[Myelinization of oligodendrocytes in experimental degeneration of the corpus callosum].

An ultrastructural study of myelinated oligodendrocytes and aberrant myelin sheaths has been carried out on the corpus callosum of the adult rat, undergoing wallerian and retrograde degeneration. Abnormal myelin configurations appear under various forms and may be explained under different processes. In some cases, the collapsed myelin sheaths are closely apposed to the cell body of the oligodendrocyte while in others the sheaths surrounding the glial perikarya are described as redundant myelin sheaths issued from small neighbouring myelinated axons. In most instances, myelin of the compact type consisting of 1 to 5 lamellae or of splitted ones between which invades oligodendroglial cytoplasm, ensheaths completely the oligodendrocytes. Myelination de novo (that is, aberrant myelination) seems to be a correct interpretation of some enwrapping sheaths of myelin but for the other myelinated oligodendrocytes it is suggested that the glial cells penetrate inside previously formed myelin sheaths following the degeneration of the axon.