[2] Synaptic vesicles are relatively simple because only a limited number of proteins fit into a sphere of 40 nm diameter.

Purified vesicles have a protein:phospholipid ratio of 1:3 with a lipid composition of 40% phosphatidylcholine, 32% phosphatidylethanolamine, 12% phosphatidylserine, 5% phosphatidylinositol, and 10% cholesterol.

[6] A spider toxin called alpha-Latrotoxin binds to neurexins, damaging vesicles and causing massive release of neurotransmitters.

This reserve pool can be quite large (~50%) in neurons grown on a glass substrate, but is very small or absent at mature synapses in intact brain tissue.

Loading of transmitter is an active process requiring a neurotransmitter transporter and a proton pump ATPase that provides an electrochemical gradient.

[citation needed] Primed vesicles fuse very quickly with the cell membrane in response to calcium elevations in the cytoplasm.

Consistent with SNAREs being essential for the fusion process, v-SNARE and t-SNARE mutants of C. elegans are lethal.

Similarly, mutants in Drosophila and knockouts in mice indicate that these SNARES play a critical role in synaptic exocytosis.

[citation needed] Two leading mechanisms of action are thought to be responsible for synaptic vesicle recycling: full collapse fusion and the "kiss-and-run" method.

[18] It has been shown that periods of intense stimulation at neural synapses deplete vesicle count as well as increase cellular capacitance and surface area.

[20] Studies suggest that the entire cycle of exocytosis, retrieval, and reformation of the synaptic vesicles requires less than 1 minute.

Ca2+ binds to specific proteins in the cytoplasm, one of which is synaptotagmin, which in turn trigger the complete fusion of the synaptic vesicle with the cellular membrane.

Tetanus toxin follows a similar pathway, but instead attacks the protein synaptobrevin on the synaptic vesicle.

It has been speculated that kiss-and-run is often employed to conserve scarce vesicular resources as well as being utilized to respond to high-frequency inputs.

[24] This reinforces the idea of a kiss-and-run fashion, the synaptic vesicle releases its payload and then separates from the membrane.

[citation needed] Ales et al. showed that raised concentrations of extracellular calcium ions shift the preferred mode of recycling and synaptic vesicle release to the kiss-and-run mechanism in a calcium-concentration-dependent manner.

[25] Experimental evidence suggests that kiss-and-run is the dominant mode of synaptic release at the beginning of stimulus trains.

[35] Whittaker's work demonstrating acetylcholine in vesicle fractions from guinea-pig brain was first published in abstract form in 1960 and then in more detail in 1963 and 1964,[36][37] and the paper of the de Robertis group demonstrating an enrichment of bound acetylcholine in synaptic vesicle fractions from rat brain appeared in 1963.

[39] Subsequent work identified the vesicular localization of other neurotransmitters, such as amino acids, catecholamines, serotonin, and ATP.