiology and calcium imaging techniques, we monitored neuronal activity evoked astrocyte ([Ca(2+)](i)) changes in mixed hippocampal cultures loaded with fluo-3 AM. Action potential firing in neurons, elicited by injecting depolarizing current pulses, was associated with ([Ca(2+)](i)) elevations in astrocytes, which could be blocked by 200 microM MCPG and also 1 microM TTX. We compared astrocytic ([Ca(2+)](i)) transients in control and 24-hour estradiol treated cultures. The amplitude of the ([Ca(2+)](i)) transient, the number of responsive astrocytes, and the ([Ca(2+)](i)) wave velocity were all significantly reduced in estradiol treated cultures. ([Ca(2+)](i)) rise in astrocytes in response to local application of the metabotropic glutamate receptor (mGluR) agonist t-ACPD was attenuated in estradiol treated cultures, suggesting functional changes in the astrocyte mGluR following 24-h treatment with estradiol. Since astrocytes can modulate synaptic transmission by release of glutamate, the attenuated ([Ca(2+)](i)) response seen following estradiol treatment could have functional consequences on astrocyte-neuron signaling.
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Affiliation(s)
- Shilpa P Rao
- Molecular Biophysics Unit, Indian Institute of Science, Bangalore, India
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162
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Delicado EG, Miras-Portugal MT, Carrasquero LMG, León D, Pérez-Sen R, Gualix J. Dinucleoside polyphosphates and their interaction with other nucleotide signaling pathways. Pflugers Arch 2006; 452:563-72. [PMID: 16688466 DOI: 10.1007/s00424-006-0066-5] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2006] [Accepted: 03/06/2006] [Indexed: 11/25/2022]
Abstract
Dinucleoside polyphosphates or Ap(n)A are a family of dinucleotides formed by two adenosines joined by a variable number of phosphates. Ap(4)A, Ap(5)A, and Ap(6)A are stored together with other neurotransmitters into secretory vesicles and are co-released to the extracellular medium upon stimulation. These compounds can interact extracellularly with some ATP receptors, both metabotropic (P2Y) and ionotropic (P2X). However, specific receptors for these substances, other than ATP receptors, have been described in presynaptic terminals form rat midbrain. These specific dinucleotide receptors are of ionotropic nature and their activation induces calcium entry into the terminals and the subsequent neurotransmitter release. Calcium signals that cannot be attributable to the interaction of Ap(n)A with ATP receptors have also been described in cerebellar synaptosomes and granule cell neurons in culture, where Ap(5)A induces CaMKII activation. In addition, cerebellar astrocytes express a specific Ap(5)A receptor coupled to ERK activation. Ap(5)A engaged to MAPK cascade by a mechanism that was insensitive to pertussis toxin and required the involvement of src and ras proteins. Diadenosine polyphosphates, acting on their specific receptors and/or ATP receptors, can also interact with other neurotransmitter systems. This broad range of actions and interactions open a promising perspective for some relevant physiological roles for the dinucleotides. However, the physiological significance of these compounds in the CNS is still to be determined.
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Affiliation(s)
- Esmerilda G Delicado
- Departamento de Bioquímica, Facultad de Veterinaria, Universidad Complutense, 28040, Madrid, Spain
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163
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Abstract
Glial cells were classically considered as supportive cells that do not contribute to information processing in the nervous system. However, considerable amount of evidence obtained by several groups during the last few years has demonstrated the existence of a bidirectional communication between astrocytes and neurons, which prompted a re-examination of the role of glial cells in the physiology of the nervous system. This review will discuss recent advances in the neuron-to-astrocyte communication, focusing on the recently reported properties of the synaptically evoked astrocyte Ca2+ signal that indicate that astrocytes show integrative properties for synaptic information processing. Indeed, we have recently shown that hippocampal astrocytes discriminate between the activity of different synapses, and respond selectively to different axon pathways. Furthermore, the astrocyte Ca2+ signal is modulated by the simultaneous activity of different synaptic inputs. This Ca2+ signal modulation depends on cellular intrinsic properties of the astrocytes, is bidirectionally regulated by the level of synaptic activity, and controls the spatial extension of the intracellular Ca2+ signal. Consequently, we propose that astrocytes can be considered as cellular elements involved in information processing by the nervous system.
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Affiliation(s)
- Gertrudis Perea
- Instituto Cajal, Consejo Superior de Investigaciones Científicas, Doctor Arce 37, Madrid 28002, Spain
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164
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Abstract
Background Recent work has indicated an increasingly complex role for astrocytes in the central nervous system. Astrocytes are now known to exchange information with neurons at synaptic junctions and to alter the information processing capabilities of the neurons. As an extension of this trend a hypothesis was proposed that astrocytes function to store information. To explore this idea the ion channels in biological membranes were compared to models known as cellular automata. These comparisons were made to test the hypothesis that ion channels in the membranes of astrocytes form a dynamic information storage device. Results Two dimensional cellular automata were found to behave similarly to ion channels in a membrane when they function at the boundary between order and chaos. The length of time information is stored in this class of cellular automata is exponentially related to the number of units. Therefore the length of time biological ion channels store information was plotted versus the estimated number of ion channels in the tissue. This analysis indicates that there is an exponential relationship between memory and the number of ion channels. Extrapolation of this relationship to the estimated number of ion channels in the astrocytes of a human brain indicates that memory can be stored in this system for an entire life span. Interestingly, this information is not affixed to any physical structure, but is stored as an organization of the activity of the ion channels. Further analysis of two dimensional cellular automata also demonstrates that these systems have both associative and temporal memory capabilities. Conclusion It is concluded that astrocytes may serve as a dynamic information sink for neurons. The memory in the astrocytes is stored by organizing the activity of ion channels and is not associated with a physical location such as a synapse. In order for this form of memory to be of significant duration it is necessary that the ion channels in the astrocyte syncytium be electrically in contact with each other. This function may be served by astrocyte gap junctions and suggests that agents that selectively block these gap junctions should disrupt memory.
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Affiliation(s)
- Robert M Caudle
- Department of Oral and Maxillofacial Surgery and Diagnostic Sciences, University of Florida College of Dentistry, Gainesville, Florida 32610, USA.
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165
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Oliet SHR, Mothet JP. Molecular determinants ofD-serine-mediated gliotransmission: From release to function. Glia 2006; 54:726-737. [PMID: 17006901 DOI: 10.1002/glia.20356] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Since the late 80s, it is recognized that functional activation of N-methyl D-aspartate receptors (NMDARs) requires the binding of both glutamate and glycine. However, the surprising discovery that the wrong isomer of serine, D-serine, is present in mammals has profoundly challenged this dogmatic model of NMDARs activation. Indeed, there are accumulating evidence indicating that D-serine is the endogenous ligand for the glycine modulatory binding site in many brain areas. D-Serine is synthesized in glial cells by serine racemase (SR) and released upon activation of glutamate receptors. Here, we will provide an overview of recent findings on the molecular and cellular mechanisms involved in the synthesis and release of this gliotransmitter. We will also emphasize the function of this novel messenger in regulating synaptic excitatory transmission and plasticity in different brain areas. Because it fulfils all criteria for a gliotransmitter, D-serine regulatory action on glutamatergic transmission further illustrates the emerging concept of the "tripartite synapse".
