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Yazawa I, Yoshida Y, Yoshimi R, Ozato K. Immature functional development of lumbar locomotor networks in adult Irf8-/- mice. Front Neurosci 2024; 17:1234215. [PMID: 38239832 PMCID: PMC10794560 DOI: 10.3389/fnins.2023.1234215] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2023] [Accepted: 12/11/2023] [Indexed: 01/22/2024] Open
Abstract
To date, research on the role of the brainstem and spinal cord in motor behavior has relied on in vitro preparations of the neonatal rodent spinal cord, with or without the brainstem; their spatial and temporal scope are subject to technical limitations imposed by low oxygen tension in deep tissues. Therefore, we created an arterially perfused in situ preparation that allowed us to investigate functional interactions in the CNS from the neonatal to adult period. Decerebrated rodents were kept alive via total artificial cardiopulmonary bypass for extracorporeal circulation; the plasma oxygen and ion components needed for survival were supplied through the blood vessels. Interferon regulatory factor 8 (IRF8) is a transcription factor that promotes myeloid cell development and stimulates innate immune responses. In the brain, IRF8 is expressed only in microglia and directs the expression of many genes that serve microglial functions. Recent evidence indicates that IRF8 affects behavior and modulates Alzheimer's disease progression in a mouse model. However, whether this immune deficiency arising from the absence of IRF8 influences the development of the neuronal network in the spinal cord is unknown. We applied the above methodology to mice of all ages and electrophysiologically explored whether the absence of IRF8 influences the development of lumbar central pattern generator (CPG) networks. In mice of all ages, bilateral neuronal discharges by the normal CPG networks activated by the modulated sympathetic tone via descending pathways at high flow rates became organized into discharge episodes punctuated by periods of quiescence. Similar discharge episodes were generated by the adult CPG networks (≥P14 days) activated by drug application. However, discharge episodes elicited by activating the neonatal-juvenile CPG networks (
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Affiliation(s)
- Itaru Yazawa
- Department of Food and Nutrition, Kyushu Nutrition Welfare University, Kitakyushu, Japan
- Laboratory of Neural Control, National Institute of Neurological Disorders and Stroke (NINDS), National Institutes of Health (NIH), Bethesda, MD, United States
| | - Yuko Yoshida
- Division of Developmental Biology, National Institute of Child Health and Human Development (NICHD), NIH, Bethesda, MD, United States
| | - Ryusuke Yoshimi
- Division of Developmental Biology, National Institute of Child Health and Human Development (NICHD), NIH, Bethesda, MD, United States
- Department of Stem Cell and Immune Regulation, Graduate School of Medicine, Yokohama City University, Yokohama, Japan
| | - Keiko Ozato
- Division of Developmental Biology, National Institute of Child Health and Human Development (NICHD), NIH, Bethesda, MD, United States
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Moreira TS, Mulkey DK, Takakura AC. Update on vascular control of central chemoreceptors. Exp Physiol 2023. [PMID: 38153366 DOI: 10.1113/ep091329] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2023] [Accepted: 12/11/2023] [Indexed: 12/29/2023]
Abstract
At least four mechanisms have been proposed to elucidate how neurons in the retrotrapezoid (RTN) region sense changes in CO2 /H+ to regulate breathing (i.e., function as respiratory chemosensors). These mechanisms include: (1) intrinsic neuronal sensitivity to H+ mediated by TASK-2 and GPR4; (2) paracrine activation of RTN neurons by CO2 -responsive astrocytes (via a purinergic mechanism); (3) enhanced excitatory synaptic input or disinhibition; and (4) CO2 -induced vascular contraction. Although blood flow can influence tissue CO2 /H+ levels, there is limited understanding of how control of vascular tone in central CO2 chemosensitive regions might contribute to respiratory output. In this review, we focus on recent evidence that CO2 /H+ -induced purinergic-dependent vasoconstriction in the ventral parafacial region near RTN neurons supports respiratory chemoreception. This mechanism appears to be unique to the ventral parafacial region and opposite to other brain regions, including medullary chemosensor regions, where CO2 /H+ elicits vasodilatation. We speculate that this mechanism helps to maintain CO2 /H+ levels in the vicinity of RTN neurons, thereby maintaining the drive to breathe. Important next steps include determining whether disruption of CO2 /H+ vascular reactivity contributes to or can be targeted to improve breathing problems in disease states, such as Parkinson's disease.
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Affiliation(s)
- Thiago S Moreira
- Department of Physiology and Biophysics, Instituto de Ciencias Biomedicas, Universidade de Sao Paulo, Sao Paulo, Brazil
| | - Daniel K Mulkey
- Department of Physiology and Neurobiology, University of Connecticut, Storrs, Connecticut, USA
| | - Ana C Takakura
- Department of Pharmacology, Instituto de Ciencias Biomedicas, Universidade de Sao Paulo, São Paulo, Brazil
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Kyriakoulis P, Kyrios M. Biological and cognitive theories explaining panic disorder: A narrative review. Front Psychiatry 2023; 14:957515. [PMID: 36793941 PMCID: PMC9924294 DOI: 10.3389/fpsyt.2023.957515] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/31/2022] [Accepted: 01/04/2023] [Indexed: 02/01/2023] Open
Abstract
The current narrative review summarizes and examines several theories of panic disorder (PD) including biological theories, encompassing neurochemical factors, metabolic and genetic theories, respiratory and hyperventilation theories and cognitive theory. Biological theories have informed the development of psychopharmacological treatments; however, they may be limited in their utility given the efficacy of psychological treatments. In particular, behavioral and, more recently, cognitive models have garnered support due to the efficacy of cognitive-behavior therapy (CBT) in treating PD. The role of combination treatments has been found to be superior in the treatment of PD in particular cases, lending support for the need for an integrated approach and model for PD given that the etiology of PD is complex and multifactorial.
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Affiliation(s)
- Peter Kyriakoulis
- Faculty of Arts, Health and Design, Swinburne University, Hawthorn, VIC, Australia
| | - Michael Kyrios
- College of Education, Psychology and Social Work, Órama Institute for Mental Health and Wellbeing, Flinders University, Bedford Park, SA, Australia
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CO 2 exposure enhances Fos expression in hypothalamic neurons in rats during the light and dark phases of the diurnal cycle. Brain Struct Funct 2022; 227:2667-2679. [PMID: 36109371 DOI: 10.1007/s00429-022-02562-2] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2021] [Accepted: 08/29/2022] [Indexed: 12/30/2022]
Abstract
Orexinergic (OX) neurons in the lateral hypothalamus (LH), perifornical area (PFA) and dorsomedial hypothalamus (DMH) play a role in the hypercapnic ventilatory response, presumably through direct inputs to central pattern generator sites and/or through interactions with other chemosensitive regions. OX neurons can produce and release orexins, excitatory neuropeptides involved in many functions, including physiological responses to changes in CO2/pH. Thus, in the present study, we tested the hypothesis that different nuclei (LH, PFA and DMH) where the orexinergic neurons are located, show distinct activation by CO2 during the light-dark cycle phases. For this purpose, we evaluated the Fos and OXA expression by immunohistochemistry to identify neurons that co-localize Fos + OXA in the LH, LPeF, MPeF and DMH in the light-inactive and dark-active phase in Wistar rats subjected to 3 h of normocapnia or hypercapnia (7% CO2). Quantitative analyses of immunoreactive neurons show that hypercapnia caused an increase in the number of neurons expressing Fos in the LH, LPeF, MPeF and DMH in the light and dark phases. In addition, the number of Fos + OXA neurons increased in the LPeF and DMH independently of the phases of the diurnal cycle; whereas in the MPeF, this increase was observed exclusively in the light phase. Thus, we suggest that OX neurons are selectively activated by hypercapnia throughout the diurnal cycle, reinforcing the differential role of nuclei in the hypothalamus during central chemosensitivity.
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Gourine AV, Dale N. Brain H + /CO 2 sensing and control by glial cells. Glia 2022; 70:1520-1535. [PMID: 35102601 DOI: 10.1002/glia.24152] [Citation(s) in RCA: 15] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2021] [Revised: 01/11/2022] [Accepted: 01/17/2022] [Indexed: 01/04/2023]
Abstract
Maintenance of constant brain pH is critically important to support the activity of individual neurons, effective communication within the neuronal circuits, and, thus, efficient processing of information by the brain. This review article focuses on how glial cells detect and respond to changes in brain tissue pH and concentration of CO2 , and then trigger systemic and local adaptive mechanisms that ensure a stable milieu for the operation of brain circuits. We give a detailed account of the cellular and molecular mechanisms underlying sensitivity of glial cells to H+ and CO2 and discuss the role of glial chemosensitivity and signaling in operation of three key mechanisms that work in concert to keep the brain pH constant. We discuss evidence suggesting that astrocytes and marginal glial cells of the brainstem are critically important for central respiratory CO2 chemoreception-a fundamental physiological mechanism that regulates breathing in accord with changes in blood and brain pH and partial pressure of CO2 in order to maintain systemic pH homeostasis. We review evidence suggesting that astrocytes are also responsible for the maintenance of local brain tissue extracellular pH in conditions of variable acid loads associated with changes in the neuronal activity and metabolism, and discuss potential role of these glial cells in mediating the effects of CO2 on cerebral vasculature.
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Affiliation(s)
- Alexander V Gourine
- Centre for Cardiovascular and Metabolic Neuroscience, Department of Neuroscience, Physiology and Pharmacology, University College London, London, UK
| | - Nicholas Dale
- School of Life Sciences, University of Warwick, Coventry, UK
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Subfornical organ interleukin 1 receptor: A novel regulator of spontaneous and conditioned fear associated behaviors in mice. Brain Behav Immun 2022; 101:304-317. [PMID: 35032573 PMCID: PMC9836229 DOI: 10.1016/j.bbi.2022.01.004] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/15/2021] [Revised: 12/25/2021] [Accepted: 01/07/2022] [Indexed: 01/14/2023] Open
Abstract
Impaired threat responding and fear regulation is a hallmark of psychiatric conditions such as post-traumatic stress disorder (PTSD) and Panic Disorder (PD). Most studies have focused on external psychogenic threats to study fear, however, accumulating evidence suggests a primary role of homeostatic perturbations and interoception in regulating emotional behaviors. Heightened reactivity to interoceptive threat carbon dioxide (CO2) inhalation associates with increased risk for developing PD and PTSD, however, contributory mechanisms and molecular targets are not well understood. Previous studies from our group suggested a potential role of interleukin 1 receptor (IL-1R1) signaling within BBB-devoid sensory circumventricular organ, the subfornical organ (SFO) in CO2-evoked fear. However, the necessity of SFO-IL-1R1 in regulating CO2-associated spontaneous fear as well as, long-term fear potentiation relevant to PD/PTSD has not been investigated. The current study tested male mice with SFO-targeted microinfusion of the IL-1R1 antagonist (IL-1RA) or vehicle in a recently developed CO2-startle-fear conditioning-extinction paradigm. Consistent with our hypothesis, SFO IL-1RA treatment elicited significant attenuation of freezing and increased rearing during CO2 inhalation suggesting SFO-IL1R1 regulation of spontaneous fear to CO2. Intriguingly, SFO IL-1RA treatment normalized CO2-associated potentiation of conditioned fear and impaired extinction a week later suggesting modulation of long-term fear by SFO-IL-1R1 signaling. Post behavior FosB mapping revealed recruitment of prefrontal cortex-amygdala-periaqueductal gray (PAG) areas in SFO-IL-1RA mediated effects. Additionally, we localized cellular IL-1R1 expression within the SFO to blood vessel endothelial cells and observed CO2-induced alterations in IL-1β/IL-1R1 expression in peripheral mononuclear cells and SFO. Lastly, CO2-evoked microglial activation was attenuated in SFO-IL-1RA treated mice. These observations suggest a peripheral monocyte-endothelial-microglia interplay in SFO-IL-1R1 modulation of CO2-associated spontaneous fear and delayed fear memory. Collectively, our data highlight a novel, "bottom-up" neuroimmune mechanism that integrates interoceptive and exteroceptive threat processing of relevance to fear-related pathologies.
