Specific absorption rate in rats exposed to 2,450-MHz microwaves under seven exposure conditions

The specific absorption rate in different brain regions of rats exposed to electromagnetic plane waves

Accurate dosimetry of a specific brain region in rats exposed to an electromagnetic field (EMF) is essential for studies focusing on dose-effect relationship of the region. However, only dosimetry of whole brain or whole body were evaluated in most of previous studies. In this study, a numerical voxel rat model with 10 segmented brain regions was constructed. Then, the effects of frequency, incidence direction, and E-polarization direction of plane wave EMF on brain region averaged specific absorption rate (BRSAR) of rats were investigated. At last, the reliability of using whole-body averaged SAR (WBDSAR) and whole-brain averaged SAR (WBRSAR) as estimations of BRSAR were also evaluated. Our results demonstrated that the BRSAR depended on the frequency, incidence direction, and E-polarization direction of the EMF. Besides, the largest deviation could be up to 13.1 dB between BRSAR and WBDSAR and 9.59 dB between BRSAR and WBRSAR. The results suggested that to establish an accurate dose-effect relationship, the variance of the BRSAR induced by alteration of frequency, incidence direction, and E-polarization direction of EMF should be avoided or carefully evaluated. Furthermore, the use of WBDSAR and WBRSAR as estimations of BRSAR should be restricted to certain conditions such that the deviations are not too large.

Can Low-Level Exposure to Radiofrequency Fields Effect Cognitive Behaviour in Laboratory Animals? A Systematic Review of the Literature Related to Spatial Learning and Place Memory

This review considers whether exposure to low-level radiofrequency (RF) fields, mostly associated with mobile phone technology, can influence cognitive behaviour of laboratory animals. Studies were nominated for inclusion using an a priori defined protocol with preselected criteria, and studies were excluded from analysis if they did not include sufficient details about the exposure, dosimetry or experimental protocol, or if they lacked a sham-exposed group. Overall, 62 studies were identified that have investigated the effects of RF fields on spatial memory and place learning and have been published since 1993. Of these, 17 studies were excluded, 20 studies reported no significant field-related effects, 21 studies reported significant impairments or deficits, and four studies reported beneficial consequences. The data do not suggest whether these outcomes are related to specific differences in exposure or testing conditions, or simply represent chance. However, some studies have suggested possible molecular mechanisms for the observed effects, but none of these has been substantiated through independent replication. Further behavioural studies could prove useful to resolve this situation, and it is suggested that these studies should use a consistent animal model with standardized exposure and testing protocols, and with detailed dosimetry provided by heterogeneous, anatomically-realistic animal models.

What is the impact of electromagnetic waves on epileptic seizures?

BACKGROUND

The effects of electromagnetic waves (EMWs) on humans and their relationship with various disorders have been investigated. We aimed to investigate the effects of exposure to different frequencies of EMWs in various durations in a mouse epilepsy model induced by pentylenetetrazole (PTZ).

MATERIAL AND METHODS

A total of 180 4-week-old male mice weighing 25-30 g were used in this study. Each experimental group consisted of 10 mice. They were exposed to 900, 700, 500, 300, and 100 MHz EMWs for 20 hours, 12 hours and 2 hours. Following electromagnetic radiation exposure, 60 mg/kg of PTZ was injected intraperitoneally to all mice. Each control was also injected with PTZ without any exposure to EMW. The latency of initial seizure and most severe seizure onset were compared with controls.

RESULTS

The shortest initial seizure latency was noted in the 12-hour group, followed by the 700 MHz. The mean initial seizure latencies in the 2-hour EMW exposed group was significantly shorter compared to that in the 12- and 20-hour groups. There was no significant difference between 12- and 20-hour EMW exposed groups. There was a significant difference between control and 2- and 10-hour EMW exposed groups. No statistically significant differences were noted in mean latencies of the most severe seizure latency, following 20-, 12-, and 2- hour EMW exposed groups and control groups.

CONCLUSIONS

Our findings suggest that acute exposure to EMW may facilitate epileptic seizures, which may be independent of EMW exposure time. This information might be important for patients with epilepsy. Further studies are needed.

