ABSTRACT
The important role the olfactory system plays in food acquisition and mating behaviors is reflected in the substantial development of this sensory modality in the majority of vertebrate species with, perhaps, the exception of primates. In view of these lifesustaining roles, the common dogma posits that a system as important to survival as olfaction must have mechanisms to protect the sensory cells within the olfactory receptor epithelium from the materials in inspired air, both toxicants and odorants. Also, a means should exist to prevent access of extrinsic substances to the central nervous system (CNS). As discussed below (see also Chapter 3), several mechanisms have been proposed that would protect the epithelium from toxic exposure. Included among these mechanisms are intracellular detoxification of molecules, removal of substances by ligand-specific binding proteins contained in mucosal secretions, surveillance by immune system cells, as well as degeneration and replacement of damaged receptor neurons with new cells derived from basal stem cells. Recent data indicate, however, that these protective mechanisms can be overwhelmed, resulting in access of xenobiotics from the nares to the CNS and to the systemic circulation.
