Sensing magnetic directions in birds: radical pair processes involving cryptochrome

Avian navigation: the geomagnetic field provides compass cues but not a bicoordinate "map" plus a brief discussion of the alternative infrasound direction-finding hypothesis

The geomagnetic field (GMF) is a worldwide source of compass cues used by animals and humans alike. The inclination of GMF flux lines also provides information on geomagnetic latitude. A long-disputed question, however, is whether horizontal gradients in GMF intensity, in combination with changes in inclination, provide bicoordinate "map" information. Multiple sources contribute to the total GMF, the largest of which is the core field. The ubiquitous crustal field is much less intense, but in both land and marine settings is strong enough at low altitudes (< 700 m; sea level) to mask the core field's weak N-S intensity gradient (~ 3-5 nT/km) over 10 s to 100 s of km. Non-orthogonal geomagnetic gradients, the lack of consistent E-W gradients, and the local masking of core-field intensity gradients by the crustal field, therefore, are grounds for rejection of the bicoordinate geomagnetic "map" hypothesis. In addition, the alternative infrasound direction-finding hypothesis is briefly reviewed. The GMF's diurnal variation has long been suggested as a possible Zeitgeber (timekeeper) for circadian rhythms and could explain the GMF's non-compass role in the avian navigational system. Requirements for detection of this weaker diurnal signal (~ 20-50 nT) might explain the magnetic alignment of resting and grazing animals.

Magnetic Stimulation as a Therapeutic Approach for Brain Modulation and Repair: Underlying Molecular and Cellular Mechanisms

Neurological and psychiatric diseases generally have no cure, so innovative non-pharmacological treatments, including non-invasive brain stimulation, are interesting therapeutic tools as they aim to trigger intrinsic neural repair mechanisms. A common brain stimulation technique involves the application of pulsed magnetic fields to affected brain regions. However, investigations of magnetic brain stimulation are complicated by the use of many different stimulation parameters. Magnetic brain stimulation is usually divided into two poorly connected approaches: (1) clinically used high-intensity stimulation (0.5-2 Tesla, T) and (2) experimental or epidemiologically studied low-intensity stimulation (μT-mT). Human tests of both approaches are reported to have beneficial outcomes, but the underlying biology is unclear, and thus optimal stimulation parameters remain ill defined. Here, we aim to bring together what is known about the biology of magnetic brain stimulation from human, animal, and in vitro studies. We identify the common effects of different stimulation protocols; show how different types of pulsed magnetic fields interact with nervous tissue; and describe cellular mechanisms underlying their effects-from intracellular signalling cascades, through synaptic plasticity and the modulation of network activity, to long-term structural changes in neural circuits. Recent advances in magneto-biology show clear mechanisms that may explain low-intensity stimulation effects in the brain. With its large breadth of stimulation parameters, not available to high-intensity stimulation, low-intensity focal magnetic stimulation becomes a potentially powerful treatment tool for human application.

Low-level EMF effects on wildlife and plants: What research tells us about an ecosystem approach

There is enough evidence to indicate we may be damaging non-human species at ecosystem and biosphere levels across all taxa from rising background levels of anthropogenic non-ionizing electromagnetic fields (EMF) from 0 Hz to 300 GHz. The focus of this Perspective paper is on the unique physiology of non-human species, their extraordinary sensitivity to both natural and anthropogenic EMF, and the likelihood that artificial EMF in the static, extremely low frequency (ELF) and radiofrequency (RF) ranges of the non-ionizing electromagnetic spectrum are capable at very low intensities of adversely affecting both fauna and flora in all species studied. Any existing exposure standards are for humans only; wildlife is unprotected, including within the safety margins of existing guidelines, which are inappropriate for trans-species sensitivities and different non-human physiology. Mechanistic, genotoxic, and potential ecosystem effects are discussed.

The rational design of iron-sulfur cluster binding site for prolonged stability in magnetoreceptor MagR

Iron-sulfur proteins play essential roles in a wide variety of cellular processes such as respiration, photosynthesis, nitrogen fixation and magnetoreception. The stability of iron-sulfur clusters varies significantly between anaerobic and aerobic conditions due to their intrinsic sensitivity to oxygen. Iron-sulfur proteins are well suited to various practical applications as molecular redox sensors or molecular “wires” for electron transfer. Various technologies have been developed recently using one particular iron-sulfur protein, MagR, as a magnetic tag. However, the limited protein stability and low magnetic sensitivity of MagR hindered its wide application. Here in this study, the iron-sulfur binding site of pigeon clMagR was rationally re-designed. One such mutation, T57C in pigeon MagR, showed improved iron-sulfur binding efficiency and higher iron content, as well as prolonged thermostability. Thus, clMagRT57C can serve as a prototype for further design of more stable and sensitive magnetic toolbox for magnetogenetics in the future.

Neural Circuit Repair by Low-Intensity rTMS

Electromagnetic brain stimulation is a promising treatment in neurology and psychiatry. However, clinical outcomes are variable and underlying mechanisms remain ill-defined, impeding the development of new effective stimulation protocols. There is increasing application of repetitive transcranial magnetic stimulation (rTMS) to the cerebellum to induce forebrain plasticity through its long-distance cerebello-cerebral circuits. To better understand what magnetic stimulation does within the cerebellum, we have developed tools to generate defined low-intensity (LI) magnetic fields and deliver them in vivo, in 3D organotypic culture and in primary cultures, over a range of stimulation parameters. Here we show that low-intensity rTMS (LI-rTMS) to the cerebellum induces axon growth and synapse formation providing olivocerebellar reinnervation. This repair depends on stimulation pattern, with complex biomimetic patterns being most effective, and this requires the presence of a cellular magnetoreceptor, cryptochrome. To explain these reparative changes, we found that repair-promoting LI-rTMS patterns, but not ineffective ones, increased c-fos expression in Purkinje neurons, consistent with the production of reactive oxygen species by activated cryptochrome. Rather than activating neurons via induced electric currents, we propose that weak magnetic fields act through cryptochrome, activating intracellular signals that induce climbing fibre-Purkinje cell reinnervation. This information opens new routes to optimize cerebellar magnetic stimulation and its potential role as an effective treatment for neurological diseases.

