Radicular myelinopathy in aging rats.

Naturally occurring degenerative lesions of nerve fibers in the spinal cord, spinal roots and peripheral nerves in nine male rats 877 days old were swollen myelin sheaths, forming "myelin bubbles." The myelin swellings were distributed throughout the spinal tracts and the peripheral nerves, but most frequently in the lumbar ventral spinal roots. Although most axons surrounded by swollen myelin were intact, some were constricted and degenerated, while others showed signs of remyelination.