Non-thermal" Effects on the Blood-Brain Barrier in Fischer rats by exposure to microwaves

Effect of 915 MHz electromagnetic fields (EMF) on the blood brain-barrier (BBB) permeability has been studied in Fischer 344 rats of both sexes. Male and female Fischer 344 rats were exposed in a Transverse Electromagnetic Transmission line chamber to microwaves of 915 MHz as continuous wave (CW) and pulse-modulated with different pulse power and at various time intervals. The CW-pulse power varied from 0.001W to 10 W and the exposure time from 2 min. to 960 min. In each experiment we randomly placed 4 rats in excited and 4 control rats in non-excited TEM-cells respectively. The rats were not anaesthetised during the exposure. The rats were exposed to 915 MHz microwaves, either continuous wave (CW) or pulse modulated at 4,8,16 or 217 Hz with 0.57 ms pulse width, or pulse modulated at 50 Hz with 6.6 ms pulse width as well as from a real GSM-900 telephone. All animals were sacrificed by perfusion-fixation of the brains under chloralhydrate anaesthesia after the exposure. The brains were then perfused, first with saline for 3-4 minutes, and then with 4% formaldehyde for 5-6 minutes. Whole coronal sections of the brains were dehydrated and embedded in paraffin and sectioned at 5 μm. The degree of albumin leakage was demonstrated immune-histo-chemically and classified in order of increased number of albumin extravasations by a rank number: 0 - 0.5 - 1.0 - 1.5 - 2 - 3. Pathological albumin leakage was judged as albumin extravasations equal to or larger than 1. The frequency of pathological rats in all control groups was about 17%. Among rats exposed to pulse modulated microwaves the ratio of pathological rats was 170/481(0.35±0.03) and among rats exposed to continuous wave exposure (CW) it was 74/149 (0.50±0.07). These results are both highly significantly different to their corresponding controls (p<0.0001). The rats were exposed to SAR various values: 0.2; 2; (20-40); (100-500); (1000-3000) mW/kg. In the 217 Hz modulated group (GSM simulated) we found the most increased ratio of albumin extravasations OR= 4 at 0.2 mW/kg. But no significant increased ratio at SAR 2000 mW/kg. The response curve of OR versus log(SAR) had the shape of a bathtub, with a minimum at a100 mW/kg. A similar curve was recorded for OR versus Specific Absorbed Energy (SAE Joule / kg) with a minimum at 100 J/kg. Similar response curves were recorded for the various modulation frequencies 4; 8; 16; 50 Hz. We found no pronounced difference between the various modulation frequencies other than the effect of CW exposure seems to be more effective than pulse modulated exposure in opening the BBB at high SAR values 100-2000 mW/kg. Conclusion: The opening of the BBB is most effective at SAR values in the range of 0.1-0.5 mW.kg-1 and less effective in the range of 50-500 mW.kg-1. In this low SAR range thermal effects are unlikely. Thus there seems to be a non-thermal mechanism involved triggering the opening of the BBB. (Less)