[Exposure to neurotoxic substances versus stress]

It has long been known that exposure to a stressor may initiate progressive and long-lasting (or even permanent) functional changes in the central nervous system. They are manifested by an altered, decreased or increased responsiveness of the body not only to the generating stressor, but also to other unrelated stressors. Numerous experimental studies have shown that the sensitivity of the body to chemical stressors may be influenced by a prior exposure to nonchemical stressors, e.g., physical or psychological, and vice versa. The purpose of this work is to point out the implications of this observation for epidemiological and experimental studies on health effects of chemical exposure and for establishing the hygiene standards of exposure.