We propose to use Drosophila as a model system for determining how neurotransmitter release and plasticity are regulated at individual active zones (AZs). Synaptic vesicle fusion occurs through a highly probabilistic process, often with only a small percent of action potentials triggering release from individual AZs. Although AZs largely share the same complement of proteins, release probability (Pr) is highly variable across different neurons and between AZs of the same neuron. Indeed, some AZ-specific proteins are non-uniformly distributed, and the molecular composition of AZs can undergo rapid changes. To date, Ca2+ channel abundance and Ca2+ influx have been most strongly linked to Pr heterogeneity, though other factors are likely to contribute as well. The Drosophila neuromuscular junction (NMJ) has emerged as a robust model system to characterize determinants of Pr. By transgenically expressing GCaMP Ca2+ sensors targeted to the postsynaptic membrane, single synaptic vesicle fusion events at individual AZs can be imaged by following spatially localized Ca2+ influx induced upon glutamate receptor opening. This enabled us to generate Pr maps for evoked and spontaneous fusion for all AZs, leading to the surprising observation that AZs formed by a single motor neuron have a heterogeneous distribution of Pr, with neighboring AZs often showing ~50-fold differences in strength. In addition, 10% of the AZ population supports only spontaneous release, while another 15% are functionally silent for both evoked and spontaneous fusion. In this proposal, we will determine how Pr is uniquely set for individual AZs and what molecular, structural, and developmental variables govern Pr heterogeneity. We will also examine how presynaptic Ca2+ channels traffic to and between AZs, and how plasticity alters these processes. These approaches should provide new insights into the complement of AZ proteins that functionally regulate Pr, spontaneous release, and silent synapses, and how they cooperate with presynaptic Ca2+ channels to set Pr across a functionally diverse set of AZs. Disruptions of synapse formation and function have been linked to a host of neurological and psychiatric diseases, reflecting the importance of these processes. The experiments described in this proposal will generate new insights into important elements that define the strength and release mode of individual AZs at an unprecedented resolution.

Public Health Relevance

This research will define basic mechanisms underlying neurotransmitter release and calcium channel trafficking at single active zones. Alterations in synaptic signaling have been linked to numerous neurological and psychiatric diseases of the human brain. By defining how neurons communicate at synapses, our research will provide a foundation for developing therapeutic approaches for brain diseases that alter synapse formation and function.

Agency
National Institute of Health (NIH)
Institute
National Institute of Mental Health (NIMH)
Type
Research Project (R01)
Project #
5R01MH104536-07
Application #
9883839
Study Section
Synapses, Cytoskeleton and Trafficking Study Section (SYN)
Program Officer
Kim, Douglas S
Project Start
2014-06-01
Project End
2023-12-31
Budget Start
2020-01-01
Budget End
2020-12-31
Support Year
7
Fiscal Year
2020
Total Cost
Indirect Cost
Name
Massachusetts Institute of Technology
Department
Psychology
Type
Schools of Arts and Sciences
DUNS #
001425594
City
Cambridge
State
MA
Country
United States
Zip Code
02142