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Zoccal DB, Vieira BN, Mendes LR, Evangelista AB, Leirão IP. Hypoxia sensing in the body: An update on the peripheral and central mechanisms. Exp Physiol 2024; 109:461-469. [PMID: 38031809 PMCID: PMC10988761 DOI: 10.1113/ep091206] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2023] [Accepted: 11/15/2023] [Indexed: 12/01/2023]
Abstract
An adequate supply of O2 is essential for the maintenance of cellular activity. Systemic or local hypoxia can be experienced during decreased O2 availability or associated with diseases, or a combination of both. Exposure to hypoxia triggers adjustments in multiple physiological systems in the body to generate appropriate homeostatic responses. However, with significant reductions in the arterial partial pressure of O2, hypoxia can be life-threatening and cause maladaptive changes or cell damage and death. To mitigate the impact of limited O2 availability on cellular activity, O2 chemoreceptors rapidly detect and respond to reductions in the arterial partial pressure of O2, triggering orchestrated responses of increased ventilation and cardiac output, blood flow redistribution and metabolic adjustments. In mammals, the peripheral chemoreceptors of the carotid body are considered to be the main hypoxic sensors and the primary source of excitatory feedback driving respiratory, cardiovascular and autonomic responses. However, current evidence indicates that the CNS contains specialized brainstem and spinal cord regions that can also sense hypoxia and stimulate brain networks independently of the carotid body inputs. In this manuscript, we review the discoveries about the functioning of the O2 chemoreceptors and their contribution to the monitoring of O2 levels in the blood and brain parenchyma and mounting cardiorespiratory responses to maintain O2 homeostasis. We also discuss the implications of the chemoreflex-related mechanisms in paediatric and adult pathologies.
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Affiliation(s)
- Daniel B. Zoccal
- Department of Physiology and Pathology, School of Dentistry of AraraquaraSão Paulo State University (UNESP)AraraquaraSão PauloBrazil
| | - Beatriz N. Vieira
- Department of Physiology and Pathology, School of Dentistry of AraraquaraSão Paulo State University (UNESP)AraraquaraSão PauloBrazil
| | - Letícia R. Mendes
- Department of Physiology and Pathology, School of Dentistry of AraraquaraSão Paulo State University (UNESP)AraraquaraSão PauloBrazil
| | - Andressa B. Evangelista
- Department of Physiology and Pathology, School of Dentistry of AraraquaraSão Paulo State University (UNESP)AraraquaraSão PauloBrazil
| | - Isabela P. Leirão
- Department of Physiology and Pathology, School of Dentistry of AraraquaraSão Paulo State University (UNESP)AraraquaraSão PauloBrazil
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2
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Ni R, Straumann N, Fazio S, Dean-Ben XL, Louloudis G, Keller C, Razansky D, Ametamey S, Mu L, Nombela-Arrieta C, Klohs J. Imaging increased metabolism in the spinal cord in mice after middle cerebral artery occlusion. PHOTOACOUSTICS 2023; 32:100532. [PMID: 37645255 PMCID: PMC10461215 DOI: 10.1016/j.pacs.2023.100532] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/12/2022] [Revised: 07/13/2023] [Accepted: 07/13/2023] [Indexed: 08/31/2023]
Abstract
Emerging evidence indicates crosstalk between the brain and hematopoietic system following cerebral ischemia. Here, we investigated metabolism and oxygenation in the spleen and spinal cord in a transient middle cerebral artery occlusion (tMCAO) model. Sham-operated and tMCAO mice underwent [18F]fluorodeoxyglucose (FDG)-positron emission tomography (PET) to assess glucose metabolism. Naïve, sham-operated and tMCAO mice underwent multispectral optoacoustic tomography (MSOT) assisted by quantitative model-based reconstruction and unmixing algorithms for accurate mapping of oxygenation patterns in peripheral tissues at 24 h after reperfusion. We found increased [18F]FDG uptake and reduced MSOT oxygen saturation, indicating hypoxia in the thoracic spinal cord of tMCAO mice compared with sham-operated mice but not in the spleen. Reduced spleen size was observed in tMCAO mice compared with sham-operated mice ex vivo. tMCAO led to an increase in the numbers of mature T cells in femoral bone marrow tissues, concomitant with a stark reduction in these cell subsets in the spleen and peripheral blood. The combination of quantitative PET and MSOT thus enabled observation of hypoxia and increased metabolic activity in the spinal cord of tMCAO mice at 24 h after occlusion compared to sham-operated mice.
