451
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Gómez-Gonzalo M, Losi G, Brondi M, Uva L, Sato SS, de Curtis M, Ratto GM, Carmignoto G. Ictal but not interictal epileptic discharges activate astrocyte endfeet and elicit cerebral arteriole responses. Front Cell Neurosci 2011; 5:8. [PMID: 21747758 PMCID: PMC3128928 DOI: 10.3389/fncel.2011.00008] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2011] [Accepted: 06/06/2011] [Indexed: 12/03/2022] Open
Abstract
Activation of astrocytes by neuronal signals plays a central role in the control of neuronal activity-dependent blood flow changes in the normal brain. The cellular pathways that mediate neurovascular coupling in the epileptic brain remain, however, poorly defined. In a cortical slice model of epilepsy, we found that the ictal, seizure-like discharge, and only to a minor extent the interictal discharge, evokes both a Ca2+ increase in astrocyte endfeet and a vasomotor response. We also observed that rapid ictal discharge-induced arteriole responses were regularly preceded by Ca2+ elevations in endfeet and were abolished by pharmacological inhibition of Ca2+ signals in these astrocyte processes. Under these latter conditions, arterioles exhibited after the ictal discharge only slowly developing vasodilations. The poor efficacy of interictal discharges, compared with ictal discharges, to activate endfeet was confirmed also in the intact in vitro isolated guinea pig brain. Although the possibility of a direct contribution of neurons, in particular in the late response of cerebral blood vessels to epileptic discharges, should be taken into account, our study supports the view that astrocytes are central for neurovascular coupling also in the epileptic brain. The massive endfeet Ca2+ elevations evoked by ictal discharges and the poor response to interictal events represent new information potentially relevant to interpret data from diagnostic brain imaging techniques, such as functional magnetic resonance, utilized in the clinic to localize neural activity and to optimize neurosurgery of untreatable epilepsies.
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452
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Dai M, Shi X. Fibro-vascular coupling in the control of cochlear blood flow. PLoS One 2011; 6:e20652. [PMID: 21673815 PMCID: PMC3106013 DOI: 10.1371/journal.pone.0020652] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2010] [Accepted: 05/06/2011] [Indexed: 12/20/2022] Open
Abstract
Background Transduction of sound in the cochlea is metabolically demanding. The lateral
wall and hair cells are critically vulnerable to hypoxia, especially at high
sound levels, and tight control over cochlear blood flow (CBF) is a
physiological necessity. Yet despite the importance of CBF for hearing,
consensus on what mechanisms are involved has not been obtained. Methodology/Principal Findings We report on a local control mechanism for regulating inner ear blood flow
involving fibrocyte signaling. Fibrocytes in the super-strial region are
spatially distributed near pre-capillaries of the spiral ligament of the
albino guinea pig cochlear lateral wall, as demonstrably shown in
transmission electron microscope and confocal images. Immunohistochemical
techniques reveal the inter-connected fibrocytes to be positive for
Na+/K+ ATPase β1 and S100. The connected fibrocytes display
more Ca2+ signaling than other cells in the cochlear lateral
wall as indicated by fluorescence of a Ca2+ sensor, fluo-4.
Elevation of Ca2+ in fibrocytes, induced by photolytic
uncaging of the divalent ion chelator o-nitrophenyl EGTA,
results in propagation of a Ca2+ signal to neighboring
vascular cells and vasodilation in capillaries. Of more physiological
significance, fibrocyte to vascular cell coupled signaling was found to
mediate the sound stimulated increase in cochlear blood flow (CBF).
Cyclooxygenase-1 (COX-1) was required for capillary dilation. Conclusions/Significance The findings provide the first evidence that signaling between fibrocytes and
vascular cells modulates CBF and is a key mechanism for meeting the cellular
metabolic demand of increased sound activity.
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Affiliation(s)
- Min Dai
- Oregon Hearing Research Center, Department of Otolaryngology/Head and
Neck Surgery, Oregon Health & Science University, Portland, Oregon, United
States of America
| | - Xiaorui Shi
- Oregon Hearing Research Center, Department of Otolaryngology/Head and
Neck Surgery, Oregon Health & Science University, Portland, Oregon, United
States of America
- The Institute of Microcirculation, Chinese Academy of Medical Sciences
and Peking Union Medical College, Beijing, China
- Department of Otolaryngology, Renji Hospital, Shanghai Jiao Tong
University, Shanghai, China
- * E-mail:
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453
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Rasmussen P, Wyss MT, Lundby C. Cerebral glucose and lactate consumption during cerebral activation by physical activity in humans. FASEB J 2011; 25:2865-73. [DOI: 10.1096/fj.11-183822] [Citation(s) in RCA: 65] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- Peter Rasmussen
- Zurich Centre for Integrative Human PhysiologyDepartment of PhysiologyUniversity of ZurichSwitzerland
| | - Matthias T. Wyss
- Institute of Pharmacology and ToxicologyUniversity of ZurichSwitzerland
| | - Carsten Lundby
- Zurich Centre for Integrative Human PhysiologyDepartment of PhysiologyUniversity of ZurichSwitzerland
- Institute of Pharmacology and ToxicologyUniversity of ZurichSwitzerland
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454
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Lactate transport and metabolism in the human brain: implications for the astrocyte-neuron lactate shuttle hypothesis. J Neurosci 2011; 31:4768-70. [PMID: 21451014 DOI: 10.1523/jneurosci.6612-10.2011] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
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455
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Fast and reversible stimulation of astrocytic glycolysis by K+ and a delayed and persistent effect of glutamate. J Neurosci 2011; 31:4709-13. [PMID: 21430169 DOI: 10.1523/jneurosci.5311-10.2011] [Citation(s) in RCA: 143] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Synaptic activity is followed within seconds by a local surge in lactate concentration, a phenomenon that underlies functional magnetic resonance imaging and whose causal mechanisms are unclear, partly because of the limited spatiotemporal resolution of standard measurement techniques. Using a novel Förster resonance energy transfer-based method that allows real-time measurement of the glycolytic rate in single cells, we have studied mouse astrocytes in search for the mechanisms responsible for the lactate surge. Consistent with previous measurements with isotopic 2-deoxyglucose, glutamate was observed to stimulate glycolysis in cultured astrocytes, but the response appeared only after a lag period of several minutes. Na(+) overloads elicited by engagement of the Na(+)-glutamate cotransporter with d-aspartate or application of the Na(+) ionophore gramicidin also failed to stimulate glycolysis in the short term. In marked contrast, K(+) stimulated astrocytic glycolysis by fourfold within seconds, an effect that was observed at low millimolar concentrations and was also present in organotypic hippocampal slices. After removal of the agonists, the stimulation by K(+) ended immediately but the stimulation by glutamate persisted unabated for >20 min. Both stimulations required an active Na(+)/K(+) ATPase pump. By showing that small rises in extracellular K(+) mediate short-term, reversible modulation of astrocytic glycolysis and that glutamate plays a long-term effect and leaves a metabolic trace, these results support the view that astrocytes contribute to the lactate surge that accompanies synaptic activity and underscore the role of these cells in neurometabolic and neurovascular coupling.
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456
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Liu X, Li C, Gebremedhin D, Hwang SH, Hammock BD, Falck JR, Roman RJ, Harder DR, Koehler RC. Epoxyeicosatrienoic acid-dependent cerebral vasodilation evoked by metabotropic glutamate receptor activation in vivo. Am J Physiol Heart Circ Physiol 2011; 301:H373-81. [PMID: 21602473 DOI: 10.1152/ajpheart.00745.2010] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Group I metabotropic glutamate receptors (mGluR) on astrocytes have been shown to participate in cerebral vasodilation to neuronal activation in brain slices. Pharmacological stimulation of mGluR in brain slices can produce arteriolar constriction or dilation depending on the initial degree of vascular tone. Here, we examined whether pharmacological stimulation of mGluR in vivo increases cerebral blood flow. A 1-mM solution of the group I mGluR agonist (S)-3,5-dihydroxyphenylglycine (DHPG) superfused at 5 μl/min over the cortical surface of anesthetized rats produced a 30 ± 2% (±SE) increase in blood flow measured by laser-Doppler flowmetry after 15-20 min. The response was completely blocked by superfusion of group I mGluR antagonists and attenuated by superfusion of an epoxyeicosatrienoic acid (EET) antagonist (5 ± 4%), an EET synthesis inhibitor (11 ± 3%), and a cyclooxygenase-2 inhibitor (15 ± 3%). The peak blood flow response was not significantly affected by administration of inhibitors of cyclooxygenase-1, neuronal nitric oxide synthase, heme oxygenase, adenosine A(2B) receptors, or an inhibitor of the synthesis of 20-hydroxyeicosatetraenoic acid (20-HETE). The blood flow response gradually waned following 30-60 min of DHPG superfusion. This loss of the flow response was attenuated by a 20-HETE synthesis inhibitor and was prevented by superfusion of an inhibitor of epoxide hydrolase, which hydrolyzes EETs. These results indicate that pharmacological stimulation of mGluR in vivo increases cerebral blood flow and that the response depends on the release of EETs and a metabolite of cyclooxygenase-2. Epoxide hydrolase activity and 20-HETE synthesis limit the duration of the response to prolonged mGluR activation.
