Biological effects of low-frequency pulsed magnetic fields on the embryonic central nervous system development. A histological and histochemical study

Numerous experiments have yielded contradictory results on the harmful action of magnetic fields on embryonic development. Pulsed magnetic fields appear to be able to delay normal development of embryos. In the present study, fertilized Gallus domesticus eggs were exposed during incubation to pulsed magnetic fields (harmonic signals of 10 μT for 1 second with silences of 0.5 seconds) of 50 or 100 Hz frequency. Embryos extracted at 45 h of exposure to fields of 50 Hz or 100 Hz frequency had significantly (p<0.05) fewer somite pairs compared with controls of the same age. At 15 days of incubation, only embryos exposed to a 10 μT- 50 Hz field had a significantly (p<0.05) higher somatic weight. At 21 days of incubation, a significantly lower somatic weight (p<0.01) and development stage (p<0.05) was found in embryos exposed to a 10 μT-100 Hz field than in controls, while a lower development stage (p<0.05) alone was observed in those exposed to a 10 μT-50 Hz field. In addition, animals showed higher expression of the neural marker NSE (neural specific enolase) after 21 days of development as determined by immunohistochemistry, with very low expression of glycosaminoglycans identified by alcyan blue staining. These results suggest that pulsed magnetic fields may be able to hinder normal embryonic development in vivo and to alter normal neural function, at least at the intensities and frequencies analyzed in the present study.     

Environmental magnetic fields: Influences on early embryogenesis

A 10-mG, 50 to 60-Hz magnetic field is in the intensity and frequency range that people worldwide are often exposed to in homes and in the workplace. Studies about the effects of 50- to 100-Hz electromagnetic fields on various species of animal embryos (fish, chick, fly, sea urchin, rat, and mouse) indicate that early stages of embryonic development are responsive to fluctuating magnetic fields. Chick, sea urchin, and mouse embryos are responsive to magnetic field intensities of 10–100 mG. Results from studies on sea urchin embryos indicate that exposure to conditions of rotating 60-Hz magnetic fields, e.g., similar to those in our environment, interferes with cell proliferation at the morula stage in a manner dependent on field intensity. The cleavage stages, prior to the 64-cell stage, were not delayed by this rotating 60-Hz magnetic field suggesting that the ionic surges, DNA replication, and translational events essential for early cleavage stages were not significantly altered. Studies of histone synthesis in early sea urchin embryos indicated that the rotating 60-Hz magnetic field decreased zygotic expression of “early” histone genes at the morula stage and suggests that this decrease in early histone production was limiting to cell proliferation. Whether these comparative observations from animal development studies will be paralleled by results from studies of human embryogenesis, as suggested by some epidemiology studies, has yet to be established.     

A simple experiment to study electromagnetic field effects: Protection induced by short-term exposures to 60 Hz magnetic fields

Stress proteins are important in protection during cardiac ischemia/reperfusion (cessation and return of blood flow) and are reportedly induced by electromagnetic (EM) fields. This suggests a possible ischemia protection role for EM exposures. To test this, chick embryos (96 h) were exposed to 60 Hz magnetic fields prior to being placed into anoxia. Survival was 39.6% (control), and 68.7% (field-exposed). As a positive control, embryos were heated prior to anoxia (57.6% survival). We conclude that: 1) 60 Hz magnetic field exposures reduce anoxia-induced mortality in chick embryos, comparable to reductions observed following heat stress, and 2) this is a simple and rapid experiment to demonstrate the existence of weak EM field effects. Bioelectromagnetics 19:498–500, 1998. © 1998 Wiley-Liss, Inc.     

Applied AC and DC magnetic fields cause alterations in the mitotic cycle of early sea urchin embryos

This study demonstrates that exposure to 60 Hz magnetic fields (3.4–8.8 mT) and magnetic fields over the range DC-600 kHz (2.5–6.5 mT) can alter the early embryonic development of sea urchin embryos by inducing alterations in the timing of the cell cycle. Batches of fertilized eggs were exposed to the fields produced by a coil system. Samples of the continuous cultures were taken and scored for cell division. The times of both the first and second cell divisions were advanced by ELF AC fields and by static fields. The magnitude of the 60 Hz effect appears proportional to the field strength over the range tested. The relationship to field frequency was nonlinear and complex. For certain frequencies above the ELF range, the exposure resulted in a delay of the onset of mitosis. The advance of mitosis was also dependent on the duration of exposure and on the timing of exposure relative to fertilization. © 1995 Wiley-Liss, Inc.     

