Endogenous activation of presynaptic kainate receptors downregulates MF-GPSCs. A, Superimposed individual traces of MF-GPSCs evoked in the presence of GYKI 52466 (30 μm) and GYKI 52466 plus DNQX (50 μm). Note that, in this and in the following experiments, GYKI 52466 was always present in the bathing solution in control conditions. Below, Averaged traces (successes plus failures). Note that DNQX enhanced the amplitude of the first response and reduced the number of synaptic failures. B, Summary plot showing the mean amplitude of GPSCs obtained in eight cells in the presence of DNQX, l-AP4, and PTX. Vertical bars are SEM. The horizontal dashed line refers to the mean amplitude value measured before DNQX. C, Superimposed individual traces (above) and average traces (below) of MF-GPSCs evoked in the presence of GYKI 52466 (30 μm) and GYKI 52466 plus UBP 302 (10 μm). D, As in B, but in the presence of UBP 302, l-AP4, and PTX (n = 19).