Characterization of single vesicle recycling kinetics and other presynaptic properties at small central terminals

• Main Author: Wagner, Milena Maria
• Published: University of Sussex 2017
• Subjects: 612.8; QP0361 Nervous system
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.703564

Sustained neural activity critically relies on the ongoing function of small central synapses. In particular, activity-driven fusion and recycling of neurotransmitter-filled vesicles at presynaptic terminals are key processes responsible for information transfer. Despite the fact that vesicle exocytosis and endocytosis are of great interest, the mechanisms of their regulation are still poorly understood. Moreover, hippocampal synapses exhibit high levels of variability in their structure and function, but the basis for this remains unclear. The aim of this work was to investigate these fundamental properties and establish key rules of regulation. Specifically, we wanted to test whether the timing of endocytosis of single synaptic vesicles was characteristic at individual boutons, and to investigate structural and molecular properties of synapses that underlie their particular behaviour. To explore this, we used a variety of optical imaging techniques in rat hippocampal neurons based on acutely applied probes such as FM1-43 dye, fluorescently tagged antibodies and genetically encoded reporters of presynaptic function, as well as ultrastructural readouts using electron microscopy. We found that although the timing of vesicle retrieval, measured with the optical reporter sypHy2x, was highly variable across the population of synapses, individual boutons showed signature endocytic kinetics. We also uncovered the properties of synapses that determine this behaviour, and demonstrated that these could be modulated, leading to predictable changes in the timing of recycling. These findings offer new insights into the rules that govern the function of presynaptic terminals. A second related objective examined was whether amyloid beta, the misfolding protein implicated in Alzheimer's disease, causes changes that are detrimental for efficient vesicle recycling. We showed that oligomeric amyloid beta 1-42 impaired endocytosis and disrupted other related presynaptic processes. We suggest that vesicle recycling mechanisms are important target substrates in Alzheimer's disease providing potential new avenues for development of therapeutic approaches.