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Threonine Concentration in the Prepyriform Cortex Has Separate Effects on Dietary Selection and Intake of a Threonine-Imbalanced Diet by Rats¹

Department of Physiological Sciences, School of Veterinary Medicine, and Food Intake Laboratory, University of California, Davis, CA 95616

Dietary selection and intake of a threonine-imbalanced diet were evaluated after increasing the concentration of the dietary limiting amino acid in the prepyriform cortex. Selection against the threonine-imbalanced diet in favor of a protein-free diet was reversed when 2 or 4 nmol threonine was injected bilaterally into the prepyriform cortex. However, intake of the threonine-imbalanced diet was significantly increased only after injection of 2 nmol threonine. The reduced intake of the threonine-imbalanced diet, compared to the basal diet, after injection of 4 nmol threonine was not the result of an excess in the concentration of amino acid (or nitrogen) injected into the PPC because intake of the threonine-basal diet was not reduced when 4 nmol threonine was administered. Intake of the threonine-imbalanced diet was also increased after injection of 2 nmol threonine plus 2 nmol isoleucine but not after injections of 2 nmol isoleucine. The changes in food intake when an imbalanced diet is fed appear to be the result of at least two separable responses: recognition of a diet as having an amino acid imbalance, as indicated by dietary choice, and reduction in food intake. The results of this study indicate that changing the concentration of the dietary limiting amino acid in the prepyriform cortex influenced dietary selection and food intake separately.

KEY WORDS: • amino acid imbalance • dietary selection • food intake • prepyriform cortex • rats

¹ This research was supported by funds from National Institutes of Health Grants AM-07355 and BRS-2-SO7-RR05437 and the U.S. Department of Agriculture Grant CRCR-1-2418.

Manuscript received 23 October 1990. Revision accepted 16 January 1991.