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Affiliation(s)
- Xiaoguang Liu
- Department of Anesthesiology and Critical Care Medicine, Johns Hopkins University, Baltimore, Maryland, USA
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457
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The physiology of developmental changes in BOLD functional imaging signals. Dev Cogn Neurosci 2011; 1:199-216. [PMID: 22436508 DOI: 10.1016/j.dcn.2011.04.001] [Citation(s) in RCA: 112] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2011] [Revised: 04/18/2011] [Accepted: 04/19/2011] [Indexed: 12/14/2022] Open
Abstract
BOLD fMRI (blood oxygenation level dependent functional magnetic resonance imaging) is increasingly used to detect developmental changes of human brain function that are hypothesized to underlie the maturation of cognitive processes. BOLD signals depend on neuronal activity increasing cerebral blood flow, and are reduced by neural oxygen consumption. Thus, developmental changes of BOLD signals may not reflect altered information processing if there are concomitant changes in neurovascular coupling (the mechanism by which neuronal activity increases blood flow) or neural energy use (and hence oxygen consumption). We review how BOLD signals are generated, and explain the signalling pathways which convert neuronal activity into increased blood flow. We then summarize in broad terms the developmental changes that the brain's neural circuitry undergoes during growth from childhood through adolescence to adulthood, and present the changes in neurovascular coupling mechanisms and energy use which occur over the same period. This information provides a framework for assessing whether the BOLD changes observed during human development reflect altered cognitive processing or changes in neurovascular coupling and energy use.
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458
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Ng FS, Tangredi MM, Jackson FR. Glial cells physiologically modulate clock neurons and circadian behavior in a calcium-dependent manner. Curr Biol 2011; 21:625-34. [PMID: 21497088 PMCID: PMC3081987 DOI: 10.1016/j.cub.2011.03.027] [Citation(s) in RCA: 109] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2010] [Revised: 02/09/2011] [Accepted: 03/09/2011] [Indexed: 01/12/2023]
Abstract
BACKGROUND An important goal of contemporary neuroscience research is to define the neural circuits and synaptic interactions that mediate behavior. In both mammals and Drosophila, the neuronal circuitry controlling circadian behavior has been the subject of intensive investigation, but roles for glial cells in the networks controlling rhythmic behavior have only begun to be defined in recent studies. RESULTS Here, we show that conditional, glial-specific genetic manipulations affecting membrane (vesicle) trafficking, the membrane ionic gradient, or calcium signaling lead to circadian arrhythmicity in adult behaving Drosophila. Correlated and reversible effects on a clock neuron peptide transmitter (PDF) and behavior demonstrate the capacity for glia-to-neuron signaling in the circadian circuitry. These studies also reveal the importance of a single type of glial cell-the astrocyte-and glial internal calcium stores in the regulation of circadian rhythms. CONCLUSIONS This is the first demonstration in any system that adult glial cells can physiologically modulate circadian neuronal circuitry and behavior. A role for astrocytes and glial calcium signaling in the regulation of Drosophila circadian rhythms emphasizes the conservation of cellular and molecular mechanisms that regulate behavior in mammals and insects.
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Affiliation(s)
- Fanny S. Ng
- Department of Neuroscience, Center for Neuroscience Research Tufts University School of Medicine, 136 Harrison Avenue, Boston, MA 02111
| | - Michelle M. Tangredi
- Department of Neuroscience, Center for Neuroscience Research Tufts University School of Medicine, 136 Harrison Avenue, Boston, MA 02111
| | - F. Rob Jackson
- Department of Neuroscience, Center for Neuroscience Research Tufts University School of Medicine, 136 Harrison Avenue, Boston, MA 02111
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459
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Kleinfeld D, Blinder P, Drew PJ, Driscoll JD, Muller A, Tsai PS, Shih AY. A guide to delineate the logic of neurovascular signaling in the brain. FRONTIERS IN NEUROENERGETICS 2011; 3:1. [PMID: 21559095 PMCID: PMC3085135 DOI: 10.3389/fnene.2011.00001] [Citation(s) in RCA: 60] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/08/2010] [Accepted: 04/11/2011] [Indexed: 01/26/2023]
Abstract
The neurovascular system may be viewed as a distributed nervous system within the brain. It transforms local neuronal activity into a change in the tone of smooth muscle that lines the walls of arterioles and microvessels. We review the current state of neurovascular coupling, with an emphasis on signaling molecules that convey information from neurons to neighboring vessels. At the level of neocortex, this coupling is mediated by: (i) a likely direct interaction with inhibitory neurons, (ii) indirect interaction, via astrocytes, with excitatory neurons, and (iii) fiber tracts from subcortical layers. Substantial evidence shows that control involves competition between signals that promote vasoconstriction versus vasodilation. Consistent with this picture is evidence that, under certain circumstances, increased neuronal activity can lead to vasoconstriction rather than vasodilation. This confounds naïve interpretations of functional brain images. We discuss experimental approaches to detect signaling molecules in vivo with the goal of formulating an empirical basis for the observed logic of neurovascular control.
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Affiliation(s)
- David Kleinfeld
- Department of Physics, University of California San Diego La Jolla, CA, USA
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460
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Neuronal-astrocyte metabolic interactions: understanding the transition into abnormal astrocytoma metabolism. J Neuropathol Exp Neurol 2011; 70:167-76. [PMID: 21293295 DOI: 10.1097/nen.0b013e31820e1152] [Citation(s) in RCA: 82] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
Abstract
Brain function depends on complex metabolic interactions among only a few different cell types, with astrocytes providing critical support for neurons. Astrocyte functions include buffering the extracellular space, providing substrates to neurons, interchanging glutamate and glutamine for synaptic transmission with neurons, and facilitating access to blood vessels. Whereas neurons possess highly oxidative metabolism and easily succumb to ischemia, astrocytes rely more on glycolytic metabolism and hence are less susceptible tolack of oxygen. Astrocytoma cells seem to retain basic metabolic mechanisms of astrocytes; for example, they show a high glycolytic rate, lactate extrusion, ability to flourish under hypoxia, and opportunistic use of mechanisms to enhance cell division and maintain growth. Differences in metabolism between neurons and astrocytes may also extend to astrocytoma cells, providing therapeutic opportunities against astrocytomas, including sensitivity to acetate, a high rate of glycolysis and lactate extrusion, glutamate uptake transporters, differential sensitivities of monocarboxylate transporters, presence of glycogen, high interlinking with gap junctions, use of nicotinamide adenine dinucleotide phosphate for lipid synthesis, using different isoforms of synthetic enzymes (e.g. isocitrate dehydrogenase, pyruvate carboxylase, pyruvate kinase, lactate dehydrogenase), and different glucose uptake mechanisms. These unique metabolic susceptibilities may augment conventional therapeutic attacks based on cell division differences and surface receptors alone.
