NMDA receptor antagonist D-APV depresses excitatory activity produced by normorphine in rat hippocampal slices.

Both pentylenetetrazole and normorphine increased CA1 pyramidal cell sensitivity to afferent stimulation and caused the appearance of synchronous afterpotentials (secondary spikes). D-2-Amino-5-phosphonovalerate (D-APV) attenuated secondary spikes induced by both drugs, but had no effect on the change in excitability of the primary population spike. These results suggest that both opiates and GABA receptor antagonists are able to unmask NMDA receptors in the in vitro rat hippocampus slice preparation.