Brain hsp70 expression and DNA damage in mice exposed to extremely low frequency magnetic fields: A dose-response study

Purpose : To determine whether a dose-response relationship exists among exposure to extremely low frequency magnetic fi elds (ELF-MF) at diff erent densities and 70-kDa heat shock protein (hsp70) expression and DNA damage in mouse brain. Materials and methods : Male CD1 mice were exposed to ELF-MF (50 Hz; 0.1, 0.2, 1 or 2 mT) for 7 days (15 h/day) and sacrificed either at the end of exposure or after 24 h. Hsp70 expression was determined in cerebral cortex-striatum, hippocampus and cerebellum by real-time reverse-transcriptase polymerase chain reaction (RT-PCR) and Western blot analysis. Primary DNA damage was evaluated in the same tissues by comet assay. Sham-exposed mice were used as controls. Results : No changes in both hsp70 mRNA and corresponding protein occurred following exposure to ELF-MF, except for a weak increase in the mRNA in hippocampus of exposed mice to 0.1 mT ELF-MF. Only mice exposed to 1 or 2 mT and sacrifi ced immediately after exposure presented DNA strand breaks higher than controls in all the cerebral areas; such DNA breakage reverted to baseline in the mice sacrifi ced 24 h after exposure. Conclusions : These data show that high density ELF-MF only induce reversible brain DNA damage while they do not aff ect hsp70 expression.