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461
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Noguchi K, Matsumoto N, Shiozaki T, Tasaki O, Ogura H, Kuwagata Y, Sugimoto H, Seiyama A. Effects of timing and duration of hypothermia on survival in an experimental gerbil model of global ischaemia. Resuscitation 2011; 82:481-6. [DOI: 10.1016/j.resuscitation.2010.09.477] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2010] [Revised: 09/15/2010] [Accepted: 09/23/2010] [Indexed: 10/18/2022]
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462
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Abstract
Macroscopic changes in cerebral blood flow, such as those captured by functional imaging of the brain, require highly organized, large-scale dynamics of astrocytes, glial cells that interact with both neuronal and cerebrovascular networks. However, astrocyte activity has been studied mainly at the level of individual cells, and information regarding their collective behavior is lacking. In this work, we monitored calcium activity simultaneously from hundreds of mouse hippocampal astrocytes in vivo and found that almost all astrocytes participated en masse in regenerative waves that propagated from cell to cell (referred to here as "glissandi"). Glissandi emerged depending on the neuronal activity and accompanied a reduction in infraslow fluctuations of local field potentials and a decrease in the flow of red blood cells. This novel phenomenon was heretofore overlooked, probably because of the high vulnerability of astrocytes to light damage; glissandi occurred only when observed at much lower laser intensities than previously used.
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463
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Suzuki A, Stern SA, Bozdagi O, Huntley GW, Walker RH, Magistretti PJ, Alberini CM. Astrocyte-neuron lactate transport is required for long-term memory formation. Cell 2011; 144:810-23. [PMID: 21376239 PMCID: PMC3073831 DOI: 10.1016/j.cell.2011.02.018] [Citation(s) in RCA: 1137] [Impact Index Per Article: 87.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2010] [Revised: 09/21/2010] [Accepted: 02/08/2011] [Indexed: 11/18/2022]
Abstract
We report that, in the rat hippocampus, learning leads to a significant increase in extracellular lactate levels that derive from glycogen, an energy reserve selectively localized in astrocytes. Astrocytic glycogen breakdown and lactate release are essential for long-term but not short-term memory formation, and for the maintenance of long-term potentiation (LTP) of synaptic strength elicited in vivo. Disrupting the expression of the astrocytic lactate transporters monocarboxylate transporter 4 (MCT4) or MCT1 causes amnesia, which, like LTP impairment, is rescued by L-lactate but not equicaloric glucose. Disrupting the expression of the neuronal lactate transporter MCT2 also leads to amnesia that is unaffected by either L-lactate or glucose, suggesting that lactate import into neurons is necessary for long-term memory. Glycogenolysis and astrocytic lactate transporters are also critical for the induction of molecular changes required for memory formation, including the induction of phospho-CREB, Arc, and phospho-cofilin. We conclude that astrocyte-neuron lactate transport is required for long-term memory formation.
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Affiliation(s)
- Akinobu Suzuki
- Department of Neuroscience, Mount Sinai School of Medicine, New York, New York 10029
| | - Sarah A. Stern
- Department of Neuroscience, Mount Sinai School of Medicine, New York, New York 10029
| | - Ozlem Bozdagi
- Department of Neuroscience, Mount Sinai School of Medicine, New York, New York 10029
- Department of Psychiatry, Mount Sinai School of Medicine, New York, New York 10029
| | - George W. Huntley
- Department of Neuroscience, Mount Sinai School of Medicine, New York, New York 10029
| | - Ruth H. Walker
- Department of Neurology, James J. Peters VAMC, Bronx, NY 10468
| | - Pierre J. Magistretti
- Laboratory of Neuroenergetics and Cellular Dynamics, Brain Mind Institute, Ecole Polytechnique Fédérale de Lausanne (EPFL) and Center for Psychiatric Neuroscience, University of Lausanne-CHUV, Lausanne, Switzerland
| | - Cristina M. Alberini
- Department of Neuroscience, Mount Sinai School of Medicine, New York, New York 10029
- Department of Psychiatry, Mount Sinai School of Medicine, New York, New York 10029
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464
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Neuwelt EA, Bauer B, Fahlke C, Fricker G, Iadecola C, Janigro D, Leybaert L, Molnar Z, O’Donnell M, Povlishock J, Saunders N, Sharp F, Stanimirovic D, Watts R, Drewes L. Engaging neuroscience to advance translational research in brain barrier biology. Nat Rev Neurosci 2011; 12:169-82. [PMID: 21331083 PMCID: PMC3335275 DOI: 10.1038/nrn2995] [Citation(s) in RCA: 392] [Impact Index Per Article: 30.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
The delivery of many potentially therapeutic and diagnostic compounds to specific areas of the brain is restricted by brain barriers, of which the most well known are the blood-brain barrier (BBB) and the blood-cerebrospinal fluid (CSF) barrier. Recent studies have shown numerous additional roles of these barriers, including an involvement in neurodevelopment, in the control of cerebral blood flow, and--when barrier integrity is impaired--in the pathology of many common CNS disorders such as Alzheimer's disease, Parkinson's disease and stroke.
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Affiliation(s)
- Edward A. Neuwelt
- Oregon Health & Science University, Portland, Oregon
- Portland Veterans Affairs Medical Center, Portland, Oregon
| | | | | | | | | | | | | | | | | | | | | | - Frank Sharp
- University of California at Davis, Davis, California
| | | | - Ryan Watts
- Genentech, Inc., South San Francisco, California
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465
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466
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Kulik TB, Aronhime SN, Echeverry G, Beylin A, Winn HR. The relationship between oxygen and adenosine in astrocytic cultures. Glia 2011; 58:1335-44. [PMID: 20607719 DOI: 10.1002/glia.21011] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Brain tissue oxygenation affects cerebral function and blood flow (CBF). Adenosine (Ado), a purine nucleoside, moderates neuronal activity, and arterial diameter. The cellular source of Ado in brain remains elusive; however, astrocytes are a logical site of production. Using astrocytic cultures, we tested the hypothesis that astrocytic derived Ado reflects cerebral oxygenation. We found that during alterations in pO(2), extracellular levels of Ado [Ado](e) changed rapidly. Graded reductions of oxygen tension revealed that[Ado](e) reached 10(-7) M to 10(-6) M with a pO(2) of 30-10mmHg, comparable with [Ado](e) and oxygen levels found in brain tissue during normoxemia. Higher O(2) levels were associated with a depression of [Ado](e). Under conditions of low pO(2) (pO(2) <or= 3 mmHg), inhibition of extracellular catabolism of adenosine monophosphate (AMP) prevented an increase of [Ado](e) and resulted in a rise in [AMP](e). The rise in [AMP](e) preceded the increase in [Ado](e). In the presence of nucleoside transporter inhibitors, accumulation of [Ado](e) persisted. On the basis of our studies in culture we conclude that astrocytes are a significant source of Ado and that during hypoxia, the changes in [Ado](e) are in a range to affect both neuronal activity as well as CBF.
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Affiliation(s)
- Tobias B Kulik
- Department of Neurosurgery, Mount Sinai School of Medicine, New York, New York
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467
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Kantevari S, Gordon GRJ, MacVicar BA, Ellis-Davies GCR. A practical guide to the synthesis and use of membrane-permeant acetoxymethyl esters of caged inositol polyphosphates. Nat Protoc 2011; 6:327-37. [PMID: 21372813 DOI: 10.1038/nprot.2010.194] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
This protocol describes a method for efficient chemical synthesis of an analog of inositol-1,4,5-trisphosphate (IP(3)) hexakis acetoxymethyl ester having an ortho-nitroveratryl photochemical caging group on the 6-hydroxyl position. The six esters render the probe membrane permeant, such that it can be loaded into intact living cells in vitro or in vivo. Inside cells, the caged IP(3) is inert until activated by two-photon excitation at 720 nm. The photoliberated signaling molecule can mobilize release of Ca(2+) from intracellular stores on the endoplasmic reticulum. When co-loaded with the fluorescent Ca(2+) indicator rhod-2, one laser can be used for stimulating and monitoring intracellular Ca(2+) signaling with single-cell resolution. This protocol has chemistry and biology sections; the former describes the organic synthesis of the caged IP(3), which requires 12 d, and the latter an application to a day-long study of astrocyte-regulated neuronal function in living brain slices acutely isolated from rats. As Ca(2+) is the single most important intracellular second messenger and the IP(3)-Ca(2+) signaling cascade is used by many cells to produce increases in Ca(2+) concentration, this method should be widely applicable for the study of a variety of physiological processes in intact biological systems.
