Dose- and time-dependent responses for micronucleus induction by X-rays and fast neutrons in gill cells of medaka (Oryzias latipes).
Medaka fish (Oryzias latipes) were exposed to various doses of X-rays or fast neutrons, and the frequency of micronucleated cells (MNCs) was measured in gills sampled at 12- or 24-hr intervals from 12 to 96 hr after exposure. The resulting time course of MNC frequency was biphasic, with a clear peak 24 hr after exposure, irrespective of the kind of radiation applied and the dose used. The half-life of MNCs induced in the gill tissues by the two exposures fluctuated around 28 hr, with no significant dose-dependent trend for either X-ray- or neutron-exposed fish. As assayed 24 hr after exposure, the MNC frequency increased linearly over the control level with increasing doses of both X-rays and fast neutrons. The relative biological effectiveness (RBE) of fast neutrons to X-rays for MNC induction was estimated to be 4.3 +/- 0.6. This value is close to the RBE value of 5.1 +/- 0.3 reported for fast neutron induction of somatic crossing-over mutations in Drosophila melanogaster that arise from recombination repair of DNA double-strand breaks. These results and other data support our conclusion that the medaka gill cell micronucleus assay is a reliable short-term test for detecting potential inducers of DNA double-strand breaks.
Department of Human and Environmental Sciences, Osaka Shin-Ai College, Tsurumi, Tsurumi-ku, Japan. takai@osaka-shinai.ac.jp
Akinori
A
Takai
Nao
N
Kagawa
Kazuo
K
Fujikawa
D000818:Animals; D004307:Dose-Response Relationship, Radiation; D005880:Gills / Q000528:radiation effects* / Q000648:ultrastructure; D048629:Micronuclei, Chromosome-Defective; D009502:Neutrons; D014965:X-Rays