Electrophysiological and behavioral studies of taste discrimination in the axolotl (ambystoma mexicanum)

Electrophysiological and behavioral experiments were performed to determine whether the taste system of the aquatic salamander, axolotl, discriminates taste stimuli. Taste responses were recorded extracellularly from the glossopharyngeal nerve bundle. The behavioral responses of axolotls towards various concentrations of NaCl, KCl, citric acid, quinine-hydrochloride, and sucrose were quantified by measuring the ratio of rejection towards gel pellets, each containing either unitary stimuli or binary mixtures of these chemicals. Rejection ratios [rejection/ (rejection + swallowing)] towards the unitary stimuli except sucrose increased with concentration, but were not a single function of the magnitude of neural response induced by the stimuli. Degree of rejection was different depending on the quality of taste stimuli, suggesting that information processing of taste quality occurs in axolotls. The potential of NaCl to induce positive feeding behavior (swallowing) was suggested by a reduction in the rejection ratio of quinine-tainted pellets when they were mixed with 100 mM NaCl. Differential behavioral responses to quinine and NaCl show that axolotls have the ability to discriminate the taste quality of these stimuli.