A sequential three-pool model of the recycling pool. (A) Representative normalized RP depletion rate (Rdepl) trace after RRP depletion with double-exponential fitting (white curve, also as three-pool model fitting) under 50-Hz stimulation. (B) Representative Rdepl trace at 20 Hz with three-pool model fitting (white curve). (C) Schematic of sequential three-pool model of vesicle recycling. (D) Statistics of RPP size at 20-Hz (55.68 ± 4.7%, n = 4) and 50-Hz stimulation (62.79 ± 3.13%, n = 4). (E) Statistics of the RRP size (0.79 ± 0.09%), RPP size (57.53 ± 3.10%), and PMP size (41.68 ± 3.17%) related to RP size (n = 9). (F) Quantification of dissected synaptic vesicle pools in terms of total vesicles in the calyceal terminal.