Dosimetry of a set-up for the exposure of newborn mice to 2.45-GHZ WiFi frequencies

This work describes the dosimetry of a two waveguide cell system designed to expose newborn mice to electromagnetic fields associated with wireless fidelity signals in the frequency band of 2.45 GHz. The dosimetric characterisation of the exposure system was performed both numerically and experimentally. Specific measures were adopted with regard to the increase in both weight and size of the biological target during the exposure period. The specific absorption rate (SAR, W kg(-1)) for 1 W of input power vs. weight curve was assessed. The curve evidenced an SAR pattern varying from <1 W kg(-1) to >6 W kg(-1) during the first 5 weeks of the life of mice, with a peak resonance phenomenon at a weight around 5 g. This curve was used to set the appropriate level of input power during experimental sessions to expose the growing mice to a defined and constant dose.

Radiation characteristics of ingested wireless device at frequencies from 430 MHz to 3 GHz

In order to assess the compliance of high frequency ingested wireless devices (IWD) within the safety guidelines worldwide, the biological effects and the radiation efficiency of the IWD in a realistic human body model were studied using the Finite-Difference Time-Domain (FDTD) method. Simulations were carried out for three orientations of the IWD at seven positions in the human body model. Specific Absorption Rate (SAR), temperature rise, near field and far field characteristics were analyzed at frequencies from 430 MHz to 3 GHz. Results showed that the radiation intensity outside the body decreased with frequency. Furthermore, the orientation and position of the IWD, which gave maximum radiation efficiency, was frequency dependent. In our experiment, when the IWD was located at the front-most and back-most positions of the small intestine, the electric intensity outside the human body was maximum and minimum, respectively. The position influences the radiation efficiency of the IWD more than its orientation.

Variation of radiation effects and signal efficiency with distance between electromagnetic source and trunk model

The concern on radiation effect and efficiency of wireless device are reemerged due to the increasing application of implanted and ingested bi-directional wireless devices. In this study, Finite-Difference Time-Domain (FDTD) method is applied to analyze the variation of biological effect and signal strength with distance between electromagnetic source and trunk model. FDTD simulations are carried out for 900 MHz system with a half-wavelength dipole antenna. The distance is changed from 25 mm to 1 mm within the range of lambda/2pi. Specific Absorption Rate (SAR) distributions for various vertical and horizontal slices of the human trunk are calculated. The computational results are interpreted in terms of international safety guidelines for human health, showing that the distance has less influence on the signal efficiency. However, peak SAR, the maximums of 1-g and 10-g averaged SAR values normalized to 2.5 mW input power decrease from 0.26 W/kg, 0.04 W/kg, and 0.0188 W/kg to 0.0158 W/kg, 0.0114 W/kg, and 0.008 W/kg respectively. Considering the link performance of wireless device and safety guidelines of radiation exposure, we recommend that the antenna outside body need to keep a suitable distance from human body. In this simulation, 12 mm is the optimized distance.

Radiofrequency Dosimetry for the Ferris-Wheel Mouse Exposure System

Numerical and experimental methods were employed to assess the individual and collective dosimetry of mice used in a bioassay on the exposure to pulsed radiofrequency energy at 900 MHz in the Ferris-wheel exposure system (Utteridge et al., Radiat. Res. 158, 357-364, 2002). Twin-well calorimetry was employed to measure the whole-body specific absorption rate (SAR) of mice for three body masses (23 g, 32 g and 36 g) to determine the lifetime exposure history of the mice used in the bioassay. Calorimetric measurements showed about 95% exposure efficiency and lifetime average whole-body SARs of 0.21, 0.86, 1.7 and 3.4 W kg(-1) for the four exposure groups. A larger statistical variation in SAR was observed in the smallest mice because they had the largest variation in posture inside the plastic restrainers. Infrared thermography provided SAR distributions over the sagittal plane of mouse cadavers. Thermograms typically showed SAR peaks in the abdomen, neck and head. The peak local SAR at these locations, determined by thermometric measurements, showed peak-to-average SAR ratios below 6:1, with typical values around 3:1. Results indicate that the Ferris wheel fulfills the requirement of providing a robust exposure setup, allowing uniform collective lifetime exposure of mice.

