Chemoreceptor Response in Frog, as Modified by Temperature Change.

In the preceding experiment14) the stimulating effectiveness of various salts on chemoreceptors of a frog was investigated, by recording the integrated responses of the glossopharyngeal nerve. In the present paper the experiments on the effect of temperature on the glossopharyngeal nerve response to various taste stimuli are described. The effect of temperature on the neural response to taste stimuli has recently been investigated by KIMURA7), by recording impulse discharges in single glossopharyngeal nerve fibers of a frog. He has found that the optimum temperature, at which the greatest response to a particular taste stimulus is obtained, differs according to the stimulus employed; the optimum temperature for the NaCl and quinine responses lies at 25•‹-30•Ž, that for the CaCl2 response at 30•Ž and that for the water response at 20•Ž, while the acid response does not change in magnitude between 5° and 20•Ž. The more or less similar conclusion was obtained by ABBOTT on the chorda tympani response of rat1). However, very recent studies on the chorda tympani responses in cats by NAGAKI, YAMASHITA and SATO11) and YAMASHITA, YAMADA and SATO15) and in rats by SATO and YAMASHITA13) have shown that the neural taste response is greatest at about 30•Ž or at the temperature of the tongue mostly regardless of the stimuli used. Therefore, in the present study, in order to see whether or not the differences between the results obtained in cats and rats and those obtained in frogs were really true, the effect of temperature on the taste response of a frog was re-examined, by recording the integrated response of the whole glossopharyngeal nerve. To measure only the change in the magnitude of taste responses in the nerve due to temperature change and to exclude thermal responses, the most of the experiments were carried out by use of a preadaptation method1), in which the temperature of the tongue was preliminarily adapted to the same temperature as that of the stimulus.