Abstract
Sixteen pregnant rats of Donryu Strain were given intravenously with a single dose of 50 mg/ kg of Ethylnitrosourea (ENU) on the 15th day (Group I, 9 rats) and the 20th day (Group II, 7 rats) of gestation.A total of 126 tumors (Group I, 61 and Group II, 65) were produced in 92 of 117 treated offspring which had survived into tumor bearing age. The mean survival time of Group I rats with tumor developement was 317 days after brith and that of Group II rats was 276.The sites of the total of 126 tumors were formed as following : 27 were produced in the brain (Group I, 21 and Group II, 6), 21 in the spinal cord, 42 in the cranial nerve and ganglia, 8 in the spinal nerve roots, 6 in the peripheral nerves and 22 in the extraneural organs. The neural tumors amouted 104, comprising 82.5% of the total number of the neoplasm.Significant differences in incidence of the tumors of the brain and those in extraneural organs were demonstrated between Group I and Group II rats.According to the cytology and the pattern of predominant tumor cells, tumors of the brain and spinal cord were classified into the following types : mixed glioma (18), oligodendroglioma (18), anaplastic astrocytoma or anaplastic glioma (6), ependymoma-like tumor (5) and unclassified tumor (1). The histology of mixed glioma and oligodendroglioma were most common. 5 tumors produced in the spinal cord were classified as ependymoma-like tumor and they showed an isomorphic cell appearance with such architectural characteristics as crowns of cell nuclei around vascular vessels and pseudorosettes. No tumors were found with typical ependymal rosettes.Almost all the cranial nerve tumors were located in the trigeminal nerve and Gasserian ganglia, microscopically the majority of neurinomas were highly anaplastic with friquent mitotic figures.Besides grossly visible tumors, histological examinations of the brain and the spinal cord disclosed a total of 138 (Group I, 84 and Group II, 54) foci of glial cell hyperplasia or tumors of microscopic size. Sites of predilection for such foci or small microtumors were the subcortical white matter of the brain, the basal ganglia, the spinal cord, the hippocumpus and the periventricular areas. The predominant cell type of such lesions was either oligodendroglial or astrocytic glia. With increasing tumor size, a number of microtumors with a mixed cellular composition became frequent. There are no focus of the ependymal cell hyperplasia.The transplantation experiment demonstrated that anaplastic neurinomas were highly transplantable and capable of subsequent transfers through a number of generations.This experiment demonstrated that a single transplacental exposure of ENU was capable of inducing neuroectodermal tumors, and probably taget cells of it were the astroglia, the oligodendroglia and Schwann's sheath cells.
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