The effects of chronic trichloroethylene exposure on neurobehavioral functioning in the rat.

Groups of rats were exposed by inhalation to either clean air (Controls) or trichloroethylene at 500, 1000 or 1500 ppm TCE for 16 hr/day, 5 days/week for 18 weeks. At preselected intervals, animals were evaluated for changes in: spontaneous activity, gripstrength, coordinated hindlimb movement, performance of a discrete-trial operant two-choice visual discrimination task, and peripheral nerve conduction velocity. Compared to Controls, TCE-treated rats showed no significant differences in open field behavior, fore- and hindlimb gripstrength or coordinated movement throughout the exposure period. Peripheral nerve conduction time was also unaffected. In contrast, TCE produced progressively marked changes in the speed and patterning of responding in the two-choice visual discrimination task. Two-choice response latency, for example, demonstrated an approximately four-fold increase (p less than 0.001) in the highest dose group. In addition, a recurrent within-week functional tolerance developed for all TCE-exposed groups. However, tolerance was lost in the TCE 1500 group as exposure became chronic. Finally, following the termination of exposure, there was no carry-over of TCE-related effects on any of the measures and performance quickly returned to baseline levels. This profile of effects argues for a primary involvement of the CNS with chronic TCE exposure and is quite unlike that seen with, e.g., n-hexane and carbon disulfide. Such findings underscore the differences in the effects which can be produced by long-term exposure to organic solvents and emphasize the need for a battery of tests in the evaluation of neurotoxicant-induced changes in nervous system functioning.