Morphological correlates of functionally defined synaptic vesicle populations

By combining photoconversion of FM1-43-stained vesicles and electron micros copy of hippocampal synapses, we find evidence that the population of morph ologically docked synaptic vesicles corresponds to the release-ready neurot ransmitter quanta. Furthermore, those synaptic vesicles that are participat ing in cycles of exo- and endocytosis tend to be closer to the active zone than vesicles that are being held in reserve.