Amino acid imbalance, a nutritional model: serotonin3 mediation of aversive responses.

The feeding responses to essential dietary amino acid (AA) disproportion have been useful in nutritional studies. These responses involve first: recognition of the imbalance and second: rejection of the diet, likely via development of a learned aversion. In the rat, we have studied the role of the limiting AA and protein synthesis in the recognition phase by replacement of the limiting AA into a brain area essential for the initial depressed feeding response. We have also reported a reciprocal relationship between serotonin (5HT) activity and intake of imbalanced diets. High doses of the 5HT3 receptor antagonist, ICS 205-930 (ICS; 9 mg/kg IP), restored food intake to 85% or more of control intake. In the present experiments, similar treatment with ICS blocked the classical conditioned taste aversion to a saccharin solution paired with lithium chloride. These results suggest that the increased intake of AA imbalanced diets after ICS may be due to 5HT-mediated blockade of a learned aversion.