51
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Dzamba D, Honsa P, Anderova M. NMDA Receptors in Glial Cells: Pending Questions. Curr Neuropharmacol 2013; 11:250-62. [PMID: 24179462 PMCID: PMC3648778 DOI: 10.2174/1570159x11311030002] [Citation(s) in RCA: 70] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2012] [Revised: 01/08/2013] [Accepted: 02/02/2013] [Indexed: 01/28/2023] Open
Abstract
Glutamate receptors of the N-methyl-D-aspartate (NMDA) type are involved in many cognitive processes, including behavior, learning and synaptic plasticity. For a long time NMDA receptors were thought to be the privileged domain of neurons; however, discoveries of the last 25 years have demonstrated their active role in glial cells as well. Despite the large number of studies in the field, there are many unresolved questions connected with NMDA receptors in glia that are still a matter of debate. The main objective of this review is to shed light on these controversies by summarizing results from all relevant works concerning astrocytes, oligodendrocytes and polydendrocytes (also known as NG2 glial cells) in experimental animals, further extended by studies performed on human glia. The results are divided according to the study approach to enable a better comparison of how findings obtained at the mRNA level correspond with protein expression or functionality. Furthermore, special attention is focused on the NMDA receptor subunits present in the particular glial cell types, which give them special characteristics different from those of neurons – for example, the absence of Mg2+ block and decreased Ca2+ permeability. Since glial cells are implicated in important physiological and pathophysiological roles in the central nervous system (CNS), the last part of this review provides an overview of glial NMDA receptors with respect to ischemic brain injury.
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Affiliation(s)
- David Dzamba
- Department of Cellular Neurophysiology, Institute of Experimental Medicine AS CR, Prague, Czech Republic and Second Medical Faculty, Charles University, Prague, Czech Republic
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52
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Dallérac G, Chever O, Rouach N. How do astrocytes shape synaptic transmission? Insights from electrophysiology. Front Cell Neurosci 2013; 7:159. [PMID: 24101894 PMCID: PMC3787198 DOI: 10.3389/fncel.2013.00159] [Citation(s) in RCA: 108] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2013] [Accepted: 09/02/2013] [Indexed: 02/01/2023] Open
Abstract
A major breakthrough in neuroscience has been the realization in the last decades that the dogmatic view of astroglial cells as being merely fostering and buffering elements of the nervous system is simplistic. A wealth of investigations now shows that astrocytes actually participate in the control of synaptic transmission in an active manner. This was first hinted by the intimate contacts glial processes make with neurons, particularly at the synaptic level, and evidenced using electrophysiological and calcium imaging techniques. Calcium imaging has provided critical evidence demonstrating that astrocytic regulation of synaptic efficacy is not a passive phenomenon. However, given that cellular activation is not only represented by calcium signaling, it is also crucial to assess concomitant mechanisms. We and others have used electrophysiological techniques to simultaneously record neuronal and astrocytic activity, thus enabling the study of multiple ionic currents and in depth investigation of neuro-glial dialogues. In the current review, we focus on the input such approach has provided in the understanding of astrocyte-neuron interactions underlying control of synaptic efficacy.
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Affiliation(s)
- Glenn Dallérac
- Neuroglial Interactions in Cerebral Physiopathology, Center for Interdisciplinary Research in Biology, CNRS UMR 7241, INSERM U1050, Collège de France Paris, France
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53
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Lesion-induced alterations in astrocyte glutamate transporter expression and function in the hippocampus. ISRN NEUROLOGY 2013; 2013:893605. [PMID: 24078881 PMCID: PMC3775433 DOI: 10.1155/2013/893605] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/03/2013] [Accepted: 07/27/2013] [Indexed: 11/18/2022]
Abstract
Astrocytes express the sodium-dependent glutamate transporters GLAST and GLT-1, which are critical to maintain low extracellular glutamate concentrations. Here, we analyzed changes in their expression and function following a mechanical lesion in the CA1 area of organotypic hippocampal slices. 6-7 days after lesion, a glial scar had formed along the injury site, containing strongly activated astrocytes with increased GFAP and S100 β immunoreactivity, enlarged somata, and reduced capability for uptake of SR101. Astrocytes in the scar's periphery were swollen as well, but showed only moderate upregulation of GFAP and S100 β and efficiently took up SR101. In the scar, clusters of GLT-1 and GLAST immunoreactivity colocalized with GFAP-positive fibers. Apart from these, GLT-1 immunoreactivity declined with increasing distance from the scar, whereas GLAST expression appeared largely uniform. Sodium imaging in reactive astrocytes indicated that glutamate uptake was strongly reduced in the scar but maintained in the periphery. Our results thus show that moderately reactive astrocytes in the lesion periphery maintain overall glutamate transporter expression and function. Strongly reactive astrocytes in the scar, however, display clusters of GLAST and GLT-1 immunoreactivity together with reduced glutamate transport activity. This reduction might contribute to increased extracellular glutamate concentrations and promote excitotoxic cell damage at the lesion site.