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Abstract
Brain PCO2 is sensed primarily via changes in [H+]. Small pH changes are detected in the medulla oblongata and trigger breathing adjustments that help maintain arterial PCO2 constant. Larger perturbations of brain CO2/H+, possibly also sensed elsewhere in the CNS, elicit arousal, dyspnea, and stress, and cause additional breathing modifications. The retrotrapezoid nucleus (RTN), a rostral medullary cluster of glutamatergic neurons identified by coexpression of Phoxb and Nmb transcripts, is the lynchpin of the central respiratory chemoreflex. RTN regulates breathing frequency, inspiratory amplitude, and active expiration. It is exquisitely responsive to acidosis in vivo and maintains breathing autorhythmicity during quiet waking, slow-wave sleep, and anesthesia. The RTN response to [H+] is partly an intrinsic neuronal property mediated by proton sensors TASK-2 and GPR4 and partly a paracrine effect mediated by astrocytes and the vasculature. The RTN also receives myriad excitatory or inhibitory synaptic inputs including from [H+]-responsive neurons (e.g., serotonergic). RTN is silenced by moderate hypoxia. RTN inactivity (periodic or sustained) contributes to periodic breathing and, likely, to central sleep apnea. RTN development relies on transcription factors Egr2, Phox2b, Lbx1, and Atoh1. PHOX2B mutations cause congenital central hypoventilation syndrome; they impair RTN development and consequently the central respiratory chemoreflex.
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Affiliation(s)
- Patrice G Guyenet
- Department of Pharmacology, University of Virginia, Charlottesville, VA, United States.
| | - Douglas A Bayliss
- Department of Pharmacology, University of Virginia, Charlottesville, VA, United States
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Abstract
The clinical term dyspnea (a.k.a. breathlessness or shortness of breath) encompasses at least three qualitatively distinct sensations that warn of threats to breathing: air hunger, effort to breathe, and chest tightness. Air hunger is a primal homeostatic warning signal of insufficient alveolar ventilation that can produce fear and anxiety and severely impacts the lives of patients with cardiopulmonary, neuromuscular, psychological, and end-stage disease. The sense of effort to breathe informs of increased respiratory muscle activity and warns of potential impediments to breathing. Most frequently associated with bronchoconstriction, chest tightness may warn of airway inflammation and constriction through activation of airway sensory nerves. This chapter reviews human and functional brain imaging studies with comparison to pertinent neurorespiratory studies in animals to propose the interoceptive networks underlying each sensation. The neural origins of their distinct sensory and affective dimensions are discussed, and areas for future research are proposed. Despite dyspnea's clinical prevalence and impact, management of dyspnea languishes decades behind the treatment of pain. The neurophysiological bases of current therapeutic approaches are reviewed; however, a better understanding of the neural mechanisms of dyspnea may lead to development of novel therapies and improved patient care.
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Affiliation(s)
- Andrew P Binks
- Department of Basic Science Education, Virginia Tech Carilion School of Medicine, Roanoke, VA, United States; Faculty of Health Sciences, Virginia Tech, Blacksburg, VA, United States.
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Gourine AV, Spyer KM. Geoff Burnstock, purinergic signalling, and chemosensory control of breathing. Auton Neurosci 2021; 235:102839. [PMID: 34198056 DOI: 10.1016/j.autneu.2021.102839] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2021] [Revised: 06/11/2021] [Accepted: 06/20/2021] [Indexed: 12/14/2022]
Abstract
This article is the authors' contribution to the tribute issue in honour of Geoffrey Burnstock, the founder of this journal and the field of purinergic signalling. We give a brief account of the results of experimental studies which at the beginning received valuable input from Geoff, who both directly and indirectly influenced our research undertaken over the last two decades. Research into the mechanisms controlling breathing identified ATP as the common mediator of the central and peripheral chemosensory transduction. Studies of the sources and mechanisms of chemosensory ATP release in the CNS suggested that this signalling pathway is universally engaged in conditions of increased metabolic demand by brain glial cells - astrocytes. Astrocytes appear to function as versatile CNS metabolic sensors that detect changes in brain tissue pH, CO2, oxygen, and cerebral perfusion pressure. Experimental studies on various aspects of astrocyte biology generated data indicating that the function of these omnipresent glial cells and communication between astrocytes and neurons are governed by purinergic signalling, - first discovered by Geoff Burnstock in the 70's and researched through his entire scientific career.
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Affiliation(s)
- Alexander V Gourine
- Centre for Cardiovascular and Metabolic Neuroscience, Department of Neuroscience, Physiology & Pharmacology, University College London, Gower Street, London WC1E 6BT, UK.
| | - K Michael Spyer
- Centre for Cardiovascular and Metabolic Neuroscience, Department of Neuroscience, Physiology & Pharmacology, University College London, Gower Street, London WC1E 6BT, UK
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CO 2-Sensitive Connexin Hemichannels in Neurons and Glia: Three Different Modes of Signalling? Int J Mol Sci 2021; 22:ijms22147254. [PMID: 34298872 PMCID: PMC8304244 DOI: 10.3390/ijms22147254] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2021] [Revised: 06/29/2021] [Accepted: 07/01/2021] [Indexed: 01/28/2023] Open
Abstract
Connexins can assemble into either gap junctions (between two cells) or hemichannels (from one cell to the extracellular space) and mediate cell-to-cell signalling. A subset of connexins (Cx26, Cx30, Cx32) are directly sensitive to CO2 and fluctuations in the level within a physiological range affect their open probability, and thus, change cell conductance. These connexins are primarily found on astrocytes or oligodendrocytes, where increased CO2 leads to ATP release, which acts on P2X and P2Y receptors of neighbouring neurons and changes excitability. CO2-sensitive hemichannels are also found on developing cortical neurons, where they play a role in producing spontaneous neuronal activity. It is plausible that the transient opening of hemichannels allows cation influx, leading to depolarisation. Recently, we have shown that dopaminergic neurons in the substantia nigra and GABAergic neurons in the VTA also express Cx26 hemichannels. An increase in the level of CO2 results in hemichannel opening, increasing whole-cell conductance, and decreasing neuronal excitability. We found that the expression of Cx26 in the dopaminergic neurons in the substantia nigra at P7-10 is transferred to glial cells by P17-21, displaying a shift from being inhibitory (to neuronal activity) in young mice, to potentially excitatory (via ATP release). Thus, Cx26 hemichannels could have three modes of signalling (release of ATP, excitatory flickering open and shut and inhibitory shunting) depending on where they are expressed (neurons or glia) and the stage of development.
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Katsuki S, Ikeda K, Onimaru H, Dohi K, Izumizaki M. Effects of acetylcholine on hypoglossal and C4 nerve activity in brainstem-spinal cord preparations from newborn rat. Respir Physiol Neurobiol 2021; 293:103737. [PMID: 34229065 DOI: 10.1016/j.resp.2021.103737] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2021] [Revised: 06/17/2021] [Accepted: 07/01/2021] [Indexed: 11/17/2022]
Abstract
Effects of acetylcholine (ACh) on respiratory activity have been an intriguing theme especially in relation to central chemoreception and the control of hypoglossal nerve activity. We studied the effects of ACh on hypoglossal and phrenic (C4) nerve activities and inspiratory and pre-inspiratory neurons in the rostral ventrolateral medulla in brainstem-spinal cord preparations from newborn rats. ACh application increased respiratory rhythm, decreased inspiratory hypoglossal and C4 nerve burst amplitude, and enhanced pre-inspiratory hypoglossal activity. ACh induced membrane depolarization of pre-inspiratory neurons that might be involved in facilitation of respiratory rhythm by ACh. Effects of ACh on hypoglossal and C4 nerve activity were partially reversed by a nicotinic receptor blocker, mecamylamine. Further application of a muscarinic receptor antagonist, oxybutynin, resulted in slight increase of hypoglossal (but not C4) burst amplitude. Thus, ACh induced different effects on hypoglossal and C4 nerve activity in the brainstem-spinal cord preparation.
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Affiliation(s)
- Shino Katsuki
- Department of Physiology, Showa University School of Medicine, Tokyo 142-8555, Japan; Department of Emergency, Disaster and Critical Care Medicine, Showa University, Tokyo 142-8555, Japan
| | - Keiko Ikeda
- Department of Oral Physiology, Showa University School of Dentistry, 1-5-8 Hatanodai, Shinagawa-ku, Tokyo 142-8555, Japan
| | - Hiroshi Onimaru
- Department of Physiology, Showa University School of Medicine, Tokyo 142-8555, Japan.
| | - Kenji Dohi
- Department of Emergency, Disaster and Critical Care Medicine, Showa University, Tokyo 142-8555, Japan
| | - Masahiko Izumizaki
- Department of Physiology, Showa University School of Medicine, Tokyo 142-8555, Japan
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Dale N. CO 2 sensing by connexin26 and its role in the control of breathing. Interface Focus 2021; 11:20200029. [PMID: 33633831 DOI: 10.1098/rsfs.2020.0029] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 12/09/2020] [Indexed: 12/14/2022] Open
Abstract
Breathing is essential to provide the O2 required for metabolism and to remove its inevitable CO2 by-product. The rate and depth of breathing is controlled to regulate the excretion of CO2 to maintain the pH of arterial blood at physiological values. A widespread consensus is that chemosensory cells in the carotid body and brainstem measure blood and tissue pH and adjust the rate of breathing to ensure its homeostatic regulation. In this review, I shall consider the evidence that underlies this consensus and highlight historical data indicating that direct sensing of CO2 also plays a significant role in the regulation of breathing. I shall then review work from my laboratory that provides a molecular mechanism for the direct detection of CO2 via the gap junction protein connexin26 (Cx26) and demonstrates the contribution of this mechanism to the chemosensory regulation of breathing. As there are many pathological mutations of Cx26 in humans, I shall discuss which of these alter the CO2 sensitivity of Cx26 and the extent to which these mutations could affect human breathing. I finish by discussing the evolution of the CO2 sensitivity of Cx26 and its link to the evolution of amniotes.
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Affiliation(s)
- Nicholas Dale
- School of Life Sciences, University of Warwick, Coventry CV4 7AL, UK
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van de Wiel J, Meigh L, Bhandare A, Cook J, Nijjar S, Huckstepp R, Dale N. Connexin26 mediates CO 2-dependent regulation of breathing via glial cells of the medulla oblongata. Commun Biol 2020; 3:521. [PMID: 32958814 PMCID: PMC7505967 DOI: 10.1038/s42003-020-01248-x] [Citation(s) in RCA: 23] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2020] [Accepted: 08/21/2020] [Indexed: 01/12/2023] Open
Abstract
Breathing is highly sensitive to the PCO2 of arterial blood. Although CO2 is detected via the proxy of pH, CO2 acting directly via Cx26 may also contribute to the regulation of breathing. Here we exploit our knowledge of the structural motif of CO2-binding to Cx26 to devise a dominant negative subunit (Cx26DN) that removes the CO2-sensitivity from endogenously expressed wild type Cx26. Expression of Cx26DN in glial cells of a circumscribed region of the mouse medulla - the caudal parapyramidal area - reduced the adaptive change in tidal volume and minute ventilation by approximately 30% at 6% inspired CO2. As central chemosensors mediate about 70% of the total response to hypercapnia, CO2-sensing via Cx26 in the caudal parapyramidal area contributed about 45% of the centrally-mediated ventilatory response to CO2. Our data unequivocally link the direct sensing of CO2 to the chemosensory control of breathing and demonstrates that CO2-binding to Cx26 is a key transduction step in this fundamental process.
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Affiliation(s)
| | - Louise Meigh
- School of Life Sciences, University of Warwick, Coventry, CV4 7AL, UK
| | - Amol Bhandare
- School of Life Sciences, University of Warwick, Coventry, CV4 7AL, UK
| | - Jonathan Cook
- School of Life Sciences, University of Warwick, Coventry, CV4 7AL, UK
| | - Sarbjit Nijjar
- School of Life Sciences, University of Warwick, Coventry, CV4 7AL, UK
| | - Robert Huckstepp
- School of Life Sciences, University of Warwick, Coventry, CV4 7AL, UK
| | - Nicholas Dale
- School of Life Sciences, University of Warwick, Coventry, CV4 7AL, UK.
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Hill E, Dale N, Wall MJ. Moderate Changes in CO 2 Modulate the Firing of Neurons in the VTA and Substantia Nigra. iScience 2020; 23:101343. [PMID: 32683315 PMCID: PMC7371905 DOI: 10.1016/j.isci.2020.101343] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2020] [Revised: 04/30/2020] [Accepted: 07/01/2020] [Indexed: 12/21/2022] Open
Abstract
The substantia nigra (SN) and ventral tegmental area (VTA) are vital for the control of movement, goal-directed behavior, and encoding reward. Here we show that the firing of specific neuronal subtypes in these nuclei can be modulated by physiological changes in the partial pressure of carbon dioxide (PCO2). The resting conductance of substantia nigra dopaminergic neurons in young animals (postnatal days 7-10) and GABAergic neurons in the VTA is modulated by changes in the level of CO2. We provide several lines of evidence that this CO2-sensitive conductance results from connexin 26 (Cx26) hemichannel expression. Since the levels of PCO2 in the blood will vary depending on physiological activity and pathology, this suggests that changes in PCO2 could potentially modulate motor activity, reward behavior, and wakefulness.