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Affiliation(s)
- Ruiqing Ni
- Institute for Regenerative Medicine, University of Zurich, Zurich, Switzerland
- Institute for Biomedical Engineering, Department of Information Technology and Electrical Engineering, University of Zurich & ETH Zurich, Zurich, Switzerland
- Zentrum für Neurowissenschaften Zurich, Zurich, Switzerland
| | - Nadja Straumann
- Institute for Regenerative Medicine, University of Zurich, Zurich, Switzerland
| | - Serana Fazio
- Department of Medical Oncology and Hematology, University and University Hospital Zurich, Zurich, Switzerland
| | - Xose Luis Dean-Ben
- Institute for Biomedical Engineering, Department of Information Technology and Electrical Engineering, University of Zurich & ETH Zurich, Zurich, Switzerland
| | - Georgios Louloudis
- Institute for Biomedical Engineering, Department of Information Technology and Electrical Engineering, University of Zurich & ETH Zurich, Zurich, Switzerland
| | - Claudia Keller
- Center for Radiopharmaceutical Sciences ETH, PSI and USZ, Institute of Pharmaceutical Sciences, Department of Chemistry and Applied Biosciences, ETH Zurich, Zurich, Switzerland
| | - Daniel Razansky
- Institute for Biomedical Engineering, Department of Information Technology and Electrical Engineering, University of Zurich & ETH Zurich, Zurich, Switzerland
- Zentrum für Neurowissenschaften Zurich, Zurich, Switzerland
| | - Simon Ametamey
- Center for Radiopharmaceutical Sciences ETH, PSI and USZ, Institute of Pharmaceutical Sciences, Department of Chemistry and Applied Biosciences, ETH Zurich, Zurich, Switzerland
| | - Linjing Mu
- Center for Radiopharmaceutical Sciences ETH, PSI and USZ, Institute of Pharmaceutical Sciences, Department of Chemistry and Applied Biosciences, ETH Zurich, Zurich, Switzerland
| | - César Nombela-Arrieta
- Department of Medical Oncology and Hematology, University and University Hospital Zurich, Zurich, Switzerland
| | - Jan Klohs
- Institute for Biomedical Engineering, Department of Information Technology and Electrical Engineering, University of Zurich & ETH Zurich, Zurich, Switzerland
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Barioni NO, Derakhshan F, Tenorio Lopes L, Onimaru H, Roy A, McDonald F, Scheibli E, Baghdadwala MI, Heidari N, Bharadia M, Ikeda K, Yazawa I, Okada Y, Harris MB, Dutschmann M, Wilson RJA. Novel oxygen sensing mechanism in the spinal cord involved in cardiorespiratory responses to hypoxia. SCIENCE ADVANCES 2022; 8:eabm1444. [PMID: 35333571 PMCID: PMC8956269 DOI: 10.1126/sciadv.abm1444] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/28/2021] [Accepted: 02/04/2022] [Indexed: 05/05/2023]
Abstract
As blood oxygenation decreases (hypoxemia), mammals mount cardiorespiratory responses, increasing oxygen to vital organs. The carotid bodies are the primary oxygen chemoreceptors for breathing, but sympathetic-mediated cardiovascular responses to hypoxia persist in their absence, suggesting additional high-fidelity oxygen sensors. We show that spinal thoracic sympathetic preganglionic neurons are excited by hypoxia and silenced by hyperoxia, independent of surrounding astrocytes. These spinal oxygen sensors (SOS) enhance sympatho-respiratory activity induced by CNS asphyxia-like stimuli, suggesting they bestow a life-or-death advantage. Our data suggest the SOS use a mechanism involving neuronal nitric oxide synthase 1 (NOS1) and nicotinamide adenine dinucleotide phosphate (NADPH) oxidase (NOX). We propose NOS1 serves as an oxygen-dependent sink for NADPH in hyperoxia. In hypoxia, NADPH catabolism by NOS1 decreases, increasing availability of NADPH to NOX and launching reactive oxygen species-dependent processes, including transient receptor potential channel activation. Equipped with this mechanism, SOS are likely broadly important for physiological regulation in chronic disease, spinal cord injury, and cardiorespiratory crisis.
