Stimulus-induced increase of taste responses in the hamster chorda tympani by repeated exposure to 'novel' tastants

Variations in amplitude of responses of the chorda tympani to repeated application of various novel tastants were measured in familiarized and control groups of adult hamsters. Three groups of 10 hamsters were pre-exposed to 5 mM dulcin, 50 mM potassium l-glutamate (KGlu) or 1 mM 5′guanosine monophosphate (5′GMP). In the fourth group, the tongue was rinsed with 5′GMP for 20 min just prior to recording from the chorda tympani. The tastants were novel to the fifth group (naïve control). A series of 17 stimuli was repeated six times and responses were quantified relative to the initial response of each of the 50 hamsters. The responses of the chorda tympani increased with repetition in the control group. In contrast, no increase in amplitude of response to the pre-exposed tastants or to stimuli with qualitatively related tastes was observed in the group familiarized with either KGlu or 5′GMP. These results indicate that the response of the chorda tympani depends on previous exposure to a tastant. The sensitivity of taste cells appears to be modulated, possibly by stimulus-induced supplementary receptors.