Synaptic vesicle endocytosis and recycling

Abstract ‘The yang having reached its climax retreats in favor of the yin; the yin having reached its climax retreats in favor of the yang.’ -Wang Chu’ung (AD 80) on Tai Chi Tu Exocytosis and endocytosis, the yin and yang elements of the vesicle cycle, must be well balanced to ensure continuous synaptic transmission. At nerve terminals, the number of synaptic vesicles is insufficient to account for the number of quanta released during a short burst of intense nerve activity. Axonal transport of newly synthesized vesicle proteins occurs too slowly to refill the vesicle pool at the required rates. Under these circumstances, the only way to rapidly replenish synaptic vesicles is to recycle them locally through endocytosis. Thus, a major challenge is to understand how synaptic vesicles are faithfully and efficiently recovered.