Central injection of L- and D-aspartate attenuates isolation-induced stress behavior in chicks possibly through different mechanisms

Intracerebroventricular (i.c.v.) injection of L- and D-aspartate (L- and D-Asp) has been shown to have a sedative effect with and without a hypnotic effect, respectively, in neonatal chicks experiencing isolation stress. However, the mechanisms of the different stress-attenuating functions of L- and D-Asp have not yet been fully clarified. In the present study, we investigated the involvement of the N-methyl-Daspartate (NMDA) receptor in order to reveal the receptor-mediated function of L- and D-Asp. To reveal whether L-and D-Asp act through the NMDA receptor, (þ)–MK-801, which is an antagonist of NMDA receptors, was used in the current study. In experiment 1, the chicks were injected i.c.v. with either saline, (þ)–MK-801, L-Asp or L-Asp plus (þ)–MK-801. The sedative and hypnotic effects induced by L-Asp were blocked by co-administration with (þ)–MK-801. In experiment 2, the chicks were injected i.c.v. with either saline, (þ)–MK-801, D-Asp or D-Asp plus (þ)–MK-801. Importantly, the sedative effects induced by D-Asp were shifted to hypnotic effects by co-administration with (þ)–MK-801. Taken together, L-Asp could induce sedative and hypnotic effects for stress behaviors through the NMDA receptor, but the attenuation of stress behaviors by D-Asp might be via simultaneous involvement of other receptors besides the NMDA receptor in this process. These differences may explain the different functional mechanisms of L- and D-Asp in the central nervous system

Oral administration of D-aspartate, but not L-aspartate, depresses rectal temperature and alters plasma metabolites in chicks

Aims: L-Aspartate (L-Asp) and D-aspartate (D-Asp) are physiologically important amino acids in mammals and birds. However, the functions of these amino acids have not yet been fully understood. In this study, we therefore examined the effects of L-Asp and D-Asp in terms of regulating body temperature, plasma metabolites and catecholamines in chicks. Main methods: Chicks were first orally administered with different doses (0, 3.75, 7.5 and 15 mmol/kg body weight) of L- or D-Asp to monitor the effects of these amino acids on rectal temperature during 120 min of the experimental period. Key findings: Oral administration of D-Asp, but not of L-Asp, linearly decreased the rectal temperature in chicks. Importantly, orally administered D-Asp led to a significant reduction in body temperature in chicks even under high ambient temperature (HT) conditions. However, centrally administered D-Asp did not significantly influence the body temperature in chicks. As for plasma metabolites and catecholamines, orally administered D-Asp led to decreased triacylglycerol and uric acid concentrations and increased glucose and chlorine concentrations but did not alter plasma catecholamines. Significance: These results suggest that oral administration of D-Asp may play a potent role in reducing body temperature under both normal and HT conditions. The alteration of plasma metabolites further indicates that D-Asp may contribute to the regulation of metabolic activity in chicks