Two types of synaptic facilitation recorded in pyramidal cells of in vitro hippocampal slices from guinea pigs.

PyramidaL cells in CA1 hippocampus show two types of increase in the excitatory postsynaptic potential (EPSP) during paired pulse stimulation of the afferent fibres in stratum radiatum. For 15-300 ms interstimulus intervals, both the initial slope and the peak amplitude of the EPSP are increased, which is mainly due to an increased excitatory synaptic current. For 300 ms-2 s intervals, the predominant change is an increase in the peak amplitude. The latter type of facilitation is caused by a decrease in a superimposed inhibitory postsynaptic potential (IPSP).