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Tenorio-Lopes L, Kinkead R. Sex-Specific Effects of Stress on Respiratory Control: Plasticity, Adaptation, and Dysfunction. Compr Physiol 2021; 11:2097-2134. [PMID: 34107062 DOI: 10.1002/cphy.c200022] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
As our understanding of respiratory control evolves, we appreciate how the basic neurobiological principles of plasticity discovered in other systems shape the development and function of the respiratory control system. While breathing is a robust homeostatic function, there is growing evidence that stress disrupts respiratory control in ways that predispose to disease. Neonatal stress (in the form of maternal separation) affects "classical" respiratory control structures such as the peripheral O2 sensors (carotid bodies) and the medulla (e.g., nucleus of the solitary tract). Furthermore, early life stress disrupts the paraventricular nucleus of the hypothalamus (PVH), a structure that has emerged as a primary determinant of the intensity of the ventilatory response to hypoxia. Although underestimated, the PVH's influence on respiratory function is a logical extension of the hypothalamic control of metabolic demand and supply. In this article, we review the functional and anatomical links between the stress neuroendocrine axis and the medullary network regulating breathing. We then present the persistent and sex-specific effects of neonatal stress on respiratory control in adult rats. The similarities between the respiratory phenotype of stressed rats and clinical manifestations of respiratory control disorders such as sleep-disordered breathing and panic attacks are remarkable. These observations are in line with the scientific consensus that the origins of adult disease are often found among developmental and biological disruptions occurring during early life. These observations bring a different perspective on the structural hierarchy of respiratory homeostasis and point to new directions in our understanding of the etiology of respiratory control disorders. © 2021 American Physiological Society. Compr Physiol 11:1-38, 2021.
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Affiliation(s)
- Luana Tenorio-Lopes
- Department of Physiology and Pharmacology, Hotchkiss Brain Institute, The University of Calgary, Calgary, Alberta, Canada
| | - Richard Kinkead
- Département de Pédiatrie, Centre de Recherche de l'Institut Universitaire de Cardiologie et de Pneumologie de Québec, Université Laval, Quebec City, Quebec, Canada
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Abstract
Air-breathing animals do not experience hyperoxia (inspired O2 > 21%) in nature, but preterm and full-term infants often experience hyperoxia/hyperoxemia in clinical settings. This article focuses on the effects of normobaric hyperoxia during the perinatal period on breathing in humans and other mammals, with an emphasis on the neural control of breathing during hyperoxia, after return to normoxia, and in response to subsequent hypoxic and hypercapnic challenges. Acute hyperoxia typically evokes an immediate ventilatory depression that is often, but not always, followed by hyperpnea. The hypoxic ventilatory response (HVR) is enhanced by brief periods of hyperoxia in adult mammals, but the limited data available suggest that this may not be the case for newborns. Chronic exposure to mild-to-moderate levels of hyperoxia (e.g., 30-60% O2 for several days to a few weeks) elicits several changes in breathing in nonhuman animals, some of which are unique to perinatal exposures (i.e., developmental plasticity). Examples of this developmental plasticity include hypoventilation after return to normoxia and long-lasting attenuation of the HVR. Although both peripheral and CNS mechanisms are implicated in hyperoxia-induced plasticity, it is particularly clear that perinatal hyperoxia affects carotid body development. Some of these effects may be transient (e.g., decreased O2 sensitivity of carotid body glomus cells) while others may be permanent (e.g., carotid body hypoplasia, loss of chemoafferent neurons). Whether the hyperoxic exposures routinely experienced by human infants in clinical settings are sufficient to alter respiratory control development remains an open question and requires further research. © 2020 American Physiological Society. Compr Physiol 10:597-636, 2020.
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Affiliation(s)
- Ryan W Bavis
- Department of Biology, Bates College, Lewiston, Maine, USA
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3
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Caballero-Eraso C, Shin MK, Pho H, Kim LJ, Pichard LE, Wu ZJ, Gu C, Berger S, Pham L, Yeung HYB, Shirahata M, Schwartz AR, Tang WYW, Sham JSK, Polotsky VY. Leptin acts in the carotid bodies to increase minute ventilation during wakefulness and sleep and augment the hypoxic ventilatory response. J Physiol 2018; 597:151-172. [PMID: 30285278 DOI: 10.1113/jp276900] [Citation(s) in RCA: 42] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2018] [Accepted: 10/03/2018] [Indexed: 01/10/2023] Open
Abstract
KEY POINTS Leptin is a potent respiratory stimulant. A long functional isoform of leptin receptor, LepRb , was detected in the carotid body (CB), a key peripheral hypoxia sensor. However, the effect of leptin on minute ventilation (VE ) and the hypoxic ventilatory response (HVR) has not been sufficiently studied. We report that LepRb is present in approximately 74% of the CB glomus cells. Leptin increased carotid sinus nerve activity at baseline and in response to hypoxia in vivo. Subcutaneous infusion of leptin increased VE and HVR in C57BL/6J mice and this effect was abolished by CB denervation. Expression of LepRb in the carotid bodies of LepRb deficient obese db/db mice increased VE during wakefulness and sleep and augmented the HVR. We conclude that leptin acts on LepRb in the CBs to stimulate breathing and HVR, which may protect against sleep disordered breathing in obesity. ABSTRACT Leptin is a potent respiratory stimulant. The carotid bodies (CB) express the long functional isoform of leptin receptor, LepRb , but the role of leptin in CB has not been fully elucidated. The objectives of the current study were (1) to examine the effect of subcutaneous leptin infusion on minute ventilation (VE ) and the hypoxic ventilatory response to 10% O2 (HVR) in C57BL/6J mice before and after CB denervation; (2) to express LepRb in CB of LepRb -deficient obese db/db mice and examine its effects on breathing during sleep and wakefulness and on HVR. We found that leptin enhanced carotid sinus nerve activity at baseline and in response to 10% O2 in vivo. In C57BL/6J mice, leptin increased VE from 1.1 to 1.5 mL/min/g during normoxia (P < 0.01) and from 3.6 to 4.7 mL/min/g during hypoxia (P < 0.001), augmenting HVR from 0.23 to 0.31 mL/min/g/Δ F I O 2 (P < 0.001). The effects of leptin on VE and HVR were abolished by CB denervation. In db/db mice, LepRb expression in CB increased VE from 1.1 to 1.3 mL/min/g during normoxia (P < 0.05) and from 2.8 to 3.2 mL/min/g during hypoxia (P < 0.02), increasing HVR. Compared to control db/db mice, LepRb transfected mice showed significantly higher VE throughout non-rapid eye movement (20.1 vs. -27.7 mL/min respectively, P < 0.05) and rapid eye movement sleep (16.5 vs 23.4 mL/min, P < 0.05). We conclude that leptin acts in CB to augment VE and HVR, which may protect against sleep disordered breathing in obesity.
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Affiliation(s)
- Candela Caballero-Eraso
- Division of Pulmonary and Critical Care Medicine, Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, MD, USA.,Unidad Médico-Quirúrgica de Enfermedades Respiratorias, Instituto de Biomedicina de Sevilla (IBiS), Centro de Investigación Biomédica en Red de Enfermedades Respiratorias (CIBERES), Hospital Universitario Virgen del Rocío/Universidad de Sevilla, Sevilla, Spain
| | - Mi-Kyung Shin
- Division of Pulmonary and Critical Care Medicine, Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, MD, USA
| | - Huy Pho
- Division of Pulmonary and Critical Care Medicine, Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, MD, USA
| | - Lenise J Kim
- Division of Pulmonary and Critical Care Medicine, Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, MD, USA.,Departamento de Psicobiologia, Universidade Federal de São Paulo, São Paulo, Brazil
| | - Luis E Pichard
- Division of Pulmonary and Critical Care Medicine, Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, MD, USA
| | - Zhi-Juan Wu
- Division of Pulmonary and Critical Care Medicine, Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, MD, USA
| | - Chenjuan Gu
- Division of Pulmonary and Critical Care Medicine, Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, MD, USA
| | - Slava Berger
- Division of Pulmonary and Critical Care Medicine, Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, MD, USA
| | - Luu Pham
- Division of Pulmonary and Critical Care Medicine, Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, MD, USA
| | - Ho-Yee Bonnie Yeung
- Department of Environmental Health and Engineering, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD, USA
| | - Machiko Shirahata
- Department of Environmental Health and Engineering, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD, USA
| | - Alan R Schwartz
- Division of Pulmonary and Critical Care Medicine, Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, MD, USA
| | - Wan-Yee Winnie Tang
- Department of Environmental Health and Engineering, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD, USA
| | - James S K Sham
- Division of Pulmonary and Critical Care Medicine, Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, MD, USA
| | - Vsevolod Y Polotsky
- Division of Pulmonary and Critical Care Medicine, Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, MD, USA
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4
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Porzionato A, Macchi V, De Caro R. Central and peripheral chemoreceptors in sudden infant death syndrome. J Physiol 2018; 596:3007-3019. [PMID: 29645275 PMCID: PMC6068209 DOI: 10.1113/jp274355] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2017] [Accepted: 03/20/2018] [Indexed: 11/08/2022] Open
Abstract
The pathogenesis of sudden infant death syndrome (SIDS) has been ascribed to an underlying biological vulnerability to stressors during a critical period of development. This paper reviews the main data in the literature supporting the role of central (e.g. retrotrapezoid nucleus, serotoninergic raphe nuclei, locus coeruleus, orexinergic neurons, ventral medullary surface, solitary tract nucleus) and peripheral (e.g. carotid body) chemoreceptors in the pathogenesis of SIDS. Clinical and experimental studies indicate that central and peripheral chemoreceptors undergo critical development during the initial postnatal period, consistent with the age range of SIDS (<1 year). Most of the risk factors for SIDS (gender, genetic factors, prematurity, hypoxic/hyperoxic stimuli, inflammation, perinatal exposure to cigarette smoke and/or substance abuse) may structurally and functionally affect the developmental plasticity of central and peripheral chemoreceptors, strongly suggesting the involvement of these structures in the pathogenesis of SIDS. Morphometric and neurochemical changes have been found in the carotid body and brainstem respiratory chemoreceptors of SIDS victims, together with functional signs of chemoreception impairment in some clinical studies. However, the methodological problems of SIDS research will have to be addressed in the future, requiring large and highly standardized case series. Up-to-date autopsy protocols should be produced, involving substantial, and exhaustive sampling of all potentially involved structures (including peripheral arterial chemoreceptors). Morphometric approaches should include unbiased stereological methods with three-dimensional probes. Prospective clinical studies addressing functional tests and risk factors (including genetic traits) would probably be the gold standard, allowing markers of intrinsic or acquired vulnerability to be properly identified.
