Pheromones are nature's messengers of love: chemicals that help animals identify mates and get them in the mood for romance, even over long distances. But how pheromones act on the brain remains vague. Now, neuroscientists have directly spotted the first receptor to bind a known pheromone. This major step will help scientists dissect the molecular machinery involved in complex behaviors like courtship and aggression.
The mouse vomeronasal organ--a cavity tucked inside the nostrils--features a dense network of neurons that sense pheromones. These neurons are directly wired to brain areas driving sexual appetite, aggression, and stress, but they bypass those involved in voluntary actions. Earlier this year, researchers analyzing the sequenced mouse genome brought to light a family of 150 genes that might code for pheromone receptors. All the genes are expressed only in vomeronasal sensory neurons. Consistent with a role as pheromone sensor, each neuron expresses only one of these genes. But subsequent studies pointed to other functions for these genes, and their role as receptors remained unclear.
Now, neuroscientist Ivan Rodriguez and colleagues at the Universities of Geneva and Lausanne in Switzerland have examined neurons that express a gene called V1rb2, one member of the putative pheromone receptor family. The team first engineered mice in which neurons with V1rb2 also gave off a green glow when exposed to certain wavelengths of light. Rodriguez and his team then used electrodes to measure the activity of the glowing neurons in response to about 20 known pheromones. The green cells revved up their activity when exposed to a particular pheromone found in mice urine. In contrast, neurons lacking V1rb2 didn't respond to this pheromone at all, the team reports online 18 November in Nature Neuroscience.
The findings fill an important gap, says neuroscientist Catherine Dulac of Harvard University: "It's an experiment that somebody had to do." But the really important question now, she says, is how pheromone signals go from the receptor into the neuron and affect processes in the brain that mediate behavior.
--CHRISTIAN HEUSS
Related sites
Catherine Dulac's Web page
The Vomeronasal Organ
A tutorial on the sense of smell
American Psychological Association article about pheromones
