d-Serine is a coagonist of N-methyl-d-aspartate (NMDA) receptors that occurs at high levels
in the brain. Biosynthesis of d-serine is carried out by serine racemase, which converts l-to d-
serine. d-Serine has been demonstrated to occur in glial cells, leading to the proposal that
astrocytes are the only source of d-serine. We now report significant amounts of serine
racemase and d-serine in primary neuronal cultures and neurons in vivo. Several neuronal
culture types expressed serine racemase, and d-serine synthesis was comparable with that …