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Affiliation(s)
- Nicole O. Barioni
- Department of Physiology and Pharmacology, Hotchkiss Brain Institute and Alberta Children’s Hospital Research Institute, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada
| | - Fatemeh Derakhshan
- Department of Physiology and Pharmacology, Hotchkiss Brain Institute and Alberta Children’s Hospital Research Institute, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada
| | - Luana Tenorio Lopes
- Department of Physiology and Pharmacology, Hotchkiss Brain Institute and Alberta Children’s Hospital Research Institute, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada
| | - Hiroshi Onimaru
- Department of Physiology, Showa University School of Medicine, Tokyo, Japan
| | - Arijit Roy
- Department of Physiology and Pharmacology, Hotchkiss Brain Institute and Alberta Children’s Hospital Research Institute, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada
| | - Fiona McDonald
- Department of Physiology and Pharmacology, Hotchkiss Brain Institute and Alberta Children’s Hospital Research Institute, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada
| | - Erika Scheibli
- Department of Physiology and Pharmacology, Hotchkiss Brain Institute and Alberta Children’s Hospital Research Institute, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada
| | - Mufaddal I. Baghdadwala
- Department of Physiology and Pharmacology, Hotchkiss Brain Institute and Alberta Children’s Hospital Research Institute, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada
| | - Negar Heidari
- Department of Physiology and Pharmacology, Hotchkiss Brain Institute and Alberta Children’s Hospital Research Institute, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada
| | - Manisha Bharadia
- Department of Physiology and Pharmacology, Hotchkiss Brain Institute and Alberta Children’s Hospital Research Institute, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada
| | - Keiko Ikeda
- Division of Internal Medicine, Murayama Medical Center, Musashimurayama, Tokyo, Japan
| | - Itaru Yazawa
- Global Research Center for Innovative Life Science, Peptide Drug Innovation, Hoshi University School of Pharmacy and Pharmaceutical Sciences, Tokyo 142-8501, Japan
| | - Yasumasa Okada
- Division of Internal Medicine, Murayama Medical Center, Musashimurayama, Tokyo, Japan
| | - Michael B. Harris
- Department of Biological Sciences, California State University Long Beach, Long Beach, CA 90840, USA
| | - Mathias Dutschmann
- Florey Institute of Neuroscience and Mental Health, University of Melbourne, Melbourne, Victoria, 3052, Australia
| | - Richard J. A. Wilson
- Department of Physiology and Pharmacology, Hotchkiss Brain Institute and Alberta Children’s Hospital Research Institute, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada
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Paton JFR, Machado BH, Moraes DJA, Zoccal DB, Abdala AP, Smith JC, Antunes VR, Murphy D, Dutschmann M, Dhingra RR, McAllen R, Pickering AE, Wilson RJA, Day TA, Barioni NO, Allen AM, Menuet C, Donnelly J, Felippe I, St-John WM. Advancing respiratory-cardiovascular physiology with the working heart-brainstem preparation over 25 years. J Physiol 2022; 600:2049-2075. [PMID: 35294064 PMCID: PMC9322470 DOI: 10.1113/jp281953] [Citation(s) in RCA: 20] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2021] [Accepted: 03/04/2022] [Indexed: 11/24/2022] Open
Abstract
Twenty‐five years ago, a new physiological preparation called the working heart–brainstem preparation (WHBP) was introduced with the claim it would provide a new platform allowing studies not possible before in cardiovascular, neuroendocrine, autonomic and respiratory research. Herein, we review some of the progress made with the WHBP, some advantages and disadvantages along with potential future applications, and provide photographs and technical drawings of all the customised equipment used for the preparation. Using mice or rats, the WHBP is an in situ experimental model that is perfused via an extracorporeal circuit benefitting from unprecedented surgical access, mechanical stability of the brain for whole cell recording and an uncompromised use of pharmacological agents akin to in vitro approaches. The preparation has revealed novel mechanistic insights into, for example, the generation of distinct respiratory rhythms, the neurogenesis of sympathetic activity, coupling between respiration and the heart and circulation, hypothalamic and spinal control mechanisms, and peripheral and central chemoreceptor mechanisms. Insights have been gleaned into diseases such as hypertension, heart failure and sleep apnoea. Findings from the in situ preparation have been ratified in conscious in vivo animals and when tested have translated to humans. We conclude by discussing potential future applications of the WHBP including two‐photon imaging of peripheral and central nervous systems and adoption of pharmacogenetic tools that will improve our understanding of physiological mechanisms and reveal novel mechanisms that may guide new treatment strategies for cardiorespiratory diseases.
