Actions of piperidine and dimethylphenylpiperazinium (DMPP) on afferent discharges of the cat's carotid body.

Chemoreceptor discharges were recorded in vivo from fine filaments of carotid sinus nerve; their frequency was used as index of receptor activity. Effects of piperidine on chemoreceptors were studied and compared with those of dimethylphenylpiperazinium (DMPP) on chemoreceptors in adult cats. Intracarotid-arterial injections of piperidine produced a transient increase in chemoreceptor discharges, the threshold dose ranging from 10 to 50 microgram i.a. The excitatory effect of piperidine was not affected by atropine, hexamethonium or GABA. DMPP (0.2-0.5 microgram i.a.) induced a marked increase in chemoreceptor discharges, which was abolished by hexamethonium, but not by atropine. DMPP ((2--5 microgram i.a.) induced sinus baroreceptor excitation, but piperidine did not. The results indicate that piperidine exerted excitatory effects on carotid body chemoreceptors, possibly acting on nerve endings of chemoreceptor afferent fibers.