Influence of extremely low frequency magnetic fields on juvenile development and behaviour in a mouse model

Introduction: Modern society's constant exposure to electro-magnetic fields has raised a number of concerns including possible effects on developing organ systems and reproduction. Especially in the range of extremely low frequencies epidemiological and experimental data are not consistent. The presented data show the results of a pre- and postnatal exposure study in 2 sub-sets performed on behalf of the German Federal Office for Radiation Protection (BfS) in an animal model with magnetic field ranges covering epidemiological threshold values for children as well as occupational safety limits. Methods: Time-mated CD-1 mice were exposed to 50 Hz sinusoidal magnetic fields of 10 MicroT, 1 mT or 10 mT continuously for 20 h/d starting gestational day 10. Two additional control groups were either cage controls or sham exposed. Temperature, relative humidity and noise level were controlled and did not differ between experimental groups. Dams were allowed to litter naturally and litters were standardized at postnatal day (PND) 4-8 pups. Litters were weaned PND 21 and the animals group housed afterwards. Clinical observations were performed daily and bodyweight measurements at PND 4, 7, 10, 14, 17, 21 and weekly afterwards up to PND 90. In a second subset with analogous set-up, additionally reflex ontogenesis was tested PND 1-3 for surface righting and PND 10-12 for negative geotaxis. Spontaneous locomotor activity and functional observational battery were tested PND 20, 30 and 60, auditory startle reflex with habituation and pre-pulse inhibition at PND 20 and 60. Vaginal opening and the corresponding bodyweight were assessed PND 22-30. Differences between experimental groups were considered statistically significant when p < 0.05. ANOVA and Dunnett's test or Chi Square testing were performed depending on data type. Results: The exposure did not affect maternal clinical findings, bodyweight or delivery data. Pre- and postnatal mortality were low and did not differ between exposure and control groups. Pup bodyweight development did not differ between sham and field exposure groups but was slightly elevated or decreased (1 sub-study each) in cage controls. No differences were seen in reflex development and behavioural testings. No dose-related effect was seen in age at vaginal opening but the parameter was achieved at a higher bodyweight in all exposure groups and cage controls in comparison to sham controls, again with no apparent dose-relation. Conclusion: The presented data do not imply a detrimental effect of extremely low frequency magnetic fields on the reproductive performance, any teratogenic effects, the postnatal survival or reflex and behavioural development.