Exposure to time varying magnetic fields associated with magnetic resonance imaging reduces fentanyl-induced analgesia in mice

The effects of exposure to clinical magnetic resonance imaging (MRI) on analgesia induced by the mu opiate agonist, fentanyl, was examined in mice. During the dark period, adult male mice were exposed for 23.2 min to the time-varying (0.6 T/sec) magnetic field (TVMF) component of the MRI procedure. Following this exposure, the analgesic potency of fentanyl citrate (0.1 mg/kg) was determined at 5, 10, 15, and 30 min post-injection, using a thermal test stimulus (hot-plate 50 degrees C). Exposure to the magnetic-field gradients attenuated the fentanyl-induced analgesia in a manner comparable to that previously observed with morphine. These results indicate that the time-varying magnetic fields associated with MRI have significant inhibitory effects on the analgesic effects of specific mu-opiate-directed ligands.     

50 Hz magnetic fields of 1 mT do not promote lymphoma development in AKR/J mice

Some epidemiological studies suggest that exposure to power-frequency magnetic fields increases the risk of leukemia, especially in children with high residential exposures. In contrast, most animal studies did not find a correlation between magnetic-field exposure and hematopoietic diseases. The present study was performed to investigate whether chronic, high-level (1 mT) magnetic-field exposure had an influence on lymphoma development in a mouse strain that is genetically predisposed to thymic lymphoblastic lymphoma. Three groups of 160 unrestrained female AKR/J mice were sham-exposed or exposed to sinusoidal 50 Hz magnetic fields beginning at the age of 12 weeks for 32 weeks, 7 days per week, either for 24 h per day or only during nighttime (12 h). Exposure was carried out in a blind design. Exposure did not affect survival time, body weight, lymphoma development or hematological parameters. The resulting data do not support the hypothesis that exposure to sinusoidal 50 Hz magnetic fields is a significant risk factor for hematopoietic diseases, even at this relatively high exposure level.     

Effects of 100-Hz magnetic fields with various waveforms on the development of chick embryos

Summary Chick embroys were exposed during their 52 first hours of development to 100-Hz magnetic fields. Sinusoidal, square and pulsed waveforms were used at average field strengths from 0.1 A/m to 80 A/m. After exposure, the embryos were examined for abnormalities and classified by the developmental stages. When bipolar oscillations (oscillating at both sides of the zero-level) were used, the percentage of abnormal embryos was significantly increased above 1 A/m. In exposure to unipolar square waves, no significant effect on the percentage of abnormalities could be demonstrated. The developmental stage was possibly affected by unipolar square waves at 0.1 A/m, all other field strengths and wave-forms being apparently ineffective.     

Effects of permanent magnetic fields on in vitro growth of Cymbidium and Spathiphyllum shoots

Magnetic fields affect biological systems. However, this is the first study on the effects of permanent magnetic fields (MFs) on the micropropagation of two ornamental plants, Spathiphyllum cv. i.e ‘Merry’ and Cymbidium Music Hour ‘Maria’. Cymbidium and Spathiphyllum shoots cultured in the ‘Miracle Pack’? culture system were exposed to MFs of different intensities, polarities, and duration of exposure. The results show that by increasing intensity from 5 × 10⁻⁶ Tesla (T) as the geo-magnetic field to 0.1, 0.15, and 0.2 T negatively influenced height and fresh mass of roots of Cymbidium plants (except for 0.1 T–S and 0.2 T–N treatments), but had no significant effect on other plantlet parameters. Long-term exposure (1, 2, or 3 mo) of Cymbidium shoots to 0.15 T–MFs negatively influenced plant height, positively affected the number of leaves (with the exception of 0.15 T–S—1 mo), and had no clear effect on other parameters compared to the control. MFs (0.1, 0.15, and 0.2 T), regardless of their polarity, increased chlorophyll content (SPAD value) and the number of leaves, but slightly decreased the dry mass of Spathiphyllum shoots. Different exposure duration to 0.15 T (i.e., 2, 4, or 8 wk) had no significant influence on Spathiphyllum plantlet development other than increasing the SPAD value. These two ornamentals could serve as model systems to study plant development, space production, yield maximization, and the development of new morphotypes essential for the floricultural market.     

