Influence of electromagnetic fields on the efflux of calcium ions from brain tissue in vitro: a three-model analysis consistent with the frequency response up to 510 Hz

The frequency dependence of electromagnetic field-induced calcium-ion efflux from chicken brain tissues has been examined at 15-Hz intervals over the range 1-510 Hz. The electric field component was 15 Vrms/m and the magnetic component varied between 59 and 69 nTrms. No patterns of response as a function of frequency could be readily discerned when the differences in mean efflux values between exposed and sham samples were compared. However, the calculated P-value, a function that combines at each frequency the difference between the means of the exposed and sham groups with the variance of each group, does provide a basis for hypothesizing the existence of three frequency-dependent patterns in the data. One pattern includes all the highly significant (P less than .01) responses which occur between 15 and 315 Hz, at 30-Hz intervals; two independent trials at 165 Hz, giving nonsignificant responses (P greater than .5), break this pattern into two groups of five frequencies each, which is contrary to the expected result for a simple Lorentz-force interaction. However, another pattern of significant results at 60, 90, and 180 Hz, but not at 300 Hz, is consistent with a Lorentz-force model. A third pattern, composed of only one significant response at 405 Hz, is very close to the resonance predicted on a linear extrapolation from high-frequency data for 13carbon atoms. This hypothetical ordering of the frequency-response profile provides the basis for future experimental designs to test each possible interaction model and for their connection to the calcium-ion efflux endpoint.     

Effects of sinusoidal electromagnetic fields on histopathology and structures of brains of preincubated white Leghorn chicken embryos

There are several reports indicating linkages between exposures to 50-60?Hz electromagnetic fields and abnormalities in the early stages of chicken embryonic development. Based on our previous published research carried out at the Department of Animal Sciences, Faculty of Biological Sciences, Shahid Beheshti University, effects of sinusoidal electromagnetic fields on histopathology and structures of brains of preincubated white leghorn hen eggs were investigated. Three hundred healthy fresh fertilized eggs (55-65?gr) were divided into three groups of experimental (n?=?50), control (n?=?75), and sham (n?=?75). Experimental eggs (inside the coil) were exposed to 3 different intensities of 1.33, 2.66, and 7.32?mT and sham groups were located inside the same coil with no exposure, for 24?h before incubation. Control, sham, and experimental groups were all incubated in an incubator (38?±?0.5(°)C, 60% humidity) for 14 days. 14-day old chicken embryos were removed by C-sections, and the brains of all embryos of all groups were fixed in formalin(10%), stained with H&E and TUNEL assay, for studying the histopatholog and process of apoptosis. The brains of other embryos were prepared for Scanning Electeron Microscope. Results showed electromagnetic fields have toxic effects on brain cells by increasing the number of apoptotic cells and degeneration of brains' tissues of exposed chicken embryos. These findings suggest that the electromagnetic fields induce brain damages at different levels.     

Lack of an effect of static magnetic field on calcium efflux from isolated chick brains

45Ca2+ efflux from neonatal isolated chick brains was measured. The brains were exposed to uniform or nonuniform static magnetic fields. The field intensity ranged from 200-900 mT. The exposure took place during incubation and/or when efflux was being measured. No difference appeared in the 45Ca2+ efflux between controls and exposed brains.     

Rats are not aversive when exposed to 60-Hz magnetic fields at 3.03 mT.

