EMF Database abstract: ACUTE LOW-INTENSITY MICROWAVE EXPOSURE INCREASES DNA SINGLE-STRAND BREAKS IN RAT BRAIN CELLS.

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Last modified on: Monday, July 31, 2000
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ACUTE LOW-INTENSITY MICROWAVE EXPOSURE INCREASES DNA SINGLE-STRAND BREAKS IN RAT BRAIN CELLS.
(Eng.) Lai, H.; Singh, N. P. [Dept. of Pharmacology, SJ-30, Univ. of Washington, Seattle, WA 98195 (RR/H.L.)] Bioelectromagnetics 16(3):207-210; 1995
Funding: NIEHS Grant No. ES-03712

Induction of DNA damage in brain cells by acute low-intensity microwave irradiation was studied in rats using an alkaline microgel electrophoresis technique. Male Sprague-Dawley rats were exposed or sham exposed to continuous (CW) or pulsed wave (PW) circularly polarized 2,450-MHz microwaves for 2 hr. The PW microwaves consisted of 2-usec pulse trains having a pulse repetition rate of 500 pulses per second. Power densities of 1 and 2 mW/cm2 were used, producing SARs of 0.6 and 1.2 W/kg. Local SARs produced by this system in 8 brain regions ranged from 0.5 to 2.0 W/kg. Animals were exposed in a cylindrical waveguide system as described by Guy et al. (Radio Sci 14(6S):63-74, 1979; BENER Abstract No. B-6559). Immediately or 4 hr after the end of exposure rats were decapitated and the brains were removed. In rats exposed to PW microwaves, the hippocampus was dissected out and homogenized separately from other brain tissues. In rats exposed to CW microwave radiation, the whole brain was homogenized. The DNA was extracted from the homogenates. The extent of DNA damage was evaluated by measuring the levels of DNA single strand breaks using a single-cell alkaline microgel electrophoresis assay developed by Singh et al. (Int J Radiat Biol 66:23-28, 1994). In this assay, cells are suspended in buffered N-t-butyl-alpha-phenylnitrone in 0.5% agarose, a thin gel layer is formed on a microscope slide, cells are lysed in place, treated with proteinase K to inactivate DNAase, and subjected to slab gel electrophoresis. Slides are then examined by fluorescence microscopy to measure the length of the "tail" of DNA fragments revealed by electrophoresis, which is used as a quantitative measure of single-strand DNA breaks. Data were analyzed by analysis of variance and groups were compared by the Newman-Keuls test. All experiments were run blind by operators doing the exposure and the DNA assay. Exposure to PW microwaves did not induce any DNA damage in rats examined immediately after exposure ended. Significant increases (p<0.01 and p<0.001) in the level of single-strand DNA breaks was seen in both the hippocampi and other brain tissues from rats processed 4 hr after exposure ended. The level of damage was dose-related, increasing with increasing SAR. For example, data given in figures for whole brain cells exposed to PW microwaves indicated an increase in mean DNA migration from approximately 150 (microns) in sham-exposed controls to 190 at 0.6 W/kg and 240 at 1.2 W/kg. Following exposure to CW microwave radiation, significant increases in DNA damage were seen in rats examined both immediately and 4 hr after exposure. The authors concluded that acute microwave exposure increases the amount of DNA single strand breakage in brain cells of rats. The mechanism of interaction between microwaves and DNA is not known. An increase in the amount of DNA single strand breakage could reflect an increase in the breakage rate or an impairment of DNA repair processes. No simple explanation exists for the different responses of brain cell DNA to PW and CW microwaves. This finding supports the view that biological responses to microwaves depend on the parameters of the radiation. (19 Refs). [Copyright 2000, Information Ventures, Inc.]
AUTHOR KEY WORDS: Microwaves, Brain cells, DNA damage, Rats, Single-strand

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