Examples of recovery from paired pulse depression of EPSCs evoked in HCs by depolarizing steps (–70 to –10 mV, 50 ms) applied to simultaneously voltage-clamped rods. In the left column are initial control EPSCs, and in the right column are the EPSCs evoked after an interpulse interval of 500 ms. The stimulus protocol is illustrated at the bottom of the figure. (A) The fast, ribbon-related component (arrows) of the EPSC in this vehicle control (0.1% DMSO) rod/HC pair recovered by ∼40% after a 500-ms interval. (B) HC EPSCs from a different rod/HC pair after introducing dynasore (80 µM) into the presynaptic rod through a patch pipette. After introducing dynasore into the rod, the fast EPSC component (arrow) showed less recovery after 0.5 s than in the control response illustrated in A. (C) The fast EPSC component recorded from a voltage-clamped HC also showed little recovery with an interpulse interval of 0.5 s after dyngo-4A (30 µM) was introduced into a rod through a patch pipette. (D) Similar to the other inhibitors, the fast HC EPSC showed little recovery with an interpulse interval of 0.5 s after DIP (1 mM) was introduced into a rod through a patch pipette.