Short and long term effects of methyl- and ethylnitrosourea (MNU & ENU) on the developing nervous system of the rat. I. Long term effects: the induction of (multiple) gliomas.

Single injections on ENU to WAG-rats were given in the perinatal period and repeated injections of MNU to adult WAG-rats. In the tables illustrating the various experiments, the occurrence of tumors is given for each animal; the tumors are classified according to their sites. For the brain tumors a subdivision is made between those macroscopically visible and those discovered only under microscopy. It is noteworthy that the ratio between neural and extraneural tumors in the perinatally exposed animals is rather constant (about 90 and 10 per cent, respectively). In the experiments on young adult rats neural tumors still predominate, but estraneural ones rise to about 40 per cent. The incidence of neural tumors is impressively high in perinatal induction experiments (greater than 95 per cent). Almost all CNS tumors showed the characteristics of oligodendrogliomas; highly differentiated in the smaller tumors and more anaplastic with regressive changes in the larger ones.