Effects of non-ionizing electromagnetic fields on flora and fauna, Part 2 impacts: how species interact with natural and man-made EMF

Ambient levels of nonionizing electromagnetic fields (EMF) have risen sharply in the last five decades to become a ubiquitous, continuous, biologically active environmental pollutant, even in rural and remote areas. Many species of flora and fauna, because of unique physiologies and habitats, are sensitive to exogenous EMF in ways that surpass human reactivity. This can lead to complex endogenous reactions that are highly variable, largely unseen, and a possible contributing factor in species extinctions, sometimes localized. Non-human magnetoreception mechanisms are explored. Numerous studies across all frequencies and taxa indicate that current low-level anthropogenic EMF can have myriad adverse and synergistic effects, including on orientation and migration, food finding, reproduction, mating, nest and den building, territorial maintenance and defense, and on vitality, longevity and survivorship itself. Effects have been observed in mammals such as bats, cervids, cetaceans, and pinnipeds among others, and on birds, insects, amphibians, reptiles, microbes and many species of flora. Cyto- and geno-toxic effects have long been observed in laboratory research on animal models that can be extrapolated to wildlife. Unusual multi-system mechanisms can come into play with non-human species - including in aquatic environments - that rely on the Earth's natural geomagnetic fields for critical life-sustaining information. Part 2 of this 3-part series includes four online supplement tables of effects seen in animals from both ELF and RFR at vanishingly low intensities. Taken as a whole, this indicates enough information to raise concerns about ambient exposures to nonionizing radiation at ecosystem levels. Wildlife loss is often unseen and undocumented until tipping points are reached. It is time to recognize ambient EMF as a novel form of pollution and develop rules at regulatory agencies that designate air as 'habitat' so EMF can be regulated like other pollutants. Long-term chronic low-level EMF exposure standards, which do not now exist, should be set accordingly for wildlife, and environmental laws should be strictly enforced - a subject explored in Part 3.

Chronobiology Meets Quantum Biology: A New Paradigm Overlooking the Horizon?

Biological processes and physiological functions in living beings are featured by oscillations with a period of about 24 h (circadian) or cycle at the second and third harmonic (ultradian) of the basic frequency, driven by the biological clock. This molecular mechanism, common to all kingdoms of life, comprising animals, plants, fungi, bacteria, and protists, represents an undoubted adaptive advantage allowing anticipation of predictable changes in the environmental niche or of the interior milieu. Biological rhythms are the field of study of Chronobiology. In the last decade, growing evidence hints that molecular platforms holding up non-trivial quantum phenomena, including entanglement, coherence, superposition and tunnelling, bona fide evolved in biosystems. Quantum effects have been mainly implicated in processes related to electromagnetic radiation in the spectrum of visible light and ultraviolet rays, such as photosynthesis, photoreception, magnetoreception, DNA mutation, and not light related such as mitochondrial respiration and enzymatic activity. Quantum effects in biological systems are the field of study of Quantum Biology. Rhythmic changes at the level of gene expression, as well as protein quantity and subcellular distribution, confer temporal features to the molecular platform hosting electrochemical processes and non-trivial quantum phenomena. Precisely, a huge amount of molecules plying scaffold to quantum effects show rhythmic level fluctuations and this biophysical model implies that timescales of biomolecular dynamics could impinge on quantum mechanics biofunctional role. The study of quantum phenomena in biological cycles proposes a profitable “entanglement” between the areas of interest of these seemingly distant scientific disciplines to enlighten functional roles for quantum effects in rhythmic biosystems.

Human magnetic sense is mediated by a light and magnetic field resonance-dependent mechanism

Numerous organisms use the Earth’s magnetic field as a sensory cue for migration, body alignment, or food search. Despite some contradictory reports, yet it is generally accepted that humans do not sense the geomagnetic field. Here, we demonstrate that a magnetic field resonance mechanism mediates light-dependent magnetic orientation in men, using a rotary chair experiment combined with a two-alternative forced choice paradigm. Two groups of subjects were classified with different magnetic orientation tendencies depending on the food context. Magnetic orientation of the subjects was sensitive to the wavelength of incident light and was critically dependent on blue light reaching the eyes. Importantly, it appears that a magnetic field resonance-dependent mechanism mediates these responses, as evidenced by disruption or augmentation of the ability to orient by radiofrequency magnetic fields at the Larmor frequency and the dependence of these effects on the angle between the radiofrequency and geomagnetic fields. Furthermore, inversion of the vertical component of the geomagnetic field revealed a non-canonical inclination compass effect on the magnetic orientation. These results establish the existence of a human magnetic sense and suggest an underlying quantum mechanical magnetoreception mechanism.

Effects of non-ionizing electromagnetic fields on flora and fauna, part 1. Rising ambient EMF levels in the environment

Ambient levels of electromagnetic fields (EMF) have risen sharply in the last 80 years, creating a novel energetic exposure that previously did not exist. Most recent decades have seen exponential increases in nearly all environments, including rural/remote areas and lower atmospheric regions. Because of unique physiologies, some species of flora and fauna are sensitive to exogenous EMF in ways that may surpass human reactivity. There is limited, but comprehensive, baseline data in the U.S. from the 1980s against which to compare significant new surveys from different countries. This now provides broader and more precise data on potential transient and chronic exposures to wildlife and habitats. Biological effects have been seen broadly across all taxa and frequencies at vanishingly low intensities comparable to today's ambient exposures. Broad wildlife effects have been seen on orientation and migration, food finding, reproduction, mating, nest and den building, territorial maintenance and defense, and longevity and survivorship. Cyto- and geno-toxic effects have been observed. The above issues are explored in three consecutive parts: Part 1 questions today's ambient EMF capabilities to adversely affect wildlife, with more urgency regarding 5G technologies. Part 2 explores natural and man-made fields, animal magnetoreception mechanisms, and pertinent studies to all wildlife kingdoms. Part 3 examines current exposure standards, applicable laws, and future directions. It is time to recognize ambient EMF as a novel form of pollution and develop rules at regulatory agencies that designate air as 'habitat' so EMF can be regulated like other pollutants. Wildlife loss is often unseen and undocumented until tipping points are reached. Long-term chronic low-level EMF exposure standards, which do not now exist, should be set accordingly for wildlife, and environmental laws should be strictly enforced.

The discovery of the use of magnetic navigational information

The magnetic field of the Earth provides animals with various kinds of information. Its use as a compass was discovered in the mid-1960s in birds, when it was first met with considerable skepticism, because it initially proved difficult to obtain evidence for magnetic sensitivity by conditioning experiments. Meanwhile, a magnetic compass was found to be widespread. It has now been demonstrated in members of all vertebrate classes, in mollusks and several arthropod species, in crustaceans as well as in insects. The use of the geomagnetic field as a 'map' for determining position, although already considered in the nineteenth century, was demonstrated by magnetically simulating displacements only after 2000, namely when animals, tested in the magnetic field of a distant site, responded as if they were physically displaced to that site and compensated for the displacement. Another use of the magnetic field is that as a 'sign post' or trigger: specific magnetic conditions elicit spontaneous responses that are helpful when animals reach the regions where these magnetic characteristics occur. Altogether, the geomagnetic field is a widely used valuable source of navigational information for mobile animals.

