Synaptic vesicles, which are present at all mature synapses, differ from synapse to synapse and are affected by synaptic activity. Antibodies specifically directed against synaptic vesicles could be used to locate synapses, to characterize the synaptic type and measure synaptic development and activity. Highly pure cholinergic synaptic vesicles have been isolated in large quantities from the electric organ of Narcine brasiliensis. Using these vesicles as antigens, antibodies have been generated which are specifically directed against vesicle antigens. By absorption, antibodies specific to internal vesicle antigens have been obtained. Immunocytochemical studies have shown that the antibodies to Narcine synaptic vesicles bind specifically to the nerve terminal regions of the frog and rat neuromuscular junctions. We plan to utilize this crossreactivity in several ways. We will determine morphologically and biochemically if the antigens which our sera recognize in the rat and frog neuromuscular junctions are on synaptic vesicles, and which antigens are shared. We will explore the specificity of the antibodies for cholinergic or non-cholinergic synapses. Finally we will utilize the antibodies to monitor synaptic development and attempt to monitor synaptic activity. When our monoclonal antibodies to synaptic vesicles are available in sufficient quantity, they will be utilized in this work. Finally, using immunoadsorption and monoclonal antibody procedures we will attempt to identify antigens in rat synaptic vesicles which are not present in Narcine synaptic vesicles.