Effects of weak magnetic fields on the production of reactive oxygen species in peritoneal neutrophils in mice

The influence of weak magnetic fields of different types on the rate of the formation of reactive oxygen species in mouse peritoneal neutrophils has been studied. It was found that the exposure of neutrophils activated by phorbol 12-myristate 13-acetate to the magnetic field tuned to the parametric resonance for Ca2+ ions leads to a decrease in the rate of the reactive oxygen species (ROS) generation by 23%. Conversely, the generation of ROS in neutrophils exposed to the same field but stimulated by the bacterial peptide FMLP (N-formyl-L-methionyl-L-leucyl-L-phenylalanine) increased by about 21%. Pulsed magnetic fields also changed the rate of ROS generation in phorbol-stimulated neutrophils by about 20%, but the sign of the effects observed in this case was opposite to those induced by the magnetic field tuned to the parametric resonance for Ca2+ ions.     

Transmission of time varying magnetic field through body tissue

Based on the principles of interaction of electromagnetic waves with semi-infinite media, a simplified model is developed for the study of biological tissue — EM wave interaction problems. The four common types of biological tissues viz, bone, blood, alveolar and muscle tissue, each in turn has been considered. Expression for the transmission loss of the incident EM waves have been derived and numerically evaluated. The results indicate that there is a frequency dependence of the transmission loss and variations with tissue type exist and that losses become significant above 30 MHz. Attenuation for muscular tissue is maximum at frequencies of about 200 MHz whereas the corresponding frequency for lung tissue is nearly the double. Suitable experiments have been designed and performed to verify the salient results of the model and a fair degree of agreement has been found between the experimental results and theoretical predictions. Possibilities for the improvement of the model and future applications of the model have been outlined.     

Effects of static magnetic fields on diffusion in solutions

Static magnetic fields affect the diffusion of biological particles in solutions through the Lorentz force and Maxwell stress. These effects were analyzed theoretically to estimate the threshold field strength for these effects. Our results show that the Lorentz force suppresses the diffusion of charged particles such as Na+, K+, Ca2+, Cl-, and plasma proteins. However, the threshold is so high, i.e., more than 10(4) T, that the Lorentz force does not affect the ion diffusion at typical field strengths (a few Tesla at most). Since the threshold of gradient fields for producing a change in ion diffusion through the Maxwell stress is more than 10(5) T2/m for paramagnetic molecules (FeCl3, O2) and plasma proteins, their diffusion would be unaffected by typical gradient fields (100 T2/m at most) and even by high gradient fields (less than 10(5) T2/m) used in magnetic separation techniques. In contrast, movement of deoxygenated erythrocytes and FeCl3 colloids (more than 10(3) molecules) is influenced by the usual gradient fields due to a volume effect.     

Effects of time-varying uniform magnetic fields on Natural Killer cell activity and antibody response in mice

Natural Killer cell activity and antibody response were studied in Balb/c mice which were exposed in vivo to uniform pulsed magnetic fields (square-wave, 0.8 Hz, 120 mT maximum field strength, 0.1 s rise-time) for 5 days, 10 h/day. No effects were found in antibody response to sheep red blood cell (SRBC) immunization as assayed by counting the plaque-forming cells (PFC) in the spleens of animals on the sixth day. Following 5-day exposures, the activity of Natural Killer (NK) cells was measured in vitro by challenge with YAC-1 cells, in experiments in which mice were not immunized. An increase of NK cytotoxic activity due to exposure was found which depended on the age of the mice (effect observed above 12 weeks) and on the strength of the applied field (effect observed above 30 mT). © 1993 Wiley-Liss. Inc.     

Micronuclei in the blood and bone marrow cells of mice exposed to specific complex time‐varying pulsed magnetic fields

For 8 weeks, adult CD‐1 male mice were continuously exposed to complex time‐varying pulsed magnetic fields (PMF) generated in the horizontal direction by a set of square Helmholtz coils. The PMF were <1000 Hz and delivered at a peak flux density of 1 mT. Sham‐exposed mice were kept in a similar exposure system without a PMF. Positive control animals exposed to 1 Gy gamma radiation were also included in the study. Blood samples were collected before (time 0) and at 2, 4, 6, and 8 weeks. All mice were euthanized at the end of 8 weeks and their bone marrow was collected. From each blood and bone marrow sample, smears were prepared on microscope slides, fixed in absolute methanol, air‐dried, and stained with acridine orange. All slides were coded and examined using a fluorescence microscope. The extent of genotoxicity and cytotoxicity was assessed from the incidence of micronuclei (MN) and percent polychromatic erythrocytes (PCE) in the blood and bone marrow, respectively. The data indicated that both indices in PMF‐exposed mice were not significantly different from those observed in sham‐exposed animals. In contrast, positive control mice exhibited significantly increased MN, and decreased percentages of PCE in both tissues. Thus, the overall data suggested that 8 weeks of continuous exposure to PMF did not induce significantly increased genotoxicity and cytotoxicity in experimental mice. Further investigations are underway using other genotoxicity assays (comet assay, γ‐H2AX foci, and chromosomal aberrations) to assess genotoxicity following PMF exposure. Bioelectromagnetics 31:445–453, 2010. © 2010 Wiley‐Liss, Inc.     