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54
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Marx G, Gilon C. The molecular basis of memory. Part 2: chemistry of the tripartite mechanism. ACS Chem Neurosci 2013; 4:983-93. [PMID: 23419130 DOI: 10.1021/cn300237r] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
Abstract
We propose a tripartite mechanism to describe the processing of cognitive information (cog-info), comprising the (1) neuron, (2) surrounding neural extracellular matrix (nECM), and (3) numerous "trace" metals distributed therein. The neuron is encased in a polyanionic nECM lattice doped with metals (>10), wherein it processes (computes) and stores cog-info. Each [nECM:metal] complex is the molecular correlate of a cognitive unit of information (cuinfo), similar to a computer "bit". These are induced/sensed by the neuron via surface iontophoretic and electroelastic (piezoelectric) sensors. The generic cuinfo are used by neurons to biochemically encode and store cog-info in a rapid, energy efficient, but computationally expansive manner. Here, we describe chemical reactions involved in various processes that underline the tripartite mechanism. In addition, we present novel iconographic representations of various types of cuinfo resulting from"tagging" and cross-linking reactions, essential for the indexing cuinfo for organized retrieval and storage of memory.
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Affiliation(s)
| | - Chaim Gilon
- Institute of Chemistry, Hebrew University, Jerusalem, Israel
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55
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6-Hydroxydopamine promotes iron traffic in primary cultured astrocytes. Biometals 2013; 26:705-14. [DOI: 10.1007/s10534-013-9647-x] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2013] [Accepted: 06/08/2013] [Indexed: 01/19/2023]
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56
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Rose CR, Karus C. Two sides of the same coin: sodium homeostasis and signaling in astrocytes under physiological and pathophysiological conditions. Glia 2013; 61:1191-205. [PMID: 23553639 DOI: 10.1002/glia.22492] [Citation(s) in RCA: 88] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2012] [Accepted: 02/06/2013] [Indexed: 11/07/2022]
Abstract
The intracellular sodium concentration of astrocytes is classically viewed as being kept under tight homeostatic control and at a relatively stable level under physiological conditions. Indeed, the steep inwardly directed electrochemical gradient for sodium, generated by the Na⁺/K⁺-ATPase, contributes to maintain the electrochemical gradient of K⁺ and the highly K⁺-based negative membrane potential, and is a central element in energizing membrane transport. As such it is tightly coupled to the homeostasis of extra- and intracellular potassium, calcium or pH and to the reuptake of transmitters such as glutamate. Recent studies, however, have demonstrated that this picture is far too simplistic. It is now firmly established that transmitters, most notably glutamate, and excitatory neuronal activity evoke long-lasting sodium transients in astrocytes, the properties of which are distinctly different from those of activity-related glial calcium signals. From these studies, it emerges that sodium homeostasis and signaling are two sides of the same coin: sodium-dependent transporters, primarily known for their role in ion regulation and homeostasis, also generate relevant ion signals during neuronal activity. The functional consequences of activity-related sodium transients are manifold and are just coming into view, enabling surprising and important new insights into astrocyte function and neuron-glia interaction in the brain. The present review will highlight current knowledge about the mechanisms that contribute to sodium homeostasis in astrocytes, present recent data on the spatial and temporal properties of activity-related glial sodium signals and discuss their functional consequences with a special emphasis on pathophysiological conditions.
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Affiliation(s)
- Christine R Rose
- Institute of Neurobiology, Faculty of Mathematics and Natural Sciences, Heinrich Heine University Düsseldorf, Düsseldorf, Germany.
