Chorda Tympani Responses to Gustatory Stimuli in Developing Rats

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Abstract
The developmental change in rat taste sensitivity during the period from postnatal wk 2-12 was studied by recording the responses of the chorda tympani nerve to lingual stimulation by NaCl, LiCl, KCl, NH4Cl, HCl, quinine hydrochloride (Q-HCl) and sucrose. The threshold for all stimulants except sucrose was lower in the 3 wk old rats than the 12 wk old rats. The order of magnitudes for the normalized neural responses to the 0.1 M monochloride salts of the gustatory nerves was NH4Cl > NaCl = LiCl > KCl in the 3 wk old rats and NaCl = LiCl > NH4Cl > KCl in the 12 wk old rats. The magnitude of the normalized responses to NH4Cl, HCl and Q-HCl at nearly all concentrations was greater at 3 wk than 12 wk; the magnitude of the responses to NaCl and LiCl at high concentrations was less at 3 wk than at 12 wk. Changes in the gustatory sensitivity to various taste stimuli during development were classified into the following 2 types: sensitivity-decreasing type, the magnitude of the response to NH4Cl, Q-HCl and HCl was greatest during the 1st few wk and then decreased and sensitivity-increasing type, the magnitude of the response to NaCl, LiCl and sucrose showed an increase accompanying the growth of rats from around the 2nd wk after birth.