CARDIO-VENTILATORY CONTROL IN RAINBOW-TROUT .2. REFLEX EFFECTS OF EXOGENOUS NEUROCHEMICALS

The effects of various neurochemicals were examined in intact, unanest hetized rainbow trout (Oncorhynchus mykiss) to assess the role of bran chial O-2-sensitive chemoreceptors in the cardio-ventilatory responses to exogenous neurochemicals. Cyanide stimulated ventilation and elici ted bradycardia when given externally but only stimulated ventilation when injected internally. Norepinephrine increased heart rate, blood p ressure and ventilatory rate but opercular pressure was not affected. Dopamine had no effect on either heart or ventilatory rate but increas ed blood pressure and decreased opercular pressure. Serotonin stimulat ed heart rate and ventilation but decreased blood pressure. Acetylchol ine and nicotine stimulated all cardio-ventilatory variables. Muscarin e decreased heart rate and blood pressure and had a biphasic effect on ventilation. These results, combined with the results from the preced ing study, suggest that the cardio-ventilatory effects of exogenously administered (1) cyanide are entirely mediated by gill O-2 receptors, (2) serotonin, and cholinergic drugs could be partly mediated by O-2 r eceptors and (3) catecholaminergic drugs are not mediated by O-2 recep tors.