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Affiliation(s)
- Julian F R Paton
- Manaaki Manawa - The Centre for Heart Research, Faculty of Medical & Health Science, University of Auckland, Park Road, Grafton, Auckland, 1142, New Zealand
| | - Benedito H Machado
- Department of Physiology, School of Medicine of Ribeirão Preto, University of São Paulo, Ribeirão Preto, São Paulo, Brazil
| | - Davi J A Moraes
- Department of Physiology, School of Medicine of Ribeirão Preto, University of São Paulo, Ribeirão Preto, São Paulo, Brazil
| | - Daniel B Zoccal
- Department of Physiology and Pathology, School of Dentistry of Araraquara, São Paulo State University, Araraquara, São Paulo, Brazil
| | - Ana P Abdala
- School of Physiology, Pharmacology and Neuroscience, Faculty of Biomedical Sciences, University of Bristol, Bristol, England, BS8 1TD, UK
| | - Jeffrey C Smith
- Cellular and Systems Neurobiology Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland, USA
| | - Vagner R Antunes
- Department of Physiology and Biophysics, Institute of Biomedical Sciences, University of São Paulo, São Paulo, Brazil
| | - David Murphy
- Molecular Neuroendocrinology Research Group, Bristol Medical School: Translational Health Sciences, University of Bristol, Bristol, UK
| | - Mathias Dutschmann
- Florey institute of Neuroscience and Mental Health, University of Melbourne, 30, Royal Parade, Parkville, Victoria, 3052, Australia
| | - Rishi R Dhingra
- Florey institute of Neuroscience and Mental Health, University of Melbourne, 30, Royal Parade, Parkville, Victoria, 3052, Australia
| | - Robin McAllen
- Florey institute of Neuroscience and Mental Health, University of Melbourne, 30, Royal Parade, Parkville, Victoria, 3052, Australia
| | - Anthony E Pickering
- School of Physiology, Pharmacology and Neuroscience, Faculty of Biomedical Sciences, University of Bristol, Bristol, England, BS8 1TD, UK
| | - Richard J A Wilson
- Department of Physiology and Pharmacology, Hotchkiss Brain Institute and Alberta Children's Hospital Research Institute, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada
| | - Trevor A Day
- Department of Physiology and Pharmacology, Hotchkiss Brain Institute and Alberta Children's Hospital Research Institute, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada.,Department of Biology, Faculty of Science and Technology, Mount Royal University, Calgary, Alberta, Canada
| | - Nicole O Barioni
- Department of Physiology and Pharmacology, Hotchkiss Brain Institute and Alberta Children's Hospital Research Institute, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada
| | - Andrew M Allen
- Department of Anatomy & Physiology, The University of Melbourne, Victoria, 3010, Australia
| | - Clément Menuet
- Institut de Neurobiologie de la Méditerranée, INMED UMR1249, INSERM, Aix-Marseille Université, Marseille, France
| | - Joseph Donnelly
- Department of Medicine, Faculty of Medical and Health Sciences, The University of Auckland, New Zealand
| | - Igor Felippe
- Manaaki Manawa - The Centre for Heart Research, Faculty of Medical & Health Science, University of Auckland, Park Road, Grafton, Auckland, 1142, New Zealand
| | - Walter M St-John
- Emeritus Professor, Department of Physiology and Neurobiology, Geisel School of Medicine at Dartmouth, Dartmouth, New Hampshire, USA
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Cates MJ, Dickinson CJ, Hart ECJ, Paton JFR. Neurogenic hypertension and elevated vertebrobasilar arterial resistance: is there a causative link? Curr Hypertens Rep 2012; 14:261-9. [PMID: 22562144 DOI: 10.1007/s11906-012-0267-6] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
There is evidence of sympathetic overdrive in a significant proportion of patients with essential hypertension and an animal model of the condition, the spontaneously hypertensive rat (SHR). The reasons for this remain elusive. However, there is also evidence of narrowing of the arteries supplying the brainstem in the SHR and hypertensive humans. In this review, we discuss the possible role of brainstem hypoperfusion in driving increased sympathetic activity and hypertension.
