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Burggren W, Fahlman A, Milsom W. Breathing patterns and associated cardiovascular changes in intermittently breathing animals: (Partially) correcting a semantic quagmire. Exp Physiol 2024; 109:1051-1065. [PMID: 38502538 PMCID: PMC11215480 DOI: 10.1113/ep091784] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2024] [Accepted: 02/29/2024] [Indexed: 03/21/2024]
Abstract
Many animal species do not breathe in a continuous, rhythmic fashion, but rather display a variety of breathing patterns characterized by prolonged periods between breaths (inter-breath intervals), during which the heart continues to beat. Examples of intermittent breathing abound across the animal kingdom, from crustaceans to cetaceans. With respect to human physiology, intermittent breathing-also termed 'periodic' or 'episodic' breathing-is associated with a variety of pathologies. Cardiovascular phenomena associated with intermittent breathing in diving species have been termed 'diving bradycardia', 'submersion bradycardia', 'immersion bradycardia', 'ventilation tachycardia', 'respiratory sinus arrhythmia' and so forth. An examination across the literature of terminology applied to these physiological phenomena indicates, unfortunately, no attempt at standardization. This might be viewed as an esoteric semantic problem except for the fact that many of the terms variously used by different authors carry with them implicit or explicit suggestions of underlying physiological mechanisms and even human-associated pathologies. In this article, we review several phenomena associated with diving and intermittent breathing, indicate the semantic issues arising from the use of each term, and make recommendations for best practice when applying specific terms to particular cardiorespiratory patterns. Ultimately, we emphasize that the biology-not the semantics-is what is important, but also stress that confusion surrounding underlying mechanisms can be avoided by more careful attention to terms describing physiological changes during intermittent breathing and diving.
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Affiliation(s)
- Warren Burggren
- Developmental Integrative Biology Group, Department of Biological SciencesUniversity of North TexasDentonTexasUSA
| | - Andreas Fahlman
- Fundación OceanogràficValenciaSpain
- Kolmården Wildlife ParkKolmårdenSweden
- IFMLinkoping UniversityLinkopingSweden
| | - William Milsom
- Department of ZoologyUniversity of British ColumbiaVancouverBritish ColumbiaCanada
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2
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Rocha GC, Castro SA, Taylor EW, Tavares D, Leite CAC. A Decerebrate Preparation of the Rattlesnake, Crotalus durissus, Provides an Experimental Model for Study of Autonomic Modulation of the Cardiovascular System in Reptiles. Physiol Biochem Zool 2021; 94:269-285. [PMID: 34142933 DOI: 10.1086/714973] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
AbstractThe South American rattlesnake, Crotalus durissus, has been successfully used as an experimental model to study control of the cardiovascular system in squamate reptiles. Recent technical advances, including equipment miniaturization, have lessened the impact of instrumentation on in vivo recordings, and an increased range of anesthetic drugs has improved recording conditions for in situ preparations. Nevertheless, any animal-based experimental approach has to manage limitations regarding the avoidance of pain and stress the stability of the preparation and duration of experiments and the potentially overriding effects of anesthesia. To address such aspects, we tested a new experimental preparation, the decerebrate rattlesnake, in a study of the autonomic control of cardiovascular responses following the removal of general anesthesia. The preparation exhibited complex cardiovascular adjustments to deal with acute increases in venous return (caused by tail lifting), to compensate for blood flow reduction in the cephalic region (caused by head lifting), for body temperature control (triggered by an external heating source), and in response to stimulation of chemoreceptors (triggered by intravenous injection of NaCN). The decerebrate preparation retained extensive functional integrity of autonomic centers, and it was suitable for monitoring diverse cardiac and vascular variables. Furthermore, reanesthetizing the preparation markedly blunted cardiovascular performance. Isoflurane limited the maintenance of recovered cardiovascular variables in the prepared animal and reduced or abolished the observed cardiovascular reflexes. This preparation enables the recording of multiple concomitant cardiovascular variables for the study of mechanistic questions regarding the central integration of autonomic reflex responses in the absence of anesthesia.
