Fig. 6

Stimulation of neuronal activity in juvenile mice promotes myelination and results in thicker myelin sheaths. a, b Representative immunogold electron microscopic images of the corpus callosum of GFP control (a) and hM3Dq/GFP (b) mice at P21, following a week of CNO administration (P14–20). Myelinated and unmyelinated GFP⁺ axons are pseudo-colored green and red, respectively. c, d Higher magnification of immunogold-positive axons from GFP control (c) and hM3Dq/GFP (d) mice. e No primary antibody control sections had almost no gold deposits. f Analysis of the density of GFP⁺ axons in each condition. g Quantification of the percentage of GFP⁺ axons myelinated in each condition; hM3Dq/GFP mice displayed a significant increase in the percentage of GFP⁺ axons that were myelinated compared to GFP only control mice (Welch’s corrected unpaired two-tailed t-test: **P < 0.01, n = 5 mice/condition). h Quantification of the density of myelinated GFP^– axons in each condition. i, j Analysis of myelin thickness (g-ratios) for GFP⁺ and GFP^– axons in GFP control (i) and hM3Dq/GFP (j) mice. k Comparison of the g-ratios of the GFP⁺ population in GFP control and hM3Dq/GFP mice. l Breakdown of g-ratios for each group by axonal size. Colors of conditions matched for i–k. Two-way ANOVA with Tukey’s multiple comparisons test: *P < 0.05, ****P < 0.0001, n = 5 mice/condition,  ± s.e.m. Scale bars = 5 µm (a, b), 1 µm (c, d), 2.5 µm (e). See also Supplementary Fig. 5