Repeated exposure to low-level extremely low frequency-modulated microwaves affects baseline and scopolamine-modified electroencephalograms in freely moving rats

Purpose : To compare in the electroencephalogram of rats the effects of scopolamine (an acetylcholine receptor antagonist) alone and after repeated exposure to low-level microwaves modulated at extremely low frequency. Materials and methods : Averaged frequency spectra (0.5-30 Hz) of the electroencephalogram were studied in freely moving rats with carbon electrodes implanted into the somatosensory cortex. The rats were repeatedly (3 days, 30 min day^-1 ) exposed to low-intensity ((approximately equal)0.3 mW cm^-2) microwaves (915 MHz, 20-ms pulse duration), amplitude modulated (square-wave) at extremely low frequency (4 Hz). Results : The exposure to extremely low frequency microwaves alone significantly enhanced the fast electroencephalographic rhythms (18-30 Hz). This effect was observed neither in subsequent sham-exposure experiment nor in radiation-naïve animals. In the microwave-exposed rats, scopolamine (0.1 mg kg^-1 , subcutaneously) did not cause a slowing in the electroencephalogram that was shown in non-exposed rats. Asimilarity between the scopolamine-induced electroencephalogram effect in the microwaveexposed rats and that of physostigmine (enhancing the acetylcholine level in the brain) in radiation-naive animals was noted. This paradoxical phenomenon stimulates new experimentation for understanding its mechanism(s). Conclusions : The data obtained provide additional evidence that repeated low-level exposure to extremely low frequency microwaves can modify an activity of cholinergic system in the brain.