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Affiliation(s)
- Stéphane H R Oliet
- INSERM U378 and Université Victor Segalen Bordeaux 2, 146 rue Léo Saignat, 33077 Bordeaux, France
| | - Jean-Pierre Mothet
- INSERM U378 and Université Victor Segalen Bordeaux 2, 146 rue Léo Saignat, 33077 Bordeaux, France
- Institut de Neurobiologie Alfred Fessard, Laboratoire de Neurobiologie Cellulaire et Moléculaire, CNRS UPR9040, 1 avenue de la Terrasse, 91198 Gif-sur-Yvette, France
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166
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Rousse I, Robitaille R. Calcium signaling in Schwann cells at synaptic and extra-synaptic sites: Active glial modulation of neuronal activity. Glia 2006; 54:691-699. [PMID: 17006897 DOI: 10.1002/glia.20388] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Glial cells are widely dispersed in the central nervous system (CNS) as well as in the peripheral nervous system (PNS). In the PNS, perisynaptic Schwann cells (PSCs) are the glial cells associated with the pre- and postsynaptic elements of the neuromuscular junction (NMJ). They, as other glial cells of the CNS, respond to high-frequency motor nerve stimulation with an increase in intracellular Ca(2+). In addition to detecting and responding to neurotransmission, PSCs are involved in short-term plasticity events where they depress neurotransmission through G-protein-dependent mechanisms and potentiate synaptic activity via Ca(2+)-dependent mechanisms. In this review, we will discuss evidence that outlines the role of PSCs in short- and long-term modulation of synaptic activity. We will also emphasize present functional similarities and differences in PSC activation at different NMJs. The importance of glial-neural interactions along myelinating axons will also be discussed.
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Affiliation(s)
- Isabelle Rousse
- Département de Physiologie, Université de Montréal, Station Centre-Ville, Montreal, Québec, Canada H3C 3J7
- Centre de Recherche en Sciences Neurologiques, Université de Montréal, Station Centre-Ville, Montreal, Québec, Canada H3C 3J7
| | - Richard Robitaille
- Département de Physiologie, Université de Montréal, Station Centre-Ville, Montreal, Québec, Canada H3C 3J7
- Centre de Recherche en Sciences Neurologiques, Université de Montréal, Station Centre-Ville, Montreal, Québec, Canada H3C 3J7
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167
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Abstract
According to the astrocyte-neurone-lactate shuttle (ANLS) hypothesis, activated neurones use lactate released by astrocytes as their energy substrate. The hypothesis, based largely on in vitro experiments, postulates that lactate is derived from the uptake by astrocytes of synaptically released glutamate. The time course of changes in lactate, derived from in vivo experiments, is incompatible with the ANLS model. Neuronal activation leads to a delayed rise in lactate followed by a slow decay, which greatly outlasts the period of neuronal activation. The present review proposes that the uptake of stimulated glutamate release from astrocytes, rather than synaptically released glutamate, is the source of lactate released following neuronal activation. This rise in lactate occurs too late to provide energy for neuronal activity. Furthermore, there is no evidence that lactate undergoes local oxidative phosphorylation. In conclusion, under physiological conditions, there is no evidence that lactate is a significant source of energy for activated neurones.
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Affiliation(s)
- Marianne Fillenz
- University Laboratory of Physiology, Parks Road, Oxford OX1 3PT, UK.
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168
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Crippa D, Schenk U, Francolini M, Rosa P, Verderio C, Zonta M, Pozzan T, Matteoli M, Carmignoto G. Synaptobrevin2-expressing vesicles in rat astrocytes: insights into molecular characterization, dynamics and exocytosis. J Physiol 2005; 570:567-82. [PMID: 16322057 PMCID: PMC1479876 DOI: 10.1113/jphysiol.2005.094052] [Citation(s) in RCA: 107] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
The SNARE-dependent exocytosis of glutamate-containing vesicles in astrocytes is increasingly viewed as an important signal at the basis of the astrocyte-to-neurone communication system in the brain. Here we provide further insights into the molecular features and dynamics of vesicles in cultured astrocytes. We found that immunoisolated synaptobrevin2 vesicles are clear vesicles quite heterogenous in size and contain the vesicular glutamate transporter v-Glut-2. Moreover, they are immunopositive for synaptotagmin IV, for AMPA receptor subunits GluR2,3 and, to a lesser extent, for GluR1. We also provide direct evidence for the functional expression of v-Glut-2 in astrocytes and demonstrate that synaptobrevin2-positive vesicles can specifically take up (3H)L-glutamate via a bafilomycin-sensitive mechanism. Finally, by time lapse confocal microscopy, we show that a subpopulation of vesicles (tagged with a synaptobrevin2-EGFP chimera) is highly mobile and can fuse with the plasma membrane, preferentially at the level of the astrocyte processes, in a Ca2+-dependent manner. These latter observations, together with the evidence reported here for the expression of functional v-Glut-2 in synaptobrevin2-positive vesicles, provide a molecular basis for regulated exocytosis in astrocyte.
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Affiliation(s)
- Debora Crippa
- Istituto di Neuroscienze CNR and Dipartimento di Scienze Biomediche Sperimentali, Università di Padova, Viale G. Colombo 3, 35121 Padova, Italy
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169
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Rossi D, Brambilla L, Valori CF, Crugnola A, Giaccone G, Capobianco R, Mangieri M, Kingston AE, Bloc A, Bezzi P, Volterra A. Defective tumor necrosis factor-alpha-dependent control of astrocyte glutamate release in a transgenic mouse model of Alzheimer disease. J Biol Chem 2005; 280:42088-96. [PMID: 16253995 DOI: 10.1074/jbc.m504124200] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The cytokine tumor necrosis factor-alpha (TNFalpha) induces Ca2+-dependent glutamate release from astrocytes via the downstream action of prostaglandin (PG) E2. By this process, astrocytes may participate in intercellular communication and neuromodulation. Acute inflammation in vitro, induced by adding reactive microglia to astrocyte cultures, enhances TNFalpha production and amplifies glutamate release, switching the pathway into a neurodamaging cascade (Bezzi, P., Domercq, M., Brambilla, L., Galli, R., Schols, D., De Clercq, E., Vescovi, A., Bagetta, G., Kollias, G., Meldolesi, J., and Volterra, A. (2001) Nat. Neurosci. 4, 702-710). Because glial inflammation is a component of Alzheimer disease (AD) and TNFalpha is overexpressed in AD brains, we investigated possible alterations of the cytokine-dependent pathway in PDAPP mice, a transgenic model of AD. Glutamate release was measured in acute hippocampal and cerebellar slices from mice at early (4-month-old) and late (12-month-old) disease stages in comparison with age-matched controls. Surprisingly, TNFalpha-evoked glutamate release, normal in 4-month-old PDAPP mice, was dramatically reduced in the hippocampus of 12-month-old animals. This defect correlated with the presence of numerous beta-amyloid deposits and hypertrophic astrocytes. In contrast, release was normal in cerebellum, a region devoid of beta-amyloid deposition and astrocytosis. The Ca2+-dependent process by which TNFalpha evokes glutamate release in acute slices is distinct from synaptic release and displays properties identical to those observed in cultured astrocytes, notably PG dependence. However, prostaglandin E2 induced normal glutamate release responses in 12-month-old PDAPP mice, suggesting that the pathology-associated defect involves the TNFalpha-dependent control of secretion rather than the secretory process itself. Reduced expression of DENN/MADD, a mediator of TNFalpha-PG coupling, might account for the defect. Alteration of this neuromodulatory astrocytic pathway is described here for the first time in relation to Alzheimer disease.
