Fig. 1. A schematic diagram of olfactory signal transduction. Olfactory signal transduction begins with the activation of an olfactory receptor (OR) in the ciliary membrane; this leads to an increase in cyclic AMP (cAMP) synthesis through the activation of adenylate cyclase type III (ACIII) via a G protein (G_olf)-coupled cascade. The increase in cAMP concentration causes cyclic nucleotide-gated (CNG) channels to open, leading to an increase in intracellular Ca²⁺ concentration and depolarization of the cell membrane by the Ca²⁺-activated Clchannel. Among several molecules of the olfactory signal transduction, OR, olfactory marker protein (OMP), G_olf protein α-subunit (Gα_olf), and ACIII have known to be olfactory specific molecules.