exposed to trichloroethylene environmentally. Experimental studies have been less clear about such effects, but the extent to which this has been addressed is limited and, in some published reports, is not interpretable with respect to outcome.

A related function that clearly seems to be affected by trichloroethylene is motor function, as has been demonstrated in experimental studies as well as in occupational cohorts. As with other behavioral functions, the trichloroethylene exposure conditions under which such effects occur are not yet known. It may be important to define such conditions, particularly if, as suggested by other reports, trichloroethylene might contribute to neurodegenerative disorders such as Parkinson’s disease. The earliest signs of motor dysfunction could serve as biomarkers of such a contribution.

Many neurological and behavioral disorders represent complex multifactorial etiologies. Given the broad spectrum of its effects across behavioral domains as well as neurotransmitter systems (and other as yet unknown mechanisms), it is possible that trichloroethylene may contribute as a risk factor to other neurodegenerative and behavioral diseases or dysfunctions, acting in conjunction with other risk modifiers that may include genetic background (P-450 polymorphisms) and lifestyle factors (e.g., alcohol consumption), aging, and other factors that are undetermined.

Recommendation:

Studies of additional functional end points, including cognitive deficits and motor and sensory function in response to chronic exposures to trichloroethylene would be of value to risk assessment.

Current evidence suggests the possibility of multiple mechanisms by which trichloroethylene may act, with the recognition that these mechanisms may also depend on the parameters of exposure. Extant literature already documents changes in long-term potentiation as well as alterations in functions of several neurotransmitter systems, a basis from which complex cognitive functions as well as other behavioral domains could be impaired.

Recommendation:

Additional research is required to elucidate the underlying modes of action of trichloroethylene-induced neurotoxicity.



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