The development of experimental brain tumours. A sequential light and electron microscope study of the subependymal plate. I. Early lesions (abnormal cell clusters).

Pregnant BD-IX rats were given a single intraperitoneal injection of 30 mg of N-ethyl-N-nitrosourea (ENU) per kg of body weight on the 15th day of gestation. The offspring were killed at fortnightly intervals between 2 and 20 weeks of age. The subependymal plate region adjacent to the lateral ventricles was examined by light and electron microscopy to study the early stages in the development of brain tumours. Abnormal clusters of undifferentiated subpendymal plate cells were found in regions away from the plate from 8 weeks of age onwards. In addition focal cellular hyperplasia within the subependymal plate was also seen. These clusters, which often occurred around neurones and blood vessels, were thought to represent the earliest, morphologically detectable changes in the development of cerebral gliomas.