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Santin JM. How important is the CO 2 chemoreflex for the control of breathing? Environmental and evolutionary considerations. Comp Biochem Physiol A Mol Integr Physiol 2017; 215:6-19. [PMID: 28966145 DOI: 10.1016/j.cbpa.2017.09.015] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2017] [Revised: 09/19/2017] [Accepted: 09/19/2017] [Indexed: 12/27/2022]
Abstract
Haldane and Priestley (1905) discovered that the ventilatory control system is highly sensitive to CO2. This "CO2 chemoreflex" has been interpreted to dominate control of resting arterial PCO2/pH (PaCO2/pHa) by monitoring PaCO2/pHa and altering ventilation through negative feedback. However, PaCO2/pHa varies little in mammals as ventilation tightly couples to metabolic demands, which may minimize chemoreflex control of PaCO2. The purpose of this synthesis is to (1) interpret data from experimental models with meager CO2 chemoreflexes to infer their role in ventilatory control of steady-state PaCO2, and (2) identify physiological causes of respiratory acidosis occurring normally across vertebrate classes. Interestingly, multiple rodent and amphibian models with minimal/absent CO2 chemoreflexes exhibit normal ventilation, gas exchange, and PaCO2/pHa. The chemoreflex, therefore, plays at most a minor role in ventilatory control at rest; however, the chemoreflex may be critical for recovering PaCO2 following acute respiratory acidosis induced by breath-holding and activity in many ectothermic vertebrates. An apparently small role for CO2 feedback in the genesis of normal breathing contradicts the prevailing view that central CO2/pH chemoreceptors increased in importance throughout vertebrate evolution. Since the CO2 chemoreflex contributes minimally to resting ventilation, these CO2 chemoreceptors may have instead decreased importance throughout tetrapod evolution, particularly with the onset and refinement of neural innovations that improved the matching of ventilation to tissue metabolic demands. This distinct and elusive "metabolic ventilatory drive" likely underlies steady-state PaCO2 in air-breathers. Uncovering the mechanisms and evolution of the metabolic ventilatory drive presents a challenge to clinically-oriented and comparative respiratory physiologists alike.
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Santin JM, Hartzler LK. Reassessment of chemical control of breathing in undisturbed bullfrogs, Lithobates catesbeianus, using measurements of pulmonary ventilation. Respir Physiol Neurobiol 2016; 224:80-9. [DOI: 10.1016/j.resp.2015.09.013] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2015] [Revised: 09/26/2015] [Accepted: 09/27/2015] [Indexed: 11/28/2022]
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Santin JM, Hartzler LK. Control of lung ventilation following overwintering conditions in bullfrogs, Lithobates catesbeianus. J Exp Biol 2016; 219:2003-14. [DOI: 10.1242/jeb.136259] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2015] [Accepted: 04/14/2016] [Indexed: 12/19/2022]
Abstract
Ranid frogs in northern latitudes survive winter at cold temperatures in aquatic habitats often completely covered by ice. Cold-submerged frogs survive aerobically for several months relying exclusively on cutaneous gas exchange while maintaining temperature-specific acid-base balance. Depending on the overwintering hibernaculum, frogs in northern latitudes could spend several months without access to air, need to breathe, or chemosensory drive to use neuromuscular processes that regulate and enable pulmonary ventilation. Therefore, we performed experiments to determine whether aspects of the respiratory control system of bullfrogs, Lithobates catesbeianus, are maintained or suppressed following minimal use of air breathing in overwintering environments. Based on the necessity for control of lung ventilation in early spring, we hypothesized that critical components of the respiratory control system of bullfrogs would be functional following simulated overwintering. We found that bullfrogs recently removed from simulated overwintering environments exhibited similar resting ventilation when assessed at 24°C compared to warm-acclimated control bullfrogs. Additionally, ventilation met resting metabolic and, presumably, acid-base regulation requirements, indicating preservation of basal respiratory function despite prolonged disuse in the cold. Recently emerged bullfrogs underwent similar increases in ventilation during acute oxygen lack (aerial hypoxia) compared to warm-acclimated frogs; however, CO2-related hyperventilation was significantly blunted following overwintering. Overcoming challenges to gas exchange during overwintering have garnered attention in ectothermic vertebrates, but this study uncovers robust and labile aspects of the respiratory control system at a time point correlating with early spring following minimal/no use of lung breathing in cold-aquatic overwintering habitats.
