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

众所周知，食物摄入量以及生长速度受到膳食氨基酸不平衡的抑制。膳食氨基酸组成模式影响食物摄入的一个可能机制是通过大脑中氨基酸谱的变化。然而，关于雏鸡中的机制的信息很少。本研究旨在探讨饲粮氨基酸不平衡或侧脑室注射氨基酸或代谢产物对雏鸡摄食行为的影响，苯丙氨酸（Phe）或色氨酸（Trp）过量可引起雏鸡厌食，侧脑室注射Phe或Trp也可降低雏鸡摄食量。相反，中枢注射蛋氨酸（Met）或亮氨酸（Leu）可刺激雏鸡的摄食行为。提示Leu的中枢作用可能是通过多巴胺能系统产生代谢产物谷氨酸。赖氨酸的代谢产物哌啶酸可能作用于GABA能系统，抑制雏鸡摄食。与哺乳动物一样，谷氨酸、GABA和甘氨酸在鸡的摄食行为中也起着重要的调节作用。但由于GABA制剂在蛋鸡体内对肉鸡的影响不一致，因此在蛋鸡和肉鸡体内存在差异。这些结果表明，氨基酸和/或这些代谢产物的膳食氨基酸组成模式可能会影响通过血管在中枢神经系统的鸡的摄食调节。

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.