DESCRIPTION: The vomeronasal system of mammals is chemoarchitecturally heterogeneous. Two populations of receptor cells, located at different depths of the vomeronasal sensory epithelium, project to different portions of the accessory olfactory bulb. We will continue to investigate this heterogeneity by investigating functional differences between the two portions of the vomeronasal system using a variety of techniques. We will determine whether the anterior or posterior accessory bulb is critical for response to pheromones involved in estrous cycling. We will determine which subdivision of the vomeronasal system is activated by odors from same-sex and opposite-sex conspecifics using anatomical, calcium imaging and electrophysiological techniques. We will determine the source(s) of pheromonal odors and conduct preliminary purification of these pheromones. We will investigate whether olfactory marker protein expression can be induced by pheromonal odors. At the completion of these studies we will be able to state whether the two parts of the vomeronasal system are differentially involved in behaviors shown to use vomeronasallymediated stimuli.