Effects of chorda tympani nerve anesthesia on taste responses in the NST

Human clinical and psychophysical observations suggest that the tastesystem is able to compensate for losses in peripheral nerve input, sincepatients do not commonly report decrements in whole mouth taste followingchorda tympani nerve damage or anesthesia. Indeed, neurophysiological datafrom the rat nucleus of the solitary tract (NST) suggests that a release ofinhibition (disinhibition) may occur centrally following chorda tympaninerve anesthesia. Our purpose was to study this possibility further. Werecorded from 59 multi- and single- unit taste-responsive sites in the ratNST before, during and after recovery from chorda tympani nerve anesthesia.During anesthesia, average anterior tongue responses were eliminated but nocompensatory increases in palatal or posterior tongue responses wereobserved. However, six individual sites displayed increased tasteresponsiveness during anesthesia. The average increase was 32.9%.Therefore, disinhibition of taste responses was observed, but infrequentlyand to a small degree in the NST At a subset of sites, chordatympani-mediated responses decreased while greater superficialpetrosal-mediated responses remained the same during anesthesia. Since thiseffect was accompanied by a decrease in spontaneous activity, we proposethat taste compensation may result in part by a change in signal-to-noiseratio at a subset of sites.