RELIABILITY AND STATE DEPENDENCE OF PYRAMIDAL CELL-INTERNEURON SYNAPSES IN THE HIPPOCAMPUS - AN ENSEMBLE APPROACH IN THE BEHAVING RAT

Spike transmission probability between pyramidal cells and interneuron s in the CA1 pyramidal layer was investigated in the behaving rat by t he simultaneous recording of neuronal ensembles. Population synchrony was strongest during sharp wave (SPW) bursts. However, the increase wa s three times larger for pyramidal cells than for interneurons. The co ntribution of single pyramidal cells to the discharge of interneurons was often large (up to 0.6 probability), as assessed by the presence o f significant (<3 ms) peaks in the cross-correlogram. Complex-spike bu rsts were more effective than single spikes. Single cell contribution was higher between SPW bursts than during SPWs or theta activity. Henc e, single pyramidal cells can reliably discharge interneurons, and the probability of spike transmission is behavior dependent.