Numerical computation of distortions in magnetic fields and induced currents in physiological solutions produced by microscope objectives

Identifying distortions produced by commonly employed microscope objectives and their components in uniform DC and 60 Hz AC magnetic fields is important in imaging studies involving exposure of cells to spatially uniform or nonuniform magnetic fields. In this study, DC and 60 Hz AC magnetic flux densities were numerically computed in the presence of finite element models of various components of commonly utilized microscope objectives, as well as a model of a complete objective. Also computed were the distortions in the current density induced by an applied time-varying magnetic field in a physiological buffer contained within a Petri dish. We show that the magnetic flux density could be increased up to 65% in the presence of the nickel-chrome plating of an objective housing and that the presence of ferromagnetic components like a screw or spring could produce peaks that are 7% higher than the undistorted value of magnetic flux density. In addition, a slight tilt of 1% in the objective with respect to the magnetic field could cause a 93% deviation in magnetic flux density from the unperturbed value. These results correlate well with previously published experimental measurements that showed the presence of significant and sometimes asymmetric distortions in both DC and 60 Hz magnetic fields. Moreover, this study further reports that induced current density changed up to 37% compared to values in the absence of the objective. The existence of distortions in applied magnetic fields and induced currents could affect the interpretation of results of cell function studies if it is assumed that the cells are exposed to uniform magnetic flux densities in the presence of a microscope objective. Such assumptions of uniform magnetic flux density could also account for the lack of reproducibility in several studies that examined changes in intracellular calcium by imaging techniques.     

A scheme for incorporating DC magnetic fields into epidemiological studies of EMF exposure

Experimental data on calcium-ion release in chicken brain tissue suggest that biological effects of electric and magnetic fields (EMFs) are concentrated near certain “active combinations” of DC magnetic field strength and “effective” AC magnetic field frequencies. We hypothesize that active AC/DC combinations may exist and suggest that epidemiologic data, coupled with DC magnetic field measurements, may be used to identify critical exposure conditions. An empirical model is used to calculate these multiple active combinations at any given DC magnetic field strength and to define a rating system that incorporates the proximity of AC magnetic field frequencies generated by electric power lines to the new, computed effective frequencies. Such an exposure score may be useful in investigating correlations of EMF exposure with disease incidence. For 60 Hz and 50 Hz, the highest EMF exposure scores occurred at DC field strengths of 506 mG and 422 mG, respectively. The exposure score contains a factor which may be adjusted to reflect the importance of harmonics of the AC magnetic field as well as of the fundamental frequency. Using this factor, we consider two important special cases consistent with chick brain data: 1) we consider active pairs associated with all detectable harmonics (up to 660 Hz) without regard to relative intensity of the harmonics, and 2) we use the relative intensities of the AC field frequencies to adjust their contribution to the exposure score. © 1993 Wiley-Liss. Inc.     

Effects of static magnetic fields on plasma levels of angiotensin II and aldosterone associated with arterial blood pressure in genetically hypertensive rats

Effects of static magnetic fields (SMFs) on development of hypertension were investigated using young male, stroke resistant, spontaneously hypertensive rats (SHRs) beginning at 7 weeks of age. SHRs were randomly assigned to two different exposure groups or an unexposed group. The SHRs in the exposure groups were constantly exposed to two different types of external SMFs of 3.0-10.0 mT or 8.0-25.0 mT for 12 weeks. The SMFs were generated from permanent magnetic plates attached to the rat cage. The blood pressure (BP) of each rat was determined at weekly intervals using indirect tail-cuff method. The SMFs suppressed and retarded the development of hypertension in both exposed groups to a statistically significant extent for several weeks, as compared with an unexposed group. The antipressor effects were related to the extent of reduction in plasma levels of angiotensin II and aldosterone in the SHRs. These results suggest that the SMFs of mT intensities with spatial gradients could be attributable to suppression of early BP elevation via hormonal regulatory system.     

Effects of prooxidants on human serum exposed to 50 Hz magnetic fields

The purpose of this article is to evaluate magnetic field effects (50 Hz, different magnetic intensities) on the chemiluminescence intensity of human serum. We find that 1 and 2 h of exposure increased the chemiluminescence emission. The addition to the serum of prooxidants FeCl(2) and H(2)O(2) in different concentrations increased the chemiluminescence intensity even more.     