Effects of magnetic fields on fyke net performance

The effects of magnetic fields generated by ferritic magnets and mounted in entrances to fyke nets were studied in 1999–2002. With respect to all fish species trapped (perch, pike, roach, rudd, bleak, bream, ruffe) except eel, the catch potential of magnet‐rigged fyke nets was found to be significantly higher (almost 50% on average) when compared with controls. Differences in magnet placement (N or S poles inside the traps) proved to have no significant importance on the number of fish that chose to enter the fyke nets. Specific behavioural mechanisms in adult fish towards magnetic fields as well as application of fishing gear magnet rigging in fisheries practice in inland waters are discussed.     

Effects of extremely-low-frequency magnetic fields on biological magnetite

Adair [Bioelectromagnetics 14:1–4, 1993] writes that “the effects of 60 Hz magnetic fields of 5 μT (50 mG) or less on biological structures holding magnetite (Fe₃O₄) are shown to be much smaller than those from thermal agitation; hence such interactions cannot be expected to be biologically significant.” This conclusion is questioned, because it appears to be based on a model that probably has very limited validity for pertinent biological systems. Furthermore, biologically plausible parameters can be selected to show that even this particular model does not exclude biologically significant effects of 60 Hz magnetic fields below 5 μT. Reported experimental results indicate effects in mammals of 50 Hz fields at the 1 μT level. © 1994 Wiley-Liss, Inc.     

Effects of ELF magnetic fields on biological magnetite

The effects of 60 Hz magnetic fields of 5 μT (50 mG) or less on biological structures holding magnetite (Fe₃O₄) are shown to be much smaller than that from thermal agitation; hence such interactions cannot be expected to be biologically significant. © 1993 Wiley-Liss, Inc.     

Effect of magnetic fields on tumor growth and viability

Breast cancer is the most common nonskin cancer and is the second leading cause of cancer-related deaths in women. Most methods of intervention involve combinations of surgery, chemotherapy, and ionizing radiation. Both chemotherapy and ionizing radiation can be effective against many types of cancer, but they also harm normal tissues. The use of nonionizing, magnetic fields has shown early promise in a number of in vitro and animal studies. Our study tested the effect of varying durations of magnetic exposure on tumor growth and viability in mice injected with breast cancer cells. Cancer cells were labeled through stable expression of firefly luciferase for monitoring of tumor growth and progression by using an in vivo imaging system. We hypothesized that magnetic field exposure would influence tumor growth and progression. Our results showed that exposure of the mice to magnetic fields for 360 min daily for as long as 4 wk suppressed tumor growth. Our study is unique in that it uses an in vivo imaging system to monitor the growth and progression of tumors in real time in individual mice. Our findings support further exploration of the potential of magnetic fields in cancer therapeutics, either as adjunct or primary therapy.     

Effects of pulsed magnetic fields on the developing mouse embryo

The influence of a pulsed magnetic field (PMF; sawtooth with 45-μs linear rise time and 5-μs decay time, peak strength of 15 μT, and frequency 20 pps) on the embryogenesis of CBA/S mice was investigated in five experiments based on a total of 707 exposed and 543 unexposed primigravidas. Sham and PMF exposures began on day 1 of gestation (experiments 1 and 2), on day 2 (experiment 3), on day 5 (experiment 4). and on day 7 (experiment 5): all exposures continued until day 19 post conception (p.c.) when they were terminated, at which time the following variables were measured: number of implants; number of placental resorptions; number of living fetuses; number of dead fetuses; number of malformations in living and dead fetuses; and length and body mass of living fetuses. Control dams were sham-exposed concurrently with corresponding. PMF-exposed dams. With the exception of experiment 5, in which exposure to PMF started on day 7 p.c., all groups of exposed mice had significantly more placental resorptions when compared with concurrent controls. The increased resorption rate was not reflected in a reduction in litter size or in the number of litters. A significant increase in malformed fetuses was not seen in any of the exposed groups, or when groups were pooled. Only in experiment 1 was the number of dead fetuses affected by exposure to PMF. The effect of PMF on the implantation rate was not significant. Body mass and length of exposed fetuses were significantly reduced only when the PMF treatment began on day 7 p.c. That PMF-treated mice had significantly more placental resorptions when exposure began on day 5 p.c. or earlier (before implantation), but not when exposure began on day 7 (after implantation), may indicate a causative pre-implantation effect. Because a PMF-induced increase in the number of resorptions has not been observed in other strains of mice, the effect might be strain-related. © 1993 Wiley-Liss, Inc.     