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Affiliation(s)
- Joseph M. Santin
- Wright State University, Department of Biological Sciences, 3640 Colonel Glenn. Hwy. Dayton, OH 45435, USA
- Wright State University, Biomedical Sciences PhD Program, 3640 Colonel Glenn. Hwy. Dayton, OH 45435, USA
| | - Lynn K. Hartzler
- Wright State University, Department of Biological Sciences, 3640 Colonel Glenn. Hwy. Dayton, OH 45435, USA
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Santin JM, Watters KC, Putnam RW, Hartzler LK. Temperature influences neuronal activity and CO2/pH sensitivity of locus coeruleus neurons in the bullfrog, Lithobates catesbeianus. Am J Physiol Regul Integr Comp Physiol 2013; 305:R1451-64. [DOI: 10.1152/ajpregu.00348.2013] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
The locus coeruleus (LC) is a chemoreceptive brain stem region in anuran amphibians and contains neurons sensitive to physiological changes in CO2/pH. The ventilatory and central sensitivity to CO2/pH is proportional to the temperature in amphibians, i.e., sensitivity increases with increasing temperature. We hypothesized that LC neurons from bullfrogs, Lithobates catesbeianus, would increase CO2/pH sensitivity with increasing temperature and decrease CO2/pH sensitivity with decreasing temperature. Further, we hypothesized that cooling would decrease, while warming would increase, normocapnic firing rates of LC neurons. To test these hypotheses, we used whole cell patch-clamp electrophysiology to measure firing rate, membrane potential ( Vm), and input resistance ( Rin) in LC neurons in brain stem slices from adult bullfrogs over a physiological range of temperatures during normocapnia and hypercapnia. We found that cooling reduced chemosensitive responses of LC neurons as temperature decreased until elimination of CO2/pH sensitivity at 10°C. Chemosensitive responses increased at elevated temperatures. Surprisingly, chemosensitive LC neurons increased normocapnic firing rate and underwent membrane depolarization when cooled and decreased normocapnic firing rate and underwent membrane hyperpolarization when warmed. These responses to temperature were not observed in nonchemosensitive LC neurons or neurons in a brain stem slice 500 μm rostral to the LC. Our results indicate that modulation of cellular chemosensitivity within the LC during temperature changes may influence temperature-dependent respiratory drive during acid-base disturbances in amphibians. Additionally, cold-activated/warm-inhibited LC neurons introduce paradoxical temperature sensitivity in respiratory control neurons of amphibians.
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Affiliation(s)
- Joseph M. Santin
- Department of Biological Sciences, Wright State University, Dayton, Ohio; and
| | - Kayla C. Watters
- Department of Biological Sciences, Wright State University, Dayton, Ohio; and
| | - Robert W. Putnam
- Department of Neuroscience, Cell Biology, and Physiology, Wright State University, Dayton, Ohio
| | - Lynn K. Hartzler
- Department of Biological Sciences, Wright State University, Dayton, Ohio; and
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Bartman ME, Wilkerson JER, Johnson SM. 5-HT3 receptor-dependent modulation of respiratory burst frequency, regularity, and episodicity in isolated adult turtle brainstems. Respir Physiol Neurobiol 2010; 172:42-52. [PMID: 20399913 DOI: 10.1016/j.resp.2010.04.008] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2009] [Revised: 04/10/2010] [Accepted: 04/11/2010] [Indexed: 11/19/2022]
Abstract
To determine the role of central serotonin 5-HT(3) receptors in respiratory motor control, respiratory motor bursts were recorded from hypoglossal (XII) nerve rootlets on isolated adult turtle brainstems during bath-application of 5-HT(3) receptor agonists and antagonists. mCPBG and PBG (5-HT(3) receptor agonists) acutely increased XII burst frequency and regularity, and decreased bursts/episode. Tropisetron and MDL72222 (5-HT(3) antagonists) increased bursts/episode, suggesting endogenous 5-HT(3) receptor activation modulates burst timing in vitro. Tropisetron blocked all mCPBG effects, and the PBG-induced reduction in bursts/episode. Tropisetron application following mCPBG application did not reverse the long-lasting (2h) mCPBG-induced decrease in bursts/episode. We conclude that endogenous 5-HT(3) receptor activation regulates respiratory frequency, regularity, and episodicity in turtles and may induce a form of respiratory plasticity with the long-lasting changes in respiratory regularity.
