Increased resorptions in CBA mice exposed to low-frequency magnetic fields: An attempt to replicate earlier observations

This paper has two aims. First, it reports the findings of a study on the effects of low-frequency magnetic fields on reproduction. Second, it serves as an example of an attempt to replicate the results of an experimental study in an independent laboratory and discusses some of the problems of replication studies. To try to replicate the findings of a study reporting increased resorptions (fetal loss) in mice exposed to 20 kHz magnetic fields with sawtooth waveform and to study the possible effects of 50 Hz sinusoidal fields, pregnant mice were exposed to magnetic fields from day 0 to 18 of pregnancy, 24 h per day. The flux densities of the vertical magnetic fields were 15 μT (peak-to-peak) at 20 kHz and 13 or 130 μT (root mean square) at 50 Hz. Two strains of animals were used: CBA/S mice imported from the laboratory reporting the original observations, and a closely related strain CBA/Ca. The CBA/S mice were cleaned of pathogenic microbes and parasites before they were imported into our laboratory. The magnetic field exposures did not affect resorption rate in CBA/Ca mice. In CBA/S, the frequency of resorptions was higher in the exposed mice than in the control group. However, the increase was not significantly different from either the no-effect hypothesis or the results of the original study we were attempting to replicate. Differences between the two studies and difficulties in interpreting the results are discussed. It is concluded that the results tend more to support than argue against increased resorptions in CBA/S mice exposed to the 20 kHz magnetic field. The results demonstrate that animal strain is an important variable in bioelectromagnetics research: even closely related strains may show different responses to magnetic field exposure. Bioelectromagnetics 18:410–417, 1997. © 1997 Wiley-Liss, Inc.     

还田秸秆分解与氮素释放的动态模拟

还田秸秆的分解与氮素释放动态是作物养分管理的重要依据。建立了秸秆分解氮素释放动态的“整吞”式动态模拟模型。模型由秸秆有机质分解和残余有机质含氮率动态模拟两部分组成,有机质分解的温度效应用指数函数描述,水分效应用分段线性函数描述,用“标准天”反映温度与水分的综合影响,残余有机质含氮率动态变化用“标准天”为变量的函数模拟,初始秸秆含氮量与残余秸秆含氮量之差即为秸秆分解的氮素净释放。“整吞”式较之“吃馅饼”式建模构思,所需参数少且易通过实验获得,增加了模型的可用性,利用在淮北滨海地区小麦的试验资料对模型的有效性进行了验证。     

Power frequency magnetic field exposures among nurses in a neonatal intensive care unit and a normal newborn nursery

Given the current interest in potential carcinogenic and developmental effects of exposure to extremely-low-frequency electromagnetic fields, there is a need to identify cohorts of exposed female workers for future epidemiologic investigations. This study was designed to test the hypothesis that nurses working in neonatal intensive care units (NICU) may be significantly exposed to power-frequency magnetic fields. An electromagnetic field monitor was used to measure magnetic fields at distances of 5, 15, 30, and 60 cm from the surfaces of each device used in the NICU. Six female nurses assigned to the NICU (the “exposed” group) and six female nurses working in the normal newborn nursery (the “referent” group) wore EMDEX dosimeters for the entire duration of their 12 h shifts. An investigator kept a detailed log of each NICU subject's whereabouts for the first one-third of her shift. Magnetic fields at 5 cm from the front (defined by the nurses' usual work area) of the NICU devices ranged from less than 0.1 to 114 μT and in all cases decreased considerably with increasing distance. The geometric mean of the shift-time-weighted average exposure of the NICU nurses was 0.17 μT compared with 0.11 μT for the normal newborn nurses. The percentage of time when subjects were exposed to magnetic fields of 0.4 μT or greater ranged from 5.8% to 15.6% for the NICU nurses, 0.4% to 2.9% for five of the comparison group nurses, and was 9.4% for one of the normal newborn nurses with unidentified aberrantly high exposures. Log data revealed that the vast majority of observed peaks among NICU nurses occurred while subjects were in close proximity to infant bed units. We conclude that NICU nurses represent one female-intensive job sector with intermittent high exposures to ELF magnetic fields and encourage larger exposure studies of nurses in a variety of medical settings. © 1994 Wiley-Liss, Inc.     

Pulsed electromagnetic fields stimulation affects BMD and local factor production of rats with disuse osteoporosis

Pulsed electromagnetic fields (PEMF) have been used widely to treat nonunion fractures and related problems in bone healing, as a biological and physical method. With the use of Helmholtz coils and PEMF stimulators to generate uniform time‐varying electromagnetic fields, the effects of extremely low frequency electromagnetic fields on bone mineral density (BMD) and local factor production in disuse osteoporosis (DOP) rats were investigated. Eighty 4‐month‐old female Sprague Dawley (SD) rats were randomly divided into intact (INT) group, DOP group, calcitonin‐treated (CT) group, and PEMF stimulation group. The right hindlimbs of all the rats were immobilized by tibia‐tail fixation except for those rats in the INT group. Rats in the CT group were injected with calcitonin (2 IU/kg, i.p., once a day) and rats in the PEMF group were irradiated with PEMF immediately postoperative. The BMD, serum transforming growth factor‐beta 1 (TGF‐β1), and interleukin‐6 (IL‐6) concentration of the proximal femur were measured 1, 2, 4, and 8 weeks after treatment. Compared with the CT and DOP groups, the BMD and serum TGF‐β1 concentration in the PEMF group increased significantly after 8 weeks. The IL‐6 concentration in the DOP group was elevated significantly after operation. The PEMF group showed significantly lower IL‐6 level than the DOP group. The results found demonstrate that PEMF stimulation can efficiently suppress bone mass loss. We, therefore, conclude that PEMF may affect bone remodeling process through promoting TGF‐β1 secretion and inhibiting IL‐6 expression. Bioelectromagnetics 31:113–119, 2010. © 2009 Wiley‐Liss, Inc.     

