Authors

Orendácová J, Raceková E, Orendác M, Martoncíková M, Saganová K, Lievajová K, Abdiová H, Labun J, Gálik J. (2009). Immunohistochemical study of postnatal neurogenesis after whole-body exposure to electromagnetic fields: evaluation of age-and dose-related changes in rats. Cell Mol Neurobiol. 29(6-7):981-990.

Background and Objective
This study was conducted to examine the effects of electromagnetic fields (EMF) on rat postnatal neurogenesis. The study also examined the effect of animals’ age and EMF dose on such effects.  Neurogenesis is the process of neuronal generation and is manifested by proliferation and migration of neural cell precursors. Although previous numbers of neurobiological studies demonstrated that various EMF frequencies induce changes in the nervous tissue of experimental animals, evidence for EMF impact on the health of the nervous system remains uncertain.

Methods
The rats were exposed to a pulse-wave EMF of 2.45 GHz, at mean power density 2.8 mW/cm2, in a purpose-designed exposure chamber. Two experimental groups were created in which two different exposure doses were related to the exposure durations. The animals irradiated for 2 days (4 hours/day) were considered as the short-term exposure dose group, while animals in the long-term exposure group were irradiated for 3 days (8 hours/day).  Both newborn and senescent animals were used in the experiments. After dosing, animals were euthanized and brain material was immediately removed and prepared for analysis. Sections of brain tissues of experimental animals were examined using light microscope for BrdU staining (indication for proliferation). The values of the experimental and control groups were evaluated with one-way ANOVA and Tukey-Kramer tests.

Results
Results in the short-term irradiation for newborn experimental group (2 days (4 hours/day) of whole-body EMF exposure was applied to newborn rats) showed significant changes in BrdU positive cell numbers in all the evaluated experimental groups: after 2 weeks of post-irradiation survival, the number of BrdU positive cells reached the minimum of all the values, which occurred during the post-irradiation survival. During the next 2 weeks of post-irradiation survival, the number of BrdU positive cells increased till the second peak of the proliferating cell values, and then at the end of the 4th week of CPI survival, the number of BrdU positive cells declined toward the values characteristic for the control rats of young adult age. For long exposure groups, significant growth retardation was evident in the irradiated rats from the first week of CPI survival. At the microscopical level, only a few BrdU-labeled cells were visible within the RMS as a characteristic outcome of diminished proliferation activity. Immunohistochemical examination of tissues in senescent animals (both short term and long term) showed no significant changes in BrdU positive cell numbers within the RMS in comparison to those in the senescent controls.

Interpretation
In summary, two extremes of evaluated ages, newborn and senescent, were meant to represent a pivotal distinction between the risks of EMF for neurogenesis. Two different irradiation doses, short-term, 2 days exposure (4 hours/day), versus long-term, 3 days exposure (8 hours/day) were used. The results showed possible risk of pulsed EMF for rat postnatal neurogenesis in relation to the animal age, and similarly to the applied EMF doses. The effects were only manifested in newborn animals which indicate an age-dependent post-irradiation predetermination of proliferation activity. This may also be related to the aging brain should be more radioresistant due to its slower proliferating activity. The adult age post-irradiation increase in proliferation found in previous studies is in good accordance with our observations of the newborn post-irradiation dynamics observed during the first two post-irradiation weeks.

Conclusions
It can be concluded from the current study that whole-body exposure to pulsed EMF of mean power density 2.8 mW/cm2 induces significant age and dose-related changes in proliferation within the RMS in rats. The age-related effects were related to the age-related characteristic development of neuronal cells.


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