In the normal adult CNS some general functions of oligodendrocytes are well established. Most oligodendrocytes are located in white matter where their primary role is to form myelin (Bunge, 1968). The myelin sheath is a fatty insulation composed of modified plasma membrane that surrounds axons and promotes the rapid and efficient conduction of electrical impulses along myelinated axons (Bunge, 1968). An individual oligodendrocyte is capable of myelinating up to 60 different axons depending on the specific axon tract and axon diameter. Myelination is essential for the normal functioning of the mature CNS. Disruption of CNS myelin through injury, pathological degeneration (Waxman, 1991), or genetic intervention (Nave, 1995) leads to severe functional deficits and frequently a reduction in life span. Even focal myelin loss, as occurs in demyelinating diseases such as multiple sclerosis, results in a rapid loss of neurologic function (Waxman, 1991)