Dependence of paired-pulse ratio of EPSC amplitude on interstimulus time intervals. A, representative EPSC traces from type I DMX (top), type II DMX (middle) and dm-cNTS (NTS; bottom) neurons evoked by successive stimuli that were delivered at inter-stimulus intervals of 20, 60, 100, 220, 300 ms and 10 s. Seven traces are overlaid and aligned at the first EPSC waveform (long arrow at the left) for each neuron. Each trace is an average of 8 responses. B, summary of the paired-pulse ratio at different ISIs. Mean and SEM of the PPR values measured in type I (n = 4-19) and type II (n = 3-13) DMX neurons and dm-cNTS neurons (n = 4-9). Note that the ISI-dependence of PPR values also differed among these three neuron groups. The PPR values at each ISI were statistically compared to those at ISI of 10 s in each neuron group. At all time points, the PPR was significantly smaller (ANOVA; P < 0.05), except at 100 ms and 1 s for type I DMX neurons, at which the PPR was not significantly different from that at 10 s.