The morphological and biological changes in long term culture cells of normal-appearing trigeminal nerves from 2, 8, and 30-day-old S-D rats administered transplacentaLly with 75 mg ENU/kg were examined. After a marked degeneration of cells, crisscross multiple proliferative foci of transformed spindle cells appeared at the 3rd passage culture from 2 and 8-day-old rats, but not form 30-day-old rats. The transformed cells with S-100 protein and basal lamina had Schwann cell characteristics. Transformed spindle cells continued to form a crisscross pattern more than 700 days and some transformed spindle cells became round in shape 3-6 months after the primary culture. These transformed cells were transplantable to newborn S-D rats and the transplanted tumors were histologically similar to those of malignant Schwannoma of trigeminal nerves induced by ENU. Round-shaped transformed cells were more malignant than spindle-shaped cells and produced rapidly growing transplanted tumors. Spontaneous transformation with multinucleated giant cells occurred in one of the control cultures. These results indicate that the sequential changes of ENU-treated trigeminal nerves in vitro were corresponded to developmental changes of malignant Schwannoma in vivo induced by ENU. This system will be useful for analysis of ENU-carcinogenesis.</p
