Chapter 33 - Behavioral toxicity of nerve agents

Abstract

The behavioral changes belong to the most important and frequent symptoms of acute and delayed toxicity of organophosphorus nerve agents. The incidence of behavioral effects is higher in individuals who have been severely exposed to nerve agents, but they may also occur in individuals who have received a low-level exposure below those producing convulsions and other severe clinical signs of toxicity. The behavioral effects usually start within a few hours and last from several days to several weeks or months. The most frequent symptoms include disruption of cognitive functions, feelings of uneasiness, tenseness, and fatigue. Persistent severe alteration in behavior and cognitive functions, especially impairment of learning and memory, was observed after exposure to high doses of nerve agents as a result of severe brain neuropathology that involves neuronal degeneration and necrosis of various brain regions including the hippocampus that is connected with the alteration of cognitive functions. Nevertheless, repeated or long-term exposure to low levels of nerve agents can also cause behavioral alterations due to downregulation of muscarinic receptors in the hippocampus as a reaction on acetylcholine accumulation at muscarinic receptor sites due to acetylcholinesterase inhibition.