Taste responses from the chorda tympani nerve in young and old Fischer rats

To determine whether neurophysiological taste responses are different in young and old rats, recordings were made from the whole chorda tympani nerve which innervates taste buds on the anterior tongue. Fischer 344 male and female rats in three age groups were studied: 5 to 7 months, 23 to 25 months, and 29 to 32 months. Chemical stimuli included single concentrations of five salts, two acids, sucrose and quinine hydrochloride, and concentration series of the five salts. Neural response magnitudes were expressed as ratios relative to the NaCl(0.1M) response. Substantial neural responses were obtained to all chemicals at all ages. Response ratios for NH4Cl and sucrose, however, increased significantly with age; ratios for MgCl2 and citric acid decreased. Ratios for HCl decreased when data from either sex were analyzed separately. Shapes of response/concentration functions for NaCl, but not other salts, also differed with age. In general, though, the magnitudes of all age-related differences were small and neural recordings demonstrate that the peripheral taste system functions well in old age.