Biochemical effects of high intensity constant magnetic fields on worker honey bees

Hemolymph samples from adult bees that had completed their pupal development and emergence in a 7 Tesla field contained a lower percentage of glucose than controls, indicating that trehalase enzyme activity in honey bees is reduced in strong magnetic fields. Significantly more phospholipids were found in the intestines of magnetic field-exposed bees than in controls. No significant differences were found for fatty acids, triacylglycerols, or steroids.     

Light-dependent and -independent behavioral effects of extremely low frequency magnetic fields in a land snail are consistent with a parametric resonance mechanism

Exposure to extremely low frequency (ELF) magnetic fields has been shown to attenuate endogenous opioid peptide mediated antinociception or “analgaesia” in the terrestrial pulmonate snail, Cepaea nemoralis. Here we examine the roles of light in determining this effect and address the mechanisms associated with mediating the effects of the ELF magnetic fields in both the presence and absence of light. Specifically, we consider whether the magnetic field effects involve an indirect induced electric current mechanism or a direct effect such as a parametric resonance mechanism (PRM). We exposed snails in both the presence and absence of light at three different frequencies (30, 60, and 120 Hz) with static field values (B_DC) and ELF magnetic field amplitude (peak) and direction (B_AC) set according to the predictions of the PRM for Ca²⁺. Analgaesia was induced in snails by injecting them with an enkephalinase inhibitor, which augments endogenous opioid (enkephalin) activity. We found that the magnetic field exposure reduced this opioid-induced analgaesia significantly more if the exposure occurred in the presence rather than the absence of light. However, the percentage reduction in analgaesia in both the presence and absence of light was not dependent on the ELF frequency. This finding suggests that in both the presence and the absence of light the effect of the ELF magnetic field was mediated by a direct magnetic field detection mechanism such as the PRM rather than an induced current mechanism. Bioelectromagnetics 18:284–291, 1997. © 1997 Wiley-Liss, Inc.     

Effects of strong static magnetic fields used in magnetic resonance imaging on insulin-secreting cells

The magnetic flux density of MRI for clinical diagnosis has been steadily increasing. However, there remains very little biological data regarding the effect of strong static magnetic fields (SMFs) on human health. To evaluate the effects of strong SMFs on biological systems, we cultured insulin-secreting cells under exposure to sham and SMF conditions (3-10 T of magnetic flux density, and 0-41.7 T/m of magnetic field gradient) for 0.5 or 1 h, and analyzed insulin secretion, mRNA expression, glucose-stimulated insulin secretion, insulin content, cell proliferation and cell number. Exposure to SMF with a high magnetic field gradient for 1 h significantly increased insulin secretion and insulin 1 mRNA expression. Exposure to SMF with a high magnetic flux density for 0.5 h significantly enhanced responsiveness to glucose stimulation. Exposure to SMF did not affect the insulin content, cell proliferation or cell number. Our results suggested that MRI systems with a higher magnetic flux density might not cause cell proliferative or functional damages on insulin-secreting cells, and that SMF with a high magnetic field gradient might be used clinically after thorough in vivo investigations are conducted.     

Static and ELF magnetic fields induce tumor growth inhibition and apoptosis

The ability of static and extremely low frequency (ELF) Magnetic Fields (MF) to interfere with neoplastic cell function has been evaluated. In vitro experiments were carried out to study the role of MF characteristics (intensity, frequency, and modulation) on two transformed cell lines (WiDr human colon adenocarcinoma and MCF-7 human breast adenocarcinoma) and one nontransformed cell line (MRC-5 embryonal lung fibroblast). Increase in cell death morphologically consistent with apoptosis was reported exclusively in the two transformed cell lines. Cell-death induction was observed with MF of more than 1 mT. It was independent of the MF frequency and increased when modulated MF (static with a superimposition of ELF at 50 Hz) were used. Based on the in vitro results, four different MF exposure characteristics were selected and used to treat nude mice xenografted with WiDr cells. The treatment of nude mice bearing WiDr tumors subcutaneously. with daily exposure for 70 min to MF for 4 weeks caused significant tumor growth inhibition (up to 50%) by the end of the treatment when modulated MF were used for at least 60% of the whole treatment period and the time-averaged total MF intensity was higher than 3.59 mT. No toxic morphological changes induced by exposure were observed in renewing, slowly proliferating, or static normal cells. A discussion on the possible biophysical mechanism at the base of the observed biological results is also offered.     