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Guagnoni IN, Armelin VA, da Silva Braga VH, Rantin FT, Florindo LH. Postprandial cardiorespiratory responses and the regulation of digestion-associated tachycardia in Nile tilapia (Oreochromis niloticus). J Comp Physiol B 2020; 191:55-67. [PMID: 33005989 DOI: 10.1007/s00360-020-01317-x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2020] [Revised: 08/29/2020] [Accepted: 09/20/2020] [Indexed: 11/25/2022]
Abstract
Cardiorespiratory adjustments that occur after feeding are essential to supply the demands of digestion in vertebrates. The well-documented postprandial tachycardia is triggered by an increase in adrenergic activity and by non-adrenergic non-cholinergic (NANC) factors in mammals and crocodilians, while it is linked to a withdrawal of vagal drive and NANC factors in non-crocodilian ectotherms-except for fish, in which the sole investigation available indicated no participation of NANC factors. On the other hand, postprandial ventilatory adjustments vary widely among air-breathing vertebrates, with different species exhibiting hyperventilation, hypoventilation, or even no changes at all. Regarding fish, which live in an environment with low oxygen capacitance that requires great ventilatory effort for oxygen uptake, data on the ventilatory consequences of feeding are also scarce. Thus, the present study sought to investigate the postprandial cardiorespiratory adjustments and the mediation of digestion-associated tachycardia in the unimodal water-breathing teleost Oreochromis niloticus. Heart rate (fH), cardiac autonomic tones, ventilation rate (fV), ventilation amplitude, total ventilation and fH/fV variability were assessed both in fasting and digesting animals under untreated condition, as well as after muscarinic cholinergic blockade with atropine and double autonomic blockade with atropine and propranolol. The results revealed that digestion was associated with marked tachycardia in O. niloticus, determined by a reduction in cardiac parasympathetic activity and by circulating NANC factors-the first time such positive chronotropes were detected in digesting fish. Unexpectedly, postprandial ventilatory alterations were not observed, although digestion triggered mechanisms that were presumed to increase oxygen uptake, such as cardiorespiratory synchrony.
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Affiliation(s)
- Igor Noll Guagnoni
- Department of Zoology and Botany, Institute of Biosciences, Languages and Exact Sciences, São Paulo State University (UNESP), Rua Cristóvão Colombo, 2265, São José do Rio Preto, SP, 15054-000, Brazil.,National Institute of Science and Technology in Comparative Physiology (INCT, FAPESP/CNPq), São Paulo, Brazil
| | - Vinicius Araújo Armelin
- Department of Zoology and Botany, Institute of Biosciences, Languages and Exact Sciences, São Paulo State University (UNESP), Rua Cristóvão Colombo, 2265, São José do Rio Preto, SP, 15054-000, Brazil.,Department of Physiology, Institute of Biosciences, University of São Paulo (USP), Rua do Matão, Travessa 14, 321, São Paulo, SP, 05508-090, Brazil.,National Institute of Science and Technology in Comparative Physiology (INCT, FAPESP/CNPq), São Paulo, Brazil
| | - Victor Hugo da Silva Braga
- Department of Zoology and Botany, Institute of Biosciences, Languages and Exact Sciences, São Paulo State University (UNESP), Rua Cristóvão Colombo, 2265, São José do Rio Preto, SP, 15054-000, Brazil.,National Institute of Science and Technology in Comparative Physiology (INCT, FAPESP/CNPq), São Paulo, Brazil
| | - Francisco Tadeu Rantin
- Department of Physiological Sciences, Federal University of São Carlos (UFSCar), Rodovia Washington Luiz, km 235, São Carlos, SP, 13565‑905, Brazil.,National Institute of Science and Technology in Comparative Physiology (INCT, FAPESP/CNPq), São Paulo, Brazil
| | - Luiz Henrique Florindo
- Department of Zoology and Botany, Institute of Biosciences, Languages and Exact Sciences, São Paulo State University (UNESP), Rua Cristóvão Colombo, 2265, São José do Rio Preto, SP, 15054-000, Brazil. .,Aquaculture Center (CAUNESP), São Paulo State University (UNESP), Rodovia Prof. Paulo Donato Castellane, n/n, Jaboticabal, SP, 14884-900, Brazil. .,National Institute of Science and Technology in Comparative Physiology (INCT, FAPESP/CNPq), São Paulo, Brazil.
