Nose Receptors May Sniff out Social Cues

Your nose can detect bread baking, natural gas leaking, day-old garbage reeking and countless other scents. New research suggests it may also be able to sniff out subtler signals, like signs of stress or signals from the opposite sex. Researchers have discovered a family of receptors that can detect such signals in mice and are found in humans, too.

A patch of tissue on the roof of the nasal cavity called the olfactory epithelium houses the large family of receptors responsible for detecting odors. "Dr. Linda B. Buck, along with Dr. Richard Axel, received the Nobel Prize in 2004 for identifying the gene family for these odorant receptors.

But noses have another function in mice and many other animals. They detect chemical signals called pheromones from other members of their species warning of danger, staking out territory or trying to attract a mate. Pheromones are generally detected by a structure in the nose called the vomeronasal organ. The vomeronasal organ isn't thought to be functional in humans, but research has shown that, in mice, at least, the responses to some pheromones involve the olfactory epithelium.

Dr. Buck and her colleague Dr. Stephen D. Liberles, both at the Fred Hutchinson Cancer Research Center, thus set out to hunt for pheromone receptors in the olfactory epithelium. Funded by NIH's National Institute on Deafness and Other Communication Disorders (NIDCD) and the Howard Hughes Medical Institute, they searched the mouse's olfactory epithelium for receptors that don't respond to odors.

In the July 30 online issue of Nature, they reported their discovery of the genes for a family of receptors known as trace amine-associated receptors, or TAARs. When the TAARs were exposed to an array of chemicals, several were activated by compounds found in mouse urine, which is known to play a major role in sending social cues between rodents. One TAAR detected a compound linked to stress, whereas two others detected compounds enriched in male urine, one of which is reportedly a pheromone.

“Scientists once thought that the olfactory epithelium was responsible for detecting odors while the vomeronasal organ was responsible for detecting pheromones, and the two structures were considered completely separate,” Dr. Barry Davis, director of NIDCD's taste and smell program, says “But this research identifies a new class of receptors in the olfactory epithelium that are able to detect pheromones.”

There are 15 types of TAARs in the mouse's olfactory epithelia. Humans have six types, and TAARs have also been reported in fish. These receptors could serve could serve to detect pheromones used as social and reproductive cues by a wide range of animals. What they might do in humans remains to be discovered.

— by Jennifer Wenger and Harrison Wein