Potentiation of synaptic reflexes by D-serine in the rat spinal cord in vitro

6-Cyano-7-nitroquinoxaline-2,3-dione (CNQX) (10 μM) depressed dorsal root-evoked ventral and dorsal root potentials of the in vitro immature rat spinal cord to 26.3 ± 5.2 S.E.M. and 40.8 ± 2.7% of control values respectively. These depressant effects of CNQX were partially reversed by D-serine (EC 50 values 39.7 μM ± 8.7 S.E.M. N = 6 and 34.9 ± 12.5 μM, N = 5 for ventral potential and dorsal root potential respectively). Under our experimental conditions, which included the presence of Mg 2+ (0.75 mM) in the bathing medium, no measurable potentiation of these synaptic reflexes by D-serine was recorded in the absence of CNQX. These data indicate that CNQX, in addition to its depressant effect at non-NMDA receptors, depresses an NMDA receptor-mediated component of segmental transmission through its action at the glycine site of the NMDA receptor complex.