Hypothermia induces micronuclei in mouse bone marrow cells

We investigated the effect of hypothermia on micronucleus induction in mouse bone marrow cells. Reserpine, which was negative in an in vitro chromosome aberration test, was administered intraperitoneally at 1, 5, 10, 100, and 1000 mg/kg to mice to induce hypothermia. Doses of 10-1000 mg/kg decreased rectal temperature to less than 33.3 degrees C from 24 h to 96 h after dosing and produced a statistically significant (p < 0.01) increase in micronucleated polychromatic erythrocyte frequencies (4.0-12.0/1000). When mice that were administered reserpine at 50, 100, or 200 mg/kg were exposed to an environmental temperature of 30 degrees C for 40 h to keep their body temperature within normal range, the frequency of micronucleated erythrocytes did not increase, while it did without increased environmental temperature. In addition, relatively large micronuclei (diameter of micronucleus > or = 1/4 diameter of cytoplasm) accounted for approximately 50% of the induced micronuclei. The results suggest that the low body temperature of less than 33 degrees C for 40 h induced micronuclei in bone marrow cells, and one possible mechanism was disturbance of the mitotic apparatus.