Signaling in the Mammalian Vomeronasal Organ

Pheromones are chemical signals which provide conspecifics information about gender, dominance and reproductive status [1]. They elicit innate and stereotypical reproductive and social behaviors, along with neuroendocrine and physiological changes. The vomeronasal organ, as part of the accessory olfactory system, is the site for pheromone binding to specific receptors, thus initiating a signal transduction pathway leading from the vomeronasal neurons to the hypothalamuspituitary axis, via the medial amygdale [2]. Molecular evidence has led to the isolation of three independent families of vomeronasal receptor genes (VR) known as V1Rs [3], V2Rs [4-6], and V3rs (Pantages and Dulac [7]) that encode putative pheromone receptors. Vomeronasal neurons are classified based on the vomeronasal receptor type and the G-protein to which they are coupled. Vomeronasal receptor neurons with cell bodies in the apical half of the sensory epithelium express the G-protein alpha subunit Gαi2 and project to the anterior part of the Anterior Open Bite (AOB), whereas neurons in the basal regions of the Vomeronasal organ (VNO) neuroepithelium express the G protein alpha subunit Gαo and project to the posterior regions of the AOB [810]. More recent studies have introduced the formyl peptide receptor (FPR) as a possible chemosensory receptor [11]. FPRs are selectively expressed in the neuroepithelium, express either Gαi2 or Gαo, and are highly dispersed throughout the neuroepithelium [12]. Possible roles for the FPRs include the assessment of conspecifics or other species, based on variability in normal bacterial or mitochrondrial proteins [13]. Recently, it has also been shown that the two classes of vomeronasal receptors V1Rs and V2Rs use different strategies to encode chemosensory information [14].