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Affiliation(s)
- Michelle E Bartman
- Department of Comparative Biosciences, School of Veterinary Medicine, University of Wisconsin, 2015 Linden Drive, Madison, WI 53706, USA
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Davies BL, Brundage CM, Harris MB, Taylor BE. Lung respiratory rhythm and pattern generation in the bullfrog: role of neurokinin-1 and mu-opioid receptors. J Comp Physiol B 2009; 179:579-92. [PMID: 19184042 DOI: 10.1007/s00360-009-0339-3] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2008] [Revised: 12/29/2008] [Accepted: 01/02/2009] [Indexed: 02/03/2023]
Abstract
Location of the lung respiratory rhythm generator (RRG) in the bullfrog brainstem was investigated by examining neurokinin-1 and mu-opioid receptor (NK1R, muOR) colocalization by immunohistochemistry and characterizing the role of these receptors in lung rhythm and episodic pattern generation. NK1R and muOR occurred in brainstems from all developmental stages. In juvenile bullfrogs a distinct area of colocalization was coincident with high-intensity fluorescent labeling of muOR; high-intensity labeling of muOR was not distinctly and consistently localized in tadpole brainstems. NK1R labeling intensity did not change with development. Similarity in colocalization is consistent with similarity in responses to substance P (SP, NK1R agonist) and DAMGO (muOR agonist) when bath applied to bullfrog brainstems of different developmental stages. In early stage tadpoles and juvenile bullfrogs, SP increased and DAMGO decreased lung burst frequency. In juvenile bullfrogs, SP increased lung burst frequency, episode frequency, but decreased number of lung bursts per episode and lung burst duration. In contrast, DAMGO decreased lung burst frequency and burst cycle frequency, episode frequency, and number of lung bursts per episode but increased all other lung burst parameters. Based on these results, we hypothesize that NK1R and muOR colocalization together with a metamorphosis-related increase in muOR intensity marks the location of the lung RRG but not necessarily the lung episodic pattern generator.
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Affiliation(s)
- B L Davies
- Institute of Arctic Biology, University of Alaska Fairbanks, Rm 311 Irving I, 902 N Koyukuk Drive, Fairbanks, AK 99775, USA
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Belzile O, Gulemetova R, Kinkead R. Effects of medullary Raphé stimulation on fictive lung ventilation during development in Rana catesbeiana. J Exp Biol 2007; 210:2046-56. [PMID: 17562878 DOI: 10.1242/jeb.003202] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
SUMMARY
To better understand serotonergic modulation of air breathing during bullfrog development, we measured changes in fictive lung ventilation frequency associated with focal stimulation of the rostral region of the medullary Raphé neurons. Electrical (3 to 33 Hz) and chemical(glutamate microinjections; 0.5 mol l–1, 0.3–10 nl)activation of Raphé neurons was performed in brainstem preparations from three developmental stages (pre- and metamorphic tadpoles and adult frogs). Fictive lung ventilation was recorded extracelluarly from the Vth and Xth cranial nerves. Electrical stimulation of Raphé neurons caused a frequency-dependent increase in lung burst frequency in pre-metamorphic tadpoles only. In metamorphic tadpoles, an increase in fictive lung ventilation was observed at 20 Hz only. Electrical stimulation had no effect in preparations from adult frogs. Glutamate microinjections elicited similar responses as a lung burst frequency increase was observed in the pre-metamorphic group only. Regardless of the stimulation technique used, the increase in fictive lung ventilation was attenuated by the selective 5-HT3 antagonist tropisetron (5–20 μmol l–1). Results from immunohistochemical analysis of the Raphé region stimulated do not correlate with functional data as the number of 5-HT immunoreactive neurons within this region increases during development. We conclude that, in this preparation, stimulation of lung ventilation by the medullary Raphé is restricted to early(pre-metamorphic) stages.