CRY1 Gene Polymorphism and Racing Performance of Homing Pigeons

Cryptochromes (CRY) are the family of proteins proposed as the putative magnetoreceptor molecules. In birds, among others in pigeons, CRY1 is widely expressed in a retina. Homing pigeons are known for their navigational abilities, and pigeon racing is a popular sport. So, the purpose of this study was to analyze the variability of the nucleotide sequence of the homing pigeon CRY1 gene, spanning the region coding the two amino acids W320 and W374 of Trp-triad, and estimate the relationship between genotypes and the racing performance. Investigations were carried out on 129 pigeons. Analysis of sequencing results indicated the AG to TT change within the seventh intron of CRY1 gene. Genotypes were determined by the forced PCR-RFLP method. The influence of detected polymorphism on the results of racing pigeons in 100-400 km flights was shown. The AG/TT individuals achieved significantly higher (p ≤ 0.05) mean values of ace points (AP) than the AG/AG ones. Regarding the detected nucleotide change localization, the polymorphism may be involved in CRY1 gene expression modulation. The AG to TT change in CRY1 gene may be considered as a potential genetic marker of racing performance in homing pigeons.

The diversity of photosensitivity and its implications for light pollution

Artificial light at night (ALAN) is a pervasive anthropogenic pollutant, emanating from urban and suburban developments and reaching nearly all ecosystems from dense forests to coastlines. One proposed strategy for attenuating the consequences of ALAN is to modify its spectral composition to forms that are less disruptive for photosensory systems. However, ALAN is a complicated pollutant to manage due to the extensive variation in photosensory mechanisms and the diverse ways these mechanisms manifest in biological and ecological contexts. Here, we highlight the diversity in photosensitivity across taxa and the implications of this diversity in predicting biological responses to different forms of night lighting. We curated this paper to be broadly accessible and inform current decisions about the spectrum of electric lights used outdoors. We advocate that efforts to mitigate light pollution should consider the unique ways species perceive ALAN, as well as how diverse responses to ALAN scale up to produce diverse ecological outcomes.

The Magnetic Compass of Birds: The Role of Cryptochrome

The geomagnetic field provides directional information for birds. The avian magnetic compass is an inclination compass that uses not the polarity of the magnetic field but the axial course of the field lines and their inclination in space. It works in a flexible functional window, and it requires short-wavelength light. These characteristics result from the underlying sensory mechanism based on radical pair processes in the eyes, with cryptochrome suggested as the receptor molecule. The chromophore of cryptochrome, flavin adenine dinucleotide (FAD), undergoes a photocycle, where radical pairs are formed during photo-reduction as well as during re-oxidation; behavioral data indicate that the latter is crucial for detecting magnetic directions. Five types of cryptochromes are found in the retina of birds: cryptochrome 1a (Cry1a), cryptochrome 1b, cryptochrome 2, cryptochrome 4a, and cryptochrome 4b. Because of its location in the outer segments of the ultraviolet cones with their clear oil droplets, Cry1a appears to be the most likely receptor molecule for magnetic compass information.

Cryptochromes in Mammals and Birds: Clock or Magnetic Compass?

Species throughout the animal kingdom use the Earth's magnetic field (MF) to navigate using either or both of two mechanisms. The first relies on magnetite crystals in tissue where their magnetic moments align with the MF to transduce a signal transmitted to the central nervous system. The second and the subject of this paper involves cryptochrome (CRY) proteins located in cone photoreceptors distributed across the retina, studied most extensively in birds. According to the "Radical Pair Mechanism" (RPM), blue/UV light excites CRY's flavin cofactor (FAD) to generate radical pairs whose singlet-to-triplet interconversion rate is modulated by an external MF. The signaling product of the RPM produces an impression of the field across the retinal surface. In birds, the resulting signal on the optic nerve is transmitted along the thalamofugal pathway to the primary visual cortex, which projects to brain regions concerned with image processing, memory, and executive function. The net result is a bird's orientation to the MF's inclination: its vector angle relative to the Earth's surface. The quality of ambient light (e.g., polarization) provides additional input to the compass. In birds, the Type IV CRY isoform appears pivotal to the compass, given its positioning within retinal cones; a cytosolic location therein indicating no role in the circadian clock; relatively steady diurnal levels (unlike Type II CRY's cycling); and a full complement of FAD (essential for photosensitivity). The evidence indicates that mammalian Type II CRY isoforms play a light-independent role in the cellular molecular clock without a photoreceptive function.

A comparative analysis of cone photoreceptor morphology in bowhead and beluga whales

The cetacean visual system is a product of selection pressures favoring underwater vision, yet relatively little is known about it across taxa. Previous studies report several mutations in the opsin genetic sequence in cetaceans, suggesting the evolutionary complete or partial loss of retinal cone photoreceptor function in mysticete and odontocete lineages, respectively. Despite this, limited anatomical evidence suggests cone structures are partially maintained but with absent outer and inner segments in the bowhead retina. The functional consequence and anatomical distributions associated with these unique cone morphologies remain unclear. The current study further investigates the morphology and distribution of cone photoreceptors in the bowhead whale and beluga retina and evaluates the potential functional capacity of these cells' alternative to photoreception. Refined histological and advanced microscopic techniques revealed two additional cone morphologies in the bowhead and beluga retina that have not been previously described. Two proteins involved in magnetosensation were present in these cone structures suggesting the possibility for an alternative functional role in responding to changes in geomagnetic fields. These findings highlight a revised understanding of the unique evolution of cone and gross retinal anatomy in cetaceans, and provide prefatory evidence of potential functional reassignment of these cells.

Diversity of Light Sensing Molecules and Their Expression During the Embryogenesis of the Cuttlefish (Sepia officinalis)

Eyes morphologies may differ but those differences are not reflected at the molecular level. Indeed, the ability to perceive light is thought to come from the same conserved gene families: opsins and cryptochromes. Even though cuttlefish (Cephalopoda) are known for their visually guided behaviors, there is a lack of data about the different opsins and cryptochromes orthologs represented in the genome and their expressions. Here we studied the evolutionary history of opsins, cryptochromes but also visual arrestins in molluscs with an emphasis on cephalopods. We identified 6 opsins, 2 cryptochromes and 1 visual arrestin in Sepia officinalis and we showed these families undergo several duplication events in Mollusca: one duplication in the arrestin family and two in the opsin family. In cuttlefish, we studied the temporal expression of these genes in the eyes of embryos from stage 23 to hatching and their expression in two extraocular tissues, skin and central nervous system (CNS = brain + optic lobes). We showed in embryos that some of these genes (Sof_CRY₆, Sof_reti-1, Sof_reti-2, Sof_r-opsin1 and Sof_v-arr) are expressed in the eyes and not in the skin or CNS. By looking at a juvenile and an adult S. officinalis, it seems that some of these genes (Sof_r-opsin1 and Sof_reti1) are used for light detection in these extraocular tissues but that they set-up later in development than in the eyes. We also showed that their expression (except for Sof_CRY₆) undergoes an increase in the eyes from stage 25 to 28 thus confirming their role in the ability of the cuttlefish embryos to perceive light through the egg capsule. This study raises the question of the role of Sof_CRY₆ in the developing eyes in cuttlefish embryos and the role and localization of xenopsins and r-opsin2. Consequently, the diversity of molecular actors involved in light detection both in the eyes and extraocular tissues is higher than previously known. These results open the way for studying new molecules such as those of the signal transduction cascade.