Reception and learning of electric fields in bees

Honeybees, like other insects, accumulate electric charge in flight, and when their body parts are moved or rubbed together. We report that bees emit constant and modulated electric fields when flying, landing, walking and during the waggle dance. The electric fields emitted by dancing bees consist of low- and high-frequency components. Both components induce passive antennal movements in stationary bees according to Coulomb''s law. Bees learn both the constant and the modulated electric field components in the context of appetitive proboscis extension response conditioning. Using this paradigm, we identify mechanoreceptors in both joints of the antennae as sensors. Other mechanoreceptors on the bee body are potentially involved but are less sensitive. Using laser vibrometry, we show that the electrically charged flagellum is moved by constant and modulated electric fields and more strongly so if sound and electric fields interact. Recordings from axons of the Johnston organ document its sensitivity to electric field stimuli. Our analyses identify electric fields emanating from the surface charge of bees as stimuli for mechanoreceptors, and as biologically relevant stimuli, which may play a role in social communication.     

核磁共振磁场照射对子代大鼠海马突触形态的影响

研究观察了孕期磁共振磁场照射对子代大鼠海马突触超微结构的影响。SD孕鼠妊娠第12-18d给予0．35T核磁共振(magnetic resonance imaging,MRI)磁场照射。测量1、2和5月龄雌性仔鼠海马CAl区和齿状回的突触结构参数,用立体计量学方法进行定量测定。结果显示,磁场照射可引起2月龄子代大鼠海马CAl区突触间隙增宽．齿状回突触活性区长度变短、突触界面曲率和活性区面密度减小;5月龄子代大鼠CAl区突触间隙增宽,突触后致密物变薄,突触界面曲率减小,齿状回突触间隙增宽。结果提示,妊娠期接受MRI磁场照射可引起海马突触超微结构的改变。对这些结构变化与行为损害之间的关系进行了讨论。     

Lithium as a normal metabolite: some implications for cyclotron resonance of ions in magnetic fields

Cyclotron resonance of ions has been proposed as a mechanism by which weak, extremely-low-frequency (ELF) electromagnetic fields can act on biological systems. Critics of a mechanism predicated on resonance of lithium have argued that this element is virtually absent from the internal milieu of mammals and otherwise plays no role in the normal physiological functioning of the organism. Sophisticated techniques of trace-element analysis have recently revealed that lithium is a normal constituent of tissues of assayed mammals, including those of rats and human beings. There is evidence, too, that lithium is an important, biologically-active element. Cyclotron resonance may or may not be a mechanism by which ELF- and static-magnetic fields at low strengths combine to affect the organism, but rejection of this mechanism on the grounds that lithium is absent or is physiologically inadequate is unwarranted. Lithium is normally present and is metabolically active in many tissues, especially those of the neuroendocrine system.     

Present and future magnetic resonance sources of exposure to static fields

This paper considers the exposure of humans to static magnetic fields due to magnetic resonance imaging (MRI) procedures. It briefly introduces the types of magnetic fields associated with MRI. It then discusses trends in the number of people exposed to MRI, the field strength of the magnets used in MRI, and the types of applications of MRI. It also considers the types of staff who are exposed to magnetic fields due to MRI, and the alternative techniques that would be used in the absence of MRI.     

