FIGURE 1.

Schematic diagram of vesicle fusion and recycling at the axon terminal. (A) Vesicle approaches the plasma membrane. (B) Vesicle engages in membrane fusion resulting in a fusion pore, thereby releasing some neurotransmitters. (C) The pore expands and the vesicle completely merges with the plasma membrane. (D) The cell replenishes its vesicle pool by endocytosis forming a new, unfilled vesicle. (E) The newly formed vesicle is filled with neurotransmitters. (F) The filled vesicle is brought back into the pool of available vesicles for subsequent rounds of vesicle fusion. (G) Rather than entering the pathway in (D), the vesicle engages in a “kiss-and-run” event in which some neurotransmitters are allowed to be released before closing. The vesicle is then detached from the presynaptic membrane and recycled into the presynaptic vesicle pool.