Arabidopsis cryptochrome is responsive to Radiofrequency (RF) electromagnetic fields

How living systems respond to weak electromagnetic fields represents one of the major unsolved challenges in sensory biology. Recent evidence has implicated cryptochrome, an evolutionarily conserved flavoprotein receptor, in magnetic field responses of organisms ranging from plants to migratory birds. However, whether cryptochromes fulfill the criteria to function as biological magnetosensors remains to be established. Currently, theoretical predictions on the underlying mechanism of chemical magnetoreception have been supported by experimental observations that exposure to radiofrequency (RF) in the MHz range disrupt bird orientation and mammalian cellular respiration. Here we show that, in keeping with certain quantum physical hypotheses, a weak 7 MHz radiofrequency magnetic field significantly reduces the biological responsivity to blue light of the cryptochrome receptor cry1 in Arabidopsis seedlings. Using an in vivo phosphorylation assay that specifically detects activated cryptochrome, we demonstrate that RF exposure reduces conformational changes associated with biological activity. RF exposure furthermore alters cryptochrome-dependent plant growth responses and gene expression to a degree consistent with theoretical predictions. To our knowledge this represents the first demonstration of a biological receptor responding to RF exposure, providing important new implications for magnetosensing as well as possible future applications in biotechnology and medicine.

Fe3O4 Mesocrystals with Distinctive Magnetothermal and Nanoenzyme Activity Enabling Self-Reinforcing Synergistic Cancer Therapy

Magnetite (Fe₃O₄) nanoparticles have been extensively used in noninvasive cancer treatment, for example, magnetic hyperthermia (MH) and chemodynamic therapy (CDT). However, how to achieve a highly efficient MH-CDT synergistic therapy based only on a single component of Fe₃O₄ still remains a challenge. Herein, hollow Fe₃O₄ mesocrystals (MCs) are constructed via a modified solvothermal method. Owing to the distinctive magnetic property of the mesocrystalline structure, Fe₃O₄ MCs show excellent magnetothermal conversion efficiency with a specific absorption rate of 722 w g^-1 at a Fe concentration of 0.6 mg mL^-1, much higher than that of Fe₃O₄ polycrystals (PCs). Moreover, Fe₃O₄ MCs also exhibit higher peroxidase-like activity than Fe₃O₄ PCs, which may be ascribed to the higher ratio of Fe²⁺/Fe³⁺ and more oxygen defects in the Fe₃O₄ MCs. Detailed in vivo results confirm that Fe₃O₄ MCs can instantly initiate CDT by producing the detrimental ^•OH, and such boosted reactive oxygen levels not only induces cell apoptosis but also reduces the expression of heat shock proteins, thus enabling low-temperature-mediated MH. More importantly, the in situ rising temperature resulted from MH in turn facilitates CDT, thus achieving a self-augmented synergistic effect between MH and CDT.

Near-Null Geomagnetic Field as an Innovative Method of Fruit Storage

The article presents the findings of a study investigating the effects of storing Jonagold apples for six weeks in a condition in which the vertical component of the geomagnetic field has been eliminated (near null GMF) and in control conditions representing those applied in traditional storage (i.e., in the local geomagnetic field (local GMF)). Analyses of the fruit were performed before the start of and three times during the experiment (i.e., following four, five and six weeks in storage). The contents of simple sugars were measured using the HPLC (high performance liquid chromatography) method; refractometry was applied to identify total extract; thermogravimetry was used to measure the water content, volatile substances and total ash; calorific value and intensity of respiration were examined by measuring CO2 emissions. Significant differences were found between the apples stored in the experimental and under control conditions, showing an advantage of storage in a condition with the vertical component of the geomagnetic field removed. Statistically significant differences were mainly identified in the speed of starch conversion into simple sugars, as well as the intensity of respiration and the appearance of the two groups of apples. Storage of fruit in a compensated geomagnetic field proved to be an effective method permitting an extended duration of storage without significant deterioration of the physicochemical and organoleptic properties of apples.

Cryptochrome mediated magnetic sensitivity in Arabidopsis occurs independently of light-induced electron transfer to the flavin

Arabidopsis cryptochrome-dependent magnetosensitivity occurs via a reaction that does not require light. This excludes radical pairs formed during light-triggered electron transfer to the flavin.

Neural circuit repair by low-intensity magnetic stimulation requires cellular magnetoreceptors and specific stimulation patterns

Although electromagnetic brain stimulation is a promising treatment in neurology and psychiatry, clinical outcomes are variable, and underlying mechanisms are ill-defined, which impedes the development of new effective stimulation protocols. Here, we show, in vivo and ex vivo, that repetitive transcranial magnetic stimulation at low-intensity (LI-rTMS) induces axon outgrowth and synaptogenesis to repair a neural circuit. This repair depends on stimulation pattern, with complex biomimetic patterns being particularly effective, and the presence of cryptochrome, a putative magnetoreceptor. Only repair-promoting LI-rTMS patterns up-regulated genes involved in neuronal repair; almost 40% of were cryptochrome targets. Our data open a new framework to understand the mechanisms underlying structural neuroplasticity induced by electromagnetic stimulation. Rather than neuronal activation by induced electric currents, we propose that weak magnetic fields act through cryptochrome to activate cellular signaling cascades. This information opens new routes to optimize electromagnetic stimulation and develop effective treatments for different neurological diseases.

Melatonin Levels and Low-Frequency Magnetic Fields in Humans and Rats: New Insights From a Bayesian Logistic Regression

The present analysis revisits the impact of extremely low-frequency magnetic fields (ELF-MF) on melatonin (MLT) levels in human and rat subjects using both a parametric and non-parametric approach. In this analysis, we use 62 studies from review articles. The parametric approach consists of a Bayesian logistic regression (LR) analysis and the non-parametric approach consists of a Support Vector analysis, both of which are robust against spurious/false results. Both approaches reveal a unique well-ordered pattern, and show that human and rat studies are consistent with each other once the MF strength is restricted to cover the same range (with B ≲ 50 μT). In addition, the data reveal that chronic exposure (longer than ∼22 days) to ELF-MF appears to decrease MLT levels only when the MF strength is below a threshold of ~30 μT ( log B thr [ μ T ] = 1 . 4 - 0 . 4 + 0 . 7 ), i.e., when the man-made ELF-MF intensity is below that of the static geomagnetic field. Studies reporting an association between ELF-MF and changes to MLT levels and the opposite (no association with ELF-MF) can be reconciled under a single framework. Bioelectromagnetics. 2019;40:539-552. © 2019 Bioelectromagnetics Society.

