title: Relative biological effectiveness of fission neutrons for induction of micronucleus formation in mouse reticulocytes in vivo.
abstract: Following whole-body irradiation of ICR mice with various doses of fission neutrons or X-rays, the frequency of micronuclei (MNs) in peripheral blood reticulocytes was measured at 12 h intervals beginning immediately after irradiation and ending at 72 h after irradiation. The resulting time-course curve of MN frequency had a clear peak 36 h after irradiation, irrespective of the type of radiation applied and the dose used. The MN frequency, averaged as the unweighted mean over the experimental time course, showed a linear increase with increasing dose of either fission neutrons or X-rays. The linear response to X-rays supports reported conclusion that induction of MN formation in reticulocytes is a dose-rate independent phenomenon. The relative biological effectiveness (RBE) of fission neutrons to X-rays for MN induction was estimated to be 1.9 +/- 0.3. This value is considerably lower than the RBE value of 4.6 +/- 0.5 reported for the same fission neutrons for induction of lymphocyte apoptosis in the thymus of ICR mice that represents dose-rate independent, one-track event. Based on these results, we propose that MNs increased in reticulocytes after irradiation mostly represent acentric fragments caused by single chromosome breaks, and that some confounding factor is operating in erythroblasts for the formation of aberrations from non-rejoining DNA double-strand breaks more severely after high-LET radiation than after low-LET radiation.
authors.affiliation: Department of Life Science, Faculty of Science and Technology, Kinki University, Higashiosaka 577-8502, Japan.
authors.forename: Nao
authors.initials: N
authors.lastname: Kagawa
authors.forename: Masahiko
authors.initials: M
authors.lastname: Shimura
authors.forename: Akinori
authors.initials: A
authors.lastname: Takai
authors.forename: Satoru
authors.initials: S
authors.lastname: Endo
authors.forename: Kazuo
authors.initials: K
authors.lastname: Fujikawa
mesh_terms: D000818:Animals; D004307:Dose-Response Relationship, Radiation; D051379:Mice; D008813:Mice, Inbred ICR; D015162:Micronucleus Tests; D009502:Neutrons; D012156:Reticulocytes / Q000528:radiation effects* / Q000648:ultrastructure