Fig. 4

Activity stimulation results in increased myelination in an axon-selective manner. a, b Representative examples of GFP control (a) or hM3Dq/GFP (b) mouse callosal axons labeled with PAN-NF (blue), GFP (green), and MBP (red), with white arrows indicating myelinated GFP⁺ axons. c, d Although the total number of MBP⁺ rings in the corpus callosum was similar (c), the proportion of myelin rings with GFP⁺ axons was significantly higher in the hM3Dq-expressing mice compared to controls (d). e The percentage of GFP⁺ axons that colocalized with MBP⁺ rings was significantly higher in hM3Dq/GFP mice compared to GFP controls. f An equivalent percentage of PAN-NF⁺ axons co-expressed GFP in the hM3Dq/GFP and GFP control groups. g The percentage of PAN-NF⁺ axons that colocalized with MBP⁺ rings was higher in hM3Dq/GFP mice compared to GFP controls. h The percentage of GFP⁺ and GFP^– PAN-NF⁺ axons that were colocalized with MBP⁺ rings in each group. i The overall change in myelination in hM3Dq/GFP mice was much more pronounced in GFP⁺ axons compared to GFP^– axons (values computed as fold change from mean density of GFP^+/− PAN-NF⁺ MBP⁺ axons in GFP control mice). Welch’s corrected unpaired two-tailed t-test: ****P < 0.0001, ***P < 0.001, **P < 0.01, *P < 0.05; n = 8 Control mice (GFP only), n = 12 hM3Dq/GFP mice,  ± s.e.m. Scale bars = 2 µm (a, b)