Effect of magnetic field on the accumulation of polyhydroxyalkanoates (PHAs) by microorganism in activated sludge

The effect of static magnetic field on polyhydroxyalkanoates (PHAs) syntheses by activated sludge under aerobic dynamic feeding (ADF) was evaluated in sequence batch reactors (SBR), with magnetic field intensities of 42, 21, 11 and 7 millitesla (mT) exposure in the feast, feast-famine and famine periods, respectively, and one control group without magnetic field exposure. Under each level of magnetic field intensity, the effect of magnetic field exposed in the famine period to PHAs syntheses was most significant in comparison with that in the feast or feast-famine period. Maximal hydroxybutyrate (HB) and (HV) yield occurred at 21 and 11 mT, respectively, and the minimal yield occurred at 42 mT during exposure in the famine period. The maximum biodegradable rate constant of PHA was noted at 11 mT during exposure in the famine period.     

A system for simultaneous exposure of small animals to 60-Hz electric and magnetic fields

Equipment designed for simultaneous exposure of rodents to 60-Hz electric and magnetic fields is described. Three identical systems were constructed, each capable of continuous exposure of 256 rats or 640 mice to a nominal electric field at less than 50 kV/m, and to horizontal and vertical magnetic fields at less than 1 mT. Design features, construction details, and results of various tests of the systems are described. Tests were made: of phase relations between electric and magnetic fields; of uniformity of electric and magnetic fields; of changes across time in electric-field intensity as a result of animals' soiling of cages and various washing routines; of resistance of bedding material during humid and dry conditions; and of acoustic noise due to background, to field-generation equipment, and to air conditioning equipment. The results demonstrated that fields were effectively generated but that significant and troublesome changes in electric-field intensity occurred because of cage-soiling. However, when cages were frequently cleaned, field intensities were consistent from one exposure to another.     

60 Hz magnetic fields and central cholinergic activity: effects of exposure intensity and duration.

In previous research, we have found that acute exposure to a 60 Hz magnetic field caused a decrease in cholinergic activity in the frontal cortex and hippocampus of the rat. In the present study, the effects of exposure to different intensities of the magnetic field and durations of exposure were investigated. Rats were exposed to a 60 Hz magnetic field for 60 min at a flux density of either 0.5, 1.0, 1.5, or 2.0 mT. A significant decrease in cholinergic activity was observed in the frontal cortex and hippocampus immediately after exposure to the 2.0 mT field. No significant effect was observed at lower intensities. In another experiment, effect of exposure to a 1.0 mT magnetic field for 30, 45, 60, and 90 min was investigated. A decrease in cholinergic activity was found in both brain areas after 90 min of exposure. No significant effect was observed after shorter durations of exposure. In a further experiment, the exposure duration was extended to 3 h at flux densities of 0.5, 0.1, and 0.05 mT. A significant decrease in cholinergic activity was observed in the frontal cortex and hippocampus of the rat immediately after exposure to all the intensities. It is concluded that the intensity and duration of exposure interact. By increasing the duration of exposure, effects can be observed at lower intensities.     

Measurement and analysis of static magnetic fields that block action potentials in cultured neurons

To characterize the properties of static magnetic fields on firing of action potentials (AP) by sensory neurons in cell culture, we developed a mathematical formalism based on the expression for the magnetic field of a single circular current loop. The calculated fields fit closely the field measurements taken with a Hall effect gaussmeter. The biological effect induced by different arrays of permanent magnets depended principally on the spatial variation of the fields, quantified by the value of the gradient of the field magnitude. Magnetic arrays of different sizes (macroarray: four center-charged neodymium magnets of ?14 mm diameter; microarray: four micromagnets of the same material but of ?0.4 mm diameter) allowed comparison of fields with similar gradients but different intensities at the cell position. These two arrays had a common gradient value of ?1 mT/mm and blocked >70% of AP. Alternatively, cells placed in a field strength of ?0.2 mT and a gradient of ?0.02 mT/mm produced by the macroarray resulted in no significant reduction of firing; a microarray field of the same strength but with a higher gradient of ?1.5 mT/mm caused ?80% AP blockade. The experimental threshold gradient and the calculated threshold field intensity for blockade of action potentials by these arrays were estimated to be ?0.02 mT/mm and ?0.02 mT, respectively. In conclusion, these findings suggest that spatial variation of the magnetic field is the principal cause of AP blockade in dorsal root ganglia in vitro. © 1995 Wiley-Liss, Inc.     