Thirty-five years in bioelectromagnetics research

For 35 years, I have been involved in various bioelectromagnetics research projects including acute and long-term radiofrequency (RF) bioeffects studies, dosimetry, exposure systems, MRI safety, cancer studies involving hyperthermia and electrochemical treatment, development of RF exposure and measurement standards, and product compliance. My first study demonstrated that effects on isolated nerve and muscle preparations were due to thermal effects of RF exposure. The recording of cochlear microphonics in animals shows the mechanical nature of the microwave auditory effect. In 1992, we published the results of a large-scale lifetime study in which 100 rats were sham-exposed and 100 rats were exposed for 21 h/day for 25 months to a pulsed RF signal. In dosimetry studies, human models were employed as well as many animal species including mice, rats, rabbits, monkeys, and birds of many sizes. Cancer hyperthermia studies demonstrated that knowledge of temperature distribution was crucial for successful treatment. Research on electrochemical treatment of tumors with direct current involved cellular, animal, and clinical studies. Over the past few decades, there has been rather extensive investigation of the public health impact of RF exposure. In my opinion, future research in bioelectromagnetics should place greater emphasis on medical applications.

Acute effects of pulsed microwaves and 3-nitropropionic acid on neuronal ultrastructure in the rat caudate-putamen

Ultrastructure of the medium sized "spiny" neuron in rat dorsal-lateral caudate-putamen was assessed after administration of 3-nitropropionic acid (3-NP) and exposure to pulsed microwaves. Sprague-Dawley male rats were given two daily intraperitoneal doses of 0 or 10 mg/kg 3-NP and 1.5 h after each dose were exposed to microwave radiation at a whole body averaged specific absorption rate (SAR) of 0 (sham exposure), 0.6, or 6 W/kg for 30 min. Microwave exposure consisted of 1.25 GHz radiation delivered as 5.9 micros pulses with repetition frequency 10 Hz. Tissue samples taken 2-3 h after the second sham or microwave exposure showed no injury with light microscope methods. Blinded qualitative assessment of ultrastructure of randomly selected neurons from the same samples did reveal differences. Subsequent detailed, quantitative measurements showed that, when followed by sham exposure, administration of 3-NP significantly increased endoplasmic reticulum (ER) intracisternal width, ER area density, and nuclear envelope thickness. Microwave exposure at 6 W/kg alone also significantly increased these measures. Exposure of 3-NP treated animals at 6 W/kg significantly increased effects of 3-NP on ultrastructure. Although exposure at 0.6 W/kg alone did not affect ultrastructure measures, exposure of 3-NP treated animals at 0.6 W/kg reduced the effects of 3-NP. We concluded that 3-NP changed neuronal ultrastructure and that the microwave exposures used here changed neuronal ultrastructure in ways that depended on microwave SAR and neuron metabolic status. The apparent cancellation of 3-NP induced changes by exposure to pulsed microwaves at 0.6 W/kg indicated the possibility that such exposure can protect against the effects of mitochondrial toxins on the nervous system.

Microwave effects on the nervous system

Studies have evaluated the electroencephalography (EEG) of humans and laboratory animals during and after Radiofrequency (RF) exposures. Effects of RF exposure on the blood-brain barrier (BBB) have been generally accepted for exposures that are thermalizing. Low level exposures that report alterations of the BBB remain controversial. Exposure to high levels of RF energy can damage the structure and function of the nervous system. Much research has focused on the neurochemistry of the brain and the reported effects of RF exposure. Research with isolated brain tissue has provided new results that do not seem to rely on thermal mechanisms. Studies of individuals who are reported to be sensitive to electric and magnetic fields are discussed. In this review of the literature, it is difficult to draw conclusions concerning hazards to human health. The many exposure parameters such as frequency, orientation, modulation, power density, and duration of exposure make direct comparison of many experiments difficult. At high exposure power densities, thermal effects are prevalent and can lead to adverse consequences. At lower levels of exposure biological effects may still occur but thermal mechanisms are not ruled out. It is concluded that the diverse methods and experimental designs as well as lack of replication of many seemingly important studies prevents formation of definite conclusions concerning hazardous nervous system health effects from RF exposure. The only firm conclusion that may be drawn is the potential for hazardous thermal consequences of high power RF exposure.