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Affiliation(s)
- Andrea Porzionato
- Section of Anatomy, Department of NeuroscienceUniversity of PadovaItaly
| | - Veronica Macchi
- Section of Anatomy, Department of NeuroscienceUniversity of PadovaItaly
| | - Raffaele De Caro
- Section of Anatomy, Department of NeuroscienceUniversity of PadovaItaly
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5
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Developmental plasticity in the neural control of breathing. Exp Neurol 2017; 287:176-191. [DOI: 10.1016/j.expneurol.2016.05.032] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2016] [Revised: 05/13/2016] [Accepted: 05/26/2016] [Indexed: 12/14/2022]
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6
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Respiratory neuroplasticity – Overview, significance and future directions. Exp Neurol 2017; 287:144-152. [DOI: 10.1016/j.expneurol.2016.05.022] [Citation(s) in RCA: 44] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2016] [Accepted: 05/17/2016] [Indexed: 01/10/2023]
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7
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Pamenter ME, Powell FL. Time Domains of the Hypoxic Ventilatory Response and Their Molecular Basis. Compr Physiol 2016; 6:1345-85. [PMID: 27347896 DOI: 10.1002/cphy.c150026] [Citation(s) in RCA: 84] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Ventilatory responses to hypoxia vary widely depending on the pattern and length of hypoxic exposure. Acute, prolonged, or intermittent hypoxic episodes can increase or decrease breathing for seconds to years, both during the hypoxic stimulus, and also after its removal. These myriad effects are the result of a complicated web of molecular interactions that underlie plasticity in the respiratory control reflex circuits and ultimately control the physiology of breathing in hypoxia. Since the time domains of the physiological hypoxic ventilatory response (HVR) were identified, considerable research effort has gone toward elucidating the underlying molecular mechanisms that mediate these varied responses. This research has begun to describe complicated and plastic interactions in the relay circuits between the peripheral chemoreceptors and the ventilatory control circuits within the central nervous system. Intriguingly, many of these molecular pathways seem to share key components between the different time domains, suggesting that varied physiological HVRs are the result of specific modifications to overlapping pathways. This review highlights what has been discovered regarding the cell and molecular level control of the time domains of the HVR, and highlights key areas where further research is required. Understanding the molecular control of ventilation in hypoxia has important implications for basic physiology and is emerging as an important component of several clinical fields. © 2016 American Physiological Society. Compr Physiol 6:1345-1385, 2016.
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Affiliation(s)
| | - Frank L Powell
- Physiology Division, Department of Medicine, University of California San Diego, La Jolla, California, USA
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8
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Logan S, Tobin KE, Fallon SC, Deng KS, McDonough AB, Bavis RW. Chronic intermittent hyperoxia alters the development of the hypoxic ventilatory response in neonatal rats. Respir Physiol Neurobiol 2015; 220:69-80. [PMID: 26444750 DOI: 10.1016/j.resp.2015.09.015] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2015] [Revised: 08/18/2015] [Accepted: 09/28/2015] [Indexed: 11/18/2022]
Abstract
Chronic exposure to sustained hyperoxia alters the development of the respiratory control system, but the respiratory effects of chronic intermittent hyperoxia have rarely been investigated. We exposed newborn rats to short, repeated bouts of 30% O2 or 60% O2 (5 bouts h(-1)) for 4-15 days and then assessed their hypoxic ventilatory response (HVR; 10 min at 12% O2) by plethysmography. The HVR tended to be enhanced by intermittent hyperoxia at P4 (early phase of the HVR), but it was significantly reduced at P14-15 (primarily late phase of the HVR) compared to age-matched controls; the HVR recovered when individuals were returned to room air and re-studied as adults. To investigate the role of carotid body function in this plasticity, single-unit carotid chemoafferent activity was recorded in vitro. Intermittent hyperoxia tended to decrease spontaneous action potential frequency under normoxic conditions but, contrary to expectations, hypoxic responses were only reduced at P4 (not at P14) and only in rats exposed to higher O2 levels (i.e., intermittent 60% O2). Rats exposed to intermittent hyperoxia had smaller carotid bodies, and this morphological change may contribute to the blunted HVR. In contrast to rats exposed to intermittent hyperoxia beginning at birth, two weeks of intermittent 60% O2 had no effect on the HVR or carotid body size of rats exposed beginning at P28; therefore, intermittent hyperoxia-induced respiratory plasticity appears to be unique to development. Although both intermittent and sustained hyperoxia alter carotid body development and the HVR of rats, the specific effects and time course of this plasticity differs.
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Affiliation(s)
- Sarah Logan
- Department of Biology, Bates College, Lewiston, ME 04240 USA
| | | | - Sarah C Fallon
- Department of Biology, Bates College, Lewiston, ME 04240 USA
| | - Kevin S Deng
- Department of Biology, Bates College, Lewiston, ME 04240 USA
| | - Amy B McDonough
- Department of Biology, Bates College, Lewiston, ME 04240 USA
| | - Ryan W Bavis
- Department of Biology, Bates College, Lewiston, ME 04240 USA.
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9
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Bavis RW, Fallon SC, Dmitrieff EF. Chronic hyperoxia and the development of the carotid body. Respir Physiol Neurobiol 2013; 185:94-104. [PMID: 22640932 PMCID: PMC3448014 DOI: 10.1016/j.resp.2012.05.019] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2012] [Revised: 05/18/2012] [Accepted: 05/20/2012] [Indexed: 01/27/2023]
Abstract
Preterm infants often experience hyperoxia while receiving supplemental oxygen. Prolonged exposure to hyperoxia during development is associated with pathologies such as bronchopulmonary dysplasia and retinopathy of prematurity. Over the last 25 years, however, experiments with animal models have revealed that moderate exposures to hyperoxia (e.g., 30-60% O(2) for days to weeks) can also have profound effects on the developing respiratory control system that may lead to hypoventilation and diminished responses to acute hypoxia. This plasticity, which is generally inducible only during critical periods of development, has a complex time course that includes both transient and permanent respiratory deficits. Although the molecular mechanisms of hyperoxia-induced plasticity are only beginning to be elucidated, it is clear that many of the respiratory effects are linked to abnormal morphological and functional development of the carotid body, the principal site of arterial O(2) chemoreception for respiratory control. Specifically, developmental hyperoxia reduces carotid body size, decreases the number of chemoafferent neurons, and (at least transiently) diminishes the O(2) sensitivity of individual carotid body glomus cells. Recent evidence suggests that hyperoxia may also directly or indirectly impact development of the central neural control of breathing. Collectively, these findings emphasize the vulnerability of the developing respiratory control system to environmental perturbations.
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Affiliation(s)
- Ryan W Bavis
- Department of Biology, Bates College, Lewiston, ME 04240, USA.
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10
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Porzionato A, Macchi V, Stecco C, De Caro R. The carotid body in Sudden Infant Death Syndrome. Respir Physiol Neurobiol 2012; 185:194-201. [PMID: 22613076 DOI: 10.1016/j.resp.2012.05.013] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2012] [Revised: 05/10/2012] [Accepted: 05/14/2012] [Indexed: 12/01/2022]
Abstract
The aim of the present study is to provide a review of cytochemical, clinical and experimental data indicating disruption of perinatal carotid body maturation as one of the possible mechanisms underlying SIDS pathogenesis. SIDS victims have been reported to show alterations in respiratory regulation which may partly be ascribed to peripheral arterial chemoreceptors. Carotid body findings in SIDS victims, although not entirely confirmed by other authors, have included reductions in glomic tissue volume and cytoplamic granules of type I cells, changes in cytological composition (higher percentages of progenitor and type II cells) and increases in dopamine and noradrenaline contents. Prematurity and environmental factors, such as exposure to tobacco smoke, substances of abuse, hyperoxia and continuous or intermittent hypoxia, increase the risk of SIDS and are known to affect carotid body functional and structural maturation adversely, supporting a role for peripheral arterial chemoreceptors in SIDS.
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Affiliation(s)
- Andrea Porzionato
- Section of Anatomy, Department of Molecular Medicine, University of Padova, Italy.
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11
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Chavez-Valdez R, Mason A, Nunes AR, Northington FJ, Tankersley C, Ahlawat R, Johnson SM, Gauda EB. Effect of hyperoxic exposure during early development on neurotrophin expression in the carotid body and nucleus tractus solitarii. J Appl Physiol (1985) 2012; 112:1762-72. [PMID: 22422797 DOI: 10.1152/japplphysiol.01609.2011] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Synaptic activity can modify expression of neurotrophins, which influence the development of neuronal circuits. In the newborn rat, early hyperoxia silences the synaptic activity and input from the carotid body, impairing the development and function of chemoreceptors. The purpose of this study was to determine whether early hyperoxic exposure, sufficient to induce hypoplasia of the carotid body and decrease the number of chemoafferents, would also modify neurotrophin expression within the nucleus tractus solitarii (nTS). Rat pups were exposed to hyperoxia (fraction of inspired oxygen 0.60) or normoxia until 7 or 14 days of postnatal development (PND). In the carotid body, hyperoxia decreased brain-derived neurotrophic factor (BDNF) protein expression by 93% (P = 0.04) after a 7-day exposure, followed by a decrease in retrogradely labeled chemoafferents by 55% (P = 0.004) within the petrosal ganglion at 14 days. Return to normoxia for 1 wk after a 14-day hyperoxic exposure did not reverse this effect. In the nTS, hyperoxia for 7 days: 1) decreased BDNF gene expression by 67% and protein expression by 18%; 2) attenuated upregulation of BDNF mRNA levels in response to acute hypoxia; and 3) upregulated p75 neurotrophic receptor, truncated tropomyosin kinase B (inactive receptor), and cleaved caspase-3. These effects were not observed in the locus coeruleus (LC). Hyperoxia for 14 days also decreased tyrosine hydroxylase levels by 18% (P = 0.04) in nTS but not in the LC. In conclusion, hyperoxic exposure during early PND reduces neurotrophin levels in the carotid body and the nTS and shifts the balance of neurotrophic support from prosurvival to proapoptotic in the nTS, the primary brain stem site for central integration of sensory and autonomic inputs.
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Affiliation(s)
- Raul Chavez-Valdez
- Department of Pediatrics, Division of Neonatology, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21287-3200, USA
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12
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Nichols NL, Dale EA, Mitchell GS. Severe acute intermittent hypoxia elicits phrenic long-term facilitation by a novel adenosine-dependent mechanism. J Appl Physiol (1985) 2012; 112:1678-88. [PMID: 22403346 DOI: 10.1152/japplphysiol.00060.2012] [Citation(s) in RCA: 94] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Acute intermittent hypoxia [AIH; 3, 5-min episodes; 35-45 mmHg arterial PO(2) (Pa(O(2)))] elicits serotonin-dependent phrenic long-term facilitation (pLTF), a form of phrenic motor facilitation (pMF) initiated by G(q) protein-coupled metabotropic 5-HT(2) receptors. An alternate pathway to pMF is induced by G(s) protein-coupled metabotropic receptors, including adenosine A(2A) receptors. AIH-induced pLTF is dominated by the serotonin-dependent pathway and is actually restrained via inhibition from the adenosine-dependent pathway. Here, we hypothesized that severe AIH shifts pLTF from a serotonin-dependent to an adenosine-dependent form of pMF. pLTF induced by severe (25-30 mmHg Pa(O(2))) and moderate (45-55 mmHg Pa(O(2))) AIH were compared in anesthetized rats, with and without intrathecal (C4) spinal A(2A) (MSX-3, 130 ng/kg, 12 μl) or 5-HT receptor antagonist (methysergide, 300 μg/kg, 15 μl) injections. During severe, but not moderate AIH, progressive augmentation of the phrenic response during hypoxic episodes was observed. Severe AIH (78% ± 8% 90 min post-AIH, n = 6) elicited greater pLTF vs. moderate AIH (41% ± 12%, n = 8; P < 0.05). MSX-3 (28% ± 6%; n = 6; P < 0.05) attenuated pLTF following severe AIH, but enhanced pLTF following moderate AIH (86% ± 26%; n = 8; P < 0.05). Methysergide abolished pLTF after moderate AIH (12% ± 5%; n = 6; P = 0.035), but had no effect after severe AIH (66 ± 13%; n = 5; P > 0.05). Thus severe AIH shifts pLTF from a serotonin-dependent to an adenosine-dependent mechanism; the adenosinergic pathway inhibits the serotonergic pathway following moderate AIH. Here we demonstrate a novel adenosine-dependent pathway to pLTF following severe AIH. Shifts in the mechanisms of respiratory plasticity provide the ventilatory control system greater flexibility as challenges that differ in severity are confronted.
