Figure 5. Faster recovery of EPSCs from STD in KI. A, Representative traces showing depression of EPSC amplitudes during 0.2 s stimulation at 100 Hz and recovery at different time delays after the train. B–D, Time course of EPSC depression during a 10 Hz (B), 100 Hz (C), or 300 Hz (D) stimulus train. At 10 Hz, the amplitudes of the EPSCs at the end of the train were 32.2 ± 2.7% (n = 17) and 54.4 ± 3.1% (n = 7) of the first pulse for WT and KI, respectively. At 100 Hz, the magnitude of depression was larger in WT (WT: 10.7 ± 2.2%, n = 14 vs KI: 16.7 ± 2.2%, n = 9; Student's t test, p < 0.05). At 300 Hz, the depression was larger in the KI (WT: 14.4 ± 1.1%, n = 8 vs KI: 5.1 ± 0.1%, n = 5; Student's t test, p = 0.02). E–G, Time course of recovery from synaptic depression was measured by eliciting a single test EPSC at increasing time intervals after the conditioning train. Recovery following 10 Hz trains (E) was fitted with a single exponential decay function with time constants τWT = 4.04 ± 0.26 s (n = 13) and τKI = 2.17 ± 0.7 s (n = 7), t test, p < 0.001). After a 100 Hz train (F), recovery in WT was fitted with a single exponential function (τ = 2.0 ± 0.4 s, n = 1 3), but recovery in KI needed the sum of two exponential functions for an appropriate fit (τKI,f: 94 ± 5 ms [52%], τKI,s: 2.2 ± 0.4 s [48%]). Recovery from STD after 300 Hz stimuli usually followed a double exponential time course, but in this case, no differences were found between the genotypes (τWT,f = 182 ± 45 ms [36%] and τWT,s = 2.8 ± 0.5 s [64%]; τKI,f = 141 ± 17 ms [60%] and τKI,f = 2.77 ± 0.45 s [40%]). H–M, Time course of recovery from synaptic depression before and after EGTA-AM incubation. Filled symbols represent control data (without EGTA-AM) and empty symbols represent preincubated with EGTA-AM data. The subtraction between data in the presence and absence of EGTA-AM are shown as diamonds. Recovery time course after 10 Hz were similar for both genotypes (WT: 3.9 ± 1.2 s; n = 4 and KI: 2.9 ± 0.5 s; n = 4; Student's t test, p = 0.26; after 100 Hz, WT: 2.8 ± 0.9 s; n = 5 and KI: 2.7 ± 0.9 s; n = 4; Student's t test, p = 0.47).