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4
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Kolesnikova EE. Neurophysiological Mechanisms of Respiratory Activity in Cyclostomes and Fish during Aquatic Breathing. J EVOL BIOCHEM PHYS+ 2019. [DOI: 10.1134/s0022093019020017] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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5
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Armelin VA, Braga VHDS, Teixeira MT, Rantin FT, Florindo LH, Kalinin AL. Gill denervation eliminates the barostatic reflex in a neotropical teleost, the tambaqui (Colossoma macropomum). FISH PHYSIOLOGY AND BIOCHEMISTRY 2016; 42:1213-1224. [PMID: 26932845 DOI: 10.1007/s10695-016-0211-9] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/17/2016] [Accepted: 02/18/2016] [Indexed: 06/05/2023]
Abstract
The baroreflex is one of the most important regulators of cardiovascular homeostasis in vertebrates. It begins with the monitoring of arterial pressure by baroreceptors, which constantly provide the central nervous system with afferent information about the status of this variable. Any change in arterial pressure relative to its normal state triggers autonomic responses, which are characterized by an inversely proportional change in heart rate and systemic vascular resistance and which tend to restore pressure normality. Although the baroreceptors have been located in mammals and other terrestrial vertebrates, their location in fish is still not completely clear and remains quite controversial. Thus, the objective of this study was to locate the baroreceptors in a teleost, the Colossoma macropomum. To do so, the occurrence and efficiency of the baroreflex were both analyzed when this mechanism was induced by pressure imbalancements in intact fish (IN), first-gill-denervated fish (G1), and total-gill-denervated fish (G4). The pressure imbalances were initiated through the administration of the α1-adrenergic agonist phenylephrine (100 µg kg(-1)) and the α1-adrenergic antagonist prazosin (1 mg kg(-1)). The baroreflex responses were then analyzed using an electrocardiogram that allowed for the measurement of the heart rate, the relationship between pre- and post-pharmacological manipulation heart rates, the time required for maximum chronotropic baroreflex response, and total heart rate variability. The results revealed that the barostatic reflex was attenuated in the G1 group and nonexistent in G4 group, findings which indicate that baroreceptors are exclusively located in the gill arches of C. macropomum.
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Affiliation(s)
- Vinicius Araújo Armelin
- Department of Physiological Sciences, Federal University of São Carlos (UFSCar), Rodovia Washington Luiz, km 235, São Carlos, SP, 13565-905, Brazil
- National Institute of Science and Technology in Comparative Physiology (INCT - FAPESP/CNPq), São Paulo, Brazil
| | - Victor Hugo da Silva Braga
- Department of Zoology and Botany, São Paulo State University (UNESP), Rua Cristóvão Colombo, 2265, São José do Rio Preto, SP, 15054-000, Brazil
- National Institute of Science and Technology in Comparative Physiology (INCT - FAPESP/CNPq), São Paulo, Brazil
| | - Mariana Teodoro Teixeira
- Department of Zoology and Botany, São Paulo State University (UNESP), Rua Cristóvão Colombo, 2265, São José do Rio Preto, SP, 15054-000, Brazil
- National Institute of Science and Technology in Comparative Physiology (INCT - FAPESP/CNPq), São Paulo, Brazil
| | - Francisco Tadeu Rantin
- Department of Physiological Sciences, Federal University of São Carlos (UFSCar), Rodovia Washington Luiz, km 235, São Carlos, SP, 13565-905, Brazil
- National Institute of Science and Technology in Comparative Physiology (INCT - FAPESP/CNPq), São Paulo, Brazil
| | - Luiz Henrique Florindo
- Department of Zoology and Botany, São Paulo State University (UNESP), Rua Cristóvão Colombo, 2265, São José do Rio Preto, SP, 15054-000, Brazil.