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Affiliation(s)
- Daniela Rossi
- Department of Pharmacological Sciences, Center of Excellence on Neurodegenerative Diseases, University of Milan, via Balzaretti, 9, 20133 Milan, Italy
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170
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Perea G, Araque A. Glial calcium signaling and neuron–glia communication. Cell Calcium 2005; 38:375-82. [PMID: 16105683 DOI: 10.1016/j.ceca.2005.06.015] [Citation(s) in RCA: 161] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2005] [Accepted: 06/28/2005] [Indexed: 11/16/2022]
Abstract
The existence of bidirectional signaling between astrocytes and neurons has revealed an important active role of astrocytes in the physiology of the nervous system. As a consequence, there is a new concept of the synaptic physiology-"the tripartite synapse", where astrocytes exchange information with the pre- and postsynaptic elements and participate as dynamic regulatory elements in neurotransmission. The control of the Ca2+ excitability in astrocytes is a key element in this loop of information exchange. The ability of astrocytes to respond to neuronal activity and discriminate between the activity of different synapses, the modulation of the astrocytic cellular excitability by the synaptic activity, and the expression of cellular intrinsic properties indicate that astrocytes are endowed with cellular computational characteristics that process synaptic information. Therefore, we propose that astrocytes can be considered as cellular elements involved in the information processing by the nervous system.
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Affiliation(s)
- Gertrudis Perea
- Instituto Cajal, Consejo Superior de Investigaciones Científicas, Doctor Arce 37, Madrid 28002, Spain
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171
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Volterra A, Meldolesi J. Astrocytes, from brain glue to communication elements: the revolution continues. Nat Rev Neurosci 2005; 6:626-40. [PMID: 16025096 DOI: 10.1038/nrn1722] [Citation(s) in RCA: 1228] [Impact Index Per Article: 64.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
For decades, astrocytes have been considered to be non-excitable support cells of the brain. However, this view has changed radically during the past twenty years. The recent recognition that they are organized in separate territories and possess active properties--notably a competence for the regulated release of 'gliotransmitters', including glutamate--has enabled us to develop an understanding of previously unknown functions for astrocytes. Today, astrocytes are seen as local communication elements of the brain that can generate various regulatory signals and bridge structures (from neuronal to vascular) and networks that are otherwise disconnected from each other. Examples of their specific and essential roles in normal physiological processes have begun to accumulate, and the number of diseases known to involve defective astrocytes is increasing.
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Affiliation(s)
- Andrea Volterra
- Department of Cell Biology and Morphology, University of Lausanne, Rue du Bugnon 9, 1005 Lausanne, Switzerland.
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172
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Seigneur J, Kroeger D, Nita DA, Amzica F. Cholinergic action on cortical glial cells in vivo. ACTA ACUST UNITED AC 2005; 16:655-68. [PMID: 16093563 DOI: 10.1093/cercor/bhj011] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022]
Abstract
This study aims at understanding complex interactions between cortical neurons, glia and blood supply developing during the transition from slow-wave sleep to wakefulness. In spite of essential advances from in vitro and culture preparations, the basic mechanisms of glial interactions with their cellular and ionic environment had remained uninvestigated in vivo. Here we approach this issue by performing simultaneous intracellular recordings of cortical neurons and glia, together with measurements of cerebral blood flow (CBF), extracellular K+ concentrations and local field potentials in both anesthetized (ketamine-xylazine) and naturally behaving cats. Under anesthesia, cortical activation was elicited with electric stimulation of cholinergic nuclei (pedunculopontine tegmental in the brainstem and/or nucleus basalis in the basal forebrain). Iontophoretic application of acetylcholine on the recorded cells was also used. In the vast majority of cases (> 80%) glial cells were hyperpolarized during electric stimulation or spontaneous activation. This result was also obtained in all cases where iontophoresis was used or when glutamatergic kainate/quisqualate receptors were blocked with 6-cyano-7-nitroquinoxaline-2,3-dione. The glial hyperpolarization was associated with steady neuronal depolarization, increased CBF, lower extracellular K+ concentration, increased membrane resistance, decreased membrane capacitance and persistent positive DC field potentials. In some cases of cortical activation (< 20%), glial cells displayed sustained depolarizing potentials, in parallel with neuronal depolarization, decreased CBF and more negative DC field potentials. The above-mentioned effects of cholinergic activation were blocked by the muscarinic antagonist scopolamine. We propose that the glial response to cholinergic activation results from the balance between the direct hyperpolarizing action of acetylcholine and the depolarizing modulation of glutamate from the neighboring neurons, in addition to the modulation of the interglial communication pathway and/or the ionic traffic across blood vessels.
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Affiliation(s)
- Josée Seigneur
- Laboratoire de neurophysiologie, Faculté de médecine, Université Laval, Quebec, Canada G1K 7P4
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173
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Li H, Zhang J, Xiong W, Xu T, Cao J, Xu L. Long-term depression in rat CA1-subicular synapses depends on the G-protein coupled mACh receptors. Neurosci Res 2005; 52:287-94. [PMID: 15893398 DOI: 10.1016/j.neures.2005.04.002] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2004] [Revised: 03/14/2005] [Accepted: 04/07/2005] [Indexed: 11/24/2022]
Abstract
The subiculum, which is the primary target of CA1 pyramidal neurons and sending efferent fibres to many brain regions, serves as a hippocampal interface in the neural information processes between hippocampal formation and neocortex. Long-term depression (LTD) is extensively studied in the hippocampus, but not at the CA1-subicular synaptic transmission. Using whole-cell EPSC recordings in the brain slices of young rats, we demonstrated that the pairing protocols of low frequency stimulation (LFS) at 3 Hz and postsynaptic depolarization of -50 mV elicited a reliable LTD in the subiculum. The LTD did not cause the changes of the paired-pulse ratio of EPSC. Furthermore, it did not depend on either NMDA receptors or voltage-gated calcium channels (VGCCs). Bath application of the G-protein coupled muscarinic acetylcholine receptors (mAChRs) antagonists, atropine or scopolamine, blocked the LTD, suggesting that mAChRs are involved in the LTD. It was also completely blocked by either the Ca2+ chelator BAPTA or the G-protein inhibitor GDP-beta-S in the intracellular solution. This type of LTD in the subiculum may play a particular role in the neural information processing between the hippocampus and neocortex.
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Affiliation(s)
- Hongbin Li
- Laboratory of Learning and Memory, Kunming Institute of Zoology, The Chinese Academy of Sciences, Kunming 650223, PR China
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174
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Potokar M, Kreft M, Pangrsic T, Zorec R. Vesicle mobility studied in cultured astrocytes. Biochem Biophys Res Commun 2005; 329:678-83. [PMID: 15737639 DOI: 10.1016/j.bbrc.2005.02.030] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2005] [Indexed: 01/23/2023]
Abstract
Astrocytes release many neuroactive substances, which are stored in membrane bound vesicles and may play a role in synapse modulation and in the coupling between neuronal activity and the local blood flow. However, the mobility of these vesicles in astrocytes has not been studied yet. We here used a fluorescently tagged proatrial natriuretic peptide to label single vesicles and dynamic microscopy to monitor their mobility. To track and analyze labeled vesicles, we employed a computer software. We found two modes of vesicle mobility, directional and non-directional. The mobility of non-directional vesicles is likely determined mainly by free diffusion. Only directional vesicles displayed a straight-line motion. The relationship of mean square displacement with time in directional vesicles resembled a quadratic function, indicating that in addition to free diffusion other mechanisms may contribute to vesicle movements in astrocytes, the biophysical properties of which are similar to those of neurons.
