Figure 2. Heterochronic parabiosis stimulates OPC differentiation and remyelination.

(A) Quantification of oligodendrocytes shows few CC1⁺/Olig2⁺ cells present in the lesion at 7dpl, independent of age. Higher oligodendrocyte densities at 14dpl indicates the generation of new oligodendrocytes, with significantly more differentiation occurring in heterochronic-old animals than in isochronic-old controls at 14 and 21dpl. Data are means ± SEM. (B) Oligodendrocytes in the lesion at 14dpl. Representative fields are shown for each parabiotic condition. (C) Ranking analysis of remyelination at 21dpl (rank 1 equals least remyelination). N ≥ 8 per group, horizontal line indicates median for each data set. Data analyzed by Kruskal-Wallis test followed by Dunn’s post test (D) Toluidine blue stained resin sections of lesions: representative images for each parabiotic condition at 21dpl. Widespread remyelination is evident in lesions in isochronic-young animals, contrasting with the relative paucity of remyelination in lesions of isochronic-old animals. Heterochronic-old animals showed increased remyelination compared to isochronic-old controls. Insets show magnification of boxed area. (E) Quantification of oligodendrocyte (Olig2⁺/CC1⁺) density in lesions of isochronic-young and heterochronic-young animals at 21dpl (n=4 animals per group). Data are means ± SEM and were analyzed with an unpaired two-tailed t test. No significant difference between the two groups was found. (F) Ranking analysis of remyelination at 21dpl (n=7 animals per group). Rank 1 equals least remyelination. The median is indicated by a horizontal line for each data set. Data were analyzed with a Mann-Whitney test, which did not detect a significant difference between the two groups. *denotes p < 0.05, **denotes p < 0.001, ns = not significant. Scale bars: B 50 μm, D 20μm (insets 2 μm)). See also Fig. S2.