Magnetic material in the head of the common Pacific dolphin

Neuroanatomy of the Cetacean Sensory Systems

Cetaceans have undergone profound sensory adaptations in response to their aquatic environment during evolution. These adaptations are characterised by anatomo-functional changes in the classically defined sensory systems, shaping their neuroanatomy accordingly. This review offers a concise and up-to-date overview of our current understanding of the neuroanatomy associated with cetacean sensory systems. It encompasses a wide spectrum, ranging from the peripheral sensory cells responsible for detecting environmental cues, to the intricate structures within the central nervous system that process and interpret sensory information. Despite considerable progress in this field, numerous knowledge gaps persist, impeding a comprehensive and integrated understanding of their sensory adaptations, and through them, of their sensory perspective. By synthesising recent advances in neuroanatomical research, this review aims to shed light on the intricate sensory alterations that differentiate cetaceans from other mammals and allow them to thrive in the marine environment. Furthermore, it highlights pertinent knowledge gaps and invites future investigations to deepen our understanding of the complex processes in cetacean sensory ecology and anatomy, physiology and pathology in the scope of conservation biology.

Passive electroreception in bottlenose dolphins (Tursiops truncatus): implication for micro- and large-scale orientation

For the two dolphin species Sotalia guianensis (Guiana dolphin) and Tursiops truncatus (bottlenose dolphin), previous research has shown that the vibrissal crypts located on the rostrum represent highly innervated, ampullary electroreceptors and that both species are correspondingly sensitive to weak electric fields. In the present study, for a comparative assessment of the sensitivity of the bottlenose dolphin's electroreceptive system, we determined detection thresholds for DC and AC electric fields with two bottlenose dolphins. In a psychophysical experiment, the animals were trained to respond to electric field stimuli using the go/no-go paradigm. We show that the two bottlenose dolphins are able to detect DC electric fields as low as 2.4 and 5.5 µV cm-1, respectively, a detection threshold in the same order of magnitude as those in the platypus and the Guiana dolphin. Detection thresholds for AC fields (1, 5 and 25 Hz) were generally higher than those for DC fields, and the sensitivity for AC fields decreased with increasing frequency. Although the electroreceptive sensitivity of dolphins is lower than that of elasmobranchs, it is suggested that it allows for both micro- and macro-scale orientation. In dolphins pursuing benthic foraging strategies, electroreception may facilitate short-range prey detection and target-oriented snapping of their prey. Furthermore, the ability to detect weak electric fields may enable dolphins to perceive the Earth's magnetic field through induction-based magnetoreception, thus allowing large-scale orientation.

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.

Chain-Like Structures of Biogenic and Nonbiogenic Magnetic Nanoparticles in Vascular Tissues

In this paper, slices of organs from various organisms (animals, plants, fungi) were investigated by using atomic force microscopy and magnetic force microscopy to identify common features of localization of both biogenic and nonbiogenic magnetic nanoparticles. It was revealed that both biogenic and nonbiogenic magnetic nanoparticles are localized in the form of chains of separate nanoparticles or chains of conglomerates of nanoparticles in the walls of the capillaries of animals and the walls of the conducting tissue of plants and fungi. Both biogenic and nonbiogenic magnetic nanoparticles are embedded as a part of the transport system in multicellular organisms. In connection with this, a new idea of the function of biogenic magnetic nanoparticles is discussed, that the chains of biogenic magnetic nanoparticles and chains of conglomerates of biogenic magnetic nanoparticles represent ferrimagnetic organelles of a specific purpose. Besides, magnetic dipole-dipole interaction of biogenic magnetic nanoparticles with magnetically labeled drugs or contrast agents for magnetic resonance imaging should be considered when designing the drug delivery and other medical systems because biogenic magnetic nanoparticles in capillary walls will serve as the trapping centers for the artificial magnetic nanoparticles. The aggregates of both artificial and biogenic magnetic nanoparticles can be formed, contributing to the risk of vascular occlusion. Bioelectromagnetics. 43:119-143, 2022. © 2021 Bioelectromagnetics Society.

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.