Thirty-two male rats were tested in two replicates of an experiment to determine whether body currents induced by 60-Hz magnetic fields might lead to avoidance behavior comparable to that which results from exposure to strong 60-Hz electric fields. The test apparatus was a two-compartment Plexiglas shuttlebox enclosed in a sound-attenuating plywood chamber, which in turn was encompassed by two copper bus bars that, when energized, served as a source of 60-Hz magnetic fields. Location of the rat, and traverse activity in the shuttlebox were monitored by nine infra-red photo detectors equally spaced along the length of the apparatus. Rats were divided into 2 groups: 1 group of rats (n = 8 per group per replicate) was sham exposed while rats in the other group (n = 8 per group per replicate) were exposed to a 3.03 mT (30.3 G), 60-Hz magnetic field whenever they traversed to or were located on the side (L or R) predetermined as the exposed side. To control artifact incident to side preference, the side exposed (L or R) was alternated over the exposed rats. Each rat was tested individually in a 1-h session. A 2-factor ANOVA (exposed vs. control, replicate 1 vs. replicate 2) failed to reveal any significant effects due to either factor or to an interaction between factors. These data demonstrate that rats do not avoid exposure to 60-Hz magnetic fields at a flux density of 3.03 mT and further imply that the avoidance by rats of high level 60-Hz electric fields is mediated by something other than the internal body currents induced by the exposure.     

The influence of temperature during electric- and magnetic-field-induced alteration of calcium-ion release from in vitro brain tissue

A technique based on release of calcium ions from in vitro preparations of avian brain tissues has been used by several investigators to demonstrate a biological effect of weak electric and magnetic fields. When the tissues have been exposed to ELF-modulated, VHF or UHF fields, enhanced release of calcium ions has resulted. In contrast, when the tissues have been exposed directly to an ELF field, outcomes have differed. Both inhibition and enhancement in release of calcium ions have been reported. We now find that either outcome--or a null result--is possible, depending on the temperature of tissue samples before and during exposure. Avian-brain tissues were exposed to 16-Hz sinusoidal electromagnetic fields at 14.1 Vrms/m (in air) and 64 nTrms. During 20-min exposures, as tissue-sample temperature rose by 0.7 to 2.5 degrees C to a final temperature of 35, 36, or 37, but not of 38 or 39 degrees C, an enhanced release of ions was observed. When the temperature was stable during exposure (i.e., constant within +/- 0.3 degrees C) at a final value of 36 or 37, but not of 35 or 38 degrees C, the quantity of ions released was reduced. And when descending by 0.7 to 1.5 degrees C to any final temperature from 35 to 38 degrees C, a null result occurred. These findings may reconcile the apparent disagreement in the direction of a field-induced response, and they may explain why experimental outcomes have been difficult to confirm in some laboratories. Of greater importance, the findings may also provide insight into the mechanism of the field-induced phenomenon.     

Effects of ELF (1-120 Hz) and modulated (50 Hz) RF fields on the efflux of calcium ions from brain tissue in vitro

We have previously shown that 16-Hz, sinusoidal electromagnetic fields can cause enhanced efflux of calcium ions from chick brain tissue, in vitro, in two intensity regions centered on 6 and 40 Vp-p/m. Alternatively, 1-Hz and 30-Hz fields at 40 Vp-p/m did not cause enhanced efflux. We now demonstrate that although there is no enhanced efflux associated with a 42-Hz field at 30, 40, 50, or 60 Vp-p/m, a 45-Hz field causes enhanced efflux in an intensity range around 40 Vp-p/m that is essentially identical to the response observed for 16-Hz fields. Fields at 50 Hz induce enhanced efflux in a narrower intensity region between 45 and 50 Vp-p/m, while radiofrequency carrier waves, amplitude modulated at 50 Hz, also display enhanced efflux over a narrow power density range. Electromagnetic fields at 60 Hz cause enhanced efflux only at 35 and 40 Vp-p/m, intensities slightly lower than those that are effective at 50 Hz. Finally, exposures over a series of frequencies at 42.5 Vp-p/m reveal two frequency regions that elicit enhanced efflux--one centered on 15 Hz, the other extending from 45 to 105 Hz.     

