Extracellular amino acid profiles in the paraventricular nucleus of the rat hypothalamus are influenced by diet composition

One possible mechanism by which food consumption signals feeding centers is through the resulting changes in amino acid profiles in the brain. In this study we examined the effect of voluntary consumption of a 50% protein diet or a 0% protein (carbohydrate) diet on extracellular amino acid profiles in the hypothalamic paraventricular nucleus (PVN) of freely moving rats from 1800 to 2100 h. Dialysates were continuously collected via microdialysis probes inserted in the PVN at 1500 h. Extracellular concentrations of isoleucine, leucine, methionine. tyrosine and valine were elevated within the first or second 20 min following the start of the 50% protein diet (P<0.05). The ratio of tryptophan to the total branched-chain amino acids (BCAA) in extracellular fluid increased following consumption of the carbohydrate diet (P<0.05), but decreased after the protein diet. An elevated ratio of tyrosine to BCAA was observed at the end of the measurement following the protein-free meal. It is concluded that amino acid concentrations in extracellular fluid of the PVN change rapidly after food consumption and that the changes are influenced by dietary composition. (C) 2001 Elsevier Science B.V. All rights reserved.