One of the recent controversies in olfaction has been the relative contribution of the cAMP and InsP3 (IP3) second messenger pathways in olfactory transduction, especially in vertebrates, and whether individual odorants specifically act via the two pathways. This controversy has been profitably addressed in a recent study by Takeuchi et al. (2003)(in this issue).
Odorants are known to bind to highly selective G protein–coupled receptors, heavily concentrated on the cilia and dendritic knob of each olfactory receptor neuron (ORN). From genetic studies it has been suggested that there are ∼500–1,000 different odorant receptors (e.g., in mouse) and that each ORN probably only expresses one type of receptor (Buck, 1996). Furthermore, the evidence suggests that ORNs of a particular type converge to the same glomerulus in the olfactory bulb (Sullivan and Dryer, 1996).
It was proposed by Sklar...
