Response properties of the glossopharyngeal taste system of the mud puppy (Necturus maculosus)

Summary

The general properties of the glossopharyngeal taste system of the mud puppy,Necturus maculosus, were determined using standard electrophysiological recording techniques. Electrical activity from the whole nerve was quantified by an electronic integrator. The tongue was stimulated with diverse stimuli over an extended range of concentrations: the electrolytes, NaCl, KCl, CaCl₂, CsCl, LiCl, and NH₄C1; the amino acids, L-alanine, DL-alanine, and glycine; and stimuli representing the four basic taste qualities in humans, HCl (sour), quinine hydrochloride (bitter), sucrose (sweet), and NaCl (salty). The response pattern to all stimuli was identical: a phasic increase in activity which adapted nearly to baseline within 10 s (Fig. 4A), a response which was directly related to stimulus concentration (Fig. 4B). HCl was the most effective stimulus tested, whereas CsCl and sucrose were the least (Figs. 4, 6), However, the stimulus-response (SR) function for L-alanine suggested that saturation was reached and that threshold was far below 0.001 mol/l, the lowest concentration tested (Fig. 5B).

Punctate chemical stimulation revealed that the gustatory receptive field of the glossopharyngeal nerve was predominantly in the central portion of the tongue (Fig. 3). The distribution of the taste buds was studied with light and scanning electron microscopy and the location of the gustatory dermal papilla associated with each bud was mapped (Fig. 2). Comparison of this distribution with the receptive field showed regions with many buds but low responsiveness, areas in which the facial and vagus nerves probably contribute to the total taste system ofNecturus.