Electron microscopic observations on allergic encephalomyelitis in the rabbit.

Allergic encephalomyelitis was produced in rabbits by injection of white matter from bovine brain plus adjuvants. Electron microscopy revealed focal demyelinization in both the spinal roots and cord. The peripheral lesions were characterized by vacuolization of Schwann cytoplasm, destruction of the myelin sheath, and by some appearances suggesting remyelinization. In the cord there was a marked perivascular inflammatory infiltration with focal destruction of the blood-brain barrier as demonstrated by formation of an abnormal interstitial space about capillaries. Mitochondria of oligodendroglia were strikingly swollen whereas those of other cells were morphologically normal. Axons were denuded of their myelin sheaths and the myelin detritus sequestered within gitter cells. Fibrous astrocytic gliosis occurred to some degree. Focal evidences of myelin reformation were noted centrally as well as peripherally. Allergic encephalomyelitis, as a primary demyelinating lesion, is contrasted with Wallerian degeneration in which myelin degeneration is secondary to destruction of the axon.