A group of researchers from the University of Kentucky, Duke University and Max Planck Research have identified the receptors activated by two odours using a new method that tracks responses to smells in live mice.
Using a fluorescent protein to mark nerve cells activated by odours the team identified receptors that allow mouse nerve cells to respond to two odours, eugenol, which is a component of several spices, most notably cloves; and muscone, known as musk.
This new method could help the medical community understand how these receptors allow mice, and eventually humans, to detect and discriminate odors, similar to the way in which the three receptors in the retinas of the eyes allow humans to discriminate colours. But unlike vision and hearing, the details of how the odour receptors discriminate odours, much like colour in vision or pitch in sound, are unknown.
The team state that before researchers have a medical application in mind, they must first create a roadmap for these receptors.
Scientists have been pursuing this holy grail of the sense of smell since Richard Axel and Linda Buck discovered these odorant receptors and their role in the organization of the olfactory system, winning them the Nobel Prize in Physiology or Medicine in 2004.
The challenge has been scientists’ ability to identify which receptors are activated by certain smells, particularly since humans have about 400 such receptors (mice have an astounding 1,100 receptors).
By using this new invention, called the Kentucky In Vivo Odorant-Ligand Receptor Assay, or in short, ‘the Kentucky Assay,’ scientists are now able to determine which receptors respond to certain odours in awake, freely behaving animals. There are many practical applications for this knowledge.
Knowing which receptors respond to a chemical would help us devise better flavors and fragrances. But perhaps more tantalizing is the idea that we could potentially design receptor blockers for offensive odours.