Ethidium bromide induced demyelination in the spinal cord of the cat.

Small volumes of ethidium bromide were injected into the dorsal column of the spinal cord of cats. Oligodendrocytes and astrocytes showed morphological evidence of intoxication by ethidium bromide from 2 days after injection. However, apart from around the point of injection and the needle tract, demyelination did not occur until between 8 and 14 days. Both oligodendrocytes and astrocytes were absent from the demyelinated area at 14 days and all but a small number of demyelinated axons were remyelinated by Schwann cells. These cells first appeared in the lesion at 10 days, but axon association and myelination did not occur until 16 days. This model of experimental demyelination indicates once again that Schwann cell invasion of demyelinated areas in the CNS occurs if both oligodendrocytes and astrocytes are destroyed. None of the lesions in the present investigation were in continuity with root entry zones, indicating that this location is not a prerequisite for Schwann cell invasion of the CNS.