Fig. 3

Chronic NF-κB activation in OLs leads to white matter loss in the corpus callosum. a and b Luxol Fast Blue (LFB) staining revealed a significant decrease (B) in the width of the CC in IKK2-CA^{PLP−CreERT2} animals at 20 wpi (Bregma—2 mm; 3wpi: Control: 366 ± 9.0 μm, IKK2-CA^{PLP−CreERT2}: 352 ± 13.3 μm; 20wpi: Control: 405 ± 10.0 μm, IKK2-CA^{PLP−CreERT2}: 364.6 ± 12.6 μm, n = 3–4). c to f Myelinated axons do not show differences in myelin sheath structure. Ultrastructural analysis using electron microscopy reveals proper myelination of single axons in the CC (c and d). G-ratio, the ratio of the inner and outer diameter of the myelin sheath used as reference for optimal myelination, did not differ between IKK2-CA^{PLP−CreERT2} and control animals at both time points (e and f). g NF-κB activation in OLs affects overall axonal myelination. The percentage of myelinated axons is significantly decreased in the CC of IKK2-CA^{PLP−CreERT2} animals at 20 wpi. Number of myelinated axons remain at the level of 3 wpi in IKK2-CA^{PLP−CreERT2} mice (3 wpi: Control: 42.1 ± 3.2%, IKK2-CA^{PLP−CreERT2}: 37.7 ± 3.6%; 20 wpi: Control: 74.4 ± 2.1%, IKK2-CA^{PLP−CreERT2}: 46.7 ± 4.0%, n = 5). h Axon diameter of unmyelinated axons is significantly increased in the CC of IKK2-CA^{PLP−CreERT2} animals 20 wpi in comparison to IKK2-CA^{PLP−CreERT2} animals at 3 wpi as well as controls (3 wpi: Control: 0.24 ± 0.01 μm, IKK2-CA^{PLP−CreERT2}: 0.27 ± 0.02 μm; 20 wpi: Control: 0.25 ± 0.01 μm, IKK2-CA^{PLP−CreERT2}: 0.35 ± 0.01 μm, n = 5). Data are shown as mean ± SEM. Black dots/grey bars, control; red dots/bars, IKK2-CA.^{PLP−CreERT2}. Statistical analysis: Two-tailed Mann–Whitney-U Test, Two-way ANOVA multiple comparison test followed by Bonferroni´s post hoc test, (*p < 0.05; **p < 0.01; ***p < 0.001; ****p < 0.0001 NS, non-significant (p > 0.05))