Carbon disulfide neurotoxicity in rats: VII. Behavioral evaluations using a functional observational battery

The neurobehavioral consequences of inhalational exposure to carbon disulfide (CS2) were evaluated as part of a joint project between the National Institute of Environmental Health Sciences and the U.S. Environmental Protection Agency. Behavioral changes in rats were measured using a functional observational battery (FOB), which is a series of observations and manipulations designed to assess the neuronal integrity of autonomic, motor, sensory, and integrative functions. Young adult male and female Fischer-344 rats were exposed to one of four CS2 concentrations (0, 50, 500, or 800 ppm, six hours/day, five days/week) and tested at the end of one of several exposure durations (two, four, eight, or 13 weeks). All rats were also tested before exposure began to obtain baseline values. Neuromuscular deficits which were more pronounced in the hindlimbs, e.g., decreased strength and gait alterations, were detected in rats of both sexes. These changes were closely related to CS2 concentration and exposure duration, with mild gait changes evident after only two weeks of exposure. Other effects, mostly observed at 13 weeks, included decreased responsiveness to a visual stimulus and mild tremors. Reactivity in response to handling was generally increased, and excitability in the open field was decreased, in rats tested after the shorter exposures (two and four weeks). Thus, the exposure-concentration and -duration characteristics of the neuromotor syndrome produced by CS2 were detected and defined using the FOB. These studies provide a more complete evaluation of rats under these CS2 exposure conditions, which can then be used to compare with other mechanistic-related endpoints from this collaborative study.