Comparison of central effects of L-ornithine metabolites on the stress responses of neonatal chicks

Recently, we observed that central administration of L-arginine attenuated the stress responses of neonatal chicks by inducing a sedative and hypnotic effect. In addition, L-ornithine, which is produced from L-arginine in the brain, appeared to interact with L-arginine during a stress response. Several putative metabolites from L-ornithine, including L-citrullme and D-ornithine, were therefore investigated in the present study. The effects of intracerebroventricular injection of L-ornithine, L-citrulline and D-ornithine were compared in chicks under an isolation-induced stress. L-ornithine greatly attenuated the stress response and induced sedative and hypnotic effects. D-ornithine weakly attenuated the stress responses, while L-citrulline had no effect.