Response kinetics of olfactory receptor neurons and the implications in olfactory coding

Olfaction begins with the detection of odorants by olfactory receptor neurons (ORNs) in the nasal cavity. Olfactory transduction is mediated by a G protein–coupled transduction cascade culminating in the opening of the two olfactory transduction ion channels, the olfactory CNG channel and the Ca-activated Cl channel anoctamin 2 (Ano2), and ultimately action potential (AP) generation. The mechanisms that activate olfactory transduction have been understood quite well over the last two decades. Mechanisms of response adaptation, however, have actually become much less clear, with mechanisms previously thought to be important now suggested to play less significant roles, raising the question of which transduction components are the target of adaptational feedback. Because ORNs are often stimulated rhythmically by the inhalation of odorants, fast response termination should be a prerequisite to adequately resolve the temporal aspect of the stimulus. Recent progress suggests that mechanisms that regulate ciliary Ca transients dictate kinetics of transduction termination. Ultimately, the question to answer is how ORNs code for “natural” stimuli in the behaving animal.