Biogenic Metal Oxides

Biogenic metal oxides (MxOy) feature structures as highly functional and unique as the organisms generating them. They have caught the attention of scientists for the development of novel materials by biomimicry. In order to understand how biogenic MxOy could inspire novel technologies, we have reviewed examples of all biogenic MxOy, as well as the current state of understanding of the interactions between the inorganic MxOy and the biological matter they originate from and are connected to. In this review, we first summarize the origins of the precursors that living nature converts into MxOy. From the point-of-view of our materials chemists, we present an overview of the biogenesis of silica, iron and manganese oxides, as the only reported biogenic MxOy to date. These MxOy are found across all five kingdoms (bacteria, protoctista, fungi, plants and animals). We discuss the key molecules involved in the biosynthesis of MxOy, the functionality of the MxOy structures, and the techniques by which the biogenic MxOy can be studied. We close by outlining the biomimetic approaches inspired by biogenic MxOy materials and their challenges, and we point at promising directions for future organic-inorganic materials and their synthesis.

Physiological origin of biogenic magnetic nanoparticles in health and disease: from bacteria to humans

The discovery of biogenic magnetic nanoparticles (BMNPs) in the human brain gives a strong impulse to study and understand their origin. Although knowledge of the subject is increasing continuously, much remains to be done for further development to help our society fight a number of pathologies related to BMNPs. This review provides an insight into the puzzle of the physiological origin of BMNPs in organisms of all three domains of life: prokaryotes, archaea, and eukaryotes, including humans. Predictions based on comparative genomic studies are presented along with experimental data obtained by physical methods. State-of-the-art understanding of the genetic control of biomineralization of BMNPs and their properties are discussed in detail. We present data on the differences in BMNP levels in health and disease (cancer, neurodegenerative disorders, and atherosclerosis), and discuss the existing hypotheses on the biological functions of BMNPs, with special attention paid to the role of the ferritin core and apoferritin.

Magnetic nanoparticles: surface effects and properties related to biomedicine applications

Due to finite size effects, such as the high surface-to-volume ratio and different crystal structures, magnetic nanoparticles are found to exhibit interesting and considerably different magnetic properties than those found in their corresponding bulk materials. These nanoparticles can be synthesized in several ways (e.g., chemical and physical) with controllable sizes enabling their comparison to biological organisms from cells (10–100 μm), viruses, genes, down to proteins (3–50 nm). The optimization of the nanoparticles’ size, size distribution, agglomeration, coating, and shapes along with their unique magnetic properties prompted the application of nanoparticles of this type in diverse fields. Biomedicine is one of these fields where intensive research is currently being conducted. In this review, we will discuss the magnetic properties of nanoparticles which are directly related to their applications in biomedicine. We will focus mainly on surface effects and ferrite nanoparticles, and on one diagnostic application of magnetic nanoparticles as magnetic resonance imaging contrast agents.

Bioinspired greigite magnetic nanocrystals: chemical synthesis and biomedicine applications

Large scale greigite with uniform dimensions has stimulated significant demands for applications such as hyperthermia, photovoltaics, medicine and cell separation, etc. However, the inhomogeneity and hydrophobicity for most of the as prepared greigite crystals has limited their applications in biomedicine. Herein, we report a green chemical method utilizing β-cyclodextrin (β-CD) and polyethylene glycol (PEG) to synthesize bioinspired greigite (Fe₃S₄) magnetic nanocrystals (GMNCs) with similar structure and magnetic property of magnetosome in a large scale. β-CD and PEG is responsible to control the crystal phase and morphology, as well as to bound onto the surface of nanocrystals and form polymer layers. The GMNCs exhibit a transverse relaxivity of 94.8 mM⁻¹s⁻¹ which is as high as iron oxide nanocrystals, and an entrapment efficiency of 58.7% for magnetic guided delivery of chemotherapeutic drug doxorubicin. Moreover, enhanced chemotherapeutic treatment of mice tumor was obtained via intravenous injection of doxorubicin loaded GMNCs.

