A, cumulative amplitudes of EPSCs during a 100 Hz train in WT (•) and KO (○) mice (data taken from Fig. 5A). Data points in the range of the 16–20th EPSC amplitudes were fitted by linear regression and extrapolated to time zero to estimate the readily releasable pool size of synaptic vesicles (Nq). B, left panel, Nq estimated in individual cells; right panel, release probability (p) estimated from the first EPSC amplitude divided by Nq. In WT and KO mice, Nq was 2.71 ± 0.40 nA (n = 12) and 2.76 ± 0.49 nA (n = 12), respectively, whereas p was 0.49 ± 0.05 (n = 12) and 0.56 ± 0.05 (n = 12), respectively. Neither p nor Nq was significantly different between WT and KO mice. Error bars indicate s.e.m.