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 int ake of an amino acid imbalanced diet (IMB), due in part to a drop in the co ncentration of the dietary limiting amino (DLAA) in the anterior piriform c ortex (APC). Administration of the DLAA, but not of a non-limiting amino ac id into the APC, blocks the anorectic response to IMB. To our knowledge, th e 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 L H is a potential chemosensory area for DLAA. Our objectives were: (1) to de termine whether injections of the DLAA threonine into the lateral hypothala mus (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 sti mulated DEV intake during the first 6 h at the 0.25 and 1-nmol doses by app roximately 26 and 24%, respectively. Threonine (0.25, 2.5 nmol) did not alt er 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 fo r indispensable amino acids; and (2) both the APC and LH are part of a circ uit that is involved in the short term anorectic response to amino acid imb alanced diets. (C 2000 Elsevier Science B.V. All rights reserved.