Can craving be modeled in animals? The relapse prevention perspective

The mechanism that underlies craving is unknown, and this makes it difficult to model craving in any general way in animals. However, there is considerable evidence that conditioned "drug-like" and "drug-opposite" responses play a part in relapse during abstinence. In so much as these conditioned responses represent one type of mechanism that leads to craving, they can be used to develop animal models of craving. Indeed, there are several types of model already available that are based on drug-conditioned responses, and that are relevant. However, most current "drug conditioning models" have not been developed with the specific intention of modeling factors that predispose to relapse, and they have deficiencies for this purpose as a result. In addition, some of the drug-conditioning models are unsuitable for the study of alcohol rather than for more positively reinforcing drugs such as cocaine. This commentary considers first whether the existing models, and the concepts behind them, can be adapted to provide "craving models" and, secondly, whether the resulting models may be used to evaluate anti-relapse drugs. This purpose requires two levels of complexity, simple "screening tests" that suggest that a drug may be worth evaluating further, and models of more complex behavior that have face validity to relapse in the human subject, and have predictive value for therapeutic use in relapse. Finally, rather different animal models, based on the concepts of extinction and reinstatement, might be used to answer fundamental questions as to the mechanisms of relapse into use of alcohol. All the proposed types of animal models of craving are based on conditioned reinforcements, rather than being based on reinforcing effects of the drugs themselves (as are most of the current models). However, if the development of "craving models" based on conditioning will help us better understand relapse, then the therapeutic benefits that can be expected will make the effort worthwhile.