Fig. 5

Chronic demyelination of spared axons in Myrf ICKO six weeks following SCI. a Whole cross sections of control and Myrf ICKO spinal cords at lesion epicenter stained with Toluidine blue at six WPI. The majority of myelin is found in the ventrolateral white matter. b High magnification images of box inset from a in Myrf ICKO and control animals. c Quantification of myelinated axons in the spared white matter. Myrf ICKO animals have significantly fewer myelinated axons when compared to control animals (df = 8, t = 2.475, P = 0.038, Student’s t test). d Example transmission electron micrographs of the injured mouse lesion epicenters. Blue shading depicts thinly myelinated axons, pink shading depicts axons devoid of myelin, and green shading depicts axons with thick myelin sheaths. Many thinly myelinated axons are found in control mice whereas Myrf ICKO mice are almost completely devoid of thinly myelinated large caliber axons, and instead have demyelinated axons greater than 1 µm in size at six WPI. e Frequency distribution of g-ratios of myelinated axons indicate a shift towards higher g-ratios (more thinly myelinated axons) in the controls relative to Myrf ICKO (P < 0.001, Kolmogorov–Smirnov test). f Scatter plot comparing g-ratio to axon diameter of axons quantified in the spared white matter of injured animals demonstrating a difference between controls and Myrf ICKO (F = 25, DFn = 1, DFd = 1340, P < 0.0001, linear regression). Dashed box highlights axons that lack myelin. g Quantification showing more unmyelinated axons larger than 1 µm in the spared white matter of Myrf ICKO compared to controls at six WPI (df = 6, t = 4.858, P = 0.003, Student’s t-test). ^*P ≤ 0.05, ^**P ≤ 0.01 Scale bars = 100 µm (a), 5 µm (b), 1 µm (f). Error bars are mean ± SEM