ENHANCEMENT OF MURINE GUSTATORY NEURAL RESPONSES TO D-AMINO ACIDS BY SACCHARIN

Taste enhancing effects of sodium saccharin (Sac) on responses to particular sweet-tasting D-amino acids were found during the recording of mouse chorda tympani nerve responses to various taste stimuli in C57BL and BALB strains. In both strains, responses to D-tryptophan and D-histidine significantly increased (167.7-216.7% of control) after the stimulation with Sac as compared with those applied before Sac. In C57BL mice, the enhancement by Sac was also observed in response to D-phenylalanine (262.5% of control), but this was not the case for BALB mice, suggesting a prominent strain difference in response to D-phenylalanine, as shown previously. Responses to other sweet-tasting D- and L-amino acids and sugars were not enhanced by Sac. Enhancement of responses to these D-amino acids by Sac was also evident when responses to a mixture of D-amino acids and Sac were compared with the sum of responses to each component, although in this response analysis, the calculated magnitude of enhancement generally become smaller (135.7-180.5% of the sum) and enhancement of D-histidine responses disappeared. Except for Sac, various sweet-tasting amino acids and sugars and NaCl also tested showed no enhancing effect on D-phenylalanine responses in C57BL mice. Sac and D-amino acids, to which responses were enhanced by Sac, possess some common molecular features, namely ring structures. This structural similarity probably relates to the occurrence of the enhancement at the receptor sites.