Fifty-hertz magnetic fields induce free radical formation in mouse bone marrow-derived promonocytes and macrophages

Our findings show a significant increase of free radical production after exposure to 50 Hz electromagnetic fields at a flux density of 1 mT to mouse bone marrow-derived (MBM) promonocytes and macrophages, indicating the cell-activating capacity of extremely low frequency magnetic fields (ELF-MF). We demonstrate that after exposure to ELF-MF mainly superoxide anion radicals were produced, both in MBM macrophages (33%) and also in their precursor cells (24%). To elucidate whether NADPH- or NADH-oxidase functions are target proteins for MF interaction, the flavoprotein inhibitor diphenyleneiodonium chloride (DPI) was used. MF-induced free radical production was not inhibited by DPI, whereas tetradecanoylphorbolacetate (TPA)-induced free radical production was diminished by about 70%. TPA is known to induce a direct activation of NADPH-oxidase through the PKC pathway. Since DPI lacks an inhibitory effect in MF-exposed MBM cells, we suggest that 50 Hz MF stimulates the NADH-oxidase pathway to produce superoxide anion radicals, but not the NADPH pathway. Furthermore, we showed an oscillation (1-10 days) in superoxide anion radical release in mouse macrophages, indicating a cyclic pattern of NADH-oxidase activity.     

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.     

Primary physical mechanism of the biological effects of weak magnetic fields

The primary physical mechanism of the magnetoreception of weak magnetic fields is considered. It imposes limits on the magnetic biological effect at the stage prior to the involvement of specific biophysical and biochemical mechanisms, i.e., regardless of the nature of the target of the magnetic field. It has been shown that the biological effects of weak magnetic fields have, in general, non-linear and spectral properties. Observation of these characteristics gives information not only on the gyromagnetic ratio, but also on the parameters of the interaction between the target and its immediate surroundings. This makes it possible for one to develop schemes for the identification of the biophysical mechanisms of magnetoreception.     

Agonists of proteinase-activated receptor 2 induce inflammation by a neurogenic mechanism

Trypsin and mast cell tryptase cleave proteinase-activated receptor 2 and, by unknown mechanisms, induce widespread inflammation. We found that a large proportion of primary spinal afferent neurons, which express proteinase-activated receptor 2, also contain the proinflammatory neuropeptides calcitonin gene-related peptide and substance P. Trypsin and tryptase directly signal to neurons to stimulate release of these neuropeptides, which mediate inflammatory edema induced by agonists of proteinase-activated receptor 2. This new mechanism of protease-induced neurogenic inflammation may contribute to the proinflammatory effects of mast cells in human disease. Thus, tryptase inhibitors and antagonists of proteinase-activated receptor 2 may be useful anti-inflammatory agents.     

ELF magnetic fields induce internalization of gap junction protein connexin 43 in Chinese hamster lung cells

We have previously demonstrated that exposure of Chinese hamster lung (CHL) cells to 50 Hz magnetic fields (MFs) and/or 12-O-tetradecanoylphorbol-3-acetate (TPA)-inhibited gap junctional intercellular communication (GJIC). To explore and compare the mechanisms of GJIC inhibition induced by extremely low frequency (ELF) MF and TPA, the number and localization of connexin 43 (C x 43) were studied. The localization of C x 43 was determined with indirect immunofluorescence histochemical analysis and detected by confocal microscopy after exposing CHL cells to 50 Hz sinusoidal magnetic field at 0.8 mT for 24 h without or with TPA (5 ng/ml) for the last 1 h. The C x 43 levels in nuclei and in cytoplasm were examined by Western blotting analysis. The results showed that the cells exposed to MF and/or TPA displayed individual plaques at regions of intercellular contact, which were fewer than the normal cells in number, while the number of C x 43 in cytoplasm increased and congregated near the nuclei. Western blot analysis further demonstrated the quantity of changes in location of Cx43. These results suggest that reduction of C x 43 at regions of intercellular contact may be one of the mechanisms of GJIC inhibition induced by ELF MF.     