- National Institute of Science and Technology in Comparative Physiology (INCT - FAPESP/CNPq), São Paulo, Brazil.
- Aquaculture Center (CAUNESP), São Paulo State University (UNESP), Rodovia Prof. Paulo Donato Castellane, n/n, Jaboticabal, SP, 14884-900, Brazil.
| | - Ana Lúcia Kalinin
- Department of Physiological Sciences, Federal University of São Carlos (UFSCar), Rodovia Washington Luiz, km 235, São Carlos, SP, 13565-905, Brazil
- National Institute of Science and Technology in Comparative Physiology (INCT - FAPESP/CNPq), São Paulo, Brazil
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Porteus C, Hedrick MS, Hicks JW, Wang T, Milsom WK. Time domains of the hypoxic ventilatory response in ectothermic vertebrates. J Comp Physiol B 2011; 181:311-33. [PMID: 21312038 PMCID: PMC3058336 DOI: 10.1007/s00360-011-0554-6] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2010] [Revised: 01/11/2011] [Accepted: 01/19/2011] [Indexed: 01/19/2023]
Abstract
Over a decade has passed since Powell et al. (Respir Physiol 112:123-134, 1998) described and defined the time domains of the hypoxic ventilatory response (HVR) in adult mammals. These time domains, however, have yet to receive much attention in other vertebrate groups. The initial, acute HVR of fish, amphibians and reptiles serves to minimize the imbalance between oxygen supply and demand. If the hypoxia is sustained, a suite of secondary adjustments occur giving rise to a more long-term balance (acclimatization) that allows the behaviors of normal life. These secondary responses can change over time as a function of the nature of the stimulus (the pattern and intensity of the hypoxic exposure). To add to the complexity of this process, hypoxia can also lead to metabolic suppression (the hypoxic metabolic response) and the magnitude of this is also time dependent. Unlike the original review of Powell et al. (Respir Physiol 112:123-134, 1998) that only considered the HVR in adult animals, we also consider relevant developmental time points where information is available. Finally, in amphibians and reptiles with incompletely divided hearts the magnitude of the ventilatory response will be modulated by hypoxia-induced changes in intra-cardiac shunting that also improve the match between O(2) supply and demand, and these too change in a time-dependent fashion. While the current literature on this topic is reviewed here, it is noted that this area has received little attention. We attempt to redefine time domains in a more 'holistic' fashion that better accommodates research on ectotherms. If we are to distinguish between the genetic, developmental and environmental influences underlying the various ventilatory responses to hypoxia, however, we must design future experiments with time domains in mind.
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Affiliation(s)
- Cosima Porteus
- Department of Zoology, University of British Columbia, Vancouver, BC, V6T 1Z4, Canada.
