Oral administration of L-serine reduces the locomotor activity of socially isolated rats.

L-Serine is considered a functional amino acid in the central nervous system, since intracerebroventricular injection of L-serine induced sedative and hypnotic effects in neonatal chicks exposed to acute stressful conditions. Accordingly, L-serine is a candidate anti-stress factor, but the effect of daily intake of L-serine on behavior of animals exposed to chronic stress has not been investigated. In the present study, we exposed rats to social isolation stress for 4 weeks, and home cage test and open field test were concluded to evaluate the effect of L-serine on behavior. To investigate L-serine supplementation modifies the brain L-serine and its metabolite contents, free amino acid contents were measured by a high performance liquid chromatography. L-Serine in the drinking water increased L-serine levels in some brain areas, but changes in its metabolites were almost negligible. L-Serine decreased locomotor activity in rats exposed to a familiar environment. In addition, L-serine decreased exploratory behavior of isolated rats, even in a novel environment. Our results could suggest that daily intake of L-serine can attenuate symptoms induced by chronic stress.