Alterations in Plasma Levels of Amino Acids after Intracerebroventricular Administration of L-Serine or D-Serine in Conscious and Freely Moving Rats

ABSTRACT

L-Serine has a role in cellular proliferation, being a precursor for protein synthesis, and is also important for brain development. D-Serine plays a role as the endogenous co-agonist at the glycine site on the N-methyl-D-aspartate (NMDA) receptors in the brain. Accumulating evidence suggests that abnormality of D-serine levels might be involved in the pathophysiology of schizophrenia. Using the automated blood sampling system, we examined whether or not intracerebroventricular (icv) infusion of L- and D-isomers of serine could affect plasma levels of amino acids in conscious and freely moving rats. The icv infusion of L-serine significantly decreased the plasma levels of glycine, glutamate, and Dserine, but not glutamine and L-serine. Furthermore, the icv infusion of D-serine significantly decreased the plasma levels of glycine, glutamate, and L-serine, but not glutamine. Expectedly, a marked increase of plasma D-serine was detected after icv infusion of D-serine. These findings suggest that the metabolic pathway for L- and D-serine may be markedly different in the rat brain.