(A) Averaged EPSC amplitude and charge versus stimulus number during train of stimuli at 2, 50 and 100 Hz. At 50 Hz EPSC amplitude and EPSC charge are represented by light and dark green squares, respectively. At 2 Hz, EPSC amplitudes and EPSC charge are represented with red diamonds and orange diamonds, respectively. Note strong facilitation at 50 and 100 Hz, no facilitation at 2 Hz. (B) Left and right panels represent the number of quanta released during trains of 50 stimuli at 2, 50 and 100 Hz. Left panel: Cumulative number of quanta release versus stimulus number at 2 Hz (red line), 50 Hz (green line) and 100 Hz (blue line). Note that the superposition of values at 50 Hz and 100 Hz mask the values at 100 Hz. Right panel: Box-plots showing the corresponding cumulative number of quanta released at the 50th stimulus. No difference was observed between 50 and 100 Hz (t-test, p=0.82). Mean and median values are indicated in red and black, respectively. (C) Representative recording traces of EPSCs evoked at 100 Hz and 2 Hz. Inset: The first EPSCs observed during 100 Hz train. The stimulus artifacts have been subtracted for the 100 Hz train. (D) left, schematics showing the two modes of stimulation. Extracellular stimulations in the molecular layer (ML) (upper panel) activated beams of PFs (in red) whereas stimulations of the granule cell layer (GCL) (lower panel) led to sparse activations of PFs (in green) Non-stimulated GCs are represented in light blue. Stimulated areas are represented by concentric orange circles. Right, two examples of the time course of EPSC amplitudes following stimulation of PFs (upper panel) or of GC somata (lower panel) at 0.033 Hz (gray points) and 2 Hz (red or green points respectively). (E) Mean normalized EPSC amplitude during sustained 2 Hz stimulations of PFs or GC somata (red and green points respectively). Note the delay before the actual induction of LFD. The depression was fitted by a monoexponential function (tau = 21.7 s, white line). (F) Selected time course of LFD recorded in 5 PCs showing differences in the onset and the plateau of depression. (G, H) LFDs elicited in the same cell share the same profile of depression. (G) Time courses of two successive LFDs elicited in the same cell. The second LFD protocol (LFD#2, blue points) was performed after a resting period of 5 min (LFD#1, green points). inset, traces correspond to averaged EPSCs recorded during LFD#1 and LFD#2 (green and blue traces, respectively) at the indicated stimulus numbers. (H1) EPSC amplitudes recorded at the first stimulus of LFD#1 (green points) and LFD#2 (blue points). The similar sizes of EPSC amplitudes in LFD#1 and LFD#2 indicates full recovery from depression during the resting period (paired t-test performed on EPSCs#1 of LFD#1 and LFD#2, p=0.94, n = 8). (H2) Superimposition of mean EPSC amplitudes recorded during LFD#1 (green points) and LFD#2 (blue points). Same set of experiment as in H1. (H3) Box-plots showing the cumulative number of quanta released during LFD#1 and LFD#2 (number of quanta released during LFD: 49.5 quanta ± 18.8 quanta for LFD#1 versus 45.6 quanta ±, 14.5 quanta for LFD#2, paired t-test, p=0.47, n = 8), the plateau of LFD#1 and LFD#2 (mean percentage of initial response for LFD: 13.9 ± 5.2% for LFD#1 versus 11.8% ±, 3.2 for LFD#2, paired t-test, p=0.39, n = 8) and the delay before the onset of depression (15.6 stimuli ± 6.6 stimuli for LFD#1 versus 17.4 stimuli ± 7.2 for LFD#2. paired t-test, p=0.13, n = 8). Since none of these parameters were statistically different between the two conditions, LFD#1 and LFD#2 were considered identical. Blue and red lines indicate median and mean values respectively. Same set of experiments as in H1, H2.