MODIFICATION BY TEMPERATURE CHANGE OF GUSTATORY IMPULSE DISCHARGES IN CHORDA TYMPANI FIBRES OF RATS

Abstract

1. Interaction of thermal with gustatory stimulations of the tongue was examined by recording impulse discharges in single chorda tympani fibres of rats. 2. When temperature of a taste solution flowing over the tongue was lowered or raised suddenly, a transient change in the impulse frequency was observed: In some fibres cooling produced an increase in the impulse frequency and warming a decrease, while in other fibres a fall in the frequency was brought about by a cold solution and a rise by a warm solution. 3. Changes in the impulse frequency after sudden temperature change of taste solutions depended inversely on the impulse frequency before thermal change but not on cold sensitivity of the unit. 4. Relationships between the magnitude of response to NaCl solutions of varying concentrations and temperature, to which the tongue had been adapted, were determined. In a few fibres the impulse frequency produced by NaCl solutions of 0.003-0.3M decreases monotonically with increasing temperature, while in other fibres it becomes high with increasing temperature up to 30°C and declines above it. In the remaining fibres a rise in temperature results in a decrease in the impulse frequency with NaCl solutions of low concentrations while the frequency increases with a rise in temperature with those of high concentrations. 5. Certain correlations appear to exist between dependence of impulse frequency in response to NaCl on temperature and sensitivity of units to the four basic stimuli. 6. The response magnitude-concentration relationships at various temperatures were found to be expressed approximately by a power function of a form R=KSⁿ. The value of the exponent n becomes high with a rise in temperature up to 30°C but decreases slightly with its further rise, the average value of n for NaCl being 0.8 at 20°C, 1.6 at 30°C and 1.4 at 40°C.