ION cyclotron resonance: Geomagnetic strategy for living systems?

Except for relatively few polarity reversals the magnitude of the magnetic dipole moment of the earth has remained constant since life first began, allowing evolutionary processes to integrate the geomagnetic field (GMF) into several biological functions. One of these, bearing the classical signature of an ion cyclotron resonance (ICR)-like interaction, results in biological change associated with enhanced proton transport. The wide range of cation masses over which this effect is found suggest a fundamental biological dependence on the GMF, one that functions equally well for electric as well as magnetic fields. Such generalization of ICR requires two things: transparency of tissues to the GMF and suitably tuned ELF resonant magnetic or electric fields. To complement the widely reported ICR responses to applied AC magnetic fields, we hypothesize the existence of weak endogenous ICR electric field oscillations within the cell. This equivalence implies that even in the absence of applied AC magnetic fields, biological systems will exhibit intrinsic GMF-dependent ion cyclotron resonance intracellular interactions. Many ICR effects that have been reported appear as antagonist pairs suggesting that the characteristics of the GMF have not only been incorporated into the genome but also appear to function in an endocrine-like manner.     

New model for the avian magnetic compass

It is proposed that the avian magnetic compass depends on the angle between the horizontal component B(h) of the geomagnetic field (GMF) and E(r), the radial electric field distribution generated by gamma-oscillations within the optic tectum (TeO). We hypothesize that the orientation of the brain relative to B(h) is perceived as a set of electric field ion cyclotron resonance (ICR) frequencies that are distributed in spatially recognizeable regions within the TeO. For typical GMF intensities, the expected ICR frequencies fall within the 20-50 Hz range of gamma-oscillation frequencies observed during visual stimulation. The model builds on the fact that the superficial lamina of the TeO receive signals from the retina that spatially map the visual field. The ICR frequencies are recruited from the local wide-band gamma-oscillations and are superposed on the tectum for interpretation along with other sensory data. As a first approximation, our analysis is restricted to the medial horizontal plane of the TeO. For the bird to fly in a preferred, previously mapped direction relative to B(h), it hunts for that orientation that positions the frequency maxima at appropriate locations on the TeO. This condition can be maintained even as B(h) varies with geomagnetic latitude during the course of long-distance flights. The magnetovisual coordinate system (straight phi, omega) overlaying the two halves of the tectal surface in a nonsymmetric way may imply an additional orienting function for the TeO over and above that of a simple compass (e.g., homing navigation as distinct from migrational navigation).     

A geomagnetic declination compass for horizontal orientation in fruit flies

The Earth's geomagnetic field (GMF) is known to act as a sensory cue for magnetoreceptive animals such as birds, sea turtles, and butterflies in long‐distance migration, as well as in flies, cockroaches, and cattle in short‐distance movement or body alignment. Despite a wealth of information, the way that GMF components are used and the functional modality of the magnetic sense are not clear. A GMF component, declination, has never been proven to be a sensory cue in a defined biological context. Here, we show that declination acts as a compass for horizontal food foraging in fruit flies. In an open‐field test, adopting the food conditioning paradigm, food‐trained flies significantly orientated toward the food direction under ambient GMF and under eastward‐turned magnetic field in the absence of other sensory cues. Moreover, a declination change within the natural range, by alteration only of either the east–west or north–south component of the GMF, produced significant orientation of the trained flies, indicating that they can detect and use the difference in these horizontal GMF components. This study proves that declination difference can be used for horizontal foraging, and suggests that flies have been evolutionarily adapted to incorporate a declination compass into their multi‐modal sensorimotor system.     

Some magnetic-biological problems of distant and long-term space flights

Some magnetobiological problems of orbital (in the geomagnetic field--GMF) and interplanetary (in hypomagnetic conditions) flights are considered. The influence of electromagnetic fields (EMF) created by systems and equipment of the space vehicle (SV) are touched also. A level of the geomagnetic field (GMF) onboard during the orbital flights is discussed. Its periodic variations onboard owing to movement of SV on an orbit are analyzed. The reader's attention in attracted to the papers by R.M. Baevsky et al. in which the influence of magnetic storms and periodic variations of GMS on the cardiovascular system of astronauts onboard are shown. Possible ways and mechanisms of the influence are discussed. The wrong assertions in a number of works namely that at orbital flights an appreciable electrical field is induced in an organism of an astronaut in a space-craft and the electrical field may by responsible for some biological impacts are analyzed. The situation at the future in the terplanetary flights (for example Martian missions) when a crew and biological objects for a long time will be in the interplanetary magnetic field (by several orders less then GMF) is considered. As applied to the flights the opportunities of generation onboard the "artificial" GMF are outlined. The ensuing biological and technical questions are discussed.     

