Permeability of the blood-brain barrier induced by 915 MHz electromagnetic radiation, continuous wave and modulated at 8, 16, 50 and 200 Hz

• The biological effects of electromagnetic fields (EMFs) on the blood-brain barrier (BBB) can be studied in sensitive and specific models. In a previous investigation of the permeability of the BBB after exposure to the various EMF -components of proton magnetic resonance imaging (MRI), we found that exposure to MRI induced leakage of Evans-blue-labelled proteins which do not normally pass the BBB of rats. In the present investigation we exposed male and female Fischer 344 rats in a TEM cell to 915 MHz microwaves as continuous waves and modulated at various low frequencies (8, 16, 50 and 200 Hz). The rats were not anaesthetized during the exposure. After exposure the brains were perfused first with saline for 3-4 minutes and then with 4% formaldehyde. Central coronal sections of the brains were dehydrated and embedded in paraffin and sectioned at 5 μm. Albumin and fibrinogen were demonstrated immunohistochemically. The results show albumin leakage in 5 out of 62 of the controls and in 56 out of 184 of the animals exposed to 915 MHz microwaves. With continuous waves these are 14 positive findings out of 35 which differs significantly from the results obtained with the controls (p = 0.0002). With pulsed 915 MHz microwaves at modulation frequencies of 200, 50, 16 and 8 Hz, 42 findings out of 149 were positive, which is significant at the p = 0.001 level. This reveals that both continuous and pulsed 915 MHz microwaves are able to open up the BBB for albumin passage. However, there is no significant difference between continuous and pulsed 915 MHz microwaves in this respect. The question of whether the opening of the BBB constitutes a health hazard requires further investigation.

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