DIFFERENCES IN TASTE RESPONSES TO POLYCOSE AND COMMON SUGARS IN THE RAT AS REVEALED BY BEHAVIORAL AND ELECTROPHYSIOLOGICAL STUDIES

Behavioral and electrophysiological experiments were performed to exam ine the suggestion that rats have two types of carbohydrate taste rece ptors, one for polysaccharides (e.g., Polycose) and one for common sug ars (e.g., sucrose). Qualitative difference between the tastes of Poly cose and sugars including sucrose, maltose, glucose, and fructose was surveyed by means of a conditioned taste aversion paradigm in which th e number of licks for 20 s to each taste stimulus was measured. Aversi ve conditioning to Polycose did not generalize to sugars, while aversi ve conditioning to sucrose generalized to other sugars, but not to Pol ycose. In the electrophysiological study, taste responses of the whole chorda tympani were recorded. A proteolytic enzyme, pronase E, suppre ssed nerve responses to both Polycose and sugars to less than 50%. A n ovel anti-sweet peptide, gurmarin, strongly suppressed responses to su gars, but had essentially no effect on Polycose responses. On the othe r hand, KHCO3 enhanced responses to sugars to about 300%, but had litt le effect on Polycose responses. These results have confirmed the noti on that rats can differentiate the tastes between Polycose and common sugars and that rats have two types of carbohydrate receptors.