Effects of sinusoidal electromagnetic fields on histopathology and structures of brains of preincubated white leghorn chicken embryos

There are several reports indicating linkages between exposures to 50–60 Hz electromagnetic fields and abnormalities in the early stages of chicken embryonic development. Based on our previous published research carried out at the Department of Animal Sciences, Faculty of Biological Sciences, Shahid Beheshti University, effects of sinusoidal electromagnetic fields on histopathology and structures of brains of preincubated white leghorn hen eggs were investigated. Three hundred healthy fresh fertilized eggs (55–65 gr) were divided into three groups of experimental (n = 50), control (n = 75), and sham (n = 75). Experimental eggs (inside the coil) were exposed to 3 different intensities of 1.33, 2.66, and 7.32 mT and sham groups were located inside the same coil with no exposure, for 24 h before incubation. Control, sham, and experimental groups were all incubated in an incubator (38 ± 0.5^°C, 60% humidity) for 14 days. 14-day old chicken embryos were removed by C-sections, and the brains of all embryos of all groups were fixed in formalin(10%), stained with H&E and TUNEL assay, for studying the histopatholog and process of apoptosis. The brains of other embryos were prepared for Scanning Electeron Microscope. Results showed electromagnetic fields have toxic effects on brain cells by increasing the number of apoptotic cells and degeneration of brains' tissues of exposed chicken embryos. These findings suggest that the electromagnetic fields induce brain damages at different levels.     

Determination of electric current distributions in animals and humans exposed to a uniform 60-Hz high-intensity electric field

The thermographic method for determining specific absorption rate (SAR) in animals and models of tissues or bodies exposed to electromagnetic fields was applied to the problem of quantifying the current distribution in homogeneous bodies of arbitrary shape exposed to 60-Hz electric fields. The 60-Hz field exposures were simulated by exposing scale models of high electrical conductivity to 57.3-MHz VHF fields of high strength in a large 3.66 × 3.66 × 2.44-m TE₁₀₁ mode resonant cavity. After exposure periods of 2–30 s, the models were quickly disassembled so that the temperature distribution (maximum value up to 7 °C) along internal cross-sectional planes of the model could be recorded thermographically. The SAR, W′, calculated from the temperature changes at any point in the scale model was used to determine the SAR, W, for a full-scale model exposed to a 60-Hz electric field of the same strength by the relation W = (60/ f² · (σ′/σ) · W′ where f′ is the model exposure frequency, σ′ is the conductivity of the scale model at the VHF exposure frequency, and σ is the conductivity of the full-scale subject at 60 Hz. The SAR was used to calculate either the electric field strength or the current density for the full-scale subject. The models were used to simulate the exposure of the full-scale subject located either in free space or in contact with a conducting ground plane. Measurements made on a number of spheroidal models with axial ratios from 1 to 10 and conductivity from 1 to 10 s/m agreed well with theoretical predictions. Maximum current densities of 200 nA/cm² predicted in the ankles of man models and 50 nA/cm² predicted in the legs of pig models exposed to 60-Hz fields at 1kV/m agreed well with independent measurements on full-scale models.     

A role for the magnetic field in the radiation-induced efflux of calcium ions from brain tissue in vitro

Two independent laboratories have demonstrated that electromagnetic radiation at specific frequencies can cause a change in the efflux of calcium ions from brain tissue in vitro. In a local geomagnetic field (LGF) at a density of 38 microTesla (microT), 15- and 45-Hz electromagnetic signals (40 Vp-p/m in air) have been shown to induce a change in the efflux of calcium ions from the exposed tissues, whereas 1- and 30-Hz signals do not. We now show that the effective 15-Hz signal can be rendered ineffective when the LGF is reduced to 19 microT with Helmholtz coils. In addition, the ineffective 30-Hz signal becomes effective when the LGF is changed to +/- 25.3 microT or to +/- 76 microT. These results demonstrate that the net intensity of the LGF is an important variable. The results appear to describe a resonance-like relationship in which the frequency of the electromagnetic field that can induce a change in efflux is proportional to a product of LGF density and an index, 2n + 1, where n = 0,1. These phenomenological findings may provide a basis for evaluating the apparent lack of reproducibility of biological effects caused by low-intensity extremely-low-frequency (ELF) electromagnetic signals. In future investigations of this phenomenon, the LGF vector should be explicitly described. If the underlying mechanism involves a general property of tissue, then research conducted in the ambient electromagnetic environment (50/60 Hz) may be subjected to unnoticed and uncontrolled influences, depending on the density of the LGF.     