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7
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Johnson SM, Moris CM, Bartman ME, Wiegel LM. Excitatory and inhibitory effects of opioid agonists on respiratory motor output produced by isolated brainstems from adult turtles (Trachemys). Respir Physiol Neurobiol 2009; 170:5-15. [PMID: 19833235 DOI: 10.1016/j.resp.2009.10.004] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2008] [Revised: 10/05/2009] [Accepted: 10/06/2009] [Indexed: 02/07/2023]
Abstract
To determine how central opioid receptor activation alters turtle breathing, respiratory-related hypoglossal (XII) motor bursts were recorded from isolated adult turtle brainstems during 60 min bath applications of agonists for delta- (DOR), kappa- (KOR), or nociceptin/orphanin (NOR) receptors. DADLE (DOR agonist) abolished XII burst frequency at 0.3-0.5 microM. DPDPE (DOR agonist) increased frequency by 40-44% at 0.01-0.1 microM and decreased frequency by 88+/-8% at 1.0 microM. U-50488 and U-59693 (KOR agonists) decreased frequency by 65-68% at 100 and 50 microM, respectively. Orphanin (NOR agonist) decreased frequency by 31-51% at 1.0-2.0 microM during the first 30 min period. Orphanin (0.5 and 2.0 microM) increased bursts/episode. Although morphine (10 microM) abolished frequency in nearly all brainstems, subsequent co-application of phenylephrine (alpha(1)-adrenergic agonist, 20-100 microM) with morphine restored activity to 16-78% of baseline frequency. Thus, DOR, KOR, and NOR activation regulates frequency and NOR activation regulates episodicity, while alpha(1)-adrenergic receptor activation reverses opioid-induced respiratory depression in turtles.
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Affiliation(s)
- Stephen M Johnson
- Department of Comparative Biosciences, School of Veterinary Medicine, University of Wisconsin, Madison, WI 53706, USA.
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8
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Fong AY, Zimmer MB, Milsom WK. The conditional nature of the “Central Rhythm Generator” and the production of episodic breathing. Respir Physiol Neurobiol 2009; 168:179-87. [DOI: 10.1016/j.resp.2009.05.012] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2009] [Revised: 05/20/2009] [Accepted: 05/28/2009] [Indexed: 12/01/2022]
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9
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Perry S, Jonz M, Gilmour K. Chapter 5 Oxygen Sensing And The Hypoxic Ventilatory Response. FISH PHYSIOLOGY 2009. [DOI: 10.1016/s1546-5098(08)00005-8] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
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10
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Leite CAC, Florindo LH, Kalinin AL, Milsom WK, Rantin FT. Gill chemoreceptors and cardio-respiratory reflexes in the neotropical teleost pacu, Piaractus mesopotamicus. J Comp Physiol A Neuroethol Sens Neural Behav Physiol 2007; 193:1001-11. [PMID: 17680247 DOI: 10.1007/s00359-007-0257-3] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2006] [Revised: 07/16/2007] [Accepted: 07/17/2007] [Indexed: 10/23/2022]
Abstract
This study examined the location and distribution of O(2) chemoreceptors involved in cardio-respiratory responses to hypoxia in the neotropical teleost, the pacu (Piaractus mesopotamicus). Intact fish and fish experiencing progressive gill denervation by selective transection of cranial nerves IX and X were exposed to gradual hypoxia and submitted to intrabuccal and intravenous injections of NaCN while their heart rate, ventilation rate and ventilation amplitude were measured. The chemoreceptors producing reflex bradycardia were confined to, but distributed along all gill arches, and were sensitive to O(2) levels in the water and the blood. Ventilatory responses to all stimuli, though modified, continued following gill denervation, however, indicating the presence of internally and externally oriented receptors along all gill arches and either in the pseudobranch or at extra-branchial sites. Chemoreceptors located on the first pair of gill arches and innervated by the glossopharyngeal nerve appeared to attenuate the cardiac and respiratory responses to hypoxia. The data indicate that the location and distribution of cardio-respiratory O(2) receptors are not identical to those in tambaqui (Colossoma macropomum) despite their similar habitats and close phylogenetic lineage, although the differences between the two species could reduce to nothing more than the presence or absence of the pseudobranch.
