A NEUROPHYSIOLOGICAL STUDY ON ASTRINGENT TASTE

Taste reaction to tannic acid solution in the rat was investigated. Responses of the chorda tympani, glossopharyngeal and lingual nerves to this solution applied to the tongue were recorded. Results obtained are as follows:Previous application of tannic acid solution to the tongue surface suppressed the integrated responses of the whole chorda tympani and glossopharyngeal nerve to successive applications of each of the four standard taste solutions (sodium chloride, tartaric acid, sucrose and quinine-HCl). The degree of the suppressive effect by tannic acid solution was not identical in each of the taste stimuli.Single fiber analysis of taste effectiveness of tannic acid solution revealed that the broad sensitivity taste fibers of the chorda tympani and of the glossopharyngeal nerve responded to tannic acid solution applied to the tongue surface. The responses of these fibers to the four standard taste solutions were suppressed by preceding application of tannic acid, while the narrow sensitivity taste fibers in the chorda tympani and the glossopharyngeal nerves did not respond at all to tannic acid solution. The responses of the narrow sensitivity taste fibers to a standard taste solution were not affected by previously applied tannic acid solutions.Tannic acid solution did not evoke any responses of the mechano-and thermal sensitive fibers in the lingual nerve. The astringent taste is the result of excitation of the broad sensitivity taste fibers.