Strain differences of tumorigenic effect of neonatally administered N-ethyl-N-nitrosourea in rats.

The tumorigenicity of neonatally administered N-ethyl-N-nitrosourea (ENU) was studied in four different inbred strain rats, that is Wistar/Furth (WF), Long-Evans (LE), F1 of Wistar/Furth and Long-Evans (F1) and Fischer 344 (F344) rats. All strains developed tumors of the nervous system with high incidence (97-100%) during 6 months of observation. The incidence of tumor of the central nervous system, including the brain (82-88%) and the spinal cord (53-76%), was high in all strains, but that of the peripheral nervous system, including the cranial nerve (21-89%) and the spinal root (13-93%), differed by strain. The peripheral nervous system of WF and F344 rats had a low susceptibility to the tumorigenic effect of ENU, but that of LE rats had a high susceptibility. Many brain tumors were induced in the temporal and frontal cortex and subcortex in all strains of rats. Spinal cord tumors were observed at all levels of the white matter of the spinal cord without any predilection site. Spinal root tumors were located in lumbosacral plexuses in WF and F344 rats, but in LE and F1 rats cervical and thoracic root tumors were also observed. Histological examination revealed that most of the brain and spinal cord tumors were oligodendroglioma, but in F344 rats about half of the brain tumors were mixed glioma. Epidermoid cysts of the lumbar spinal cord were observed only in F344 rats. Tumors of the peripheral nervous system were so-called anaplastic schwannoma.