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Angiotensin II-derived reactive oxygen species underpinning the processing of the cardiovascular reflexes in the medulla oblongata. Neurosci Bull 2011; 27:269-74. [PMID: 21788998 DOI: 10.1007/s12264-011-1529-z] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
The brainstem is a major site in the central nervous system involved in the processing of the cardiovascular reflexes such as the baroreflex and the peripheral chemoreflex. The nucleus tractus solitarius and the rostral ventrolateral medulla are 2 important brainstem nuclei, and they play pivotal roles in autonomic cardiovascular regulation. Angiotensin II is one of the neurotransmitters involved in the processing of the cardiovascular reflexes within the brainstem. It is well-known that one of the mechanisms by which angiotensin II exerts its effect is via the activation of pathways that generate reactive oxygen species (ROS). In the central nervous system, ROS are reported to be involved in several pathological diseases such as hypertension, heart failure and sleep apnea. However, little is known about the role of ROS in the processing of the cardiovascular reflexes within the brainstem. The present review mainly discussed some recent findings documenting a role for ROS in the processing of the baroreflex and the peripheral chemoreflex in the brainstem.
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Waki H, Bhuiyan MER, Gouraud SS, Takagishi M, Hatada A, Kohsaka A, Paton JFR, Maeda M. Acute reductions in blood flow restricted to the dorsomedial medulla induce a pressor response in rats. J Hypertens 2011; 29:1536-45. [PMID: 21666494 DOI: 10.1097/hjh.0b013e3283484106] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
OBJECTIVES The brainstem nucleus of the solitary tract (nucleus tractus solitarii, NTS) is a pivotal region for regulating the set-point of arterial pressure, the mechanisms of which are not fully understood. Based on evidence that the NTS exhibits O2-sensing mechanisms, we examined whether a localized disturbance of blood supply, resulting in hypoxia in the NTS, would lead to an acute increase in arterial pressure. METHODS Male Wistar rats were used. Cardiovascular parameters were measured before and after specific branches of superficial dorsal medullary veins were occluded; we assumed these were drainage vessels from the NTS and would produce stagnant hypoxia. Hypoxyprobe-1, a marker for detecting cellular hypoxia in the post-mortem tissue, was used to reveal whether vessel occlusion induced hypoxia within the NTS. RESULTS Following vessel occlusion, blood flow in the dorsal surface of the medulla oblongata including the NTS region showed an approximately 60% decrease and was associated with hypoxia in neurons located predominantly in the caudal part of the NTS as revealed using hypoxyprobe-1. Arterial pressure increased and this response was pronounced significantly in both magnitude and duration when baroreceptor reflex afferents were sectioned. CONCLUSION These results suggest that localized hypoxia in the NTS increases arterial pressure. We suggest this represents a protective mechanism whereby the elevated systemic pressure is a compensatory mechanism to enhance cerebral perfusion. Whether this physiological mechanism has any relevance to neurogenic hypertension is discussed.
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Affiliation(s)
- Hidefumi Waki
- Department of Physiology, Wakayama Medical University School of Medicine, Wakayama, Japan.
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Braga VA, Medeiros IA, Ribeiro TP, França-Silva MS, Botelho-Ono MS, Guimarães DD. Angiotensin-II-induced reactive oxygen species along the SFO-PVN-RVLM pathway: implications in neurogenic hypertension. Braz J Med Biol Res 2011; 44:871-6. [PMID: 21755262 DOI: 10.1590/s0100-879x2011007500088] [Citation(s) in RCA: 68] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2011] [Accepted: 06/16/2011] [Indexed: 02/07/2023] Open
Abstract
Neurogenic hypertension has been the subject of extensive research worldwide. This review is based on the premise that some forms of neurogenic hypertension are caused in part by the formation of angiotensin-II (Ang-II)-induced reactive oxygen species along the subfornical organ-paraventricular nucleus of the hypothalamus-rostral ventrolateral medulla pathway (SFO-PVN-RVLM pathway). We will discuss the recent contribution of our laboratory and others regarding the mechanisms by which neurons in the SFO (an important circumventricular organ) are activated by Ang-II, how the SFO communicates with two other important areas involved in sympathetic activity regulation (PVN and RVLM) and how Ang-II-induced reactive oxygen species participate along the SFO-PVN-RVLM pathway in the pathogenesis of neurogenic hypertension.
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Affiliation(s)
- V A Braga
- Laboratório de Tecnologia Farmacêutica, Universidade Federal da Paraíba, João Pessoa, PB, Brasil.