Exposure chamber for determining the biological effects of electric and magnetic fields on dairy cows

An exposure chamber was designed to study the effects of electric and magnetic fields (EMF) on oestrous cycles, hormonal profile during gestation, pineal function, quantity and quality of milk production, feed intake, and central nervous system of dairy cattle. The chamber was 15 x 10 x 3 m; and the control system was fully computerized so that the field intensities can be varied and monitored continuously, on site or remotely. During exposure to EMF, milk production, feed consumption, and health were monitored closely and blood and cerebral spinal fluid were continuously sampled. The chamber characteristics allow use of a wide range of exposure such as electric fields (0-30 kV/m) and magnetic fields (0-100 microT) at frequencies ranging from 45 to 3000 Hz.     

Effect of extremely low frequency electromagnetic field on brain histopathology of Caspian Sea Cyprinus carpio

There is limited research on the effect of electromagnetic field on aquatic organisms, especially freshwater fish species. This study was conducted to evaluate the effect of extremely low frequency electromagnetic field (ELF-EMF) (50 Hz) exposure on brain histopathology of Cyprinus carpio, one of the important species of Caspian Sea with significant economic value. A total of 200 healthy fish were used in this study. They were classified randomly in two groups: sham-exposed group and experimental group, which were exposed to five different magnetic field intensities (0.1, 1, 3, 5, and 7 mT) at two different exposure times (0.5 and 1 h). Histologic results indicate that exposure of C. carpio to artificial ELF-EMF caused severe histopathological changes in the brain at field intensities ≥3 mT leading to brain necrosis. Field intensity and duration of exposure were key parameters in induction of lesion in the brain. Further studies are needed to elucidate exact mechanism of EMF exposure on the brain.     

Magnetic Navigation

Recent evidence suggests that some amphibians, reptiles and birds may be capable of homing using information about geographic position (“map” information) derived from subtle geographic gradients in the earth's magnetic field. The “magnetic map” hypothesis faces numerous theoretical difficulties, however, due to the extremely high level of sensitivity that would be necessary to detect natural magnetic gradients, and to the presence of spatial irregularities and temporal variation in the geomagnetic field that might make map coordinates derived from magnetic gradients unreliable. To date, the majority of studies carried out to test the magnetic map hypothesis have involved field observations of the effects on homing orientation of naturally occurring spatial or temporal variation in the geomagnetic field. While providing an important first step, these studies are subject to the criticism that the observed changes in homing orientation could result from effects on a magnetic compass, or some other unidentified component of the navigational system, rather than from effects on a magnetic map. The recent development of experimental systems in which navigational ability can be studied under controlled or semi-controlled laboratory conditions has opened up the possibility of using new experimental approaches to more rigorously test the magnetic map hypothesis. After briefly reviewing the available evidence of the geomagnetic field's involvement in the map component of homing, a simple graphical model is presented which describes how the home direction derived from a bicoordinate map varies as a function of the value of one of the map coordinates when the value of the second map coordinate is held constant. In studies of homing orientation in which the value of a specific magnetic field parameter (e.g., total intensity, inclination, etc.) can be varied independently of other putative map parameters, the graphical model can be used to generate qualitative predictions about the changes in the direction of homing orientation that should be observed if the magnetic field parameter being manipulated serves as one coordinate of a bicoordinate map. The relationship between the direction of homing orientation and the value of a putative magnetic map parameter can also be used to generate quantitative predictions about characteristics of the local gradient of that magnetic field parameter in the vicinity of the home site (i.e., the alignment and “home value” of the local gradient) which can then be compared with actual measured values. Together, the qualitative and quantitative predictions of the graphical model permit rigorous tests of whether one or both coordinates of a bicoordinate navigational map are derived from the geomagnetic field.     

Devices for gradient static magnetic field exposure

We describe devices designed for magnetic field exposures in which field amplitude and gradients are controlled simultaneously. Dosimetry based on field continuation of high resolution magnetic field scans and numerical models is compared with validation measurements. The dosimetry variables we consider are based on the assumption that the biological or chemical system under study has field transducers that are spatially isotropic, so that absolute field amplitude and two gradient components fully describe local exposure.     

