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. 2017 Jul 19;11:211. doi: 10.3389/fncel.2017.00211

Figure 1.

Figure 1

Developmental changes in vesicular release. (A) Example traces of miniature inhibitory postsynaptic currents (mIPSCs) from different postnatal ages recorded in the presence of 0.5 μM tetrodotoxin (TTX). (B) Developmental increase of mIPSC frequency in spherical bushy cells (SBCs). Each symbol represents the value of a single cell. The solid black line connects the median mIPSC frequencies for age groups P1 (triangles), P2–4 (green circles), P7–8 (black circles), P11–13 (gray circles) and P23–25 (magenta circles; effect of age p < 0.001, analysis of variance (ANOVA), post hoc pairwise comparisons: *p < 0.05, **p < 0.01, ***p < 0.001). Miniature IPSCs occurring at low frequency could be detected in 50% of the cells at P1. (C) Mean cumulative distribution functions (CDFs) of mIPSC amplitudes (left), 10%–90% rise times (middle) and decay time constants (right) obtained from different age groups. The mIPSC amplitudes increased and the rise times accelerated up to P23–25 (all pairwise comparisons: p < 0.001, K-S tests). The decay time constant showed no developmental change. Inset (left) shows mean ± SEM conductances at different age groups calculated from mIPSC amplitudes obtained in each cell; *p < 0.05, ***p < 0.001, ANOVA). Insets (middle, right) show median mIPSCs at P7 (black) and P24 (magenta). Traces were normalized to the peak to highlight the differences in mIPSC kinetics. (D) Representative IPSC traces evoked by single stimulation of inhibitory inputs in a P8 (left) and a P25 SBC (middle). Traces on the right were peak-normalized to highlight the difference in decay. Mean eIPSC amplitudes and conductances were similar for P7–8 and P22–30 cells (n = 16, n = 43, respectively). Note the shorter rise time and longer decay time in maturity (p < 0.001, t-test). (E,F) Top: IPSCs evoked by a repetitive stimulation (100 Hz, 50 pulses) at P8 and P25. Middle: raster plots showing the temporal precision of the IPSCs evoked during five repetitions. Each line represents the time point of a single peak response. Note the failures in a P8 SBC, particularly occurring late in the train. At P25 each stimulus reliably evoked a response. Bottom: developmental decrease of peak-amplitude depression. I-peak amplitudes were calculated as foot-to-peak for each IPSC throughout the train and plotted for representative cells from P8 and P25 (gray dots). Black lines show average for amplitudes elicited during five repetitions. Note the pronounced depression after few initial events at P8, which is much less pronounced at P25.