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What Your Nose Knows: Special Receptors May Be Sniffing Out Human Pheromones
Your nose may be tasked with more than the detection of bread baking, natural gas leaking, or day-old garbage reeking. It also might be used to sniff out subtler signals that humans send to other humans. Although scientists have long known that animals use special chemicals called pheromones among members of their species to warn of danger, stake out territory, or attract a mate, it has been less clear how humans make use of this unique form of instant messaging to communicate with each other. The organ once thought to be chiefly responsible for pheromone detection – the vomeronasal organ – is considered nonfunctional in humans.
In a study published in the July 30 online issue of Nature, NIDCD-funded researcher Linda B. Buck, Ph.D., and her colleague Stephen D. Liberles, Ph.D., have identified a family of receptors in the mouse's olfactory epithelium, a patch of sensory neurons on the roof of the nasal cavity, that are activated by naturally produced chemicals that may influence a mouse’s social and mating behavior. The olfactory epithelium is best known for housing the large family of receptors responsible for detecting odors. (Dr. Buck and Richard Axel, M.D., received the Nobel Prize in 2004 for identifying the gene family that produces the roughly 1,000 G protein-coupled odorant receptors in mice.)
“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,” says Barry Davis, Ph.D., director of NIDCD’s taste and smell program. “But this research identifies a new class of receptors in the olfactory epithelium that are able to detect pheromones.” Based on these and other recent findings, the detection of odors and pheromones could involve a sharing of responsibilities between the two structures in some animals, he said.
The team combed the mouse’s olfactory epithelium for receptors that don’t respond to odors and then used molecular biology techniques to pinpoint the genes that give rise to these receptors. They identified a group of genes that encode a family of receptors known as trace amine-associated receptors, or TAARs. Like odorant receptors, TAARs are distributed on specific sensory neurons throughout the olfactory epithelium. When the TAARs were exposed to an array of chemicals, several were activated by chemicals* found in mouse urine, a substance known to play a major role in sending social cues in rodents. Two of the receptors detect chemicals* found in male urine, one of which is reportedly a pheromone produced by male mice to accelerate puberty in female mice.
The researchers note that TAAR receptors are not only found in mice, which possess 15 members, but also humans, which possess six members, and fish. Because TAARs are almost exclusively found in olfactory epithelia in these diverse species, the researchers suggest that that they are likely to serve as specialized receptors in the detection of pheromones used as social and reproductive cues in a wide range of animals, humans included.
The study was funded by the NIDCD and the Howard Hughes Medical Institute (HHMI), Chevy Chase, MD. Drs. Buck and Liberles both represent the Fred Hutchinson Cancer Research Center, Seattle, and HHMI.
*Corrected August 22, 2006.