The electromagnetic basis of social interactions

It has been established that living things are sensitive to extremely low-frequency magnetic fields at vanishingly small intensities, on the order of tens of nT. We hypothesize, as a consequence of this sensitivity, that some fraction of an individual’s central nervous system activity can be magnetically detected by nearby individuals. Even if we restrict the information content of such processes to merely simple magnetic cues that are unconsciously received by individuals undergoing close-knit continuing exposure to these cues, it is likely that they will tend to associate these cues with the transmitting individual, no less than would occur if such signals were visual or auditory. Furthermore, following what happens when one experiences prolonged exposure to visual and like sensory inputs, it can be anticipated that such association occurring magnetically will eventually also enable the receiving individual to bond to the transmitting individual. One can readily extrapolate from single individuals to groups, finding reasonable explanations for group behavior in a number of social situations, including those occurring in families, animal packs, gatherings as found in concerts, movie theaters and sports arenas, riots and selected predatory/prey situations. The argument developed here not only is consistent with the notion of a magnetic sense in humans, but also provides a new approach to electromagnetic hypersensitivity, suggesting that it may simply result from sensory overload.     

Extremely low-frequency electromagnetic field promotes astrocytic differentiation of human bone marrow mesenchymal stem cells by modulating SIRT1 expression

It has been shown that extremely low-frequency electromagnetic fields (ELFMF) affect regulation of cell fate and differentiation. Thus, the aim of this study was to investigate the role of ELFMFs in the enhancement of astrocytic differentiation. ELFMF exposure reduced the rate of proliferation and enhanced astrocytic differentiation. The ELFMF-treated cells showed increased levels of the astrocyte marker (GFAP), while those of the early neuronal marker (Nestin) and stemness marker (OCT3/4) were downregulated. The reactive oxygen species (ROS) level was observed to be significantly elevated after ELFMF exposure, which strengthens the modulatory role of SIRT1 and SIRT1 downstream molecules (TLE1, HES1, and MASH1) during astrocytic differentiation. After nicotinamide (5 mM) mediated inhibition of SIRT1, levels of TLE1, HES1, and MASH1 were examined; TLE1 was significantly upregulated and MASH1 was downregulated. These results suggest that ELFMFs induce astrocytic differentiation through activation of SIRT1 and SIRT1 downstream molecules.     

Reactive Oxygen Species: Potential Regulatory Molecules in Response to Hypomagnetic Field Exposure

Organisms, including humans, could be exposed to hypomagnetic fields (HMFs, intensity <5 μT), e.g. in some artificially shielded magnetic environments and during deep-space flights. Previous studies have demonstrated that HMF exposure could have negative effects on the central nervous system and embryonic development in many animals. However, the underlying mechanisms remain unknown. Studies have revealed that HMFs affect cellular reactive oxygen species (ROS) levels and thereby alter physiological and biological processes in organisms. ROS, the major component of highly active free radicals, which are ubiquitous in biological systems, were hypothesized to be the candidate signaling molecules that regulate diverse physiological processes in response to changes in magnetic fields. Here, we summarize the recent advances in the study of HMF-induced negative effects on the central nervous system and early embryonic development in animals, focusing on cellular ROS and their role in response to HMFs. Furthermore, we discuss the potential mechanism through which HMFs regulate ROS levels in cells. © 2020 Bioelectromagnetics Society     

Seed germination requirements of Trembleya laniflora (Melastomataceae), an endemic species from neotropical montane rocky savannas

Trembleya laniflora is an endemic shrub from neotropical montane rocky savannas of southeastern Brazil. It has been indicated as a potential candidate for ecological restoration of abandoned iron‐ore mines due to heavy metal accumulation. Here, we evaluated the seed germination requirements of T. laniflora. Seeds collected in 2005 and 2008 were set to germinate under a broad range of temperature and light conditions. Seed viability was estimated by dissecting seeds under a dissecting microscope for embryo presence/absence. Seeds were photoblastic and optimum temperature range was 20–25°C, coinciding with the onset of the rainy season. Seeds were viable after 42 months of storage, which together with small seeds that easily get buried and light requirement for germination suggest formation of soil seed banks. Except the large fraction of embryoless seeds, almost all tested seeds germinated when incubated under light conditions; therefore, T. laniflora should be regarded to have nondormant seeds. Easiness of burial resulting from small seed size and positive photoblastism may both contribute to incorporation into soil seed banks. Our data suggest that the long‐term storage of T. laniflora seeds provides a useful strategy for plant reintroduction.