To study whether exposure to 1 mT (50 Hz) magnetic field for 1 or 7 days could elicit primary DNA damage in the brains of young mice and/or activate endogenous cytoprotective systems such as heat shock response.
The mice were randomly divided into three groups: (1) exposure group (n = 38); (2) sham exposure group (n = 36), and (3) cage control (n = 25). The exposed mice were further divided into three subgroups: (1) exposed for 1 day and sacrificed immediately at the end of exposure (n = 10); (2) exposed for 7 days and sacrificed at the end of exposure (n = 19); and (3) exposed for 7 days and sacrificed 24 h after exposure (n = 9). The sham exposed group was similarly divided into three subgroups (n = 10, 17, and 9, respectively).
Positive controls for DNA damage were performed with X-radiation (6 Gy). Positive control for heat shock protein expression was performed with mice kept at 43°C (until rectal temperature reached 42°C)
|Exposure duration||continuous for 1 day or 7 days (15 h per day)|
|Chamber||during exposure mice were housed in a plastic cage placed in the center of exposure device|
|Setup||each coil 6 cm wide (internal dimensions 43.5 x 40.5 cm; external dimensions of 44.5 x 41.5 cm) with 200 turns of insulated copper wire (diameter 1.6 mm);|
|Sham exposure||A sham exposure was conducted.|
The data showed an increase in primary DNA damage in all cerebral areas of the exposed mice (15 h or 7 days) sacrificed immediately at the end of exposure, as compared to controls. DNA damage appeared to be repaired in mice sacrificed 24 h after a 7-day exposure.
Neither a short (15 h) nor long (7 days) magnetic field exposure induced Hsp70 expression, metabolic and behavioural changes.
In conclusion, the results indicate that in vivo extremely low frequency magnetic field exposure induce a reversible brain DNA damage while they do not elicit a stress response.