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Affiliation(s)
- Emily Hill
- School of Life Sciences, University of Warwick, Gibbet Hill, Coventry CV4 7AL, UK.
| | - Nicholas Dale
- School of Life Sciences, University of Warwick, Gibbet Hill, Coventry CV4 7AL, UK
| | - Mark J Wall
- School of Life Sciences, University of Warwick, Gibbet Hill, Coventry CV4 7AL, UK.
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Guyenet PG, Stornetta RL, Souza GMPR, Abbott SBG, Shi Y, Bayliss DA. The Retrotrapezoid Nucleus: Central Chemoreceptor and Regulator of Breathing Automaticity. Trends Neurosci 2019; 42:807-824. [PMID: 31635852 DOI: 10.1016/j.tins.2019.09.002] [Citation(s) in RCA: 120] [Impact Index Per Article: 24.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2019] [Revised: 08/28/2019] [Accepted: 09/05/2019] [Indexed: 12/15/2022]
Abstract
The ventral surface of the rostral medulla oblongata has been suspected since the 1960s to harbor central respiratory chemoreceptors [i.e., acid-activated neurons that regulate breathing to maintain a constant arterial PCO2 (PaCO2)]. The key neurons, a.k.a. the retrotrapezoid nucleus (RTN), have now been identified. In this review we describe their transcriptome, developmental lineage, and anatomical projections. We also review their contribution to CO2 homeostasis and to the regulation of breathing automaticity during sleep and wake. Finally, we discuss several mechanisms that contribute to the activation of RTN neurons by CO2in vivo: cell-autonomous effects of protons; paracrine effects of pH mediated by surrounding astrocytes and blood vessels; and excitatory inputs from other CO2-responsive CNS neurons.
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Affiliation(s)
- Patrice G Guyenet
- Department of Pharmacology, University of Virginia, Charlottesville, VA 22908, USA.
| | - Ruth L Stornetta
- Department of Pharmacology, University of Virginia, Charlottesville, VA 22908, USA
| | - George M P R Souza
- Department of Pharmacology, University of Virginia, Charlottesville, VA 22908, USA
| | - Stephen B G Abbott
- Department of Pharmacology, University of Virginia, Charlottesville, VA 22908, USA
| | - Yingtang Shi
- Department of Pharmacology, University of Virginia, Charlottesville, VA 22908, USA
| | - Douglas A Bayliss
- Department of Pharmacology, University of Virginia, Charlottesville, VA 22908, USA
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Cummins EP, Strowitzki MJ, Taylor CT. Mechanisms and Consequences of Oxygen and Carbon Dioxide Sensing in Mammals. Physiol Rev 2019; 100:463-488. [PMID: 31539306 DOI: 10.1152/physrev.00003.2019] [Citation(s) in RCA: 63] [Impact Index Per Article: 12.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Molecular oxygen (O2) and carbon dioxide (CO2) are the primary gaseous substrate and product of oxidative phosphorylation in respiring organisms, respectively. Variance in the levels of either of these gasses outside of the physiological range presents a serious threat to cell, tissue, and organism survival. Therefore, it is essential that endogenous levels are monitored and kept at appropriate concentrations to maintain a state of homeostasis. Higher organisms such as mammals have evolved mechanisms to sense O2 and CO2 both in the circulation and in individual cells and elicit appropriate corrective responses to promote adaptation to commonly encountered conditions such as hypoxia and hypercapnia. These can be acute and transient nontranscriptional responses, which typically occur at the level of whole animal physiology or more sustained transcriptional responses, which promote chronic adaptation. In this review, we discuss the mechanisms by which mammals sense changes in O2 and CO2 and elicit adaptive responses to maintain homeostasis. We also discuss crosstalk between these pathways and how they may represent targets for therapeutic intervention in a range of pathological states.
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Affiliation(s)
- Eoin P Cummins
- UCD Conway Institute, Systems Biology Ireland and the School of Medicine, University College Dublin, Belfield, Dublin, Ireland
| | - Moritz J Strowitzki
- UCD Conway Institute, Systems Biology Ireland and the School of Medicine, University College Dublin, Belfield, Dublin, Ireland
| | - Cormac T Taylor
- UCD Conway Institute, Systems Biology Ireland and the School of Medicine, University College Dublin, Belfield, Dublin, Ireland
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Dospinescu VM, Nijjar S, Spanos F, Cook J, de Wolf E, Biscotti MA, Gerdol M, Dale N. Structural determinants of CO 2-sensitivity in the β connexin family suggested by evolutionary analysis. Commun Biol 2019; 2:331. [PMID: 31508505 PMCID: PMC6726660 DOI: 10.1038/s42003-019-0576-2] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2018] [Accepted: 08/08/2019] [Indexed: 12/24/2022] Open
Abstract
A subclade of connexins comprising Cx26, Cx30, and Cx32 are directly sensitive to CO2. CO2 binds to a carbamylation motif present in these connexins and causes their hemichannels to open. Cx26 may contribute to CO2-dependent regulation of breathing in mammals. Here, we show that the carbamylation motif occurs in a wide range of non-mammalian vertebrates and was likely present in the ancestor of all gnathostomes. While the carbamylation motif is essential for connexin CO2-sensitivity, it is not sufficient. In Cx26 of amphibia and lungfish, an extended C-terminal tail prevents CO2-evoked hemichannel opening despite the presence of the motif. Although Cx32 has a long C-terminal tail, Cx32 hemichannels open to CO2 because the tail is conformationally restricted by the presence of proline residues. The loss of the C-terminal tail of Cx26 in amniotes was an evolutionary innovation that created a connexin hemichannel with CO2-sensing properties suitable for the regulation of breathing.
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Affiliation(s)
| | - Sarbjit Nijjar
- School of Life Sciences, University of Warwick, Coventry, CV4 7AL UK
| | - Fokion Spanos
- School of Life Sciences, University of Warwick, Coventry, CV4 7AL UK
| | - Jonathan Cook
- School of Life Sciences, University of Warwick, Coventry, CV4 7AL UK
| | - Elizabeth de Wolf
- School of Life Sciences, University of Warwick, Coventry, CV4 7AL UK
| | - Maria Assunta Biscotti
- Dipartimento di Scienze della Vita e dell’Ambiente, Università Politecnica delle Marche, 60131 Ancona, Italy
| | - Marco Gerdol
- Dipartimento di Scienze della Vita, Università di Trieste, 34127 Trieste, Italy
| | - Nicholas Dale
- School of Life Sciences, University of Warwick, Coventry, CV4 7AL UK
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Wu Y, Proch KL, Teran FA, Lechtenberg RJ, Kothari H, Richerson GB. Chemosensitivity of Phox2b-expressing retrotrapezoid neurons is mediated in part by input from 5-HT neurons. J Physiol 2019; 597:2741-2766. [PMID: 30866045 PMCID: PMC6826216 DOI: 10.1113/jp277052] [Citation(s) in RCA: 31] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2018] [Accepted: 03/07/2019] [Indexed: 01/18/2023] Open
Abstract
KEY POINTS Neurons of the retrotrapezoid nucleus (RTN) and medullary serotonin (5-HT) neurons are both candidates for central CO2 /pH chemoreceptors, but it is not known how interactions between them influence their responses to pH. We found that RTN neurons in brain slices were stimulated by exogenous 5-HT and by heteroexchange release of endogenous 5-HT, and these responses were blocked by antagonists of 5-HT7 receptors. The pH response of RTN neurons in brain slices was markedly reduced by the same antagonists of 5-HT7 receptors. Similar results were obtained in dissociated, primary cell cultures prepared from the ventral medulla, where it was also found that the pH response of RTN neurons was blocked by preventing 5-HT synthesis and enhanced by blocking 5-HT reuptake. Exogenous 5-HT did not enable latent intrinsic RTN chemosensitivity. RTN neurons may play more of a role as relays from other central and peripheral chemoreceptors than as CO2 sensors. ABSTRACT Phox2b-expressing neurons in the retrotrapezoid nucleus (RTN) and serotonin (5-HT) neurons in the medullary raphe have both been proposed to be central respiratory chemoreceptors. How interactions between these two sets of neurons influence their responses to acidosis is not known. Here we recorded from mouse Phox2b+ RTN neurons in brain slices, and found that their response to moderate hypercapnic acidosis (pH 7.4 to ∼7.2) was markedly reduced by antagonists of 5-HT7 receptors. RTN neurons were stimulated in response to heteroexchange release of 5-HT, indicating that RTN neurons are sensitive to endogenous 5-HT. This electrophysiological behaviour was replicated in primary, dissociated cell cultures containing 5-HT and RTN neurons grown together. In addition, pharmacological inhibition of 5-HT synthesis in culture reduced RTN neuron chemosensitivity, and blocking 5-HT reuptake enhanced chemosensitivity. The effect of 5-HT on RTN neuron chemosensitivity was not explained by a mechanism whereby activation of 5-HT7 receptors enables or potentiates intrinsic chemosensitivity of RTN neurons, as exogenous 5-HT did not enhance the pH response. The ventilatory response to inhaled CO2 of mice was markedly decreased in vivo after systemic treatment with ketanserin, an antagonist of 5-HT2 and 5-HT7 receptors. These data indicate that 5-HT and RTN neurons may interact synergistically in a way that enhances the respiratory chemoreceptor response. The primary role of RTN neurons may be as relays and amplifiers of the pH response from 5-HT neurons and other chemoreceptors rather than as pH sensors themselves.
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Affiliation(s)
- Yuanming Wu
- Department of NeurologyUniversity of IowaIowa CityIA52242USA
| | - Katherine L. Proch
- Department of NeurologyUniversity of IowaIowa CityIA52242USA
- Graduate Program in NeuroscienceUniversity of IowaIowa CityIA52242USA
| | - Frida A. Teran
- Department of NeurologyUniversity of IowaIowa CityIA52242USA
- Graduate Program in NeuroscienceUniversity of IowaIowa CityIA52242USA
- Iowa Neuroscience InstituteUniversity of IowaIowa CityIA52242USA
| | | | - Harsh Kothari
- Department of PediatricsUniversity of IowaIowa CityIA52242USA
| | - George B. Richerson
- Department of NeurologyUniversity of IowaIowa CityIA52242USA
- Graduate Program in NeuroscienceUniversity of IowaIowa CityIA52242USA
- Department of Molecular Physiology & BiophysicsUniversity of IowaIowa CityIA52242USA
- Neurology ServiceVeterans Affairs Medical CenterIowa CityIA52242USA
- Iowa Neuroscience InstituteUniversity of IowaIowa CityIA52242USA
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Patrone LGA, Duarte JB, Bícego KC, Steiner AA, Romanovsky AA, Gargaglioni LH. TRPV1 Inhibits the Ventilatory Response to Hypoxia in Adult Rats, but Not the CO₂-Drive to Breathe. Pharmaceuticals (Basel) 2019; 12:ph12010019. [PMID: 30682830 PMCID: PMC6469189 DOI: 10.3390/ph12010019] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2018] [Revised: 11/27/2018] [Accepted: 12/07/2018] [Indexed: 12/31/2022] Open
Abstract
Receptors of the transient receptor potential (TRP) channels superfamily are expressed in many tissues and have different physiological functions. However, there are few studies investigating the role of these channels in cardiorespiratory control in mammals. We assessed the role of central and peripheral TRPV1 receptors in the cardiorespiratory responses to hypoxia (10% O2) and hypercapnia (7% CO2) by measuring pulmonary ventilation (V˙E), heart rate (HR), mean arterial pressure (MAP) and body temperature (Tb) of male Wistar rats before and after intraperitoneal (AMG9810 [2.85 µg/kg, 1 mL/kg]) or intracebroventricular (AMG9810 [2.85 µg/kg, 1 µL] or AMG7905 [28.5 μg/kg, 1 µL]) injections of TRPV1 antagonists. Central or peripheral injection of TRPV1 antagonists did not change cardiorespiratory parameters or Tb during room air and hypercapnic conditions. However, the hypoxic ventilatory response was exaggerated by both central and peripheral injection of AMG9810. In addition, the peripheral antagonist blunted the drop in Tb induced by hypoxia. Therefore, the current data provide evidence that TRPV1 channels exert an inhibitory modulation on the hypoxic drive to breathe and stimulate the Tb reduction during hypoxia.