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Affiliation(s)
- C A C Leite
- Department of Physiological Sciences, Federal University of São Carlos, Via Washington Luiz, km 235, P.O. Box 676, São Carlos, SP, 13565-905, Brazil
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Vulesevic B, Perry SF. Developmental plasticity of ventilatory control in zebrafish, Danio rerio. Respir Physiol Neurobiol 2006; 154:396-405. [PMID: 16446127 DOI: 10.1016/j.resp.2006.01.001] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2005] [Revised: 01/03/2006] [Accepted: 01/04/2006] [Indexed: 11/20/2022]
Abstract
To determine whether development of ventilatory control in zebrafish (Danio rerio) exhibits plasticity, embryos were exposed to hypoxia, hyperoxia or hypercapnia for the first 7 days post-fertilization. Their acute reflex breathing responses to ventilatory stimuli (hypoxia, hypercapnia and external cyanide) were assessed when they had reached maturity (3 months or older). Zebrafish reared under hyperoxic conditions exhibited significantly higher breathing frequencies at rest (283+/-27min(-1) versus 212+/-16min(-1) in control fish); breathing frequency was unaffected in adult fish subjected to hyperoxia for 7 days. The respiratory responses of fish reared in hyperoxic water to acute hypoxia, hypercapnia or external cyanide were blunted (hypoxia, cyanide) or eliminated (hypercapnia). Adult fish exposed for 7 days to hyperoxia showed no change in acute responses to these stimuli. The respiratory responses to acute hypoxia, hypercapnia or external cyanide of fish reared under hypoxic or hypercapnic conditions were similar to those in fish reared under normal conditions. A subset of all fish examined exhibited episodic breathing; an analysis of breathing patterns demonstrated that fish reared under hypercapnic conditions had an increased tendency to display episodic breathing. The results of this study reveal that there is flexibility in the design and functioning of the embryonic or larval respiratory system in zebrafish.
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Affiliation(s)
- B Vulesevic
- Department of Biology, University of Ottawa, 10 Marie Curie, Ottawa, Ont., Canada K1N 6N5
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12
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Vulesevic B, McNeill B, Perry SF. Chemoreceptor plasticity and respiratory acclimation in the zebrafishDanio rerio. J Exp Biol 2006; 209:1261-73. [PMID: 16547298 DOI: 10.1242/jeb.02058] [Citation(s) in RCA: 78] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
SUMMARYThe goals of this study were to assess the respiratory consequences of exposing adult zebrafish Danio rerio to chronic changes in water gas composition (hypoxia, hyperoxia or hypercapnia) and to determine if any ensuing effects could be related to morphological changes in branchial chemoreceptors. To accomplish these goals, we first modified and validated an established non-invasive technique for continuous monitoring of breathing frequency and relative breathing amplitude in adult fish. Under normal conditions 20% of zebrafish exhibited an episodic breathing pattern that was composed of breathing and non-breathing (pausing/apneic) periods. The pausing frequency was reduced by acute hypoxia (PwO2<130 mmHg)and increased by acute hyperoxia (PwO2>300 mmHg), but was unaltered by acute hypercapnia.Fish were exposed for 28 days to hyperoxia (PwO2>350 mmHg), or hypoxia (PwO2=30 mmHg) or hypercapnia(PwCO2=9 mmHg). Their responses to acute hypoxia or hypercapnia were then compared to the response of control fish kept for 28 days in normoxic and normocapnic water. In control fish, the ventilatory response to acute hypoxia consisted of an increase in breathing frequency while the response to acute hypercapnia was an increase in relative breathing amplitude. The stimulus promoting the hyperventilation during hypercapnia was increased PwCO2 rather than decreased pH. Exposure to prolonged hyperoxia decreased the capacity of fish to increase breathing frequency during hypoxia and prevented the usual increase in breathing amplitude during acute hypercapnia. In fish previously exposed to hyperoxia,episodic breathing continued during acute hypoxia until PwO2 had fallen below 70 mmHg. In fish chronically exposed to hypoxia, resting breathing frequency was significantly reduced (from 191±12 to 165±16 min–1); however, the ventilatory responses to hypoxia and hypercapnia were unaffected. Long-term exposure of fish to hypercapnic water did not markedly modify the breathing response to acute hypoxia and modestly blunted the response to hypercapnia.To determine whether branchial chemoreceptors were being influenced by long-term acclimation, all four groups of fish were acutely exposed to increasing doses of the O2 chemoreceptor stimulant, sodium cyanide,dissolved in inspired water. Consistent with the blunting of the ventilatory response to hypoxia, the fish pre-exposed to hyperoxia also exhibited a blunted response to NaCN. Pre-exposure to hypoxia was without effect whereas prior exposure to hypercapnia increased the ventilatory responses to cyanide.To assess the impact of acclimation to varying gas levels on branchial O2 chemoreceptors, the numbers of neuroepithelial cells (NECs) of the gill filament were quantified using confocal immunofluorescence microscopy. Consistent with the blunting of reflex ventilatory responses, fish exposed to chronic hyperoxia exhibited a significant decrease in the density of NECs from 36.8±2.8 to 22.7±2.3 filament–1.