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57
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Pál I, Nyitrai G, Kardos J, Héja L. Neuronal and astroglial correlates underlying spatiotemporal intrinsic optical signal in the rat hippocampal slice. PLoS One 2013; 8:e57694. [PMID: 23469218 PMCID: PMC3585794 DOI: 10.1371/journal.pone.0057694] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2012] [Accepted: 01/28/2013] [Indexed: 11/24/2022] Open
Abstract
Widely used for mapping afferent activated brain areas in vivo, the label-free intrinsic optical signal (IOS) is mainly ascribed to blood volume changes subsequent to glial glutamate uptake. By contrast, IOS imaged in vitro is generally attributed to neuronal and glial cell swelling, however the relative contribution of different cell types and molecular players remained largely unknown. We characterized IOS to Schaffer collateral stimulation in the rat hippocampal slice using a 464-element photodiode-array device that enables IOS monitoring at 0.6 ms time-resolution in combination with simultaneous field potential recordings. We used brief half-maximal stimuli by applying a medium intensity 50 Volt-stimulus train within 50 ms (20 Hz). IOS was primarily observed in the str. pyramidale and proximal region of the str. radiatum of the hippocampus. It was eliminated by tetrodotoxin blockade of voltage-gated Na(+) channels and was significantly enhanced by suppressing inhibitory signaling with gamma-aminobutyric acid(A) receptor antagonist picrotoxin. We found that IOS was predominantly initiated by postsynaptic Glu receptor activation and progressed by the activation of astroglial Glu transporters and Mg(2+)-independent astroglial N-methyl-D-aspartate receptors. Under control conditions, role for neuronal K(+)/Cl(-) cotransporter KCC2, but not for glial Na(+)/K(+)/Cl(-) cotransporter NKCC1 was observed. Slight enhancement and inhibition of IOS through non-specific Cl(-) and volume-regulated anion channels, respectively, were also depicted. High-frequency IOS imaging, evoked by brief afferent stimulation in brain slices provide a new paradigm for studying mechanisms underlying IOS genesis. Major players disclosed this way imply that spatiotemporal IOS reflects glutamatergic neuronal activation and astroglial response, as observed within the hippocampus. Our model may help to better interpret in vivo IOS and support diagnosis in the future.
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Affiliation(s)
- Ildikó Pál
- Department of Functional Pharmacology, Institute of Molecular Pharmacology, Research Centre for Natural Sciences, Hungarian Academy of Sciences, Budapest, Hungary.
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58
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The astrocytic contribution to neurovascular coupling – Still more questions than answers? Neurosci Res 2013; 75:171-83. [DOI: 10.1016/j.neures.2013.01.014] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2012] [Revised: 12/15/2012] [Accepted: 12/30/2012] [Indexed: 01/03/2023]
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59
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Verkhratsky A, Reyes RC, Parpura V. TRP channels coordinate ion signalling in astroglia. Rev Physiol Biochem Pharmacol 2013; 166:1-22. [PMID: 23784619 DOI: 10.1007/112_2013_15] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Astroglial excitability is based on highly spatio-temporally coordinated fluctuations of intracellular ion concentrations, among which changes in Ca(2+) and Na(+) take the leading role. Intracellular signals mediated by Ca(2+) and Na(+) target numerous molecular cascades that control gene expression, energy production and numerous homeostatic functions of astrocytes. Initiation of Ca(2+) and Na(+) signals relies upon plasmalemmal and intracellular channels that allow fluxes of respective ions down their concentration gradients. Astrocytes express several types of TRP channels of which TRPA1 channels are linked to regulation of functional expression of GABA transporters, whereas TRPV4 channels are activated following osmotic challenges and are up-regulated in ischaemic conditions. Astrocytes also ubiquitously express several isoforms of TRPC channels of which heteromers assembled from TRPC1, 4 and/or 5 subunits that likely act as stretch-activated channels and are linked to store-operated Ca(2+) entry. The TRPC channels mediate large Na(+) fluxes that are associated with the endoplasmic reticulum Ca(2+) signalling machinery and hence coordinate Na(+) and Ca(2+) signalling in astroglia.
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Affiliation(s)
- Alexei Verkhratsky
- Faculty of Life Sciences, The University of Manchester, Oxford Road, Manchester, M13 9PT, UK,
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60
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Abstract
Astrocytes exhibit their excitability based on variations in cytosolic Ca(2+) levels, which leads to variety of signalling events. Only recently, however, intracellular fluctuations of more abundant cation Na(+) are brought in the limelight of glial signalling. Indeed, astrocytes possess several plasmalemmal molecular entities that allow rapid transport of Na(+) across the plasma membrane: (1) ionotropic receptors, (2) canonical transient receptor potential cation channels, (3) neurotransmitter transporters and (4) sodium-calcium exchanger. Concerted action of these molecules in controlling cytosolic Na(+) may complement Ca(2+) signalling to provide basis for complex bidirectional astrocyte-neurone communication at the tripartite synapse.
