Fig. 5.

The twitcher (twi) mouse develops progressive demyelination of the spinal cord and peripheral nerve. At 30 days of age the spinal cord appears normal (a) but a nerve root (arrow) seen at higher power (b) shows that demyelination has begun in the PNS but not CNS. By 50 days however the spinal cord is extensively demyelinated (c) with only the cortico-spinal tract (arrowhead) appearing to have retained myelin. In the area marked in (c) (arrow) there is clear demyelination of both the PNS and CNS (d). In the CNS, the white matter is invaded by unique, large macrophages known as globoid cells. These are seen in areas of severe demyelination (e and f). In some cases they are close to thinly demyelinated and myelinated axons that may be remyelinated or hypomyelinated (f). Toluidine blue. Scale bar: 0.2 mm (a, c), 20 μm (b, d–f).