Mice were exposed to a single 15-ms or 25-ms pulse of 2,450-MHz microwaves which increased brain temperature by 2 degrees C or 4 degrees C, respectively. Immediately after exposure, the mice became hypokinetic but began recovering within 5 minutes. The 25-ms pulse (18.7 j deposited in the brain) caused a significant decrease in acetylcholine content of the whole brain, probably owing to increased permeability of the membrane.

Effect of short electromagnetic pulses on brain acetylcholine content and spontaneous motor activity of mice

Inflammatory responses, which were induced in rats by a subcutaneous injection of sheep red blood cells (SRBC) into footpads, and in mice, by tail-vein trauma due to sequential bleeding, were observed in animals that had been pretreated wth 26-MHz radio-frequency radiation (RFR) or with a frank thermal burden. Pretreatment of rats by RFR decreased the severity of SRBC-induced inflammation; averaged thickness of the footpad was less by 33.0% and 45.6%, respectively, than thicknesses observed in thermally treated and control animals. White blood cell (WBC) counts in RFR pretreated, tail-vein traumatized mice remained constant, in contrast to the leukocytosis that was observed in air-heated and in sham-exposed animals. Moreover, the inflammatory response in RFR-treated mice was accompanied by a well-defined but transient refractory state in the number of circulating specialized leukocytes. The 92-hour time course of the refractory state was characterized by a transient fourfold decrease of lymphocytes and a fourfold increase of neutrophils that peaked three hours after exposure; these changes were in marked contrast to those observed in thermal and passive controls. The results indicate that RFR can attenuate an inflammatory reaction. This inhibitory property may have relevance to immunocompetency of cell-mediated immunity (CMI), since CMI responses invoke nonspecific inflammatory reactions.

Effects of radio‐frequency radiation on inflammation

The significance of the enzyme cholinesterase in studies on the biological effects of microwaves is discussed. Experiments were performed on the direct effect of microwave radiation on the enzyme activity in aqueous solution, and in rabbit blood. Microwave radiation was found to have an effect only when the temperature increase was great enough to denature the enzyme.

Studies on the interaction of microwave radiation with cholinesterase.

To understand the biological effects of radio frequency (RF) fields on humans, both in vitro and in vivo studies exposing cell cultures, isolated tissues, and animals have been conducted. Dosimetry of nonionizing radiation is far more complicated than that of ionizing radiation. Field frequency and polarization, tissue dielectric properties, object size and shape, and the presence of metallic stimulating and recording instruments can all affect energy absorption in exposed subjects, either in vitro or in vivo. In addition, temperature control in an exposure system can influence biological responses. Different exposure systems are reviewed in this paper. Relevance of the systems to wireless technology research is discussed.

State of the Science Regarding in Vitro and in Vivo Exposure Systems for RF Studies

An exposure system that addresses difficulties that arise for exposure of small animals at low frequencies with a high exposure level is presented. The system, intended to operate at 27 MHz, consists of two identical transverse electro-magnetic (TEM) cells for exposure and sham exposure of groups of 16 free-running mice housed in pairs within standard cages, capable of exposure over extended daily periods while being provided food and water. Inclusion of the exposure cell in a half-wavelength resonator has been developed as a new paradigm to enhance field strength for an increase of >50-fold in available specific absorption rate (SAR) levels compared to traditional TEM cell configurations. The system described allows both daily and weekly exposure schedules and supports blinded protocols with continuous wave (CW) and amplitude modulation (AM) signals with programmable modulation depths and frequencies. Electric field (E-field) homogeneity across the TEM cell along a vertical plane (orthogonal to the axis of the TEM line) was within 3.3%, and 3.1% along the horizontal plane. Accurate and comprehensive dosimetric assessments based on whole-body and organ-specific SAR essential for in vivo bioelectromagnetic experiments are presented, which takes into account various factors (e.g., mouse activities, close proximity, and field homogeneity). Average SAR levels are controllable in the range of 1 mW/kg to 2 W/kg, with expanded uncertainty (k = 2) of 1 dB and instantaneous variation (k = 1) of 4 dB.

An HF exposure system for mice with improved efficiency

While present standards for exposure to radio frequency (rf) fields are largely based on calculation of the thermal insult that results from exposure to such fields, the nature of biochemical changes induced by the thermal insult is of practical importance in determining the extent of exposure damage. Earlier work has been summarized by Michaelson.' An effect on cell synchrony was described by Prince and associate^.^ The present work was initiated when it was noticed that plasma metal content seemed altered in several species exposed to high-frequency band fields.

J. W. Frazer

Papers

A comparison of thermal and radio‐frequency exposure effects on trace metal content of blood plasma and liver cell fractions of rodents*†