Taste nerve responses during licking behavior in rats: importance of saliva in responses to sweeteners.

Taste responses of the rat chorda tympani nerve, innervating taste cells on the anterior part of the tongue, were recorded under awake and anesthetic conditions. Responses to licking of taste solutions in conscious animals were compared with those to taste solutions poured onto the tongue, without contamination of saliva, in anesthetized ones. The most noticeable finding was that sweet-tasting substances such as sugars and amino acids elicited larger magnitudes of neural responses (2-4 times) under awake condition than under anesthetic experimental condition. We conclude that a proper ionic composition of mucous substances covering the surface of the taste cell membrane is important in generating good responses to sweeteners as observed in licking rats.