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Affiliation(s)
- Nicole L Nichols
- Department of Comparative Biosciences, University of Wisconsin, School of Veterinary Medicine, Madison, Wisconsin 53706, USA
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13
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Abstract
The discovery of the sensory nature of the carotid body dates back to the beginning of the 20th century. Following these seminal discoveries, research into carotid body mechanisms moved forward progressively through the 20th century, with many descriptions of the ultrastructure of the organ and stimulus-response measurements at the level of the whole organ. The later part of 20th century witnessed the first descriptions of the cellular responses and electrophysiology of isolated and cultured type I and type II cells, and there now exist a number of testable hypotheses of chemotransduction. The goal of this article is to provide a comprehensive review of current concepts on sensory transduction and transmission of the hypoxic stimulus at the carotid body with an emphasis on integrating cellular mechanisms with the whole organ responses and highlighting the gaps or discrepancies in our knowledge. It is increasingly evident that in addition to hypoxia, the carotid body responds to a wide variety of blood-borne stimuli, including reduced glucose and immune-related cytokines and we therefore also consider the evidence for a polymodal function of the carotid body and its implications. It is clear that the sensory function of the carotid body exhibits considerable plasticity in response to the chronic perturbations in environmental O2 that is associated with many physiological and pathological conditions. The mechanisms and consequences of carotid body plasticity in health and disease are discussed in the final sections of this article.
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Affiliation(s)
- Prem Kumar
- School of Clinical and Experimental Medicine, College of Medical and Dental Sciences, The University of Birmingham, Birmingham, United Kingdom.
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14
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Teppema LJ, Dahan A. The Ventilatory Response to Hypoxia in Mammals: Mechanisms, Measurement, and Analysis. Physiol Rev 2010; 90:675-754. [DOI: 10.1152/physrev.00012.2009] [Citation(s) in RCA: 257] [Impact Index Per Article: 18.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
The respiratory response to hypoxia in mammals develops from an inhibition of breathing movements in utero into a sustained increase in ventilation in the adult. This ventilatory response to hypoxia (HVR) in mammals is the subject of this review. The period immediately after birth contains a critical time window in which environmental factors can cause long-term changes in the structural and functional properties of the respiratory system, resulting in an altered HVR phenotype. Both neonatal chronic and chronic intermittent hypoxia, but also chronic hyperoxia, can induce such plastic changes, the nature of which depends on the time pattern and duration of the exposure (acute or chronic, episodic or not, etc.). At adult age, exposure to chronic hypoxic paradigms induces adjustments in the HVR that seem reversible when the respiratory system is fully matured. These changes are orchestrated by transcription factors of which hypoxia-inducible factor 1 has been identified as the master regulator. We discuss the mechanisms underlying the HVR and its adaptations to chronic changes in ambient oxygen concentration, with emphasis on the carotid bodies that contain oxygen sensors and initiate the response, and on the contribution of central neurotransmitters and brain stem regions. We also briefly summarize the techniques used in small animals and in humans to measure the HVR and discuss the specific difficulties encountered in its measurement and analysis.
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Affiliation(s)
- Luc J. Teppema
- Department of Anesthesiology, Leiden University Medical Center, Leiden, The Netherlands
| | - Albert Dahan
- Department of Anesthesiology, Leiden University Medical Center, Leiden, The Netherlands
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15
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Kinkead R, Gulemetova R. Neonatal maternal separation and neuroendocrine programming of the respiratory control system in rats. Biol Psychol 2010; 84:26-38. [DOI: 10.1016/j.biopsycho.2009.09.001] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2009] [Revised: 08/28/2009] [Accepted: 09/02/2009] [Indexed: 10/20/2022]
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MacFarlane PM, Wilkerson JER, Lovett-Barr MR, Mitchell GS. Reactive oxygen species and respiratory plasticity following intermittent hypoxia. Respir Physiol Neurobiol 2009; 164:263-71. [PMID: 18692605 DOI: 10.1016/j.resp.2008.07.008] [Citation(s) in RCA: 64] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2008] [Revised: 07/13/2008] [Accepted: 07/15/2008] [Indexed: 11/18/2022]
Abstract
The neural network controlling breathing exhibits plasticity in response to environmental or physiological challenges. For example, while hypoxia initiates rapid and robust increases in respiratory motor output to defend against hypoxemia, it also triggers persistent changes, or plasticity, in chemosensory neurons and integrative pathways that transmit brainstem respiratory activity to respiratory motor neurons. Frequently studied models of hypoxia-induced respiratory plasticity include: (1) carotid chemosensory plasticity and metaplasticity induced by chronic intermittent hypoxia (CIH), and (2) acute intermittent hypoxia (AIH) induced phrenic long-term facilitation (pLTF) in naïve and CIH preconditioned rats. These forms of plasticity share some mechanistic elements, although they differ in anatomical location and the requirement for CIH preconditioning. Both forms of plasticity require serotonin receptor activation and formation of reactive oxygen species (ROS). While the cellular sources and targets of ROS are not well known, recent evidence suggests that ROS modify the balance of protein phosphatase and kinase activities, shifting the balance towards net phosphorylation and favoring cellular reactions that induce and/or maintain plasticity. Here, we review possible sources of ROS, and the impact of ROS on phosphorylation events relevant to respiratory plasticity.
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Affiliation(s)
- P M MacFarlane
- Department of Comparative Biosciences, School of Veterinary Medicine, University of Wisconsin, 2015 Linden Drive, Madison, WI 53706, USA.
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McGuire M, Liu C, Cao Y, Ling L. Formation and maintenance of ventilatory long-term facilitation require NMDA but not non-NMDA receptors in awake rats. J Appl Physiol (1985) 2008; 105:942-50. [PMID: 18583381 DOI: 10.1152/japplphysiol.01274.2006] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
N-methyl-d-aspartate (NMDA) receptor antagonism in the phrenic motonucleus area eliminates phrenic long-term facilitation (pLTF; a persistent augmentation of phrenic nerve activity after episodic hypoxia) in anesthetized rats. However, whether NMDA antagonism can eliminate ventilatory LTF (vLTF) in awake rats is unclear. The role of non-NMDA receptors in LTF is also unknown. Serotonin receptor antagonism before, but not after, episodic hypoxia eliminates pLTF, suggesting that serotonin receptors are required for induction, but not maintenance, of pLTF. However, because NMDA and non-NMDA ionotropic glutamate receptors are directly involved in mediating the inspiratory drive to phrenic, hypoglossal, and intercostal motoneurons, we hypothesized that these receptors are required for both formation and maintenance of vLTF. vLTF, induced by five episodes of 5-min poikilocapnic hypoxia (10% O(2)) with 5-min normoxia intervals, was measured with plethysmography in conscious adult male Sprague-Dawley rats. Either (+/-)-2-amino-5-phosphonovaleric acid (APV; NMDA antagonist, 1.5 mg/kg) or 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX; non-NMDA antagonist, 10 mg/kg) was systemically (ip) injected approximately 30 min before hypoxia. APV was also injected immediately after or 20 min after episodic hypoxia in additional groups. As control, vehicle was similarly injected in each rat 1-2 days before. Regardless of being injected before or after episodic hypoxia, vehicle did not alter vLTF ( approximately 23%), whereas APV eliminated vLTF while having little effect on baseline ventilation or hypoxic ventilatory response. In contrast, CNQX enhanced vLTF ( approximately 34%) while decreasing baseline ventilation. Collectively, these results suggest that activation of NMDA but not non-NMDA receptors is necessary for formation and maintenance of vLTF in awake rats.
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Affiliation(s)
- Michelle McGuire
- Div. of Sleep Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, MA 02115, USA
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Tadjalli A, Duffin J, Li YM, Hong H, Peever J. Inspiratory activation is not required for episodic hypoxia-induced respiratory long-term facilitation in postnatal rats. J Physiol 2007; 585:593-606. [PMID: 17932158 DOI: 10.1113/jphysiol.2007.135798] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Episodic hypoxia causes repetitive inspiratory activation that induces a form of respiratory plasticity termed long-term facilitation (LTF). While LTF is a function of the hypoxic exposures and inspiratory activation, their relative importance in evoking LTF is unknown. The aims of this study were to: (1) dissociate the relative roles played by episodic hypoxia and respiratory activation in LTF; and (2) determine whether the magnitude of LTF varies as a function of hypoxic intensity. We did this by examining the effects of episodic hypoxia in postnatal rats (15-25 days old), which unlike adult rats exhibit a prominent hypoxia-induced respiratory depression. We quantified inspiratory phrenic nerve activity generated by the in situ working-heart brainstem before, during and for 60 min after episodic hypoxia. We demonstrate that episodic hypoxia evokes LTF despite the fact that it potently suppresses inspiratory activity during individual hypoxic exposures (P < 0.05). Specifically, we show that after episodic hypoxia (three 5 min periods of 10% O2) respiratory frequency increased to 40 +/- 3.3% above baseline values over the next 60 min (P < 0.001). Continuous hypoxia (15 min of 10% O2) had no lasting effects on respiratory frequency (P > 0.05). To determine if LTF magnitude was affected by hypoxic intensity, the episodic hypoxia protocol was repeated under three different O2 tensions. We demonstrate that the magnitude and time course of LTF depend on hypoxic severity, with more intense hypoxia inducing a more potent degree of LTF. We conclude that inspiratory activation is not required for LTF induction, and that hypoxia per se is the physiological stimulus for eliciting hypoxia-induced respiratory LTF.
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Affiliation(s)
- Arash Tadjalli
- Dept. Cell and Systems Biology, Systems Neurobiology Laboratory, University of Toronto, 25 Harbord Street, Toronto, Ontario, M5S 3G5, Canada
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Szdzuy K, Mortola JP. Ventilatory chemosensitivity of the 1-day-old chicken hatchling after embryonic hypoxia. Am J Physiol Regul Integr Comp Physiol 2007; 293:R1640-9. [PMID: 17686884 DOI: 10.1152/ajpregu.00422.2007] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We investigated the effects of sustained embryonic hypoxia on the neonatal ventilatory chemosensitivity. White Leghorn chicken eggs were incubated at 38°C either in 21% O2 throughout incubation (normoxia, Nx) or in 15% O2 from embryonic day 5 (hypoxia, Hx), hatching time included. Hx embryos hatched ∼11 h later than Nx, with similar body weights. Measurements of gaseous metabolism (oxygen consumption, V̇o2) and pulmonary ventilation (V̇e) were conducted either within the first 8 h (early) or later hours (late) of the first posthatching day. In resting conditions, Hx had similar V̇o2 and body temperature (Tb) and slightly higher V̇e and ventilatory equivalent (V̇e/V̇o2) than Nx. Ventilatory chemosensitivity was evaluated from the degree of hyperpnea (increase in V̇e) and of hyperventilation (increase in V̇e/V̇o2) during acute hypoxia (15 and 10% O2, 20 min each) and acute hypercapnia (2 and 4% CO2, 20 min each). The chemosensitivity differed between the early and late hours, and at either time the responses to hypoxia and hypercapnia were less in Hx than in Nx because of a lower increase in V̇e and a lower hypoxic hypometabolism. In a second group of Nx and Hx hatchlings, the V̇e response to 10% O2 was tested in the same hatchlings at the early and late hours. The results confirmed the lower hypoxic chemosensitivity of Hx. We conclude that hypoxic incubation affected the development of respiratory control, resulting in a blunted ventilatory chemosensitivity.
