5-HT treatment increases actin turnover and cofilin dynamics. (A) Actin turnover: maximal overtime projections of G-actin speckles (top), actin polymerization (middle), and depolymerization (bottom) before (left) and during (right) 5-HT treatment (10 µM, 20 min). (B) Summary of actin polymerization (top) and depolymerization (bottom) before and during 5-HT treatment (10 µM, 20 min). (C) Cofilin dynamics: maximal overtime projections of cofilin speckles (top), cofilin association (middle), and cofilin dissociation (bottom) before (left) and after (right) 5-HT (10 µM, 20 min). (D) Summary of cofilin association (top) and dissociation (bottom) before and after 5-HT (10 µM, 20 min); Alexa Fluor 488–G-actin and Alexa Fluor 568–cofilin were injected sequentially. Actin turnover and cofilin dynamics (A and C) maps generated as in Fig. 5. Colors in A and C indicate relative actin polymerization/depolymerization and cofilin association/dissociation rates, respectively (compare color bars). Scale bar, 5 µm. For B and D, data are mean (a.u.) ± SEM. Number of growth cones evaluated: three, pooled from three independent experiments. *, P < 0.01 with two-tailed paired t test. See also Video 4.