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Affiliation(s)
- Srinivas Kantevari
- Department of Neuroscience, Mount Sinai School of Medicine, New York, New York, USA
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468
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Slice cultures as a model to study neurovascular coupling and blood brain barrier in vitro. Cardiovasc Psychiatry Neurol 2011; 2011:646958. [PMID: 21350722 PMCID: PMC3042620 DOI: 10.1155/2011/646958] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/30/2010] [Accepted: 12/24/2010] [Indexed: 11/18/2022] Open
Abstract
Proper neuronal functioning depends on a strictly regulated interstitial environment and tight coupling of neuronal and metabolic activity involving adequate vascular responses. These functions take place at the blood brain barrier (BBB) composed of endothelial cells, basal lamina covered with pericytes, and the endfeet of perivascular astrocytes. In conventional in vitro models of the BBB, some of these components are missing.
Here we describe a new model system for studying BBB and neurovascular coupling by using confocal microscopy and fluorescence staining protocols in organotypic hippocampal slice cultures.
An elaborated network of vessels is retained in culture in spite of the absence of blood flow. Application of calcein-AM either from the interstitial or from the luminal side resulted in different staining patterns indicating the maintenance of a barrier. By contrast, the ethidium derivative MitoSox penetrated perivascular basal lamina and revealed free radical formation in contractile cells embracing the vessels, likely pericytes.
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469
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Pelligrino DA, Vetri F, Xu HL. Purinergic mechanisms in gliovascular coupling. Semin Cell Dev Biol 2011; 22:229-36. [PMID: 21329762 DOI: 10.1016/j.semcdb.2011.02.010] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2010] [Revised: 01/11/2011] [Accepted: 02/07/2011] [Indexed: 01/23/2023]
Abstract
Regional elevations in cerebral blood flow (CBF) often occur in response to localized increases in cerebral neuronal activity. An ever expanding literature has linked this neurovascular coupling process to specific signaling pathways involving neuronal synapses, astrocytes and cerebral arteries and arterioles. Collectively, these structures are termed the "neurovascular unit" (NVU). Astrocytes are thought to be the cornerstone of the NVU. Thus, not only do astrocytes "detect" increased synaptic activity, they can transmit that information to proximal and remote astrocytic sites often through a Ca(2+)- and ATP-related signaling process. At the vascular end of the NVU, a Ca(2+)-dependent formation and release of vasodilators, or substances linked to vasodilation, can occur. The latter category includes ATP, which upon its appearance in the extracellular compartment, can be rapidly converted to the potent vasodilator, adenosine, via the action of ecto-nucleotidases. In the present review, we give consideration to experimental model-specific variations in purinergic influences on gliovascular signaling mechanisms, focusing on the cerebral cortex. In that discussion, we compare findings obtained using in vitro (rodent brain slice) models and multiple in vivo models (2-photon imaging; somatosensory stimulation-evoked cortical hyperemia; and sciatic nerve stimulation-evoked pial arteriolar dilation). Additional attention is given to the importance of upstream (remote) vasodilation; the key role played by extracellular ATP hydrolysis (via ecto-nucleotidases) in gliovascular coupling; and interactions among multiple signaling pathways.
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Affiliation(s)
- Dale A Pelligrino
- Neuroanesthesia Research Laboratory, University of Illinois at Chicago, Chicago, IL 60612, USA.
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470
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Figley CR, Stroman PW. The role(s) of astrocytes and astrocyte activity in neurometabolism, neurovascular coupling, and the production of functional neuroimaging signals. Eur J Neurosci 2011; 33:577-88. [DOI: 10.1111/j.1460-9568.2010.07584.x] [Citation(s) in RCA: 162] [Impact Index Per Article: 12.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
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471
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472
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Abstract
Astrocytes form a vascular-neuronal interface and provide CNS neural networks with essential structural and metabolic support. They embrace all penetrating arterioles and capillaries, enwrap multiple neuronal somata, thousands of individual synapses, and upon activation release gliotransmitters (ATP, glutamate and D-serine) capable of modulating neuronal activity. The aim of this brief report is to review recent data implicating astrocytes in the brain mechanisms responsible for the detection of different sensory modalities and transmitting sensory information to the relevant neural networks controlling vital behaviours. The concept of astrocytes as brain interoceptors is strongly supported by our recent data obtained from studies of the central nervous mechanisms underlying the chemosensory control of breathing. At the level of the medulla oblongata, astrocytes indeed act as functional central respiratory chemoreceptors, sensing changes in the arterial blood and brain levels of /pH and then imparting these changes on the activity of the respiratory network to induce adaptive changes in lung ventilation.
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Affiliation(s)
- Alexander V Gourine
- Neuroscience, Physiology & Pharmacology, University College London, London WC1E 6BT, UK.
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473
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Abstract
Astrocytes are the most numerous cells in the CNS. It is a defining feature of brain anatomy that every astrocyte has at least one contact with the vasculature, termed an endfoot. Collectively, all endfeet completely circumscribe all vessels in the brain. This unique anatomical feature has profound functional significance, as astrocyte endfeet have been discovered to release diffusible messengers that communicate directly with underlying smooth muscle cells to change arterial diameter and thereby regulate cerebral blood flow. A growing body of data now demonstrates that astrocytes serve as a bridge, relaying information on the level of neural activity to blood vessels in order to co-ordinate oxygen and glucose delivery with the energy demands of the tissue. In particular, astrocytes respond to elevations in extracellular glutamate as a consequence of synaptic transmission through the activation of group 1 metabotropic glutamate receptors. These Gq-coupled receptors elevate intracellular calcium via IP(3) signalling, which activates phospholipase A2 and generates arachidonic acid. Arachidonic acid acts as a signalling molecule or is converted to several lipid derivates, including prostaglandin E(2) and epoxyeicosatrienoic acids. Each of these lipids acts on vascular smooth muscle cells via different mechanisms to affect vessel diameter. Arachidonic acid initiates the production of 20-hydroxyeicosatetraenoic acid to cause vasoconstriction, whereas prostaglandin E(2) and epoxyeicosatrienoic acids cause vasodilatation. Factors that determine whether constrictor or dilatory pathways predominate involve nitric oxide and brain metabolic elements, such as oxygen, lactate and adenosine. Thus, astrocytes are thought to be capable of bidirectional control of arterial diameter, and the type of influence depends on the state of brain activity.
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Affiliation(s)
- Grant R J Gordon
- University of British Columbia, Department of Psychiatry, Vancouver, BC, Canada
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474
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Changes in cytosolic glucose level in ATP stimulated live astrocytes. Biochem Biophys Res Commun 2011; 405:308-13. [PMID: 21237134 DOI: 10.1016/j.bbrc.2011.01.035] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2011] [Accepted: 01/07/2011] [Indexed: 11/24/2022]
Abstract
Astrocytes which lie between brain capillaries and neuronal terminals are the primary site of glucose uptake and have a key role in coupling synaptic activity to glucose utilization in the central nervous system (CNS). We used a fluorescence resonance energy transfer (FRET) based approach to monitor cytosolic glucose in astrocytes. We determined the effect of increasing extracellular glucose concentrations on FRET ratio as a measure of increased cytosolic glucose in astrocytes. By briefly raising extracellular glucose concentration, astrocytes responded promptly by increased cytosolic glucose levels, which was manifested by decreased time-dependent FRET ratio. The FRET ratio fall-time recorded at low extracellular D-glucose concentration change (from 0 to 0.5 mM) was 53 s, whereas 17 s was recorded by raising extracellular concentration of D-glucose from 0 to 10 mM, which is likely due to facilitated d-glucose entry along the increased D-glucose gradient across the plasmalemma. The relationship between the extracellular glucose concentration and the FRET ratio change is limited to the maximal ratio change, where the D-glucose plasma membrane permeability is balanced by the cytosolic utilization. We measured the effect of extracellular ATP, an important extracellular messenger for astrocyte-to-astrocyte communication, on intracellular glucose concentration. The results show that stimulation of astrocytes with ATP (1 mM) decreases cytosolic glucose concentration with a time constant of ∼145 s. The mechanism of this change is discussed.