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Affiliation(s)
- Kirsten Szdzuy
- Dept. of Physiology, McGill Univ., 3655 Promenade Sir William Osler, Montreal, Quebec, H3G 1Y6 Canada.
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Bavis RW, Russell KE, Simons JC, Otis JP. Hypoxic ventilatory responses in rats after hypercapnic hyperoxia and intermittent hyperoxia. Respir Physiol Neurobiol 2007; 155:193-202. [DOI: 10.1016/j.resp.2006.06.006] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2006] [Revised: 06/19/2006] [Accepted: 06/20/2006] [Indexed: 10/24/2022]
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Kwak DJ, Kwak SD, Gauda EB. The effect of hyperoxia on reactive oxygen species (ROS) in rat petrosal ganglion neurons during development using organotypic slices. Pediatr Res 2006; 60:371-6. [PMID: 16940233 DOI: 10.1203/01.pdr.0000239817.39407.61] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Hyperoxia, during development in rats, results in hypoxic chemosensitivity ablation, carotid body hypoplasia, and reduced chemoafferents. We hypothesized that hyperoxia increases reactive oxygen species (ROS) in cell bodies of chemoafferents. Organotypic slices of petrosal-nodose ganglia from rats at day of life (DOL) 5-6 and 17-18 were exposed to 8%, 21%, or 95% O(2) for 4 h in the presence or absence of the ROS-sensitive fluorescent indicator, CM-H(2)DCFDA, and propidium iodide was used to determine the relationship between cell death and oxygen tension. In tissue slices from DOL 5-6 rats, fluorescence intensity was 182.5 +/- 2.9 for hypoxia, 217.5 +/- 3.3 for normoxia, and 336.6 +/- 3.8 for hyperoxia, (mean +/- SEM, p < 0.001, ANOVA). Normoxia increased ROS levels by 19.2% from hypoxia (p < 0.01) with a further increase of 54.8% from normoxia to hyperoxia (p < 0.001). In tissue slices from DOL 17-18 rats, ROS levels increased with increasing oxygen tension but were less than in younger animals (p < 0.01, ANOVA). The antioxidants, NAC and TEMPO-9-AC, attenuated ROS levels and cell death. Electron microscopy demonstrated that hyperoxia damages the ultrastructure within petrosal ganglion neurons. Hyperoxic-induced increased levels of ROS in petrosal ganglion neurons may contribute to loss of hypoxic chemosensitivity during early postnatal development.
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Affiliation(s)
- Daniel J Kwak
- The John Hopkins Hospital, Research Laboratories, Baltimore, MD 21287-3200, USA
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Kwak DJ, Kwak SD, Gauda EB. The effect of hyperoxia on reactive oxygen species (ROS) in petrosal and nodose ganglion neurons during development (using organotypic slices). ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2006; 580:111-4; discussion 351-9. [PMID: 16683706 DOI: 10.1007/0-387-31311-7_17] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/09/2023]
Affiliation(s)
- D J Kwak
- Department of Pediatrics, Johns Hopkins University School of Medicine, Baltimore, MD 21287-3200, USA
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Bavis RW. Developmental plasticity of the hypoxic ventilatory response after perinatal hyperoxia and hypoxia. Respir Physiol Neurobiol 2005; 149:287-99. [PMID: 16203217 DOI: 10.1016/j.resp.2005.04.003] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2004] [Revised: 03/31/2005] [Accepted: 04/01/2005] [Indexed: 10/25/2022]
Abstract
Both genetic and environmental factors influence the normal development of the respiratory control system. This review examines the role perinatal O2 plays in the development of normoxic breathing and the hypoxic ventilatory response in mammals. Hyperoxia and hypoxia elicit plasticity in respiratory control that is unique to development and may persist weeks to years after return to normoxia. Specifically, both hyperoxia and hypoxia during early postnatal development attenuate the adult hypoxic ventilatory response, but the underlying mechanisms for this plasticity differ. Hyperoxia attenuates the hypoxic ventilatory response through potentially life-long changes in carotid body function. Neonatal hypoxia appears to have short-term effects on carotid body function, but persistent changes in the hypoxic ventilatory response may instead reflect changes in respiratory mechanics or related neural pathways. Overall, it appears that a relatively narrow range of environmental O2 is consistent with "normal" postnatal respiratory control development, predisposing animals to potentially maladaptive plasticity in the face of disease or atypical environmental conditions.
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Affiliation(s)
- Ryan W Bavis
- Department of Biology, Bates College, 44 Campus Ave., Carnegie Science Hall, Lewiston, ME 04240, USA.
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Kinkead R, Genest SE, Gulemetova R, Lajeunesse Y, Laforest S, Drolet G, Bairam A. Neonatal maternal separation and early life programming of the hypoxic ventilatory response in rats. Respir Physiol Neurobiol 2005; 149:313-24. [PMID: 15894516 DOI: 10.1016/j.resp.2005.04.014] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2004] [Revised: 04/14/2005] [Accepted: 04/14/2005] [Indexed: 11/29/2022]
Abstract
The neonatal period is critical for central nervous system (CNS) development. Recent studies have shown that this basic neurobiological principle also applies to the neural circuits regulating respiratory activity as exposure to excessive or insufficient chemosensory stimuli during early life can have long-lasting consequences on the performance of this vital system. Although the tactile, olfactory, and auditory stimuli that the mother provides to her offspring during the neonatal period are not directly relevant to respiratory homeostasis, they likely contribute to respiratory control development. This review outlines the rationale for the link between maternal stimuli and programming of the hypoxic ventilatory response during early life, and presents recent results obtained in rats indicating that experimental disruption of mother-pup interaction during this critical period elicits significant phenotypic plasticity of the hypoxic ventilatory response.
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Affiliation(s)
- Richard Kinkead
- Pediatrics, Centre de Recherche Hospitalier Universitaire de Québec, Université Laval, Québec, Qué., Canada.
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McGuire M, Zhang Y, White DP, Ling L. Phrenic long-term facilitation requires NMDA receptors in the phrenic motonucleus in rats. J Physiol 2005; 567:599-611. [PMID: 15932891 PMCID: PMC1474185 DOI: 10.1113/jphysiol.2005.087650] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
Abstract
Exposure to episodic hypoxia induces a persistent augmentation of respiratory activity, known as long-term facilitation (LTF). LTF of phrenic nerve activity has been reported to require serotonin receptor activation and protein syntheses. However, the underlying cellular mechanism still remains poorly understood. NMDA receptors play key roles in synaptic plasticity (e.g. some forms of hippocampal long-term potentiation). The present study was designed to examine the role of NMDA receptors in phrenic LTF and test if the relevant receptors are located in the phrenic motonucleus. Integrated phrenic nerve activity was measured in anaesthetized, vagotomized, neuromuscularly blocked and artificially ventilated rats before, during and after three episodes of 5 min isocapnic hypoxia (P(a,O2) = 30-45 mmHg), separated by 5 min hyperoxia (50% O2). Either saline (as control) or the NMDA receptor antagonist MK-801 (0.2 mg kg(-1), i.p.) was systemically injected approximately 1 h before hypoxia. Phrenic LTF was eliminated by the MK-801 injection (vehicle, 32.8 +/- 3.7% above baseline in phrenic amplitude at 60 min post-hypoxia; MK-801, -0.5 +/- 4.1%, means +/- S.E.M.), with little change in both the CO2-apnoeic threshold and the hypoxic phrenic response (HPR). Vehicle (saline, 5 x 100 nl) or MK-801 (10 microM; 5 x 100 nl) was also microinjected into the phrenic motonucleus region in other groups. Phrenic LTF was eliminated by the MK-801 microinjection (vehicle, 34.2 +/- 3.4%; MK-801, -2.5 +/- 2.8%), with minimal change in HPR. Collectively, these results suggest that the activation of NMDA receptors in the phrenic motonucleus is required for the episodic hypoxia-induced phrenic LTF.
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Affiliation(s)
- Michelle McGuire
- Division of Sleep Medicine, Brigham and Women's Hospital, Harvard Medical School, 75 Francis Street, Boston, MA 02115, USA
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McGuire M, Ling L. Ventilatory long-term facilitation is greater in 1- vs. 2-mo-old awake rats. J Appl Physiol (1985) 2005; 98:1195-201. [PMID: 15591293 DOI: 10.1152/japplphysiol.00996.2004] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Respiratory long-term facilitation (LTF) declines in middle-aged vs. adult male rats. Chronic intermittent hypoxia (CIH; 5 min 11–12% O2/5 min air, 12 h/night, 7 nights) enhances LTF in adult rats. However, LTF in immature rats and the effect of early CIH are unevaluated. The present study compared LTF in 1- and 2-mo-old rats and examined the effect of neonatal CIH (initiated at 2 days after birth) on the LTF. Ventilatory LTF, elicited by 5 ( protocol 1) or 10 ( protocol 2) episodes of poikilocapnic hypoxia (5 min 12% O2/5 min air), was measured twice by plethysmography on the same male conscious rat when it was 1 and 2 mo old. In untreated (without CIH) rats, both resting ventilation (54.7 ± 0.6 vs. 43.0 ± 0.2 ml·100 g−1·min−1) and hypoxic ventilatory response (131 ± 4 vs. 66 ± 3% above baseline) were greater in 1- vs. 2-mo-old rats. Protocol 1 elicited LTF in 1-mo-old (12.5 ± 1.0% above baseline) but not 2-mo-old rats. Protocol 2 elicited a greater LTF in 1-mo-old (24.3 ± 0.8%) vs. 2-mo-old rats (18.2 ± 0.5%). In CIH-treated rats, protocol 1 also elicited LTF in 1-mo-old (13.1 ± 1.5%) but not 2-mo-old rats. Protocol 2 elicited LTF in both age groups, but LTF was enhanced by the CIH only in 1-mo-old rats (28.8 ± 0.9%). These results suggest that ventilatory LTF and hypoxic ventilatory response are greater in male rats shortly before their sexual maturity and that the neonatal CIH somewhat enhances ventilatory LTF ∼3 wk after CIH, but this enhancement does not last to adulthood.