鸟类磁感受的生物物理机制研究进展

行为学实验表明,许多鸟类能够感受到地磁信息,并利用地磁信息完成迁徙或归巢。地磁场信息能提供可靠导航信息,磁力线可提供罗盘信息,而磁场强度和倾角可提供位置信息。文章介绍了鸟类磁感受机制的两种重要假说——基于磁铁矿的磁感受假说和化学磁感受假说,阐明了两种假说的理论原理及实验证据,对地磁信息传导神经通路与处理脑区做了评述,并展望了其发展方向。     

Avian magnetic compass can be tuned to anomalously low magnetic intensities

The avian magnetic compass works in a fairly narrow functional window around the intensity of the local geomagnetic field, but adjusts to intensities outside this range when birds experience these new intensities for a certain time. In the past, the geomagnetic field has often been much weaker than at present. To find out whether birds can obtain directional information from a weak magnetic field, we studied spontaneous orientation preferences of migratory robins in a 4 µT field (i.e. a field of less than 10 per cent of the local intensity of 47 µT). Birds can adjust to this low intensity: they turned out to be disoriented under 4 µT after a pre-exposure time of 8 h to 4 µT, but were able to orient in this field after a total exposure time of 17 h. This demonstrates a considerable plasticity of the avian magnetic compass. Orientation in the 4 µT field was not affected by local anaesthesia of the upper beak, but was disrupted by a radiofrequency magnetic field of 1.315 MHz, 480 nT, suggesting that a radical-pair mechanism still provides the directional information in the low magnetic field. This is in agreement with the idea that the avian magnetic compass may have developed already in the Mesozoic in the common ancestor of modern birds.     

A Role for the Geomagnetic Field in Cell Regulation

We advance the hypothesis that biological systems utilize the geomagnetic field (GMF) for functional purposes by means of ion cyclotron resonance-like (ICR) mechanisms. Numerous ICR-designed experiments have demonstrated that living things are sensitive, in varying degrees, to magnetic fields that are equivalent to both changes in the general magnetostatic intensity of the GMF, as well as its temporal perturbations. We propose the existence of ICR-like cell regulation processes, homologous to the way that biochemical messengers alter the net biological state through competing processes of enhancement and inhibition. In like manner, combinations of different resonance frequencies all coupled to the same local magnetic field provide a unique means for cell regulation. Recent work on ultraweak ICR magnetic fields by Zhadin and others fits into our proposed framework if one assumes that cellular systems generate time-varying electric fields of the order 100 mV/cm with bandwidths that include relevant ICR frequencies.     

Magnetic orientation in birds: non-compass responses under monochromatic light of increased intensity

Migratory Australian silvereyes (Zosterops lateralis) were tested under monochromatic light at wavelengths of 424 nm blue and 565 nm green. At a low light level of 7 x 10(15) quanta m(-2) s(-1) in the local geomagnetic field, the birds preferred their seasonally appropriate southern migratory direction under both wavelengths. Their reversal of headings when the vertical component of the magnetic field was inverted indicated normal use of the avian inclination compass. A higher light intensity of 43 x 10(15) quanta m(-2) s(-1), however, caused a fundamental change in behaviour: under bright blue, the silvereyes showed an axial tendency along the east-west axis; under bright green, they showed a unimodal preference of a west-northwesterly direction that followed a shift in magnetic north, but was not reversed by inverting the vertical component of the magnetic field. Hence it is not based on the inclination compass. The change in behaviour at higher light intensities suggests a complex interaction between at least two receptors. The polar nature of the response under bright green cannot be explained by the current models of light-dependent magnetoreception and will lead to new considerations on these receptive processes.     