Excitation of magnetic fields by a circularly polarized laser pulse in a plasma channel

The excitation of quasistatic magnetic fields by a circularly polarized laser pulse in a plasma channel is considered. It is shown that, to second order in the amplitude of the electric field of the laser pulse, circular rotation of the plane of polarization of the laser radiation in a radially nonuniform plasma gives rise to a nonlinear azimuthal current and leads to the excitation of the radial and axial components of the magnetic field. The dependence of the magnetic field distribution over the plasma channel on the spatial dimensions of the pulse and on the channel width is investigated for a moderate-power laser pulse. The structure of the magnetic fields excited by a relativistic laser pulse in a wide plasma channel is analyzed.     

Exposure to a moderate intensity static magnetic field enhances the hypotensive effect of a calcium channel blocker in spontaneously hypertensive rats

We investigated the combined effects of a moderate intensity static magnetic field (SMF) and an L-type voltage-gated Ca(2+) channel blocker, nicardipine in stroke-resistant spontaneously hypertensive rats during the development of hypertension. Five-week-old male rats were exposed to SMF intensity up to 180 mT (B(max)) with a peak spatial gradient of 133 mT/mm for 14 weeks. Four experimental groups of 14 animals each were examined: (1) sham exposure with intraperitoneal (ip) saline injection (control); (2) SMF exposure with ip saline injection (SMF); (3) sham exposure with ip nicardipine injection (NIC); (4) SMF exposure with ip nicardipine injection (SMF + NIC). A disc-shaped permanent magnet or a dummy magnet was implanted in the vicinity adjacent to the left carotid sinus baroreceptor region in the neck of each rat. Nicardipine (2 mg/kg ip) was administered three times a week for 14 weeks, and then 15 min after each injection, arterial blood pressure (BP), heart rate (HR), baroreflex sensitivity (BRS), skin blood flow (SBF), skin blood velocity (SBV), plasma nitric oxide (NO) metabolites (NO(x) = NO(2) (-) + NO(3) (-)), plasma catecholamine levels and behavioral parameters of a functional observational battery were monitored. The action of nicardipine significantly decreased BP, and increased HR, SBF, SBV, plasma epinephrine and norepinephrine in the NIC group compared with the control respective age-matched group without changing plasma NO(x) levels. Neck exposure to SMF alone for 5-8 weeks significantly suppressed or retarded the development of hypertension together with increased BRS in SMF group. Furthermore, the exposure to SMF for 1-8 weeks significantly promoted the nicardipine-induced BP decrease in the SMF + NIC group compared with the respective NIC group. Moreover, the SMF induced a significant increase in plasma NO(x) in the nicardipine-induced hypotension. There were no significant differences in any of the physiological or behavioral parameters measured between the SMF + NIC and the NIC groups, nor between the SMF and the control groups. These results suggest that the SMF may enhance nicardipine-induced hypotension by more effectively antagonizing the Ca(2+) influx through the Ca(2+) channels compared with the NIC treatment alone. Furthermore, the enhanced antihypertensive effects of the SMF on the nicardipine-treated group appear to be partially related to the increased NO(x). Theoretical considerations suggest that the applied SMF (B(max) 40 mT, 0 Hz) can be converted into a changing magnetic field (B(max) 30-40 mT, 5.7-6.5 Hz or 7.5-8.3 Hz) in the baroreceptor region by means of the carotid artery pulsation. Therefore, we propose that the moderate intensity changing magnetic field, i.e., the magnetic field modulated by the pulse rate, may influence the activity of baroreceptor and baroreflex function.     

System for the exposure of cell suspensions to power-frequency electric fields

A system is described that uses an oscillating magnetic field to produce power-frequency electric fields with strengths in excess of those produced in an animal or human standing under a high-voltage electric-power transmission line. In contrast to other types of exposure systems capable of generating fields of this size, no electrodes are placed in the conducting growth media: the possibility of electrode contamination of the exposed suspension is thereby eliminated. Electric fields in the range 0.02–3.5 V/m can be produced in a cell culture with total harmonic distortions less than 1.5%. The magnetic field used to produce electric fields for exposure is largely confined within a closed ferromagnetic circuit, and experimental and control cells are exposed to leakage magnetic flux densities less than 5 μT. The temperatures of the experimental and control cell suspensions are held fixed within ±0.1°C by a water bath. Special chambers were developed to hold cell cultures during exposure and sham exposure. Chinese hamster ovary (CHO) cells incubated in these chambers grew for at least 48 h and had population doubling times of 16–17 h, approximately the same as for CHO cells grown under standard cell-culture conditions.     

