PERMEABILITY OF THE BLOOD-BRAIN-BARRIER INDUCED BY 915 MHZ ELECTROMAGNETIC-RADIATION, CONTINUOUS-WAVE AND MODULATED AT 8, 16, 50, AND 200 HZ

Biological effects of electromagnetic fields (EMF) on the blood-brain barrier (BBB) can be studied in sensitive and specific models. In a pr evious investigation of the permeability of the blood-brain barrier af ter exposure to the various EMF-components of proton magnetic resonanc e imaging (MRI), we found that the exposure to MRI induced leakage of Evans Blue labeled proteins normally not passing the BBB of rats [Salf ord et al. (1992), in: Resonance Phenomena in Biology, Oxford Universi ty Press, pp. 87-91]. In the present investigation we exposed male and female Fischer 344 rats in a transverse electromagnetic transmission line chamber to microwaves of 915 MHz as continuous wave (CW) and puls e-modulated with repetition rates of 8, 16, 50, and 200 s-1. The speci fic energy absorption rate (SAR) varied between 0.016 and 5 W/kg. The rats were not anesthetized during the 2-hour exposure. All animals wer e sacrificed by perfusion-fixation of the brains under chloral hydrate anesthesia about 1 hour after the exposure. The brains were perfused with saline for 3-4 minutes, and thereafter fixed in 4% formaldehyde f or 5-6 minutes. Central coronal sections of the brains were dehydrated and embedded in paraffin and sectioned at 5 mum. Albumin and fibrinog en were demonstrated immunohistochemically. The results show albumin l eakage in 5 of 62 of the controls and in 56 of 184 of the animals expo sed to 915 MHz microwaves. Continuous wave resulted in 14 positive fin dings of 35, which differ significantly from the controls (P = 0.002). With pulsed 915 MHz microwaves with repetition rates of 200, 50, 16, and 8 s-1, 42 of 149 were positive, which is highly significant at the P = 0.001 level. This reveals that both CW and pulsed 915 MHz microwa ves have the potential 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 frequency of occurrence of extrav asates (26%) was found to be independent of SAR for SAR < 2.5 W/kg, bu t rose significantly for the higher SAR values (to 43%). The question of whether the opening of the blood-brain barrier constitutes a health hazard demands further investigation. (C) 1994 Wiley-Liss, Inc.