[Electronmicroscopic investigations of N. trigeminus of rats during the phase of tumour induction by ethylnitrosourea (author's transl)].

A single subcutaneous application of ENU to newborn rats causes after 2--4 days lethal and sublethal toxic lesions in some of the Schwann cells and their corresponding axons and myelin sheaths. The sublethally damaged Schwann cells show mainly alterations of myelin sheath formation. The ensuing regeneration produces between the 28.--35. day not only normal Schwann cells but also abnormal ones. These are characterized by atypical nuclei and a gradual loss of their functional relation to axons and are therefore regarded as Schwann cells in blastomatous transformation. The deviation from the normal of the NAD-linked L-alpha-glycerol-3-phosphate dehydrogenase caused by ENU correlates with the described morphological findings. Inspite of its partially unspecific character it may therefore be considered as an early indication of a beginning tumorous transformation.