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Affiliation(s)
- B Vulesevic
- Department of Biology, University of Ottawa, 10 Marie Curie, Ottawa, ON K1N 6N5, Canada
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Johnson SM, Creighton RJ. Spinal cord injury-induced changes in breathing are not due to supraspinal plasticity in turtles (Pseudemys scripta). Am J Physiol Regul Integr Comp Physiol 2005; 289:R1550-61. [PMID: 16099823 DOI: 10.1152/ajpregu.00397.2005] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
After occurrence of spinal cord injury, it is not known whether the respiratory rhythm generator undergoes plasticity to compensate for respiratory insufficiency. To test this hypothesis, respiratory variables were measured in adult semiaquatic turtles using a pneumotachograph attached to a breathing chamber on a water-filled tank. Turtles breathed room air (2 h) before being challenged with two consecutive 2-h bouts of hypercapnia (2 and 6% CO2or 4 and 8% CO2). Turtles were spinalized at dorsal segments D8–D10so that only pectoral girdle movement was used for breathing. Measurements were repeated at 4 and 8 wk postinjury. For turtles breathing room air, breathing frequency, tidal volume, and ventilation were not altered by spinalization; single-breath (singlet) frequency increased sevenfold. Spinalized turtles breathing 6–8% CO2had lower ventilation due to decreased frequency and tidal volume, episodic breathing (breaths/episode) was reduced, and singlet breathing was increased sevenfold. Respiratory variables in sham-operated turtles were unaltered by surgery. Isolated brain stems from control, spinalized, and sham turtles produced similar respiratory motor output and responded the same to increased bath pH. Thus spinalized turtles compensated for pelvic girdle loss while breathing room air but were unable to compensate during hypercapnic challenges. Because isolated brain stems from control and spinalized turtles had similar respiratory motor output and chemosensitivity, breathing changes in spinalized turtles in vivo were probably not due to plasticity within the respiratory rhythm generator. Instead, caudal spinal cord damage probably disrupts spinobulbar pathways that are necessary for normal breathing.
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Affiliation(s)
- Stephen M Johnson
- Dept. of Comparative Biosciences, School of Veterinary Medicine, Univ. of Wisconsin, 2015 Linden Drive, Madison, WI 53706, USA.
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Reid SG, Perry SF, Gilmour KM, Milsom WK, Rantin FT. Reciprocal modulation of O2 and CO2 cardiorespiratory chemoreflexes in the tambaqui. Respir Physiol Neurobiol 2005; 146:175-94. [PMID: 15766906 DOI: 10.1016/j.resp.2004.12.008] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2004] [Revised: 12/14/2004] [Accepted: 12/15/2004] [Indexed: 10/25/2022]
Abstract
This study examined the effect of acute hypoxic and hypercapnic cardiorespiratory stimuli, superimposed on existing cardiorespiratory disturbances in tambaqui. In their natural habitat, these fish often encounter periods of hypoxic hypercapnia that can be acutely exacerbated by water turnover. Tambaqui were exposed to periods of normoxia, hypoxia, hyperoxia and hypercapnia during which, externally oriented O2 and CO2 chemoreceptors were further stimulated, by administration into the inspired water of sodium cyanide and CO2-equilibrated water, respectively. Hyperoxic water increased the sensitivity of the NaCN-evoked increase in breathing frequency (f(R)) and decrease in heart rate. Hypoxia and hypercapnia attenuated the increase in f(R) but, aside from blood pressure, did not influence the magnitude of NaCN-evoked cardiovascular changes. Water PO2 influenced the magnitude of the CO2-evoked cardiorespiratory changes and the sensitivity of CO2-evoked changes in heart rate and blood flow. The results indicate that existing respiratory disturbances modulate cardiorespiratory responses to further respiratory challenges reflecting both changes in chemosensitivity and the capacity for further change.
