Validation and in vitro neurotoxicity

1. Validation of in vitro systems for studying neurotoxicants generally has not been accomplished, although in vitro tests have been used as screens to identify potential neurotoxic hazards and to study mechanisms. 2. A number of factors need to be taken into account when a test is validated: (i) a rationale for developing the test; (ii) clear biological or pathophysiological relevance of the endpoint to the effect detected in vivo; (iii) a standardized protocol and evidence of intra- and interlaboratory reproducibility; (iv) testing of chemicals representative of the categories of interest, including very toxic, moderately toxic and relatively non-toxic substances; and (v) a method to statistically evaluate the data. 3. Proper validation should lead to methods which can be used by regulatory agencies to make decisions regarding hazard/risk.