Radial arm maze performance of rats following repeated low level microwave radiation exposure

We examined the possibility of changes in "working" memory of rats following whole body exposure to microwave (MW) radiation. During each of 10 days, we exposed rats within circularly polarized waveguides for 45 min to 2450 MHz fields at whole body SARs of 0.6 W/kg (2 micros pulses, 500 pps), followed by testing in a 12 arm, radial arm maze (RAM). Rats received a preexposure injection of one of three psychoactive compounds or saline, to determine whether a compound would interact with MW exposure to affect performance in the maze. Error rate, i.e., reentry into arms already visited, and time to criterion data for 10 consecutive days of testing were analyzed by a three way analysis of variance (ANOVA) using main effects of "exposure" and "drug" and a repeated factor of "test day." Our alpha limit for significance was P <.05. Analyzes of error rates revealed no significant exposure effect, no significant drug effect and no significant interaction between the two main factors. There was a significant difference in test days, as expected, with repeated test-trial days, which indicates that learning was accomplished. There was no significant interaction of test day and the other two factors. The results of our analyzes of time to criterion data included no significant exposure effect, a significant drug effect, a significant test day effect, and a significant interaction between drug and test day factors. Post hoc analyzes of the drug factor revealed that rats treated with either physostigmine or nalrexone hydrochloride, took significantly longer to complete the maze task than rats pretreated with saline or with naloxone methodide. We conclude that there is no evidence from the current study that exposure to of MW radiation under parameters examined caused decrements in the ability of rats to learn the spatial memory task.

Dosimetry in mice exposed to 1.6 GHz microwaves in a carrousel irradiator

We have developed a carrousel irradiator for mice which delivers a head-first and near-field radiofrequency exposure that more closely simulates cellular telephone and radio use than conventional whole body exposure systems. Mouse cadavers were placed on the carrousel irradiator and exposed with their noses 5 mm from the feedpoint of a 1.6 GHz antenna. Local measured specific absorption rates (SAR) in brain regions corresponding to the frontal cortex, medial caudate putamen, and midhippocampal areas were 2.9, 2.4, and 2.2 W/kg per watt of irradiated power, respectively. In addition, average SAR was estimated to be 3.4 W/kg per watt along the sagittal plane of the brain, 2.0 W/kg per watt along the sagittal plane of the body, and between 6.8 and 8.1 W/kg per watt at peak locations along the sagittal plane at the body surface. This detailed SAR information in mice is critical to the interpretation of biological studies of IRIDIUM exposure, and similar analysis should be included for all studies of in vivo exposure of small animals to microwaves.

Cardiovascular and thermal effects of microwave irradiation at 1 and/or 10 GHz in anesthetized rats

Relatively large thermal gradients may exist during exposure of an animal to microwaves (MWs), particularly at high frequencies. Differences in thermal gradients within the body may lead to noticeable differences in the magnitude of cardiovascular changes resulting from MW exposure. This study compares the thermal distribution and cardiovascular effects of exposure to a single MW frequency with effects of simultaneous exposure to two frequencies. Ketamine-anesthetized male Sprague-Dawley rats (n = 58) were exposed individually to one of three conditions: 1-GHz, 10-GHz, or combined 1- and 10-GHz MWs at an equivalent whole-body specific absorption rate of 12 W/kg. The continuous-wave irradiation was conducted under far-field conditions with animals in E orientation (left lateral exposure, long axis parallel to the electric field) or in H orientation (left lateral exposure, long axis perpendicular to the electric field). Irradiation was started when colonic temperature was 37.5 degrees C and was continued until lethal temperatures were attained. Colonic, tympanic, left and right subcutaneous, and tail temperatures, and arterial blood pressure, heart rate, and respiratory rate were continuously recorded. In both E and H orientations, survival time (i.e., time from colonic temperature of 37.5 degrees C until death) was lowest in animals exposed at 1-GHz, intermediate in those exposed at 1- and 10-GHz combined, and greatest in the 10-GHz group (most differences statistically significant). At all sites (with the exception of right subcutaneous), temperature values in the 1- and 10-GHz combined group were between those of the single-frequency exposure groups in both E and H orientations. During irradiation, arterial blood pressure initially increased and then decreased until death. Heart rate increased throughout the exposure period. The general, overall patterns of these changes were similar in all groups. The results indicate that no unusual physiological responses occur during multi-frequency MW exposure, when compared with results of single-frequency exposure. Bioelectromagnetics 21:159-166, 2000. Published 2000 Wiley-Liss, Inc.