Magnetoreception in birds

Birds can use two kinds of information from the geomagnetic field for navigation: the direction of the field lines as a compass and probably magnetic intensity as a component of the navigational ‘map’. The direction of the magnetic field appears to be sensed via radical pair processes in the eyes, with the crucial radical pairs formed by cryptochrome. It is transmitted by the optic nerve to the brain, where parts of the visual system seem to process the respective information. Magnetic intensity appears to be perceived by magnetite-based receptors in the beak region; the information is transmitted by the ophthalmic branch of the trigeminal nerve to the trigeminal ganglion and the trigeminal brainstem nuclei. Yet in spite of considerable progress in recent years, many details are still unclear, among them details of the radical pair processes and their transformation into a nervous signal, the precise location of the magnetite-based receptors and the centres in the brain where magnetic information is combined with other navigational information for the navigational processes.

Chemical compass behaviour at microtesla magnetic fields strengthens the radical pair hypothesis of avian magnetoreception

The fact that many animals, including migratory birds, use the Earth's magnetic field for orientation and compass-navigation is fascinating and puzzling in equal measure. The physical origin of these phenomena has not yet been fully understood, but arguably the most likely hypothesis is based on the radical pair mechanism (RPM). Whilst the theoretical framework of the RPM is well-established, most experimental investigations have been conducted at fields several orders of magnitude stronger than the Earth's. Here we use transient absorption spectroscopy to demonstrate a pronounced orientation-dependence of the magnetic field response of a molecular triad system in the field region relevant to avian magnetoreception. The chemical compass response exhibits the properties of an inclination compass as found in migratory birds. The results underline the feasibility of a radical pair based avian compass and also provide further guidelines for the design and operation of exploitable chemical compass systems.

Effects of 50 Hz magnetic fields on circadian rhythm control in mice

Artificial light and power frequency magnetic fields are ubiquitous in the built environment. Light is a potent zeitgeber but it is unclear whether power frequency magnetic fields can influence circadian rhythm control. To study this possibility, 8-12-week-old male C57BL/6J mice were exposed for 30 min starting at zeitgeber time 14 (ZT14, 2 h into the dark period of the day) to 50 Hz magnetic fields at 580 μT using a pair of Helmholtz coils and/or a blue LED light at 700 lux or neither. Our experiments revealed an acute adrenal response to blue light, in terms of increased adrenal per1 gene expression, increased serum corticosterone levels, increased time spent sleeping, and decreased locomotor activity (in all cases, P < 0.0001) compared to an unexposed control group. There appeared to be no modulating effect of the magnetic fields on the response to light, and there was also no effect of the magnetic fields alone (in both cases, P > 0.05) except for a decrease in locomotor activity (P < 0.03). Gene expression of the cryptochromes cry1 and cry2 in the adrenals, liver, and hippocampus was also not affected by exposures (in all cases, P > 0.05). In conclusion, these results suggest that 50 Hz magnetic fields do not significantly affect the acute light response to a degree that can be detected in the adrenal response. Bioelectromagnetics. 2019;9999:XX-XX. © 2019 Bioelectromagnetics Society.

Magnetic sensitivity mediated by the Arabidopsis blue-light receptor cryptochrome occurs during flavin reoxidation in the dark

Arabidopsis cryptochrome mediates responses to magnetic fields that have been applied in the absence of light, consistent with flavin reoxidation as the primary detection mechanism. Cryptochromes are highly conserved blue-light-absorbing flavoproteins which have been linked to the perception of electromagnetic stimuli in numerous organisms. These include sensing the direction of the earth's magnetic field in migratory birds and the intensity of magnetic fields in insects and plants. When exposed to light, cryptochromes undergo flavin reduction/reoxidation redox cycles leading to biological activation which generate radical pairs thought to be the basis for magnetic sensitivity. However, the nature of the magnetically sensitive radical pairs and the steps at which they act during the cryptochrome redox cycle are currently a matter of debate. Here, we investigate the response of Arabidopsis cryptochrome-1 in vivo to a static magnetic field of 500 μT (10 × earth's field) using both plant growth and light-dependent phosphorylation as an assay. Cryptochrome responses to light were enhanced by the magnetic field, as indicated by increased inhibition of hypocotyl elongation and increased cryptochrome phosphorylation. However, when light and dark intervals were given intermittently, a plant response to the magnetic field was observed even when the magnetic field was given exclusively during the dark intervals between light exposures. This indicates that the magnetically sensitive reaction step in the cryptochrome photocycle must occur during flavin reoxidation, and likely involves the formation of reactive oxygen species.

Low-intensity electromagnetic fields induce human cryptochrome to modulate intracellular reactive oxygen species

Exposure to man-made electromagnetic fields (EMFs), which increasingly pollute our environment, have consequences for human health about which there is continuing ignorance and debate. Whereas there is considerable ongoing concern about their harmful effects, magnetic fields are at the same time being applied as therapeutic tools in regenerative medicine, oncology, orthopedics, and neurology. This paradox cannot be resolved until the cellular mechanisms underlying such effects are identified. Here, we show by biochemical and imaging experiments that exposure of mammalian cells to weak pulsed electromagnetic fields (PEMFs) stimulates rapid accumulation of reactive oxygen species (ROS), a potentially toxic metabolite with multiple roles in stress response and cellular ageing. Following exposure to PEMF, cell growth is slowed, and ROS-responsive genes are induced. These effects require the presence of cryptochrome, a putative magnetosensor that synthesizes ROS. We conclude that modulation of intracellular ROS via cryptochromes represents a general response to weak EMFs, which can account for either therapeutic or pathological effects depending on exposure. Clinically, our findings provide a rationale to optimize low field magnetic stimulation for novel therapeutic applications while warning against the possibility of harmful synergistic effects with environmental agents that further increase intracellular ROS.

Repetitive low-intensity magnetic stimulation has been used in the treatment of disease for over 50 years. Associated benefits have included alleviation of depression, memory loss, and symptoms of Parkinson disease, as well as accelerated bone and wound healing and the treatment of certain cancers, independently of surgery or drugs. However, the cellular mechanisms underlying these effects remain unclear. Here, we demonstrate that repetitive magnetic field exposure in human cells stimulates production of biological stress response chemicals known as reactive oxygen species (ROS). At moderate doses, we find that reactive oxygen actively stimulates cellular repair and stress response pathways, which might account for the observed therapeutic effects to repetitive magnetic stimulation. We further show that this response requires the function of a well-characterized, evolutionarily conserved flavoprotein receptor known as cryptochrome, which has been implicated in magnetic sensing in organisms ranging from plants to flies, including migratory birds. We conclude that exposure to weak magnetic fields induces the production of ROS in human cells and that this process requires the presence of the cryptochrome receptor.

