Delayed myelin and axonal degeneration in the CC caused by systemic 5-FU treatment (representative electron micrographs of longitudinal sections of axons). Sections were taken from midline coronal sections of the CC. (a) A representative image from a sham-treated control animal, showing normal myelinated axons and the normal axonal cytoskeleton structures; (b-f) representative images from a 5-FU-treated animal, showing several pathological changes of both the myelin and axonal structures. Asterisks, axonal abnormality; single arrows, damaged myelin sheaths; double arrows, myelin debris; arrowheads, engulfed myelin debris. (b) Several swollen axons with disrupted cytoskeleton (asterisks), damaged myelin sheaths (single arrows) and myelin debris (double arrows) can be seen. (c) Several swollen axons (asterisks) with or without myelin can be seen, the axoplasm of which show disruption of cytoskeleton and altered organelles. (d) Several axons (asterisks) with absent or degenerating myelin (arrows) can be seen; one axon shows a severely damaged axonal structure and myelin on one side of a node of Ranvier (n) and partially disrupted myelin sheath on the other side (arrow). (e) Several loci of myelin degeneration can be seen (arrows); one axon seems to be transected on one side of a node of Ranvier (n). An axon next to it shows partial degeneration of the myelin sheath and disruption of the cytoskeleton (asterisk). (f) Edema in what is likely to be a process of an astrocyte can be seen, with some engulfed myelin debris (arrowhead) and the adjacent axons are distorted; there are also swollen axons (asterisks) with and without myelin (arrows).