Gustatory preference-aversion thresholds are increased by ibotenic acid lesion of the lateral hypothalamus in the rat

The main purpose of this study was to quantitate possible changes in the rewarding and aversive values of certain gustatory stimuli produced by bilateral ibotenic acid lesions of the lateral hypothalamus in the rat. Non-operated rats served as controls. Thirteen days after the operation, rats were placed on a water-deprivation schedule during 5 consecutive days. Rats were then given the choice of one of 5 concentrations of saccharin solution, using a two-bottle procedure. Fluid intake across concentrations generated a preference-aversion curve. The same type of procedure was used to obtain the aversion curve for increasing concentrations of quinine solution. The lesioned rats as well as the control animals showed a clear preference-aversion response to saccharin solutions and an aversive response to quinine solutions. However, the highest preference score of the lesioned rats was obtained with a saccharin concentration 3 times higher than the concentration preferred by the control rats. Moreover, unlike control rats operated animals did not show aversion to the highest concentrations of saccharin solutions. Finally in the lesioned rats the aversion threshold to quinine solutions was obtained with concentration 5 times higher than the concentration inducing aversion in the control rats. At the end of these experiments, rats used as controls were submitted, in turn, to bilateral lesion of the lateral hypothalamus. The change in the preference-aversion threshold of these rats in the saccharin choice procedure was the same as that observed with naive rats. Taken together, these results suggest that in the normal rat the palatability of certain gustatory stimuli is modulated by the intrinsic neurons of the lateral hypothalamus.