Taste responses to amino acids in the southern leopard frog, Rana sphenocephala

Integrated taste recordings of the glossopharyngeal (IX) nerve innervating the tongue of the southern leopard frog were studied in response to various amino acids and quinine hydrochloride. Amino acids and quinine hydrochloride elicited primarily phasic taste responses. Acidic (L-aspartic and L-glutamic) and basic (L-lysine and L-arginine) amino acids, adjusted to pH8, were effective taste stimuli. All glossopharyngeal nerve twigs that responded to amino acid stimuli also responded to quinine; however, not all quinine-sensitive IX nerve bundles were responsive to amino acids. Electrophysiological thresholds for amino acids were estimated to be 2.5-10 mM, whereas threshold for quinine hydrochloride averaged approximately 10 microM.