Abstract
Public interest has been growing regarding various hazardous factors, which may affect the development of the central nervous system (CNS) of children. However, no simple method has been developed for identifying neuronal damages in developing mammalian embryos, because they develop in the mother's body and the developmental process cannot be examined directly. In contrast, medaka embryos develop outside the mother's body, and their chorions are transparent. Consequently, all gross abnormalities in these living embryos can be detected throughout the entire period of development using an ordinary stereomicroscope. In this study, early and late medaka embryos were subjected to a single acute dose of 10 Gy of X-ray irradiation, which is a lower dose than the LD50 of the embryos.The effects of X-ray irradiation on the developing CNS were examined in the living embryos under a stereomicroscope for 10 days. After X-ray irradiation, all embryos survived; however, many clusters of dead cells were observed in the CNS of the embryos from 4h to 6h after irradiation. These dead cells disappeared thereafter, and the irradiated embryos continued to develop normally. At the hatching period, however, the irradiated embryos had smaller brains and exhibited abnormal histologies of the brain and retina. These results suggest that living medaka embryos are useful for screening the developmental neurotoxicity effects of various hazardous factors. Now, we are studying on the late medaka embryos, which were irradiated with a single acute dose of 5Gy of X-ray.
