Studies on blood-brain barrier permeability after microwave-radiation

Abstract

Since the reported alterations of permeability of the blood-brain barrier by microwave radiation have implications for safety considerations in man, studies were conducted to replicate some of the initial investigations. No transfer of parenterally-administered fluorescein across the blood-brain barrier of rats after 30 min of 1.2-GHz radiation at power densities from 2--75 mW/cm2 was noted. Increased fluorescein uptake was seen only when the rats were made hyperthermic in a warm-air environment. Similarly, no increase of brain uptake of 14C-mannitol using the Oldendorf dual isotope technique was seen as a result of exposure to pulsed 1.3-GHz radiation at peak power densities up to 20 mW/cm2, or in the continuous wave mode from 0.1--50 mW/cm2. An attempt to alter the permeability of the blood-brain barrier for serotonin with microwave radiation was unsuccessful. From these studies it would appear that the brain must be made hyperthermic for changes in permeability of the barrier induced by microwave radiation to occur.

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“…Merritt (1977) endeavored to repeat the experiments of Oscar and Hawkins, but did not obtain sliiii.lar results. Data from three of his experiments indicated that hypertherrnia of the brain is necessary to alter prrneabi1ity.…”

USAFSAM Review and Analysis of Radiofrequency Radiation Bioeffects Literature. Fifth Report.

“…Both of these groups used anesthetized animals. Frey et al (1975) claimed to see alterations of BBB permeability to NaFl under 0 certain RFR-exposure conditions, but their results could not be confirmed by Merritt et al (1978),…”

“…The authors noted that Oscar and Hawkins (1977), who used the brainuptake-index (BUI) technique of Oldendorf (1970), had reported that BBB permeability to mannitol and inulin in the rat could be increased by exposure to 1.3-GHz CW or pulsed RFR at an average power density of 3 mW/sq cm, that attempts by Merritt et al (1978) to replicate these results using identical exposure parameters and conditions were unsuccessful, and that in another attempt with 2.45-GHz RFR, Preston et al (1979) were unable to obtain significant changes in cerebral permeability to mannitol. They also noted that Oscar et al (1981), using the in-vivo C-14-iodoantipyrine technique, had obtained increased cerebral blood flow from RFR exposure, which could affect BUI estimates of BBB permeability.…”

“…Sodium fluorescein (NaFl) was used as a tracer in previous studies on effects of RFR on the BBB by Frey et al (1975), and by Merritt et al (1978). Both of these groups used anesthetized animals.…”

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“…An Oldendorf [1970] double isotope procedure for studying blood-brain barrier was also used by Merritt et al [1978]. Four different 1. were not used.…”