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Geomagnetic Field Effects on Living Systems

Cell membranes can be extremely sensitive to a force, and there are a number of models as to how

the movement of magnetite particles could afect the function of ion channels, and thereby result in the

conversion of the magnetic energy into a change to the membrane potential (Vácha, 2017, based on Shaw

et al., 2015). Here, two hypothetical representations of how Fe oxide particles may transform magnetic

energy into physical force via opening the cation channel in the cell membrane, hence enabling neural

signalization (Vácha, 2017, based on Shaw et al., 2015). A cluster of superparamagnetic particles attached

by a cytoskeletal flament to the gating domain of force-gated channel moves along the GMF force. Te

chain of single-domain grains having stable moment rotates accordingly to the external feld and the

flament transfers the torque to the channel.

Tis model has several characteristic features that are well met in certain animals (Vácha, 2017): Most

important, (1) such a magnetoreceptor does not require light to function; (2) it is a receptor sensitive

on principle to the polarity of the MF, that is, distinguishing magnetic north from south; (3) its mag­

netic properties may also be impacted by a strong and short pulse of the external feld; and (4) another

supporting argument is the discovery of Fe oxide particles in animal tissues. Teir occurrence and

properties have been documented relatively extensively in invertebrates and in social insects in popular

(Wajnberg et al., 2010).

Magnetite was also found in specialized cells in honeybees (Gould et al., 1978) and pigeons (Wallcott

et al., 1979). In pigeons, the detector is localized in innervated tissue in the ethmoid sinus near the nose

(the upper beak) (Wallcott et al., 1979). Moreover, it has been reported that night-migratory songbirds

have a magnetic compass in their eyes and a second magnetic sense in the ophthalmic branch of the tri­

geminal nerve (V1) (Kishkinev et al., 2013). Te second magnetic sense is assumed to be magnetite iron

oxide nanoparticles-based and located in the upper beak (frst described by Beason and Semm, 1987).

In this case, Solov’yov and Greiner (2007) suggested that the pull or push to the magnetite assemblies,

which are connected to the cell membrane, may reach a value of ~0.2 pN, and this value would be suf­

fcient to excite specifc mechanoreceptive membrane channels in the nerve cells.

Electrophysiological recordings from V1 and the trigeminal ganglion of the bobolink (Dolichonyx

oryzivorus) by Beason and Semm claimed that V1 transmits magnetic information (Beason and

Semm, 1987; Semm and Beason, 1990), but the relevance of these studies is questionable, since, despite

several serious attempts, nobody has managed to replicate them (Mouritsen and Hore, 2012). In two

recent independent studies, migratory European robins (Heyers et al., 2010) and non-migratory hom­

ing pigeons (Wu and Dickman, 2011) were exposed to changing magnetic stimuli, and neuronal activ­

ity in the V1-recipient regions in the hindbrain was quantifed using ZENK (Heyers et al., 2010) or

c-fos (Wu and Dickman, 2011) expression. Te results suggest that neurons in the trigeminal nuclei

are most probably activated by magnetic stimuli. Tus, V1 seems to transmit magnetic information

into the brain in diferent avian species, but the biological function of this information remains

unknown (Heyers et al., 2010). It has ofen been assumed that this information is perceived by a puta­

tive magnetic map organ associated with the trigeminal nerve (Fleissner et al., 2003, 2007; Mora et al.,

2004; Falkenberg et al., 2010; Heyers et al., 2010), even though the receptors remain to be identifed

with certainty (Mouritsen, 2012; Treiber et al., 2012). Kishkinev et al. (2013) found that the ability of

Eurasian reed warblers (Acrocephalus scirpaceus) which are typical long-distance night-migratory

songbirds, to correct for an eastward displacement, requires intact V1. Tus, Kishkinev et al. (2013)

suggested that some kind of map information is transmitted via V1 into the brain. In the case of the

non-migratory homing pigeons, Lefeldt et al. (2014) suggested that the trigeminal system is involved

in processing MF information and that V1 transmits this information from V1-associated magneto-

sensors to the brain.

Tus, magnetite organs have since been found in a strikingly long list of vertebrates, including fsh,

amphibians, reptiles, birds, and mammals (Wiltschko and Wiltschko, 2005). Teoretical calculations

(Kirschvink and Gould, 1981) suggest that these organs have more than enough magnetite crystals to

measure map location, at least in most places on the globe. Tus, many magnetites have been found in

the body of a variety of animal species including humans (Kirschvink et al., 1992a,b; Gould, 2008a,b),