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Affiliation(s)
- Michelle McGuire
- Div. of Sleep Medicine at BIDMC, Brigham and Women's Hospital, 75 Francis St., Boston, MA 02115, USA
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Kinkead R, Gulemetova R, Bairam A. Neonatal maternal separation enhances phrenic responses to hypoxia and carotid sinus nerve stimulation in the adult anesthetized rat. J Appl Physiol (1985) 2005; 99:189-96. [PMID: 15790692 DOI: 10.1152/japplphysiol.00070.2005] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
In awake animals, our laboratory recently showed that the hypoxic ventilatory response of adult male (but not female) rats previously subjected to neonatal maternal separation (NMS) is 25% greater than controls (Genest SE, Gulemetova R, Laforest S, Drolet G, and Kinkead R. J Physiol 554: 543-557, 2004). To begin mechanistic investigations of the effects of this neonatal stress on respiratory control development, we tested the hypothesis that, in male rats, NMS enhances central integration of carotid body chemoafferent signals. Experiments were performed on two groups of adult male rats. Pups subjected to NMS were placed in a temperature-controlled incubator 3 h/day from postnatal day 3 to postnatal day 12. Control pups were undisturbed. At adulthood (8-10 wk), rats were anesthetized (urethane; 1.6 g/kg), paralyzed, and ventilated with a hyperoxic gas mixture [inspired O2 fraction (Fi(O2)) = 0.5], and phrenic nerve activity was recorded. The first series of experiments aimed to demonstrate that NMS-related enhancement of the inspiratory motor output (phrenic) response to hypoxia occurs in anesthetized animals also. In this series, rats were exposed to moderate, followed by severe, isocapnic hypoxia (Fi(O2) = 0.12 and 0.08, respectively, 5 min each). NMS enhanced both the frequency and amplitude components of the phrenic response to hypoxia relative to controls, thereby validating the use of this approach. In a second series of experiments, NMS increased the amplitude (but not the frequency) response to unilateral carotid sinus nerve stimulation (stimulation frequency range: 0.5-33 Hz). We conclude that enhancement of central integration of carotid body afferent signal contributes to the larger hypoxic ventilatory response observed in NMS rats.
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Affiliation(s)
- Richard Kinkead
- Centre de Recherche, Hôpital St.-François d'Assise, Department of Pediatrics, Laval University, Québec City, Québec, Canada G1L 3L5.
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Gauda EB, McLemore GL, Tolosa J, Marston-Nelson J, Kwak D. Maturation of peripheral arterial chemoreceptors in relation to neonatal apnoea. ACTA ACUST UNITED AC 2004; 9:181-94. [PMID: 15050211 DOI: 10.1016/j.siny.2003.11.002] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
Apnoea and periodic breathing are the hallmarks of breathing for the infant who is born prematurely. Sustained respiration is obtained through modulation of respiratory-related neurons with inputs from the periphery. The peripheral arterial chemoreceptors, uniquely and reflexly change ventilation in response to changes in oxygen tension. The chemoreflex in response to hypoxia is hyperventilation, bradycardia and vasoconstriction. The fast response time of the peripheral arterial chemoreceptors to changes in oxygen and carbon dioxide tension increases the risk of more periodicity in the breathing pattern. As a result of baseline hypoxaemia, peripheral arterial chemoreceptors contribute more to baseline breathing in premature than in term infants. While premature infants may have an augmented chemoreflex, infants who develop bronchopulmonary dysplasia have a blunted chemoreflex at term gestation. The development of chemosensitivity of the peripheral arterial chemoreceptors and environmental factors that might cause maldevelopment of chemosensitivity with continued maturation are reviewed in an attempt to help explain the physiology of apnoea of prematurity and the increased incidence of sudden infant death syndrome (SIDS) in infants born prematurely and those who are exposed to tobacco smoke.
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Affiliation(s)
- Estelle B Gauda
- Department of Pediatrics, Johns Hopkins Medical Institutions, Baltimore, MD 21287-3200, USA.
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Prieto-Lloret J, Caceres AI, Obeso A, Rocher A, Rigual R, Agapito MT, Bustamante R, Castañeda J, Perez-Garcia MT, Lopez-Lopez JR, Gonzalez C. Ventilatory responses and carotid body function in adult rats perinatally exposed to hyperoxia. J Physiol 2004; 554:126-44. [PMID: 14678497 PMCID: PMC1664733 DOI: 10.1113/jphysiol.2003.049445] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Hypoxia increases the release of neurotransmitters from chemoreceptor cells of the carotid body (CB) and the activity in the carotid sinus nerve (CSN) sensory fibers, elevating ventilatory drive. According to previous reports, perinatal hyperoxia causes CSN hypotrophy and varied diminishment of CB function and the hypoxic ventilatory response. The present study aimed to characterize the presumptive hyperoxic damage. Hyperoxic rats were born and reared for 28 days in 55%-60% O2; subsequent growth (to 3.5-4.5 months) was in a normal atmosphere. Hyperoxic and control rats (born and reared in a normal atmosphere) responded with a similar increase in ventilatory frequency to hypoxia and hypercapnia. In comparison with the controls, hyperoxic CBs showed (1) half the size, but comparable percentage area positive to tyrosine hydroxylase (chemoreceptor cells) in histological sections; (2) a twofold increase in dopamine (DA) concentration, but a 50% reduction in DA synthesis rate; (3) a 75% reduction in hypoxia-evoked DA release, but normal high [K+]0-evoked release; (4) a 75% reduction in the number of hypoxia-sensitive CSN fibers (although responding units displayed a nearly normal hypoxic response); and (5) a smaller percentage of chemoreceptor cells that increased [Ca2+]1 in hypoxia, although responses were within the normal range. We conclude that perinatal hyperoxia causes atrophy of the CB-CSN complex, resulting in a smaller number of chemoreceptor cells and fibers. Additionally, hyperoxia damages O2-sensing, but not exocytotic, machinery in most surviving chemoreceptor cells. Although hyperoxic CBs contain substantially smaller numbers of chemoreceptor cells/sensory fibers responsive to hypoxia they appear sufficient to evoke normal increases in ventilatory frequency.
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Affiliation(s)
- J Prieto-Lloret
- Departamento de Bioquimica y Biología Molecular y Fisiología/Instituto de Biología y Genética Molecular, Universidad de Valladolid/Consejo Superior de Investigaciones Científicas, Facultad de Medicina, 47005 Valladolid, Spain
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McGuire M, Zhang Y, White DP, Ling L. Serotonin receptor subtypes required for ventilatory long-term facilitation and its enhancement after chronic intermittent hypoxia in awake rats. Am J Physiol Regul Integr Comp Physiol 2003; 286:R334-41. [PMID: 14551171 DOI: 10.1152/ajpregu.00463.2003] [Citation(s) in RCA: 86] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Respiratory long-term facilitation (LTF), a serotonin-dependent, persistent augmentation of respiratory activity after episodic hypoxia, is enhanced by pretreatment of chronic intermittent hypoxia (CIH; 5 min 11-12% O2-5 min air, 12 h/night for 7 nights). The present study examined the effects of methysergide (serotonin 5-HT1,2,5,6,7 receptor antagonist), ketanserin (5-HT2 antagonist), or clozapine (5-HT2,6,7 antagonist) on both ventilatory LTF and the CIH effect on ventilatory LTF in conscious male adult rats to determine which specific receptor subtype(s) is involved. In untreated rats (i.e., animals not exposed to CIH), LTF, induced by five episodes of 5-min poikilocapnic hypoxia (10% O2) separated by 5-min normoxic intervals, was measured twice by plethysmography. Thus the measurement was conducted 1-2 days before (as control) and approximately 1 h after systemic injection of methysergide (1 mg/kg ip), ketanserin (1 mg/kg), or clozapine (1.5 mg/kg). Resting ventilation, metabolic rate, and hypoxic ventilatory response (HVR) were unchanged, but LTF ( approximately 18% above baseline) was eliminated by each drug. In CIH-treated rats, LTF was also measured twice, before and approximately 8 h after CIH. Vehicle, methysergide, ketanserin, or clozapine was injected approximately 1 h before the second measurement. Neither resting ventilation nor metabolic rate was changed after CIH and/or any drug. HVR was unchanged after methysergide and ketanserin but reduced in four of seven clozapine rats. The CIH-enhanced LTF ( approximately 28%) was abolished by methysergide and clozapine but only attenuated by ketanserin (to approximately 10%). Collectively, these data suggest that ventilatory LTF requires 5-HT2 receptors and that the CIH effect on LTF requires non-5-HT2 serotonin receptors, probably 5-HT6 and/or 5-HT7 subtype(s).
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Affiliation(s)
- Michelle McGuire
- Division of Sleep Medicine, Brigham and Women's Hospital, Harvard Medical School, 75 Francis St., Boston, MA 02115, USA
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Bavis RW, Olson EB, Vidruk EH, Bisgard GE, Mitchell GS. Level and duration of developmental hyperoxia influence impairment of hypoxic phrenic responses in rats. J Appl Physiol (1985) 2003; 95:1550-9. [PMID: 12819216 DOI: 10.1152/japplphysiol.01043.2002] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Developmental hyperoxia (1-4 wk of 60% O2) causes long-lasting impairment of hypoxic phrenic responses in rats. We hypothesized that shorter or less severe hyperoxic exposures would produce similar changes. Hypoxic phrenic responses were measured in 3- to 5-mo-old, urethane-anesthetized rats exposed to 60% O2 for postnatal day 1 or week 1 or to 30% O2 for postnatal week 1. Whereas 1 day of 60% O2 had no lasting effects (P > 0.05 vs. control), both 1 wk of 60% O2 and 1 wk of 30% O2 decreased adult hypoxic phrenic responses (P < 0.05 vs. control), although the effects of 30% O2 were smaller. Hypoxic ventilatory responses (expressed as the ratio of minute ventilation to metabolic CO2 production) were also reduced in unanesthetized rats (5-10 mo old) exposed to 1 wk of 60% O2 during development (P < 0.05). An age-dependent increase toward normal hypoxic phrenic responses was observed in rats exposed to 1 wk of 60% O2 (P < 0.05), suggesting a degree of spontaneous recovery not observed after 1 mo of 60% O2. These data indicate that long-lasting effects of developmental hyperoxia depend on the level and duration of hyperoxic exposure.
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Affiliation(s)
- R W Bavis
- Biology Dept., Bates College, Carnegie Science Bldg., 44 Campus Ave., Lewiston, ME 04240, USA.
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McGuire M, Zhang Y, White DP, Ling L. Chronic intermittent hypoxia enhances ventilatory long-term facilitation in awake rats. J Appl Physiol (1985) 2003; 95:1499-508. [PMID: 12819226 DOI: 10.1152/japplphysiol.00044.2003] [Citation(s) in RCA: 86] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
This study examined the effect of chronic intermittent hypoxia (CIH: 5 min 11-12% O2/5 min air, 12 h/night, 7 nights) on ventilatory long-term facilitation (LTF) and determined the persistence period of this CIH effect in awake rats. LTF, elicited by 5 or 10 episodes of 5 min 12% O2, was measured four times in the same Sprague-Dawley rats by plethysmography, before and 8 h, 3 days, and 7 days after CIH treatment. Resting ventilation was unchanged after CIH. Five episodes of 12% O2 did not initially elicit LTF but elicited LTF (23.5 +/- 1.4% above baseline) 8 h after CIH, which partially remained at 3 days (11.4 +/- 2.2%, P < 0.05) and disappeared at 7 days. Ten episodes initially elicited LTF (17.7 +/- 1.1%, 45-min duration) and elicited an enhanced LTF (29.1 +/- 1.5%, 75 min) 8 h after CIH. These results demonstrated that CIH enhanced ventilatory LTF in conscious, freely behaving rats in two ways: 1) a previously ineffective protocol induced LTF; and 2) LTF magnitude was increased and LTF duration prolonged, and this CIH effect on LTF persisted for at least 3 days.
