Effects of threonine injections in the lateral hypothalamus on intake of amino acid imbalanced diets in rats.

Previous work from this laboratory suggests that animals decrease their intake of an amino acid imbalanced diet (IMB), due in part to a drop in the concentration of the dietary limiting amino (DLAA) in the anterior piriform cortex (APC). Administration of the DLAA, but not of a non-limiting amino acid into the APC, blocks the anorectic response to IMB. To our knowledge, the effects of DLAA injections on intake of a diet devoid of the DLAA (DEV), have not been examined in areas outside the APC. We hypothesized that the LH is a potential chemosensory area for DLAA. Our objectives were: (1) to determine whether injections of the DLAA threonine into the lateral hypothalamus (LH) alter intake of a threonine-devoid diet (DEV); and (2) to examine the dose-response effects of threonine injections into the LH on intake of threonine-corrected diet (COR). Administration of threonine into the LH stimulated DEV intake during the first 6 h at the 0.25 and 1-nmol doses by approximately 26 and 24%, respectively. Threonine (0.25, 2.5 nmol) did not alter COR intake at any time during the first 12 h. Our results suggest that: (1) the LH, along with the APC, likely acts as a chemosensory brain area for indispensable amino acids; and (2) both the APC and LH are part of a circuit that is involved in the short term anorectic response to amino acid imbalanced diets.