OCAM reveals segregated mitral/tufted cell pathways in developing accessory olfactory bulb

Two functional subsets of vomeronasal sensory neurons project their axons to two segregated zones in the accessory olfactory bulb (AOB). Using immunohistochemical methods with antibodies against the novel cell adhesion molecule OCAM, we provide evidence that the segregation of functional pathways is maintained at the level of mitral/tufted (M/T) cells of the mouse AOB and that this pattern emerges early in ontogeny. During embryonic and postnatal development OCAM was strongly expressed by M/T cells in the caudal zone of the AOB where OCAM-negative vomeronasal axons terminated. In contrast, rostral zone M/T cells innervated by OCAM-positive vomeronasal axons displayed no or faint OCAM immunoreactivity. Differential expression of OCAM in segregated M/T cell pathways suggests that OCAM may be involved in defining compartments of connectivity and setting up functional subdivisions in the developing AOB.