Functional heterogeneity at the level of an individual neurotransmitter release site at the adult neuromuscular junction

Neurotransmitter release at the neuromuscular junction (NMJ) has historically been studied using intracellular electrophysiological methods that only report the summed impact of total transmitter release from the entire synapse, which at neuromuscular synapse includes ~700 individual release sites, or active zones (AZs). Most investigations into NMJ presynaptic function have assumed that all AZs are roughly similar, each containing uniformly low probability individual vesicle release sites, that are recruited for participation during an action potential by random stochastic processes related to calcium channel gating and calcium-triggered vesicle fusion. To date, there have been few structural or immunohistochemical reports that have revealed significant heterogeneity in AZ organization within individual neuromuscular synapses. We developed new optical reporters for use at the NMJ with single vesicle release resolution. The development of these experimental tools to investigate regulation of neurotransmitter release at a single AZ level, we will be able to reinvestigate the control of transmitter release at a resolution that has not previously been possible. Such an investigation will redefine the ways in which we understand presynaptic physiology and modulation of neurotransmitter release in healthy and disease states