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Affiliation(s)
- Maja Potokar
- Laboratory of Neuroendocrinology-Molecular Cell Physiology, Institute of Pathophysiology, Medical Faculty, University of Ljubljana, Zaloska 4, SI-1000 Ljubljana, Slovenia; Celica Biomedical Sciences Center, Stegne 21c, SI-1000 Ljubljana, Slovenia
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175
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Benediktsson AM, Schachtele SJ, Green SH, Dailey ME. Ballistic labeling and dynamic imaging of astrocytes in organotypic hippocampal slice cultures. J Neurosci Methods 2005; 141:41-53. [PMID: 15585287 DOI: 10.1016/j.jneumeth.2004.05.013] [Citation(s) in RCA: 143] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2004] [Revised: 05/19/2004] [Accepted: 05/19/2004] [Indexed: 10/26/2022]
Abstract
Protoplasmic astrocytes in mammalian CNS tissues in vivo have a highly complex 3D morphology, but in dissociated cell cultures they often assume a flattened, fibroblast-like morphology bearing only a few, simple processes. By fluorescent labeling and confocal reconstruction we show that many astrocytes in organotypic hippocampal slice cultures exhibit a more native complex cytoarchitecture. Although astrocytes at the surface of slice cultures show a reactive form with several thick glial fibrillary acidic protein (GFAP)-positive processes, astrocytes situated in deeper portions of tissue slices retain a highly complex 3D morphology with many fine spine- or veil-like protrusions. Dozens of astrocytes can be labeled in single slice cultures by gene gun-mediated ballistic delivery of gold or tungsten particles carrying cDNAs (Biolistics), lipophilic dyes (DiOlistics), or fluorescent intracellular calcium indicators (Calistics). Expression of a membrane-targeted form of eGFP (Lck-GFP) is superior to soluble eGFP for resolving fine astrocytic processes. Time-lapse confocal imaging of Lck-GFP transfected astrocytes or "calistically" labeled astrocytes show structural remodeling and calcium transients, respectively. This approach provides an in vitro system for investigating the functional architecture, development and dynamic remodeling of astrocytes and their relationships to neurons and glia in live mammalian brain tissues.
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Affiliation(s)
- Adrienne M Benediktsson
- Program in Neuroscience and Department of Biological Sciences, 369 Biology Building, The University of Iowa, Iowa City, IA 52242, USA
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176
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Cuevas ME, Carrasco MA, Fuentes Y, Castro P, Nualart F, Roa J, Aguayo LG. The presence of glia stimulates the appearance of glycinergic synaptic transmission in spinal cord neurons. Mol Cell Neurosci 2005; 28:770-8. [PMID: 15797723 DOI: 10.1016/j.mcn.2005.01.001] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2004] [Revised: 01/10/2005] [Accepted: 01/11/2005] [Indexed: 10/25/2022] Open
Abstract
Previous studies, using electrophysiological and fluorimetric analysis with a calcium sensitive dye, have shown that 5-7 DIV developing spinal cord neurons displayed high levels of glycinergic transmission. GABAergic and AMPAergic neurotransmission contributed much less to the overall transmission. Here, we show that culturing neurons in absence of a glia cell monolayer reduced the frequency of glycinergic spontaneous IPSCs (0.1 +/- 0.01 Hz), without altering the level of overall transmission (3 +/- 1.1 Hz). The predominant transmission was mediated by GABA(A) receptors (72% of total synaptic events). In addition, combination of bicuculline and CNQX blocked synaptically mediated calcium transients recorded with fluo-3. Furthermore, application of glycine revealed the presence of extrasynaptic receptors in these neurons (25 +/- 6 pA/pF). Culturing neurons on a glial cell monolayer increased the frequency of glycinergic currents (0.4 +/- 0.02 Hz), without changing the amplitude of the current (20 +/- 4 pA). The use of a glia-conditioned media reversed the effect of growing the neurons in a glia-deprived condition. These results indicate that the establishment of glycinergic transmission is dependent on the presence of a glia derived soluble factor. However, functional GlyRs were still able to insert in the neuronal membrane in a glia-independent manner.
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Affiliation(s)
- Magdalena E Cuevas
- Department of Physiology, University of Concepción, PO Box 160-C, Concepción, Chile
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177
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Tuppo EE, Arias HR. The role of inflammation in Alzheimer's disease. Int J Biochem Cell Biol 2005; 37:289-305. [PMID: 15474976 DOI: 10.1016/j.biocel.2004.07.009] [Citation(s) in RCA: 478] [Impact Index Per Article: 25.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 07/09/2004] [Indexed: 11/17/2022]
Abstract
Considerable evidence gained over the past decade has supported the conclusion that neuroinflammation is associated with Alzheimer's disease (AD) pathology. Inflammatory components related to AD neuroinflammation include brain cells such as microglia and astrocytes, the classic and alternate pathways of the complement system, the pentraxin acute-phase proteins, neuronal-type nicotinic acetylcholine receptors (AChRs), peroxisomal proliferators-activated receptors (PPARs), as well as cytokines and chemokines. Both the microglia and astrocytes have been shown to generate beta-amyloid protein (Abeta), one of the main pathologic features of AD. Abeta itself has been shown to act as a pro-inflammatory agent causing the activation of many of the inflammatory components. Further substantiation for the role of neuroinflammation in AD has come from studies that demonstrate patients who took non-steroidal anti-inflammatory drugs had a lower risk of AD than those who did not. These same results have led to increased interest in pursuing anti-inflammatory therapy for AD but with poor results. On the other hand, increasing amount of data suggest that AChRs and PPARs are involved in AD-induced neuroinflammation and in this regard, future therapy may focus on their specific targeting in the AD brain.
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Affiliation(s)
- Ehab E Tuppo
- Center for Aging, University of Medicine and Dentistry of New Jersey-School of Osteopathic Medicine, Stratford, NJ 08084, USA.
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178
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Nishimaru H, Restrepo CE, Ryge J, Yanagawa Y, Kiehn O. Mammalian motor neurons corelease glutamate and acetylcholine at central synapses. Proc Natl Acad Sci U S A 2005; 102:5245-9. [PMID: 15781854 PMCID: PMC555035 DOI: 10.1073/pnas.0501331102] [Citation(s) in RCA: 186] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Motor neurons (MNs) are the principal neurons in the mammalian spinal cord whose activities cause muscles to contract. In addition to their peripheral axons, MNs have central collaterals that contact inhibitory Renshaw cells and other MNs. Since its original discovery >60 years ago, it has been a general notion that acetylcholine is the only transmitter released from MN synapses both peripherally and centrally. Here, we show, using a multidisciplinary approach, that mammalian spinal MNs, in addition to acetylcholine, corelease glutamate to excite Renshaw cells and other MNs but not to excite muscles. Our study demonstrates that glutamate can be released as a functional neurotransmitter from mammalian MNs.
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Affiliation(s)
- Hiroshi Nishimaru
- Mammalian Locomotor Laboratory, Department of Neuroscience, Karolinska Institutet, Retzius väg 8, 171 77 Stockholm, Sweden
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179
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Abstract
Glia have moved into the spotlight as participants in synaptic signaling. Recent work by Bergles and colleagues extends this active role by showing that oligodendrocyte precursors cells (OPCs) in the hippocampus receive functional glutamatergic and GABAergic synapses. Synaptic signaling in these cells could provide a mechanism for activity-dependent modulation of OPC proliferation and differentiation.
