Synapsin redistributes toward the sites of bouton outgrowth. A, An example showing accumulation of Syn-mRFP fluorescence upon stimulation (arrowheads) in the vicinity of newly formed boutons (arrows). B, An example showing that Syn-mRFP fluorescence does not increase at the sites where growth does not occur. C, The increase in fluorescence was significant (p < 0.05 per 1-way ANOVA) at sites where boutons were formed. The sites where multiple boutons were formed show a stronger increase (p < 0.004 per Tukey's post hoc test). Data collected from seven larvae (control, n = 66; single, n = 60; multiple, n = 26). D, Cumulative frequency distributions of the increase in fluorescence. The distributions of the Syn-mRFP fluorescence increase are shifted to the right for the sites where a single bouton was formed, and the curve is shifted even farther to the right for the sites where multiple boutons were formed. Both datasets (single and multiple boutons) are significantly different from control per Kolmogorov–Smirnov test (p < 0.05 for single boutons; p < 0.01 for multiple boutons).