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475
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Mishra A, Newman EA. Inhibition of inducible nitric oxide synthase reverses the loss of functional hyperemia in diabetic retinopathy. Glia 2011; 58:1996-2004. [PMID: 20830810 DOI: 10.1002/glia.21068] [Citation(s) in RCA: 79] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Neuronal activity leads to arteriole dilation and increased blood flow in retinal vessels. This response, termed functional hyperemia, is diminished in the retinas of diabetic patients, possibly contributing to the development of diabetic retinopathy. The mechanism responsible for this loss is unknown. Here we show that light-evoked arteriole dilation was reduced by 58% in a streptozotocin-induced rat model of type 1 diabetes. Functional hyperemia is believed to be mediated by glial cells and we found that glial-evoked vasodilation was reduced by 60% in diabetic animals. The diabetic retinas showed neither a decrease in the thickness of the retinal layers nor an increase in neuronal loss, although signs of early glial reactivity and an upregulation of inducible nitric oxide synthase (iNOS) were detected. Inhibition of iNOS restored both light- and glial-evoked dilations to control levels. These findings suggest that high NO levels resulting from iNOS upregulation alters glial control of vessel diameter and may underlie the loss of functional hyperemia observed in diabetic retinopathy. Restoring functional hyperemia by iNOS inhibition may limit the progression of retinopathy in diabetic patients.
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Affiliation(s)
- Anusha Mishra
- Department of Neuroscience, University of Minnesota, Minneapolis, Minnesota, USA
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476
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Three-dimensional positron emission tomography/computed tomography analysis of 13NO3- uptake and 13N distribution in growing kohlrabi. Anal Chem 2010; 83:578-84. [PMID: 21182306 DOI: 10.1021/ac102510f] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
We report the application of three-dimensional positron emission tomography/computed tomography (PET/CT) for the analysis of (13)NO(3)(-) uptake and (13)N distribution in growing kohlrabi. The analytical procedures, equipment parameters, and image reconstruction mode for plant imaging were tested and selected. (13)N in growing kohlrabi plants was imaged versus time using both PET movies and PET/CT tomograms. The (13)NO(3)(-) transport velocity in kohlrabi from root to petiole was estimated to be 1.0 cm/min. The appearance of shell-shaped (13)NO(3)(-) transport pathways, corresponding to the kohlrabi corm, suggests the existence of special routes with higher efficiency for (13)NO(3)(-) transport, which tends to have the shortest distances to the leaves or buds. Standardized uptake values (SUVs), used as the representative figures for describing (13)N distribution, were quantified versus time at some putative sites of interest. For multiple analysis of the same-plant, (13)N distribution in kohlrabi under normal conditions, methionine sulfoximine (MSX) stress, and recovery from MSX stress was examined. The (13)N distribution variation studies were also done under the above three growth conditions. Our results suggest a significant downregulation of nitrate uptake in kohlrabi in the presence of MSX.
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477
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Zheng W, Watts LT, Holstein DM, Prajapati SI, Keller C, Grass EH, Walter CA, Lechleiter JD. Purinergic receptor stimulation reduces cytotoxic edema and brain infarcts in mouse induced by photothrombosis by energizing glial mitochondria. PLoS One 2010; 5:e14401. [PMID: 21203502 PMCID: PMC3008710 DOI: 10.1371/journal.pone.0014401] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2010] [Accepted: 11/15/2010] [Indexed: 11/18/2022] Open
Abstract
Treatments to improve the neurological outcome of edema and cerebral ischemic stroke are severely limited. Here, we present the first in vivo single cell images of cortical mouse astrocytes documenting the impact of single vessel photothrombosis on cytotoxic edema and cerebral infarcts. The volume of astrocytes expressing green fluorescent protein (GFP) increased by over 600% within 3 hours of ischemia. The subsequent growth of cerebral infarcts was easily followed as the loss of GFP fluorescence as astrocytes lysed. Cytotoxic edema and the magnitude of ischemic lesions were significantly reduced by treatment with the purinergic ligand 2-methylthioladenosine 5' diphosphate (2-MeSADP), an agonist with high specificity for the purinergic receptor type 1 isoform (P2Y(1)R). At 24 hours, cytotoxic edema in astrocytes was still apparent at the penumbra and preceded the cell lysis that defined the infarct. Delayed 2MeSADP treatment, 24 hours after the initial thrombosis, also significantly reduced cytotoxic edema and the continued growth of the brain infarction. Pharmacological and genetic evidence are presented indicating that 2MeSADP protection is mediated by enhanced astrocyte mitochondrial metabolism via increased inositol trisphosphate (IP(3))-dependent Ca(2+) release. We suggest that mitochondria play a critical role in astrocyte energy metabolism in the penumbra of ischemic lesions, where low ATP levels are widely accepted to be responsible for cytotoxic edema. Enhancement of this energy source could have similar protective benefits for a wide range of brain injuries.
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Affiliation(s)
- Wei Zheng
- Department of Cellular and Structural Biology, University of Texas Health Science Center at San Antonio, San Antonio, Texas, United States of America
| | - Lora Talley Watts
- Department of Cellular and Structural Biology, University of Texas Health Science Center at San Antonio, San Antonio, Texas, United States of America
| | - Deborah M. Holstein
- Department of Cellular and Structural Biology, University of Texas Health Science Center at San Antonio, San Antonio, Texas, United States of America
| | - Suresh I. Prajapati
- Greenhey Children's Cancer Research Institute, University of Texas Health Science Center at San Antonio, San Antonio, Texas, United States of America
| | - Charles Keller
- Department of Cellular and Structural Biology, University of Texas Health Science Center at San Antonio, San Antonio, Texas, United States of America
- Greenhey Children's Cancer Research Institute, University of Texas Health Science Center at San Antonio, San Antonio, Texas, United States of America
| | - Eileen H. Grass
- Department of Cellular and Structural Biology, University of Texas Health Science Center at San Antonio, San Antonio, Texas, United States of America
| | - Christi A. Walter
- Department of Cellular and Structural Biology, University of Texas Health Science Center at San Antonio, San Antonio, Texas, United States of America
| | - James D. Lechleiter
- Department of Cellular and Structural Biology, University of Texas Health Science Center at San Antonio, San Antonio, Texas, United States of America
- * E-mail:
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478
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Figueiredo M, Lane S, Tang F, Liu BH, Hewinson J, Marina N, Kasymov V, Souslova EA, Chudakov DM, Gourine AV, Teschemacher AG, Kasparov S. Optogenetic experimentation on astrocytes. Exp Physiol 2010; 96:40-50. [PMID: 21041318 DOI: 10.1113/expphysiol.2010.052597] [Citation(s) in RCA: 67] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Affiliation(s)
- M Figueiredo
- School of Physiology and Pharmacology, School of Medical Sciences, University of Bristol, Bristol BS8 1TD, UK
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479
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Abstract
Glutamate is the major excitatory neurotransmitter in the central nervous system. Although glutamate mediates synaptically confined point-to-point transmission, it has been suggested that under certain conditions glutamate may escape from the synaptic cleft (glutamate spillover), accumulate in the extrasynaptic space, and mediate volume transmission to regulate important brain functions. However, the inability to directly measure glutamate dynamics around active synapses has limited our understanding of glutamatergic volume transmission. The recent development of a family of fluorescent glutamate indicators has enabled the visualization of extrasynaptic glutamate dynamics in brain tissues. In this topical review, we examine glutamate as a volume transmitter based on novel results of glutamate imaging in the brain.
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Affiliation(s)
- Yohei Okubo
- Department of Pharmacology, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan
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480
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Hahn T, Heinzel S, Plichta MM, Reif A, Lesch KP, Fallgatter AJ. Neurovascular Coupling in the Human Visual Cortex Is Modulated by Cyclooxygenase-1 (COX-1) Gene Variant. Cereb Cortex 2010; 21:1659-66. [DOI: 10.1093/cercor/bhq236] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
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481
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Abd-El-Basset EM, Abd-El-Barr MM. Effect of interleukin-1β on the expression of actin isoforms in cultured mouse astroglia. Anat Rec (Hoboken) 2010; 294:16-23. [PMID: 21157913 DOI: 10.1002/ar.21303] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2008] [Accepted: 09/27/2010] [Indexed: 12/20/2022]
Abstract
Cytokines are soluble mediators that are thought to act as communication signals between astroglia and neighboring neural cells. They are both released by, and act on, astroglia. It is hypothesized that it is this effect on astroglia that may be important in widespread phenomena including traumatic brain injury, inflammation, and scar formation. In this article, we examine the effect of mouse recombinant interleukin-1β (IL-1β) on the morphology, organization, and expression of glial fibrillary acidic protein (GFAP) and actin isoforms in cultured mouse astroglia. This study shows that the majority of the astroglia treated with IL-1β acquire long processes. Immunofluorescence staining shows that there are no remarkable changes in the organization of GFAP, F-actin, α-smooth muscle (α-sm) actin, and β-actin isoforms. In fluorescent microplate assay, the short-term treated astroglia (range, 1-2 days) show an increase in the intensity of GFAP and β-actin isoform over the level observed in untreated control, whereas no remarkable changes are observed in the intensity of α-sm actin isoform. In the case of long-term treatment (range, 4-8 days), the intensity of GFAP and α-sm actin isoform progressively decreases below the level of untreated control. In addition, the intensity of β-actin isoform increases above the control level. These results have been confirmed by immunoblotting experiments. The upregulation of β-actin isoform may be important in limiting the noxious effects of an inflammatory reaction. This gives credence to the hypothesis that it might be possible to modulate astroglial effects on neuronal inflammation and scar formation with appropriate therapies.