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Affiliation(s)
- Linda S Overstreet
- Vollum Institute, L474, Oregon Health & Sciences University, 3181 SW Sam Jackson Park Road, Portland, OR 97239, USA.
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180
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Abstract
During the past few years, it has been established that astrocytes sense neuronal activity and are involved in signal transmission. Neuronal stimulation triggered electrophysiological and/or Ca(2+) responses in astrocyte cultures and in acute brain slices. Present even within one given brain region, different pathways of neuron-to-astrocyte communication involving different receptor systems have been described. These mechanisms include glutamatergic and NO-mediated signaling. Neuron-to-astrocyte signaling can be confined to subcellular compartments, the microdomains, or it can activate the entire cell. It can even trigger a multicellular response in astrocytes, a Ca(2+) wave. This form of astrocyte long-range signal propagation can occur independently, in pure astrocyte cultures, but it can also be triggered by neuronal activity. Astrocytes also exhibit spontaneous Ca(2+) activity. Neuronal activity in acute brain slices can organize this activity into complex synchronous networks. One of the functional consequences of neuron-to-astrocyte signaling might be the neuronal control of microcirculation using astrocytes as a mediator.
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Affiliation(s)
- Carola G Schipke
- Max Delbrück Center for Molecular Medicine (MDC) Berlin, Germany
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181
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Rodríguez MJ, Martínez-Sánchez M, Bernal F, Mahy N. Heterogeneity between hippocampal and septal astroglia as a contributing factor to differential in vivo AMPA excitotoxicity. J Neurosci Res 2004; 77:344-53. [PMID: 15248290 DOI: 10.1002/jnr.20177] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Astroglial participation in the regional differences of vulnerability to alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA)-induced neurodegeneration was investigated in the rat hippocampus and medial septum using L-alpha-aminoadipate (alpha-AA) as a specific astroglial toxin. alpha-AA was microinjected in the hippocampus and the medial septum and a time-course study was carried out between 2 hr and 3 days. When compared to controls, microinjection of alpha-AA in the hippocampus induced within 3 days a reversible loss of glial fibrillary acidic protein (GFAP) immunostaining and a microglial reaction without any neuronal loss, whereas in the medial septum it caused no effects on astroglial, microglial, or neuronal populations. Differences in hippocampus and medial septum vulnerability were also evidenced when alpha-AA was co-injected with AMPA and neurodegeneration was assessed in terms of neuronal loss, glial reactions, calcification, and atrophy of the area. In the hippocampus, alpha-AA increased AMPA excitotoxicity with marked disorganization of all hippocampal subfields, increased neuronal loss, a more important astroglial reaction, a larger area of microgliosis, and a greater abundance of calcium deposits. By contrast, in the medial septum alpha-AA did not modify any parameter of the AMPA-induced lesion. In conclusion, the presence of different astroglial populations in hippocampus and medial septum results in a different participation to AMPA excitotoxicity that may determine, at least in part, the specific regional vulnerability to neurodegeneration.
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Affiliation(s)
- Manuel J Rodríguez
- Unitat de Bioquímica, Institut d'Investigacions Biomèdiques August Pi i Sunyer (IDIBAPS), Facultat de Medicina, Universitat de Barcelona, Barcelona, Spain
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182
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Abstract
For many years, astrocytes and oligodendrocytes were considered the inert partners of neurons in the central nervous system (CNS), but several recent studies have dramatically challenged this view. Glial cells express a large number of different voltage- and ligand-gated ion channels (Verkhratsky and Steinhäuser. Brain Res Rev 32:380-412, 2000) as well as G-protein-coupled receptors (Verkhratsky et al. Physiol Rev 78:99-141, 1998)-machinery necessary to sense and respond to neuronal activity. These findings raised the fundamental question as to whether glial receptors are stimulated under physiological conditions, and what sorts of events are triggered by such activation. During the early 1990s, P. Haydon and colleagues made the seminal observation that [Ca(2+)](i) rises in cultured astrocytes are associated with the release of glutamate, which suggested that astrocytes respond to activation and play active modulatory roles in intercellular communication (Parpura et al. Nature 369:744-747, 1994). Subsequent studies performed in situ confirmed and extended this initial observation. In this review, we will focus specifically on the hippocampus and sum up evidence of bidirectional communication between astrocytes and neurons emerging from recent studies using acute slice preparations.
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Affiliation(s)
- Andrea Volterra
- Department of Cell Biology and Morphology, University of Lausanne, Lausanne, Switzerland
- Department of Pharmacological Sciences, Center of Excellence on Neurodegenerative Diseases, University of Milan, Milan, Italy
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183
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Fellin T, Carmignoto G. Neurone-to-astrocyte signalling in the brain represents a distinct multifunctional unit. J Physiol 2004; 559:3-15. [PMID: 15218071 PMCID: PMC1665073 DOI: 10.1113/jphysiol.2004.063214] [Citation(s) in RCA: 206] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Astrocytes can respond to neurotransmitters released at the synapse by generating elevations in intracellular Ca(2+) concentration ([Ca(2+)](i)) and releasing glutamate that signals back to neurones. This discovery opens new perspectives for the possible participation of these glial cells in actual information processing by the brain and raises the hypothesis that astrocyte activation by neuronal signals plays a key role in distinct, functional events. Depending on the level of neuronal activity, the [Ca(2+)](i) response that is activated by neurotransmitters can either remain restricted to an astrocytic process or it can propagate as an intracellular [Ca(2+)](i) wave to other astrocytic processes in contact with different neurones, astrocytes, microglia or endothelial cells of cerebral arterioles. Glutamate release triggered by the [Ca(2+)](i) rise at the astrocytic process represents a feedback, short-distance signal that affects synaptic transmission locally. The release of glutamate as well as of other compounds far away from the site of initial activation represents a feedforward, long-distance signal that can be involved in the regulation of distinct processes. For instance, through the release of vasoactive molecules from the astrocytic processes in contact with cerebral arterioles, the neurone-astrocyte-endothelial cell signalling pathway plays a pivotal role in the neuronal control of vascular tone. In this article we will review recent results that should persuade us to reshape our current thinking on the roles of astroglial cells in the brain. We propose that neurones and astrocytes represent an integral unit that has a distinctive role in different fundamental events in brain function. Furthermore, while recent findings provide important evidences for the vesicular hypothesis of glutamate release, we discuss also the proposals for a possible physiological role of hemichannels and purinergic P2X(7) receptors in glutamate release from astrocytes. A full clarification of the functional significance of the bidirectional communication that astrocytes establish with neurones as well as with other brain cells represents one of the most intriguing challenges in neurobiological research at the moment and should fuel stimulating debates in years to come.
