Trout's Snout Holds Receptor Cells That Navigate Using Earth's Magnetic Field

By Chelsea Whyte on July 10, 2012 4:05 PM EDT

RAINBOW TROUT
For the rainbow trout, the nose knows. Scientists have discovered magnetic receptors inside the cells of the trout's nasal cavity, which help the fish navigate using the Earth's magnetic fields. (Photo: Creative Commons: El Frito)

Migratory animals, such as fish and birds, have long been known to use the Earth's magnetic field to navigate, but just how they do it has been a mystery. Now, scientists have discovered iron in the cells of a trout's snout that may be the key to their biological compass.

Figuring out where these cells lie in the body is like looking for a needle in a haystack - since magnetic fields easily got through skin, the cells used for spatial orientation could be anywhere.

"The magnetic field penetrates the whole body, and therefore there is no reason why the magnetic (sensitive) cells have to be at the periphery (of the body)," said geophysicist and study author Michael Winklhofer of Ludwig Maximilian University of Munich, according to the Milwaukee Journal Sentinel.

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Recent research has shown that the nasal cavity of fish contain cells with magnetic properties, so the research team started with the olfactory tissue from a rainbow trout.

They used enzymes to separate the tissue into individual cells and then stimulated them with an artificial, rotating magnetic field. They were able to identify the cells that responded - no easy feat, as there are only about 1 to 4 magnetoreceptor cells for every 10,000 in the nasal tissue.

The receptor cells probably contain magnetite, the most magnetic naturally-occuring mineral, which can pick up on the Earth's relatively weak magnetic field. When exposed to the magnetic field, the magnetite spins around within the membrane, orienting the cell like a microscopic compass.

These magnetoreceptor cells are so few and far between because while they can sense magnetic fields, they also create a small one of their own, which creates a kind of signal interference should there be too many in a small area.

These small crystals of magnetite are coupled to the cell membrane, which can change the potential for electricity activity crossing the cell membrane when the animal crosses ambient magnetic fields.

"This explains why low-frequency magnetic fields generated by powerlines disrupt navigation relative to the geomagnetic field and may induce other physiological effects," says Winklhofer.

These cellular magnets were found to be 100 times more sensitive to magnetic fields than previously estimated, giving the trout a stronger sense of true north than we ever thought.

"For decades, scientists have been searching for the cells responsible for magnetosensation," David Keays, a neuroscientist at the Research Institute of Molecular Pathology in Vienna, told Science News. "They're the biological equivalent of the elusive Higgs boson."

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