Neural communication is governed by the release of neurotransmitter-containing vesicles at the synaptic active zone (AZ). Several fundamental forms of neurotransmitter release are present at synapses, including synchronous mono- and multi-vesicular release, asynchronous and spontaneous release. Each of these release mechanisms plays important and distinct roles in synaptic development and function. However, despite several decades of research, how these canonical forms or release are organized and regulated in central synapses is poorly understood. This includes some of the most fundamental features of release, including the number, spatial organization and reuse of release sites supporting different forms of release, all of which remain largely undetermined because of the extremely small size and relative inaccessibility of central synapses to conventional recording techniques. Moreover, how the spatiotemporal properties and reuse of the release sites are regulated by neural activity is largely unknown. To overcome these limitations, we developed a nanoscale-resolution imaging approach that in combination with a pH-sensitive fluorescent indicator genetically tagged to the vesicle lumen, allows us to resolve individual vesicle fusion events at the AZ with ~27 nm precision. With this approach we have uncovered the presence of multiple distinct release sites in central synapses and demonstrated that their spatiotemporal properties are regulated by neural activity. By complementing this approach with computational single-molecule tools we are also able to robustly detect all other canonical forms of release. Our approach also permits us to visualize and track translocation of individual synaptic vesicles to the AZ, a critical time-limiting step in the refilling of the release sites during neural activity. Here we propose to combine this nanoscale-resolution imaging approach with advanced computational, genetic and pharmacological tools to study, at a single-vesicle level, the mechanisms governing organization and regulation of the canonical forms of neurotransmitter release at individual central synapses. We will further define the mechanisms governing vesicle translocation to the release sites and their activity-dependent regulation. These studies will provide major new insights into fundamental mechanisms of synaptic function.

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PROJECT NARRRATIVE The mechanisms controlling neurotransmitter release at synapses remain fundamental unresolved questions in neuroscience and are critical to understanding many aspects of brain function and neural excitability disorders. This proposal utilizes innovative nanoscale-resolution imaging technology we developed to elucidate the mechanisms regulating canonical forms of neurotransmitter release in central synapses. The proposed studies will gain insights into fundamental principles controlling synaptic function.

National Institute of Health (NIH)
National Institute of Neurological Disorders and Stroke (NINDS)
Research Project (R01)
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Leenders, Miriam
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Washington University
Anatomy/Cell Biology
Schools of Medicine
Saint Louis
United States
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