Effect of the monoamine uptake inhibitor imipramine on IPSCs evoked by minimal stimulation. A, Superimposed IPSCs in control (trace 1), in the presence of imipramine (1 μm; trace 2), and in the combined presence of imipramine (1 μm) and SCH23390 (0.1 μm; trace 3). Each trace represents the average of 10–15 traces. B, Time course of change in the IPSC amplitude during perfusion with imipramine (IMI) and imipramine together with SCH23390 (IMI+SCH). The amplitude of evoked IPSCs was increased by imipramine associated with a decrease in failure number. Subsequent application of SCH23390 decreased the amplitude of the IPSCs below control level, whereas the failure rate increased, indicating a tonic effect of endogenous DA on GABA release. Each point represents the amplitude of an IPSC evoked by minimal stimulation at a repetition rate of 0.1 Hz.