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Affiliation(s)
- E M Abd-El-Basset
- Department of Anatomy, Faculty of Medicine, Kuwait University, Kuwait.
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482
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Attwell D, Buchan AM, Charpak S, Lauritzen M, Macvicar BA, Newman EA. Glial and neuronal control of brain blood flow. Nature 2010; 468:232-43. [PMID: 21068832 PMCID: PMC3206737 DOI: 10.1038/nature09613] [Citation(s) in RCA: 1665] [Impact Index Per Article: 118.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Blood flow in the brain is regulated by neurons and astrocytes. Knowledge of how these cells control blood flow is crucial for understanding how neural computation is powered, for interpreting functional imaging scans of brains, and for developing treatments for neurological disorders. It is now recognized that neurotransmitter-mediated signalling has a key role in regulating cerebral blood flow, that much of this control is mediated by astrocytes, that oxygen modulates blood flow regulation, and that blood flow may be controlled by capillaries as well as by arterioles. These conceptual shifts in our understanding of cerebral blood flow control have important implications for the development of new therapeutic approaches.
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Affiliation(s)
- David Attwell
- Department of Neuroscience, Physiology and Pharmacology, University College London, Gower Street, London WC1E 6BT, UK.
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483
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Lee JH, Durand R, Gradinaru V, Zhang F, Goshen I, Kim DS, Fenno LE, Ramakrishnan C, Deisseroth K. Lee et al. reply. Nature 2010. [DOI: 10.1038/nature09533] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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484
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Abstract
We report new results on blood flow modeling over large volumes of cortical gray matter of primate brain. We propose a network method for computing the blood flow, which handles realistic boundary conditions, complex vessel shapes, and complex nonlinear blood rheology. From a detailed comparison of the available models for the blood flow rheology and the phase separation effect, we are able to derive important new results on the impact of network structure on blood pressure, hematocrit, and flow distributions. Our findings show that the network geometry (vessel shapes and diameters), the boundary conditions associated with the arterial inputs and venous outputs, and the effective viscosity of the blood are essential components in the flow distribution. In contrast, we show that the phase separation effect has a minor function in the global microvascular hemodynamic behavior. The behavior of the pressure, hematocrit, and blood flow distributions within the network are described through the depth of the primate cerebral cortex and are discussed.
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485
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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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486
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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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487
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Bittner CX, Loaiza A, Ruminot I, Larenas V, Sotelo-Hitschfeld T, Gutiérrez R, Córdova A, Valdebenito R, Frommer WB, Barros LF. High resolution measurement of the glycolytic rate. FRONTIERS IN NEUROENERGETICS 2010; 2. [PMID: 20890447 PMCID: PMC2947927 DOI: 10.3389/fnene.2010.00026] [Citation(s) in RCA: 112] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/25/2010] [Accepted: 07/20/2010] [Indexed: 01/01/2023]
Abstract
The glycolytic rate is sensitive to physiological activity, hormones, stress, aging, and malignant transformation. Standard techniques to measure the glycolytic rate are based on radioactive isotopes, are not able to resolve single cells and have poor temporal resolution, limitations that hamper the study of energy metabolism in the brain and other organs. A new method is described in this article, which makes use of a recently developed FRET glucose nanosensor to measure the rate of glycolysis in single cells with high temporal resolution. Used in cultured astrocytes, the method showed for the first time that glycolysis can be activated within seconds by a combination of glutamate and K+, supporting a role for astrocytes in neurometabolic and neurovascular coupling in the brain. It was also possible to make a direct comparison of metabolism in neurons and astrocytes lying in close proximity, paving the way to a high-resolution characterization of brain energy metabolism. Single-cell glycolytic rates were also measured in fibroblasts, adipocytes, myoblasts, and tumor cells, showing higher rates for undifferentiated cells and significant metabolic heterogeneity within cell types. This method should facilitate the investigation of tissue metabolism at the single-cell level and is readily adaptable for high-throughput analysis.
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488
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Targeting S100B in Cerebral Ischemia and in Alzheimer's Disease. Cardiovasc Psychiatry Neurol 2010; 2010. [PMID: 20862385 PMCID: PMC2939387 DOI: 10.1155/2010/687067] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/31/2010] [Revised: 06/25/2010] [Accepted: 07/20/2010] [Indexed: 11/18/2022] Open
Abstract
S100B is an EF-hand calcium-binding protein that exerts both intracellular and extracellular effects on a variety of cellular processes. The protein is predominantly expressed in the central nervous system by astrocytes, both physiologically and during the course of neurological disease. In the healthy adult brain and during development, constitutive S100B expression acts as a trophic factor to drive neurite extension and to referee neuroplasticity. Yet, when induced during central nervous system disease, the protein can take on maladaptive roles and thereby exacerbate brain pathology. Based on genetic and pharmacological lines of evidence, we consider such deleterious roles of S100B in two common brain pathologies: ischemic stroke and Alzheimer's disease (AD). In rodent models of ischemic brain damage, S100B is induced early on during the subacute phase, where it exacerbates gliosis and delayed infarct expansion and thereby worsens functional recovery. In mouse models of AD, S100B drives brain inflammation and gliosis that accelerate cerebral amyloidosis. Pharmacological inhibition of S100B synthesis mitigates hallmark pathologies of both brain diseases, opening the door for translational approaches to treat these devastating neurological disorders.
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489
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Astrocytic gap junctional communication is reduced in amyloid-β-treated cultured astrocytes, but not in Alzheimer's disease transgenic mice. ASN Neuro 2010; 2:e00041. [PMID: 20730033 PMCID: PMC2922840 DOI: 10.1042/an20100017] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2010] [Revised: 07/22/2010] [Accepted: 07/23/2010] [Indexed: 12/21/2022] Open
Abstract
Alzheimer's disease is characterized by accumulation of amyloid deposits in brain, progressive cognitive deficits and reduced glucose utilization. Many consequences of the disease are attributed to neuronal dysfunction, but roles of astrocytes in its pathogenesis are not well understood. Astrocytes are extensively coupled via gap junctions, and abnormal trafficking of metabolites and signalling molecules within astrocytic syncytia could alter functional interactions among cells comprising the neurovascular unit. To evaluate the influence of amyloid-beta on astrocyte gap junctional communication, cultured astrocytes were treated with monomerized amyloid-β(1-40) (1 μmol/l) for intervals ranging from 2 h to 5 days, and the areas labelled by test compounds were determined by impaling a single astrocyte with a micropipette and diffusion of material into coupled cells. Amyloid-β-treated astrocytes had rapid, sustained 50-70% reductions in the area labelled by Lucifer Yellow, anionic Alexa Fluor® dyes and energy-related compounds, 6-NBDG (a fluorescent glucose analogue), NADH and NADPH. Amyloid-β treatment also caused a transient increase in oxidative stress. In striking contrast with these results, spreading of Lucifer Yellow within astrocytic networks in brain slices from three regions of 8.5-14-month-old control and transgenic Alzheimer's model mice was variable, labelling 10-2000 cells; there were no statistically significant differences in the number of dye-labelled cells among the groups or with age. Thus amyloid-induced dysfunction of gap junctional communication in cultured astrocytes does not reflect the maintenance of dye transfer through astrocytic syncytial networks in transgenic mice; the pathophysiology of Alzheimer's disease is not appropriately represented by the cell culture system.
