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Oxygen-sensitive chemoreceptors and cardioventilatory control in carp Lumsden, Amanda Lloyd


Carp responded to changes in partial pressure of oxygen in the water, both increases and decreases, in a manner similar to other teleost fish. Hypoxia resulted in significant increases in ventilation (both frequency and amplitude). A reflex hypoxic bradycardia, however, was not observed in the present study and, in fact, a tachycardia occurred at one hour and persisted through the remainder of the experiment. There was a significant decrease in ventilatory frequency during hyperoxia, while ventilatory amplitude, as well as heart rate, did not change from normoxic control values. NaCN (5 mg/ml) administered through a mouth cannulae in carp resulted in rapid, albeit transient, increases in frequency "and amplitude of ventilation which were significantly different from control water injections. The response to NaCN was over within a minute following administration of NaCN (evidenced by the significant decrease in respiratory frequency). Heart rate was unaffected by NaCN and the absence of the bradycardia. Internal injections of NaCN (5-10 mg/ml) into the dorsal aorta of carp produced no cardioventilatory responses. Carbon monoxide (21.2 ± 9.0%) had no effect on ventilation in carp, however, it increased heart rate significantly. This indicates that carp possess 02-sensitive chemoreceptors capable of monitoring changes in 02 content, independent of changes in 02 partial pressure, but they are not involved in the control of breathing. This refutes my hypothesis that changes in 02 content of the blood in carp modulate cardioventilatory effects. Hyperoxic hypercapnia significantly increased the frequency of ventilation after the first five minutes of exposure. This increase in ventilation during hyperoxic hypercapnia indicates that in carp, C02 is acting directly on a receptor, as opposed to indirectly through Bohr and Root effects in the blood. The changes in breathing pattern, with hypoxia, CO, and C02 occurred in the same manner for all carp (i.e. there was an increase in the number of breaths in an episode and a decrease in the number of episodes in a minute until a continuous breathing pattern was achieved).

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