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Affiliation(s)
- Luis Gustavo A Patrone
- Department of Animal Morphology and Physiology, Faculty of Agricultural and Veterinarian Sciences, UNESP at Jaboticabal, Rod. Prof. Paulo Donato Castellane s/n, Jaboticabal SP 14870-000, Brazil.
| | - Jaime B Duarte
- Department of Animal Morphology and Physiology, Faculty of Agricultural and Veterinarian Sciences, UNESP at Jaboticabal, Rod. Prof. Paulo Donato Castellane s/n, Jaboticabal SP 14870-000, Brazil.
| | - Kênia Cardoso Bícego
- Department of Animal Morphology and Physiology, Faculty of Agricultural and Veterinarian Sciences, UNESP at Jaboticabal, Rod. Prof. Paulo Donato Castellane s/n, Jaboticabal SP 14870-000, Brazil.
| | - Alexandre A Steiner
- Department of Immunology, Institute of Biomedical Sciences, University of Sao Paulo, Sao Paulo 05508-090, Brazil.
| | - Andrej A Romanovsky
- Thermoregulation and Systemic Inflammation Laboratory (FeverLab), Trauma Research, St. Joseph's Hospital and Medical Center, Phoenix, AZ 85013, USA.
| | - Luciane H Gargaglioni
- Department of Animal Morphology and Physiology, Faculty of Agricultural and Veterinarian Sciences, UNESP at Jaboticabal, Rod. Prof. Paulo Donato Castellane s/n, Jaboticabal SP 14870-000, Brazil.
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Marina N, Turovsky E, Christie IN, Hosford PS, Hadjihambi A, Korsak A, Ang R, Mastitskaya S, Sheikhbahaei S, Theparambil SM, Gourine AV. Brain metabolic sensing and metabolic signaling at the level of an astrocyte. Glia 2018; 66:1185-1199. [PMID: 29274121 PMCID: PMC5947829 DOI: 10.1002/glia.23283] [Citation(s) in RCA: 77] [Impact Index Per Article: 12.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2017] [Revised: 10/04/2017] [Accepted: 11/29/2017] [Indexed: 12/18/2022]
Abstract
Astrocytes support neuronal function by providing essential structural and nutritional support, neurotransmitter trafficking and recycling and may also contribute to brain information processing. In this article we review published results and report new data suggesting that astrocytes function as versatile metabolic sensors of central nervous system (CNS) milieu and play an important role in the maintenance of brain metabolic homeostasis. We discuss anatomical and functional features of astrocytes that allow them to detect and respond to changes in the brain parenchymal levels of metabolic substrates (oxygen and glucose), and metabolic waste products (carbon dioxide). We report data suggesting that astrocytes are also sensitive to circulating endocrine signals-hormones like ghrelin, glucagon-like peptide-1 and leptin, that have a major impact on the CNS mechanisms controlling food intake and energy balance. We discuss signaling mechanisms that mediate communication between astrocytes and neurons and consider how these mechanisms are recruited by astrocytes activated in response to various metabolic challenges. We review experimental data suggesting that astrocytes modulate the activities of the respiratory and autonomic neuronal networks that ensure adaptive changes in breathing and sympathetic drive in order to support the physiological and behavioral demands of the organism in ever-changing environmental conditions. Finally, we discuss evidence suggesting that altered astroglial function may contribute to the pathogenesis of disparate neurological, respiratory and cardiovascular disorders such as Rett syndrome and systemic arterial hypertension.
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Affiliation(s)
- Nephtali Marina
- Centre for Cardiovascular and Metabolic Neuroscience, Neuroscience, Physiology & PharmacologyUniversity College LondonLondonWC1E 6BTUnited Kingdom
- Research Department of Metabolism and Experimental Therapeutics, Division of MedicineUniversity College LondonLondonWC1E 6JJUnited Kingdom
| | - Egor Turovsky
- Laboratory of Intracellular SignallingInstitute of Cell Biophysics, Russian Academy of SciencesPushchinoRussia
| | - Isabel N Christie
- Centre for Cardiovascular and Metabolic Neuroscience, Neuroscience, Physiology & PharmacologyUniversity College LondonLondonWC1E 6BTUnited Kingdom
| | - Patrick S Hosford
- Centre for Cardiovascular and Metabolic Neuroscience, Neuroscience, Physiology & PharmacologyUniversity College LondonLondonWC1E 6BTUnited Kingdom
| | - Anna Hadjihambi
- Centre for Cardiovascular and Metabolic Neuroscience, Neuroscience, Physiology & PharmacologyUniversity College LondonLondonWC1E 6BTUnited Kingdom
| | - Alla Korsak
- Centre for Cardiovascular and Metabolic Neuroscience, Neuroscience, Physiology & PharmacologyUniversity College LondonLondonWC1E 6BTUnited Kingdom
| | - Richard Ang
- Centre for Cardiovascular and Metabolic Neuroscience, Neuroscience, Physiology & PharmacologyUniversity College LondonLondonWC1E 6BTUnited Kingdom
| | - Svetlana Mastitskaya
- Centre for Cardiovascular and Metabolic Neuroscience, Neuroscience, Physiology & PharmacologyUniversity College LondonLondonWC1E 6BTUnited Kingdom
| | - Shahriar Sheikhbahaei
- Centre for Cardiovascular and Metabolic Neuroscience, Neuroscience, Physiology & PharmacologyUniversity College LondonLondonWC1E 6BTUnited Kingdom
| | - Shefeeq M Theparambil
- Centre for Cardiovascular and Metabolic Neuroscience, Neuroscience, Physiology & PharmacologyUniversity College LondonLondonWC1E 6BTUnited Kingdom
| | - Alexander V Gourine
- Centre for Cardiovascular and Metabolic Neuroscience, Neuroscience, Physiology & PharmacologyUniversity College LondonLondonWC1E 6BTUnited Kingdom
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Neuromedin B Expression Defines the Mouse Retrotrapezoid Nucleus. J Neurosci 2017; 37:11744-11757. [PMID: 29066557 DOI: 10.1523/jneurosci.2055-17.2017] [Citation(s) in RCA: 54] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2017] [Revised: 10/09/2017] [Indexed: 11/21/2022] Open
Abstract
The retrotrapezoid nucleus (RTN) consists, by definition, of Phox2b-expressing, glutamatergic, non-catecholaminergic, noncholinergic neurons located in the parafacial region of the medulla oblongata. An unknown proportion of RTN neurons are central respiratory chemoreceptors and there is mounting evidence for biochemical diversity among these cells. Here, we used multiplexed in situ hybridization and single-cell RNA-Seq in male and female mice to provide a more comprehensive view of the phenotypic diversity of RTN neurons. We now demonstrate that the RTN of mice can be identified with a single and specific marker, Neuromedin B mRNA (Nmb). Most (∼75%) RTN neurons express low-to-moderate levels of Nmb and display chemoreceptor properties. Namely they are activated by hypercapnia, but not by hypoxia, and express proton sensors, TASK-2 and Gpr4. These Nmb-low RTN neurons also express varying levels of transcripts for Gal, Penk, and Adcyap1, and receptors for substance P, orexin, serotonin, and ATP. A subset of RTN neurons (∼20-25%), typically larger than average, express very high levels of Nmb mRNA. These Nmb-high RTN neurons do not express Fos after hypercapnia and have low-to-undetectable levels of Kcnk5 or Gpr4 transcripts; they also express Adcyap1, but are essentially devoid of Penk and Gal transcripts. In male rats, Nmb is also a marker of the RTN but, unlike in mice, this gene is expressed by other types of nearby neurons located within the ventromedial medulla. In sum, Nmb is a selective marker of the RTN in rodents; Nmb-low neurons, the vast majority, are central respiratory chemoreceptors, whereas Nmb-high neurons likely have other functions.SIGNIFICANCE STATEMENT Central respiratory chemoreceptors regulate arterial PCO2 by adjusting lung ventilation. Such cells have recently been identified within the retrotrapezoid nucleus (RTN), a brainstem nucleus defined by genetic lineage and a cumbersome combination of markers. Using single-cell RNA-Seq and multiplexed in situ hybridization, we show here that a single marker, Neuromedin B mRNA (Nmb), identifies RTN neurons in rodents. We also suggest that >75% of these Nmb neurons are chemoreceptors because they are strongly activated by hypercapnia and express high levels of proton sensors (Kcnk5 and Gpr4). The other RTN neurons express very high levels of Nmb, but low levels of Kcnk5/Gpr4/pre-pro-galanin/pre-pro-enkephalin, and do not respond to hypercapnia. Their function is unknown.
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Tseng CT, Sakai DM, Libin M, Mostowy M, Cheetham J, Campoy L, Gleed RD, Martin-Flores M. Partial neuromuscular block impairs arytenoid abduction during hypercarbic challenge in anesthetized dogs. Vet Anaesth Analg 2017; 44:1049-1056. [PMID: 28967478 DOI: 10.1016/j.vaa.2017.05.003] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2016] [Revised: 03/27/2017] [Accepted: 05/05/2017] [Indexed: 11/26/2022]
Abstract
OBJECTIVE To evaluate the effect of two levels of partial neuromuscular block (NMB) on arytenoid abduction, tidal volume (VT) and peak inspiratory flow (PIF) in response to a hypercarbic challenge in anesthetized dogs. STUDY DESIGN Prospective laboratory study. ANIMALS Eleven healthy male Beagle dogs aged 3-5 years. METHODS Dogs were anesthetized with propofol and dexmedetomidine infusions. The rima glottidis was observed via an endoscope placed through a laryngeal mask airway. Atracurium infusion was titrated to obtain two levels of partial NMB. The normalized glottal gap area (NGGA; glottal gap area normalized to height squared of rima glottidis) at peak inspiration during a hypercarbic challenge (10% CO2 inspired for 1 minute) was measured at baseline, during mild [train-of-four (TOF) ratio 0.4-0.6] and shallow (TOF ratio 0.7-0.9) NMB, and 30 minutes after spontaneous recovery from NMB. The VT and PIF were measured at the same time points and compared using anova for repeated measures and Tukey's post hoc tests. RESULTS The NGGA and VT were significantly lower than baseline during both levels of partial NMB with no difference between mild and shallow NMB (p < 0.05). They returned to baseline values after spontaneous recovery from NMB. PIF was not altered significantly during partial NMB. CONCLUSIONS AND CLINICAL RELEVANCE The NGGA and VT at peak inspiration in response to a hypercarbic challenge were reduced during partial NMB block, with decreased abduction of the arytenoid cartilages. This dysfunction was present even at shallow levels of NMB.
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Affiliation(s)
- Chia T Tseng
- Department of Clinical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY, USA
| | - Daniel M Sakai
- Department of Clinical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY, USA
| | - Madeline Libin
- Department of Clinical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY, USA
| | - Monika Mostowy
- Department of Clinical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY, USA
| | - Jonathan Cheetham
- Department of Clinical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY, USA
| | - Luis Campoy
- Department of Clinical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY, USA
| | - Robin D Gleed
- Department of Clinical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY, USA
| | - Manuel Martin-Flores
- Department of Clinical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY, USA.
