Biogenic magnetite as a basis for magnetic field detection in animals

Magnetic fields abolish the enhanced nocturnal analgesic response to morphine in mice

Mice given morphine displayed diel rhythms in the latency of their behavioral response to placement on a hot plate, there being a several fold increase in their nocturnal reaction times. Exposure to a rotating magnetic field eliminated the day-night analgesia rhythms, reducing over 5-10 days the enhanced nocturnal latencies to those found during the day. The attenuation returned to normal nocturnal levels several days after removal of the rotating magnetic field and could be subsequently re-established by reapplication of the magnetic field condition. It is suggested that these changes in analgesia may reflect alterations in the activity of the pineal gland during exposure to magnetic fields.

The horizontal magnetic dance of the honeybee is compatible with a single-domain ferromagnetic magnetoreceptor

Although honeybees are able to sense the geomagnetic field, very little is known about the method in which they are able to detect it. The recent discovery of biochemically precipitated magnetite (Fe3O4) in bees, however, suggests the possibility that they might use a simple compass organelle for magnetoreception. If so, their orientation accuracy ought to be related to the accuracy of the compass, e.g. it should be poor in a weak background fields and enhanced in strong fields. When dancing to the magnetic directions on a horizontal honeycomb, bees clearly show this type of alignment behavior. A least-squares fit between the expected alignment of a compass and this horizontal dance data is consistent with this hypothesis, and implies that the receptors have magnetic moments of 5 x 10(-13) emu, or magnetite volumes near 10(-15) cm3. Additional considerations suggest that these crystals are slightly sub-spherical and single-domain in size, held symmetrically in their receptors, and have a magnetic orientation energy of approximately to 6 kT in the geomagnetic field. A model of a magnetite-based magnetoreceptor consistent with these constraints is discussed.