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Key Words
- 6-NBDG, 6-[N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino]-6-deoxyglucose
- A350, Alexa Fluor® 350
- A568, Alexa Fluor® 568
- APP, amyloid-β precursor protein
- Cx, connexin
- DCF, dichlorofluorescein
- DMEM, Dulbecco's modified Eagle's medium
- FBS, fetal bovine serum
- GFAP, glial fibrillary acidic protein
- H2DCF-DA, carboxydihydrodichlorofluorescein diacetate
- L-LME, L-leucine methyl ester hydrochloride
- ROS, reactive oxygen species
- SR101, sulforhodamine 101
- STZ, streptozotocin
- aCSF, artificial cerebral spinal fluid
- amyloid protein
- astrocyte
- connexin
- dBcAMP, dibutyryl cAMP
- dye transfer
- gap junction
- metabolite trafficking
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490
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Filosa JA. Vascular tone and neurovascular coupling: considerations toward an improved in vitro model. FRONTIERS IN NEUROENERGETICS 2010; 2:16. [PMID: 20802803 PMCID: PMC2928708 DOI: 10.3389/fnene.2010.00016] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/01/2010] [Accepted: 06/28/2010] [Indexed: 11/13/2022]
Abstract
Neurovascular research has made significant strides toward understanding how the brain neurovascular unit accomplishes rapid and spatial increases in blood flow following neuronal activation. Among the experimental models used, the in vitro brain slice preparation provides unique information revealing the potential signals and cellular mechanisms involved in functional hyperemia. The most crucial limitation of this model, however, is the lack of intraluminal pressure and flow in the vessels being studied. Moreover, differences in basal vascular tone have led to varied interpretations regarding the polarity of vascular responses following neuron-to-glial stimulation. Given the complexity of astrocyte-induced neurovascular responses, we propose the use of a modified in vitro brain slice preparation, where intraluminal arteriolar pressure and flow are retained. Throughout this review, we discuss the advantages and disadvantages to be considered when using brain slices for neurovascular studies. Potential ways to overcome the current limitations are proposed.
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Affiliation(s)
- Jessica A. Filosa
- Department of Physiology, Medical College of GeorgiaAugusta, GA, USA
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491
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Carp SA, Dai GP, Boas DA, Franceschini MA, Kim YR. Validation of diffuse correlation spectroscopy measurements of rodent cerebral blood flow with simultaneous arterial spin labeling MRI; towards MRI-optical continuous cerebral metabolic monitoring. BIOMEDICAL OPTICS EXPRESS 2010; 1:553-565. [PMID: 21258489 PMCID: PMC3017992 DOI: 10.1364/boe.1.000553] [Citation(s) in RCA: 86] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/01/2010] [Revised: 07/13/2010] [Accepted: 07/13/2010] [Indexed: 05/18/2023]
Abstract
Cerebral blood flow (CBF) during stepped hypercapnia was measured simultaneously in the rat brain using near-infrared diffuse correlation spectroscopy (DCS) and arterial spin labeling MRI (ASL). DCS and ASL CBF values agree very well, with high correlation (R=0.86, p< 10(-9)), even when physiological instability perturbed the vascular response. A partial volume effect was evident in the smaller magnitude of the optical CBF response compared to the MRI values (averaged over the cortical area), primarily due to the inclusion of white matter in the optically sampled volume. The 8.2 and 11.7 mm mid-separation channels of the multi-distance optical probe had the lowest partial volume impact, reflecting ~75 % of the MR signal change. Using a multiplicative correction factor, the ASL CBF could be predicted with no more than 10% relative error, affording an opportunity for real-time relative cerebral metabolism monitoring in conjunction with MR measurement of cerebral blood volume using super paramagnetic contrast agents.
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Affiliation(s)
- S. A. Carp
- Athinoula A. Martinos Center for Biomedical Imaging,
Massachusetts General Hospital, Harvard Medical School, Charlestown, MA, 02129,
USA
| | - G. P. Dai
- Athinoula A. Martinos Center for Biomedical Imaging,
Massachusetts General Hospital, Harvard Medical School, Charlestown, MA, 02129,
USA
| | - D. A. Boas
- Athinoula A. Martinos Center for Biomedical Imaging,
Massachusetts General Hospital, Harvard Medical School, Charlestown, MA, 02129,
USA
| | - M. A. Franceschini
- Athinoula A. Martinos Center for Biomedical Imaging,
Massachusetts General Hospital, Harvard Medical School, Charlestown, MA, 02129,
USA
| | - Y. R. Kim
- Athinoula A. Martinos Center for Biomedical Imaging,
Massachusetts General Hospital, Harvard Medical School, Charlestown, MA, 02129,
USA
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492
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Ectopic vesicular neurotransmitter release along sensory axons mediates neurovascular coupling via glial calcium signaling. Proc Natl Acad Sci U S A 2010; 107:15258-63. [PMID: 20696909 DOI: 10.1073/pnas.1003501107] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
Neurotransmitter release generally is considered to occur at active zones of synapses, and ectopic release of neurotransmitters has been demonstrated in a few instances. However, the mechanism of ectopic neurotransmitter release is poorly understood. We took advantage of the intimate morphological and functional proximity of olfactory receptor axons and specialized glial cells, olfactory ensheathing cells (OECs), to study ectopic neurotransmitter release. Axonal stimulation evoked purinergic and glutamatergic Ca(2+) responses in OECs, indicating ATP and glutamate release. In axons expressing synapto-pHluorin, stimulation evoked an increase in synapto-pHluorin fluorescence, indicative of vesicle fusion. Transmitter release was dependent on Ca(2+) and could be inhibited by bafilomycin A1 and botulinum toxin A. Ca(2+) transients in OECs evoked by ATP, axonal stimulation, and laser photolysis of NP-EGTA resulted in constriction of adjacent blood vessels. Our results indicate that ATP and glutamate are released ectopically by vesicles along axons and mediate neurovascular coupling via glial Ca(2+) signaling.
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493
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Sakadzić S, Roussakis E, Yaseen MA, Mandeville ET, Srinivasan VJ, Arai K, Ruvinskaya S, Devor A, Lo EH, Vinogradov SA, Boas DA. Two-photon high-resolution measurement of partial pressure of oxygen in cerebral vasculature and tissue. Nat Methods 2010; 7:755-9. [PMID: 20693997 PMCID: PMC2932799 DOI: 10.1038/nmeth.1490] [Citation(s) in RCA: 302] [Impact Index Per Article: 21.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2009] [Accepted: 07/06/2010] [Indexed: 12/14/2022]
Abstract
The ability to measure oxygen partial pressure (pO2) with high temporal and spatial resolution in three dimensions is crucial for understanding oxygen delivery and consumption in normal and diseased brain. Among existing pO2 measurement methods, phosphorescence quenching is optimally suited for the task. However, previous attempts to couple phosphorescence with two-photon laser scanning microscopy have faced substantial difficulties because of extremely low two-photon absorption cross-sections of conventional phosphorescent probes. Here, we report the first practical in vivo two-photon high-resolution pO2 measurements in small rodents’ cortical microvasculature and tissue, made possible by combining an optimized imaging system with a two-photon-enhanced phosphorescent nanoprobe. The method features a measurement depth of up to 250 µm, sub-second temporal resolution and requires low probe concentration. Most importantly, the properties of the probe allowed for the first direct high-resolution measurement of cortical extravascular (tissue) pO2, opening numerous possibilities for functional metabolic brain studies.
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Affiliation(s)
- Sava Sakadzić
- Photon Migration Imaging Laboratory, Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital and Harvard Medical School, Charlestown, MA, USA
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494
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495
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Gourine AV, Kasymov V, Marina N, Tang F, Figueiredo MF, Lane S, Teschemacher AG, Spyer KM, Deisseroth K, Kasparov S. Astrocytes control breathing through pH-dependent release of ATP. Science 2010; 329:571-5. [PMID: 20647426 PMCID: PMC3160742 DOI: 10.1126/science.1190721] [Citation(s) in RCA: 651] [Impact Index Per Article: 46.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Astrocytes provide structural and metabolic support for neuronal networks, but direct evidence demonstrating their active role in complex behaviors is limited. Central respiratory chemosensitivity is an essential mechanism that, via regulation of breathing, maintains constant levels of blood and brain pH and partial pressure of CO2. We found that astrocytes of the brainstem chemoreceptor areas are highly chemosensitive. They responded to physiological decreases in pH with vigorous elevations in intracellular Ca2+ and release of adenosine triphosphate (ATP). ATP propagated astrocytic Ca2+ excitation, activated chemoreceptor neurons, and induced adaptive increases in breathing. Mimicking pH-evoked Ca2+ responses by means of optogenetic stimulation of astrocytes expressing channelrhodopsin-2 activated chemoreceptor neurons via an ATP-dependent mechanism and triggered robust respiratory responses in vivo. This demonstrates a potentially crucial role for brain glial cells in mediating a fundamental physiological reflex.