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23
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Oliveira LM, Tuppy M, Moreira TS, Takakura AC. Role of the locus coeruleus catecholaminergic neurons in the chemosensory control of breathing in a Parkinson's disease model. Exp Neurol 2017; 293:172-180. [DOI: 10.1016/j.expneurol.2017.04.006] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2016] [Revised: 04/11/2017] [Accepted: 04/14/2017] [Indexed: 01/05/2023]
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24
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Laouafa S, Perrin-Terrin AS, Jeton F, Elliot-Portal E, Tam R, Bodineau L, Voituron N, Soliz J. Pharmacological, but not genetic, alteration of neural Epo modifies the CO 2/H + central chemosensitivity in postnatal mice. Respir Physiol Neurobiol 2017; 242:73-79. [PMID: 28396201 DOI: 10.1016/j.resp.2017.04.003] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2016] [Revised: 03/24/2017] [Accepted: 04/05/2017] [Indexed: 11/24/2022]
Abstract
Cerebral erythropoietin (Epo) plays a crucial role for respiratory control in newborn rodents. We showed previously that soluble Epo receptor (sEpoR: an Epo antagonist) reduces basal ventilation and hypoxic hyperventilation at postnatal day 10 (P10) and in adult mice. However, at these ages (P10 and adulthood), Epo had no effect on central chemosensitivity. Nevertheless, it is known that the sensitivity to CO2/H+ during the mammalian respiratory network maturation process is age-dependent. Accordingly, in this study we wanted to test the hypothesis that cerebral Epo is involved in the breathing stimulation induced by the activation of central CO2/H+ chemoreceptors at earlier postnatal ages. To this end, en bloc brainstem-spinal cord preparations were obtained from P4 mice and the fictive breathing response to CO2-induced acidosis or metabolic acidosis was analyzed. This age (P4) was chosen because previous research from our laboratory showed that Epo altered (in a dose- and time-dependent manner) the fictive ventilation elicited in brainstem-spinal cord preparations. Moreover, as it was observed that peripheral chemoreceptors determined the respiratory sensitivity of central chemoreceptors to CO2, the use of this technique restricts our observations to central modulation. Our results did not show differences between preparations from control and transgenic animals (Tg21: overexpressing cerebral Epo; Epo-TAgh: cerebral Epo deficient mice). However, when Tg21 brainstem preparations were incubated for 1h with sEpoR, or with inhibitors of ERK/Akt (thus blocking the activation of the Epo molecular pathway), the fictive breathing response to CO2-induced acidosis was blunted. Our data suggest that variation of the Epo/sEpoR ratio is central to breathing modulation during CO2 challenges, and calls attention to clinical perspectives based on the use of Epo drugs at birth in hypoventilation cases.
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Affiliation(s)
- Sofien Laouafa
- Université Laval, Faculté de Médecine, Centre de Recherche Institut universitaire de cardiologie et de pneumologie de Québec, Département de Pédiatrie, Québec, QC, Canada; LEHNA, UMR CNRS 5023, Ecologie des Hydrosystèmes Naturels et Anthropisés, Université de Lyon, Université Lyon 1, ENTPE, 6 rue Raphael Dubois, 69622 Villeurbanne, France
| | - Anne-Sophie Perrin-Terrin
- Université Paris 13, Sorbonne Paris Cité, UFR SMBH, Laboratoire "Hypoxie et poumons", EA 2363, 93017 Bobigny, France; Sorbonne Universités, UPMC Univ Paris 06, INSERM, UMR_S1158 Neurophysiologie Respiratoire Expérimentale et Clinique, F-75013, Paris, France
| | - Florine Jeton
- Université Paris 13, Sorbonne Paris Cité, UFR SMBH, Laboratoire "Hypoxie et poumons", EA 2363, 93017 Bobigny, France
| | - Elizabeth Elliot-Portal
- Université Laval, Faculté de Médecine, Centre de Recherche Institut universitaire de cardiologie et de pneumologie de Québec, Département de Pédiatrie, Québec, QC, Canada; Molecular biology and Biotechnology Institute, Universidad Mayor de San Andres, La Paz, Bolivia
| | - Rose Tam
- Université Laval, Faculté de Médecine, Centre de Recherche Institut universitaire de cardiologie et de pneumologie de Québec, Département de Pédiatrie, Québec, QC, Canada
| | - Laurence Bodineau
- Sorbonne Universités, UPMC Univ Paris 06, INSERM, UMR_S1158 Neurophysiologie Respiratoire Expérimentale et Clinique, F-75013, Paris, France
| | - Nicolas Voituron
- Université Paris 13, Sorbonne Paris Cité, UFR SMBH, Laboratoire "Hypoxie et poumons", EA 2363, 93017 Bobigny, France
| | - Jorge Soliz
- Université Laval, Faculté de Médecine, Centre de Recherche Institut universitaire de cardiologie et de pneumologie de Québec, Département de Pédiatrie, Québec, QC, Canada; Molecular biology and Biotechnology Institute, Universidad Mayor de San Andres, La Paz, Bolivia.
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25
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Müller CJT, Quintino-dos-Santos JW, Schimitel FG, Tufik S, Beijamini V, Canteras NS, Schenberg LC. On the verge of a respiratory-type panic attack: Selective activations of rostrolateral and caudoventrolateral periaqueductal gray matter following short-lasting escape to a low dose of potassium cyanide. Neuroscience 2017; 348:228-240. [DOI: 10.1016/j.neuroscience.2017.02.022] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2016] [Revised: 12/05/2016] [Accepted: 02/12/2017] [Indexed: 10/20/2022]
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26
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Boutin RCT, Alsahafi Z, Pagliardini S. Cholinergic modulation of the parafacial respiratory group. J Physiol 2016; 595:1377-1392. [PMID: 27808424 DOI: 10.1113/jp273012] [Citation(s) in RCA: 37] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2016] [Accepted: 10/28/2016] [Indexed: 01/06/2023] Open
Abstract
KEY POINTS This study investigates the effects of cholinergic transmission on the expiratory oscillator, the parafacial respiratory group (pFRG) in urethane anaesthetized adult rats. Local inhibition of the acetyl cholinesterase enzyme induced activation of expiratory abdominal muscles and active expiration. Local application of the cholinomimetic carbachol elicited recruitment of late expiratory neurons, expiratory abdominal muscle activity and active expiration. This effect was antagonized by local application of the muscarinic antagonists scopolamine, J104129 and 4DAMP. We observed distinct physiological responses between the more medial chemosensitive region of the retrotrapezoid nucleus and the more lateral region of pFRG. These results support the hypothesis that pFRG is under cholinergic neuromodulation and the region surrounding the facial nucleus contains a group of neurons with distinct physiological roles. ABSTRACT Active inspiration and expiration are opposing respiratory phases generated by two separate oscillators in the brainstem: inspiration driven by a neuronal network located in the preBötzinger complex (preBötC) and expiration driven by a neuronal network located in the parafacial respiratory group (pFRG). While continuous activity of the preBötC is necessary for maintaining ventilation, the pFRG behaves as a conditional expiratory oscillator, being silent in resting conditions and becoming rhythmically active in the presence of increased respiratory drive (e.g. hypoxia, hypercapnia, exercise and through release of inhibition). Recent evidence from our laboratory suggests that expiratory activity in the principal expiratory pump muscles, the abdominals, is modulated in a state-dependent fashion, frequently occurring during periods of REM sleep. We hypothesized that acetylcholine, a neurotransmitter released in wakefulness and REM sleep by mesopontine structures, contributes to the activation of pFRG neurons and thus acts to promote the recruitment of expiratory abdominal muscle activity. We investigated the stimulatory effect of cholinergic neurotransmission on pFRG activity and recruitment of active expiration in vivo under anaesthesia. We demonstrate that local application of the acetylcholinesterase inhibitor physostigmine into the pFRG potentiated expiratory activity. Furthermore, local application of the cholinomimetic carbachol into the pFRG activated late expiratory neurons and induced long lasting rhythmic active expiration. This effect was completely abolished by pre-application of the muscarinic antagonist scopolamine, and more selective M3 antagonists 4DAMP and J104129. We conclude that cholinergic muscarinic transmission contributes to excitation of pFRG neurons and promotes both active recruitment of abdominal muscles and active expiratory flow.
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Affiliation(s)
- Rozlyn C T Boutin
- Department of Physiology, Women and Children's Health Research Institute & Neuroscience and Mental Health Institute, University of Alberta, 3020F Katz Group Centre, Edmonton, AB, T6G 2E1, Canada
| | - Zaki Alsahafi
- Department of Physiology, Women and Children's Health Research Institute & Neuroscience and Mental Health Institute, University of Alberta, 3020F Katz Group Centre, Edmonton, AB, T6G 2E1, Canada
| | - Silvia Pagliardini
- Department of Physiology, Women and Children's Health Research Institute & Neuroscience and Mental Health Institute, University of Alberta, 3020F Katz Group Centre, Edmonton, AB, T6G 2E1, Canada
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Huckstepp RTR, Llaudet E, Gourine AV. CO2-Induced ATP-Dependent Release of Acetylcholine on the Ventral Surface of the Medulla Oblongata. PLoS One 2016; 11:e0167861. [PMID: 27936179 PMCID: PMC5148032 DOI: 10.1371/journal.pone.0167861] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2016] [Accepted: 11/21/2016] [Indexed: 12/04/2022] Open
Abstract
Complex mechanisms that detect changes in brainstem parenchymal PCO2/[H+] and trigger adaptive changes in lung ventilation are responsible for central respiratory CO2 chemosensitivity. Previous studies of chemosensory signalling pathways suggest that at the level of the ventral surface of the medulla oblongata (VMS), CO2-induced changes in ventilation are (at least in part) mediated by the release and actions of ATP and/or acetylcholine (ACh). Here we performed simultaneous real-time biosensor recordings of CO2-induced ATP and ACh release from the VMS in vivo and in vitro, to test the hypothesis that central respiratory CO2 chemosensory transduction involves simultaneous recruitment of purinergic and cholinergic signalling pathways. In anaesthetised and artificially ventilated rats, an increase in inspired CO2 triggered ACh release on the VMS with a peak amplitude of ~5 μM. Release of ACh was only detected after the onset of CO2-induced activation of the respiratory activity and was markedly reduced (by ~70%) by ATP receptor blockade. In horizontal slices of the VMS, CO2-induced release of ATP was reliably detected, whereas CO2 or bath application of ATP (100 μM) failed to trigger release of ACh. These results suggest that during hypercapnia locally produced ATP induces or potentiates the release of ACh (likely from the medullary projections of distal groups of cholinergic neurones), which may also contribute to the development and/or maintenance of the ventilatory response to CO2.
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Affiliation(s)
- Robert T. R. Huckstepp
- Centre for Cardiovascular and Metabolic Neuroscience, Neuroscience, Physiology and Pharmacology, University College London, London, United Kingdom
- School of Life Sciences, University of Warwick, Coventry, United Kingdom
| | - Enrique Llaudet
- School of Life Sciences, University of Warwick, Coventry, United Kingdom
| | - Alexander V. Gourine
- Centre for Cardiovascular and Metabolic Neuroscience, Neuroscience, Physiology and Pharmacology, University College London, London, United Kingdom
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28
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Vollmer LL, Ghosal S, McGuire JL, Ahlbrand RL, Li KY, Santin JM, Ratliff-Rang CA, Patrone LGA, Rush J, Lewkowich IP, Herman JP, Putnam RW, Sah R. Microglial Acid Sensing Regulates Carbon Dioxide-Evoked Fear. Biol Psychiatry 2016; 80:541-51. [PMID: 27422366 PMCID: PMC5014599 DOI: 10.1016/j.biopsych.2016.04.022] [Citation(s) in RCA: 56] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/13/2015] [Revised: 04/08/2016] [Accepted: 04/13/2016] [Indexed: 12/11/2022]
Abstract
BACKGROUND Carbon dioxide (CO2) inhalation, a biological challenge and pathologic marker in panic disorder, evokes intense fear and panic attacks in susceptible individuals. The molecular identity and anatomic location of CO2-sensing systems that translate CO2-evoked fear remain unclear. We investigated contributions of microglial acid sensor T cell death-associated gene-8 (TDAG8) and microglial proinflammatory responses in CO2-evoked behavioral and physiological responses. METHODS CO2-evoked freezing, autonomic, and respiratory responses were assessed in TDAG8-deficient ((-/-)) and wild-type ((+/+)) mice. Involvement of TDAG8-dependent microglial activation and proinflammatory cytokine interleukin (IL)-1β with CO2-evoked responses was investigated using microglial blocker, minocycline, and IL-1β antagonist IL-1RA. CO2-chemosensitive firing responses using single-cell patch clamping were measured in TDAG8(-/-) and TDAG8(+/+) mice to gain functional insights. RESULTS TDAG8 expression was localized in microglia enriched within the sensory circumventricular organs. TDAG8(-/-) mice displayed attenuated CO2-evoked freezing and sympathetic responses. TDAG8 deficiency was associated with reduced microglial activation and proinflammatory cytokine IL-1β within the subfornical organ. Central infusion of microglial activation blocker minocycline and IL-1β antagonist IL-1RA attenuated CO2-evoked freezing. Finally, CO2-evoked neuronal firing in patch-clamped subfornical organ neurons was dependent on acid sensor TDAG8 and IL-1β. CONCLUSIONS Our data identify TDAG8-dependent microglial acid sensing as a unique chemosensor for detecting and translating hypercapnia to fear-associated behavioral and physiological responses, providing a novel mechanism for homeostatic threat detection of relevance to psychiatric conditions such as panic disorder.