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61
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Florence CM, Baillie LD, Mulligan SJ. Dynamic volume changes in astrocytes are an intrinsic phenomenon mediated by bicarbonate ion flux. PLoS One 2012; 7:e51124. [PMID: 23226475 PMCID: PMC3511399 DOI: 10.1371/journal.pone.0051124] [Citation(s) in RCA: 50] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2012] [Accepted: 10/30/2012] [Indexed: 11/18/2022] Open
Abstract
Astrocytes, the major type of non-neuronal cells in the brain, play an important functional role in extracellular potassium ([K(+)](o)) and pH homeostasis. Pathological brain states that result in [K(+)](o) and pH dysregulation have been shown to cause astrocyte swelling. However, whether astrocyte volume changes occur under physiological conditions is not known. In this study we used two-photon imaging to visualize real-time astrocyte volume changes in the stratum radiatum of the hippocampus CA1 region. Astrocytes were observed to swell by 19.0±0.9% in response to a small physiological increase in the concentration of [K(+)](o) (3 mM). Astrocyte swelling was mediated by the influx of bicarbonate (HCO(3-)) ions as swelling was significantly decreased when the influx of HCO(3-) was reduced. We found: 1) in HCO(3-) free extracellular solution astrocytes swelled by 5.4±0.7%, 2) when the activity of the sodium-bicarbonate cotransporter (NBC) was blocked the astrocytes swelled by 8.3±0.7%, and 3) in the presence of an extracellular carbonic anhydrase (CA) inhibitor astrocytes swelled by 11.4±0.6%. Because a significant HCO(3-) efflux is known to occur through the γ-amino-butyric acid (GABA) channel, we performed a series of experiments to determine if astrocytes were capable of HCO(3-) mediated volume shrinkage with GABA channel activation. Astrocytes were found to shrink -7.7±0.5% of control in response to the GABA(A) channel agonist muscimol. Astrocyte shrinkage from GABA(A) channel activation was significantly decreased to -5.0±0.6% of control in the presence of the membrane-permeant CA inhibitor acetazolamide (ACTZ). These dynamic astrocyte volume changes may represent a previously unappreciated yet fundamental mechanism by which astrocytes regulate physiological brain functioning.
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Affiliation(s)
- Clare M. Florence
- Department of Physiology, University of Saskatchewan, Saskatoon, Saskatchewan, Canada
| | - Landon D. Baillie
- Department of Physiology, University of Saskatchewan, Saskatoon, Saskatchewan, Canada
| | - Sean J. Mulligan
- Department of Physiology, University of Saskatchewan, Saskatoon, Saskatchewan, Canada
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62
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Marx G, Gilon C. The molecular basis of memory. ACS Chem Neurosci 2012; 3:633-42. [PMID: 23050060 DOI: 10.1021/cn300097b] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2012] [Accepted: 07/17/2012] [Indexed: 11/28/2022] Open
Abstract
We propose a tripartite biochemical mechanism for memory. Three physiologic components are involved, namely, the neuron (individual and circuit), the surrounding neural extracellular matrix, and the various trace metals distributed within the matrix. The binding of a metal cation affects a corresponding nanostructure (shrinking, twisting, expansion) and dielectric sensibility of the chelating node (address) within the matrix lattice, sensed by the neuron. The neural extracellular matrix serves as an electro-elastic lattice, wherein neurons manipulate multiple trace metals (n > 10) to encode, store, and decode coginive information. The proposed mechanism explains brains low energy requirements and high rates of storage capacity described in multiples of Avogadro number (N(A) = 6 × 10(23)). Supportive evidence correlates memory loss to trace metal toxicity or deficiency, or breakdown in the delivery/transport of metals to the matrix, or its degradation. Inherited diseases revolving around dysfunctional trace metal metabolism and memory dysfunction, include Alzheimer's disease (Al, Zn, Fe), Wilson's disease (Cu), thalassemia (Fe), and autism (metallothionein). The tripartite mechanism points to the electro-elastic interactions of neurons with trace metals distributed within the neural extracellular matrix, as the molecular underpinning of "synaptic plasticity" affecting short-term memory, long-term memory, and forgetting.
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Affiliation(s)
| | - Chaim Gilon
- Institute of Chemistry, Hebrew University, Jerusalem, Israel
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63
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Bradley SJ, Challiss RJ. G protein-coupled receptor signalling in astrocytes in health and disease: A focus on metabotropic glutamate receptors. Biochem Pharmacol 2012; 84:249-59. [DOI: 10.1016/j.bcp.2012.04.009] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2012] [Revised: 04/02/2012] [Accepted: 04/09/2012] [Indexed: 02/03/2023]
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64
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Kirischuk S, Parpura V, Verkhratsky A. Sodium dynamics: another key to astroglial excitability? Trends Neurosci 2012; 35:497-506. [PMID: 22633141 DOI: 10.1016/j.tins.2012.04.003] [Citation(s) in RCA: 172] [Impact Index Per Article: 14.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2012] [Revised: 04/06/2012] [Accepted: 04/10/2012] [Indexed: 11/19/2022]
Abstract
Astroglial excitability is largely mediated by fluctuations in intracellular ion concentrations. In addition to generally acknowledged Ca²⁺ excitability of astroglia, recent studies have demonstrated that neuronal activity triggers transient increases in the cytosolic Na⁺ concentration ([Na⁺](i)) in perisynaptic astrocytes. These [Na⁺](i) transients are controlled by multiple Na⁺-permeable channels and Na⁺-dependent transporters; spatiotemporally organized [Na⁺](i) dynamics in turn regulate diverse astroglial homeostatic responses such as metabolic/signaling utilization of lactate and glutamate, transmembrane transport of neurotransmitters and K⁺ buffering. In particular, near-membrane [Na⁺](i) transients determine the rate and the direction of the transmembrane transport of GABA and Ca²⁺. We discuss here the role of Na⁺ in the regulation of various systems that mediate fast bidirectional communication between neurones and glia at the single synapse level.