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Affiliation(s)
- Michelle McGuire
- Division of Sleep Medicine, Brigham and Women's Hospital, Harvard Medical School, 221 Longwood Ave., Boston, MA 02115, USA
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Zhang Y, McGuire M, White DP, Ling L. Episodic phrenic-inhibitory vagus nerve stimulation paradoxically induces phrenic long-term facilitation in rats. J Physiol 2003; 551:981-91. [PMID: 12872010 PMCID: PMC2343284 DOI: 10.1113/jphysiol.2003.048157] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
All respiratory long-term facilitation (LTF) is induced by inspiratory-excitatory stimulation, suggesting that LTF needs inspiratory augmentation and is the result of a Hebbian mechanism (coincident pre- and post-synaptic activity strengthens synapses). The present study examined the long-term effects of episodic inspiratory-inhibitory vagus nerve stimulation (VNS) on phrenic nerve activity. We hypothesized that episodic VNS would induce phrenic long-term depression. The results are compared with those obtained following serotonin receptor antagonism or episodic carotid sinus nerve stimulation (CSNS). Integrated phrenic neurograms were measured before, during and after three episodes of 5 min VNS (50 Hz, 0.1 ms), each separated by a 5 min interval, at a low (approximately 50 microA), medium (approximately 200 microA) or high (approximately 500 microA) stimulus intensity in anaesthetized, vagotomized, neuromuscularly blocked and artificially ventilated rats. Medium- and high-intensity VNS eliminated rhythmic phrenic activity during VNS, while low-intensity VNS only reduced phrenic burst frequency. At 60 min post-VNS, phrenic amplitude was higher than baseline (35 +/- 5% above baseline, mean +/- S.E.M., P < 0.05) in the high-intensity group but not in the low- (-4 +/- 4%) or medium-intensity groups (-10 +/- 15%), or in the high-intensity with methysergide group (4 mg kg(-1), i.p.) (-11 +/- 5%). These data, which are inconsistent with our hypothesis, indicate that phrenic-inhibitory VNS induces a serotonin-dependent phrenic LTF similar to that induced by phrenic-excitatory CSNS (33 +/- 7%) and may require activation of high-threshold afferent fibres. These data also suggest that the synapses on phrenic motoneurons do not use the Hebbian mechanism in this LTF, as these motoneurons were suppressed during VNS.
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Affiliation(s)
- Yi Zhang
- Division of Sleep Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts 02115, USA
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Abstract
Development of the mammalian respiratory control system begins early in gestation and does not achieve mature form until weeks or months after birth. A relatively long gestation and period of postnatal maturation allows for prolonged pre- and postnatal interactions with the environment, including experiences such as episodic or chronic hypoxia, hyperoxia, and drug or toxin exposures. Developmental plasticity occurs when such experiences, during critical periods of maturation, result in long-term alterations in the structure or function of the respiratory control neural network. A critical period is a time window during development devoted to structural and/or functional shaping of the neural systems subserving respiratory control. Experience during the critical period can disrupt and alter developmental trajectory, whereas the same experience before or after has little or no effect. One of the clearest examples to date is blunting of the adult ventilatory response to acute hypoxia challenge by early postnatal hyperoxia exposure in the newborn. Developmental plasticity in neural respiratory control development can occur at multiple sites during formation of brain stem neuronal networks and chemoafferent pathways, at multiple times during development, by multiple mechanisms. Past concepts of respiratory control system maturation as rigidly predetermined by a genetic blueprint have now yielded to a different view in which extremely complex interactions between genes, transcriptional factors, growth factors, and other gene products shape the respiratory control system, and experience plays a key role in guiding normal respiratory control development. Early-life experiences may also lead to maladaptive changes in respiratory control. Pathological conditions as well as normal phenotypic diversity in mature respiratory control may have their roots, at least in part, in developmental plasticity.
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Affiliation(s)
- John L Carroll
- Pediatric Pulmonary Medicine, Arkansas Children's Hospital, University of Arkansas for Medical Sciences, Little Rock 72202, USA.
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Bavis RW, Mitchell GS. Intermittent hypoxia induces phrenic long-term facilitation in carotid-denervated rats. J Appl Physiol (1985) 2003; 94:399-409. [PMID: 12391138 DOI: 10.1152/japplphysiol.00374.2002] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Episodic hypoxia elicits a long-lasting augmentation of phrenic inspiratory activity known as long-term facilitation (LTF). We investigated the respective contributions of carotid chemoafferent neuron activation and hypoxia to the expression of LTF in urethane-anesthetized, vagotomized, paralyzed, and ventilated Sprague-Dawley rats. One hour after three 5-min isocapnic hypoxic episodes [arterial Po(2) (Pa(O(2))) = 40 +/- 5 Torr], integrated phrenic burst amplitude was greater than baseline in both carotid-denervated (n = 8) and sham-operated (n = 7) rats (P < 0.05), indicating LTF. LTF was reduced in carotid-denervated rats relative to sham (P < 0.05). In this and previous studies, rats were ventilated with hyperoxic gas mixtures (inspired oxygen fraction = 0.5) under baseline conditions. To determine whether episodic hyperoxia induces LTF, phrenic activity was recorded under normoxic (Pa(O(2)) = 90-100 Torr) conditions before and after three 5-min episodes of isocapnic hypoxia (Pa(O(2)) = 40 +/- 5 Torr; n = 6) or hyperoxia (Pa(O(2)) > 470 Torr; n = 6). Phrenic burst amplitude was greater than baseline 1 h after episodic hypoxia (P < 0.05), but episodic hyperoxia had no detectable effect. These data suggest that hypoxia per se initiates LTF independently from carotid chemoafferent neuron activation, perhaps through direct central nervous system effects.
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Affiliation(s)
- Ryan W Bavis
- Department of Comparative Biosciences, School of Veterinary Medicine, University of Wisconsin, Madison, 53706, USA.
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Prieto-Lloret J, Caceres AI, Rigual R, Obeso A, Rocher A, Bustamante R, Castañeda J, López-López JR, Perez-Garcia T, Agapito T, González C. Effects of Perinatal Hyperoxia on Carotid Body Chemoreceptor Activity in Vitro. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2003; 536:517-24. [PMID: 14635707 DOI: 10.1007/978-1-4419-9280-2_65] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/27/2023]
Affiliation(s)
- J Prieto-Lloret
- Dept. de Bioquímica y Biología Molecular y Fisiología/(IBGM), Universidad de Valladolid/(CSIC), Facultad de Medicina, Valladolid, Spain
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Abstract
Although recent evidence demonstrates considerable neuroplasticity in the respiratory control system, a comprehensive conceptual framework is lacking. Our goals in this review are to define plasticity (and related neural properties) as it pertains to respiratory control and to discuss potential sites, mechanisms, and known categories of respiratory plasticity. Respiratory plasticity is defined as a persistent change in the neural control system based on prior experience. Plasticity may involve structural and/or functional alterations (most commonly both) and can arise from multiple cellular/synaptic mechanisms at different sites in the respiratory control system. Respiratory neuroplasticity is critically dependent on the establishment of necessary preconditions, the stimulus paradigm, the balance between opposing modulatory systems, age, gender, and genetics. Respiratory plasticity can be induced by hypoxia, hypercapnia, exercise, injury, stress, and pharmacological interventions or conditioning and occurs during development as well as in adults. Developmental plasticity is induced by experiences (e.g., altered respiratory gases) during sensitive developmental periods, thereby altering mature respiratory control. The same experience later in life has little or no effect. In adults, neuromodulation plays a prominent role in several forms of respiratory plasticity. For example, serotonergic modulation is thought to initiate and/or maintain respiratory plasticity following intermittent hypoxia, repeated hypercapnic exercise, spinal sensory denervation, spinal cord injury, and at least some conditioned reflexes. Considerable work is necessary before we fully appreciate the biological significance of respiratory plasticity, its underlying cellular/molecular and network mechanisms, and the potential to harness respiratory plasticity as a therapeutic tool.
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Affiliation(s)
- Gordon S Mitchell
- Department of Comparative Biosciences, University of Wisconsin, Madison 53706, USA.
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McGuire M, Zhang Y, White DP, Ling L. Effect of hypoxic episode number and severity on ventilatory long-term facilitation in awake rats. J Appl Physiol (1985) 2002; 93:2155-61. [PMID: 12391141 DOI: 10.1152/japplphysiol.00405.2002] [Citation(s) in RCA: 61] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Episodic hypoxia induces a persistent augmentation of respiratory activity, termed long-term facilitation (LTF). Phrenic LTF saturates in anesthetized animals such that additional episodes of stimulation cause no further increase in LTF magnitude. The present study tested the hypothesis that 1) ventilatory LTF also saturates in awake rats and 2) more severe hypoxia and hypoxic episodes increase the effectiveness of eliciting ventilatory LTF. Minute ventilation was measured in awake, male Sprague-Dawley rats by plethysmography. LTF was elicited by five episodes of 10% O(2) poikilocapnic hypoxia (magnitude: 17.3 +/- 2.8% above baseline, between 15 and 45 min posthypoxia, duration: 45 min) but not 12 or 8% O(2). LTF was also elicited by 10, 20, and 72 episodes of 12% O(2) (19.1 +/- 2.2, 18.9 +/- 1.8, and 19.8 +/- 1.6%; 45, 60, and 75 min, respectively) but not by three or five episodes. These results show that there is a certain range of hypoxia that induces ventilatory LTF and that additional hypoxic episodes may increase the duration but not the magnitude of this response.
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Affiliation(s)
- Michelle McGuire
- Division of Sleep Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts 02115, USA
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Bavis RW, Olson EB, Mitchell GS. Critical developmental period for hyperoxia-induced blunting of hypoxic phrenic responses in rats. J Appl Physiol (1985) 2002; 92:1013-8. [PMID: 11842034 DOI: 10.1152/japplphysiol.00859.2001] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Hypoxic ventilatory and phrenic responses are reduced in adult rats reared in hyperoxia (60% O(2)) for the first month of life but not after hyperoxia as adults. In this study, we identified the developmental window for susceptibility to hyperoxia. Phrenic nerve responses to hypoxia were recorded in anesthetized, vagotomized, paralyzed, and ventilated Sprague-Dawley rats (aged 3-4 mo) exposed to 60% O(2) for the first, second, third, or fourth postnatal week. Responses were compared with control rats and with rats exposed to 60% O(2) for the first month of life. Phrenic minute activity (burst amplitude x frequency) increased less during isocapnic hypoxia (arterial PO(2) = 60, 50, and 40 Torr) in rats exposed to hyperoxia for the first or second week, or the first month, of life (P < 0.01 vs. control). Functional impairment caused by 1 wk of hyperoxia diminished with increasing age of exposure (P = 0.005). Adult hypoxic phrenic responses are impaired by 1 wk of hyperoxia during the first and second postnatal weeks in rats, indicating a developmental window coincident with carotid chemoreceptor maturation.
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Affiliation(s)
- R W Bavis
- Department of Comparative Biosciences, University of Wisconsin, Madison, Wisconsin 53706, USA.