Development of chick embryos in 1 Hz to 100 kHz magnetic fields

Summary Chick embryos were exposed during their 48 first hours of development to sinusoidally oscillating magnetic fields. The frequencies 1 Hz, 10 Hz, 16.7 Hz, 30 Hz, 50 Hz, 1 kHz, 10 kHz and 100 kHz, and the field strengths 0.1, 1, 10 and 100 A/m were used. Each exposure group consisted of 20 eggs. After the exposure, the embryos were examined for abnormalities and classified by the developmental stage. The percentage of abnormal embryos (%AE) was significantly increased at frequencies from 16.7 Hz to 100 kHz. Above a threshold field strength of about 0.1 to 1 A/m, %AE was rather independent of the field strength, varying from 16% to 56% in different exposure groups. 13% of the sham-exposed control embryos (n = 150) were abnormal. Only the 0.1 A/m exposure group differed significantly from the controls at 1 Hz, and no significant effect was found at 10 Hz. The developmental stage was in general not affected by the magnetic fields, but some abnormal embryos showed retarded development.     

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.     

Ornithine decarboxylase activity in developing chick embryos after exposure to 60-hertz magnetic fields.

Fertilized white leghorn eggs were exposed to a 4 micro-Tesla (microT) 60 Hz horizontal magnetic field for 15, 18, 23 and 28 h. After exposure to the magnetic field, the embryos were isolated and assayed for ornithine decarboxylase (ODC) activity. ODC activity in magnetic field-exposed embryos was compared to ODC activity in sham-exposed embryos. ODC activity in magnetic field-exposed embryos was not statistically elevated above sham-exposed embryos.     

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.     

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.     

Mouse early embryos obtained by natural breeding or in vitro fertilization display a differential sensitivity to extremely low-frequency electromagnetic fields

We have investigated the sensitivity of pre-implantation embryos obtained by natural breeding (NB) or in vitro fertilization (IVF) to extremely low-frequency magnetic fields (ELF-MF). Fertilized eggs obtained by NB were removed from mothers 12h after mating and cultured in vitro for 5 days under continuous ELF-MF exposure (constant strength of 50Hz and various intensities, i.e. 60, 120 and 220 microT). Alternatively, zygotes obtained by IVF were subjected to ELF-MF exposure (50Hz, 60 microT), starting 12h after IVF for 5 days. We found that ELF-MF exposure causes a small yet significant (P<0.05) decrease in the survival rate of NB-derived embryos at the latest stages of pre-implantation development, i.e. the eight cell-to-blastocyst transition. In embryos exposed to the highest field intensity (220 microT), the effect became apparent somewhat earlier. When IVF-derived embryos were exposed to ELF-MF, the reduction in the rate of embryo survival was more pronounced and the difference from controls was more significant (P<0.01). Moreover, the decreased survival rate in IVF embryos became apparent as early as the first cleavage and persisted throughout pre-implantation. These results suggest that IVF-derived embryos are more sensitive than NB-generated embryos to ELF-MF, and that this sensitivity occurs earlier in development.     

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).     