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Affiliation(s)
- Lauren Larke Vollmer
- Department of Psychiatry and Behavioral Neuroscience, University of Cincinnati, Cincinnati; Neuroscience Graduate Program, University of Cincinnati, Cincinnati
| | - Sriparna Ghosal
- Department of Psychiatry and Behavioral Neuroscience, University of Cincinnati, Cincinnati; Neuroscience Graduate Program, University of Cincinnati, Cincinnati
| | - Jennifer L McGuire
- Department of Psychiatry and Behavioral Neuroscience, University of Cincinnati, Cincinnati
| | - Rebecca L Ahlbrand
- Department of Psychiatry and Behavioral Neuroscience, University of Cincinnati, Cincinnati
| | - Ke-Yong Li
- Department of Neuroscience, Cell Biology and Physiology, Wright State University, Dayton
| | - Joseph M Santin
- Department of Biological Sciences, Wright State University, Dayton
| | | | - Luis G A Patrone
- Department of Animal Morphology and Physiology, São Paulo State University, FCAV, Jaboticabal, São Paulo, Brazil
| | - Jennifer Rush
- Department of Psychiatry and Behavioral Neuroscience, University of Cincinnati, Cincinnati
| | - Ian P Lewkowich
- Division of Immunobiology, Children's Hospital Medical Center, Cincinnati
| | - James P Herman
- Department of Psychiatry and Behavioral Neuroscience, University of Cincinnati, Cincinnati; Neuroscience Graduate Program, University of Cincinnati, Cincinnati
| | - Robert W Putnam
- Department of Neuroscience, Cell Biology and Physiology, Wright State University, Dayton
| | - Renu Sah
- Department of Psychiatry and Behavioral Neuroscience, University of Cincinnati, Cincinnati; Neuroscience Graduate Program, University of Cincinnati, Cincinnati; Veterans Affairs (VA) Medical Center, Cincinnati, Ohio.
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Moreira TS, Takakura AC, Czeisler C, Otero JJ. Respiratory and autonomic dysfunction in congenital central hypoventilation syndrome. J Neurophysiol 2016; 116:742-52. [PMID: 27226447 PMCID: PMC6208311 DOI: 10.1152/jn.00026.2016] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2016] [Accepted: 05/25/2016] [Indexed: 12/22/2022] Open
Abstract
The developmental lineage of the PHOX2B-expressing neurons in the retrotrapezoid nucleus (RTN) has been extensively studied. These cells are thought to function as central respiratory chemoreceptors, i.e., the mechanism by which brain Pco2 regulates breathing. The molecular and cellular basis of central respiratory chemoreception is based on the detection of CO2 via intrinsic proton receptors (TASK-2, GPR4) as well as synaptic input from peripheral chemoreceptors and other brain regions. Murine models of congenital central hypoventilation syndrome designed with PHOX2B mutations have suggested RTN neuron agenesis. In this review, we examine, through human and experimental animal models, how a restricted number of neurons that express the transcription factor PHOX2B play a crucial role in the control of breathing and autonomic regulation.
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Affiliation(s)
- Thiago S Moreira
- Department of Physiology and Biophysics, Institute of Biomedical Sciences, University of Sao Paulo, Sao Paulo, Brazil;
| | - Ana C Takakura
- Department of Pharmacology, Institute of Biomedical Sciences, University of Sao Paulo, Sao Paulo, Brazil; and
| | - Catherine Czeisler
- The Ohio State University, College of Medicine, Department of Pathology, Division of Neuropathology, Columbus, Ohio
| | - Jose J Otero
- The Ohio State University, College of Medicine, Department of Pathology, Division of Neuropathology, Columbus, Ohio
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30
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Guyenet PG, Bayliss DA, Stornetta RL, Ludwig MG, Kumar NN, Shi Y, Burke PGR, Kanbar R, Basting TM, Holloway BB, Wenker IC. Proton detection and breathing regulation by the retrotrapezoid nucleus. J Physiol 2016; 594:1529-51. [PMID: 26748771 PMCID: PMC4799966 DOI: 10.1113/jp271480] [Citation(s) in RCA: 56] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2015] [Accepted: 01/04/2016] [Indexed: 01/26/2023] Open
Abstract
We discuss recent evidence which suggests that the principal central respiratory chemoreceptors are located within the retrotrapezoid nucleus (RTN) and that RTN neurons are directly sensitive to [H(+) ]. RTN neurons are glutamatergic. In vitro, their activation by [H(+) ] requires expression of a proton-activated G protein-coupled receptor (GPR4) and a proton-modulated potassium channel (TASK-2) whose transcripts are undetectable in astrocytes and the rest of the lower brainstem respiratory network. The pH response of RTN neurons is modulated by surrounding astrocytes but genetic deletion of RTN neurons or deletion of both GPR4 and TASK-2 virtually eliminates the central respiratory chemoreflex. Thus, although this reflex is regulated by innumerable brain pathways, it seems to operate predominantly by modulating the discharge rate of RTN neurons, and the activation of RTN neurons by hypercapnia may ultimately derive from their intrinsic pH sensitivity. RTN neurons increase lung ventilation by stimulating multiple aspects of breathing simultaneously. They stimulate breathing about equally during quiet wake and non-rapid eye movement (REM) sleep, and to a lesser degree during REM sleep. The activity of RTN neurons is regulated by inhibitory feedback and by excitatory inputs, notably from the carotid bodies. The latter input operates during normo- or hypercapnia but fails to activate RTN neurons under hypocapnic conditions. RTN inhibition probably limits the degree of hyperventilation produced by hypocapnic hypoxia. RTN neurons are also activated by inputs from serotonergic neurons and hypothalamic neurons. The absence of RTN neurons probably underlies the sleep apnoea and lack of chemoreflex that characterize congenital central hypoventilation syndrome.
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Affiliation(s)
- Patrice G Guyenet
- Department of Pharmacology, University of Virginia, Charlottesville, VA, 22908, USA
| | - Douglas A Bayliss
- Department of Pharmacology, University of Virginia, Charlottesville, VA, 22908, USA
| | - Ruth L Stornetta
- Department of Pharmacology, University of Virginia, Charlottesville, VA, 22908, USA
| | | | - Natasha N Kumar
- Department of Pharmacology, University of Virginia, Charlottesville, VA, 22908, USA
| | - Yingtang Shi
- Department of Pharmacology, University of Virginia, Charlottesville, VA, 22908, USA
| | - Peter G R Burke
- Department of Pharmacology, University of Virginia, Charlottesville, VA, 22908, USA
| | - Roy Kanbar
- Department of Pharmaceutical Sciences, Lebanese American University, Beyrouth, Lebanon
| | - Tyler M Basting
- Department of Pharmacology, University of Virginia, Charlottesville, VA, 22908, USA
| | - Benjamin B Holloway
- Department of Pharmacology, University of Virginia, Charlottesville, VA, 22908, USA
| | - Ian C Wenker
- Department of Pharmacology, University of Virginia, Charlottesville, VA, 22908, USA
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31
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Role of Astrocytes in Central Respiratory Chemoreception. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2016; 949:109-145. [PMID: 27714687 DOI: 10.1007/978-3-319-40764-7_6] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
Astrocytes perform various homeostatic functions in the nervous system beyond that of a supportive or metabolic role for neurons. A growing body of evidence indicates that astrocytes are crucial for central respiratory chemoreception. This review presents a classical overview of respiratory central chemoreception and the new evidence for astrocytes as brainstem sensors in the respiratory response to hypercapnia. We review properties of astrocytes for chemosensory function and for modulation of the respiratory network. We propose that astrocytes not only mediate between CO2/H+ levels and motor responses, but they also allow for two emergent functions: (1) Amplifying the responses of intrinsic chemosensitive neurons through feedforward signaling via gliotransmitters and; (2) Recruiting non-intrinsically chemosensitive cells thanks to volume spreading of signals (calcium waves and gliotransmitters) to regions distant from the CO2/H+ sensitive domains. Thus, astrocytes may both increase the intensity of the neuron responses at the chemosensitive sites and recruit of a greater number of respiratory neurons to participate in the response to hypercapnia.
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32
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Abstract
Recent advances have clarified how the brain detects CO2 to regulate breathing (central respiratory chemoreception). These mechanisms are reviewed and their significance is presented in the general context of CO2/pH homeostasis through breathing. At rest, respiratory chemoreflexes initiated at peripheral and central sites mediate rapid stabilization of arterial PCO2 and pH. Specific brainstem neurons (e.g., retrotrapezoid nucleus, RTN; serotonergic) are activated by PCO2 and stimulate breathing. RTN neurons detect CO2 via intrinsic proton receptors (TASK-2, GPR4), synaptic input from peripheral chemoreceptors and signals from astrocytes. Respiratory chemoreflexes are arousal state dependent whereas chemoreceptor stimulation produces arousal. When abnormal, these interactions lead to sleep-disordered breathing. During exercise, central command and reflexes from exercising muscles produce the breathing stimulation required to maintain arterial PCO2 and pH despite elevated metabolic activity. The neural circuits underlying central command and muscle afferent control of breathing remain elusive and represent a fertile area for future investigation.
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Affiliation(s)
- Patrice G Guyenet
- Department of Pharmacology, University of Virginia, 1340 Jefferson Park Avenue, Charlottesville, VA 22908-0735, USA.
| | - Douglas A Bayliss
- Department of Pharmacology, University of Virginia, 1340 Jefferson Park Avenue, Charlottesville, VA 22908-0735, USA
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Translational approach to studying panic disorder in rats: hits and misses. Neurosci Biobehav Rev 2015; 46 Pt 3:472-96. [PMID: 25316571 DOI: 10.1016/j.neubiorev.2014.10.002] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2014] [Revised: 09/26/2014] [Accepted: 10/01/2014] [Indexed: 12/30/2022]
Abstract
Panic disorder (PD) patients are specifically sensitive to 5–7% carbon dioxide. Another startling feature of clinical panic is the counterintuitive lack of increments in ‘stress hormones’. PD is also more frequent in women and highly comorbid with childhood separation anxiety (CSA). On the other hand, increasing evidence suggests that panic is mediated at dorsal periaqueductal grey matter (DPAG). In line with prior studies showing that DPAG-evoked panic-like behaviours are attenuated by clinically-effective treatments with panicolytics, we show here that (i) the DPAG harbors a hypoxia-sensitive alarm system, which is activated by hypoxia and potentiated by hypercapnia, (ii) the DPAG suffocation alarm system is inhibited by clinically-effective treatments with panicolytics, (iii) DPAG stimulations do not increase stress hormones in the absence of physical exertion, (iv) DPAG-evoked panic-like behaviours are facilitated in neonatally-isolated adult rats, a model of CSA, and (v) DPAG-evoked responses are enhanced in the late diestrus of female rats. Data are consistent with the DPAG mediation of both respiratory and non-respiratory types of panic attacks.
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34
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Abstract
In conscious mammals, hypoxia or hypercapnia stimulates breathing while theoretically exerting opposite effects on central respiratory chemoreceptors (CRCs). We tested this theory by examining how hypoxia and hypercapnia change the activity of the retrotrapezoid nucleus (RTN), a putative CRC and chemoreflex integrator. Archaerhodopsin-(Arch)-transduced RTN neurons were reversibly silenced by light in anesthetized rats. We bilaterally transduced RTN and nearby C1 neurons with Arch (PRSx8-ArchT-EYFP-LVV) and measured the cardiorespiratory consequences of Arch activation (10 s) in conscious rats during normoxia, hypoxia, or hyperoxia. RTN photoinhibition reduced breathing equally during non-REM sleep and quiet wake. Compared with normoxia, the breathing frequency reduction (Δf(R)) was larger in hyperoxia (65% FiO2), smaller in 15% FiO2, and absent in 12% FiO2. Tidal volume changes (ΔV(T)) followed the same trend. The effect of hypoxia on Δf(R) was not arousal-dependent but was reversed by reacidifying the blood (acetazolamide; 3% FiCO2). Δf(R) was highly correlated with arterial pH up to arterial pH (pHa) 7.5 with no frequency inhibition occurring above pHa 7.53. Blood pressure was minimally reduced suggesting that C1 neurons were very modestly inhibited. In conclusion, RTN neurons regulate eupneic breathing about equally during both sleep and wake. RTN neurons are the first putative CRCs demonstrably silenced by hypocapnic hypoxia in conscious mammals. RTN neurons are silent above pHa 7.5 and increasingly active below this value. During hyperoxia, RTN activation maintains breathing despite the inactivity of the carotid bodies. Finally, during hypocapnic hypoxia, carotid body stimulation increases breathing frequency via pathways that bypass RTN.