ELF magnetic fields in a city environment

Some epidemiological studies indicate an association between extremely low frequency electromagnetic field (ELF-EMF) exposure and cancer risks. These studies have mainly taken residential and occupational exposure into consideration. Outdoor environments are often considered as low level areas, but in this paper we show that this is not true in a city environment. We have mapped the ELF magnetic flux densities along certain stretches of sidewalk in central G?teborg City, Sweden. About 50% of the investigated street length shows flux densities of the same order of magnitude (0.2 microT and above) as those associated with increased risks of cancer in epidemiological studies. We conclude that the outdoor exposures in a city environment also should be considered in exposure assessments and risk evaluations. These elevated flux densities are probably due to stray currents. We also found strong magnetic flux densities (> 1.0 microT) close to ordinary distribution pillars, power substations, shoplifting alarms, and other electrical devices.     

Lymphotoxin and lipopolysaccharide induce NF-kappaB-p52 generation by a co-translational mechanism

The 'classical' NF-kappaB activation pathway proceeds via IkappaB kinase (IKK)-beta/gamma-mediated phosphorylation, induced ubiquitination and the degradation of small IkappaBs. An alternative, NF-kappaB-inducing kinase and IKK-alpha-dependent pathway, which stimulates the processing of NF-kappaB2/p100, has recently been suggested. However, no physiological stimulus has been shown to trigger the activation of this pathway. Here we demonstrate that persistent stimulation with lymphotoxin beta (LT-beta) receptor agonists or lipopolysaccharide (LPS), but not with interleukin-1beta, tumour necrosis factor-alpha or 12-O-tetradecanoylphorbol-13-acetate, induces the generation of p52 DNA-binding complexes by activating the processing of the p100 precursor. Induction of p52 DNA-binding activity is delayed in comparison with p50/p65 complexes and depends on de novo protein synthesis. p100 is constitutively and inducibly polyubiquitinated, and both ubiquitination and p52 generation are coupled to continuing p100 translation. Thus, both LT-beta receptor agonists and LPS induce NF-kappaB/p100 processing to p52 at the level of the ribosome.     

Electric fields and surface charges induced by ELF magnetic fields

A method is described for evaluating electric fields induced by ELF magnetic fields into electrically inhomogeneous, low-conductivity (less than 5 S/m) structures. It is applied to cylinders and spheres, and numerical results are given for electrical properties that are representative of some tissues, or of cells embedded either in saline solution or a tissue matrix. Surface currents on spherical cell boundaries are estimated and compared with thermal noise due to ion motion.     

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.     

Miniature-probe measurements of electric fields induced by 60 Hz magnetic fields in rats

Extremely-low-frequency (ELF) magnetic fields interact with an animal by inducing internal electric fields, which represent the internal dose from an external exposure. In this study, an electric field probe of approximately 2 mm resolution was used to measure fields induced in rat carcasses by a 60 Hz magnetic field at 1 mT. With the rat lying on its side, the probe was inserted through a small hole in the body wall, and scanned at 5 mm increments from the side with frontal and axial exposure (field horizontal) and from the front with lateral exposure (field vertical). The induced electric field declined from a maximum at the entrance to the abdomen and crossed zero to negative (180° phase shift) values within the body as expected. In general, the magnitudes of the measurements inside the abdomen were less than expected from whole-body calculations that used homogeneous-ellipsoidal models of a rat in the three orientations. The low measurements did not appear to be explained by perpendicular field components, by conductivity differences between the tissue and the probe path, or by air in the lungs. The low measurements probably result from inhomogeneities in actual rats that include conductivity differences between tissues and biological membranes. For example, an alternative model considered the abdominal cavity to be electrically isolated from the body by the diaphragm and the peritoneum and calculations from this model were in better agreement with the measurements inside the abdomen (than were the whole-body calculations). Therefore, inhomogeneities in conductivity and biomembranes such as the peritoneum should be considered in order to fully understand ELF-induced field dosimetry. © 1996 Wiley-Liss, Inc.