Synaptic vesicle pools: principles, properties and limitations

It is around three decades since the term ‘pool’ was first used to refer to a sub-population of presynaptic vesicles differentiated on the basis of their specific functional or structural characteristics. Subsequently, the idea that vesicle clusters can be sub-categorized has been widely embraced, offering an important framework for elucidating elemental principles of synaptic operation and uncovering presynaptic substrates of modulation. This short review aims to provide a contemporary perspective on the vesicle pool field, identify key remaining questions, and also to consider some of the limitations of the pool concept.