Single- and double-strand DNA breaks in rat brain cells after acute exposure to radiofrequency electromagnetic radiation

We investigated the effects of acute (2-h) exposure to pulsed (2-micros pulse width, 500 pulses s(-1)) and continuous wave 2450-MHz radiofrequency electromagnetic radiation on DNA strand breaks in brain cells of rat. The spatial averaged power density of the radiation was 2mW/cm2, which produced a whole-body average-specific absorption rate of 1.2W/kg. Single- and double-strand DNA breaks in individual brain cells were measured at 4h post-exposure using a microgel electrophoresis assay. An increase in both types of DNA strand breaks was observed after exposure to either the pulsed or continuous-wave radiation, No significant difference was observed between the effects of the two forms of radiation. We speculate that these effects could result from a direct effect of radiofrequency electromagnetic energy on DNA molecules and/or impairment of DNA-damage repair mechanisms in brain cells. Our data further support the results of earlier in vitro and in vivo studies showing effects of radiofrequency electromagnetic radiation on DNA.

Acute low-intensity microwave exposure increases DNA single-strand breaks in rat brain cells

Levels of DNA single-strand break were assayed in brain cells from rats acutely exposed to low-intensity 2450 MHz microwaves using an alkaline microgel electrophoresis method. Immediately after 2 h of exposure to pulsed (2 microseconds width, 500 pulses/s) microwaves, no significant effect was observed, whereas a dose rate-dependent [0.6 and 1.2 W/kg whole body specific absorption rate (SAR)] increase in DNA single-strand breaks was found in brain cells of rats at 4 h postexposure. Furthermore, in rats exposed for 2 h to continuous-wave 2450 MHz microwaves (SAR 1.2 W/kg), increases in brain cell DNA single-strand breaks were observed immediately as well as at 4 h postexposure.

Microwave irradiation affects radial-arm maze performance in the rat

After 45 min of exposure to pulsed 2450 MHz microwaves (2 microseconds pulses, 500 pps, 1 mW/cm2, average whole body SAR 0.6 W/kg), rats showed retarded learning while performing in the radial-arm maze to obtain food rewards, indicating a deficit in spatial "working memory" function. This behavioral deficit was reversed by pretreatment before exposure with the cholinergic agonist physostigmine or the opiate antagonist naltrexone, whereas pretreatment with the peripheral opiate antagonist naloxone methiodide showed no reversal of effect. These data indicate that both cholinergic and endogenous opioid neurotransmitter systems in the brain are involved in the microwave-induced spatial memory deficit.

Research on the neurological effects of nonionizing radiation at the University of Washington

This paper reviews research on neurological effects of low-level microwave irradiation, which was performed at the University of Washington, during the decade of the 1980s. We studied in the rat the effects of microwave exposure on the actions of various psychoactive drugs, on the activity of cholinergic systems in the brain, and on the neural mechanisms involved. Our results indicate that endogenous opioids play an important mediating role in some of the neurological effects of microwaves, and that parameters of microwave exposure are important determinants of the outcome of the microwave effects.

