5-HT reduces the amplitude of spontaneous EPSPs in giant interneurons. A, Spontaneous EPSPs recorded in a giant interneuron in control conditions. B, 5-HT depressed the amplitude of spontaneous EPSPs. C, The amplitude of spontaneous EPSPs recovered after washout. D–F, Distribution of the amplitude of spontaneous EPSPs before, during, and after application of 5-HT. The histograms in D–F represent the amplitude of synaptic events that were identified clearly as EPSPs measured over a period of time of 5 min before, during, and after bath application of 5-HT.