Roles of D-serine in the mammalian brain

D-Serine has recently been identified as a major gliotransmitter in the mammal central nervous system (CNS). The distribution of D-serine is analogous to the N-methyl-D-aspartate (NMDA)-type glutamate receptors in the brain. D-Serine is as potent as glycine as a coagonist at the glycine-binding site of NMDA receptors. Thus, D-serine has been considered as an endogenous ligand of the NMDA receptors in the brain. D-Serine is synthesized by serine racemase (SR) from L-serine. Both D-serine and SR have been enriched to astrocytes which are the dynamic partners of neurons at synapses and participate in controlling synaptic transmission, synaptic plasticity and synaptogenesis. The present review highlights the most recent findings on the molecular mechanisms of controlling D-serine metabolism in the CNS, the physiological role of D-serine in synaptic plasticity, and the pathological relevance of D-serine to schizophrenia, excitotoxicity- and neuroinflammation-induced neuronal death as well as neuropathic pain. Finally, as we have recently established SR knockout mouse strain with pure C57BL/6 genetic background, this novel mouse model will contribute the analysis of physiological and pathophysiological role of D-serine in vivo.