Coupling of pulsed electromagnetic fields (PEMF) therapy to molecular grounds of the cell

In this review we compile results cited in reliable journals that show a ratio for the use of pulsed electromagnetic fields (PEMF) in therapy, indeed. This is true especially for chronically inflamed joints. Furthermore, we try to link this therapeutic approach to the molecular background of chronic inflammation and arthritis. At first we start with the clinical outcome of PEMF therapy. Then, we look for possible triggers and an electromagnetic counterpart that is endogenously inherent in cell biology and in the tissues of interest. Finally, we want to investigate causal molecular and cellular mechanisms of possible PEMF actions. It shows that there are endogenous mechanisms, indeed, which can act as triggers for PEMF like the resting membrane potential as well as resonance mechanisms in charged moieties like membrane transporters. Especially voltage-gated calcium channels can be triggered. These may lead into specific signaling pathways and also may elicit nitric oxide as well as moderate radical reactions, which can ultimately lead to e.g. NFκB-like reactions. Concerted in the right way, these reactions can cause a kind of cell protection and ultimately lead to a dampening of inflammatory signals like interleukins.

A model of the FAD redox cycle describes the dynamics of the effect of the geomagnetic field on the human visual system

In experimental studies, we could show that the visual threshold of man is influenced by the geomagnetic field. One of the results was that the threshold shows periodic fluctuations when the vertical component of the field is reversed periodically. The maximum of these oscillations occurred at a period duration of 110 s. To explain this phenomenon, we chose the process that likely underlies the navigation of birds in the geomagnetic field: the light reaction of the FAD component of cryptochrome in the retina. The human retina contains cryptpochrome like the bird retina. Based on the investigations of Müller and Ahmad (J Biol Chem 286:21033-21040, 2011) and Solov'yov and Schulten (J Phys Chem B 116:1089-1099, 2012), we designed a model of the light-induced reduction and subsequent reoxidation of FAD. This model contains a radical pair, whose interconversion dynamics are affected by the geomagnetic field. The parameters of the model were partly calculated from the data of our experimental investigation and partly taken from the results of other authors. These parameters were then optimized by adjusting the model behaviour to the experimental results. The simulation of the finished model shows that the concentrations of all substances included show really oscillations with the frequency of the modelled magnetic field. After optimization of the parameters, the oscillations of FAD and FADH* show maximal amplitude at a period duration of 110 s, as was observed in the experiment. This makes it most likely that the signal, which influences the visual system, originates from FADH* (signalling state).

High levels of maternally transferred mercury disrupt magnetic responses of snapping turtle hatchlings (Chelydra serpentina)

The Earth's magnetic field is involved in spatial behaviours ranging from long-distance migration to non-goal directed behaviours, such as spontaneous magnetic alignment (SMA). Mercury is a harmful pollutant most often generated from anthropogenic sources that can bio-accumulate in animal tissue over a lifetime. We compared SMA of hatchling snapping turtles from mothers captured at reference (i.e., low mercury) and mercury contaminated sites. Reference turtles showed radio frequency-dependent SMA along the north-south axis, consistent with previous studies of SMA, while turtles with high levels of maternally inherited mercury failed to show consistent magnetic alignment. In contrast, there was no difference between reference and mercury exposed turtles on standard performance measures. The magnetic field plays an important role in animal orientation behaviour and may also help to integrate spatial information from a variety of sensory modalities. As a consequence, mercury may compromise the performance of turtles in a wide variety of spatial tasks. Future research is needed to determine the threshold for mercury effects on snapping turtles, whether mercury exposure compromises spatial behaviour of adult turtles, and whether mercury has a direct effect on the magnetoreception mechanism(s) that mediate SMA or a more general effect on the nervous system.

Migratory bats respond to artificial green light with positive phototaxis

Artificial light at night is spreading worldwide at unprecedented rates, exposing strictly nocturnal animals such as bats to a novel anthropogenic stressor. Previous studies about the effect of artificial light on bats focused almost exclusively on non-migratory species, yet migratory animals such as birds are known to be largely affected by light pollution. Thus, we conducted a field experiment to evaluate if bat migration is affected by artificial light at night. In late summer, we presented artificial green light of 520 nm wavelength to bats that were migrating south along the shoreline of the Baltic Sea. Using a light on-off treatment, we observed that the activity of Pipistrellus nathusii and P. pygmaeus, the two most abundant migratory species at our site, increased by more than 50% in the light-on compared to the light-off treatment. We observed an increased number of feeding buzzes during the light-on compared to the light-off treatment for P. nathusii. However, feeding activity was low in general and did not increase disproportionately during the light-on treatment in relation to the overall echolocation call activity of bats. Further, P. nathusii were attracted towards the green light at a distance of about 23 m, which is way beyond the echolocation detection range for insects of Nathusius’ bats. We therefore infer that migratory bats were not attracted to artificial green light because of high insect densities, but instead by positive phototaxis. We conclude that artificial light at night may potentially impact bat migration in a yet unrecognized way.

Mathematical analysis of the homing flights of pigeons based on GPS tracks

To analyse the effect of magnetic and olfactory deprivation on the homing flight of pigeons, we released birds from a familiar site with either their upper beak or their nostrils anaesthetized. The tracks were analysed by time lag embedding to calculate the short-term correlation dimension, a variable that reflects the degrees of freedom and thus the number of factors involved in a system. We found that higher natural fluctuations in the earth's magnetic field characterized by A _P-indices of 8 and above caused a reduction of the correlation dimension of the control birds. We thus separated the data into two groups according to whether they were recorded on magnetically quiet days or on days with higher magnetic fluctuations. Anaesthetizing the upper beak had no significant effect. Making pigeons anosmic reduced the correlation dimension on magnetically quiet days, but did not cause any reduction on days with higher fluctuations. Altogether, our data suggest an involvement of magnetic cues and olfactory factors during the homing flight and point to a robust, multi-factorial map.

Photocycle and signaling mechanisms of plant cryptochromes

Cryptochromes are flavoprotein blue light receptors that control many aspects of plant growth and development including seedling de-etiolation, elongation growth, the initiation of flowering, and entrainment of the circadian clock. Photon absorption by Arabidopsis cryptochromes cry1 and cry2 initiates electron transfer to the oxidized flavin cofactor (FADox) and formation of the presumed biological signaling state FADH°. Current literature on the nature and formation of the signaling state is reviewed, and potential novel roles for cryptochromes in oxidative stress and as magnetosensors are discussed in light of the cryptochrome photocycle.

Strategies for Pre-Emptive Mid-Air Collision Avoidance in Budgerigars

We have investigated how birds avoid mid-air collisions during head-on encounters. Trajectories of birds flying towards each other in a tunnel were recorded using high speed video cameras. Analysis and modelling of the data suggest two simple strategies for collision avoidance: (a) each bird veers to its right and (b) each bird changes its altitude relative to the other bird according to a preset preference. Both strategies suggest simple rules by which collisions can be avoided in head-on encounters by two agents, be they animals or machines. The findings are potentially applicable to the design of guidance algorithms for automated collision avoidance on aircraft.

