Chemicals Affecting the Nervous System
A variety of chemicals are known to affect the nervous system. Some directly target neural signaling pathways. These include the classic nerve agents (e.g., sarin, soman, tabun, and VX), organophosphate pesticides, and some animal toxins (e.g., botulinum toxin). Chemicals can also affect the nervous system indirectly. For example, metabolic poisons (e.g., cyanide) disrupt cellular respiration, which ultimately prevents the brain from getting sufficient oxygen and energy. Some vesicating agents (e.g., sulfur mustard) appear to have neurological effects as well, although the specific mechanism by which they affect the nervous system is poorly understood.
Neurological symptoms depend on the type of chemical, the level of exposure, and the time elapsed following exposure. Exposure to nerve agents, metabolic poisons, or high levels of sulfur mustard can trigger seizures and loss of consciousness. Other acute effects of nerve agent poisoning include muscle paralysis, cardiorespiratory depression, massive secretion from mucous membranes, eye irritation, and blurry or dim vision. Other acute effects of exposure to high doses of sulfur mustard include behavioral effects and cognitive difficulties. Nerve agents and metabolic poisons also appear to have serious long-term neurological effects, including neurodegeneration, but these have not been studied extensively.
The physical states of chemicals that affect the nervous system are an important determinant of the requirements for developing effective countermeasures. Although some chemicals that affect the nervous system exist primarily in the form of a vapor (e.g. hydrogen cyanide), others are oily liquids that are very difficult to remove from the environment and extremely toxic even at miniscule levels (e.g., VX). For these persistent agents, it would be ideal to have pretreatments with long-lasting protective effects that can be administered in advance of possible exposure to personnel who must enter contaminated sites.
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