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Fuller DD, Bavis RW, Vidruk EH, Wang ZY, Olson EB, Bisgard GE, Mitchell GS. Life-long impairment of hypoxic phrenic responses in rats following 1 month of developmental hyperoxia. J Physiol 2002; 538:947-55. [PMID: 11826178 PMCID: PMC2290109 DOI: 10.1113/jphysiol.2001.012908] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Hypoxic ventilatory and phrenic responses are reduced in adult rats (3-5 months old) exposed to hyperoxia for the first month of life (hyperoxia treated). We previously reported that hypoxic phrenic responses were normal in a small sample of 14- to 15-month-old hyperoxia-treated rats, suggesting slow, spontaneous recovery. Subsequent attempts to identify the mechanism(s) underlying this spontaneous recovery of hypoxic phrenic responses led us to re-evaluate our earlier conclusion. Experiments were conducted in two groups of aged Sprague-Dawley rats (14-15 months old) which were anaesthetized, vagotomized, neuromuscularly blocked and ventilated: (1) a hyperoxia-treated group raised in 60 % O2 for the first 28 postnatal days; and (2) an age-matched control group raised in normoxia. Increases in minute phrenic activity and integrated phrenic nerve amplitude (integral Phr) during isocapnic hypoxia (arterial partial pressures of O2, 60, 50 and 40 +/- 1 mmHg) were greater in aged control (n = 15) than hyperoxia-treated rats (n = 11; P < or = 0.01). Phrenic burst frequency during hypoxia was not different between groups. To examine the central integration of carotid chemoafferent inputs, steady-state relationships between carotid sinus nerve (electrical) stimulation frequency and phrenic nerve activity were compared in aged control (n = 7) and hyperoxia-treated rats (n = 7). Minute phrenic activity, integral Phr and burst frequency were not different between groups at any stimulation frequency between 0.5 and 20 Hz. Carotid body chemoreceptor function was examined by recording whole carotid sinus nerve responses to cessation of ventilation or injection of cyanide in aged control and hyperoxia-treated rats. Electrical activity of the carotid sinus nerve did not change in five out of five hyperoxia-treated rats in response to stimuli that evoked robust increases in carotid sinus nerve activity in five out of five control rats. Estimates of carotid body volume were lower in aged hyperoxia-treated rats (4.4 (+/- 0.2) x 10(6) microm3) compared to controls (17.4 (+/- 1.6) x 10(6) microm3; P <0.01). We conclude that exposure to hyperoxia for the first month of life causes life-long impairment of carotid chemoreceptor function and, consequently, blunted phrenic responses to hypoxia.
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Affiliation(s)
- D D Fuller
- Department of Comparative Biosciences, University of Wisconsin, 2015 Linden Drive West, Madison, WI 53076, USA.
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Fuller DD, Wang ZY, Ling L, Olson EB, Bisgard GE, Mitchell GS. Induced recovery of hypoxic phrenic responses in adult rats exposed to hyperoxia for the first month of life. J Physiol 2001; 536:917-26. [PMID: 11691883 PMCID: PMC2278901 DOI: 10.1111/j.1469-7793.2001.00917.x] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
Abstract
1. Adult rats exposed to hyperoxia for the first month of life have permanently attenuated ventilatory and phrenic nerve responses to hypoxia. We tested the hypothesis that the blunted hypoxic phrenic response in hyperoxia-treated rats (inspired O(2) fraction, F(I,O2) = 0.6 for 28 post-natal days) could be actively restored to normal by intermittent (alternating 12 % O(2)/air at 5 min intervals; 12 h per night for 1 week) or sustained (12 % O(2) for 1 week) hypoxia. 2. Phrenic responses to isocapnic hypoxia (P(a,O2) = 60, 50 and 40 +/- 2 mmHg) were assessed in the following groups of anaesthetized, vagotomized adult Sprague-Dawley rats (age 4 months), treated with a neuromuscular blocking agent and ventilated: control, hyperoxia-treated and hyperoxia-treated exposed to either intermittent or sustained hypoxia as adults. Experiments on intermittent and sustained hypoxia-treated rats were performed on the morning following hypoxic exposures. 3. Both intermittent and sustained hypoxia enhanced hypoxic phrenic responses in hyperoxia-treated rats when expressed as minute phrenic activity (P < 0.05). Increases in phrenic burst amplitude during hypoxia were greater in hyperoxia-treated rats after intermittent hypoxia (P < 0.05), and a similar but non-significant trend was observed after sustained hypoxia. Hypoxia-induced changes in phrenic burst frequency were not significantly different among groups. 4. The estimated carotid body volume in control rats (11.5 (+/- 0.7) x 10(6) microm(3)) was greater than in the other treatment groups (P < 0.05). However, carotid body volume was significantly greater in hyperoxia-treated rats exposed to sustained hypoxia (6.3 (+/- 0.3) x 10(6) microm(3); P < 0.05) compared to hyperoxia-treated rats (3.3 (+/- 0.2) x 10(6) microm(3)) or hyperoxia-treated rats exposed to intermittent hypoxia (3.8 (+/- 0.3) x 10(6) microm(3)). 5. Hypoxic phrenic responses in hyperoxia-treated rats 1 week after intermittent hypoxia were similar to responses measured immediately after intermittent hypoxia, indicating persistent functional recovery. 6. The results indicate that diminished hypoxic phrenic responses in adult rats due to hyperoxia exposure for the first 28 post-natal days can be reversed by intermittent or sustained activation of the hypoxic ventilatory control system. Although the detailed mechanisms of functional recovery are unknown, we suggest that sustained hypoxia restores carotid chemoreceptor sensitivity, whereas intermittent hypoxia primarily augments central integration of synaptic inputs from chemoafferent neurons.
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Affiliation(s)
- D D Fuller
- Department of Comparative Biosciences, University of Wisconsin, 2015 Linden Drive West, Madison, WI 53076, USA.
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Kinkead R, Bach KB, Johnson SM, Hodgeman BA, Mitchell GS. Plasticity in respiratory motor control: intermittent hypoxia and hypercapnia activate opposing serotonergic and noradrenergic modulatory systems. Comp Biochem Physiol A Mol Integr Physiol 2001; 130:207-18. [PMID: 11544068 DOI: 10.1016/s1095-6433(01)00393-2] [Citation(s) in RCA: 99] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
Experimental results consistently show that the respiratory control system is plastic, such that environmental factors and experience can modify its performance. Such plasticity may represent basic neurobiological principles of learning and memory, whereby intermittent sensory stimulation produces long-term alterations (i.e. facilitation or depression) in synaptic transmission depending on the timing and intensity of the stimulation. In this review, we propose that intermittent chemosensory stimulation produces long-term changes in respiratory motor output via specific neuromodulatory systems. This concept is based on recent data suggesting that intermittent hypoxia produces a net long-term facilitation of respiratory output via the serotonergic system, whereas intermittent hypercapnia produces a net long-term depression by a mechanism associated with the noradrenergic system. There is suggestive evidence that, although both respiratory stimuli activate both modulatory systems, the balance is different. Thus, these opposing modulatory influences on respiratory motor control may provide a 'push-pull' system, preventing unchecked and inappropriate fluctuations in ventilatory drive.
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Affiliation(s)
- R Kinkead
- Department of Pediatrics, Laval University, Quebec, Canada.
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Olson EB, Bohne CJ, Dwinell MR, Podolsky A, Vidruk EH, Fuller DD, Powell FL, Mitchel GS. Ventilatory long-term facilitation in unanesthetized rats. J Appl Physiol (1985) 2001; 91:709-16. [PMID: 11457785 DOI: 10.1152/jappl.2001.91.2.709] [Citation(s) in RCA: 127] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
We tested the hypothesis that unanesthetized rats exhibit ventilatory long-term facilitation (LTF) after intermittent, but not continuous, hypoxia. Minute ventilation (VE) and carbon dioxide production (VCO(2)) were measured in unanesthetized, unrestrained male Sprague-Dawley rats via barometric plethysmography before, during, and after exposure to continuous or intermittent hypoxia. Hypoxia was either isocapnic [inspired O(2) fraction (FI(O(2))) = 0.08--0.09 and inspired CO(2) fraction (FI(CO(2))) = 0.04] or poikilocapnic (FI(O(2)) = 0.11 and FI(CO(2)) = 0.00). Sixty minutes after intermittent hypoxia, VE or VE/VCO(2) was significantly greater than baseline in both isocapnic and poikilocapnic conditions. In contrast, 60 min after continuous hypoxia, VE and VE/VCO(2) were not significantly different from baseline values. These data demonstrate ventilatory LTF after intermittent hypoxia in unanesthetized rats. Ventilatory LTF appeared similar in its magnitude (after accounting for CO(2) feedback), time course, and dependence on intermittent hypoxia to phrenic LTF previously observed in anesthetized, vagotomized, paralyzed rats.
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Affiliation(s)
- E B Olson
- The John Rankin Laboratory of Pulmonary Medicine, Department of Preventive Medicine, University of Wisconsin School of Medicine, Madison, 53705-2368, USA.
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Mitchell GS, Baker TL, Nanda SA, Fuller DD, Zabka AG, Hodgeman BA, Bavis RW, Mack KJ, Olson EB. Invited review: Intermittent hypoxia and respiratory plasticity. J Appl Physiol (1985) 2001; 90:2466-75. [PMID: 11356815 DOI: 10.1152/jappl.2001.90.6.2466] [Citation(s) in RCA: 323] [Impact Index Per Article: 14.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Intermittent hypoxia elicits long-term facilitation (LTF), a persistent augmentation (hours) of respiratory motor output. Considerable recent progress has been made toward an understanding of the mechanisms and manifestations of this potentially important model of respiratory plasticity. LTF is elicited by intermittent but not sustained hypoxia, indicating profound pattern sensitivity in its underlying mechanism. During intermittent hypoxia, episodic spinal serotonin receptor activation initiates cell signaling events, increasing spinal protein synthesis. One associated protein is brain-derived neurotrophic factor, a neurotrophin implicated in several forms of synaptic plasticity. Our working hypothesis is that increased brain-derived neurotrophic factor enhances glutamatergic synaptic currents in phrenic motoneurons, increasing their responsiveness to bulbospinal inspiratory inputs. LTF is heterogeneous among respiratory outputs, differs among experimental preparations, and is influenced by age, gender, and genetics. Furthermore, LTF is enhanced following chronic intermittent hypoxia, indicating a degree of metaplasticity. Although the physiological relevance of LTF remains unclear, it may reflect a general mechanism whereby intermittent serotonin receptor activation elicits respiratory plasticity, adapting system performance to the ever-changing requirements of life.
