A, t-LTD induced by pre–post pairings was blocked by a specific PLC antagonist, i-U73122 (5 μm). i-U73122 blocked the induction of t-LTD (113.0 ± 7.3%, n = 5), indicating that the activation of PLC is required to induce t-LTD. Insets: averaged EPSCs before (left) or after (right) STDP protocols. B, summary of the effects of the specific group-I mGluR antagonist (LY367385, 100 μm), the M1R antagonist (pirenzepine, 1 μm), the 5-HT2AR antagonist (SR46349B, 1 μm) and the L- and T-type VSCC antagonist (mibefradil, 20 μm). t-LTD was blocked by treatment with LY367385 (135.2 ± 22.2%, n = 5), pirenzepine (96.6 ± 6.5%, n = 8) or mibefradil (94.6 ± 14.1%, n = 5). On the contrary, blockade of 5-HT2Rs did not preclude t-LTD occurrence (79.3 ± 6.9%, n = 6). Insets: averaged EPSCs before (black) or after (blue) STDP protocols in LY367385 treatment. ns: not significant, *P < 0.05, **P < 0.01.