Functioning of Synaptic Vesicle Pools: Diversity and Organizational Principles

Presynaptic nerve terminals contain a large number of vesicles filled with neurotransmitters, whose release ensures signal transmission from the presynaptic neuron to the postsynaptic cell. Despite their morphological homogeneity, synaptic vesicles (SVs) are functionally heterogeneous and are organized into distinct groups (pools) that differ in their ability for exocytosis and mobilization, recycling kinetics, and protein composition. In addition to the classic pools - the readily releasable pool (RRP), recycling pool, and reserve pool - other populations have been identified, including spontaneously recycling vesicles, vesicles of resting pool and superpool. Vesicles from different pools engage in different modes of exocytosis and endocytosis, and the extent of interpool mixing varies depending on the synapse type and physiological or pathological conditions. Changes in the organization of SV pools underlie multiple forms of synaptic plasticity. Furthermore, SV cycling is a target of several pharmacological agents, and its disruption plays a significant role in the pathogenesis of neurodegenerative diseases. This article is a systematic review of SV pools, their organizational features in central and peripheral synapses, and implications of changes in the structure of SV pools in synaptic plasticity, action of drugs, and development of neurological disorders.