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The sympathetic nervous system and blood pressure in humans: implications for hypertension. J Hum Hypertens 2011; 26:463-75. [PMID: 21734720 DOI: 10.1038/jhh.2011.66] [Citation(s) in RCA: 177] [Impact Index Per Article: 13.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
A neurogenic component to primary hypertension (hypertension) is now well established. Along with raised vasomotor tone and increased cardiac output, the chronic activation of the sympathetic nervous system in hypertension has a diverse range of pathophysiological consequences independent of any increase in blood pressure. This review provides a perspective on the actions and interactions of angiotensin II, inflammation and vascular dysfunction/brain hypoperfusion in the pathogenesis and progression of neurogenic hypertension. The optimisation of current treatment strategies and the exciting recent developments in the therapeutic targeting of the sympathetic nervous system to control hypertension (for example, catheter-based renal denervation and carotid baroreceptor stimulation) will be outlined.
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Cates MJ, Steed PW, Abdala APL, Langton PD, Paton JFR. Elevated vertebrobasilar artery resistance in neonatal spontaneously hypertensive rats. J Appl Physiol (1985) 2011; 111:149-56. [PMID: 21493719 DOI: 10.1152/japplphysiol.00220.2011] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
There is a strong correlation between increased vertebral artery resistance and arterial blood pressure in humans. The reasons for this increased resistance at high systemic pressure remain unknown, but may include raised sympathetic activity. With the recent finding that prehypertensive spontaneously hypertensive (PHSH) rats, which have raised sympathetic nerve activity, but a blood pressure comparable to normotensive rat strains, we hypothesized that its vertebrobasilar vascular resistance would already be raised and, as a consequence, would exhibit a more responsive Cushing response (e.g., brain ischemia evoked sympathoexcitation and a pressor response). We report that PHSH rats exhibited a remodeling of the basilar artery (i.e., increased wall thickness and lower lumen-to-wall thickness ratio) that occurred before the onset of hypertension. In a novel in vitro vascularly isolated, arterially perfused brain stem preparation of PHSH rats of 4-5 wk of age, brain stem vascular resistance was raised by ∼35% relative to age- and sex-matched normotensive rats (P < 0.05). In the in situ arterial perfused working heart-brain stem preparation, occlusion of both vertebral arteries in the PHSH rat resulted in a significantly greater increase in sympathetic activity (57 vs. 20%, PHSH vs. control; P < 0.01) that triggered a greater increase in arterial perfusion pressure (8 vs. 3 mmHg, PHSH vs. control; P < 0.01) compared with normotensive rats. These data indicate raised vertebrobasilar artery resistance before the onset of hypertension in the PHSH rat. With the raised responsiveness of the Cushing response in the PHSH rat, we discuss the possibility of brain stem perfusion as a central nervous system determinant of the set point of vasomotor sympathetic tone in the hypertensive condition.
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Affiliation(s)
- Matthew J Cates
- School of Physiology and Pharmacology, Bristol Heart Institute, Medical Sciences Bldg., University of Bristol, Bristol BS8 1TD, UK
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11
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Hypertension before and after posterior circulation infarction: analysis of data from the South London Stroke Register. J Stroke Cerebrovasc Dis 2011; 21:612-8. [PMID: 21482144 DOI: 10.1016/j.jstrokecerebrovasdis.2011.02.004] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2010] [Revised: 02/09/2011] [Accepted: 02/10/2011] [Indexed: 11/20/2022] Open
Abstract
BACKGROUND Postmortem data have shown that blood pressure before death correlates more closely with a narrowing of the vertebral arteries than any other vessel studied. This study explores a possible association between hypertension, both before and after posterior circulation infarction (POCI) compared to anterior circulation infarction (ACI). METHODS Patients with a first-ever stroke enrolled in the South London Stroke Register between 2000 and 2006 were included. Chi-square tests and multivariable logistic regression were used to compare risk factors including hypertension, sex, smoking history, diabetes, and hypercholesterolemia in patients with POCI compared to ACI. Chi-square testing was used to compare the incidence of newly diagnosed hypertension after POCI and ACI. Absolute blood pressure readings recorded before stroke and 7 days after stroke were also compared between groups. RESULTS On multivariable analysis, POCI was significantly associated with male sex (odds ratio [OR] 2.24; 95% confidence interval [CI] 1.55-3.22; P < .001) and hypertension (OR 1.69; 95% CI 1.15-2.50; P = .008). After stroke, patients with POCI were more likely to be newly diagnosed with hypertension during a 1-year follow-up period (OR 2.15; 95% CI 1.20-3.86; P = .009) and as an inpatient (OR 3.27; 95% CI 1.49-7.13; P = .002). Systolic blood pressure was significantly higher in the POCI group before stroke (152 v 146 mm Hg; P = .027). Diastolic blood pressure was significantly higher 7 days poststroke (81 v 74 mm Hg; P = .01) in patients not previously diagnosed with hypertension. CONCLUSIONS This study has shown a significant association between hypertension before and after POCI compared to ACI. We believe further investigation with brainstem imaging and recordings of sympathetic nervous system activity after stroke is warranted.