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Affiliation(s)
- Alexander V Gourine
- Neuroscience, Physiology, and Pharmacology, University College London, London WC1E 6BT, UK.
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496
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Chung YC, Ko HW, Bok E, Park ES, Huh SH, Nam JH, Jin BK. The role of neuroinflammation on the pathogenesis of Parkinson's disease. BMB Rep 2010; 43:225-32. [PMID: 20423606 DOI: 10.5483/bmbrep.2010.43.4.225] [Citation(s) in RCA: 115] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Parkinson's Disease (PD) is a common neurodegenerative disease characterized by the progressive degeneration of nigrostriatal dopaminergic (DA) neurons. Although the causative factors of PD remain elusive, many studies on PD animal models or humans suggest that glial activation along with neuroinflammatory processes contribute to the initiation or progression of PD. Additionally, several groups have proposed that dysfunction of the blood-brain barrier (BBB) combined with infiltration of peripheral immune cells play important roles in the degeneration of DA neurons. However, these neuroinflammatory events have only been investigated separately, and the issue of whether these phenomena are neuroprotective or neurotoxic remains controversial. We here review the current knowledge regarding the functions of these neuroinflammatory processes in the brain. Finally, we describe therapeutic strategies for the regulation of neuroinflammation with the goal of improving the symptoms of PD.
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Affiliation(s)
- Young Cheul Chung
- Department of Biochemistry & Molecular Biology, Neurodegeneration Control Research Center, School of Medicine Kyung Hee University, Seoul, Korea
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497
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Klawitter J, Gottschalk S, Hainz C, Leibfritz D, Christians U, Serkova NJ. Immunosuppressant neurotoxicity in rat brain models: oxidative stress and cellular metabolism. Chem Res Toxicol 2010; 23:608-19. [PMID: 20148532 DOI: 10.1021/tx900351q] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Coadministration of the calcineurin inhibitor cyclosporine (CsA) and the mTOR inhibitors sirolimus (SRL) or everolimus (RAD) increases the efficacy of immunosuppression after organ transplantation. Neurotoxicity of CsA is a major clinical problem. Our goal was to assess the effects of CsA, SRL, and RAD on brain cell metabolism. The studies included the comparison of immunosuppressant-mediated effects on glucose metabolism, energy production, and reactive oxygen species (ROS) formation in perfused rat brain slices, primary rat astrocytes, and C6 glioma cells. In brain slices and astrocytes, CsA inhibited Krebs cycle metabolism, while activating anaerobic glycolysis, most likely to compensate for the inhibition of mitochondrial energy production. SRL and RAD inhibited cytosolic glycolysis but did not cause changes in mitochondrial energy production. CsA + SRL inhibited Krebs cycle and glycolysis, thus reducing the ability of the cell to compensate for the negative effects of CsA on mitochondrial nucleoside triphosphate synthesis. In contrast to SRL at the concentrations tested, RAD reduced the CsA-induced ROS formation and antagonized CsA-induced effects on glucose and energy metabolism. Surprisingly, in C6 cells, SRL and RAD exposure resulted in high ROS concentrations without significant impairment of cell metabolism. Our results suggested that SRL enhances CsA-induced ROS formation and negative metabolic effects in brain cells, while RAD seems to antagonize the CsA effects. However, the three models showed different metabolic responses when challenged with the study drugs. In contrast to SRL, RAD enhances ROS formation in C6 glioma cells but has only minor effects on normal rat brain tissue.
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Affiliation(s)
- Jelena Klawitter
- Clinical Research & Development, Department of Anesthesiology, and University of Colorado Cancer Center, University of Colorado Denver, Aurora, Colorado 80045, USA.
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498
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Cauli B, Hamel E. Revisiting the role of neurons in neurovascular coupling. FRONTIERS IN NEUROENERGETICS 2010; 2:9. [PMID: 20616884 PMCID: PMC2899521 DOI: 10.3389/fnene.2010.00009] [Citation(s) in RCA: 178] [Impact Index Per Article: 12.7] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/18/2010] [Accepted: 05/26/2010] [Indexed: 11/13/2022]
Abstract
In this article, we will review molecular, anatomical, physiological and pharmacological data in an attempt to better understand how excitatory and inhibitory neurons recruited by distinct afferent inputs to the cerebral cortex contribute to the coupled hemodynamic response, and how astrocytes can act as intermediaries to these neuronal populations. We aim at providing the pros and cons to the following statements that, depending on the nature of the afferent input to the neocortex, (i) different neuronal or astroglial messengers, likely acting in sequence, mediate the hemodynamic changes, (ii) some recruited neurons release messengers that directly alter blood vessel tone, (iii) others act by modulating neuronal and astroglial activity, and (iv) astrocytes act as intermediaries for both excitatory and inhibitory neurotransmitters. We will stress that a given afferent signal activates a precise neuronal circuitry that determines the mediators of the hemodynamic response as well as the level of interaction with surrounding astrocytes.
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Affiliation(s)
- Bruno Cauli
- Laboratoire de Neurobiologie des Processus Adaptatifs, Université Pierre et Marie Curie Paris, France
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499
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Dale N, Frenguelli BG. Release of adenosine and ATP during ischemia and epilepsy. Curr Neuropharmacol 2010; 7:160-79. [PMID: 20190959 PMCID: PMC2769001 DOI: 10.2174/157015909789152146] [Citation(s) in RCA: 173] [Impact Index Per Article: 12.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2009] [Revised: 04/15/2009] [Accepted: 05/01/2009] [Indexed: 12/17/2022] Open
Abstract
Eighty years ago Drury & Szent-Györgyi described the actions of adenosine, AMP (adenylic acid) and ATP (pyrophosphoric or diphosphoric ester of adenylic acid) on the mammalian cardiovascular system, skeletal muscle, intestinal and urinary systems. Since then considerable insight has been gleaned on the means by which these compounds act, not least of which in the distinction between the two broad classes of their respective receptors, with their many subtypes, and the ensuing diversity in cellular consequences their activation invokes. These myriad actions are of course predicated on the release of the purines into the extracellular milieu, but, surprisingly, there is still considerable ambiguity as to how this occurs in various physiological and pathophysiological conditions. In this review we summarise the release of ATP and adenosine during seizures and cerebral ischemia and discuss mechanisms by which the purines adenosine and ATP may be released from cells in the CNS under these conditions.
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Affiliation(s)
- Nicholas Dale
- Department of Biological Sciences, University of Warwick, Coventry, CV4 7AL, UK
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500
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Vaarmann A, Gandhi S, Abramov AY. Dopamine induces Ca2+ signaling in astrocytes through reactive oxygen species generated by monoamine oxidase. J Biol Chem 2010; 285:25018-23. [PMID: 20547771 DOI: 10.1074/jbc.m110.111450] [Citation(s) in RCA: 92] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Dopamine is a neurotransmitter that plays a major role in a variety of brain functions, as well as in disorders such as Parkinson disease and schizophrenia. In cultured astrocytes, we have found that dopamine induces sporadic cytoplasmic calcium ([Ca(2+)](c)) signals. Importantly, we show that the dopamine-induced calcium signaling is receptor-independent in midbrain, cortical, and hippocampal astrocytes. We demonstrate that the calcium signal is initiated by the metabolism of dopamine by monoamine oxidase, which produces reactive oxygen species and induces lipid peroxidation. This stimulates the activation of phospholipase C and subsequent release of calcium from the endoplasmic reticulum via the inositol 1,4,5-trisphosphate receptor mechanism. These findings have major implications on the function of astrocytes that are exposed to dopamine and may contribute to understanding the physiological role of dopamine.
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Affiliation(s)
- Annika Vaarmann
- Department of Molecular Neuroscience, UCL Institute of Neurology, Queen Square, London WC1N 3BG, United Kingdom
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