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Affiliation(s)
- G S Mitchell
- Department of Comparative Biosciences, University of Wisconsin, Madison, Wisconsin 53706, USA
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45
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Chronic intermittent hypoxia elicits serotonin-dependent plasticity in the central neural control of breathing. J Neurosci 2001. [PMID: 11438615 DOI: 10.1523/jneurosci.21-14-05381.2001] [Citation(s) in RCA: 199] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
We tested the hypothesis that chronic intermittent hypoxia (CIH) elicits plasticity in the central neural control of breathing via serotonin-dependent effects on the integration of carotid chemoafferent inputs. Adult rats were exposed to 1 week of nocturnal CIH (11-12% O(2)/air at 5 min intervals; 12 hr/night). CIH and untreated rats were then anesthetized, paralyzed, vagotomized, and artificially ventilated. Time-dependent hypoxic responses were assessed in the phrenic neurogram during and after three 5 min episodes of isocapnic hypoxia. Integrated phrenic amplitude (integralPhr) responses during hypoxia were greater after CIH at arterial oxygen pressures (PaO(2)) between 25 and 45 mmHg (p < 0.05), but not at higher PaO(2) levels. CIH did not affect hypoxic phrenic burst frequency responses, although the post-hypoxia frequency decline that is typical in rats was abolished. integralPhr and frequency responses to electrical stimulation of the carotid sinus nerve were enhanced by CIH (p < 0.05). Serotonin-dependent long-term facilitation (LTF) of integralPhr was enhanced after CIH at 15, 30, and 60 min after episodic hypoxia (p < 0.05). Pretreatment with the serotonin receptor antagonists methysergide (4 mg/kg, i.v.) and ketanserin (2 mg/kg, i.v.) reversed CIH-induced augmentation of the short-term hypoxic phrenic response and restored the post-hypoxia frequency decline in CIH rats. Whereas methysergide abolished CIH-enhanced phrenic LTF, the selective 5-HT(2) antagonist ketanserin only partially reversed this effect. The results suggest that CIH elicits unique forms of serotonin-dependent plasticity in the central neural control of breathing. Enhanced LTF after CIH may involve an upregulation of a non-5-HT(2) serotonin receptor subtype or subtypes.
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46
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Ling L, Fuller DD, Bach KB, Kinkead R, Olson EB, Mitchell GS. Chronic intermittent hypoxia elicits serotonin-dependent plasticity in the central neural control of breathing. J Neurosci 2001; 21:5381-8. [PMID: 11438615 PMCID: PMC6762841] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2000] [Revised: 05/02/2001] [Accepted: 05/03/2001] [Indexed: 02/20/2023] Open
Abstract
We tested the hypothesis that chronic intermittent hypoxia (CIH) elicits plasticity in the central neural control of breathing via serotonin-dependent effects on the integration of carotid chemoafferent inputs. Adult rats were exposed to 1 week of nocturnal CIH (11-12% O(2)/air at 5 min intervals; 12 hr/night). CIH and untreated rats were then anesthetized, paralyzed, vagotomized, and artificially ventilated. Time-dependent hypoxic responses were assessed in the phrenic neurogram during and after three 5 min episodes of isocapnic hypoxia. Integrated phrenic amplitude (integralPhr) responses during hypoxia were greater after CIH at arterial oxygen pressures (PaO(2)) between 25 and 45 mmHg (p < 0.05), but not at higher PaO(2) levels. CIH did not affect hypoxic phrenic burst frequency responses, although the post-hypoxia frequency decline that is typical in rats was abolished. integralPhr and frequency responses to electrical stimulation of the carotid sinus nerve were enhanced by CIH (p < 0.05). Serotonin-dependent long-term facilitation (LTF) of integralPhr was enhanced after CIH at 15, 30, and 60 min after episodic hypoxia (p < 0.05). Pretreatment with the serotonin receptor antagonists methysergide (4 mg/kg, i.v.) and ketanserin (2 mg/kg, i.v.) reversed CIH-induced augmentation of the short-term hypoxic phrenic response and restored the post-hypoxia frequency decline in CIH rats. Whereas methysergide abolished CIH-enhanced phrenic LTF, the selective 5-HT(2) antagonist ketanserin only partially reversed this effect. The results suggest that CIH elicits unique forms of serotonin-dependent plasticity in the central neural control of breathing. Enhanced LTF after CIH may involve an upregulation of a non-5-HT(2) serotonin receptor subtype or subtypes.
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Affiliation(s)
- L Ling
- Departments of Comparative Biosciences and Preventive Medicine, University of Wisconsin, Madison, Wisconsin 53706, USA
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Powell FL, Dwinell MR, Aaron EA. Measuring ventilatory acclimatization to hypoxia: comparative aspects. RESPIRATION PHYSIOLOGY 2000; 122:271-84. [PMID: 10967350 DOI: 10.1016/s0034-5687(00)00165-1] [Citation(s) in RCA: 46] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
Acclimatization to hypoxia increases the hypoxic ventilatory response (HVR) in mammals. The literature on humans shows that several protocols can quantify this increase in HVR if isocapnia is maintained, regardless of the exact level of Pa(CO(2)). In rats, the isocapnic HVR also increases with chronic hypoxia and this cannot be explained by a non-specific effect of increased ventilatory drive on the HVR. Changes in arterial pH are predicted to increase the HVR during chronic hypoxia in rats but this has not been quantified. Limitations in determining mechanisms of change in the HVR from reflex experiments are discussed. Chronic hypoxia changes some, but not all, indices of ventilatory motor output that are useful for normalization between experiments on anesthetized rats. Finally, ducks also show time-dependent increases in ventilation during chronic hypoxia and birds provide a good experimental model to study reflex interactions. However, reflexes from intrapulmonary CO(2) chemoreceptors can complicate the measurement of changes in the isocapnic HVR during chronic hypoxia in birds.
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Affiliation(s)
- F L Powell
- Department of Medicine, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0623, USA.
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Bach KB, Kinkead R, Mitchell GS. Post-hypoxia frequency decline in rats: sensitivity to repeated hypoxia and alpha2-adrenoreceptor antagonism. Brain Res 1999; 817:25-33. [PMID: 9889307 DOI: 10.1016/s0006-8993(98)01181-0] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
We tested the hypothesis that the post-hypoxia frequency decline of phrenic nerve activity following brief, isocapnic hypoxic episodes in rats is diminished by prior hypoxic episodes and alpha2-adrenoreceptor antagonism. Anesthetized (urethane), artificially ventilated (FIO2=0.50) and vagotomized rats were presented with two or three, 5 min episodes of isocapnic hypoxia (FIO2 approximately 0.11), separated by 30 min of control, hyperoxic conditions. Phrenic nerve discharge, end-tidal CO2, and arterial blood gases were measured before during and after hypoxia. The average maximum frequency decline, measured 5 min after the first hypoxic episode, was 26+/-7 bursts/min below pre-hypoxic baseline values (a 70+/-16% decrease). By 30 min post-hypoxia, frequency had returned to baseline. Two groups of rats were then administered either: (1) saline (sham) or (2) the alpha2-receptor antagonist, RX821002 HCl (2-[2-(2-Methoxy-1,4-benzodioxanyl)] imidazoline hydrochloride; 0.25 mg/kg, i.v.). Isocapnic hypoxia was repeated 10 min later. In sham rats, the post-hypoxia frequency decline (PHFD) was significantly attenuated relative to the initial (control) response. However, PHFD was attenuated significantly more in RX821002-treated vs. sham rats (-3+/-3 bursts/min vs. -12+/-4 bursts/min @ 5 min post hypoxia for RX821002 and sham-treated, respectively; p<0.05). We conclude that the magnitude of PHFD is dependent on the prior history of hypoxia and that alpha2 adrenoreceptor activation plays a role in its underlying mechanism.
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Affiliation(s)
- K B Bach
- Department of Comparative Biosciences and Center for Neuroscience, School of Veterinary Medicine, University of Wisconsin, 2015 Linden Drive West, Madison, WI, 53706,
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Gozal D, Gozal E. Episodic hypoxia enhances late hypoxic ventilation in developing rat: putative role of neuronal NO synthase. THE AMERICAN JOURNAL OF PHYSIOLOGY 1999; 276:R17-22. [PMID: 9887173 DOI: 10.1152/ajpregu.1999.276.1.r17] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Nitric oxide (NO) is an excitatory neurotransmitter in the hypoxic ventilatory response (HVR). Furthermore, neuronal NO synthase (nNOS) activity in the developing rat correlates with the magnitude of late hypoxic ventilatory depression. To test the hypothesis that repeated short exposures to hypoxia may modify late HVR characteristics in young rats, we conducted 30-min hypoxic challenges in 2- to 3-day-old rat pups, before (Pre) and 6 h after (Post) they completed a series of eight cycles consisting of 5 min of hypoxia and 10 min of normoxia (Hyp-Norm) or normoxia throughout (Norm-Norm). In an additional group, similar challenges were performed after administration of either intraperitoneal vehicle or 25 mg/kg 7-nitroindazole (7-NI). Ventilation (VE) was measured using whole body plethysmography. Although no changes in peak VE responses occurred with episodic hypoxia (Pre vs. Post, P = not significant), late VE reductions were markedly attenuated in Post (DeltaVE from early to late: 7.2 +/- 1.5 ml/min in Pre vs. 4.5 +/- 1.1 ml/min in Post; P < 0.002). Furthermore, 7-NI treatment of Post animals was associated with late VE reductions to Pre levels in Hyp-Norm-exposed animals. Western blots of protein equivalents from the caudal brain stem revealed increased nNOS expression in Hyp-Norm compared with Norm-Norm (P < 0.01). Current findings suggest that repeated short hypoxic exposures improve the ability to sustain VE, which appears to be mediated by increased nNOS expression and activity in brain stem respiratory regions. We postulate that changes in nNOS may play a role in respiratory control plasticity.
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Affiliation(s)
- D Gozal
- Constance S. Kaufman Pediatric Pulmonary Research Laboratory, Departments of Pediatrics and Physiology, Tulane University School of Medicine, New Orleans, Louisiana 70112, USA
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Ling L, Olson EB, Vidruk EH, Mitchell GS. Slow recovery of impaired phrenic responses to hypoxia following perinatal hyperoxia in rats. J Physiol 1998; 511 ( Pt 2):599-603. [PMID: 9706034 PMCID: PMC2231139 DOI: 10.1111/j.1469-7793.1998.599bh.x] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
Abstract
1. Previous studies demonstrated that both ventilatory and phrenic nerve responses to acute hypoxia are greatly attenuated in adult rats (3-5 months old) previously exposed to 1 month of perinatal hyperoxia (60 % O2; perinatal treated rats). The present study tested the hypothesis that this functional impairment recovers spontaneously with advancing age in perinatal treated rats. 2. Hypoxia-induced chemoreflexes were examined by measuring integrated phrenic responses to strictly controlled isocapnic hypoxia in urethane-anaesthetized, vagotomized, paralysed and ventilated rats at different ages. 3. At 50 mmHg Pa,O2 (arterial O2 partial pressure), the hypoxia-induced increase in minute phrenic activity was significantly attenuated in both 3- to 5-month-old (166 +/- 15% of baseline) and 6-month-old (130 +/- 17%) perinatal treated rats, relative to 3- to 6-month-old, untreated control rats (279 +/- 28%; both P < 0.05). However, at 40 mmHg Pa,O2, the hypoxic minute phrenic activity response was attenuated only in 3- to 5-month-old (154 +/- 33%), but not 6-month-old (232 +/- 33%) perinatal treated rats versus control rats (293 +/- 30%). 4. The minute phrenic activity response to hypoxia was not significantly different between geriatric perinatal treated rats (14-15 months) and untreated geriatric control rats at either 50 mmHg (treated: 250 +/- 20% versus control: 274 +/- 23%) or 40 mmHg Pa,O2 (treated: 292 +/- 19% versus control: 315 +/- 36%). 5. These data suggest that partial spontaneous recovery may occur in 6-month-old perinatal treated rats and that full recovery occurs by 15 months of age.
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Affiliation(s)
- L Ling
- Department of Comparative Biosciences, University of Wisconsin, Madison, WI 53706, USA
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