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Affiliation(s)
- Olivier Belzile
- Department of Cell Biology, University of Texas Southwestern Medical Center, Dallas, TX 75390-9039, USA
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Gheshmy A, Anari A, Besada D, Reid SG. Afferent input modulates the chronic hypercapnia-induced increase in respiratory-related central pH/CO2 chemosensitivity in the cane toad (Bufo marinus). J Exp Biol 2007; 210:227-37. [PMID: 17210960 DOI: 10.1242/jeb.02606] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The goal of this study was to examine the role of respiratory-related afferent input on the chronic hypercapnia (CHC)-induced increase in central respiratory-related pH/CO2 chemosensitivity in cane toads (Bufo marinus). Toads were exposed to CHC (3.5% CO2) for 10 days, following which in vitro brainstem-spinal cord preparations were used to assess central respiratory-related pH/CO2 chemosensitivity. Motor output from the vagus nerve root was used as an index of breathing (fictive breathing). Olfactory denervation (OD), prior to exposure to CHC, was used to remove the influence of CO2-sensitive olfactory chemoreceptors, which inhibit breathing. Exposure to chronic hyperoxic hypercapnia (CHH) was used to reduce the level of arterial chemoreceptor input compared with CHC alone. In vivo experiments examined the effects of CHC, CHH and OD on the acute hypercapnic ventilatory response of intact animals. In vitro, a reduction in artifical cerebral spinal fluid (aCSF) pH increased fictive breathing in preparations taken from control and CHC animals. CHC caused an increase in fictive breathing compared with controls. OD and CHH abolished the CHC-induced augmentation of fictive breathing. In vivo, CHC did not cause an augmentation of the acute hypercapnic ventilatory response. CHH reduced the in vivo acute hypercapnic ventilatory response compared with animals exposed to CHC. In vivo, OD reduced breathing frequency and increased breath amplitude in both control and CHC animals. The results suggest that afferent input from olfactory and arterial chemoreceptors, during CHC, is involved in triggering the CHC-induced increase in central respiratory-related pH/CO2 chemosensitivity.
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Affiliation(s)
- Afshan Gheshmy
- Centre for the Neurobiology of Stress, Department of Life Sciences, University of Toronto at Scarborough, 1265 Military Trail, Toronto, ON, M1C 1A4, Canada
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Gheshmy A, Vukelich R, Noronha A, Reid SG. Chronic hypercapnia modulates respiratory-related central pH/CO2 chemoreception in an amphibian,Bufo marinus. J Exp Biol 2006; 209:1135-46. [PMID: 16513940 DOI: 10.1242/jeb.02106] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
SUMMARYAnuran amphibians have multiple populations of pH/CO2-sensitive respiratory-related chemoreceptors. This study examined in cane toads(Bufo marinus) whether chronic hypercapnia (CHC) altered the pH/CO2 sensitivity of central respiratory-related chemoreceptors in vitro and whether CHC altered the acute hypercapnic ventilatory response (HCVR; 5% CO2) in vivo. Toads were exposed to CHC(3.5% CO2) for 9 days. In vitro brainstem–spinal cord preparations were used to examine central respiratory-related pH/CO2 chemosensitivity. CHC augmented in vitro fictive breathing as the pH of the superfusate was lowered from 8.2 to 7.4. Midbrain transection in vitro (at a level known to reduce the clustering of breaths) did not alter this augmentation. In vivo, CHC did not alter the acute HCVR but midbrain transection changed the breathing pattern and increased the overall level of ventilation. CHC did not alter the effect of olfactory CO2 chemoreceptor denervation on the acute HCVR in vivo but did alter the response when returned to normal air. The results indicate that CHC increases the response of central pH/CO2chemoreceptors to changes in cerebrospinal fluid pH in vitro yet this increase is not manifest as an increase in the HCVR in vivo.
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Affiliation(s)
- Afshan Gheshmy
- The Centre for the Neurobiology of Stress, Department of Life Sciences, University of Toronto at Scarborough, 1265 Military Trail, Toronto, Ontario, M1C 1A4, 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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Tattersall GJ, de Andrade DV, Brito SP, Abe AS, Milsom WK. Regulation of ventilation in the caiman (Caiman latirostris): effects of inspired CO2 on pulmonary and upper airway chemoreceptors. J Comp Physiol B 2005; 176:125-38. [PMID: 16283333 DOI: 10.1007/s00360-005-0034-y] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2005] [Revised: 08/23/2005] [Accepted: 09/20/2005] [Indexed: 10/25/2022]
Abstract
In order to study the relative roles of receptors in the upper airways, lungs and systemic circulation in modulating the ventilatory response of caiman (Caiman latirostris) to inhaled CO2, gas mixtures of varying concentrations of CO2 were administered to animals breathing through an intact respiratory system, via a tracheal cannula by-passing the upper airways (before and after vagotomy), or via a cannula delivering gas to the upper airways alone. While increasing levels of hypercarbia led to a progressive increase in tidal volume in animals with intact respiratory systems (Series I), breathing frequency did not change until the CO2 level reached 7%, at which time it decreased. Despite this, at the higher levels of hypercarbia, the net effect was a large and progressive increase in total ventilation. There were no associated changes in heart rate or arterial blood pressure. On return to air, there was an immediate change in breathing pattern; breathing frequency increased above air-breathing values, roughly to the same maximum level regardless of the level of CO2 the animal had been previously breathing, and tidal volume returned rapidly toward resting (baseline) values. Total ventilation slowly returned to air breathing values. Administration of CO2 via different routes indicated that inhaled CO2 acted at both upper airway and pulmonary CO2-sensitive receptors to modify breathing pattern without inhibiting breathing overall. Our data suggest that in caiman, high levels of inspired CO2 promote slow, deep breathing. This will decrease dead-space ventilation and may reduce stratification in the saccular portions of the lung.
