Schematic illustrating experimental protocol for visualizing synaptic vesicle exocytosis at CA3-CA1 synapses with FM 1-43 dye. Electrical stimulation of CA3 axons (10 Hz/120 s) turns over the total recycling pool of synaptic vesicles while the dye is applied to CA1, where it is taken up by vesicles as they are endocytosed. After washing to remove bound extracellular FM 1-43, the same axons are stimulated at 5 Hz to unload the dye. Bottom left is a representative field of dye-labeled presynaptic terminals in CA1 from wild-type hippocampus. Bottom right: sample time-lapse images demonstrating stimulus-driven dye loss at synaptic puncta in different mouse genotypes as indicated. Scale bar (applies to all images), 5 μm.
