Odorant receptors make scents

The goal of making sense of the sense of smell has come a step closer. Work on fruitflies reveals that odorant receptors act as bidirectional chemical detectors and determine the function of sensory neurons. Olfaction, once thought to be a primitive sense, is now recognized as an elaborate sensory system that deploys a large family of odorant receptors to analyse the chemical environment. Interactions between these receptors and their diverse ligands translate the world of odours into a neural code, but the mechanisms governing this complex process are not totally understood. More than a decade after the discovery of odorant−receptor genes in rodents1, a study by Hallem, Ho and Carlson2, reported in Cell, now provides a missing link between the molecular biology of odorant receptors and the physiological properties of sensory neurons. Odorant−receptor proteins are exposed to the outside world on the membranes of sensory neurons. Interaction of a receptor with an odorant ligand results in a biochemical signal inside the cell that ultimately controls the generation of electrical impulses. These action potentials are transmitted down the axon of the sensory neuron to the brain, where they are integrated with other inputs. However, the mechanisms that tailor this transduction process to produce responses that are specific to particular odours are not completely understood. For example, is odorant specificity directed solely by the odorant receptor, or does it depend on other proteins