Role of amino acids in the central nervous system on the regulation of feeding behavior in chick

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It is well known that food intake, as well as growth rate, is depressed by dietary ammo acid unbalances. One possible mechanism by which dietary amino acid composition pattern affects food intake is through the resulting changes in ammo acid profiles in the brain. However, there is little information for the mechanisms in chicks. The aim of the present study was investigated the effects of dietary amino acid unbalances, or intracerebroventricularly (ICV) injection of amino acids or metabolites on feeding behavior in chicks.Phenylalanine (Phe)-or tryptophan (Trp)-excess feed induced anorexia and ICV injection of Phe or Trp also decreased food intake in chicks. In contrast, feeding behavior in chicks was stimulated by central injection of methionine (Met) or leucine (Leu). It seemed that the central effect of Leu might contribute to metabolite, glutamate via glutaminergic system. In addition, pipecolic acid, the metabolite of lysine, might act on GABAergic system and suppressed food intake in chicks. On the other hand, there was possibility that Met perse might play a role as neuromodulator.Similar to mammals, it seemed that glutamate, GABA and glycine have an important role in the regulation of feeding behavior of chicks. However, it appeared that there was difference between layer and broiler chicks because the effects of GABA agents in layers were inconsistent in broilers. These results suggest that amino acids and/or these metabolites by which dietary amino acid composition pattern may influence feeding regulation via blood vessels in the central nervous system of chicks.