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Affiliation(s)
- Tommaso Fellin
- Istituto CNR di Neuroscienze and Dipartimento di Scienze Biomediche Sperimentali, Università di Padova, Viale G. Colombo 3, 35121 Padova, Italy
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184
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Zhu Y, Kimelberg HK. Cellular expression of P2Y and beta-AR receptor mRNAs and proteins in freshly isolated astrocytes and tissue sections from the CA1 region of P8-12 rat hippocampus. BRAIN RESEARCH. DEVELOPMENTAL BRAIN RESEARCH 2004; 148:77-87. [PMID: 14757521 DOI: 10.1016/j.devbrainres.2003.10.014] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
Although almost all GFAP(+) cells in primary astrocyte cultures show functional beta-adrenergic (beta-AR) and metabotropic purinergic (P2Y) receptors, the fewer studies on astrocytes in situ have shown that a much smaller proportion express these same receptor-mediated activities. Here we show, by multiplex single cell RT-PCR, that 44% of freshly isolated, GFAP(+) astrocytes (FIAs) from the CA1 of P8-12 rat hippocampus always co-express beta-adrenergic receptor mRNA subtypes with metabotropic ATP receptor mRNA subtypes (P2Y1, P2Y2 or P2Y4). We also found that beta2 mRNA was the dominant beta-AR subtype expressed. P2Y1 mRNA always co-expresses with either one or two subtypes of P2U-like receptor (P2Y2 or P2Y4) mRNAs. Immunocytochemical studies showed a similar percentage of all FIAs expressed beta-AR and P2Y1 protein (54% and 52%, respectively), as for the mRNAs (46% and 65%, respectively). The staining of hippocampal sections for beta-AR or P2Y1 receptor plus GFAP shows that there are quite numerous, scattered star-shaped GFAP(+) astrocytes in the CA1 region of P9-10 rat hippocampus that stained positive for either of these receptors. These data show that astrocytes in situ express, and to a large extent likely co-express, beta-AR and P2Y receptors.
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Affiliation(s)
- Yingzi Zhu
- Center for Neuropharmacology and Neuroscience, USA
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185
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Abstract
Accumulating evidence has demonstrated the existence of bidirectional communication between glial cells and neurons, indicating an important active role of glia in the physiology of the nervous system. Neurotransmitters released by presynaptic terminals during synaptic activity increase intracellular Ca(2+) concentration in adjacent glial cells. In turn, activated glia may release different transmitters that can feed back to neuronal synaptic elements, regulating the postsynaptic neuronal excitability and modulating neurotransmitter release from presynaptic terminals. As a consequence of this evidence, a new concept of the synaptic physiology, the tripartite synapse, has been proposed, in which glial cells play an active role as dynamic regulatory elements in neurotransmission. In the present article we review evidence showing the ability of astrocytes to modulate synaptic transmission directly, with the focus on studies performed on cell culture preparations, which have been proved extremely useful in the characterization of molecular and cellular processes involved in astrocyte-mediated neuromodulation.
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Affiliation(s)
- Alfonso Araque
- Instituto Cajal, Consejo Superior de Investigaciones Científicas, Madrid, Spain
| | - Gertrudis Perea
- Instituto Cajal, Consejo Superior de Investigaciones Científicas, Madrid, Spain
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186
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Abstract
Abstract Although glia often envelop synapses, they have traditionally been viewed as passive participants in synaptic function. Recent evidence has demonstrated, however, that there is a dynamic two-way communication between glia and neurons at the synapse. Neurotransmitters released from presynaptic neurons evoke Ca2+ concentration increases in adjacent glia. Activated glia, in turn, release transmitters, including glutamate and ATP. These gliotransmitters feed back onto the presynaptic terminal either to enhance or to depress further release of neurotransmitter. Transmitters released from glia can also directly stimulate postsynaptic neurons, producing either excitatory or inhibitory responses. Based on these new findings, glia should be considered an active partner at the synapse, dynamically regulating synaptic transmission.
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Affiliation(s)
- Eric A Newman
- Department of Neuroscience, University of Minnesota, 6-145 Jackson Hall, 321 Church Street SE, Minneapolis, MN 55455, USA.
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187
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Towart LA, Alves SE, Znamensky V, Hayashi S, McEwen BS, Milner TA. Subcellular relationships between cholinergic terminals and estrogen receptor-alpha in the dorsal hippocampus. J Comp Neurol 2003; 463:390-401. [PMID: 12836175 DOI: 10.1002/cne.10753] [Citation(s) in RCA: 97] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
Cholinergic septohippocampal neurons are affected by circulating estrogens. Previously, we found that extranuclear estrogen receptor-alpha (ERalpha) immunoreactivity in presynaptic profiles had an overlapping distribution with cholinergic afferents in the rat hippocampal formation. To determine the subcellular relationships between cholinergic presynaptic profiles and ERalpha, hippocampal sections were dually immunolabeled for vesicular acetylcholine transporter (VAChT) and ERalpha and examined by electron microscopy. Within the hippocampal formation, immunoreactivities for VAChT and ERalpha both were presynaptic, although their subcellular targeting was distinct. VAChT immunoreactivity was found exclusively within presynaptic profiles and was associated with small synaptic vesicles, which usually filled axon terminals. VAChT-labeled presynaptic profiles were most concentrated in stratum oriens of the hippocampal CA1 region and dentate inner molecular layer and hilus. In contrast, ERalpha immunoreactivity was found in clusters affiliated either with select vesicles or with the plasmalemma within preterminal axons and axon terminals. ERalpha-immunoreactive (IR) presynaptic profiles were more evenly distributed between hippocampal lamina than VAChT-IR profiles. Quantitative ultrastructural analysis revealed that VAChT-IR presynaptic profiles contained ERalpha immunoreactivity (ranging from 3% to 17%, depending on the lamina). Additionally, VAChT-IR presynaptic profiles apposed ERalpha-IR dendritic spines, presynaptic profiles, and glial profiles; many of the latter two types of profiles abutted unlabeled dendritic spines that received asymmetric (excitatory-type) synapses from unlabeled terminals. The presence of ERalpha immunoreactivity in cholinergic terminals suggests that estrogen could rapidly and directly affect the local release and/or uptake of acetylcholine. The affiliation of cholinergic terminals with excitatory terminals near ERalpha-labeled dendritic spines or glial profiles suggests that alterations in acetylcholine release could indirectly affect estrogen-modulated structural plasticity.
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Affiliation(s)
- Laura A Towart
- Division of Neurobiology, Department of Neurology and Neuroscience, Weill Medical College of Cornell University, New York, New York 10021, USA
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188
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Gallagher CJ, Salter MW. Differential properties of astrocyte calcium waves mediated by P2Y1 and P2Y2 receptors. J Neurosci 2003; 23:6728-39. [PMID: 12890765 PMCID: PMC6740738] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/04/2023] Open
Abstract
Intercellular spread of Ca2+ waves is the primary manifestation of cell-to-cell communication among astrocytes. Ca2+ waves propagate via the release of a diffusible extracellular messenger that has been identified as ATP. In dorsal spinal astrocytes, Ca2+ waves are mediated by activation of two functionally distinct subtypes of metabotropic purinoceptor: the P2Y1 receptor and a receptor previously classified as P2U. Here, we show that the P2U receptor is molecularly and pharmacologically identical to the cloned P2Y2 receptor. Both P2Y1 and P2Y2 receptors are necessary for full Ca2+ wave propagation in spinal astrocytes. Conversely, heterologous expression of either P2Y1 or P2Y2 receptors is sufficient for Ca2+ waves, and expressing these receptor subtypes together recapitulates the characteristics of Ca2+ waves in spinal astrocytes. Thus, P2Y1 and P2Y2 receptors are both necessary and sufficient for propagation of Ca2+ waves. Furthermore, we demonstrate that there are dramatic differences in the characteristics of Ca2+ waves propagating through each receptor subtype: Ca2+ waves propagating via P2Y2 receptors travel faster and further than those propagating via P2Y1 receptors. We find that the nucleotidase apyrase selectively blocks Ca2+ wave propagation through P2Y2 receptors but accelerates Ca2+ waves propagating through P2Y1 receptors. Taking our results together with those from the literature, we suggest that mediation of Ca2+ waves by ATP leading to activation of two subtypes of receptor, P2Y1 and P2Y2, may be a general principle for gliotransmission in the CNS. Thus, processes that alter expression or function of these receptors may control the rate and extent of astrocyte Ca2+ waves.
