Oligodendrocytes with aberrant cytoplasmic processes in a human white matter disorder.

Unusual ultrastructural features of oligodendrocytes with numerous aberrant cytoplasmic processes were described in the brain biopsy from a degenerative disease of the white matter. The perikaryal regions of these oligodendrocytes contained well-developed normal cytoplasmic organelles and randomly scattered microtubules. The cytoplasmic processes were tightly packed and numerous junctional complexes were observed between the plasma membranes of these processes. Aberrant myelination by focal compaction of plasma membranes without any association of axons was also observed. These features closely resembled those of cultured isolated oligodendrocytes and were interpreted as reactive changes of oligodendrocytes to the long-standing deafferentation from axons since no axons were detected in the vicinity of these oligodendrocytes.