Avoidance methods in neurobehavioural toxicity assessments

Avoidance methods have proven their usefulness at successive stages of toxicological investigation on a variety of different agents. First- and second-tier assessments can use simple versions of active and passive avoidance tests which are able to pick up a wide range of deficits at the sensory, motor, reinforcement, and associative level. Avoidance tests are also suitable for the study of tolerance, particularly if appropriate paradigms are used to separate contingent and noncontingent components of tolerance which can be produced by different mechanisms. In addition, these methods have been used successfully in many developmental studies with early (pre- or postnatal) treatment exposure. Higher-tier assessments aimed at a better definition of toxicity mechanisms are inevitably more complex, and can only be performed with agents of particular interest. Physiological psychologists and psychopharmacologists have evolved a considerable know-how in the combined use of selected types of avoidance in such assessments concerning lesion or drug syndromes. Relatively little of this know-how has been so far exploited in toxicological studies. However, some of the results obtained with toxicants which may selectively affect particular brain areas (e.g., limbic structures) appear to be quite promising. Overall, the results obtained by the use of avoidance methods concur with others in showing the close relation between the needs of toxicological assessments and the need for selective tools or probes in basic research on CNS mechanisms and behaviour.