…inactivation (Charlton et al., 1982; Chaudhuri et al., 2005; Forsythe et al., 1998; Xu and Wu, 2005) and vesicle depletion (Custer et al., 2006; Pieribone et al., 1995; Schneggenburger et al., 2002; Xu and Wu, 2005) have varying dependence on the frequency of stimulation at different synapses,…