Structure and Function of the Vomeronasal System — The Vomeronasal Organ as a Priming Pheromone Receptor in Mammals

The vomeronasal organ (VNO), the peripheral receptor of the vomeronasal system (VNS) or accessory olfactory system (AOS), was first described as a nonsensory organ with secretory functions by Jacobson (1811). McCotter (1912) was the first to mention the VNO as an organ with an olfactory character. Almost 100 years after the description of the VNO by Jacobson, Cajal (1902, 1904) described the accessory olfactory bulb (AOB; the target organ of the axons coming from the VNO neurons) in mice. On the basis of its structure, Cajal postulated that the AOS could have a special sensitivity to some olfactory cues. From its structure, Broman (1920) considered the VNO to be an organ that received odors of substances dissolved in liquids, while Milstein (1929), by closing the vomeronasal ducts in rabbits, was led to conclude that the VNO is the most peripheral receptor of the olfactory sense with no special function. Although Milstein’s studies as well as those by others (Milhalkovics 1899) determined no special function for the VNO, they were the first to investigate the function of the VNO using an experimental procedure.