Perfusion of substance P (8 μM) had no effect on the amplitude of PS1 but reduced paired pulse depression. (a) Example synaptic response recorded from a single slice using paired pulse stimulation at an interstimulus interval of 20 ms. The response on the left was recorded under control conditions whereas the trace on the right is that recorded in the presence of substance P (8 μM). (b) Pooled time course data showing that perfusion of substance P for 10 min (black bar) had no effect on the amplitude of PS1. (c) Pooled time course data from the same set of experiments showing PS2 expressed as a % of PS1. Substance P (8 μM) perfused for 10 min (black bar) significantly increased PS2 amplitude and therefore decreased paired pulse depression. Points represent mean ± s.e.m., n = 7. (d) The effect of substance P on the full range of interstimulus intervals recorded during control conditions (open bars) and during drug perfusion (filled bars). * denotes p < 0.05, ** denotes p > 0.01, n = 9. Scale bar represents 1 mV and 10 ms.