Internodes on remyelinated optic axons are short in young and old zebrafish. (A, B) Frequency distributions of internodal lengths after remyelination in young (28 dpl) and old (3 mpl) zebrafish are different from those in age-matched unlesioned controls (p < 0.001, Kolmogorov-Smirnov test, 80–100 internodes measured per animal in n = 3 animals). Shorter internodes (1-20 μm) are more frequent in remyelinated young and old zebrafish than in controls. (C) Teased-fibre preparations illustrate shorter internodal distances on remyelinated optic axons. Arrows - nodes stained with a pan-sodium channel marker. Mean ± SEM. Scale bar: C = 6 μm.