Magnetic orientation in the semi-terrestrial amphipod, Orchestia cavimana, and its interrelationship with photo-orientation and water loss

ABSTRACT. Orchestia cavimana Heller (Amphipoda, Talitridae) were shown to orient to the geomagnetic field as well as to an anisotropic light field. When tested in an isotropic light field the orientation in the geomagnetic field was either in or opposite to the compass direction of the light vector of the anisotropic light field in which the animals had lived before the test, and this orientation was upset predictably by changing the magnetic field with Helmholtz coils. The polarity of the reaction in both magnetic orientation and photo-orientation was correlated with pre-experimental water loss. The magnetic orientation of O. cavimana is compared with that of Tenebrio molitor , and its biological significance discussed.     

Development of lateralization of the magnetic compass in a migratory bird

The magnetic compass of a migratory bird, the European robin (Erithacus rubecula), was shown to be lateralized in favour of the right eye/left brain hemisphere. However, this seems to be a property of the avian magnetic compass that is not present from the beginning, but develops only as the birds grow older. During first migration in autumn, juvenile robins can orient by their magnetic compass with their right as well as with their left eye. In the following spring, however, the magnetic compass is already lateralized, but this lateralization is still flexible: it could be removed by covering the right eye for 6 h. During the following autumn migration, the lateralization becomes more strongly fixed, with a 6 h occlusion of the right eye no longer having an effect. This change from a bilateral to a lateralized magnetic compass appears to be a maturation process, the first such case known so far in birds. Because both eyes mediate identical information about the geomagnetic field, brain asymmetry for the magnetic compass could increase efficiency by setting the other hemisphere free for other processes.     

Declination affects geomagnetic field-modulated geotaxis in fruit flies

Decades of research have established that the Earth’s magnetic field (geomagnetic field, GMF) is broadly used as a sensory cue for magnetic orientation in various animal taxa, including insects. In contrast to the investigation of the total intensity or inclination of the GMF, the effect of declination on horizontal magnetic movement has been explored in a few species, including flies, cockroaches, and dogs. However, the potential role of declination in the vertical movement in magnetosensitive organisms is yet to be reported. In this study, we provide the first evidence that declination within a natural range of change can affect static geotaxis in fruit flies, as assessed using the tube-positioning assay. In open-field measurements conducted at 22 domestic and foreign locations, the variation in declination was notably dependent upon the specific location, regardless of altitude, with similar variation in total intensity. Flies subjected to a geographic range of declination under the same total intensity and inclination exhibited remarkably different geotactic positioning scores, irrespective of GMF polarity. Notably, we observed a significant negative correlation between the geotactic score and the absolute value of declination, indicating that declination can induce negative geotaxis effects in flies. These results reveal that flies have evolved to incorporate a declination compass into their multimodal sensorimotor system and suggest that declination may be complementary to gravity in terms of environmental factor-driven negative geotaxis in flies.     

Sensitivity of biological objects to the effects of the geomagnetic field]

It is shown on the basis of calculations of energy sublevels of the hyperfine structure that the effect of the geomagnetic field upon the impurity atoms in the volume of living cells should be considered in relation to the value of geomagnetic field induction pulses delta B. When delta B > or = 10 pT and the dielectric constant epsilon > or = 10, magnetodipole transitions between sublevels of the hyperfine structure within one term are possible in impurity atoms in their 2P-state. During magnetic storms with delta B > or = 100 nT magnetodipole or magnetoquadrupole forced transitions from 2P1/2 and 2P3/2 states to 2S1/2 metastable state are possible in the resonant zones formed by intersection of hyperfine energy sublevels of the corresponding excited levels.     

A method for studying the effect of the geomagnetic field on the vital activities of microorganisms in the enteric family

