The compulsion zone: a pharmacological theory of acquired cocaine self-administration.

In rats trained to reliably self-administer cocaine, the cumulative drug level was calculated during sessions in which cocaine was administered either contingently or non-contingently. During both types of sessions a high rate of responding was observed only when cocaine levels were above the priming threshold but below the satiety threshold. When the levels of non-contingently administered cocaine were maintained between the priming and satiety thresholds for at least 5 h rats continuously maintained high rates of responding. Although it is generally assumed that rats are responding for cocaine during self-administration sessions, the persistence of responding during non-contingent administration is consistent with responding being induced by cocaine. Therefore, in contrast to the basic assumptions underlying the operant theory of self-administration behavior, choice, contingency and reinforcement are not necessary to explain acquired cocaine self-administration. The presented data demonstrate that there is no ascending limb of the dose-response curve and that the cocaine priming and satiety thresholds delineate the lower and upper limits, respectively, of a cocaine "compulsion zone". It is concluded that the self-administration paradigm is the sum of cocaine induced responding and cocaine induced satiety and which of these cocaine-induced effects occur at any time is dependent on the cocaine level. This novel pharmacokinetic/pharmacodynamic theory provides a basis for a comprehensive understanding of the cocaine self-administration paradigm.