A unique neuronal glycolipid defines rostrocaudal compartmentalization in the accessory olfactory system of rats

A monoclonal antibody, CC6, reacts with a complex glycolipid whose expression in the rat is restricted to the olfactory system. Structural analysis reveals that the glycolipid contains two alpha-fucose branches; one each at internal and external beta-galactose residues. Immunocytochemistry demonstrates in rat embryos that CC6 glycolipid expression is restricted to a subset of neurons in the vomeronasal organ (VNO) and their corresponding axon projections in the caudal accessory olfactory bulb (AOB). This pattern of expression in the accessory olfactory system is the converse of the pattern revealed by a previously characterized antiglycolipid antibody that reacts with VNO neurons projecting to the rostral AOB. The CC6-reactive glycolipid is also expressed on a subset of neurons in the main olfactory epithelium. Postnatally, axons from these CC6 positive sensory neurons converge to form a limited number of axon bundles running longitudinally through the nerve layer of the main olfactory bulb. These data provide further evidence that groups of vomeronasal and olfactory neurons expressing unique surface molecules project axons that terminate in selected targets in the AOB and OB, respectively.