Neural response of carotid chemoreceptors following dopamine blockade

The role of endogenous carotid body dopamine in the afferent chemoreceptor circuit was studied by means of haloperidol-induced dopamine antagonism. In 19 cats that were anesthetized with pentobarbital sodium and paralyzed, single carotid body nerve fibers were dissected free and placed on unipolar platinum wire electrodes. In 10 of these cats, the neural response to room air and the last 2 min of 6-min inhalations of 3, 6, and 9% CO2 were recorded, and blood samples were drawn for gas tension measurements. Haloperidol was administered at a dose (250 micrograms/kg) shown to block the inhibitory effect of injected dopamine. Following a 15-min equilibration, the CO2 response was again tested. In four other cats the CO2 response was tested with a hyperoxic background. In the remaining five cats the response to isocapnic hypoxia was recorded during administration of 15, 12, and 8% O2 before and following haloperidol. There was a significant increase in room air discharge activity and in hypoxic sensitivity following haloperidol. However, there was no significant change in hypercapnic sensitivity. These results suggest that there is a modulatory role for endogenous dopamine only in the hypoxic response.