Two vesicle pools for neurons

Yildirim Sara, Ege Kavalali, and colleagues (University of Texas Southwestern Medical Center, Dallas, TX) show that nerve terminals possess two independent vesicle populations: one for activity-dependent neurotransmitter release, and one for spontaneous release.

Activity-dependent release is the typical action potential–generating mechanism. But occasionally a vesicle leaks its contents without provocation. Most scientists figured these events—which affect synaptic development and inhibit translation in dendrites—reflect the occasional escape of a vesicle primed for activity-dependent release. But the new results reveal that spontaneously released vesicles comprise a pool of their own.

The two pools were distinguished by their filling mechanism: vesicles loaded with dyes by spontaneous endocytosis were then unloaded more rapidly by spontaneous release than by stimulated release. Activity-dependent endocytosis filled vesicles that were more rapidly unloaded by stimulated...