Fig. 1.
Gradients of serotonin elicit distinct growth cone behaviors in a dose-dependent manner. a Isolated growth cone exposed to pulsatile ejections of serotonin gradient. The pipette is located in the upper right corner. b–c Phase contrast images of growth cones trajectories at the start (0 min) and at the end (30 min). Ti = initial trajectory; Tf = final trajectory. Dotted lines denote the change in axon trajectory in respect to the micropipette that can be measured as angle of turning. b is an example of vehicle and c 5HT-Lo turning. d Growth cones turned predictably towards BDNF (n = 51, p = <0.0001) and away from sema-3A (n = 21, p = 0.0009) compared to vehicle (n = 77). Serotonin concentrations (0.5, 5, 25 and 75 μM) were not significantly different (n = 15, p =>0.999), (n = 16, p =>0.1614), (n = 14, p = 0.573), (n = 14, p =>0.999) to vehicle turning angles. Only growth cones exposed to 50 μM (n = 51, p = <0.001) and 100 μM serotonin (n = 34, p = 0.0002) showed significant motile responses. Positive angles denote attractive turning and negative angles denote repulsive turning, when compared to random growth (vehicle) (Kruskal–Wallis with Dunn’s multiple comparison post hoc test). (e) Axon extension was not significantly different in any experimental treatment (ns, p > 0.05). Scale bars are 5 μm