A, paired-pulse plasticity of MSN EPSCs recorded in control (n = 17), with DHK (300 μm, n = 8) and nipecotic acid (500 μm, n = 7). Both treatment DHK and nipecotic acid increased significantly EPSC depression for 4 and 6 ms ISIs and facilitation for ISI = 50 ms. DHK and nipecotic acid induced facilitation (which was not induced in control) for ISI = 100 ms. EPSC depression, for ISIs from 250 ms to 1 s, was not significantly affected by DHK or nipecotic acid treatments. B, effect of desensitization of AMPA receptors induced by DHK was investigated for 4 and 6 ms ISIs, by reducing the AMPA receptor desensitization with CTZ (100 μm). Paired-pulse depression was significantly increased when glutamate clearance was blocked with DHK (n = 8). CTZ (n = 7 and 9 for ISI of 4 and 6 ms, respectively) totally abolished the paired-pulse depression. ns: not significant, **P < 0.01, ***P < 0.001.