Figure 1. The FM 1-43 assay is a direct and reliable indicator of presynaptic activity in hippocampal slices.
A. The presynaptic terminal is loaded with the FM 1-43 dye (red dots) through endocytosis. The dye is then unloaded with neurotransmitter (blue) from synaptic vesicles via exocytosis. B. Fluorescent images of presynaptic boutons loaded with FM 1-43 in hippocampal slices. FM 1-43 was unloaded during synaptic stimulation starting at 0'00”. C. The rate of FM 1-43 unloading is positively associated with”] the frequency of synaptic stimulation.