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Affiliation(s)
- Sergei Kirischuk
- Institute of Physiology and Pathophysiology, Universal Medical Center of the Johannes Gutenberg University Mainz, Mainz, Germany
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65
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Parpura V, Heneka MT, Montana V, Oliet SHR, Schousboe A, Haydon PG, Stout RF, Spray DC, Reichenbach A, Pannicke T, Pekny M, Pekna M, Zorec R, Verkhratsky A. Glial cells in (patho)physiology. J Neurochem 2012; 121:4-27. [PMID: 22251135 DOI: 10.1111/j.1471-4159.2012.07664.x] [Citation(s) in RCA: 402] [Impact Index Per Article: 33.5] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Neuroglial cells define brain homeostasis and mount defense against pathological insults. Astroglia regulate neurogenesis and development of brain circuits. In the adult brain, astrocytes enter into intimate dynamic relationship with neurons, especially at synaptic sites where they functionally form the tripartite synapse. At these sites, astrocytes regulate ion and neurotransmitter homeostasis, metabolically support neurons and monitor synaptic activity; one of the readouts of the latter manifests in astrocytic intracellular Ca(2+) signals. This form of astrocytic excitability can lead to release of chemical transmitters via Ca(2+) -dependent exocytosis. Once in the extracellular space, gliotransmitters can modulate synaptic plasticity and cause changes in behavior. Besides these physiological tasks, astrocytes are fundamental for progression and outcome of neurological diseases. In Alzheimer's disease, for example, astrocytes may contribute to the etiology of this disorder. Highly lethal glial-derived tumors use signaling trickery to coerce normal brain cells to assist tumor invasiveness. This review not only sheds new light on the brain operation in health and disease, but also points to many unknowns.
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Affiliation(s)
- Vladimir Parpura
- Department of Neurobiology, Center for Glial Biology in Medicine, Civitan International Research Center, Atomic Force Microscopy & Nanotechnology Laboratories, and Evelyn F. McKnight Brain Institute, University of Alabama, Birmingham, Alabama, USA.
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66
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Scheiber IF, Schmidt MM, Dringen R. Copper export from cultured astrocytes. Neurochem Int 2011; 60:292-300. [PMID: 22226844 DOI: 10.1016/j.neuint.2011.12.012] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2011] [Revised: 12/16/2011] [Accepted: 12/22/2011] [Indexed: 01/14/2023]
Abstract
Copper is an essential trace metal that is required as a catalytic co-factor or a structural component of several important enzymes. However, since excess of copper can also harm cells due to its potential to catalyse the generation of toxic reactive oxygen species, transport of copper and the cellular copper content are tightly regulated. Astrocytes are known to efficiently take up copper ions, but it was not known whether these cells are also able to export copper. Treatment of astrocyte-rich primary cultures for 24 h with copper chloride caused a concentration-dependent increase in the specific cellular copper content. During further 24 h incubation in the absence of copper chloride, the copper-loaded astrocytes remained viable and released up to 45% of the accumulated copper. The rate of copper export was proportional to the amount of cellular copper, was almost completely prevented by lowering the incubation temperature to 4 °C and was partly prevented by the endocytosis inhibitor amiloride. Copper export is most likely mediated by the copper ATPase ATP7A, since this transporter is expressed in astrocyte cultures and its cellular location is strongly affected by the absence or the presence of extracellular copper. The potential of cultured astrocytes to export copper suggests that astrocytes provide neighbouring cells in brain with this essential trace element.
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Affiliation(s)
- Ivo F Scheiber
- Center for Biomolecular Interactions Bremen, University of Bremen, P.O. Box 330440, D-28334 Bremen, Germany
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67
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The impact of the glial spatial buffering on the K(+) Nernst potential. Cogn Neurodyn 2011; 5:285-91. [PMID: 22942917 DOI: 10.1007/s11571-011-9165-x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2011] [Revised: 06/28/2011] [Accepted: 07/07/2011] [Indexed: 10/18/2022] Open
Abstract
Astrocytes play a critical role in CNS metabolism, regulation of volume and ion homeostasis of the interstitial space. Of special relevance is their clearance of K(+) that is released by active neurons into the extracellular space. Mathematical analysis of a modified Nernst equation for the electrochemical equilibrium of neuronal plasma membranes, suggests that K(+) uptake by glial cells is not only relevant during neuronal activity but also has a non-neglectable impact on the basic electrical membrane properties, specifically the resting membrane potential, of neurons and might be clinically valuable as a factor in the genetics and epigenetics of the epilepsy and tuberous sclerosis complex.
