Autaptic excitatory munc18-1 neurons expressing M18WT or M18Y473A were subjected to stimulation trains of 100 pulses at different frequencies.(E) A single action potential or sucrose application (500 mM, 3.5 sec.) was given before (naive) or two seconds after HFS (100 pulses at 40 Hz). Average EPSC charge M18WT (Naive: 70.9 ± 19.5 pC, after HFS: 75.4 ± 17.4 pC, n=12, Paired t-test, p = 0.4049). Average EPSC charge M18Y473A (naive: 10.3 ± 4.5 pC, after HFS: 46.2 ± 14.5 pC, n=13, Wilcoxon matched-pairs signed-ranks test, p = 0.0005). Average RRP size M18WT (naive: 1.73 ± 0.69 nC, after HFS: 1.34 ± 0.54 nC, n=12, paired t-test, p = 0.0557) Average HFS size M18Y473A (naive: 0.268 ± 0.075 nC, after HFS: 0.439 ± 0.107 nC, n=13, paired t-test, p = 0.0100). Average Pves M18WT (EPSC charge / RRP charge * 100) (Naive: 7.07 ± 0.76 %, after HFS: 10.6 ± 1.6 %, n=12, paired t-test, p = 0.0201). Average Pves M18Y473A (naive: 1.98 ± 0.72 %, 12.2 ± 2.8 %, n=13, paired t-test, p = 0.0021). 