The proposed method makes it possible to find out the direct influence of the geomagnetic field (GMF) on microorganisms of the family Enterobacteriaceae (the genera Escherichia, Shigella, Salmonella). Different disturbances in the state of GMF, both in amplitude and frequency range, were modeled under laboratory conditions. Microbial cells were cultivated in sterile artesian-well water or physiological saline with no organic substrate added. Experiments were performed at room temperature for 5 and more days. In these experiments the standard dose of microbial suspension was inoculated daily into Endo medium. The differences in the reproductive capacity and survival time of microorganisms in the test and control vials were compared with the indices of geomagnetic disturbances. If the experiments were started 2-4 days before the appearance of geomagnetic disturbances, the suppression of the reproductive capacity of microorganisms occurred, then followed its stimulation; this phenomenon particularly affected Escherichia coli and Shigella sonnei. In case of the quiet state of GMF the suppression of reproductive capacity is commonly observed. If the beginning of the experiment coincides with the appearance of a magnetic storm, a sharp decrease in the reproductive capacity of microorganisms and the death of the population within 1-5 days usually occurred. The survival rate of microorganisms depended on the state of GMF disturbances. The survival time of cell generations during disturbances of GMF was considerably longer. Under the conditions of a superimposed magnetic field the reproductive capacity of microorganisms outstrips, as a rule, that developing under the conditions of the compensation of the field. Studies on the biological activity of infralow frequency showed that the multidirectional reproductivity effect was observed due to constant changes in the geomagnetic background.     

Magnetoreception through Cryptochrome May Involve Superoxide

In the last decades, it has been demonstrated that many animal species orient in the Earth magnetic field. One of the best-studied examples is the use of the geomagnetic field by migratory birds for orientation and navigation. However, the biophysical mechanism underlying animal magnetoreception is still not understood. One theory for magnetoreception in birds invokes the so-called radical-pair model. This mechanism involves a pair of reactive radicals, whose chemical fate can be influenced by the orientation with respect to the magnetic field of the Earth through Zeeman and hyperfine interactions. The fact that the geomagnetic field is weak, i.e., ∼0.5 G, puts a severe constraint on the radical pair that can establish the magnetic compass sense. For a noticeable change of the reaction yield in a redirected geomagnetic field, the hyperfine interaction has to be as weak as the Earth field Zeeman interaction, i.e., unusually weak for an organic compound. Such weak hyperfine interaction can be achieved if one of the radicals is completely devoid of this interaction as realized in a radical pair containing an oxygen molecule as one of the radicals. Accordingly, we investigate here a possible radical pair-based reaction in the photoreceptor cryptochrome that reduces the protein's flavin group from its signaling state FADH^• to the inactive state FADH^- (which reacts to the likewise inactive FAD) by means of the superoxide radical, O₂^•-. We argue that the spin dynamics in the suggested reaction can act as a geomagnetic compass and that the very low physiological concentration (nM-μM) of otherwise toxic O₂^•- is sufficient, even favorable, for the biological function.     

Power lines and the geomagnetic field

The metric of prime interest in power line epidemiological studies has been AC magnetic intensity. To consider also possible geomagnetic involvement, the orientation of a long straight power line is examined relative to a uniform geomagnetic field (GMF) with dip angle α. An expression is derived for the component of the total GMF that is parallel, at an elevation β, to the circuital magnetic field that surrounds the line. This component is a function of the angles α and β, the total geomagnetic intensity B_T, and the angle θ between the axis of the power line and magnetic north. Plotting these geomagnetic parameters for known leukemia residences allows one to test for possible ion cyclotron resonance or other GMF interactions. This approach, in principle, is an easy addition to existing or planned studies, because residential access is not required to obtain local values for α, β, θ, and B_T. We recommend including these parameters in the design of epidemiological studies examining power line fields and childhood leukemia. © 1995 Wiley-Liss, Inc.     

LIFE IN ZERO MAGNETIC FIELD. III. EFFECT ON ZINC AND COPPER IN HUMAN BLOOD SERUM DURING IN VITRO AGING

The purpose of the work was to further investigate the effect of zero magnetic field (ZMF) on the concentration of ions in the human blood compared to the effect of the normal geomagnetic field (GMF). We have investigated the total Zn and Cu concentrations in the blood serum during in vitro aging of blood. The investigation was carried out both on blood from healthy donors as well as from chronic bronchial asthma (BA) patients. Blood samples were kept for 48 hours in a Helmholtz coil compensating system to remove the static component of the geomagnetic field, at room temperature. We found that zinc concentrations in the plasma were not significantly influenced by the exposure to ZMF compared to GMF for both healthy and pathological samples. In contrast, copper concentration was found to be significantly sensitive to the magnetic environment. Healthy blood showed a slight loss of copper from the blood serum in GMF, which further increased in ZMF. BA pathology is characterized by four distinct types of disease, which showed both qualitative and quantitative distinctive sensitivity to the magnetic environment, as compared to healthy blood. The aging effect appeared to be slowed down for most of the BA types of pathologies. These results point to the sensitivity of ion binding to serum proteins and/or transport through cell membranes in the magnetic environment, in our case in the absence of the normal geomagnetic field.     

