Effect of the glycine modulatory site of the N-methyl-D-aspartate receptor on synaptic responses in kitten visual cortex.

In visual cortical slices taken from kittens, the administration of D-serine, an agonist of the N-methyl-D-aspartate receptor complex, significantly enhanced synaptically evoked responses using field potential recordings in lower layer II/III. Expression of normally appearing long-term potentiation (LTP) took place in the presence of the agonist during high-frequency stimulation (HFS). The administration of an antagonist of this receptor, 7-chloro-kynurenic acid (7-Cl KY) alone had no appreciable effect on low-frequency synaptic transmission while HFS failed to induce LTP. Combined administration of D-serine and 7-Cl KY resulted in no alteration of low-frequency synaptic transmission, although expression of LTP was normally obtained. These results suggest that in visual cortex of kittens, the availability of this glycine binding site of the NMDA receptor is necessary for the expression of LTP.