DISTRIBUTION OF DIETARY LIMITING AMINO-ACID INJECTED INTO THE PREPYRIFORM CORTEX

Diffusion or metabolism of the dietary limiting amino acid (DLAA) in the prepyriform cortex (PPC) may account for the time lag between injection of the DLAA into the PPC and the increase in intake of an amino acid-imbalanced diet. Results from the injection of [H-3]Leu +/- [C-14]Thr (DLAA) into the PPC indicated rapid (< 15 min) and limited diffusion (85-90% of recovered label was less-than-or-equal-to 1 mm from the injection site). H-3 and C-14 decreased in the trichloroacetic acid (TCA)-soluble fraction and increased in the TCA-insoluble fraction during the first 1.5 h and remained constant in the TCA-insoluble fraction 1.5-6 h after injection. An increase (approximately-50%) in H-3 in the TCA-insoluble fraction was found less-than-or-equal-to 30 min after injection of the DLAA. There was no affect of the DLAA on H-3 in the TCA-soluble fraction. These results indicated that a change in metabolism within the PPC may be responsible for the delay in onset of the feeding response after injection of the DLAA into the PPC.