Figure 3. Calcium signals in GC dendrites and presynaptic expression of CB1R at PF to GC synapses.

(A) A representative experiment is shown in which a GC was voltage-clamped, depolarized from −70 mV to 0 mV for 2 s, and the resulting dendritic calcium signal was quantified with Fura-FF. (B) Average peak dendritic calcium levels measured in 6 GCs. (C) Bath application of the CB1R agonist WIN 55,212-2 (WIN, 2 µM) reduces the amplitude of PF→GC EPSCs. EPSC amplitude is restored following bath application of AM251 (5 µM). (D) Summary of the effects of a 2 s depolarizing step (DSE, blue), WIN (red) and of AM251 (black) on the magnitude of the EPSC in GCs (n = 5). (E–F) Effects of postsynaptic depolarization and WIN on paired-pulse facilitation (20 ms ISI). Experiments were conducted in 4 mM external calcium. As shown for a representative experiment (E), WIN reduced the amplitude of the first and second EPSC. Overlay, with the traces scaled to the amplitude of the first response, shows that WIN increased pairedpulse facilitation. (F) Summary of the average paired-pulse ratio (PPR = EPSC₂/EPSC₁) in control conditions (black), following a 2 s depolarization (blue), and following WIN application (red, n = 5 GCs).