Abstract
For developing human CNS, the period of 8-15 weeks post ovulations showed the most sensitve to radiation. This period, when neural cells proliferate rapidly, correspond to embryonic day 13-13.5 in the mouse and to the developmental stages 28-30 in the medaka embryos. Mammalian embryos develop in the mother`s uterus; hence, their developmental process cannot be examined directly. In contrast, fish embryos, such as those of zebrafish and medaka, develop outside the mother`s bodies and their chorions are transparent. Consequently, all gross abnormalities can be detected throughout the entire period of their development.
In a previous study, transient radiation-induced apoptosis in the CNS is observed in all the living irradiated late medaka embryos (st.28-st.30) under a stereomicroscope, and dead cells are distributed mainly in the marginal proliferating regions of the optic tectum.
Although radiation-induced brain cell death can be also visualized histologically by the TUNEL, we could succeed a versatile method of more rapidly visualizing and precisely observing radiation-induced apoptosis in the CNS using vital dye, acridine orange (AO), without preparing histological sections. Using this method, we could visualize the entire apoptotic processes from the beginning of nuclear condensation to the end of complete elimination in living irradiated medaka embryos.
