Central administration of dipeptides, beta-alanyl-BCAAs, induces hyperactivity in chicks

Carnosine (beta-alanyl-L-histidine) is a putative neurotransmitter and has a possible role in neuron-glia cell interactions. Previously, we reported that carnosine induced hyperactivity in chicks when intracerebroventricularly (i.c.v.) administered. In the present study, we focused on other beta-alanyl dipeptides to determine if they have novel functions. In Experiment 1, i.c.v. injection of beta-alanyl-L-leucine, but not beta-alanyl-glycine, induced hyperactivity behavior as observed with carnosine. Both carnosine and beta-alanyl-L-leucine stimulated corticosterone release. Thus, dipeptides of beta-alanyl-branched chain amino acids were compared in Experiment 2. The i.c.v. injection of beta-alanyl-L-isoleucine caused a similar response as beta-alanyl-L-leucine, but beta-alanyl-L-valine was somewhat less effective than the other two dipeptides. beta-Alanyl-L-leucine strongly stimulated, and the other two dipeptides tended to stimulate, corticosterone release. These results suggest that central beta-alanyl-branched chain amino acid stimulates activity in chicks through the hypothalamus-pituitary-adrenal axis. We named beta-alanyl-L-leucine, beta-alanyl-L-isoleucine and beta-alanyl-L-valine as Excitin-1, Excitin-2 and Excitin-3, respectively.