Electron micrographs of myelinated axons in NFL-/- mice. Obvious twist of myelinated axons can be observed (A). Accumulation of mitochondria in the axon (A, arrow) and accumulation of amorphological cytoplasm materials between myelin sheath and axon (A, asterisk) were found near the node of Ranvier. Some mitochondria became enlarged and vacuolated (B, asterisks). An obvious accumulation of mitochondria could be detected in certain region of axons (C, arrow), which may lead to a giant axonal sphere stuffed with mitochondria (D). Note the large number of mitochondria that were vacuolated. (A and B from mice at age of 2 months, C and D from mice at age of 6 months).