Increase of GABA release by GRP is action potential dependent. (A) The effect of GRP (300 nM) could be blocked by TTX (1 μM, n = 4). (B) Representative sIPSCs recorded in a pyramidal neuron under baseline conditions (upper), during GRP application (middle), and after TTX was added (lower). (C) Time course of reversible drug effect of TTX (1 μM) to the enhancement of sIPSC induced by GRP treatment. (D and E) Typical examples showing the effect of GRP (300 nM) on mIPSCs in the presence of TTX. Similar results were obtained from an additional 4 neurons. (F) Statistical results showed in the presence of TTX (1 μM), GRP did not affect either amplitude or frequency of mIPSCs.