Why are living things sensitive to weak magnetic fields?

There is evidence for robust interactions of weak ELF magnetic fields with biological systems. Quite apart from the difficulties attending a proper physical basis for such interactions, an equally daunting question asks why these should even occur, given the apparent lack of comparable signals in the long-term electromagnetic environment. We suggest that the biological basis is likely to be found in the weak (～50?nT) daily swing in the geomagnetic field that results from the solar tidal force on free electrons in the upper atmosphere, a remarkably constant effect exactly in phase with the solar diurnal change. Because this magnetic change is locked into the solar-derived everyday diurnal response in living things, one can argue that it acts as a surrogate for the solar variation, and therefore plays a role in chronobiological processes. This implies that weak magnetic field interactions may have a chronodisruptive basis, homologous to the more familiar effects on the biological clock arising from sleep deprivation, phase-shift employment and light at night. It is conceivable that the widespread sensitivity of biological systems to weak ELF magnetic fields is vestigially derived from this diurnal geomagnetic effect.     

A visual pathway links brain structures active during magnetic compass orientation in migratory birds

The magnetic compass of migratory birds has been suggested to be light-dependent. Retinal cryptochrome-expressing neurons and a forebrain region, "Cluster N", show high neuronal activity when night-migratory songbirds perform magnetic compass orientation. By combining neuronal tracing with behavioral experiments leading to sensory-driven gene expression of the neuronal activity marker ZENK during magnetic compass orientation, we demonstrate a functional neuronal connection between the retinal neurons and Cluster N via the visual thalamus. Thus, the two areas of the central nervous system being most active during magnetic compass orientation are part of an ascending visual processing stream, the thalamofugal pathway. Furthermore, Cluster N seems to be a specialized part of the visual wulst. These findings strongly support the hypothesis that migratory birds use their visual system to perceive the reference compass direction of the geomagnetic field and that migratory birds "see" the reference compass direction provided by the geomagnetic field.     

Weak-field ELF magnetic interactions: Implications for biological change during paleomagnetic reversals

Contrary to the belief that paleomagnetic reversals are not biologically significant, we find good reason to think otherwise. Attention is drawn to polarity transitions, time intervals a few thousand years long that follow the collapse of the existing geomagnetic dipole moment and precede the establishment of the new, oppositely directed moment. The geomagnetic field during transitions is reduced to a maximal mean intensity about 10% of the stable field and can exhibit low-frequency perturbations comparable to numerous laboratory-based extremely low frequency (ELF) studies reporting biological interactions, making it very likely that similar interactions must occur over the course of a polarity transition. This conclusion is strengthened by reports of medical problems that significantly correlate with intense solar winds, events that also generate ELF perturbations similar to those that can occur during polarity transitions.     

Orientation by magnetic field in leaf-cutter ants, Atta colombica (Hymenoptera: Formicidae)

Leaf‐cutter ants (Atta colombica) use trail following to travel between foraging sites and the home nest. However, this combination of pheromone and visual cues is likely to be complemented by a directional reference system such as a compass, used not only when foraging but also during colony formation, where foraging trails degrade or where ants become displaced. One candidate system is the magnetic polarity compass. We tested the orientation of leaf‐cutter ants under a magnetic field of reversed‐polarity, with the prediction that the ants would show 180° deflection compared with control ants in an unchanged geomagnetic field. When the sun's disc was unobstructed by clouds, orientation was the same as that of control ants, implying that magnetic cues were not used to orient. However, when the sky was overcast, ants in the experimental treatment significantly shifted their mean orientation both in comparison with controls and reversed‐polarity ants under the sun. Although a total reversal in orientation was not induced, the results demonstrate that Atta respond to magnetic reversal in the absence of sunlight cues, and suggest a role for magnetic cues in determining direction during orientation.