Diets Deficient in Indispensable Amino Acids Rapidly Decrease the Concentration of the Limiting Amino Acid in the Anterior Piriform Cortex of Rats

Diets deficient in an indispensable amino acid have long been known to suppress food intake in rats. Detection of dietary deficiency takes place in the anterior piriform cortex (APC). Recent studies showed that the response to amino acid deficiency takes as little as 15 min to develop, but few data exist to correlate the concentration of amino acids in the APC with this rapid response. The purpose of this study was to measure the concentration of amino acids in the APC in a behaviorally relevant time frame. Rats were preconditioned by consumption of a basal diet for 7–10 d, and then given a test diet with either a control or deficient amino acid profile. Both the threonine- and leucine-deficient diets reliably depleted threonine and leucine concentration in the APC within 30 min, respectively. The control diets and a diet lacking the dispensable amino acid glycine did not lead to amino acid depletion. In combination with previous studies, the present results show that the decrease in the concentration of indispensable amino acids in the APC may be the initial sensory signal for recognition of dietary amino acid deficiency.