Potentiation of gustatory response to monosodium glutamate in rat chorda tympani fibers by addition of 5'-ribonucleotides.

5'-Ribonucleotides such as sodium 5'-inosinate (5'-IMP) , sodium 5'-guanylate (5'-GMP) and sodium 5'-xanthylate possess strong flavor-enhancing ability for humans when they are added in a minute quantity to monosodium glutamate (MSG), but little enhancement of taste occur by the addition of sodium 5'-uridylate (5'-UMP) and 5'-cytidylate (5'-CMP) to MSG5). ADACHI1) showed enhancement of the response in the chorda tympani of cats to MSG by the addition of 5'-IMP. Potentiation of the neural response magnitude by the addition of a small amount of 5'-IMP, 5'-GMP, 5'-UMP and 5'-CMP to MSG has also been demonstrated in the chorda tympani nerve of rats by SATO and AKAIKE11): The effectiveness of producing the potentiation is in the order of 5'-GMP>5'-IMP>5/-UMP>5/-CMP, and in agreement with KUNINAKA'S finding, the effectiveness of the latter two is far smaller than that of the former two. The maximum potentiation appears by replacing 1/10 and 1/5 of MSG with 5'-GMP and 5'-IMP, respectively. Addition of 5'-AMP to MSG was found to produce the potentiation similar in magnitude to that elicited by 5'-GMP (Hui and SAT04)). In order to investigate the mechanism of the potentiation in more detail, analysis of single chorda tympani fiber responses in the rat was performed in the present study. The results, on the one hand confirming those obtained with the whole chorda tympani nerve, have revealed on the other that significant potentiation of the response by the addition of 5'-GMP, 5'-IMP or 5'-AMP appears in units sensitive to sucrose and that the magnitude of responses to the mixture of MSG with the above ribonucleotides is significantly correlated with that for sucrose or saccharin. In the present paper attempts