Bioengineered probes for molecular magnetic resonance imaging in the nervous system

The development of molecular imaging probes has changed the nature of neurobiological research. Some of the most notable successes have involved the use of biological engineering techniques for the creation of fluorescent protein derivatives for optical imaging, but recent work has also led to a number of bioengineered probes for magnetic resonance imaging (MRI), the preeminent technique for noninvasive investigation of brain structure and function. Molecular MRI agents are beginning to be applied for experiments in the nervous system, where they have the potential to bridge from molecular to systems or organismic levels of analysis. Compared with canonical synthetic small molecule agents, biomolecular or semibiosynthetic MRI contrast agents offer special advantages due to their amenability to molecular engineering approaches, their properties in some cases as catalysts, and their specificity in targeting and ligand binding. Here, we discuss an expanding list of instances where biological engineering techniques have aided in the design of MRI contrast agents and reporter systems, examining both advantages and limitations of these types of probes for studies in the central nervous system.

A Candidate Magnetic Sense Organ in the Yellowfin Tuna, Thunnus albacares

Single-domain magnetite crystals have been isolated and characterized from tissue located in a sinus within the dermethmoid bone of the skull of the yellowfin tuna, Thunnus albacares. Their chemical composition, narrow size distribution, and distinctive crystal morphology indicate that these crystals are biochemical precipitates. Experiments on the interaction between particles reveal the organization of the particles in situ and suggest a possible form for candidate magnetoreceptor organelles. The consistent localization of such particles with similar arrangement within the dermethmoids of this and other pelagic fishes suggests that the ethmoid region is a possible location for a vertebrate magnetic sense organ.

Biogeochemical Conditions Favoring Magnetite Formation during Anaerobic Iron Reduction

Several anaerobic bacteria isolated from the sediments of Contrary Creek, an iron-rich environment, produced magnetite when cultured in combinations but not when cultured alone in synthetic iron oxyhydroxide medium. When glucose was added as a carbon source, the pH of the medium decreased (to 5.5) and no magnetite was formed. When the same growth medium without glucose was used, the pH increased (to 8.5) and magnetite was formed. In both cases, Fe was released into the growth medium. Geochemical equilibrium equations with E(h) and pH as master variables were solved for the concentrations of iron and inorganic carbon that were observed in the system. Magnetite was predicted to be the dominant iron oxide formed at high pHs, while free Fe or siderite were the dominant forms of iron expected at low pHs. Thus, magnetite formation occurs because of microbial alteration of the local E(h) and pH conditions, along with concurrent reduction of ferric iron (direct biological reduction or abiological oxidation-reduction reactions).

COMPLEX MAGNETIC FIELDS ENABLE STATIC MAGNETIC FIELD CUE USE FOR RATS IN RADIAL MAZE TASKS

Male Wistar rats were trained in an eight-arm radial maze task (two sessions per day, delayed-non-matching-to-sample) that included an intramaze static magnetic field "cue" (185 microT) specific to the entrance point of one of the arms. Rats were exposed daily for 60 min to a complex magnetic field waveform (theta-burst pattern, 200-500 nT), presented with several different interstimulus intervals (ISIs), either immediately following training sessions or immediately preceding testing sessions. Application of the theta-burst stimulus with a 4000 ms ISI significantly improved the rats' memory for the arm of the radial maze whose position was indicated by the presence of a static magnetic field cue. Reference memory errors were homogeneously distributed among all eight arms of the maze for sham-exposed rats, and among the other seven arms of the maze for complex magnetic field-treated rats. These results suggest that static magnetic field cues may be salient orienting cues even in a microenvironment such as a radial maze, but their use as a cue during maze learning in rats is dependent on whole-body application of a specific time-varying complex magnetic field.

Effect of static magnetic fields on bioelectric properties of the Br and N1 neurons of snail Helix pomatia

The effects of 2.7 mT and 10 mT static magnetic fields were investigated on two identified neurons with different bioelectric properties of the snail Helix pomatia. Membrane resting potential, amplitude, spiking frequency, and duration of action potential were measured. The two neurons of H. pomatia, parabolic burster Br and silent N1, showed different responses to a static magnetic field. The magnetic field of 2.7 mT intensity caused changes in the amplitude and duration of action potential of the Br neuron, whereas the 10 mT magnetic field changed the resting potential, amplitude spike, firing frequency, and duration of action potential of the Br neuron. Bioelectric parameters measured on the N1 neuron did not change significantly in these magnetic fields.