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68
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Danjo R, Kawasaki F, Ordway RW. A tripartite synapse model in Drosophila. PLoS One 2011; 6:e17131. [PMID: 21359186 PMCID: PMC3040228 DOI: 10.1371/journal.pone.0017131] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2010] [Accepted: 01/21/2011] [Indexed: 11/18/2022] Open
Abstract
Tripartite (three-part) synapses are defined by physical and functional interactions of glia with pre- and post-synaptic elements. Although tripartite synapses are thought to be of widespread importance in neurological health and disease, we are only beginning to develop an understanding of glial contributions to synaptic function. In contrast to studies of neuronal mechanisms, a significant limitation has been the lack of an invertebrate genetic model system in which conserved mechanisms of tripartite synapse function may be examined through large-scale application of forward genetics and genome-wide genetic tools. Here we report a Drosophila tripartite synapse model which exhibits morphological and functional properties similar to those of mammalian synapses, including glial regulation of extracellular glutamate, synaptically-induced glial calcium transients and glial coupling of synapses with tracheal structures mediating gas exchange. In combination with classical and cell-type specific genetic approaches in Drosophila, this model is expected to provide new insights into the molecular and cellular mechanisms of tripartite synapse function.
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Affiliation(s)
- Rie Danjo
- Department of Biology and Center for Molecular and Cellular Neuroscience, Pennsylvania State University, University Park, Pennsylvania
| | - Fumiko Kawasaki
- Department of Biology and Center for Molecular and Cellular Neuroscience, Pennsylvania State University, University Park, Pennsylvania
| | - Richard W. Ordway
- Department of Biology and Center for Molecular and Cellular Neuroscience, Pennsylvania State University, University Park, Pennsylvania
- * E-mail:
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69
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Abstract
Astrocyte-rich primary cultures were used to investigate the consequences of a copper exposure on the glucose metabolism of astrocytes. After application of CuCl(2) (30 μM) the specific cellular copper content increased from initial 1.5 ± 0.2 nmol/mg to a steady state level of 7.9 ± 0.9 nmol/mg within about 12 h. The copper accumulation was accompanied by a significant increase in the extracellular lactate concentration. The stimulating effect of copper on the lactate production remained after removal of extracellular copper. Copper treatment accelerated the rates of both glucose consumption and lactate production by about 60%. The copper induced acceleration of glycolytic flux was prevented by inhibition of protein synthesis, and additive to the stimulation of glycolysis observed for inhibitors of respiration or prolyl hydroxylases. A copper induced stimulation of glycolytic flux in astrocytes could have severe consequences for the glucose metabolism of the brain in conditions of copper overload.
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70
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Lalo U, Verkhratsky A, Pankratov Y. Ionotropic ATP receptors in neuronal-glial communication. Semin Cell Dev Biol 2011; 22:220-8. [PMID: 21320623 DOI: 10.1016/j.semcdb.2011.02.012] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2010] [Revised: 01/05/2011] [Accepted: 02/07/2011] [Indexed: 01/10/2023]
Abstract
In the central nervous system ATP is released from both neurones and astroglial cells acting as a homo- and heterocellular neurotransmitter. Glial cells express numerous purinoceptors of both ionotropic (P2X) and metabotropic (P2Y) varieties. Astroglial P2X receptors can be activated by ongoing synaptic transmission and can mediate fast local signalling through elevation in cytoplasmic Ca(2+) and Na(+) concentrations. These ionic signals can be translated into various physiological messages by numerous pathways, including release of gliotransmitters, metabolic support of neurones and regulation of activity of postsynaptic glutamate and GABA receptors. Ionotropic purinoceptors represent a novel pathway of glia-driven modulation of synaptic signalling that involves the release of ATP from neurones and astrocytes followed by activation of P2X receptors which can regulate synaptic activity by variety of mechanisms expressed in both neuronal and glial compartments.
