Abstract
Medaka is a teleost fish native to the Asian countries. It has long been the study object of biology in various fields including radiation biology, especially in Japan. Documented data on radiation effects in the medaka system are accumulating. Recently, the establishment of a transgenic medaka, cab-Tg(rag1-egfp), makes it possible to directly visualize the thymus in vivo in a real time manner (Li J. et al., Journal of Immunology, 2007). In our previous investigation, decrease in the volume of thymus was confirmed in the cab-Tg(rag1-egfp) medaka after exposure to a dose from 5 to 10 Gy of X-rays. After 10 Gy of X-ray irradiation, the volume of medaka thymus was decreased on the next day, and started to recover from 5 day. After exposure to a dose at 30Gy of X-ray, the thymus was disappeared after 2 day and recovered at 22 day. To comparatively study the effects between low and high LET irradiations on medaka thymus, in the present work, irradiations from accelerated Fe ions was verified. A total of 36 medaka fish were used in the control and the experimental groups exposed to a dose from 0.5 to 10 Gy. The preliminary data obtained so far showed that decrease in the volume of thymus in few medaka could be detectable in the 0.5 Gy-irradiated group, while this effect was observable in all the medaka receiving a dose at 2 Gy or more. The RBE of Fe-ion was estimated around 3. Further investigations are needed. These findings suggest that the cab-Tg(rag1-egfp) would be a good tool for detecting the radiation effects by monitoring the volume decrease in thymus at live.