Aligning Paramecium caudatum with static magnetic fields

As they negotiate their environs, unicellular organisms adjust their swimming in response to various physical fields such as temperature, chemical gradients, and electric fields. Because of the weak magnetic properties of most biological materials, however, they do not respond to the earth's magnetic field (5 x 10(-5) Tesla) except in rare cases. Here, we show that the trajectories of Paramecium caudatum align with intense static magnetic fields >3 Tesla. Otherwise straight trajectories curve in magnetic fields and eventually orient parallel or antiparallel to the applied field direction. Neutrally buoyant immobilized paramecia also align with their long axis in the direction of the field. We model this magneto-orientation as a strictly passive, nonphysiological response to a magnetic torque exerted on the diamagnetically anisotropic components of the paramecia. We have determined the average net anisotropy of the diamagnetic susceptibility, Deltachi(p), of a whole Paramecium: Deltachi(p) = (6.7+/- 0.7) x 10(-23) m(3). We show how the measured Deltachi(p) compares to the anisotropy of the diamagnetic susceptibilities of the components in the cell. We suggest that magnetic fields can be exploited as a novel, noninvasive, quantitative means to manipulate swimming populations of unicellular organisms.     

Influence of non-thermic AC magnetic fields on spore germination in a dimorphic fungus

Summary The influence of weak pulsed magnetic fields of low frequencies on the germination rate ofMycotypha africana was tested. This fungus grows as a mycelium (M-culture) or in a yeast-like form (Y-culture) depending upon culture conditions. 5 h and 24 h of field application enhanced the germination rate in a Y-culture up to 2 or 3 times at low intensity levels and decreased it up to a factor 4 at the intensity level 4. M-cultures exhibited the same reaction pattern after 5 h exposition and no effect after 24 h exposition. The Y/M ratio is shifted by low field intensities towards the Y-form. The occurence of stimulation as well as retardation by neighbouring intensities is discussed.     

Low stray ELF magnetic field exposure system for in vitro study

An exposure facility for wide application to cell exposure to an ELF (extremely low frequency) magnetic field was developed. It is suitable for conducting experiments under a high-intensity, variable-frequency magnetic field, on the biological effects of the ELF magnetic field in an in vitro study. The exposure system consists of Merritt's 4-square coil as a basic component to generate the required magnetic field intensity of 10 mT at 50 Hz with spatial field uniformity less than +/-3% in a 400 mm cube. Concentric compensation coils are adopted to eliminate the effects of stray fields on sham (control) samples in the vicinity of the exposure system. The uniformity of the magnetic field in the exposure coil, the increase in the power supply capacity due to the existence of compensation coils, and the stray field estimation were investigated carefully. After fabricating the system, performance tests were carried out and all the characteristics were found to be satisfactory. In addition, the ideal configuration for a concentric coil system was proposed.     

Development and evaluation of intermediate frequency magnetic field exposure system for studies of in vitro biological effects

We have developed an intermediate frequency (IF) magnetic field exposure system for in vitro studies. Since there are no previous studies on exposure to heating-frequency magnetic fields generated from an induction heating (IH) cook top, there is a strong need for such an exposure system and for biological studies of IF magnetic fields. This system mainly consists of a magnetic-field-generating coil housed inside an incubator, inside which cultured cells can be exposed to magnetic field. Two systems were prepared to allow the experiment to be conducted in a double-blind manner. The level of the generated magnetic field was set to 532 microT rms in the exposure space, 23 kHz, 80 times the value in the International Commission on Non-ionizing Radiation Protection (ICNIRP) guidelines, with a spatial field uniformity better than 3.8%. The waveforms were nearly sinusoidal. It was also confirmed that the parasitic electric field was 157 V/m rms and the induced electric field was 1.9 V/m rms. The temperature was maintained at 36.5 +/- 0.5 degrees C for 2 h. Furthermore, leaked magnetic flux density was 0.7 microT rms or lower at extremely low frequency (ELF) and IF in the stopped system when the other system was being operated, and the environmental magnetic flux density was 0.1 microT rms or lower at the center of the coils. As a result, it was confirmed that this system could be successfully used to evaluate the biological effects of exposure to IF magnetic fields.