Lack of chick embryotoxicity after 20 kHz, 1.1 mT magnetic field exposure

This investigation was undertaken because biological studies to evaluate the effects of intermediate frequency magnetic fields are insufficient. White Leghorn fertile eggs (60/group) were either exposed to a 20 kHz, 1.1 mT(rms) sinusoidal magnetic field or sham‐exposed during the first 2, 7, or 11 days of embryogenesis. Lower dose exposures at 0.011 and 0.11 mT(rms) for 2 days were also conducted to elucidate possible dose–response relationships. Additional eggs given all‐trans‐retinoic acid, a teratogen, were exposed to the 1.1 mT(rms) magnetic field for the same periods to investigate the modification of embryotoxicity. After exposure, embryos were examined for mortality and developmental abnormalities. Developmental stage, number of somite pairs, and other developmental endpoints were also evaluated. Experiments were triplicated and conducted in a blind fashion. No exposure‐related changes were found in any of the endpoints in intact embryos exposed to1.1 mT(rms) or to the lower doses of 0.11 and 0.011 mT(rms) magnetic fields. Retinoic acid administration produced embryotoxic responses, which were embryonic death and developmental abnormalities, in 40–60% of embryos in the sham‐exposed groups. The magnitude of these responses was not changed significantly by the magnetic field exposures. Under the present experimental conditions, exposure to 20 kHz magnetic field up to 1.1 mT(rms) was not embryotoxic in the chick and did not potentiate the embryotoxic action of retinoic acid. Bioelectromagnetics 30:573–582, 2009. © 2009 Wiley‐Liss, Inc.     

Electric fields induced in chicken eggs by 60-Hz magnetic fields and the dosimetric importance of biological membranes.

Chicken eggs are convenient models for observing the effects of inhomogeneities and variations, such as those found in biological membranes and in cellular conductivities, on the distribution of internal electric fields as induced by exposure to magnetic fields. The vitelline membrane separates the yolk, which has a conductivity of 0.26 S/m, from the white, which has a conductivity of 0.85 S/m. A miniaturized probe with 2.4-mm resolution was used to measure induced fields in eggs placed in a uniform, 1-mT magnetic field at 60 Hz. The E fields induced in eggs with homogenized contents agreed with expectations based on simple theory. Results were similar to intact eggs unless the probe moved the yolk off-center, which greatly perturbed the induced fields. A more reproducible arrangement, which consisted of saline-agar filled dishes with a hole cut for test samples, was developed to enhance definition of electrical parameters. With this test system, the vitelline membrane was found to be responsible for most of the perturbation of the induced field, because it electrically isolates the yolk from the surrounding white. From a theoretical viewpoint, this dosimetry for the macroscopic egg yolk is analogous to the interaction of fields with microscopic cells. These findings may have important implications for research on biological effects of ELF electromagnetic fields, especially for studies of avian embryonic development.     

Effect of electric power network frequency magnetic field on embryonic development of Ascaris suum (Nematoda)

Fertilised Ascaris suum eggs were subjected to an alternating electromagnetic field of frequency 50 Hz and density 2 mT for 60 days. The developing embryos in both control and experimental cultures were examined daily under a microscope. The experiment resulted in an accelerated rate of embryogenesis in the eggs incubated in the electromagnetic field, higher rates of malformed embryos as well as much higher mortality rate of L2 larvae.     

The superposition of a temporally incoherent magnetic field inhibits 60 Hz-induced changes in the ODC activity of developing chick embryos

Previously, we have shown that the application of a weak (4 μT) 60 Hz magnetic field (MF) can alter the magnitudes of the ornithine decarboxylase (ODC) activity peaks which occur during gastrulation and neurulation of chick embryos. We report here the ODC activity of chick embryos which were exposed to the superposition of a weak noise MF over a 60 Hz MF of equal (rms strength). In contrast to the results we obtain with a 60 Hz field alone, the activity of ODC in embryos exposed to the superposition of the incoherent and 60 Hz fields was indistinguishable from the control activity during both gastrulation and neurulation. This result adds to the body of experimental evidence which demonstrates that the superposition of an incoherent field inhibits the response of biological systems to a coherent MF. The observation that a noise field inhibits ODC activity changes is consistent with our speculation that MF-induced ODC activity changes during early development may be related to MF-induced neural tube defects at slightly later stages (which are also inhibited by the superposition of a noise field). Bioelectromagnetics 19:53–56, 1998. © 1998 Wiley-Liss, Inc.     

Effect of low-level, 60-Hz electromagnetic fields on human lymphoid cells: I. Mitotic rate and chromosome breakage in human peripheral lymphocytes

Dividing human peripheral lymphocytes from 10 normal adults (5 males and 5 females) were exposed in vitro to low level 60-Hz electromagnetic fields for 69 hours. The current density of the electrical field was 30 microA/cm2, while the magnetic field was either 1 or 2 gauss. The cytological endpoints measured were mitotic rate and chromosome breakage. No statistically significant differences, indicative of a field effect, were observed between treated and control cells whether exposed to an electric field, a magnetic field, or to various combinations of the two.     

