High body temperature induces micronuclei in mouse bone marrow

The mouse micronucleus test was conducted to investigate the effect of high body temperature on micronucleus induction. Groups of 10 male ddY mice were exposed to 30 degrees C for 1, 3 or 6 h, 37 degrees C for 0.5, 1, 2, 3 or 4 h, and 40 degrees C for 1 or 2 h. Bone marrow cells were sampled 24 h after heat exposure. Exposure of mice to 37 degrees C for 3 or 4 h and 40 degrees C for 1 or 2 h raised body temperature to approximately 40.5 degrees C and produced statistically significant increases in micronucleated polychromatic erythrocyte frequencies (8.1 +/- 4.5, 6.0 +/- 21, 5.3 +/- 3.3, 7.5 +/- 2.9 parts per thousand, respectively; control frequencies, 2.0 +/- 1.1 parts per thousand). In addition, about 25% of the induced micronuclei were relatively large (diameter of micronucleus greater than or equal to 1/4 diameter of cytoplasm). These results suggest that body temperatures of 39.5 degrees C or higher for more than 30 min induce micronuclei in bone marrow cells, and one possible mechanism is disturbance of the mitotic apparatus.