The peripheral olfactory system of vertebrates: molecular, structural and functional basics of the sense of smell

Abstract

The sense of smell provides people and animals with an abundance of information about their environment, helping them to navigate, detect potential threats, control food intake, choose sexual partners and significantly influence intraspecies social behavior. The perception of odors begins with the binding of odor molecules to specialized olfactory receptor proteins, which nearly all belong to the superfamily of G protein-coupled receptors. Altogether, five different olfactory receptor gene families have been described to date, among them the largest gene family in the genome with over 1000 genes in rodents. The signal transduction cascade coupled to the receptors has already been well characterized for this family. Three different classes of receptor neurons—ciliated, microvillous and crypt receptor neurons—can be distinguished by their anatomical and molecular characteristics. Generally, an individual receptor neuron expresses only a single olfactory receptor gene, and olfactory receptor neurons that express the same receptor converge into a common target structure, a glomerulus, which generates a receptotopic map in the first olfactory brain region, the olfactory bulb. This review article provides a general overview of the peripheral detection of odorants on the one hand, while on the other it focuses on recent advances in the field, including new findings on the peripheral modulation of olfactory signals.