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Affiliation(s)
- Ulyana Lalo
- Department of Cell Physiology and Pharmacology, University of Leicester, Leicester, UK
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71
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Palygin O, Lalo U, Verkhratsky A, Pankratov Y. Ionotropic NMDA and P2X1/5 receptors mediate synaptically induced Ca2+ signalling in cortical astrocytes. Cell Calcium 2011; 48:225-31. [PMID: 20926134 DOI: 10.1016/j.ceca.2010.09.004] [Citation(s) in RCA: 122] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2010] [Revised: 09/05/2010] [Accepted: 09/07/2010] [Indexed: 10/19/2022]
Abstract
Local, global and propagating calcium (Ca(2+)) signals provide the substrate for glial excitability. Here we analyse Ca(2+) permeability of NMDA and P2X(1/5) receptors expressed in cortical astrocytes and provide evidence that activation of these receptors trigger astroglial Ca(2+) signals when stimulated by either endogenous agonists or by synaptic release of neurotransmitters. The Ca(2+) permeability of the ionotropic receptors was determined by reversal potential shift analysis; the permeability ratio P(Ca)/P(K) was 3.1 for NMDA receptors and 2.2 for P2X(1/5) receptors. Selective stimulation of ionotropic receptors (with NMDA and α,β-methyleneATP) in freshly isolated cortical astrocytes induced ion currents associated with transient increases in cytosolic Ca(2+) concentration ([Ca(2+)](i)). Stimulation of neuronal afferents in cortical slices triggered glial synaptic currents and [Ca(2+)](i) responses, which were partially blocked by selective antagonists of NMDA (D-AP5 and UBP141) and P2X(1/5) (NF449) receptors. We conclude that ionotropic receptors contribute to astroglial Ca(2+) signalling and may provide a specific mechanism for fast neuronal-glial signalling at the synaptic level.
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Affiliation(s)
- Oleg Palygin
- Department of Biological Sciences, University of Warwick, Coventry CV4 7AL, UK
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72
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Kimelberg HK, Nedergaard M. Functions of astrocytes and their potential as therapeutic targets. Neurotherapeutics 2010; 7:338-53. [PMID: 20880499 PMCID: PMC2982258 DOI: 10.1016/j.nurt.2010.07.006] [Citation(s) in RCA: 278] [Impact Index Per Article: 19.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2010] [Accepted: 07/27/2010] [Indexed: 12/28/2022] Open
Abstract
Astrocytes are often referred to, and historically have been regarded as, support cells of the mammalian CNS. Work over the last decade suggests otherwise-that astrocytes may in fact play a more active role in higher neural processing than previously recognized. Because astrocytes can potentially serve as novel therapeutic targets, it is critical to understand how astrocytes execute their diverse supportive tasks while maintaining neuronal health. To that end, this review focuses on the supportive roles of astrocytes, a line of study relevant to essentially all acute and chronic neurological diseases, and critically re-evaluates our concepts of the functional properties of astrocytes and relates these functions and properties to the intricate morphology of these cells.
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Affiliation(s)
| | - Maiken Nedergaard
- grid.16416.340000000419369174Center for Translational Neuromedicine, Department of Neurosurgery, University of Prochester Medical School, 601 Elmwood Avenue, 114642 Rochester, New York
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73
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Honsek SD, Walz C, Kafitz KW, Rose CR. Astrocyte calcium signals at Schaffer collateral to CA1 pyramidal cell synapses correlate with the number of activated synapses but not with synaptic strength. Hippocampus 2010; 22:29-42. [DOI: 10.1002/hipo.20843] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 06/10/2010] [Indexed: 11/08/2022]
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74
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Ionotropic receptors in neuronal-astroglial signalling: what is the role of "excitable" molecules in non-excitable cells. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2010; 1813:992-1002. [PMID: 20869992 DOI: 10.1016/j.bbamcr.2010.09.007] [Citation(s) in RCA: 88] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/21/2010] [Revised: 09/13/2010] [Accepted: 09/16/2010] [Indexed: 01/02/2023]
Abstract
Astroglial cells were long considered to serve merely as the structural and metabolic supporting cast and scenery against which the shining neurones perform their illustrious duties. Relatively recent evidence, however, indicates that astrocytes are intimately involved in many of the brain's functions. Astrocytes possess a diverse assortment of ionotropic transmitter receptors, which enable these glial cells to respond to many of the same signals that act on neurones. Ionotropic receptors mediate neurone-driven signals to astroglial cells in various brain areas including neocortex, hippocampus and cerebellum. Activation of ionotropic receptors trigger rapid signalling events in astroglia; these events, represented by local Ca(2+) or Na(+) signals provide the mechanism for fast neuronal-glial signalling at the synaptic level. Since astrocytes can detect chemical transmitters that are released from neurones and can release their own extracellular signals, gliotransmitters, they are intricately involved in homocellular and heterocellular signalling mechanisms in the nervous system. This article is part of a Special Issue entitled: 11th European Symposium on Calcium.
