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Objective@#To investigate the influence of extremely low-frequency magnetic field on periodical expression of cryptochrome (Cry) gene in mouse embryonic fibroblast NIH3T3 cells.@*Methods@#The NIH3T3 cells were divided into magnetic field group and sham-exposure group. The NIH3T3 cells in the magnetic field group were stimulated by horse serum and then exposed to an extremely low-frequency magnetic field (50 Hz and 0.3 mT) for 48 hours, and those in the sham-exposure group were also stimulated by horse serum and then exposed to a coil for 48 hours. The NIH3T3 cells were collected, total RNA was extracted, and cDNA was obtained via reverse transcription. Real-time fluorescent quantitative RT-PCR was used to measure the changes in transcription cycles of Cry and Period genes in both groups.@*Results@#There was no significant difference in the proliferation rate at 0, 12, 24, and 48 hours of exposure between the two groups (P>0.05) . Both sham-exposure group and magnetic field group showed a rhythmic change in the expression of Cry gene, and compared with the sham-exposure group, the magnetic field group had a significantly shortened circadian rhythm of Cry gene in NIH3T3 cells (t=2.57, P<0.05) . Both groups had rhythmic and periodical expression of Period gene and there was no significant difference between the two groups (t=0.70, P>0.05) .@*Conclusion@#Extremely low-frequency magnetic field can significantly shorten the circadian rhythm of Cry gene in mouse embryonic fibroblasts, while there is no significant change in the circadian rhythm of Period gene.
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Aims: This report is the first study of the possible relationship between extremely low frequency (50-60 Hz, ELF) magnetic field (MF) exposure and severe cognitive dysfunction. Earlier studies investigated the relationships between MF occupational exposure and Alzheimer’s disease (AD) or dementia. These studies had mixed results, depending upon whether the diagnosis of AD or dementia was performed by experts and upon the methodology used to classify MF exposure. Study Design: Population-based case-control. Place and Duration of Study: Neurology and Preventive Medicine, Keck School of Medicine, University of Southern California, 2 years. Methodology: The study population consisted of 3050 Mexican Americans, aged 65+, enrolled in Phase 1 of the Hispanic Established Population for the Epidemiologic Study of the Elderly (H-EPESE) study. Mini-Mental State Exam (MMSE) results, primary occupational history, and other data were collected. Severe cognitive dysfunction was defined as an MMSE score below 10. The MF exposure methodology developed and used in earlier studies was used. Results: Univariate odds ratios (OR) were 3.4 (P< .03; 95% CI: 1.3-8.9) for high and 1.7 (P=.27; 95% CI: 0.7-4.1) for medium or high (M/H) MF occupations. In multivariate main effects models, the results were similar. When interaction terms were allowed in the models, the interactions between M/H or high occupational MF exposure and smoking history or age group were statistically significant, depending upon whether two (65-74, 75+) or three (65-74, 75-84, 85+) age groups were considered, respectively. When the analyses were limited to subjects aged 75+, the interactions between M/H or high MF occupations and a positive smoking history were statistically significant. Conclusion: The results of this study indicate that working in an occupation with high or M/H MF exposure may increase the risk of severe cognitive dysfunction. Smoking and older age may increase the deleterious effect of MF exposure.
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We previously demonstrated that repeated exposure to extremely low frequency magnetic fields (ELF-MF) increases locomotor activity via stimulation of dopaminergic D1 receptor (J. Pharmacol. Sci., 2007;105:367-371). Since it has been demonstrated that activator protein-1 (AP-1) transcription factors, especially 35-kDa fos-related antigen (FRA), play a key role in the neuronal and behavioral adaptation in response to various stimuli, we examined whether repeated ELF-MF exposure induces FRA-immunoreactivity (FRA-IR) in the striatum and nucleus accumbens (striatal complex) of the mice. Repeated exposure to ELF-MF (0.3 or 2.4 mT, 1 h/day, for consecutive fourteen days) significantly induced hyperlocomotor activity and FRA-IR in the striatal complex in a field intensity-dependent manner. ELF-MF-induced FRA-IR lasted for at least 1 year, while locomotor activity returned near control level 3 months after the final exposure to ELF-MF. Pretreatment with SCH23390, a dopaminergic D1 receptor antagonist, but not with sulpiride, a dopaminergic D2 receptor antagonist, significantly attenuated hyperlocomotor activity and FRA-IR induced by ELF-MF. Our results suggest that repeated exposure to ELF-MF leads to prolonged locomotor stimulation and long-term expression of FRA in the striatal complex of the mice via stimulation of dopaminergic D1 receptor.