Whole-body microwave dosimetry based on a single, gradient-layer calorimeter

A simple, cost-effective, and accurate technique to measure the whole-body-averaged specific absorption rate (SAR) in Sprague-Dawley rat carcasses by a single-gradient-layer calorimeter is described. The results of SAR determinations showed a highly linear relation between the average power density of the incident field (1.25 GHz) and the normalized heat loading of the carcasses.

Heart rate and blood pressure changes during radiofrequency irradiation and environmental heating

1. Whole-body exposure of animals to radiofrequency radiation (RFR) can cause an increase in body temperature. 2. Responses to heating, whether due to RFR or to more conventional means, include changes in heart rate and blood pressure. 3. Although cardiovascular responses to various types of heating are similar, differences in the magnitude of changes may result from different thermal gradients within the body. 4. This review compares the effects of RFR and conventional environmental heating on heart rate and blood pressure.

Corticotropin-releasing factor antagonist blocks microwave-induced decreases in high-affinity choline uptake in the rat brain

Acute (45-min) irradiation with pulsed low-level microwaves (2450-MHz, 2 microseconds pulses at 500 pps, average power density of 1 mW/cm2, whole-body average specific absorption rate of 0.6 W/kg) decreased sodium-dependent high-affinity choline uptake (HACU) activity in the frontal cortex and hippocampus of the rat. These effects were blocked by pretreating the animals before exposure with intracerebroventricular injection of the specific corticotropin-releasing factor (CRF) receptor antagonist, alpha-helical-CRF9-41 (25 micrograms). Similar injection of the antagonist had no significant effect on HACU in the brain of the sham-exposed rats. These data suggest that low-level microwave irradiation activates CRF in the brain, which in turn causes the changes in central HACU.

Thermal and physiological changes in rats exposed to CW and pulsed 2.8 GHz radiofrequency radiation in E and H orientations

Ketamine-anesthetized Sprague-Dawley rats were exposed in both E and H orientations to far-field 2.8 GHz continuous-wave (CW) and pulsed (0.5 microseconds, 500 pps) radiofrequency radiation (RFR) at equivalent whole-body average specific absorption rates (SAR) of approximately 14 W/kg. Intermittent irradiation was performed in all four exposure conditions, in the same animal, to repeatedly increase colonic temperature from 38.5 to 39.5 degrees C. Tympanic, subcutaneous (sides toward and away from RF sources), colonic, and tail temperatures, electrocardiogram, arterial blood pressure, and respiratory rate were continuously recorded. The results revealed no significant difference between the thermal effects of CW and pulsed RFR exposure. The results did show significant differences between the thermal effects of E- and H-orientation exposure. H-orientation irradiation produced significantly faster colonic temperature increases and, with the exception of the tail, produced significantly greater localized heating in the anesthetized rat, and higher local SAR in rat carcasses than did E-orientation exposure. Under all exposure conditions, heart rate and blood pressure increased significantly during irradiation and returned to baseline when exposure was discontinued. Respiratory rate remained unchanged during irradiation. There were no significant differences between the effects of E- and H-orientation exposure, or between CW and pulsed irradiation, upon heart rate, blood pressure, and respiratory rate.

Low-level microwave irradiation and central cholinergic activity: a dose-response study

Rats were irradiated with circularly polarized, 2,450-MHz pulsed microwaves (2-microseconds pulses, 500 pulses per second [pps]) for 45 min in the cylindrical waveguide system of Guy et al:(Radio Sci 14:63-74, 1979). Immediately after exposure, sodium-dependent high-affinity choline uptake, an indicator of cholinergic activity in neural tissue, was measured in the striatum, frontal cortex, hippocampus, and hypothalamus. The power density was set to give average whole-body specific absorption rates (SAR) of 0.3, 0.45, 0.6, 0.75, 0.9, or 1.2 W/kg to study the dose-response relationship between the rate of microwave energy absorption and cholinergic activity in the different areas of the brain. Decrease in choline uptake was observed in the striatum at a SAR of 0.75 W/kg and above, whereas for the frontal cortex and hippocampus, decreases in choline uptake were observed at a SAR of 0.45 W/kg and above. No significant effect was observed in the hypothalamus at the irradiation power densities studied. The probit analysis was used to determine the SAR50 in each brain area, i.e., the SAR at which 50% of maximum response was elicited. SAR50 values for the striatum, frontal cortex, and hippocampus were 0.65, 0.38, and 0.44 W/kg, respectively.

