Fig. 9.

A sequential model for emergence of vesicle pool organization during synaptic development. state 1, Depicted are synapses with recycling vesicle clusters before formation of the RRP. state 2, Shown is a transient state in which most of the functional docking sites within the active zone are populated by vesicles. The transition to state 2 may have stable intermediates, as indicated by the small arrows. To reach state 3, the number of vesicles in the synapse increases to build a reserve pool. In later stages of development the size of RRP and RP increases in parallel.