Lateral parabrachial nucleus lesions in the rat: neophobia and conditioned taste aversion

The present study investigated the hypothesis that the conditioned taste aversion (CTA) deficit consequent to lesions of the lateral parabrachial nucleus (LPBN) may be due to a disruption of neophobia. In Experiment 1, subjects were tested with one of three taste stimuli (alanine, saccharin, or quinine) and two nontaste stimuli (capsaicin and almond odor). Ibotenic acid lesions of the LPBN eliminated neophobia to alanine and saccharin but had no influence on the neophobic response to quinine, capsaicin, or almond odor. In Experiment 2, all the LPBN-lesioned (LPBNX) rats failed to develop a CTA. These results do not support the experimental hypothesis. Not only was the lesion-induced disruption of neophobia restricted to taste stimuli, the deficit was selective within that category. It is already known that LPBNX rats are unable to acquire conditioned aversions to capsaicin as well as alanine. Thus, the absence of a conditioned ingestional aversion in LPBNX rats is not predicated upon the absence of a neophobic response to the target stimulus. The present results, although exposing a stimulus selective disruption of neophobia, suggest that this deficit is independent of, rather than responsible for, the absence of conditioned ingestional aversions in rats with LPBN lesions.