Neurotoxic exposure and impairment of the chemical senses of taste and smell.

The chemical senses of taste and smell determine the flavor of foods and beverages, guide appropriate food intake, and warn of such environmental hazards as spoiled or poisonous food, leaking natural gas, smoke, and airborne pollutants. This chapter addresses the influences of neurotoxic exposures on human chemoreception and provides basic information on the adverse influences of such exposures on rodent epithelia. The focus of the chapter is in olfaction, given dearth of empiric research on the effects of neurotoxic chemical exposures on the sense of taste, i.e., sweet, sour, bitter, salty, and savory sensations. As will be apparent from the chapter, numerous neurotoxins--many of which are encountered in industrial workplaces--alter the ability to smell, including solvents, metals, and particulate matter. The olfactory system is particularly vulnerable to such agents since its receptors are more or less directly exposed to the outside environment. Importantly, some such agents can enter the brain via the olfactory nerve or surrounding perineural spaces, bypassing the blood-brain barrier and damaging central nervous system structures and inducing pathologic processes that appear to be similar to those seen in neurodegenerative diseases such as Alzheimer's and Parkinson's.