Abstract
It is well known that prenatal exposure of gamma-rays causes reduction of cell number and injury of neuronal migration in the developing cerebral cortex of mice. In order to provide information on the effects of neutrons on the fetal brain development, we previously determined the relative biological effectiveness (RBE) for 10 MeV neutrons in induction of apoptosis of the cerebral cortex neural cells of fetal mouse. RBE was about 10. Since RBE depends on neutron energy, we then aimed to examine the effect of 2MeV neutrons. Pregnant B6C3F1 mice were exposed to 2MeV neutrons (0.2Gy, 0.5Gy) or 137Cs gamma-rays (0.5Gy, 1.5Gy) on day 13.5 of gestation, and fetal brains were fixed at 1, 2, 4, 8, 12, 24, and 48hrs after exposure. The brains were sectioned at cerebral mid-plane and stained with HE or TUNEL, and the ventricular zone, intermediate zone and cortexanlage zone were analyzed quantitatively. It turned out that apoptotic cells was observed in the intermediate zone during 4 and 24 hrs after irradiation, and that the rate of apoptosis was highest at 12hrs after exposure in either neutron- or gamma-ray-exposure. It was of note that apoptosis was induced earlier by 2MeV neutrons than 10 MeV ones. Induction of p53 and caspase is under investigation.