Microwave attenuation of ethanol-induced hypothermia: ethanol tolerance, time course, exposure duration, and dose response studies

Four experiments were conducted to quantify the reported attenuation by microwave (MW) irradiation of ethanol-induced hypothermia. In one experiment rats were irradiated (continuous wave 2.45 GHz, specific absorption rate = 0.3 W/kg) or sham irradiated for 45 min, injected with 3.6 g/kg, 20% (v/v) ethanol (EtOH) or saline (NaCl) i.p.. Colonic temperature was monitored at 20-min intervals for 2 h. This procedure was repeated for 8 days to determine the rate of tolerance development to the hypothermic effect of ethanol. While MW irradiation did significantly attenuate EtOH-induced hypothermia, it did not enhance or retard the rate of tolerance development. To determine the duration of irradiation necessary to attenuate EtOH-induced hypothermia, groups of rats were irradiated or sham irradiated for 5, 15, 30, or 60 min prior to EtOH injection and subsequent temperature measurements. The attenuation was apparent only after 60 min of irradiation. To determine the duration of the attenuation effect after irradiation, rats were injected with EtOH or NaCl at 0, 30, 60, 120, or 480 min after 45 min of irradiation or sham irradiation. The attenuation effect was apparent among rats injected 0 to 30 min after irradiation and for the first 40 min for groups injected at 120 min. Additional rats were injected with NaCl or 0.9, 1.8, or 2.7 g/kg of EtOH i.p. following 45 min of irradiation or sham irradiation to determine if the attenuation effect depends on the dose of EtOH administered. Attenuation of EtOH-induced hypothermia was more apparent at lower doses of EtOH than at higher doses. These results indicate that the effect is an acute response to irradiation, and rule out several other potential explanations.

Acute low-level microwave exposure and central cholinergic activity: studies on irradiation parameters

Sodium-dependent high-affinity choline uptake was measured in the striatum, frontal cortex, hippocampus, and hypothalamus of rats after acute exposure (45 min) to pulsed (2 microseconds, 500 pps) or continuous-wave 2,450-MHz microwaves in cylindrical waveguides (Guy et al.: Radio Science 14:63-74, 1979) or miniature anechoic chambers (Guy: Journal of Microwave Power 14:327-338, 1979). In all exposure conditions, the average whole-body specific absorption rate was at 0.6 W/kg. Decrease in choline uptake was observed in the frontal cortex after microwave exposure in all of the above irradiation conditions. Regardless of the exposure system used, hippocampal choline uptake was decreased after exposure to pulsed but not continuous-wave microwaves. Striatal choline uptake was decreased after exposure to either pulsed or continuous-wave microwaves in the miniature anechoic chamber. No significant change in hypothalamic choline uptake was observed under any of the exposure conditions studied. We conclude that depending on the parameters of the radiation, microwaves can elicit specific and generalized biological effects.

Brain temperature measurements in rats: a comparison of microwave and ambient temperature exposures

In an effort to understand microwave heating better, regional brain and core temperatures of rats exposed to microwave radiation (2450 MHz) or elevated air temperatures were measured in two studies. In general, we have found no substantial evidence for temperature differentials, or "hot spots," in the brain of these animals. In the first study, after a 30-min exposure, no temperature differences between brain regions either after microwave or ambient air exposure were found. However, a highly significant correlation between brain and core temperatures was found and this correlation was the same for both microwave and ambient air heating. In the second study, time-temperature profiles were measured in rats exposed to either 30 mW/cm2 or 36.2 degrees C. In this study, the 30-min exposure period was divided into seven intervals and the change in temperature during each period was analyzed. Only the cortex showed significantly different heating rates between the air heating and microwave heating; however, this difference disappeared after the initial 5 min of exposure.