Effects of 60-Hz electric fields on specific humoral and cellular components of the immune system

We evaluated humoral and cellular functions of the immune system of Swiss-Webster mice exposed to 60-Hz electric fields at 100 kV/m. No significant differences were observed in primary antibody response to keyhole limpet hemocyanin (precipitating antibody levels) between exposed (30 or 60 days) and control mice, nor were there significant changes in mitogen-stimulation response of spleen cells from mice similarly exposed for 90 or 150 days when compared to sham-exposed animals.     

Growth rate and mitotic index analysis of Vicia faba L. roots exposed to 60-Hz electric fields

Growth, mitotic index, and growth rate recovery were determined for Vicia faba L. roots exposed to 60-Hz electric fields of 200, 290, and 360 V/m in an aqueous inorganic nutrient medium (conductivity 0.07-0.09 S/m). Root growth rate decreased in proportion to the increasing strength; the electric field threshold for a growth rate effect was about 230 V/m. The induced transmembrane potential at the threshold exposure was about 4-7 mV. The mitotic index was not affected by an electric field exposure sufficient to reduce root growth rate to about 35% of control. Root growth rate recovery from 31-96% of control occurred in 4 days after cessation of the 360 V/m exposure. The results support the postulate that the site of action of the applied electric fields is the cell membrane.     

Endocrinological effects of strong 60-Hz electric fields on rats

Adult male rats were exposed or sham-exposed to 60-Hz electric fields without spark discharges, ozone, or significant levels of other secondary variables. No effects were observed on body weights or plasma hormone levels after 30 days of exposure at an effective field strength of 68 kV/m. After 120 days of exposure (effective field strength = 64 kV/m), effects were inconsistent, with significant reductions in body weight and plasma levels of follicle-stimulating hormone and corticosterone occurring in one replicate experiment but not in the other. Plasma testosterone levels were significantly reduced after 120 days of exposure in one experiment, with a similar but not statistically significant reduction in a replicate experiment. Weanling rats, exposed or sham-exposed in electric fields with an effective field strength of 80 kV/m from 20 to 56 days of age, exhibited identical or closely similar growth trends in body and organ weights. Hormone levels in exposed and sham-exposed groups were also similar. However, there was an apparent phase shift between the two groups in the cyclic variations of concentrations of hormones at different stages of development, particularly with respect to follicle-stimulating hormone and corticosterone. We concluded that 60-Hz electric fields may bring about subtle changes in the endocrine system of rats, and that these changes may be related to alterations in episodic rhythms.     

Effects of sinusoidal 60-Hz electric and magnetic fields on ATP and oxygen levels in the slime mold, Physarum polycephalum

We have previously reported that exposing the vegetative plasmodia stage of Physarum polycephalum to either individual or simultaneously applied electric and magnetic fields (45-75 Hz, 0.14-2.0 G, and 0.035-0.7 V/m) lengthens their mitotic cycle, depresses their rate of reversible shuttle streaming, and lowers their respiration rate. In this article we report the effects of simultaneously applied electromagnetic fields (60 Hz, 1.0 G, 1.0 V/m), electric fields only (60 Hz, 1.0 V/m), magnetic fields only (60 Hz, 1.0 G) on the haploid amoeba of Physarum exposed for 120-180 days. Statistically significant depressions (about 8-11%) in ATP levels were observed with all field conditions; however, respiration was significantly decreased only when amoebae were subjected to either combined fields or electric fields alone. Magnetic fields alone failed to induce a significant decrease in respiration.     

