Functional maturation of vomeronasal neurons induced by the co-culture with accessory olfactory bulb neurons

Abstract

Pheromones are detected by the vomeronasal organ, but precise natures of detection at the cellular level are poorly understood. To characterize cellular aspects of receptivity to pheromones, we investigated responsiveness of the vomeronasal neuron (VRN) to pheromone–containing materials in the cell culture. As previously reported, VRNs in culture form a spherical structure with a central cavity, referred to as a vomeronasal pocket (VNP). We also reported the maturation of each VRN in the VNP was induced by co-culture with dissociated accessory olfactory bulb (AOB) neurons. Using this co-culture system, we applied charged compounds in mouse urine iontophoretically into the cavity of VNP using microelectrode and analyzed VNP response by a Ca²⁺ imaging method with or without cultured AOB cells. When urine compounds were ejected into the VNP co-cultured with AOB cells with a current of 1-2 μA, subpopulation of VRNs clearly showed long-lasting Ca²⁺ increases. Such Ca²⁺ increases were not observed without AOB neurons and injections of a current below 5 μA alone had no effect. Moreover, a western blotting analysis showed the expression of some putative pheromone receptors in the VNP was induced and increased with days in co-culture. These results indicate that VRNs result in expressing pheromone receptors and then acquire responsiveness to compounds in urine by interacting with AOB neurons in co-culture. [J Physiol Sci. 2006;56 Suppl:S184]