Transformation of oligodendroglia: a para- or preneoplastic effect of ethylnitrosourea on mouse brain.

The aim of this EM study was to assess the relationship of demyelination changes induced in mouse brain by a carcinogenic substance to the early steps in the evolution of neoplastic disease. The investigation on the 25 experimental mice injected at various stages of age with ethylnitrosourea revealed demyelination foci in three animals and interfascicular nests of abnormal cells in seven animals, the latter most probably being of oligodendroglial origin. The nest cells were characterized by their large size and a multitude of interdigitated cytoplasmic processes forming complicated membranous patterns. The abnormal development of oligodendroglial cytoplasmic processes is considered to be the cause of the demyelination. This previously unknown form of oligodendroglial transformation may consist in either the earliest preneoplastic changes or represent a reactive, paraneoplastic type of alteration.