Exposure of maize seeds to stationary magnetic fields: Effects on germination and early growth

The effect of the exposure of maize seeds to stationary magnetic fields on germination and early growth has been studied under laboratory conditions. Seeds were magnetically exposed to one of two magnetic field strengths, 125 or 250 mT for different periods of time. Mean germination time and the time required to obtain 10, 25, 50, 75 and 90% of seeds to germinate were calculated. The results showed a reduction of these parameters for most of magnetic treatments, therefore their rate of germination was increased.Growth data measured on the 7th and 10th day after seeding allowed us to corroborate the effect observed in germination tests. Treated plants grew higher and heavier than control; on the 10th day total length was greater than control plants exposed to stationary magnetic field, corresponding with increase of the total fresh weight. The greatest increases were obtained for plants continuously exposed to 125 or 250 mT.     

Effects of low-frequency magnetic fields on fetal development in rats

We studied effects of alternating magnetic fields on the embryonic and fetal development of rats. Mated females of the Han:Wistar-strain were sham exposed or exposed continuously to a 50-Hz field or to a 20,000 pulse-per-second (pps) sawtooth magnetic field from day 0 to day 20 of pregnancy for 24 h/day until necropsied on day 20. The respective peak-to-peak intensities of the fields were 35.6 μT (sinewave) and 15.0 μT (sawtooth). Each treatment group contained 72 bred females. Control animals were kept under the same conditions without the magnetic field. No adverse effects were seen in the dams. The mean numbers of implantations and living fetuses per litter were statistically significantly increased in the 50-Hz group. There were, however, three total resorptions of litters in dams of the control group, which contributed to the difference in the number of living fetuses. The corrected body-mass gains (gains without uterine content) of dams were similar in all groups. Pregnancy rates, incidences of resorptions. late fetal deaths, and fetal body masses were similar in all groups. The incidence of fetuses with minor skeletal anomalies was statistically significantly increased in both exposed groups. Only one serious malformation (anophthalmia, sawtooth-exposed group) and a few minor visceral malformations were found. In conclusion, the magnetic fields used in this study did not increase the incidence of major malformations or resorptions in Wistar rats. The increased number of skeletal anomalies and implantations we observed indicates, however, that some developmental effects in rats may attend exposure to time-varying magnetic fields. © 1993 Wiley-Liss. Inc.     

Effects of pulsed extremely-low-frequency magnetic fields on skin wounds in the rat

Rats with skin-wounds surgically created on their backs were exposed immediately after surgery and every 12 h thereafter to pulsed, extremely-low-frequency magnetic fields. The shape of the pulse was a positive triangle (50 Hz, 8 mT peak). The rate of healing of skin wounds was evaluated macroscopically and by light and electron microscopy at 6, 12, 21, and 42 days after the operation. A significant increase in the rate of wound contraction was found in rats treated with magnetic fields. Forty-two days after surgery all treated animals show fully closed wounds, while control rats at the same time intervals still lacked a final 6% of the wound surface to be covered. Treated rats showed earlier cellular organization, collagen formation and maturation, and a very early appearance of newly formed vascular network.     

Effect of static magnetic fields on survival of leukaemia-prone AKR mice

Summary The influence of a life-long exposure to static magnetic fields (SMF) on the lifespan of female AKR mice which develop spontaneous lymphoblastic leukaemia was investigated. Exposure all day long to a circular SMF, 4.6 mT maximal intensity or 2 h a day, 5 consecutive days a week to a uniform SMF of 400 mT did not modify the lifespan of mice. Exposure 2 h a day, 5 consecutive days a week to a uniform SMF of 600 or 800 mT modified the lifespan: about 50% of the population had a longer survival than the controls. Mice exposed 30 min a day 5 consecutive days a week to a non-uniform SMF presented the same trend.     

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.