Differential temperature dependence of taste nerve responses to various taste stimuli in dogs and rats

The temperature dependence of the canine and rat chorda tympani nerve responses to various taste stimuli was examined. The temperature dependence greatly varied with species of stimuli. In the dog, the tonic responses to fructose, sucrose, acetic acid, and guanosine 5'-monophosphate (GMP) and the response induced by the synergism between monosodium glutamate (MSG) and GMP showed peaks at approximately 30 degrees C, whereas those to NaCl, NH4Cl, and MSG showed peaks between 10 and 20 degrees C. In the rat, the tonic response to NH4Cl increased with an increase in temperature up to 45 degrees C, whereas the responses to other stimuli examined showed peaks at approximately 30 degrees C. The responses to glycine, sucrose, and quinine showed sharp temperature dependence, and the responses to acids (HCl and acetic acid) and salts (NaCl and KCl) showed relatively flat dependence. The effects of the temperature change on dose-response curves for fructose, NH4Cl, and GMP were examined using dogs. The temperature change did not practically affect the thresholds for these stimuli and affected the magnitude of the responses to higher concentrations of stimuli. The origins of the temperature dependence were discussed in terms of taste receptor mechanisms.