Axonal lesions in acute experimental demyelination: a sequential teased nerve fiber study.

The relationship between axonal degeneration and primary demyelination was studied in isolated rat sciatic nerve fibers previously exposed to antiserum from rabbits with either experimental allergic neuritis or experimental allergic encephalomyelitis, or immunized with antigalactocerebroside antiserum. Continuous demyelination over one to eight or more internodes was seen in association with phagocytic cells or, later, with increased numbers of Schwann cells. Paranodal demyelination was prominent proximal ahd distal to the zone of continuous demyelination. Axonal degeneration affected 5 to 15% of myelinated fibers exposed to antiserum and was not related to the length of demyelination must proximal to the axonal changes. At times, there were seven or eight consecutive demyelinated internodes with no distal axonal degeneration; in contrast, one demyelinated internode was often associated with axonal degeneration beginning just distally. The inflammatory reaction could account for axonal degeneration in antiserum-mediated demyelination.