Figure 1.

Electron micrographs of progression of degeneration of oligodendrocytes in the spinal cord and optic nerve of LES rats 1 to 16 wk old. (A) Spinal cord of a 1-wk-old LES rat, in which 2 glial cells interpreted as immature oligodendrocytes are surrounded by dysmyelinated neuropil with few axons surrounded by thin sheaths (asterisks). Bar, 2 μm. (B) Spinal cord of 1-wk-old LES rat. A degenerating cell is closely associated with a large adjacent axon (arrow) with a few uncompacted lamellae and numerous abnormal vesicular structures in the perikaryon. Bar, 2 μm. (C) Detail of the thinly myelinated axon (asterisk) and degenerating changes in the perikaryon of panel B. Bar, 500 nm. (D) Optic nerve of 4-wk-old LES rat. A degenerating oligodendrocyte is closely adjacent to a large adjacent axon (asterisk). Its perikaryon is enlarged and contains small vesicular structures. Bar, 1 μm. (E) Higher magnification of vesicular structures of panel D, which appear to be limited by a pentalamellar membrane (arrowheads) comprising 3 electrodense lines separated by 2 electrolucent lines with a regular periodicity. Bar, 100 nm. (F) Spinal cord of 8-wk-old LES rat. A degenerating cell forms uncompacted myelin membranes against a large adjacent axon (arrows), and its perikaryon is distended with multiple large aggregations of stacks of membranes or honeycombs (arrowheads). Bar, 1 μm. (G) Higher magnification of panel F showing a fragment of a honeycomb with aggregated vesicular structures. In some areas there are stacks of membranes (arrowheads) that have a regular periodicity of approximately 5 nm between electrodense lines (arrowhead, inset). Bar, 200 nm (inset, 100 nm). (H) Spinal cord of 16-wk-old LES rat. An oligodendrocyte in the center of the image has numerous honeycombs in its perikaryon (arrow) with a few uncompacted myelin lamellae against large adjacent axons (arrowheads). Two adjacent cells appear to be immature oligodendrocytes. Wide astroglial processes separate individual axons from each other. Bar, 2 μm. (I) Detail of a honeycomb with a stack of multiple membranes. Bar, 200 nm.