The circadecadal rhythm of oscillation of umbilical cord blood parameters correlates with geomagnetic activity - An analysis of long-term measurements (1999-2011)

Recently, we have shown that the contents of total nucleated cells (TNCs) and CD34⁺ hematopoietic stem and progenitor cells (CD34⁺ HSPCs) as well as the cord blood volume (CBV) in umbilical cord blood (UCB) show a circadecadal (~10 years) rhythm of oscillation. This observation was based on an analysis of 17,936 cord blood donations collected during 1999-2011. The aim of the present study was to investigate whether this circadecadal rhythm of oscillation in TNCs, CD34⁺ HSPCs and CBV is related to geomagnetic activity. For the analysis, the yearly averages of TNCs, CD34⁺ HSPCs and CBV in UCB were correlated with geomagnetic activity (Dcx index). Our analysis revealed that (i) all three UCB parameters were statistically significantly correlated with the level of geomagnetic activity, (ii) CBV showed a linear correlation with the Dcx index (r = 0.5290), (iii) the number of TNCs and CD34⁺ HSPCs were quadratic inversely correlated with the Dcx index (r = -0.5343 and r = -0.7749, respectively). Furthermore, (iv) CBV and the number of TNCs were not statistically significantly correlated with the number of either modest or intense geomagnetic storms per year, but (v) the number of CD34⁺ HSPCs was statistically significantly correlated with the number of modest (r = 0.9253) as well as intense (r = 0.8683) geomagnetic storms per year. In conclusion, our study suggests that UCB parameters correlate with the state of the geomagnetic field (GMF) modulated by solar activity. Possible biophysical mechanisms underlying this observation, as well as the outcome of these findings, are discussed.

Electron spin relaxation in cryptochrome-based magnetoreception

The magnetic compass sense of migratory birds is thought to rely on magnetically sensitive radical pairs formed photochemically in cryptochrome proteins in the retina. An important requirement of this hypothesis is that electron spin relaxation is slow enough for the Earth's magnetic field to have a significant effect on the coherent spin dynamics of the radicals. It is generally assumed that evolutionary pressure has led to protection of the electron spins from irreversible loss of coherence in order that the underlying quantum dynamics can survive in a noisy biological environment. Here, we address this question for a structurally characterized model cryptochrome expected to share many properties with the putative avian receptor protein. To this end we combine all-atom molecular dynamics simulations, Bloch-Redfield relaxation theory and spin dynamics calculations to assess the effects of spin relaxation on the performance of the protein as a compass sensor. Both flavin-tryptophan and flavin-Z˙ radical pairs are studied (Z˙ is a radical with no hyperfine interactions). Relaxation is considered to arise from modulation of hyperfine interactions by librational motions of the radicals and fluctuations in certain dihedral angles. For Arabidopsis thaliana cryptochrome 1 (AtCry1) we find that spin relaxation implies optimal radical pair lifetimes of the order of microseconds, and that flavin-Z˙ pairs are less affected by relaxation than flavin-tryptophan pairs. Our results also demonstrate that spin relaxation in isolated AtCry1 is incompatible with the long coherence times that have been postulated to explain the disruption of the avian magnetic compass sense by weak radiofrequency magnetic fields. We conclude that a cryptochrome sensor in vivo would have to differ dynamically, if not structurally, from isolated AtCry1. Our results clearly mark the limits of the current hypothesis and lead to a better understanding of the operation of radical pair magnetic sensors in noisy biological environments.

Coherent chemical kinetics as quantum walks. I. Reaction operators for radical pairs

Classical chemical kinetics uses rate-equation models to describe how a reaction proceeds in time. Such models are sufficient for describing state transitions in a reaction where coherences between different states do not arise, in other words, a reaction that contains only incoherent transitions. A prominent example of a reaction containing coherent transitions is the radical-pair model. The kinetics of such reactions is defined by the so-called reaction operator that determines the radical-pair state as a function of intermediate transition rates. We argue that the well-known concept of quantum walks from quantum information theory is a natural and apt framework for describing multisite chemical reactions. By composing Kraus maps that act only on two sites at a time, we show how the quantum-walk formalism can be applied to derive a reaction operator for the standard avian radical-pair reaction. Our reaction operator predicts the same recombination dephasing rate as the conventional Haberkorn model, which is consistent with recent experiments [K. Maeda et al., J. Chem. Phys. 139, 234309 (2013)], in contrast to previous work by Jones and Hore [J. A. Jones and P. J. Hore, Chem. Phys. Lett. 488, 90 (2010)]. The standard radical-pair reaction has conventionally been described by either a normalized density operator incorporating both the radical pair and reaction products or a trace-decreasing density operator that considers only the radical pair. We demonstrate a density operator that is both normalized and refers only to radical-pair states. Generalizations to include additional dephasing processes and an arbitrary number of sites are also discussed.

Coherent chemical kinetics as quantum walks. II. Radical-pair reactions in Arabidopsis thaliana

We apply the quantum-walk approach proposed in the preceding paper [A. Chia et al., preceding paper, Phys. Rev. E 93, 032407 (2016)] to a radical-pair reaction where realistic estimates for the intermediate transition rates are available. The well-known average hitting time from quantum walks can be adopted as a measure of how quickly the reaction occurs and we calculate this for varying degrees of dephasing in the radical pair. The time for the radical pair to react to a product is found to be independent of the amount of dephasing introduced, even in the limit of no dephasing where the transient population dynamics exhibits strong coherent oscillations. This can be seen to arise from the existence of a rate-limiting step in the reaction and we argue that in such examples, a purely classical model based on rate equations can be used for estimating the time scale of the reaction but not necessarily its population dynamics.

Cryptochrome 1 in Retinal Cone Photoreceptors Suggests a Novel Functional Role in Mammals

Cryptochromes are a ubiquitous group of blue-light absorbing flavoproteins that in the mammalian retina have an important role in the circadian clock. In birds, cryptochrome 1a (Cry1a), localized in the UV/violet-sensitive S1 cone photoreceptors, is proposed to be the retinal receptor molecule of the light-dependent magnetic compass. The retinal localization of mammalian Cry1, homologue to avian Cry1a, is unknown, and it is open whether mammalian Cry1 is also involved in magnetic field sensing. To constrain the possible role of retinal Cry1, we immunohistochemically analysed 90 mammalian species across 48 families in 16 orders, using an antiserum against the Cry1 C-terminus that in birds labels only the photo-activated conformation. In the Carnivora families Canidae, Mustelidae and Ursidae, and in some Primates, Cry1 was consistently labeled in the outer segment of the shortwave-sensitive S1 cones. This finding would be compatible with a magnetoreceptive function of Cry1 in these taxa. In all other taxa, Cry1 was not detected by the antiserum that likely also in mammals labels the photo-activated conformation, although Western blots showed Cry1 in mouse retinal cell nuclei. We speculate that in the mouse and the other negative-tested mammals Cry1 is involved in circadian functions as a non-light-responsive protein.