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Affiliation(s)
- Stephen G Reid
- Department of Life Sciences, The Centre for the Neurobiology of Stress, University of Toronto at Scarborough, 1265 Military Trail, Toronto, Ont., Canada M1C 1A4.
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Gilmour KM, Milsom WK, Rantin FT, Reid SG, Perry SF. Cardiorespiratory responses to hypercarbia in tambaquiColossoma macropomum: chemoreceptor orientation and specificity. J Exp Biol 2005; 208:1095-107. [PMID: 15767310 DOI: 10.1242/jeb.01480] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
SUMMARYExperiments were carried out to test the hypothesis that ventilatory and cardiovascular responses to hypercarbia (elevated water PCO2) in the tambaqui Colossoma macropomum are stimulated by externally oriented receptors that are sensitive to water CO2 tension as opposed to water pH. Cardiorespiratory responses to acute hypercarbia were evaluated in both the absence and presence of internal hypercarbia (elevated blood PCO2), achieved by treating fish with the carbonic anhydrase inhibitor acetazolamide. Exposure to acute hypercarbia (15 min at each level, final water CO2 tensions of 7.2,15.5 and 26.3 mmHg) elicited significant increases in ventilation frequency(at 26.3 mmHg, a 42% increase over the normocarbic value) and amplitude(128%), together with a fall in heart rate (35%) and an increase in cardiac stroke volume (62%). Rapid washout of CO2 from the water reversed these effects, and the timing of the changes in cardiorespiratory variables corresponded more closely to the fall in water PCO2(PwCO2) than to that in blood PCO2(PaCO2). Similar responses to acute hypercarbia (15 min,final PwCO2 of 13.6 mmHg) were observed in acetazolamide-treated (30 mg kg-1) tambaqui. Acetazolamide treatment itself, however, increased PaCO2 (from 4.81±0.58 to 13.83±0.91 mmHg, mean ± s.e.m.; N=8) in the absence of significant change in ventilation, heart rate or cardiac stroke volume. The lack of response to changes in blood PCO2 and/or pH were confirmed by comparing responses to the bolus injection of hypercarbic saline(5% or 10% CO2; 2 ml kg-1) into the caudal vein with those to the injection of CO2-enriched water (1%, 3%, 5% or 10%CO2; 50 ml kg-1) into the buccal cavity. Whereas injections of hypercarbic saline were ineffective in eliciting cardiorespiratory responses, changes in ventilation and cardiovascular parameters accompanied injection of CO2-laden water into the mouth. Similar injections of CO2-free water acidified to the corresponding pH of the hypercarbic water (pH 6.3, 5.6, 5.3 or 4.9, respectively) generally did not stimulate cardiorespiratory responses. These results are in agreement with the hypothesis that in tambaqui, externally oriented chemoreceptors that are predominantly activated by increases in water PCO2,rather than by accompanying decreases in water pH, are linked to the initiation of cardiorespiratory responses to hypercarbia.
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Affiliation(s)
- K M Gilmour
- Department of Physiological Sciences, Federal University of São Carlos, Via Washington Luiz km 235, São Carlos, SP 13565-905, Brazil.
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The Cardiorespiratory System in Tropical Fishes: Structure, Function, and Control. ACTA ACUST UNITED AC 2005. [DOI: 10.1016/s1546-5098(05)21006-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
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