Emerging evidence indicates that D-
serine rather than
glycine serves as an endogenous agonist at
glycine site of the
N-methyl-D-aspartate (
NMDA) subtype of
glutamate receptors, in several nervous tissues, including the developing cerebellum and the retina. Here, we examined whether endogenous D-
serine plays a significant role in neuronal damage resulting from excitotoxic insults in the cerebral cortex, using rat brain slices maintained in a defined
salt solution. Neuronal cell death induced by application of
NMDA or by
oxygen-
glucose deprivation (simulated
ischemia) was markedly suppressed by a competitive
glycine site antagonist 2,7-dichlorokynurenic
acid. Addition of
glycine or D-
serine did not augment neuronal damage by
NMDA or simulated
ischemia, indicating that sufficient amount of
glycine site agonist(s) is supplied endogenously within the slices. Application of
D-amino acid oxidase, an
enzyme that degrades D-
serine, markedly inhibited neuronal damage by
NMDA and simulated
ischemia, which was reversed by addition of excess D-
serine or
glycine. Sensitivity to the
glycine site antagonist of
NMDA- or
ischemia-induced damage was not affected by the presence of a non-
NMDA receptor antagonist, suggesting that
kainate receptor-stimulated D-
serine release as demonstrated in primary cultured astrocytes does not contribute significantly to the extent of neuronal injury in these settings. The present results suggest that endogenous supply of D-
serine as a
glycine site agonist is important for neuronal injury involving
NMDA receptor overactivation in the cerebral cortex.