Odorant receptors , pheromone

In this model, OBPs participate in the selective transport of pheromone and other semiochemicals to their olfactory receptors. The selectivity of the system is likely to be achieved by layers of filters [ 16], i.e., by the participation of compartmentalized OBPs and olfactory receptors. It seems that OBPs transport only a subset of compounds that reach the pore tubules. Some of these compounds may not bind to the receptors compartmentalized in the particular sensilla. The odorant receptors, on the other hand, are activated by a subset of compounds, as indicated by studies in Drosophila, showing that a single OR is activated by multiple compounds [66]. If some potential receptor ligand reaches the pore tubules but are not transported by OBPs, receptor firing is prevented because the receptors are protected by the sensillar lymph. In other words, even if neither OBPs nor odorant receptors (ORs) are extremely specific, the detectors (olfactory system) can show remarkable selectivity if they function in a two-step filter. 

Vomeronasai organ a structure possessing odorant receptors for pheromones. 

Ernes RD, Beatson SA, Ponting CP, Goodstadt L (2004) Evolution and comparative genomics of odorant- and pheromone-associated genes in rodents. Genome Res 14 591-602 Fischer A, Gilad Y, Man O, Paabo S (2005) Evolution of bitter taste receptors in humans and apes. Mol Biol Evol 22 432-436... 

Zhang X, Zhang X, et al. (2007a) Comparative genomics of odorant and pheromone receptor genes in rodents. Genomics 89(4) 441-A50... 

Rodriguez I (2004) Pheromone receptors in mammals. Horm Behav 46 219-230 Rodriguez I (2007) Odorant and pheromone receptor gene regulation in vertebrates. Curr Opin Genet Dev 17 465-470... 

In most mammalian species, two functionally distinct classes of chemicals (odorants and pheromones) are detected and processed through anatomically segregated neural pathways the main olfactory system and the vomeronasal (accessory olfactory) system (Buck 2000 Mombaerts 2004). Volatile odorants are received by a large repertoire of ORs expressed on ciliated OSNs in the OE and the information is transmitted to the main OB. By contrast, pheromones are mostly received by two families of vomeronasal receptors (VIRs and V2Rs) expressed on microvillous sensory neurons in the vomeronasal organ that project their axons to the accessory OB. 

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