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35
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Yazawa I, Shioda S. Reciprocal functional interactions between the respiration/circulation center, the upper spinal cord, and the trigeminal system. Transl Neurosci 2015; 6:87-102. [PMID: 28123792 PMCID: PMC4936616 DOI: 10.1515/tnsci-2015-0008] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2014] [Accepted: 01/19/2015] [Indexed: 11/15/2022] Open
Abstract
The interplay of neural discharge patterns involved in "respiration", "circulation", "opening movements in the mandible", and "locomotion" was investigated electrophysiologically in a decerebrate and arterially perfused in situ rat preparation. Sympathetic tone increased with increases in perfusion flow rate. All nerve discharges became clearly organized into discharge episodes of increasing frequency and duration punctuated by quiescent periods as the perfusion flow rate increased at 26°C. The modulated sympathetic tone at 10× total blood volume/ min activated the forelimb pattern generator and spontaneously generated fictive forelimb movement during discharge episodes. The coupling rhythm of respiration and locomotion during motion occurred at frequency ratios ranges of 1:2 and 1:3. Small increases in systemic pressure were always generated after the initiation of motion. Opening movements in the mandible, occurring during the inspiratory phase at all tested flow rates, were generated in both the inspiratory and expiratory phases during motion. Although the central mechanism for the entrainment of respiratory and locomotor rhythms has not been identified, a spinal-feedback mechanism generating fictive locomotion in the upper spinal cord contributed to generating the opening movement in the mandible in the expiratory phase during motion. The existence of this mechanism implies that there is a reciprocal functional interaction between the brainstem and the spinal cord, whereby the intake and output of air by the lungs is efficiently improved during movement by both nasal and mouth breathing. These results suggest that this reciprocal functional interaction plays an important role in increasing oxygenated blood flow during locomotion.
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Affiliation(s)
- Itaru Yazawa
- Department of Anatomy, Showa University School of Medicine, 1-5-8 Hatanodai, Shinagawa-ku, Tokyo 142-8555, Japan
| | - Seiji Shioda
- Department of Anatomy, Showa University School of Medicine, 1-5-8 Hatanodai, Shinagawa-ku, Tokyo 142-8555, Japan
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36
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Cheetham J, Jones A, Martin-Flores M. Effect of inhaled carbon dioxide on laryngeal abduction. J Appl Physiol (1985) 2015; 118:489-94. [DOI: 10.1152/japplphysiol.00469.2014] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Hypercapnia produces a profound effect on respiratory drive and upper airway function to maintain airway patency. Previous work has evaluated the effects of hypercapnia on the sole arytenoid abductor, the posterior cricoarytenoid (PCA), using indirect measures of function, such as electromyography and direct nerve recording. Here we describe a novel method to evaluate PCA function in anesthetized animals and use this method to determine the effects of hypercapnia on PCA function. Eight dogs were anesthetized, and a laryngeal mask airway was used, in combination with high-speed videoendoscopy, to evaluate laryngeal function. A stepwise increase in inspired partial pressure of CO2 produced marked arytenoid abduction above 70-mmHg end-tidal CO2 (ETCO2) ( P < 0.001). Glottic length increased above 80-mmHg ETCO2 ( P < 0.02), and this lead to underrepresentation of changes in glottic area, if standard measures of glottic area (normalized glottic gap area) were used. Use of a known scale to determine absolute glottic area demonstrated no plateau with increasing ETCO2 up to 120 mmHg. Ventilatory parameters also continued to increase with no evidence of a maximal response. In a second anesthetic episode, repeated bursts of transient hypercapnia for 60 s with an ETCO2 of 90 mmHg produced a 43–55% increase in glottic area ( P < 0.001) at or shortly after the end of the hypercapnic burst. A laryngeal mask airway can be used in combination with videoendoscopy to precisely determine changes in laryngeal dimensions with high temporal resolution. Absolute glottic area more precisely represents PCA function than normalized glottic gap area at moderate levels of hypercapnia.
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37
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Nishi T. Carbon dioxide sensitivity and its role in multifunctional neurons in the mollusk Onchidium. Comp Biochem Physiol A Mol Integr Physiol 2014; 179:172-81. [PMID: 25446937 DOI: 10.1016/j.cbpa.2014.10.007] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2014] [Revised: 07/30/2014] [Accepted: 10/16/2014] [Indexed: 11/17/2022]
Abstract
Intrinsically photoresponsive neurons in the abdominal ganglion of the amphibious mollusk Onchidium named Ip-1 and Ip-2 (Ip-1/2) react to several different stimuli. These neurons respond to light with slow hyperpolarization and to CO2 stimulation with slow depolarization. In this study, increasing the concentration of CO2 in the air caused hyperventilation and enlargement of the pneumostome in the intact animal. In a semi-intact preparation, pouring artificial seawater (ASW) with dissolved CO2 onto the central ganglia caused the previously closed pneumostome to open. In an ASW environment, Ip-1/2 neurons depolarized even under conditions of constant pH (alkaline ASW) and after dissolution of CO2. This depolarization prolonged the firing of action potentials in Ip-1/2 neurons. Adding protons (H+) to ASW caused Ip-1/2 depolarization only when the neurons' membranes were depolarized to a potential above the resting potential. Furthermore, in the presence of the carbonic anhydrase inhibitor acetazolamide (AZ), CO2-induced excitation in Ip-1/2 neurons was increased in both normal and alkaline ASW. These results suggest that when dissolved in ASW, CO2 directly induced the depolarizing response in Ip-1/2 neurons. Since Ip-1/2 neurons participate in pneumostome opening, these results suggest that increased CO2 levels in ASW directly stimulate CO2-sensitive central neurons, promoting ventilation.
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38
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Yazawa I. Reciprocal functional interactions between the brainstem and the lower spinal cord. Front Neurosci 2014; 8:124. [PMID: 24910591 PMCID: PMC4039168 DOI: 10.3389/fnins.2014.00124] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2014] [Accepted: 05/07/2014] [Indexed: 11/18/2022] Open
Abstract
The interplay of the neuronal discharge patterns regarding respiration and locomotion was investigated using electrophysiological techniques in a decerebrate and arterially perfused in situ mouse preparation. The phrenic, tibial, and/or peroneal nerve discharge became clearly organized into discharge episodes of increasing frequency and duration, punctuated by periods of quiescence as the perfusion flow rate increased at room temperature. The modulated sympathetic tone induced by the hyperoxic/normocapnic state was found to activate the locomotor pattern generator (LPG) via descending pathways and generate a left and right alternating discharge during discharge episodes in the motor nerves. The rhythm coupling of respiration and locomotion occurred at a 1:1 frequency ratio. Although the phrenic discharge synchronized with the tibial discharge at all flow rates tested, the time lag between peaks of the two discharges during locomotion was ≈400 ms rather than ≈200 ms, suggesting spinal feedback via ascending pathways. The incidence of the phrenic and tibial discharge episodes decreased by ≈50% after spinalization at the twelfth thoracic cord and the respiratory rhythm was more regular. These results indicate that: (i) locomotion can be generated in a hyperoxic/normocapnic state induced by specific respiratory conditions, (ii) the central mechanism regarding entrainment of respiratory and locomotor rhythms relies on spinal feedback via ascending pathways, initiated by the activated LPG generating locomotion, and (iii) the increase in respiratory rate seen during locomotion is caused not only by afferent mechanical and nociceptive inputs but also by impulses from the activated spinal cord producing a locomotor-like discharge via ascending pathways.
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Affiliation(s)
- Itaru Yazawa
- Laboratory of Neural Control, National Institute of Neurological Disorders and Stroke, National Institutes of Health , Bethesda, MD, USA
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39
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Reyes EP, Cerpa V, Corvalán L, Retamal MA. Cxs and Panx- hemichannels in peripheral and central chemosensing in mammals. Front Cell Neurosci 2014; 8:123. [PMID: 24847209 PMCID: PMC4023181 DOI: 10.3389/fncel.2014.00123] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2014] [Accepted: 04/18/2014] [Indexed: 01/08/2023] Open
Abstract
Connexins (Cxs) and Pannexins (Panx) form hemichannels at the plasma membrane of animals. Despite their low open probability under physiological conditions, these hemichannels release signaling molecules (i.e., ATP, Glutamate, PGE2) to the extracellular space, thus subserving several important physiological processes. Oxygen and CO2 sensing are fundamental to the normal functioning of vertebrate organisms. Fluctuations in blood PO2, PCO2 and pH are sensed at the carotid bifurcations of adult mammals by glomus cells of the carotid bodies. Likewise, changes in pH and/or PCO2 of cerebrospinal fluid are sensed by central chemoreceptors, a group of specialized neurones distributed in the ventrolateral medulla (VLM), raphe nuclei, and some other brainstem areas. After many years of research, the molecular mechanisms involved in chemosensing process are not completely understood. This manuscript will review data regarding relationships between chemosensitive cells and the expression of channels formed by Cxs and Panx, with special emphasis on hemichannels.
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Affiliation(s)
- Edison Pablo Reyes
- Centro de Fisiología Celular e Integrativa, Facultad de Medicina, Clínica Alemana Universidad del Desarrollo Santiago, Chile ; Dirección de Investigación, Universidad Autónoma de Chile Santiago, Chile
| | - Verónica Cerpa
- Centro de Fisiología Celular e Integrativa, Facultad de Medicina, Clínica Alemana Universidad del Desarrollo Santiago, Chile
| | - Liliana Corvalán
- Centro de Fisiología Celular e Integrativa, Facultad de Medicina, Clínica Alemana Universidad del Desarrollo Santiago, Chile
| | - Mauricio Antonio Retamal
- Centro de Fisiología Celular e Integrativa, Facultad de Medicina, Clínica Alemana Universidad del Desarrollo Santiago, Chile
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40
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Respiratory and sympathetic chemoreflex regulation by Kölliker-Fuse neurons in rats. Pflugers Arch 2014; 467:231-9. [DOI: 10.1007/s00424-014-1525-z] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2014] [Revised: 03/31/2014] [Accepted: 04/16/2014] [Indexed: 11/26/2022]
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41
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Meigh L, Greenhalgh SA, Rodgers TL, Cann MJ, Roper DI, Dale N. CO₂directly modulates connexin 26 by formation of carbamate bridges between subunits. eLife 2013; 2:e01213. [PMID: 24220509 PMCID: PMC3821526 DOI: 10.7554/elife.01213] [Citation(s) in RCA: 95] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/02/2022] Open
Abstract
Homeostatic regulation of the partial pressure of CO2 (PCO2) is vital for life. Sensing of pH has been proposed as a sufficient proxy for determination of PCO2 and direct CO2-sensing largely discounted. Here we show that connexin 26 (Cx26) hemichannels, causally linked to respiratory chemosensitivity, are directly modulated by CO2. A ‘carbamylation motif’, present in CO2-sensitive connexins (Cx26, Cx30, Cx32) but absent from a CO2-insensitive connexin (Cx31), comprises Lys125 and four further amino acids that orient Lys125 towards Arg104 of the adjacent subunit of the connexin hexamer. Introducing the carbamylation motif into Cx31 created a mutant hemichannel (mCx31) that was opened by increases in PCO2. Mutation of the carbamylation motif in Cx26 and mCx31 destroyed CO2 sensitivity. Course-grained computational modelling of Cx26 demonstrated that the proposed carbamate bridge between Lys125 and Arg104 biases the hemichannel to the open state. Carbamylation of Cx26 introduces a new transduction principle for physiological sensing of CO2. DOI:http://dx.doi.org/10.7554/eLife.01213.001 A number of gaseous molecules, including nitric oxide and carbon monoxide, play important roles in many cellular processes by acting as signalling molecules. Surprisingly, however, it has long been assumed that carbon dioxide – a gaseous molecule that is produced during cellular metabolism – is not a signalling molecule. Controlling the concentration of carbon dioxide (CO2) in a biological system is essential to sustain life, and it was thought that the body used pH – which is the concentration of hydrogen ions – as a proxy for the level of CO2. The concentration of CO2 is related to pH because CO2 reacts with water to form carbonic acid, which quickly breaks down to form hydrogen ions and bicarbonate ions. This close relationship has led many researchers to equate pH-sensing with CO2-sensing, and to suggest that a physiological receptor for CO2 does not exist. Recent research into structures called connexin hemichannels has challenged this view. Researchers found that when pH levels were held constant, increasing the level of CO2 caused the structures to open up, suggesting that CO2 could be directly detected by the hemichannels. Each hemichannel contains six connexin subunits, but the details of how the CO2 molecules interact with the individual connexin subunits to open up the hemichannels remained mysterious. Now Meigh et al. show that CO2 molecules bind to a specific amino acid (lysine) at a particular place (residue 125) in one of the connexin subunits to form a carbamate group. This group then interacts with the amino acid (arginine) at residue 104 in a neighbouring connexin subunit to form a carbamate bridge between the two subunits. This leads to structural changes that cause the gap junction hemichannels to open and release signals that can activate other cells. Since connexin hemichannels are found throughout the human body, these results suggest that CO2 might act as a signalling molecule in processes as diverse as the control of blood flow, breathing, hearing and reproduction. DOI:http://dx.doi.org/10.7554/eLife.01213.002
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Affiliation(s)
- Louise Meigh
- School of Life Sciences, University of Warwick, Coventry, United Kingdom
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Guyenet PG, Abbott SBG. Chemoreception and asphyxia-induced arousal. Respir Physiol Neurobiol 2013; 188:333-43. [PMID: 23608705 PMCID: PMC3749262 DOI: 10.1016/j.resp.2013.04.011] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2013] [Revised: 04/02/2013] [Accepted: 04/06/2013] [Indexed: 02/07/2023]
Abstract
Arousal protects against the adverse and potentially fatal effects of asphyxia during sleep. Asphyxia stimulates the carotid bodies and central chemoreceptors but the sequence of events leading to arousal is uncertain. In this review, the theoretical mechanisms leading to arousal from sleep are briefly summarized and the issue of whether central respiratory chemoreceptors (CRCs) or other types of CO2-responsive CNS neurons contribute to asphyxia-induced arousal is discussed. We focus on the role of the retrotrapezoid nucleus, the raphe and the locus coeruleus and emphasize the anatomical and neurophysiological evidence which suggests that these putative central chemoreceptors could contribute to arousal independently of their effects on breathing. Finally, we describe recent attempts to test the contribution of specific brainstem pathways to asphyxia-induced arousal using optogenetic and other tools and the possible contribution of a group of hypoxia-sensitive brainstem neurons (the C1 cells) to breathing and arousal.
