LESIONS OF THE PONTINE PARABRACHIAL NUCLEI ELIMINATE SUCCESSIVE NEGATIVE CONTRAST EFFECTS IN RATS

Rats shifted from a high to a low concentration of sucrose make fewer licks for the low concentration than rats that experience only the low concentration of sucrose. This phenomenon, referred to as successive negative contrast, is eliminated after bilateral electrolytic lesions of the amygdala. Because the amygdala receives direct projections from the gustatory zone of the parabrachial nuclei of the pens (PBN), this experiment was designed to examine this phenomenon in rats with elect rophysiologically guided bilateral electrolytic lesions of the PBN. Th e results of this experiment showed that lesions of the PBN fully prev ent contrast in rats shifted from the high to the low concentration of sucrose. Thus, an intact PBN is essential for the occurrence of succe ssive negative contrast effects in rats.