Photoreceptor-based magnetoreception: optimal design of receptor molecules, cells, and neuronal processing

Abstract

The sensory basis of magnetoreception in animals still remains a mystery. One hypothesis of magnetoreception is that photochemical radical pair reactions can transduce magnetic information in specialized photoreceptor cells, possibly involving the photoreceptor molecule cryptochrome. This hypothesis triggered a considerable amount of research in the past decade. Here, we present an updated picture of the radical-pair photoreceptor hypothesis. In our review, we will focus on insights that can assist biologists in their search for the elusive magnetoreceptors.

A behavioral perspective on the biophysics of the light-dependent magnetic compass: a link between directional and spatial perception?

“…in birds and mammals), it may be perceived as a visual image superimposed on the animal's surroundings (Ritz et al, 2000;Ritz et al, 2010). The result would be a compound visual image consisting of the sky and objects around the animal (the visual surroundings the animal 'moves through'), and the visual pattern generated by the magnetic field (effectively a simple, spherical coordinate system the animal 'moves with'; Fig.2).…”

“…In other words, the animal would be surrounded by a spherical coordinate system that is more-or-less fixed in direction as it moves through the environment. This may be complicated somewhat by the disparity between the alignment of photoreceptors in the retina and that of rays of light entering the eye through the lens and cornea, which determines the projection of the visual surroundings onto the retina (Fig.3) (see Ritz et al, 2010). The effect of this disparity would be to compress the pattern generated by the magnetic field orthogonal to the line of sight, defined here as the direction viewed by photoreceptors in the center of the retina directly opposite the lens.…”

Magnetic compass orientation in two strictly subterranean rodents: learned or species-specific innate directional preference?

“…In marked contrast to birds (Ritz et al, 2010), its magnetic compass is light independent, polarity based and insensitive to magnetic fields oscillating in the MHz range (Marhold et al, 1997a;Marhold et al, 1997b;Thalau et al, 2006). However, a brief magnetic pulse designed to alter the magnetization of singledomain magnetite can lead to a long-term (≥3months) deflection of mole-rat directional preference (Marhold et al, 1997b).…”

Magnetic orientation of garden warblers ( Sylvia borin ) under 1.4 MHz radiofrequency magnetic field

“…The situation has apparently changed with the demonstration of the effect of weak oscillating magnetic fields (OMFs) on the orientation ability of European robins (Erithacus rubecula) by the group of R. and W. Wiltschko in Frankfurt [21][22][23][24]. These experiments were specially designed to test the radical-pair theory of magnetoreception, which predicted sensitivity not only to static, but also to RF magnetic fields in the few-MHz frequency range (close to the electron spin resonance in typical geomagnetic fields).…”

“…In the extreme and most favourable for the magnetic sensitivity case when the direction of one of the electron moments is fixed by strong and anisotropic hyperfine interaction, whereas the other one is free (the 'reference-probe' model [23]), the probabilities of finding the pair of electrons in the spin-singlet state oscillates at the Larmor frequency f L ¼ g e B, where B is the magnetic field intensity and g e % 28 Hz nT 21 is the electron gyromagnetic ratio. The amplitude of the probability oscillation depends on the direction of the magnetic field as A(1 2 cos2u), where u is the angle between the magnetic field and the anisotropy axis of the 'reference' radical, and A , 1/2 is a constant depending on the details of the radical-pair formation process.…”