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Metabolism and functional roles of endogenous D-serine in mammalian brains.

It has now been well established that D-serine, a coagonist for the N-methyl-D-aspartate (NMDA) glutamate receptors (NR1/NR2 type), is maintained at a high concentration in mammalian brains for life and shows a brain-selective and NMDA receptor R2B subunit-related distribution, overturning the hitherto generally accepted theory that D-amino acid is not always present in mammalian tissues. D-Serine in the brain has been shown to be contained in both the glia and neurons and to have specific processes of biosynthesis, extracellular release, uptake, and degradation. Moreover, the selective elimination of D-serine reduces the NMDA receptor-mediated intracellular signaling and long-term potentiation of synaptic connections. Together with the anti-psychotic and anti-ataxic property of D-serine and the pivotal roles of the NMDA receptor in divergent higher brain functions, these observations support the view that the D-amino acid may be involved as an endogenous modulator for the NMDA receptor in various neuropsychiatric functions and their pathological conditions.