Relationship between field strength and arousal response in mice exposed to 60-Hz electric fields

White-footed mice, Peromyscus leucopus, were exposed to 60-Hz electric fields to study the relationship between field strength and three measures of the transient arousal response previously reported to occur with exposures at 100 kV/m. Five groups of 12 mice each were given a series of four 1-h exposures, separated by an hour, with each group exposed at one of the following field strengths: 75, 50, 35, 25, and 10 kV/m; 8 additional mice were sham-exposed with no voltage applied to the field generator. All mice were experimentally naive before the start of the experiment, and all exposures occurred during the inactive (lights-on) phase of the circadian cycle. The first exposure produced immediate increases in arousal measures, but subsequent exposures had no significant effect on any measure. These arousal responses were defined by significant increases of gross motor activity, carbon dioxide production, and oxygen consumption, and were frequently recorded with field strengths of 50 kV/m or higher. Significant arousal responses rarely occurred with exposures at lower field strengths. Responses of mice exposed at 75 and 50 kV/m were similar to previously described transient arousal responses in mice exposed to 100-kV/m electric fields. Less than half of the mice in each of the field strength groups below 50 kV/m showed arousal responses based on Z (standard) scores, but the arousals of the mice that did respond were similar to those of mice exposed at higher field strengths. Polynomial regression was used to calculate the field strength producing the greatest increases for each of the arousal measures. The results show that the amplitude of the transient arousal response is related to the strength of the electric field, but different measures of arousal may have different relationships to field strength.     

Cyclic AMP response in cells exposed to electric fields of different frequencies and intensities

The action on intracellular cyclic AMP (cAMP) of therapeutically used 4000-Hz electric fields was investigated and compared with 50-Hz data. Cultured mouse fibroblasts were exposed for 5 minutes to 4000-Hz sine wave internal electric fields between 3 mV/m and 30 V/m applied within culture medium. A statistically significant decrease in cellular cAMP concentration relative to unexposed cells was observed for fields higher than 10 mV/m. The drop in cAMP was most pronounced at lower field strengths (71 % of controls at 30 mV/m) and tended to disappear at higher field strengths. An increase of cAMP content was observed with 50-Hz electric fields, as was also the case when 4000-Hz fields were modulated with certain low frequencies.     

Modulation of tendon fibroplasia by exogenous electric currents

A chicken tendon explant model system has been developed to investigate the effects of extremely-low-frequency (ELF), low-amplitude, unipolar, square wave pulsed electric fields on fibroplasia in vitro. An electric field parameter set consisting of 1-Hz, 1-ms duration pulses, with a time-averaged current density of 7 mA/m2 (peak current density 7 A/m2) induced maximal (32%) increase in fibroblast proliferation in tendon explants exposed for 4 days. Exposure to the same field at an average current density of 1.8 mA/m2 had no effect on fibroblast proliferation, whereas exposure to current densities on greater than 10 mA/m2 inhibited proliferation and relative collagen synthesis, without affecting noncollagen protein synthesis. Fibroplasia was significantly increased in explants oriented parallel to applied electric fields having current densities of 3.5 or 7 mA/m2, but there was no detectable effect on explants oriented perpendicular to the same electric field. Fibroblast proliferation and relative collagen synthesis were inversely proportional to donor age for chickens in the 3- to 16-week age group used in this study. For these dependent variables (proliferation and relative collagen synthesis), there was no interaction between donor age and ELF electric field exposure.     

Hematologic and serum chemistry studies in rats exposed to 60-Hz electric fields

Numerous hematologic and serum chemistry variables were examined in rats exposed to unperturbed 60-Hz electric fields at 100 kV/m for 15, 30, 60, or 120 days. Each study was replicated once. Rigorous statistical evaluations of these data did not detect any consistent effect of the electric field for exposures of up to 120 days. It was, however, not unusual in any individual study to detect certain variables that were significantly different between the exposed and sham-exposed animals. This emphasizes the need for replicate designs and appropriate statistical analyses when investigating chemical or physical insults that may have minimal influence on biologic function.     