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Affiliation(s)
- Conor J Gallagher
- Programme in Brain and Behaviour, Hospital For Sick Children, University of Toronto, Toronto, Ontario M5G 1X8, Canada
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189
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Bushong EA, Martone ME, Ellisman MH. Examination of the relationship between astrocyte morphology and laminar boundaries in the molecular layer of adult dentate gyrus. J Comp Neurol 2003; 462:241-51. [PMID: 12794746 DOI: 10.1002/cne.10728] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Astrocytes are known to play an integral role in the development of compartmental boundaries in the brain and in the creation of trauma-induced boundaries. However, the physical relationship between astrocytes and such boundaries in the adult brain is less clear. If astrocytes do respect or play an ongoing role in maintaining such boundaries, a correlation between the position of such a boundary and the morphology of neighboring astrocytes might be observable. In this study, we examined the distribution of astrocytes with respect to the laminar boundaries compartmentalizing afferents to the dentate gyrus molecular layer. In addition, we attempted to determine whether astrocyte morphology is influenced by these laminar boundaries. To this end, protoplasmic astrocytes in the adult rat dentate gyrus were revealed with fluorescent tracer dyes and subsequently analyzed with respect to laminar boundaries demarcated by means of immunolabeling for the lamina-specific molecules EphA4 and neural cell adhesion molecule (N-CAM). We find that astrocyte distribution is influenced by the boundary separating the associational/commissural and perforant path afferents. In addition, we show that astrocytes in this region are polarized in their morphology, unlike typically stellate astrocytes, but that the laminar boundaries themselves do not appear to confer this morphology. This polarized morphology, however acquired, may have import for the functioning of astrocytes within the highly organized composition of the dentate gyrus molecular layer and for the overall microphysiology of this and other brain regions.
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Affiliation(s)
- Eric A Bushong
- National Center for Microscopy and Imaging Research, University of California- San Diego, La Jolla, California 92093, USA
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190
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Smith IF, Plant LD, Boyle JP, Skinner RA, Pearson HA, Peers C. Chronic hypoxia potentiates capacitative Ca2+ entry in type-I cortical astrocytes. J Neurochem 2003; 85:1109-16. [PMID: 12753070 DOI: 10.1046/j.1471-4159.2003.01785.x] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Prolonged hypoxia exerts profound effects on cell function, and has been associated with increased production of amyloid beta peptides (A beta Ps) of Alzheimer's disease. Here, we have investigated the effects of chronic hypoxia (2.5% O2, 24 h) on capacitative Ca2+ entry (CCE) in primary cultures of rat type-I cortical astrocytes, and compared results with those obtained in astrocytes exposed to A beta Ps. Chronic hypoxia caused a marked enhancement of CCE that was observed after intracellular Ca2+ stores were depleted by bradykinin application or by exposure to thapsigargin (1 microM). Exposure of cells for 24 h to 1 microM A beta P(1-40) did not alter CCE. Enhancement of CCE was not attributable to cell hyperpolarization, as chronically hypoxic cells were significantly depolarized as compared with controls. Mitochondrial inhibition [by FCCP (10 microM) and oligomycin (2.5 microg/mL)] suppressed CCE in all three cell groups, but more importantly there were no significant differences in the magnitude of CCE in the three astrocyte groups under these conditions. Similarly, the antioxidants melatonin and Trolox abolished the enhancement of CCE in hypoxic cells. Our results indicate that chronic hypoxia augments CCE in cortical type-I astrocytes, a finding which is not mimicked by A beta P(1-40) and appears to be dependent on altered mitochondrial function.
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Affiliation(s)
- I F Smith
- Institute for Cardiovascular Research, University of Leeds, Leeds, UK
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191
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Newman EA. Glial cell inhibition of neurons by release of ATP. J Neurosci 2003; 23:1659-66. [PMID: 12629170 PMCID: PMC2322877] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/01/2023] Open
Abstract
ATP is released by neurons and functions as a neurotransmitter and modulator in the CNS. Here I show that ATP released from glial cells can also serve as a potent neuromodulator, inhibiting neurons in the retina of the rat. Activation of glial cells by focal ejection of ATP, ATPgammaS, dopamine, thrombin, or lysophosphatidic acid or by mechanical stimulation evoked hyperpolarizing responses and outward currents in a subset of retinal ganglion cells by increasing a Ba(2+)-sensitive K(+) conductance in the neurons. This glia-evoked inhibition reduced the firing rate of those neurons that displayed spontaneous spike activity. The inhibition was abolished by the A(1) adenosine receptor antagonist DPCPX (8-cyclopentyl-1,3-dipropylxanthine) (10 nm) and was reduced by the ecto-ATPase inhibitor ARL-67156 (6-N,N-diethyl-D-beta,gamma-dibromomethyleneATP) (50 microm) and by the ectonucleotidase inhibitor AOPCP [adenosine-5'-O-(alpha,beta-methylene)-diphosphonate] (250 microm). Selective activation of retinal glial cells demonstrated that Müller cells, but not astrocytes, mediate the inhibition. ATP release from Müller cells into the inner plexiform layer of the retina was shown using the luciferin-luciferase chemiluminescence assay. These findings demonstrate that activated glial cells can inhibit neurons in the retina by the release of ATP, which is converted to adenosine by ectoenzymes and subsequently activates neuronal adenosine receptors. The results lend support to the hypothesis that glial cells play an active role in information processing in the CNS.
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Affiliation(s)
- Eric A Newman
- Department of Neuroscience, University of Minnesota, Minneapolis, Minnesota 55455, USA.
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192
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Fernández de Sevilla D, Buño W. Presynaptic inhibition of Schaffer collateral synapses by stimulation of hippocampal cholinergic afferent fibres. Eur J Neurosci 2003; 17:555-8. [PMID: 12581173 DOI: 10.1046/j.1460-9568.2003.02490.x] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
It has been known for decades that muscarinic agonists presynaptically inhibit Schaffer collateral synapses contacting hippocampal CA1 pyramidal neurons. However, a demonstration of the inhibition of Schaffer collateral synapses induced by acetylcholine released by cholinergic hippocampal afferents is lacking. We present original results showing that electrical stimulation at the stratum oriens/alveus with brief stimulus trains inhibited excitatory postsynaptic currents evoked by stimulation of Schaffer collaterals in CA1 pyramidal neurons of rat hippocampal slices. The increased paired-pulse facilitation and the changes in the variance of excitatory postsynaptic current amplitude that paralleled the inhibition suggest that it was mediated presynaptically. The effects of oriens/alveus stimulation were inhibited by atropine, and blocking nicotinic receptors with methyllycaconitine was ineffective, suggesting that the inhibition was mediated via the activation of presynaptic muscarinic receptors. The results provide a novel demonstration of the presynaptic inhibition of glutamatergic neurotransmission by cholinergic fibres in the hippocampus, implying that afferent cholinergic fibres regulate the strength of excitatory synaptic transmission.