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Pilowsky PM, Lung MSY, Spirovski D, McMullan S. Differential regulation of the central neural cardiorespiratory system by metabotropic neurotransmitters. Philos Trans R Soc Lond B Biol Sci 2009; 364:2537-52. [PMID: 19651655 DOI: 10.1098/rstb.2009.0092] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Central neurons in the brainstem and spinal cord are essential for the maintenance of sympathetic tone, the integration of responses to the activation of reflexes and central commands, and the generation of an appropriate respiratory motor output. Here, we will discuss work that aims to understand the role that metabotropic neurotransmitter systems play in central cardiorespiratory mechanisms. It is well known that blockade of glutamatergic, gamma-aminobutyric acidergic and glycinergic pathways causes major or even complete disruption of cardiorespiratory systems, whereas antagonism of other neurotransmitter systems barely affects circulation or ventilation. Despite the lack of an 'all-or-none' role for metabotropic neurotransmitters, they are nevertheless significant in modulating the effects of central command and peripheral adaptive reflexes. Finally, we propose that a likely explanation for the plethora of neurotransmitters and their receptors on cardiorespiratory neurons is to enable differential regulation of outputs in response to reflex inputs, while at the same time maintaining a tonic level of sympathetic activity that supports those organs that significantly autoregulate their blood supply, such as the heart, brain, retina and kidney. Such an explanation of the data now available enables the generation of many new testable hypotheses.
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Affiliation(s)
- Paul M Pilowsky
- Australian School of Advanced Medicine, Dow-Corning Building, Level 1, 3 Innovation Road, Macquarie University, 2109 NSW, Australia.
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13
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Paton JFR, Dickinson CJ, Mitchell G. Harvey Cushing and the regulation of blood pressure in giraffe, rat and man: introducing ‘Cushing's mechanism’. Exp Physiol 2008; 94:11-7. [DOI: 10.1113/expphysiol.2008.043455] [Citation(s) in RCA: 77] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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Paton JFR, Waki H. Is neurogenic hypertension related to vascular inflammation of the brainstem? Neurosci Biobehav Rev 2008; 33:89-94. [PMID: 18585782 DOI: 10.1016/j.neubiorev.2008.05.020] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2008] [Revised: 05/07/2008] [Accepted: 05/15/2008] [Indexed: 01/12/2023]
Abstract
Essential hypertension is idiopathic although it is accepted as a complex polygenic trait with underlying genetic components, which remain unknown. Our supposition is that hypertension involves activation of the sympathetic nervous system. One pivotal region controlling arterial pressure set point is nucleus tractus solitarii (NTS). We recently identified that pro-inflammatory molecules, such as junctional adhesion molecule-1 (JAM-1), were over expressed in endothelial cells of the microvasculature supplying the NTS in an animal model of human hypertension (the spontaneously hypertensive rat) compared to normotensive Wistar-Kyoto rats (WKY). Over expression of JAM-1 in NTS of WKY rats was pro-hypertensive and induced leukocyte adherence to the microvasculature. Since leukocyte adhesion causes cytokine release, we found expression of monocyte chemoattractant protein-1 (MCP-1) was higher in the NTS of SHR while inter-leukin-6 (IL-6) was lower compared to the WKY rat. Inflammation of the brainstem microvasculature may increase vascular resistance within the brainstem. High brainstem vascular resistance and its inflammation may release pathological paracrine signaling molecules affecting central neural cardiovascular activity conducive to neurogenic hypertension.
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Affiliation(s)
- Julian F R Paton
- Department of Physiology & Pharmacology, Bristol Heart Institute, School of Medical Sciences, University of Bristol, Bristol BS8 1TD, UK.
