Search

Neurotransmitter in vesicles is released through a fusion pore when vesicles fuse with the plasma membrane. Subsequent retrieval of the fused vesicle membrane is the key step in recycling exocytosed vesicles. Recent application of advanced electrophysiologic techniques to a large nerve terminal, the calyx of Held, has led to direct recordings of endocytosis, individual vesicle fusion and retrieval, and the kinetics of the fusion pore opening process and the fission pore closure process. These studies have revealed three kinetically different forms of endocytosis–rapid, slow, and bulk endocytosis–and two forms of fusion–full collapse and kiss-and-run. These research advancements are reviewed in this chapter. [ABSTRACT FROM AUTHOR]

Synaptic vesicle fusion at the plasma membrane is followed by vesicle retrieval. There are three different pathways for retrieving vesicles: classic clathrin-mediated endocytosis, a ˵kiss-and-run″ form of endocytosis, and bulk endocytosis. These forms of endocytosis may take as long as tens to hundreds of seconds or as short as one second or less. The time course of endocytosis is determined by the neuronal firing frequency and duration. The dynamic time course could be a result of multiple endocytic pathways and/or regulation by a variety of modulators. The newly formed vesicles via various endocytic pathways may join the readily releasable pool or the reserve pool, likely depending on which pathway they are generated. Vesicles in the reserve pool can be mobilized to the readily releasable pool, when the latter is depleted. Vesicle recycling is critical for the maintenance of transmitter release during repetitive stimulation. Regulation of any step in the vesicle cycling process, including endocytosis, could thus provide a mechanism by which synaptic plasticity is achieved. [ABSTRACT FROM AUTHOR]