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75
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Pereira A, Furlan FA. Astrocytes and human cognition: modeling information integration and modulation of neuronal activity. Prog Neurobiol 2010; 92:405-20. [PMID: 20633599 DOI: 10.1016/j.pneurobio.2010.07.001] [Citation(s) in RCA: 84] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2010] [Revised: 06/18/2010] [Accepted: 07/06/2010] [Indexed: 10/19/2022]
Abstract
Recent research focusing on the participation of astrocytes in glutamatergic tripartite synapses has revealed mechanisms that support cognitive functions common to human and other mammalian species, such as learning, perception, conscious integration, memory formation/retrieval and the control of voluntary behavior. Astrocytes can modulate neuronal activity by means of release of glutamate, d-serine, adenosine triphosphate and other signaling molecules, contributing to sustain, reinforce or depress pre- and post-synaptic membranes. We review molecular mechanisms present in tripartite synapses and model the cognitive role of astrocytes. Single protoplasmic astrocytes operate as a "Local Hub", integrating information patterns from neuronal and glial populations. Two mechanisms, here modeled as the "domino" and "carousel" effects, contribute to the formation of intercellular calcium waves. As waves propagate through gap junctions and reach other types of astrocytes (interlaminar, polarized, fibrous and varicose projection), the active astroglial network functions as a "Master Hub" that integrates results of distributed processing from several brain areas and supports conscious states. Response of this network would define the effect exerted on neuronal plasticity (membrane potentiation or depression), behavior and psychosomatic processes. Theoretical results of our modeling can contribute to the development of new experimental research programs to test cognitive functions of astrocytes.
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Affiliation(s)
- Alfredo Pereira
- Institute of Biosciences, State University of São Paulo (UNESP), Campus Rubião Jr., 18618-000 Botucatu-SP, Brazil.
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76
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Verkhratsky A, Parpura V, Rodríguez JJ. Where the thoughts dwell: the physiology of neuronal-glial "diffuse neural net". ACTA ACUST UNITED AC 2010; 66:133-51. [PMID: 20546785 DOI: 10.1016/j.brainresrev.2010.05.002] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2010] [Revised: 05/11/2010] [Accepted: 05/17/2010] [Indexed: 02/07/2023]
Abstract
The mechanisms underlying the production of thoughts by exceedingly complex cellular networks that construct the human brain constitute the most challenging problem of natural sciences. Our understanding of the brain function is very much shaped by the neuronal doctrine that assumes that neuronal networks represent the only substrate for cognition. These neuronal networks however are embedded into much larger and probably more complex network formed by neuroglia. The latter, although being electrically silent, employ many different mechanisms for intercellular signalling. It appears that astrocytes can control synaptic networks and in such a capacity they may represent an integral component of the computational power of the brain rather than being just brain "connective tissue". The fundamental question of whether neuroglia is involved in cognition and information processing remains, however, open. Indeed, a remarkable increase in the number of glial cells that distinguishes the human brain can be simply a result of exceedingly high specialisation of the neuronal networks, which delegated all matters of survival and maintenance to the neuroglia. At the same time potential power of analogue processing offered by internally connected glial networks may represent the alternative mechanism involved in cognition.
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77
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Understanding wiring and volume transmission. ACTA ACUST UNITED AC 2010; 64:137-59. [PMID: 20347870 DOI: 10.1016/j.brainresrev.2010.03.003] [Citation(s) in RCA: 189] [Impact Index Per Article: 13.5] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2009] [Revised: 03/17/2010] [Accepted: 03/17/2010] [Indexed: 11/23/2022]
Abstract
The proposal on the existence of two main modes of intercellular communication in the central nervous system (CNS) was introduced in 1986 and called wiring transmission (WT) and volume transmission (VT). The major criterion for this classification was the different characteristics of the communication channel with physical boundaries well delimited in the case of WT (axons and their synapses; gap junctions) but not in the case of VT (the extracellular fluid filled tortuous channels of the extracellular space and the cerebrospinal fluid filled ventricular space and sub-arachnoidal space). The basic dichotomic classification of intercellular communication in the brain is still considered valid, but recent evidence on the existence of unsuspected specialized structures for intercellular communication, such as microvesicles (exosomes and shedding vesicles) and tunnelling nanotubes, calls for a refinement of the original classification model. The proposed updating is based on criteria which are deduced not only from these new findings but also from concepts offered by informatics to classify the communication networks in the CNS. These criteria allowed the identification also of new sub-classes of WT and VT, namely the "tunnelling nanotube type of WT" and the "Roamer type of VT." In this novel type of VT microvesicles are safe vesicular carriers for targeted intercellular communication of proteins, mtDNA and RNA in the CNS flowing in the extracellular fluid along energy gradients to reach target cells. In the tunnelling nanotubes proteins, mtDNA and RNA can migrate as well as entire organelles such as mitochondria. Although the existence and the role of these new types of intercellular communication in the CNS are still a matter of investigation and remain to be fully demonstrated, the potential importance of these novel types of WT and VT for brain function in health and disease is discussed.
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