Vortex or whorl formation of cultured human corneal epithelial cells induced by magnetic fields

The terms 'vortex keratopathy' and 'hurricane keratopathy' describe two similar conditions affecting the corneal surface. In the former, a vortex or whorl pattern is seen on the corneal surface and is due to the deposition of substances such as pigment, iron or drugs in the epithelial cells. In the latter, a similar pattern is presented by migrating epithelial cells but, unlike the former, the pattern is rendered more visible by fluorescein staining. Both represent the migratory pattern of normal epithelial cells which is otherwise not visible due to the slow rate of epithelial turnover and migration. The whorl pattern has a clockwise predisposition in the majority of cases and is hypothesised to be due to the influence of ocular electro-magnetic fields on the migrating epithelial cells. In this study we tested in vitro the effect of static magnetic fields on corneal epithelial cells. We were able to reproduce dramatic vortex or whorl patterns in response to magnetic fields, but without preferential migration towards the North or South Pole.

The organization of neocortex in mammals: are species differences really so different?

By examining a variety of mammals, it is possible to determine common features of cortical organization, and from these infer homologies across species. Such analysis also enables differences in the organization of the neocortex to be identified. Species differ in the amount of cortex that is devoted to a particular sensory system, in the size and configuration of a cortical field, in the number of cortical fields, and in the pattern of connections of homologous fields. It is suggested that the plan of organization that is retained is the result of homologous developmental events, and that modifications to this plan are generated by a limited set of mechanisms. These types of changes to the common network might account for the sensory and behavioural diversity that is observed in extant mammals.

Corneal epithelial cell migration in humans: 'hurricane and blizzard keratopathy'

Replicative turnover of the corneal epithelium is believed to occur from a population of stem cells located at the corneo-scleral limbus. During the healing of corneal epithelial wounds, sheets of epithelial cells move centripetally from the limbus and circumferentially along the limbus to cover the defect. A whorled or vortex pattern, similar to that seen in cornea verticillata, has been reported to occur on the corneal surface as an effect of topical steroid medication, during the healing of grafted corneas. This condition has been termed 'hurricane keratopathy'. We have noted this appearance in 6 patients who did not have corneal grafts. In all our patients the whorled pattern was best visible on fluorescein staining. This feature differentiates 'hurricane keratopathy' from cornea verticillata secondary to deposition of substances in corneal epithelial cells. Further, in all our patients the vortex was clockwise. Examination of illustrations of 'hurricane keratopathy' and cornea verticillata reported in the literature reveals that the whorled pattern is almost always clockwise. We believe that this specific pattern is likely to be due to the effect of the electromagnetic fields of the eye on the migrating epithelial cells and present a theory to explain this phenomenon. In 3 eyes of 2 other patients with chronic epitheliopathies we observed a random distribution of cells that did not conform to any specific pattern. We have termed this condition 'blizzard keratopathy'.

Investigation of the magnetic properties of iron oxide nanoparticles used as contrast agent for MRI

Superparamagnetic iron oxide particles, a new class of contrast agents for MRI, are extremely good enhancers of proton relaxation. However, the development of such particle systems has resulted in a wide range of preparations whose physico-chemical properties differ greatly. We have conducted a set of physical experiments: X ray diffraction analysis, relaxivity measurements, susceptibility determinations, and thermomagnetic cycling on different preparations of superparamagnetic particles. Our results demonstrate a good correlation between susceptibilities measured in liquid samples at room temperature and the R2/R1 ratio. Susceptibility measurements between liquid nitrogen temperature and room temperature show three different types of behavior dependent on the size of iron oxide crystals. Comparison of heating and cooling curves from strong field thermomagnetic cycles provides information about the maghemite/magnetite crystal content. The information on magnetic properties reported in this study may help to characterize and to select these materials for use as MRI contrast agents.

