Analysis of N-Ethyl-N-nitrosourea-Induced Brain Carcinogenesis by Sequential Culturing During the Latent Period. II. Morphology of the Tumors Induced by Cell Cultures

Pregnant BD IX rats were given ip injections of N-ethyl-N-nitrosourea (ENU) or buffer on day 15 or 16 of gestation, and cultures were prepared from the brains of fetuses and offspring at different times after treatment. Cultured cells were injected sc into syngeneic rats. Some of the cultures derived 2, 111–112, and 138–145 days after exposure to carcinogen were tumorigenic. They formed malignant growths which invaded and destroyed surrounding tissues. The neoplasms showed structural differences in various areas: The cells were dispersed at random in the wide extracellular space in the center of the tumors, whereas they were arranged in bundles at the periphery. Three groups of cells were distinguished: bipolar-fusiform, polygonal-stellate, and binucleate-multinucleate. The bipolar-fusiform cells could be divided into two separate populations by use of special stains; glioblasts showed occasional weak staining for glial fibers and collagen-producing cells. The polygonal-stellate and binucleate-multinucleate cells were all of astrocytic derivation with evidence of glial fiber production. Cellular pleomorphism correlated with the length of time after which the brains were removed following ENU treatment. Glial tumors derived from brains cultured 2 days after the administration of carcinogen were more pleomorphic than those produced by cell lines prepared 111–112 days and 138–145 days after treatment. Cellular pleomorphism decreased with increasing number of transfers in tumors from some cultures prepared 111–112 days and 138–145 days after injection, but not in those derived 2 days after treatment.