Mutation Research, 304 (1994) 235-242 235 © 1994 Elsevier Science B.V. All rights reserved 0027-5107/94/$07.00 MUT 05344 Radiation-induced micronucleus formation in mouse bone marrow after low dose exposures G.C. Jagetia * and N.G. Ganapathi Department of Radiobiology, Kasturba Medical College, Manipal-576 119, Karnataka, India (Received 22 April 1993) (Revision received 2 August 1993) (Accepted 19 August 1993) Keywords: Radiation; Micronuclei; (Mice;) Bone marrow Summary The incidence of micronucleus formation was studied at 12, 24 and 36 h post-irradiation in the polychromatic (PCE) and normochromatic (NCE) erythrocytes of the bone marrow of mice whole-body exposed to 0, 3, 9, 18, 36, 54 and 72 cGy of 6°Co y-radiation. It was observed that the frequency of micronucleated polychromatic erythrocytes (MPCE) increased with the increase in exposure dose at all the post-irradiation time periods studied. Similarly, the frequency of micronucleated normochromatic erythrocytes (MNCE) also increased with the increase in exposure dose and the increase for both MPCE and MNCE was dose related. The dose-response relationship was linear-quadratic for both MPCE and MNCE. The study of mitotic index revealed that a dose as low as 9 cGy is capable of reducing the mitotic index significantly at 24 h post-irradiation and the dose response was linear-quadratic. However, no significant decline in the mitotic index was observed at 12 and 36 h post-irradiation. The evaluation of micronuclei gives an idea about the chromosomal damage as they are re- ported to arise either from acentric fragments or from whole chromosomes that fail to be incorpo- rated into daughter nuclei (Heddle and Carrano, 1977; Yamamoto and Kikuchi, 1980). Micronu- cleus formation in erythrocytes of mammalian bone marrow can be studied with a high resolu- tion power (Boiler and Schmid, 1970; Matter and * Corresponding author. Schmid, 1971; Ledebur and Schmid, 1973; Matter and Grauwiler, 1974), where it is possible to study the measurements of induced micronuclei at very low doses of radiation and chemicals. The effect of low doses of radiation on the induction of micronuclei has been studied by various workers and the reports regarding the dose response are controversial. A linear dose relationship was ob- served by Fenech and Morley (1985), while Mitchell and Norman (1987) and Ramalho et al. (1988) observed a non-linear response in cultured peripheral blood lymphocytes. Similarly, in mice Cole et al. (1981) and Uma Devi and Sharma SSDI 0027-5107(93)E0150-O