Figure 3. Train stimulation and short term plasticity experiments indicate a reduced pool size and a slightly lowered release probability.

(A) Example single ESPC traces in response to 100 Hz trains of afferent fiber stimulations in a RIM1/2 cDKO synapse (left) and in a control synapse (right). The first five EPSCs during the train are shown on increased scales in the insets.

(B) EPSC depression curves averaged over 6 and 7 trials for the same cells as shown in (A). The first six data points following normalization to the first EPSC amplitude (see right-hand y-axis) were fitted with linear functions to quantify the onset of depression in both genotypes (blue fit lines).

(C) Cumulative EPSC amplitude plots for the two cells shown in (A, B). Back-extrapolation to time zero yields the recovery-corrected pool size estimate (Schneggenburger et al., 1999). Note the much smaller value in the RIM1/2 cDKO neuron (left) as compared to the control cell (right). Data in A–C are from corresponding recordings.

(D) Plot of the normalized EPSC amplitudes during 100 Hz trains, averaged for all RIM1/2 cDKO (n = 9 cells) and control cells (n = 8). The lower panel shows the data on an expanded time scale, together with the line fits to the average data set (blue lines). Error bars represent S.E.M.

(E, F). Individual and average values of the pool size estimate (E) and of the release probability (F) for RIM1/2 cDKO (red) and control synapses (black).

Error bars = SD (except panel D; = SEM).