Intracerebroventricular injection of kynurenic acid attenuates corticotrophin-releasing hormone-augmented stress responses in neonatal chicks

In the brain of neonatal chicks, tryptophan has a sedative effect, and a part of this effect might be dependent upon its metabolite, serotonin. However, the functional mechanisms have not been fully clarified, since l-tryptophan produces kynurenic acid (KYNA) through the kynurenine pathway. The present study aimed to clarify the effect of KYNA on the stress response upon social isolation. Intracerebroventricular injection of KYNA induced a strong sedative effect under stress compared with the effect of l-tryptophan, with or without intracerebroventricular injection of corticotrophin-releasing hormone (CRH). KYNA dose-dependently induced sedative and hypnotic effects under CRH-augmented social isolation stress. Taken together, these results indicate that KYNA is a likely candidate for the sedative and hypnotic effects of tryptophan under acutely stressful conditions.