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193
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Santos MD, Pereira EFR, Aracava Y, Castro NG, Fawcett WP, Randall WR, Albuquerque EX. Low concentrations of pyridostigmine prevent soman-induced inhibition of GABAergic transmission in the central nervous system: involvement of muscarinic receptors. J Pharmacol Exp Ther 2003; 304:254-65. [PMID: 12490599 DOI: 10.1124/jpet.102.043109] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
This study was designed to investigate the effects of the cholinesterase inhibitors soman and pyridostigmine bromide (PB) on synaptic transmission in the CA1 field of rat hippocampal slices. Soman (1-100 nM, 10-15 min) decreased the amplitude of GABAergic postsynaptic currents (IPSCs) evoked by stimulation of Schaffer collaterals and recorded from CA1 pyramidal neurons. It also decreased the amplitude and frequency of spontaneous IPSCs recorded from pyramidal neurons. Whereas the maximal effect of soman on evoked GABAergic transmission was observed at 10 nM, full cholinesterase inhibition was induced by 1 nM soman. After 10-15-min exposure of hippocampal slices to 100 nM PB, GABAergic transmission was facilitated and cholinesterase activity was not significantly affected. At nanomolar concentrations, soman and PB have no direct effect on GABA(A) receptors. The effects of soman and PB on GABAergic transmission were inhibited by the m2 receptor antagonist 11-[[[2-diethylamino-O-methyl]-1-piperidinyl] acetyl]-5,11-dihydrol-6H-pyridol[2,3-b][1,4]benzodiazepine-6- one (1 nM) and the m3 receptor antagonist 4-diphenylacetoxy-N-methyl-piperidine (100 nM), respectively, and by the nonselective muscarinic receptor antagonist atropine (1 microM). Thus, changes in GABAergic transmission are likely to result from direct interactions of soman and PB with m2 and m3 receptors, respectively, located on GABAergic fibers/neurons synapsing onto the neurons under study. Although the effects of 1 nM soman and 100 nM PB were diametrically opposed, they only canceled one another when PB was applied to the neurons before soman. Therefore, PB, acting via m3 receptors, can effectively counteract effects arising from the interactions of soman with m2 receptors in the brain.
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Affiliation(s)
- Máriton D Santos
- Department of Pharmacology and Experimental Therapeutics, University of Maryland School of Medicine, Baltimore, Maryland 21201, USA
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194
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Hansson∗ E, Rönnbäck L. Astrocytic receptors and second messenger systems. ADVANCES IN MOLECULAR AND CELL BIOLOGY 2003. [DOI: 10.1016/s1569-2558(03)31021-5] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
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195
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Riquelme R, Miralles CP, De Blas AL. Bergmann glia GABA(A) receptors concentrate on the glial processes that wrap inhibitory synapses. J Neurosci 2002; 22:10720-30. [PMID: 12486165 PMCID: PMC6758425] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/28/2023] Open
Abstract
We studied the cellular and subcellular distribution of GABA(A) receptors in the Bergmann glia and Purkinje cells in the molecular layer of the cerebellum by using electron microscopy postembedding immunogold techniques. Gold particles corresponding to alpha2 and gamma1 immunoreactivity were localized in Bergmann glia processes that wrapped Purkinje cell somata, dendritic shafts, and some dendritic spines. The gold particles were mainly located on the glial plasma membrane or intracellularly but near the plasma membrane. The density of gold particles corresponding to alpha2 and gamma1 GABA(A) receptor subunits was 4.3-fold higher in the glial processes wrapping Purkinje cell somata than in the glial processes wrapping Purkinje cell dendritic spines. Moreover, the Bergmann glia GABA(A) receptors were often located in close proximity to the type II GABAergic synapses made by the basket cell axons on Purkinje cell somata. These GABAergic synapses were enriched in neuronal GABA(A) receptors containing alpha1 and beta2/3 subunits. Unexpectedly, 2.8% of the Purkinje cell dendritic spines also showed immunoreactivity for the neuronal alpha1 or beta2/3 subunits, which were located on the spine in type I synapses or extrasynaptically. Double-labeling immunogold experiments showed that approximately 50% of the dendritic spines that were immunolabeled with the neuronal GABA(A) receptors were wrapped by Bergmann glia processes containing glial GABA(A) receptors. These results are consistent with a role of the Bergmann glial GABA(A) receptors in sensing GABAergic synaptic function.
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Affiliation(s)
- Raquel Riquelme
- Department of Physiology and Neurobiology, University of Connecticut, Storrs, Connecticut 06269, USA
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196
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Fernández de Sevilla D, Cabezas C, de Prada ANO, Sánchez-Jiménez A, Buño W. Selective muscarinic regulation of functional glutamatergic Schaffer collateral synapses in rat CA1 pyramidal neurons. J Physiol 2002; 545:51-63. [PMID: 12433949 PMCID: PMC2290654 DOI: 10.1113/jphysiol.2002.029165] [Citation(s) in RCA: 86] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Analysis of the cholinergic regulation of glutamatergic neurotransmission is an essential step in understanding the hippocampus because it can influence forms of synaptic plasticity that are thought to underlie learning and memory. We studied in vitro the cholinergic regulation of excitatory postsynaptic currents (EPSCs) evoked in rat CA1 pyramidal neurons by Schaffer collateral (SC) stimulation. Using "minimal" stimulation, which activates one or very few synapses, the cholinergic agonist carbamylcholine (CCh) increased the failure rate of functional more (36 %) than of silent synapses (7 %), without changes in the EPSC amplitude. These effects of CCh were insensitive to manipulations that increased the probability of release, such as paired pulse facilitation, increases in temperature and increases in the extracellular Ca(2+) : Mg(2+) ratio. Using "conventional" stimulation, which activates a large number of synapses, CCh inhibited more the pharmacologically isolated non-NMDA (86 %) than the NMDA (47 %) EPSC. The changes in failure rate, EPSC variance and the increased paired pulse facilitation that paralleled the inhibition imply that CCh decreased release probability. Muscarine had similar effects. The inhibition by both CCh and by muscarine was prevented by atropine. We conclude that CCh reduces the non-NMDA component of SC EPSCs by selectively inhibiting transmitter release at functional synapses via activation of muscarinic receptors. The results suggest that SCs have two types of terminals, one in functional synapses, selectively sensitive to regulation through activation of muscarinic receptors, and the other in silent synapses less sensitive to that regulation. The specific inhibition of functional synapses would favour activity-dependent plastic phenomena through NMDA receptors at silent synapses without the activation of non-NMDA receptors and functional synapses.
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Affiliation(s)
- David Fernández de Sevilla
- Instituto Cajal, Consejo Superior de Investigaciones Científicas, Avenida Doctor Arce 37, 28002 Madrid, Spain
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197
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Perea G, Araque A. Communication between astrocytes and neurons: a complex language. JOURNAL OF PHYSIOLOGY, PARIS 2002; 96:199-207. [PMID: 12445897 DOI: 10.1016/s0928-4257(02)00007-4] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
In recent years, accumulating evidence suggests the existence of bidirectional communication between astrocytes and neurons, indicating an important active role of astrocytes in the physiology of the nervous system. As a consequence of this evidence, a new concept of the synaptic physiology--"the tripartite synapse"--has been proposed, in which the synapse is formed by three functional elements, i.e. the pre- and postsynaptic elements and the surrounding astrocytes. In the present article we review and discuss the current knowledge on the cellular mechanisms and physiological properties of this communication that displays highly complex characteristics. We are beginning to realize that the communication between astrocytes and neurons uses a quite complex language.
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Affiliation(s)
- Gertrudis Perea
- Instituto Cajal, Consejo Superior de Investigaciones Científicas, Madrid 28002, Spain
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