Radiation effects in the Japanese medaka (Oryzias latipes)

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In accord with recent biological analyses, medaka has been gained much attention as a model animal of human diseases whereby the genetic background of human diseases may be deduced. We investigated radiological effect on medaka with carbon ion and gamma ray irradiation. To establish the medaka as an animal model for irradiated bone response to evaluate the tolerance for and effectiveness of carbon ion radiation dose with bone metabolism. We irradiated whole body of medaka with carbon ions and gamma rays. Bone resorption in the pharyngeal bone was investigated by histological analysis. For histochemical localization of enzymatic activity of tartrate-resistant acid phosphatase (TRAP), the main marker of osteoclasts, were performed on sections of pharyngeal bone. The carbon ion irradiated medaka showed reduced size and number of osteoclast compared with the gamma ray. The TRAP activities of carbon ion irradiated osteoclasts were more suppressed than gamma ray irradiated medaka. Carbon ion irradiation had a more marked effect on osteoclast activity, and suppressed their maturation to a greater extent than gamma irradiation. These observations suggest that carbon ion irradiation induces differential modulation of osteoclast growth factor expression. Medaka shares many cellular and morphological aspects with mammals and that will allow experimental approaches to identify novel factors in bone biology under normal and pathological conditions.