title: Reciprocal modulation of O2 and CO2 cardiorespiratory chemoreflexes in the tambaqui.
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.
authors.affiliation: Department of Life Sciences, The Centre for the Neurobiology of Stress, University of Toronto at Scarborough, 1265 Military Trail, Toronto, Ont., Canada M1C 1A4. sgreid@utsc.utoronto.ca
authors.forename: Stephen G
authors.initials: SG
authors.lastname: Reid
authors.forename: Steve F
authors.initials: SF
authors.lastname: Perry
authors.forename: Kathleen M
authors.initials: KM
authors.lastname: Gilmour
authors.forename: William K
authors.initials: WK
authors.lastname: Milsom
authors.forename: F Tadeu
authors.initials: FT
authors.lastname: Rantin
mesh_terms: D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D002245:Carbon Dioxide / Q000494:pharmacology*; D002319:Cardiovascular System / Q000187:drug effects*; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005399:Fishes; D006339:Heart Rate / Q000187:drug effects; D010100:Oxygen / Q000494:pharmacology*; D012123:Pulmonary Ventilation / Q000187:drug effects; D012039:Regional Blood Flow / Q000187:drug effects; D012119:Respiration / Q000187:drug effects*; D012966:Sodium Cyanide / Q000494:pharmacology; D013997:Time Factors
chemical_list: D004791:Enzyme Inhibitors; D002245:Carbon Dioxide; D012966:Sodium Cyanide; D010100:Oxygen