Cryptochrome 2 mediates directional magnetoreception in cockroaches

The ability to perceive geomagnetic fields (GMFs) represents a fascinating biological phenomenon. Studies on transgenic flies have provided evidence that photosensitive Cryptochromes (Cry) are involved in the response to magnetic fields (MFs). However, none of the studies tackled the problem of whether the Cry-dependent magnetosensitivity is coupled to the sole MF presence or to the direction of MF vector. In this study, we used gene silencing and a directional MF to show that mammalian-like Cry2 is necessary for a genuine directional response to periodic rotations of the GMF vector in two insect species. Longer wavelengths of light required higher photon fluxes for a detectable behavioral response, and a sharp detection border was present in the cyan/green spectral region. Both observations are consistent with involvement of the FADox, FAD(•-) and FADH(-) redox forms of flavin. The response was lost upon covering the eyes, demonstrating that the signal is perceived in the eye region. Immunohistochemical staining detected Cry2 in the hemispherical layer of laminal glia cells underneath the retina. Together, these findings identified the eye-localized Cry2 as an indispensable component and a likely photoreceptor of the directional GMF response. Our study is thus a clear step forward in deciphering the in vivo effects of GMF and supports the interaction of underlying mechanism with the visual system.

Biofield Physiology: A Framework for an Emerging Discipline

Biofield physiology is proposed as an overarching descriptor for the electromagnetic, biophotonic, and other types of spatially-distributed fields that living systems generate and respond to as integral aspects of cellular, tissue, and whole organism self-regulation and organization. Medical physiology, cell biology, and biophysics provide the framework within which evidence for biofields, their proposed receptors, and functions is presented. As such, biofields can be viewed as affecting physiological regulatory systems in a manner that complements the more familiar molecular-based mechanisms. Examples of clinically relevant biofields are the electrical and magnetic fields generated by arrays of heart cells and neurons that are detected, respectively, as electrocardiograms (ECGs) or magnetocardiograms (MCGs) and electroencephalograms (EEGs) or magnetoencephalograms (MEGs). At a basic physiology level, electromagnetic activity of neural assemblies appears to modulate neuronal synchronization and circadian rhythmicity. Numerous nonneural electrical fields have been detected and analyzed, including those arising from patterns of resting membrane potentials that guide development and regeneration, and from slowly-varying transepithelial direct current fields that initiate cellular responses to tissue damage. Another biofield phenomenon is the coherent, ultraweak photon emissions (UPE), detected from cell cultures and from the body surface. A physiological role for biophotons is consistent with observations that fluctuations in UPE correlate with cerebral blood flow, cerebral energy metabolism, and EEG activity. Biofield receptors are reviewed in 3 categories: molecular-level receptors, charge flux sites, and endogenously generated electric or electromagnetic fields. In summary, sufficient evidence has accrued to consider biofield physiology as a viable scientific discipline. Directions for future research are proposed.

Magnetoreception in birds: the effect of radio-frequency fields

The avian magnetic compass, probably based on radical pair processes, works only in a narrow functional window around the local field strength, with cryptochrome 1a as most likely receptor molecule. Radio-frequency fields in the MHz range have been shown to disrupt the birds' orientation, yet the nature of this interference is still unclear. In an immuno-histological study, we tested whether the radio-frequency fields interfere with the photoreduction of cryptochrome, but this does not seem to be the case. In behavioural studies, birds were not able to adjust to radio-frequency fields like they are able to adjust to static fields outside the normal functional range: neither a 2-h pre-exposure in a 7.0 MHz field, 480 nT, nor a 7-h pre-exposure in a 1.315 MHz field, 15 nT, allowed the birds to regain their orientation ability. This inability to adjust to radio-frequency fields suggests that these fields interfere directly with the primary processes of magnetoreception and therefore disable the avian compass as long as they are present. They do not have lasting adverse after-effects, however, as birds immediately after exposure to a radio-frequency field were able to orient in the local geomagnetic field.

Cryptochromes and Hormone Signal Transduction under Near-Zero Magnetic Fields: New Clues to Magnetic Field Effects in a Rice Planthopper

Although there are considerable reports of magnetic field effects (MFE) on organisms, very little is known so far about the MFE-related signal transduction pathways. Here we establish a manipulative near-zero magnetic field (NZMF) to investigate the potential signal transduction pathways involved in MFE. We show that exposure of migratory white-backed planthopper, Sogatella furcifera, to the NZMF results in delayed egg and nymphal development, increased frequency of brachypterous females, and reduced longevity of macropterous female adults. To understand the changes in gene expression underlying these phenotypes, we examined the temporal patterns of gene expression of (i) CRY1 and CRY2 as putative magnetosensors, (ii) JHAMT, FAMeT and JHEH in the juvenile hormone pathway, (iii) CYP307A1 in the ecdysone pathway, and (iv) reproduction-related Vitellogenin (Vg). The significantly altered gene expression of CRY1 and CRY2 under the NZMF suggest their developmental stage-specific patterns and potential upstream location in magnetic response. Gene expression patterns of JHAMT, JHEH and CYP307A1 were consistent with the NZMF-triggered delay in nymphal development, higher proportion of brachypterous female adults, and the shortened longevity of macropterous female adults, which show feasible links between hormone signal transduction and phenotypic MFE. By conducting manipulative NZMF experiments, our study suggests an important role of the geomagnetic field (GMF) in modulating development and physiology of insects, provides new insights into the complexity of MFE-magnetosensitivity interactions, and represents an initial but crucial step forward in understanding the molecular basis of cryptochromes and hormone signal transduction involved in MFE.

Cues indicating location in pigeon navigation

Domesticated Rock Pigeons (Columba livia f. domestica) have been selected for returning home after being displaced. They appear to use many of the physical cue sources available in the natural environment for Map-and-Compass navigation. Two compass mechanisms that have been well documented in pigeons are a time-compensated sun compass and a magnetic inclination compass. Location-finding, or map, mechanisms have been more elusive. Visual landmarks, magnetic fields, odors, gravity and now also infrasound have been proposed as sources of information on location. Even in highly familiar locations, pigeons appear to neither use nor need landmarks and can even return to the loft while wearing frosted lenses. Direct and indirect evidence indicates magnetic field information influences pigeon navigation in ways that are consistent with magnetic map components. The role of odors is unclear; it might be motivational in nature rather than navigational. The influence of gravity must be further analyzed. Experiments with infrasound have been interpreted in the sense that they provide information on the home direction, but this hypothesis is inconsistent with the Map-and-Compass Model. All these factors appear to be components of a multifactorial system, with the pigeons being opportunistic, preferring those cues that prove most suitable in their home region. This has made understanding the roles of individual cues challenging.