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Affiliation(s)
- Glenn J Tattersall
- Department of Biology, Brock University, St Catharines, L2S 3A1, Ontario, Canada.
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Kinkead R, Belzile O, Gulemetova R. Serotonergic modulation of respiratory motor output during tadpole development. J Appl Physiol (1985) 2002; 93:936-46. [PMID: 12183489 DOI: 10.1152/japplphysiol.00104.2002] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
To test the hypothesis that serotonin (5-hydroxytryptamine; 5-HT)-receptor activation elicits age-dependent changes in respiratory motor output, we compared the effects of 5-HT bath application (5-HT concentration = 0.5-25 microM) onto in vitro brain stem preparations from pre- and postmetamorphic bullfrog tadpoles. Recording of motor output related to gill and lung ventilation showed that 5-HT elicits a dose-dependent depression of gill burst frequency in both groups. In contrast, the lung burst frequency response was stage dependent; an increase in lung burst frequency at low 5-HT concentration (< or =0.5 microM) was observed only in the postmetamorphic group. Higher 5-HT concentrations decreased lung burst frequency in all preparations. Gill burst frequency attenuation is mediated (at least in part) by 5-HT(1A)-receptor activation in an age-dependent fashion. We conclude that serotonergic modulation of respiratory motor output 1) changes during tadpole development and 2) is distinct for gill and lung ventilation.
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Affiliation(s)
- Richard Kinkead
- Department of Pediatrics, Centre de Recherche, Hôpital Saint-François d'Assise, Laval University, Quebec City, Quebec, Canada G1L 3L5.
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Sanders CE, Milsom WK. THE effects of tonic lung inflation on ventilation in the American bullfrog Rana catesbeiana Shaw. J Exp Biol 2001; 204:2647-56. [PMID: 11533114 DOI: 10.1242/jeb.204.15.2647] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
SUMMARY
This study was designed to determine whether lung inflation stimulates or inhibits breathing in frogs by examining the effect of tonic lung inflation on the ‘fictive’ breathing pattern of decerebrate, unidirectionally ventilated bullfrogs. Neural discharge was monitored in the trigeminal nerve as an indication of the frequency and force of contraction of the buccal pump, and in the laryngeal branch of the vagus nerve as an indication of glottal opening, and hence fictive lung ventilation. Based on the temporal coordination of discharge in the trigeminal and vagus nerves during naturally occurring breaths it was possible to characterize the fictive breaths as inflation, deflation or balanced breaths. Increasing lung inflation increased absolute breathing frequency by reducing the duration of apnea between breaths and promoting a change in breathing pattern from no breathing to single breaths, breathing episodes and, finally, to continuous breathing. Associated with this was a decrease in the amplitude and area of the integrated trigeminal electroneurogram associated with the lung breaths, indicative of a reduction in the force of the buccal pump, and a shift in the timing of the trigeminal and vagal discharge, indicative of a shift from inflation to deflation breaths. Taken together the data suggest that lung deflation produces infrequent, large-amplitude inflation breaths or cycles, but that progressive lung inflation changes the breathing pattern to one of high-frequency attempts to deflate the lungs that are largely passive, and accompanied by contractions of the buccal pump that are no larger than those associated with normal buccal oscillations.
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Affiliation(s)
- C E Sanders
- Department of Zoology, University of British Columbia, 6270 University Boulevard, Vancouver, British Columbia, V6T 1Z4, Canada
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