Figure 6.

Time-dependent amplitude occlusion in simple synapse recordings. A, Top, Representative traces from a presumed simple synapse recording (8 stimuli at 200 Hz, blue). In several cases (e.g., first, second, and third stimulations in first trace), double and triple responses are observed with smaller EPSC amplitudes for the second or third event compared with the first. Bottom, Stability of the summed number of released synaptic vesicles across trials (dotted line: average; traces in above panel correspond to trial numbers 25–27). B, Plot of EPSC amplitude as a function of Δt, the time interval since the previous event, reveals an amplitude drop for small Δt values (crosses: individual events; circles: averages of binned data). Extrapolation of the model exponential curve (red) to Δt = 0 suggests a maximum amplitude occlusion ω = 0.58 (see text). C, Uncorrected EPSC amplitude distribution from the experiment shown in A and B. Continuous curve: Gaussian fit (mean: 58 pA; CV: 0.53). D, Corrected amplitude distribution from the same experiment using the exponential curve shown in B for correction. The corrected amplitude distribution displays a higher mean, lower CV, and smaller skew than the uncorrected distribution. E–G, As in B–D, in another recording classified as originating from a multiple synapse. Here, the amplitude dependence on Δt is absent and the correction procedure does not affect significantly the amplitude distribution.