Chapter 4: Olfactory Transport of Manganese: Implications for Neurotoxicity

Manganese neurotoxicity following inhalation results from excessive accumulation of this metal in the brain. Inhaled manganese can gain access to the brain by three main routes: (1) direct neuronal transport via olfactory or trigeminal nerve endings in the nose; (2) transport across the pulmonary epithelium and systemic blood distribution; and (3) mucociliary elevator clearance from the lung and absorption from the gastrointestinal tract. This chapter provides an update of our understanding of the first route: direct ‘nose-to-brain’ or olfactory transport of manganese. A brief description of the olfactory system anatomy is provided with emphasis on the anatomical basis for olfactory transport. The scientific evidence in support of olfactory transport is discussed, including the use of manganese as a contrast agent for magnetic resonance imaging. The toxicological significance of this route of transport is described in terms of pathology, functional deficits, and biochemical changes.