Conditioned Avoidance Response in the Development of New Antipsychotics

Schizophrenia presents with positive/psychotic, negative and cognitive symptoms. Positive symptoms seems due to a dopamine mesolimbic overreactivity, while negative/cognitive symptoms may conversely be due to mesocortical hypo-dopaminergia. Traditional dopamine D2 receptor blocking antipsychotics (e.g. haloperidol) are effective against psychotic/positive symptoms, but less so against negative/cognitive symptoms. Some D2 receptor blockage, however, seems necessary for efficacy against psychotic symptoms. Therefore, current antipsychotic drug improvement strategies include modest D2 receptor blockage, or partial D2 stimulation, combined with adjunct pharmacological properties that may enhance: i) D2 blockage efficacy; and ii) cognitive functioning. There are also strategies with no direct D2 blockage. Clinical activity is often tested in animal screening tests (so called animal models). The screening test conditioned avoidance response in rats has shown particular sensitivity, with high predictive validity, for detection of drug antipsychotic activity. The present review assessed the significance, accuracy and use of the conditioned avoidance response test as a screening tool in current antipsychotic drug development. It was found that: i) the conditioned avoidance response test holds a strong position, is frequently used in current antipsychotic drug development, and is commonly considered a reliable screening tool, with high predictive validity, for the detection of potential antipsychotic activity; ii) in current antipsychotic drug development, the conditioned avoidance response test is able to detect pharmacological properties contributing to antipsychotic activity in the presence of sub-therapeutic D2 receptor blockade, as well as detecting antipsychotic activity of compounds having no direct D2 blocking properties.