Blockade of NMDA receptors enhances spontaneous sharp waves in rat hippocampal slices.

An in vitro model of sharp waves (SPWs) and ripples was used to investigate the involvement of NMDA receptors in SPW/ripple production. Intracellular recordings from CA3 pyramidal cells confirmed that SPWs are composed of primarily excitatory currents. Unexpectedly, NMDA receptor antagonists greatly increased the size of SPWs and ripples. This effect may have involved decreased calcium influx through NMDA receptors and a subsequent reduction in the activation of SK2 calcium-activated potassium channels. The results support the claim that activation of NMDA receptors can serve to dampen the excitation of SPWs.