Parabrachial lesions disrupt responses of rats to amino acid devoid diets, to protein-free diets, but not to high-protein diets.

Normal rats "reduce" intake of diets that lack an essential amino acid (THR-DEV), are protein free (PO%), or contain a high proportion of protein (P75%). We tested the importance of the parabrachial nuclei (PBN) in signaling such adjustments of food intake by placing electrophysiologically guided lesions in these nuclei at points that responded to gustatory stimuli. When fed the THR-DEV diet, rats with PBN lesions (PBNx) decreased their food intake significantly less than the controls (78.5 vs. 44.4%). When put on a P0% diet, PBNx animals decreased their intake only 8% compared with 23% for our CONT group. When put on a P75% diet, however, both groups decreased their intake in an equivalent amount. These experiments show that the PBN is involved in the learned aversion to an amino acid devoid diet.