Cardiorespiratory reflexes and aquatic surface respiration in the neotropical fish tambaqui (Colossoma macropomum): acute responses to hypercarbia.
We examined the cardiorespiratory responses to 6 h of acute hypercarbia (1, 2.5, and 5% CO(2)) in intact and gill-denervated (bilateral denervation of branchial branches of cranial nerves IX and X) tambaqui, Colossoma macropomum. Intact fish exposed to 1 and 2.5% CO(2) increased respiratory frequency ( f(R)) and ventilation amplitude ( V(AMP)) slowly over a 1- to 3-h period. Denervated fish did not show this response, suggesting that tambaqui possess receptors in the gills that will produce excitatory responses to low levels of hypercarbia (1 and 2.5% CO(2)) if the exposure is prolonged. The cardiac response to stimulation of these receptors with this level of CO(2) was a tachycardia and not a bradycardia. During exposure to 5% CO(2), intact fish increased f(R) and V(AMP), and showed a pronounced bradycardia after 1 h. After 2 h, the heart rate ( f(H)) started to increase, but returned to control values after 6 h. In denervated fish, the increase in f(R) was abolished. The slow increase in V(AMP) and the bradycardia were not abolished, suggesting that these changes arose from extra-branchial receptors. Neither intact nor denervated fish developed the swelling of the lower lip or performed aquatic surface respiration, even after 6 h, suggesting that these are unique responses to hypoxia and not hypercarbia.
Department of Physiological Sciences, Federal University of São Carlos, Via Washington Luiz, km 235, 13565-905 São Carlos, SP, Brazil.
Luiz H
LH
Florindo
Stephen G
SG
Reid
Ana L
AL
Kalinin
William K
WK
Milsom
Francisco T
FT
Rantin
D000704:Analysis of Variance; D000818:Animals; D001938:Brazil; D002245:Carbon Dioxide / Q000378:metabolism / Q000494:pharmacology*; D002320:Cardiovascular Physiological Phenomena; D004305:Dose-Response Relationship, Drug; D005399:Fishes / Q000502:physiology*; D005880:Gills / Q000294:innervation; D006339:Heart Rate / Q000187:drug effects; D012123:Pulmonary Ventilation / Q000187:drug effects / Q000502:physiology; D012018:Reflex / Q000187:drug effects / Q000502:physiology*; D012119:Respiration
D002245:Carbon Dioxide