Thanks to a structure called the vomeronasal organ in the nasal cavity, many mammals can "talk" to one another via pheromones that influence mating and other behaviors. Because humans lack such an accessory olfactory system, it's long been believed that we don't communicate by "social smells."
Now, however, neurobiologist Lawrence Katz and his colleagues have shown that mice do use the main olfactory system, which humans also possess, to communicate via social odors. They even isolated one such chemical from the urine of male mice that distinguishes male mice--at least to the noses of female mice.
The researchers first separated a multitude of volatile compounds from male mouse urine, then tested whether they activated neurons in the olfactory sensing region of mouse brains--called the olfactory bulb. They discovered that the response was surprisingly specific, with individual nerve cells in the olfactory bulb reacting to just one compound.
"We were mapping the olfactory bulb just as a cartographer might map the geography of a region," says Katz. "And we were surprised to find that, despite the complexity of this stimulus, the responses were concentrated in a relatively small area of the olfactory bulb."
In further studies, the scientists isolated a chemical called MTMT that female mice reacted to as a signal of the presence of males. "Humans do not have the vomeronasal organ, which is responsible for pheromone communications in most mammals," says Katz. "Yet, there are persistent reports about the influence of odorant communications in all sorts of behavior in humans--mothers recognizing infants, wives recognizing husbands, and, of course, the influence of perfumes and colognes.
"Since we've found that mice, which are well known to use odors for social communications, do so using the main olfactory system, this strongly suggests that sex-specific volatile chemicals in our bodily secretions could also be detected by similar circuitry."