Septal organ of Grüneberg is part of the olfactory system.

The olfactory system in rodents and many other mammals is classically divided into two anatomically separate, and morphologically distinct, sensory systems: the main olfactory system and the accessory olfactory system. We have now identified a novel third population of olfactory marker protein-expressing sensory neurons that is located in a discrete pocket of the rostral nasal septum, which we refer to as the septal organ of Grüneberg (SOG). Neurons in this region of the septum are located in the submucosa, in small grape-like clusters, rather than in a pseudostratified neuroepithelium, as seen in both the olfactory and vomeronasal neuroepithelia. Despite their unusual location, axons projecting from the SOG neurons fasciculate into several discrete bundles and terminate in a subset of main olfactory bulb glomeruli. These glomeruli most likely represent a subset of atypical glomeruli that are spatially restricted to the caudal main olfactory bulb. The unique rostral position of the SOG suggests that the SOG may be functionally specialized for the early detection of biologically relevant odorants.

Expression and putative role of lactoseries carbohydrates present on NCAM in the rat primary olfactory pathway.

Primary olfactory neurons project axons from the olfactory neuroepithelium lining the nasal cavity to the olfactory bulb in the brain. These axons grow within large mixed bundles in the olfactory nerve and then sort out into homotypic fascicles in the nerve fiber layer of the olfactory bulb before terminating in topographically fixed glomeruli. Carbohydrates expressed on the cell surface have been implicated in axon sorting within the nerve fiber layer. We have identified two novel subpopulations of primary olfactory neurons that express distinct alpha-extended lactoseries carbohydrates recognised by monoclonal antibodies LA4 and KH10. Both carbohydrate epitopes are present on novel glycoforms of the neural cell adhesion molecule, which we have named NOC-7 and NOC-8. Primary axon fasciculation is disrupted in vitro when interactions between these cell surface lactoseries carbohydrates and their endogenous binding molecules are inhibited by the LA4 and KH10 antibodies or lactosamine sugars. We report the expression of multiple members of the lactoseries binding galectin family in the primary olfactory system. In particular, galectin-3 is expressed by ensheathing cells surrounding nerve fascicles in the submucosa and nerve fiber layer, where it may mediate cross-linking of axons. Galectin-4, -7, and -8 are expressed by the primary olfactory axons as they grow from the nasal cavity to the olfactory bulb. A putative role for NOC-7 and NOC-8 in axon fasciculation and the expression of multiple galectins in the developing olfactory nerve suggest that these molecules may be involved in the formation of this pathway, particularly in the sorting of axons as they converge towards their target.