Comparison of the coupling of grounded humans,swine and rats to vertical, 60-Hz electric fields

Published and new data for grounded humans, swine, and rats exposed to vertical, 60-Hz electric fields are used to determine field strengths at the surfaces of the bodies and average components of induced-current density along the axes of the bodies. At the tops of the bodies, surface electric fields are increased (enhanced) over the unperturbed field strength present before the subjects entered the field by factors of 17,7, and 4 for humans, swine, and rats, respectively. For an unperturbed field strength of 10 kV/m, average induced axial current densities in the neck, chest, abdomen, and feet are: 550, 190, 250, and 2000 nA/cm², respectively, for humans; 40, 13, 20, and 1100 nA/cm², respectively, for swine; and 28, 16, 2, and 1400 nA/cm², respectively, for rats. These data are used to show that the actual electric fields experienced by animals depend strongly on the shape of the body and its orientation relative to the electric field and ground plane. This fact must be taken into account if biological data obtained with laboratory animals are to be used for the assessment of possible hazards to humans exposed to 60-Hz electric fields.     

Teratogenic effects of sinusoidal extremely low frequency electromagnetic fields on morphology of 24 hr chick embryos

To examine the potential teratogenicity of electromagnetic fields (EMF; sinusoidal and rectangular) on development of chick embryos (white leghorn), 221 freshly fertilized chicken eggs (55-65 g) were exposed during first 24 hr of postlaying incubation (38 degrees +/- 0.5 degree C) to 24 different EMFs, with 50Hz repetition rate and 8.007-10.143 mT flux density. Following exposure, the exposed fertilized chicken eggs (n = 8-10) and sham-exposed fertilized chicken eggs (n = 15) were incubated simultaneously for 8 more days and unexposed control fertilized chicken eggs (n = 20) for 9 days in absence of EMFs. The embryos were removed from egg shells and studied blind. All 24 EMF exposed-groups (inside the coil with exposure) showed an increase in the percentage of developmental anomalies compared to sham-exposed (inside the coil with no exposure) and control groups (outside the coil). Further, egg's weight was evaluated on day 9. This variable did not show significant difference between control and exposed-groups. The investigation also covered the measurement of body weight, length of crown to rump, length of tip of the beak to occipital bone, heart and liver weight. Statistical comparison between sham-exposed and control values did not show significant differences, but comparison between 8.007, 8.453 and 8.713 mT exposed-groups and control groups showed significant differences; in other exposed-groups, the changes were not significant. These results revealed that 50 Hz electromagnetic fields can induce irreversible developmental alterations in 24 hr chick embryos and confirm that its strength could be a determinant factor for the embryonic response to extremely low frequency electromagnetic fields (window effects).     

Perinatal exposure to 60-Hz electric fields: Effects on the development of the visual-evoked response in rats

Two independent series of experiments were performed on 114 male Sprague-Dawley derived, albino rat pups, which represented 61 litters in experimental series I and 53 litters in experimental series II. Animals were exposed for 20 h/day from conception to testing (postnatal days 11–20) to a vertical, 65-kV/m, 60-Hz electric field or sham-exposed. Recordings of the visual-evoked response (VER) were obtained using a small silver ball electrode placed epidurally over the visual cortex. Visual stimuli consisted of 10-μS light flashes delivered at 0.2 Hz. Computer-averaged VERs were obtained and power spectral analyses (fast Fourier transform) were performed on the tapered (split cosine-bell window), averaged VERs. The expected age-related changes were clearly evident; however, a detailed analysis of VER component latencies, peak-to-peak amplitude, and power spectra failed to reveal any consistent, statistically significant effect of exposure to 60-Hz electric fields.