Fig. 1

Increased neuronal activity promotes neurite outgrowth. A Representative images of c-Fos (red) and ChR2 (green) immunostaining. White arrows depict ChR2⁺ neurons. Scale bar: 100 μm. a. Higher magnification image of a stimulated neuron. ChR2 expression is mainly located in the membrane of large-diameter neurons. Scale bar: 20 μm. B c-Fos expression in the nucleus is increased just after optogenetic stimulation of Thy1-ChR2 DRG neurons (n = 20–25 cells). MFI: mean fluorescence intensity. a.u.: arbitrary units. Data are expressed as mean nuclear fluorescence intensity ± s.e.m. **p < 0.01 denotes significant differences in Student’s t-Test. C Stimulated neurons presented significantly higher neurite lengths when compared to non-stimulated ones. Average neurite length per neuron was determined at 24 h in vitro. Data are expressed as mean ± s.e.m. (n = 12 images; **p < 0.01 denotes significant differences in Student’s t-Test). D Stimulation did not significantly modify the neurite branching. Average number of branches for each 100 µm was determined at 24 h in vitro. Data are expressed as mean ± s.e.m (n = 12 images). E Representative images of Tuj-1 staining used to analyze neurite length. Scale bar: 200 μm