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Affiliation(s)
- Patrice G Guyenet
- Department of Pharmacology, University of Virginia, Charlottesville, VA 22908, United States.
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Guyenet PG, Abbott SBG, Stornetta RL. The respiratory chemoreception conundrum: light at the end of the tunnel? Brain Res 2013; 1511:126-37. [PMID: 23088963 PMCID: PMC3570739 DOI: 10.1016/j.brainres.2012.10.028] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2012] [Revised: 10/10/2012] [Accepted: 10/14/2012] [Indexed: 11/29/2022]
Abstract
Arterial PCO₂ is tightly regulated via changes in breathing. A rise in PCO₂ activates the carotid bodies and exerts additional effects on neurons located within the CNS, causing an increase in lung ventilation. Central respiratory chemoreception refers to the component of this homeostatic reflex that is triggered by activation of receptors located within the brain (central chemoreceptors). Throughout the body, CO₂ generally operates via the proxy of pH. Since countless proteins, ion channels and neurons display some degree of pH-sensitivity, the notion that central respiratory chemoreception could rely on a few specialized neurons seems a priori counter-intuitive. Yet, two types of neurons currently stand out as critically important for breathing regulation by CO₂: the retrotrapezoid nucleus (RTN) and the raphe. RTN neurons are glutamatergic, strongly activated by hypercapnia in vivo and by CO₂ or protons in slices. These neurons target selectively the pontomedullary regions implicated in generating the respiratory rhythm and pattern. Their response to CO₂ seems to involve both cell-autonomous and paracrine effects of CO₂, the latter presumably mediated by the surrounding glia. The specific connections that these excitatory neurons establish with the rest of the breathing network are likely to be the main explanation of their importance to respiratory chemoreception. Serotonergic neurons have a powerful stimulatory effect on breathing, they facilitate the chemoreflexes and a subset of them likely function as CO₂ sensors. Opto- and pharmacogenetic methods have played an important role in assessing the contribution of RTN and serotonergic neurons as well as glial cells to respiration. These particular experiments are emphasized here for thematic reasons although the current perception of the importance of the RTN and serotonergic cells to respiratory chemoreception also relies on many other types of evidence. A small portion of this evidence is presented as background. This article is part of a Special Issue entitled Optogenetics (7th BRES).
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Affiliation(s)
- Patrice G Guyenet
- Department of Pharmacology, University of Virginia, 1300 Jefferson Park Ave, Charlottesville, VA 22908, USA.
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Zakharova EI, Germanova EL, Kopaladze RA, Dudchenko AM. Central cholinergic systems in the mechanisms of hypoxic preconditioning: Diverse pathways of synaptic reorganization in vivo. NEUROCHEM J+ 2013. [DOI: 10.1134/s1819712413010108] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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Takakura AC, Moreira TS. Arterial chemoreceptor activation reduces the activity of parapyramidal serotonergic neurons in rats. Neuroscience 2013; 237:199-207. [PMID: 23403178 DOI: 10.1016/j.neuroscience.2013.01.069] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2012] [Revised: 01/29/2013] [Accepted: 01/30/2013] [Indexed: 02/07/2023]
Abstract
The parapyramidal (ppy) region targets primarily the intermediolateral cell column and is probably involved in breathing and thermoregulation. In the present study, we tested whether ppy serotonergic neurons respond to activation of central and peripheral chemoreceptors. Bulbospinal ppy neurons (n=30) were recorded extracellularly along with the phrenic nerve activity in urethane/α-chloralose-anesthetized, paralyzed, intact (n=7) or carotid body denervated (n=6) male Wistar rats. In intact animals, most of the ppy neurons were inhibited by hypoxia (n=14 of 19) (8% O2, 30s) (1.5 ± 0.03 vs. control: 2.4 ± 0.2 Hz) or hypercapnia (n=15 of 19) (10% CO2) (1.7 ± 0.1 vs. control: 2.2 ± 0.2 Hz), although some neurons were insensitive to hypoxia (n=3 of 19) or hypercapnia (n=4 of 19). Very few neurons (n=2 of 19) were activated after hypoxia, but not after hypercapnia. In carotid body denervated rats, all the 5HT-ppy neurons (n=11) were insensitive to hypercapnia (2.1 ± 0.1 vs. control: 2.3 ± 0.09 Hz). Biotinamide-labeled cells that were recovered after histochemistry were located in the ppy region. Most labeled cells (90%) showed strong tryptophan hydroxylase immunocytochemical reactivity, indicating that they were serotonergic. The present data reveal that peripheral chemoreceptors reduce the activity of the serotonergic premotor neurons located in the ppy region. It is plausible that the serotonergic neurons of the ppy region could conceivably regulate breathing automaticity and be involved in autonomic regulation.
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Affiliation(s)
- A C Takakura
- Department of Pharmacology, Institute of Biomedical Science, University of São Paulo, 05508-000 São Paulo, SP, Brazil
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Freet CS, Stoner JF, Tang X. Baroreflex and chemoreflex controls of sympathetic activity following intermittent hypoxia. Auton Neurosci 2013; 174:8-14. [PMID: 23305890 DOI: 10.1016/j.autneu.2012.12.005] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2012] [Revised: 11/25/2012] [Accepted: 12/15/2012] [Indexed: 11/29/2022]
Abstract
There is a large amount of evidence linking obstructive sleep apnea (OSA), and the associated intermittent hypoxia that accompanies it, with the development of hypertension. For example, cross-sectional studies demonstrate that the prevalence of hypertension increases with the severity of OSA (Bixler et al., 2000; Grote et al., 2001) and an initial determination of OSA is associated with a three-fold increase for future hypertension (Peppard et al., 2000). Interestingly, bouts of intermittent hypoxia have also been shown to affect sympathetic output associated with the baroreflex and chemoreflex, important mechanisms in the regulation of arterial blood pressure. As such, the possibility exists that changes in the baroreflex and chemoreflex may contribute to the development of chronic hypertension observed in OSA patients. The aim of the current article is to briefly review the response of the baroreflex and chemoreflex to intermittent hypoxic exposure and to evaluate evidence for the hypothesis that modification of these autonomic reflexes may, at least in part, support the comorbidity observed between chronic hypertension and OSA.
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Affiliation(s)
- Christopher S Freet
- The Pennsylvania State University College of Medicine, Department of Neural and Behavioral Sciences, Hershey, PA 17033, USA.
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Wong-Riley MTT, Liu Q, Gao XP. Peripheral-central chemoreceptor interaction and the significance of a critical period in the development of respiratory control. Respir Physiol Neurobiol 2013; 185:156-69. [PMID: 22684042 PMCID: PMC3467325 DOI: 10.1016/j.resp.2012.05.026] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2012] [Revised: 05/30/2012] [Accepted: 05/30/2012] [Indexed: 01/09/2023]
Abstract
Respiratory control entails coordinated activities of peripheral chemoreceptors (mainly the carotid bodies) and central chemosensors within the brain stem respiratory network. Candidates for central chemoreceptors include Phox2b-containing neurons of the retrotrapezoid nucleus, serotonergic neurons of the medullary raphé, and/or multiple sites within the brain stem. Extensive interconnections among respiratory-related nuclei enable central chemosensitive relay. Both peripheral and central respiratory centers are not mature at birth, but undergo considerable development during the first two postnatal weeks in rats. A critical period of respiratory development (∼P12-P13 in the rat) exists when abrupt neurochemical, metabolic, ventilatory, and electrophysiological changes occur. Environmental perturbations, including hypoxia, intermittent hypoxia, hypercapnia, and hyperoxia alter the development of the respiratory system. Carotid body denervation during the first two postnatal weeks in the rat profoundly affects the development and functions of central respiratory-related nuclei. Such denervation delays and prolongs the critical period, but does not eliminate it, suggesting that the critical period may be intrinsically and genetically determined.
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Affiliation(s)
- Margaret T T Wong-Riley
- Department of Cell Biology, Neurobiology and Anatomy, Medical College of Wisconsin, 8701 Watertown Plank Road, Milwaukee, WI 53226, USA.
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Seitz MJ, Brown R, Macefield VG. Inhibition of augmented muscle vasoconstrictor drive following asphyxic apnoea in awake human subjects is not affected by relief of chemical drive. Exp Physiol 2012; 98:405-14. [DOI: 10.1113/expphysiol.2012.067421] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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Lavezzi AM, Weese-Mayer DE, Yu MY, Jennings LJ, Corna MF, Casale V, Oneda R, Matturri L. Developmental alterations of the respiratory human retrotrapezoid nucleus in sudden unexplained fetal and infant death. Auton Neurosci 2012; 170:12-9. [PMID: 22796552 DOI: 10.1016/j.autneu.2012.06.005] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2012] [Revised: 06/16/2012] [Accepted: 06/20/2012] [Indexed: 11/19/2022]
Abstract
The study aims were twofold: 1) identify the localization and the cytoarchitecture of the retrotrapezoid nucleus (RTN) in the human fetus and infant and 2) ascertain if the RTN, given its essential role in animal studies for the maintenance of breathing and chemoreception, showed abnormalities in victims of sudden perinatal and infant death (sudden intrauterine unexplained death/SIUD - and sudden infant death syndrome/SIDS). We examined SIDS and SIUD cases and Controls (n=58) from 34 gestational weeks to 8 months of postnatal age by complete autopsy, in-depth autonomic nervous system histological examination, and immunohistochemical analysis of the PHOX2B gene, a transcriptional factor involved in Congenital Central Hypoventilation Syndrome that has been defined as a marker of rat RTN neurons. We identified a group of PHOX2B-immunopositive neurons within the caudal pons, contiguous to the facial/parafacial complex, in 90% of Controls, likely the homologous human RTN (hRTN). We observed structural and/or PHOX2B-expression abnormalities of the hRTN in 71% of SIUD/SIDS cases vs 10% of Controls (p<0.05). In conclusion we suggest that developmental abnormalities of the hRTN may seriously compromise chemoreception control, playing a critical role in the pathogenesis of both SIUD and SIDS.
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Affiliation(s)
- Anna M Lavezzi
- "Lino Rossi" Research Center for the Study and Prevention of Unexpected Perinatal Death and SIDS, Department of Biomedical, Surgical and Dental Sciences, University of Milan, Italy.
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Takakura AC, Moreira TS, De Paula PM, Menani JV, Colombari E. Control of breathing and blood pressure by parafacial neurons in conscious rats. Exp Physiol 2012; 98:304-15. [DOI: 10.1113/expphysiol.2012.065128] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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