Metabolism and physiology of glutamate in chickens

Glutamate is one of the proteinogenic and nutritionally non-essentional amino acids, and is precursor of glutamine, arginine, proline and glutathione. Glutamate also serves as the precursor for the synthesis of the inhibitory γ-aminobutyric acid (GABA) in GABAergic neurons. Among these metabolites, synthesis of arginine and proline in chickens is different from the mammals. Chickens lack carbamyl phosphate synthetase I and have relatively little ornithine transcarbamylase activities. Chickens are also unable to synthesize ornithine from glutamate and proline. These characteristics make the absolute dietary requirement of arginine in chickens. In addition, the biosynthesis of proline from glutamate is not rapid and not supports maximum growth in chicks. On the other hand, glutamate, an excitatory amino acid, acts as a neurotransmitter in the central nervous system. It can induce neuronal activity with powerful stimulatory effects. However, the central administration of glutamate attenuates stress-induced behaviors and triggers sleep-like behavior in neonatal chicks. Furthermore, glutamate plays major roles in the development of normal synaptic connections in the brain. Glutamate concentration increased in the brain with the advancement of age in developing chicks. In conclusion, glutamate is an important metabolite which plays significant roles in the development and maintenance of peripheral and central tissues in the chicken.