Evolutionary aspects of orientation and migration in birds

Evolutionary aspects of avian orientation and navigation are overviewed. A theoretical approach to the evolution of complex (endogenously programmed) migratory behavior is presented, using the comparative method of ordering a progression in existing behavioral characteristics from dispersal, to facultative migration, to obligate migration.

Electroreception and magnetoreception in simple and complex organisms

A considerable body of evidence now indicates that electromagnetic and geomagnetic detection systems exist in both simple, unicellular organisms and in more complex species such as avians, bees, and marine animals. A major challenge that faces researchers in this field is the identification of physiological mechanisms through which the detection of weak fields provides significant somatosensory cues for direction finding, foraging, and predation. Many of the anatomical, physiological, and biophysical approaches that are being taken in studies of this nature are described in the series of review articles that appear in this issue of Bioelectromagnetics.

Magnetite biomineralization and geomagnetic sensitivity in higher animals: an update and recommendations for future study

Magnetite, the only known biogenic material with ferromagnetic properties, has been identified as a biochemical precipitate in three of the five kingdoms of living organisms, with a fossil record that now extends back nearly 2 billion years. In the magnetotactic bacteria, protoctists, and fish, single-domain crystals of magnetite are arranged in membrane-bound linear structures called magnetosomes, which function as biological bar magnets. Magnetosomes in all three of these groups bear an overall structural similarity to each other, which includes alignment of the individual crystallographic [111] directions parallel to the long axis. Although the magnetosomes represent only a small volume fraction in higher organisms, enough of these highly energetic structures are present to provide sensitivity to extremely small fluctuations and gradients in the background geomagnetic field. Previous experiments with elasmobranch fish are reexamined to test the hypothesis that gradients played a role in their successful geomagnetic conditioning, and a variety of four-turn coil designs are considered that could be used to test the various hypotheses proposed for them.

Geomagnetic field detection in rodents

In addition to behavioral evidence for the detection of "earth-strength" magnetic fields (MF) by rodents, recent investigations have revealed that electrophysiological and biochemical responses to MF occur in the pineal organ and retina of rodents. In addition, ferrimagnetic deposits have been identified in the ethmoidal regions of the rodent skull. These findings point to a new sensory phenomenon, which interfaces with many fields of biology, including neuroscience, psychophysics, behavioral ecology, chronobiology and sensory physiology.

Geopsychology and geopsychopathology: mental processes and disorders associated with geochemical and geophysical factors

Temporal and regional variations in psychological processes have been associated with three geological factors. They are geochemical profiles, geomagnetic variations, and tectonic stresses. In the geochemical domain, copper, aluminum, zinc, and lithium may influence the incidence of thought disorders such as schizophrenia and senile dementia. These common elements are found in many soils and ground water. Geomagnetic variations have been correlated with enhanced anxiety, sleep disturbances, altered moods, and greater incidences of psychiatric admissions. The effects are usually brief but pervasive. Transient and very local epidemics of bizarre and unusual behaviors are sociological phenomena that sometimes precede increases in earthquake activity within a region; they have been hypothesized to be associated with tectonic strain. Many of the contemporary correlations between geological factors and human behavior are also apparent within historical data. The effects of geophysical and geochemical factors upon human behavior are not artifactual, but they are complex and often not detected by the limited scope of most studies.

Relationship of the vestibular hair cells to magnetic particles in the otolith of the guitarfish sacculus

Magnetite particles were systematically localized within the otolithic mass as a conspicuous curved band in the most ventral region of the guitarfish sacculus. The magnetite band overlaid two separated segments of neuroepithelium in the macula, a long segment oriented parallel to the longitudinal body axis, and a short segment oriented in a transverse plane. The exogenous magnetite particles differed from the endogenous otoconia both in their capacity of orienting to magnetic fields, and their difference in mass due to the higher atomic weight of iron. In addition to the normal gravistatic function of the sacculus, two additional receptor functions are hypothesized based upon the differences between the endogenous and exogenous otoconia. A geomagnetic field could induce magnetite displacements detectable by the hair cells for purposes of geomagnetic orientation. Alternatively, the greater atomic weights of magnetite, relative to that of otoconia, could result in gravitational and linear acceleration, which differed in different regions of the macula.