Fig. 1.

Basic properties of 2,5-dimethyl-4-[2-(phenylmethyl)benzoyl]-1H-pyrrole-3-carboxylic acid methyl ester (FPL)-LTD are similar at glutamatergic (FPL-eLTD) and GABAergic synapses (FPL-iLTD). (A) FPL (500 nm) induced a robust depression in MSNs clamped at −50 mV that was prevented, but not reversed, by CB₁R antagonist (AM251, 2 µm). (B) FPL-LTD was blocked by intracellular loading of the AMT inhibitor VDM11 (10 µm), indicating that eCB signaling involves a postsynaptic release step at both glutamatergic and GABAergic synapses. Example traces show excitatory postsynaptic currents (EPSCs) in a VDM11-loaded MSN at baseline (black) and post FPL treatment at t = 20–25 min (gray). (C) FPL-eLTD was significantly reduced in slices perfused with the protein translation inhibitor cycloheximide (80 µm). Bath application (filled circles) was more successful in inhibiting FPL-eLTD compared with intracellular loading (open triangles), suggesting that protein synthesis is required outside the postsynaptic cell. Example traces show EPSCs in a cycloheximide-loaded MSN clamped at baseline (black) and post FPL treatment at t = 20–25 min (gray). FPL-iLTD was also dependent on protein translation, and completely prevented in slices pretreated with cycloheximide (80 µm). The graph shows the mean inhibitory postsynaptic current (IPSC) amplitude with SEM in MSNs after 10 min treatment with 500 nm FPL (*P < 0.05). (D) Treatment with another blocker of protein synthesis, anisomycin (20 µm; filled circles) also successfully inhibited FPL-eLTD. EPSC / IPSC amplitude data are mean ± SEM. Scale bars: 100 pA and 25 ms for all traces. aCSF, artificial cerebrospinal fluid.