Trichloroethylene affects learning and decreases myelin in the rat hippocampus

The goal of the present study was to relate previously observed behavioral effects with changes in myelin in the hippocampus following exposure to the industrial solvent 1,1,2-trichloroethylene (TCE). Young adult rats exposed to TCE via their drinking water underwent tests to evaluate their ability to perform spatial navigational tasks, and their brains were examined for changes in myelin in the hippocampus. Exposure to an average daily load of 5.5 mg TCE first for 4 weeks and then to 8.5 mg for an additional 2 weeks (separated by a 2-week interval) resulted in an increased level of performance in spatial navigational tasks. Examination of the brains from these animals revealed a significant decrease in the amount of myelin in one layer of the hippocampus, the stratum lacunosum-moleculare. No increase in performance was observed in rats exposed to an average daily load of 5.5 mg TCE for 4 weeks only. A reduction in myelin was observed, however, in the stratum lacunosum-moleculare of these animals. This decrease was not as severe as that seen in the twice-exposed animals. The results of this study suggest that exposure to TCE results in a reduction of hippocampal myelin, and that this reduction may be related to the increased level of performance observed following a second exposure to TCE.