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Signalling across the blood brain barrier by angiotensin II: novel implications for neurogenic hypertension. J Mol Med (Berl) 2008; 86:705-10. [PMID: 18443753 DOI: 10.1007/s00109-008-0324-4] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2008] [Accepted: 02/08/2008] [Indexed: 02/07/2023]
Abstract
Angiotensin II (AngII) is a major culprit in essential hypertension. Based on a genetic rodent model of hypertension, we review here evidence that AngII may signal across the blood brain barrier to affect neuronal circuits within the nucleus tractus solitarii (NTS) of the brainstem, a pivotal region regulating both the baroreceptor reflex and set point control of arterial pressure. We have termed this form of signalling as vascular-neuronal signalling. We describe that the depressant action of AngII in NTS on the baroreceptor reflex is mediated via activation of endothelial nitric oxide synthase (eNOS) releasing NO that promotes release of the inhibitory transmitter-GABA. This could shunt the incoming excitatory baroreceptor afferent traffic impinging on NTS neurones. Chronic studies recording arterial pressure in conscious unrestrained rats using radio-telemetry have revealed that eNOS in NTS plays an endogenous physiological role in the homeostatic regulation of the gain of the cardiac baroreceptor reflex. However, in the spontaneously hypertensive rat, eNOS mRNA was higher (compared to normotensive rats), and its chronic blockade in NTS restored the abnormally depressed cardiac baroreceptor reflex to levels akin to normotensive rats, improved heart rate variability and lowered arterial pressure. Hence, it seems that excessive eNOS activity in NTS of the SHR contributes to the pathological state of this animal model's cardiovascular autonomic nervous system. We speculate on why eNOS activity may be up regulated in the NTS of the SHR and propose that it is a consequence of high cerebral vascular resistance and inadequate blood perfusion of the brainstem.
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Baekey DM, Dick TE, Paton JFR. Pontomedullary transection attenuates central respiratory modulation of sympathetic discharge, heart rate and the baroreceptor reflex in the in situ rat preparation. Exp Physiol 2008; 93:803-16. [PMID: 18344259 DOI: 10.1113/expphysiol.2007.041400] [Citation(s) in RCA: 67] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Previous studies have indicated a major role for the pons in the genesis of the respiratory pattern. The respiratory rhythm is coupled to the cardiovascular system to ensure optimal matching of minute ventilation and cardiac output. Since much of this coupling results from cross-talk between brainstem circuits, we have assessed the role of the pons in both the co-ordination of respiratory and cardiovascular efferent activities and the baroreceptor reflex efficacy. Using the arterially perfused in situ rat preparation, we recorded neural activities from the left phrenic nerve, central end of the vagus nerve, thoracic sympathetic chain (T8-T10) and heart rate. Respiratory sinus arrhythmia, respiratory modulation of sympathetic nerve activity (and Traube-Hering waves in arterial pressure) and postinspiratory discharges recorded from vagal efferents were eliminated after pontine transection. We also found that although the sympathetic arterial baroreflex remained intact, respiratory gating of the baroreceptor reflex (i.e. both bradycardia and sympathoinhibition) was abolished after pontine removal. We propose that neural activity of the pons is essential for physiological coupling of centrally generated respiratory and cardiovascular efferent activities.
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Affiliation(s)
- David M Baekey
- Department of Medicine, Division of Pulmonary, Critical Care and Sleep Medicine, Case Western Reserve University, 11100 Euclid Avenue, Room 622 - Mailstop 5067, Cleveland, OH 44106-5067, USA.
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Paton JFR, Waki H, Abdala APL, Dickinson J, Kasparov S. Vascular-brain signaling in hypertension: role of angiotensin II and nitric oxide. Curr Hypertens Rep 2007; 9:242-7. [PMID: 17519132 DOI: 10.1007/s11906-007-0043-1] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Paracrine signaling by nitric oxide (NO) released from microvasculature within the brain affects multiple neuronal functions. Reviewed here is a role in central cardiovascular control. Within the nucleus tractus solitarii (NTS), a major regulatory region for arterial pressure, angiotensin II stimulates NO generation from endothelial nitric oxide synthase (eNOS). This enhances c-aminobutyric acid release to depress baroreflex function. In the spontaneously hypertensive rat (SHR), eNOS mRNA in the NTS is elevated compared to normotensive rats. Chronic inhibition of eNOS activity in the NTS of SHR reduced arterial pressure and increased baroreflex gain. Thus, eNOS-generated NO in the NTS plays a major role in control of baroreflex gain and arterial pressure. Indeed, its activity contributes to hypertension in the SHR. We propose that eNOS-generated NO in the SHR may be a compensatory mechanism for any potential threat to an adequate blood supply to the brain (eg, from genetically small arteries supplying the brainstem).
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Affiliation(s)
- Julian F R Paton
- Department of Physiology, Bristol Heart Institute, School of Medical Sciences, University of Bristol, Bristol BS8 1TD, UK.
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