Biological effects of power frequency magnetic fields: Neurochemical and toxicological changes in developing chick embryos

BACKGROUND: There are several reports that indicate a linkage between exposure to power frequency (50 - 60 Hz) magnetic fields with abnormalities in the early embryonic development of the chicken. The present study was designed to understand whether power frequency electromagnetic fields could act as an environmental insult and invoke any neurochemical or toxicological changes in developing chick embryo model. METHODS: Fertilized chicken eggs were subjected to continuous exposure to magnetic fields (50 Hz) of varying intensities (5, 50 or 100 microT) for a period of up to 15 days. The embryos were taken out of the eggs on day 5, day 10 and day 15. Neurochemical (norepinephrine and 5-hydroxytryptamine) and amino acid (tyrosine, glutamine and tryptophan) contents were measured, along with an assay of the enzyme glutamine synthetase in the brain. Preliminary toxicological investigations were carried out based on aminotransferases (AST and ALT) and lactate dehydrogenase activities in the whole embryo as well as in the liver. RESULTS: The study revealed that there was a significant increase (p < 0.01 and p < 0.001) in the level of norepinephrine accompanied by a significant decrease (p < 0.01 and p < 0.001) in the tyrosine content in the brain on day 15 following exposure to 5, 50 and 100 microT magnetic fields. There was a significant increase (p < 0.001) in glutamine synthetase activity resulting in the significantly enhanced (p < 0.001) level of glutamine in the brain on day 15 (for 100 microT only). The possible mechanisms for these alterations are discussed. Further, magnetic fields had no effect on the levels of tryptophan and 5-hydroxytryptamine in the brain. Similarly, there was no effect on the activity of either aminotransferases or lactate dehydrogenase in the whole embryo or liver due to magnetic field exposure. CONCLUSIONS: Based on these studies we conclude that magnetic field-induced changes in norepinephrine levels might help explain alterations in the circadian rhythm, observed during magnetic field stress. Also, the enhanced level of glutamine can act as a contributing factor for developmental abnormalities.     

Increased dexamethasone-induced apoptosis of thymocytes from mice exposed to long-term extremely low frequency magnetic fields

To address the effect of extremely low frequency electromagnetic fields on programmed cell death we assessed both the spontaneous and dexamethasone (Dex)-induced apoptosis of thymocytes and spleen cells from mice submitted to a long-term continuous exposure of a 0.4–1.0 μT 60 Hz magnetic field or an 8–20 μT direct current (DC) magnetic field. Dex-induced apoptosis but not spontaneous apoptosis was substantially increased in thymocytes from 0.4 to 1.0 μT 60 Hz field-exposed animals. Spontaneous apoptosis and Dex-induced apoptosis of spleen cells were not affected by the 0.4–1.0 μT 60 Hz field exposure. In addition, spontaneous apoptosis and Dex-induced apoptosis of thymocytes and spleen cells from mice exposed to an 8–20 μT DC field were similar to the controls. These findings represent the first demonstration that thymocytes from mice exposed to a long-term 0.4–1.0 μT 60 Hz field may show abnormal response to Dex apoptotic stimuli. Bioelectromagnetics 19:131–135, 1998. © 1998 Wiley-Liss, Inc.     

Electromagnetic fields in combination with elevated temperatures affect embryogenesis of Drosophila.

The effect of electromagnetic fields (50 Hz, 100 microT magnetic flux density) on Drosophila embryogenesis was tested under conditions of mild thermal stress (temperatures between 34 and 37 degrees C). When exposed to these stressor(s) for 30 min during early embryogenesis those embryos which were subjected to both electromagnetic fields and elevated temperature (costress) showed pattern anomalies more frequently than embryos subjected to thermal stress alone. Furthermore, under costress conditions development was considerably delayed in three different strains tested. The use of transgenic strains with a lacZ reporter being expressed in segmental patterns facilitated the identification and quantification of the pattern anomalies.