Taste response in the facial nerve of the carp, Cyprinus carpio L

The stimulating effect of taste substances on the external chemoreceptors of the carp, Cyprinus carpio L., was studied by recording the electrical activity from the facial taste fibers innervating the facial skin surface. The integrated responses from each whole nerve bundle of the trigemino-facial complex nerve revealed that gustatory receptors on the snout of the carp were extremely sensitive to salts, acids and the extract of silk worm pupae. Quinine-HCl and sucrose elicited relatively small responses. Responses occurred to several amino acids, and especially to betaine. The threshold concentration for both mono- and di-valent salts was estimated to be about 5 X 10-3 M and that for acids about 10-4 M. Single fiber analysis was performed on 77 preparations. According to responsiveness to the 4 basic chemicals, the fibers were classified into 5 types: type I, activated by one stimulus (22 fibers out of 77); type II by two (29); type III by three (11); type IV by four (13); and type V showing inhibition by quinine-HCl (2) as their notable feature. Single fibers responsive to several amino acids, and the worm extract were found, among which the last was the most effective stimulus as shown in the whole nerve experiments.