GLYCOBIOLOGY OF THE OLFACTORY SYSTEM

The olfactory system is a highly plastic region of the nervous system. Continuous remodeling of neuronal circuits in the olfactory bulb take s place throughout life as a result of constant turnover of primary se nsory olfactory neurons in the periphery. Glycoconjugates are very imp ortant in olfactory development, regeneration and function. This artic le deals with different aspects of glycobiology relevant for the olfac tory system. Various anatomical? developmental and functional subdivis ions of the olfactory system have been labeled with exogenous lectins. The application of reverse lectin histochemistry resulted in the visu alization of endogenous lectins, involved in fasciculation of olfactor y axons. Numerous glycoproteins, among them members of the immunoglobu lin superfamily, the cadherins and integrins as well as different,glyc olipids and proteoglycans can act as surface adhesion molecules in the olfactory system. The olfactory-specific form of the sialoglycoprotei n neural cell adhesion molecule is implicated in olfactory neuronal an d axonal guidance. Glycoconjugates including laminin, fibronectin and proteoglycans are abundant components of the olfactory extracellular m atrix, influencing neurite outgrowth and cellular migration. Immunohis tochemical labeling has revealed occurrence of the carbohydrate differ entiation antigen, playing a role in neurulation and morphogenesis of the very early olfactory system. The synaptic vesicle glycoprotein, ap pearing also early in olfactory development, is used as a marker of ol factory tumors. Finally, membrane and transmembrane glycoconjugates as well as secreted glycoconjugates may act as olfactory receptor molecu les.