Distribution of d-amino-acid oxidase and d-serine in vertebrate brains

In mammalian brains, d-amino-acid oxidase activity is absent or scarce in the forebrain, is confined to the brain stem and cerebellum, and its localization is extended to the spinal cord. The oxidase-containing cells are astrocytes including Bergmann glial cells. Neither neurons, endothelial cells, oligodendrocytes nor ependymal cells show the oxidase activity. Free d-serine, a potent activator of the N-methyl-d-aspartate (NMDA) receptor, is in high levels in the forebrain (ca. 0.4 μmol/g wet weight), and in low levels in the hindbrain. Thus, the localization of the oxidase activity is inversely correlated with the distribution of d-serine in mammalian brains. This inverse correlation is generally found in vertebrate brains. These results indicate that d-amino-acid oxidase decomposes d-amino acids including d-serine in vertebrate brains, and that the magnitude of its activity is important in determining the regional concentrations of d-amino acids in the steady states.