This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The long-term goal of these studies is to understand the presynaptic mechanisms of transmitter release at fast chemical synapses. Our specific objective is to reconstruct in three dimensions the ultrastructure of the hair cell afferent synapse in order to test several aspects of our working model of this synapse's function. The hair cell afferent synapse is a ribbon-class synapse, characterized by an electron dense organelle of unknown function, the synaptic body, which appears to hover in the cytoplasm a vesicle's breadth above the active zone. Clear-core vesicles surround the synaptic body, but are also found in the cytoplasm, and associated with the plasma membrane at the active zone. What is the function of the synaptic body, and what is the functional significance of these various pools of vesicles? We will address these issues by determining the precise geometry of the active zone and synaptic body, and map the number and location of synaptic vesicles. By testing the activity-dependence of these measures, we will be able to integrate ultrastructure with ongoing physiological and mathematical modeling studies to build a more detailed understanding of the steps that lead to transmitter exocytosis.
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