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      Exposure to Blast Overpressure Impairs Cerebral Microvascular Responses and Alters Vascular and Astrocytic Structure

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          Abstract

          Exposure to blast overpressure may result in cerebrovascular impairment, including cerebral vasospasm. The mechanisms contributing to this vascular response are unclear. The aim of this study was to evaluate the relationship between blast and functional alterations of the cerebral microcirculation and to investigate potential underlying changes in vascular microstructure. Cerebrovascular responses were assessed in sham- and blast-exposed male rats at multiple time points from 2 h through 28 days after a single 130-kPa (18.9-psi) exposure. Pial microcirculation was assessed through a cranial window created in the parietal bone of anesthetized rats. Pial arteriolar reactivity was evaluated in vivo using hypercapnia, barium chloride, and serotonin. We found that exposure to blast leads to impairment of arteriolar reactivity >24 h after blast exposure, suggesting delayed injury mechanisms that are not simply attributed to direct mechanical deformation. Observed vascular impairment included a reduction in hypercapnia-induced vasodilation, increase in barium-induced constriction, and reversal of the serotonin effect from constriction to dilation. A reduction in vascular smooth muscle contractile proteins consistent with vascular wall proliferation was observed, as well as delayed reduction in nitric oxide synthase and increase in endothelin-1 B receptors, mainly in astrocytes. Collectively, the data show that exposure to blast results in delayed and prolonged alterations in cerebrovascular reactivity that are associated with changes in the microarchitecture of the vessel wall and astrocytes. These changes may contribute to long-term pathologies involving dysfunction of the neurovascular unit, including cerebral vasospasm.

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          Most cited references94

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          Pathophysiology of Migraine: A Disorder of Sensory Processing.

          Plaguing humans for more than two millennia, manifest on every continent studied, and with more than one billion patients having an attack in any year, migraine stands as the sixth most common cause of disability on the planet. The pathophysiology of migraine has emerged from a historical consideration of the "humors" through mid-20th century distraction of the now defunct Vascular Theory to a clear place as a neurological disorder. It could be said there are three questions: why, how, and when? Why: migraine is largely accepted to be an inherited tendency for the brain to lose control of its inputs. How: the now classical trigeminal durovascular afferent pathway has been explored in laboratory and clinic; interrogated with immunohistochemistry to functional brain imaging to offer a roadmap of the attack. When: migraine attacks emerge due to a disorder of brain sensory processing that itself likely cycles, influenced by genetics and the environment. In the first, premonitory, phase that precedes headache, brain stem and diencephalic systems modulating afferent signals, light-photophobia or sound-phonophobia, begin to dysfunction and eventually to evolve to the pain phase and with time the resolution or postdromal phase. Understanding the biology of migraine through careful bench-based research has led to major classes of therapeutics being identified: triptans, serotonin 5-HT1B/1D receptor agonists; gepants, calcitonin gene-related peptide (CGRP) receptor antagonists; ditans, 5-HT1F receptor agonists, CGRP mechanisms monoclonal antibodies; and glurants, mGlu5 modulators; with the promise of more to come. Investment in understanding migraine has been very successful and leaves us at a new dawn, able to transform its impact on a global scale, as well as understand fundamental aspects of human biology.
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            Glial regulation of the cerebral microvasculature.

            The brain is a heterogeneous organ with regionally varied and constantly changing energetic needs. Blood vessels in the brain are equipped with control mechanisms that match oxygen and glucose delivery through blood flow with the local metabolic demands that are imposed by neural activity. However, the cellular bases of this mechanism have remained elusive. A major advance has been the demonstration that astrocytes, cells with extensive contacts with both synapses and cerebral blood vessels, participate in the increases in flow evoked by synaptic activity. Their organization in nonoverlapping spatial domains indicates that they are uniquely positioned to shape the spatial distribution of the vascular responses that are evoked by neural activity. Astrocytic calcium is an important determinant of microvascular function and may regulate flow independently of synaptic activity. The involvement of astrocytes in neurovascular coupling has broad implications for the interpretation of functional imaging signals and for the understanding of brain diseases that are associated with neurovascular dysfunction.
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              Nitric oxide-generating vasodilators and 8-bromo-cyclic guanosine monophosphate inhibit mitogenesis and proliferation of cultured rat vascular smooth muscle cells.

              Endothelium-derived relaxing factor has been recently identified as nitric oxide. The purpose of this study was to determine if vasodilator drugs that generate nitric oxide inhibit vascular smooth muscle mitogenesis and proliferation in culture. Three chemically dissimilar vasodilators, sodium nitroprusside, S-nitroso-N-acetylpenicillamine and isosorbide dinitrate, dose-dependently inhibited serum-induced thymidine incorporation by rat aortic smooth muscle cells. Moreover, 8-bromo-cGMP mimicked the antimitogenic effect of the nitric oxide-generating drugs. The antimitogenic effect of S-nitroso-N-acetylpenicillamine was inhibited by hemoglobin and potentiated by superoxide dismutase, supporting the view that nitric oxide was the ultimate effector. Sodium nitroprusside and S-nitroso-N-acetylpenicillamine significantly decreased the proliferation of vascular smooth muscle cells. Moreover, the inhibition of mitogenesis and proliferation was shown to be independent of cell damage, as documented by several criteria of cell viability. These results suggest that endogenous nitric oxide may function as a modulator of vascular smooth muscle cell mitogenesis and proliferation, by a cGMP-mediated mechanism.
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                Author and article information

                Journal
                J Neurotrauma
                J. Neurotrauma
                neu
                Journal of Neurotrauma
                Mary Ann Liebert, Inc., publishers (140 Huguenot Street, 3rd FloorNew Rochelle, NY 10801USA )
                0897-7151
                1557-9042
                15 November 2019
                23 October 2019
                23 October 2019
                : 36
                : 22
                : 3138-3157
                Affiliations
                [ 1 ]Neurotrauma Department, Naval Medical Research Center, Silver Spring, Maryland.
                [ 2 ]Neurosurgery Department, Walter Reed National Military Medical Center, Bethesda, Maryland.
                [ 3 ]Department of Radiology and Medical Imaging, University of Virginia Medical Center, Charlottesville, Virginia.
                [ 4 ]The Henry M. Jackson Foundation for the Advancement of Military Medicine Inc., Bethesda, Maryland.
                [ 5 ]Department of Surgery, Uniformed Services University of the Health Sciences, Bethesda, Maryland.
                Author notes
                [*]Address correspondence to: Rania Abutarboush, PhD, Naval Medical Research Center, 503 Robert Grant Avenue, Silver Spring, MD 20910 rania.abutarboush.ctr@ 123456mail.mil
                Article
                10.1089/neu.2019.6423
                10.1089/neu.2019.6423
                6818492
                31210096
                c5f2c7b7-c43e-471c-a800-4df1c2f41a46
                © Rania Abutarboush et al., 2019; Published by Mary Ann Liebert, Inc.

                This Open Access article is distributed under the terms of the Creative Commons Attribution Noncommercial License ( http://creativecommons.org/licenses/by-nc/4.0/) which permits any noncommercial use, distribution, and reproduction in any medium, provided the original author(s) and the source are credited.

                History
                Page count
                Figures: 12, Tables: 1, References: 100, Pages: 20
                Categories
                Original Articles

                blast overpressure,cerebrovascular reactivity,in vivo studies,microcirculation,vascular injury

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