Amplitude fluctuations of dual-component EPSCs in hippocampal pyramidal cells: implications for long-term potentiation.

Quantal analysis has provided evidence for a presynaptic contribution to long-term potentiation in hippocampal CA1 cells. This however leaves unexplained the observation that long-term potentiation has little or no effect on the NMDA receptor-mediated component of the synaptic signal. Here, I report that, in baseline conditions, the coefficient of variation of the AMPA/kainate receptor-mediated signal (CVA/K) is consistently larger than that of the NMDA component (CVNMDA), a result which can be explained if AMPA/kainate receptors are absent or nonfunctional at a proportion of synapses. Long-term potentiation is associated with a reduction in CVA/K, but no change in either the average amplitude of the NMDA component or CVNMDA. This is consistent with the proposal that long-term potentiation induction uncovers clusters of latent AMPA/kainate receptors, with no change in transmitter release.