For synaptic transmission, a sequence of interconnected functional modules obviously organizes synaptic vesicle exo- and endocytosis. Using highly accessible Drosophila neuromuscular synapses, we seek to investigate these coupling processes in the intact living animal. Central to the project is a flash-freeze approach which allows for rapidly capturing ultrastructure after light induced stimulation. We thus hope to contribute to a deeper understanding of how functional sub-modules are coupled for efficient neurotransmission.