THE INFLUENCE OF ENVIRONMENT ON THE INDUCTION OF SENSITIZATION TO THEPSYCHOMOTOR ACTIVATING EFFECTS OF INTRAVENOUS COCAINE IN RATS IS DOSE-DEPENDENT

The acute psychomotor response and development of sensitization to amp hetamine is attenuated if LP injections are given in the cage where a rat lives relative to when injections are given in a novel but physica lly identical test environment. Furthermore, when the environmental cu es predicting IP injections are completely eliminated by using remotel y activated IV injections in the home cage, 1.0 mg/kg amphetamine prod uces a very small acute response and no sensitization. The same treatm ents do produce sensitization if IV injections are signaled by placeme nt of the rat in a novel test cage. The present experiment was designe d to determine if there is a similar effect of environmental condition on the response to IV cocaine, and to what extent the effect may be d ose-dependent. This was accomplished by comparing the psychomotor acti vating effects (rotational behavior) of repeated TV administrations of one of eight doses of cocaine (0.0: 0.3, 0.6, 1.2, 2.4, 3.6, 4.8, or 7.2 mg/kg) given in the home cage, with infusions of the same doses gi ven in a novel test cage. There was no effect of environment on the ac ute psychomotor response to cocaine. There was, however, a significant effect of environment on the induction of sensitization. A higher dos e of cocaine was required to induce sensitization when IV administrati ons were given in the home cage than when they were given in a physica lly identical but novel test environment. At high doses, however, coca ine induced sensitization regardless of environmental condition. The r esults suggest that the effect of this environmental manipulation is t o shift the dose-effect curve for the induction of sensitization, and support the notion that the ability of psychostimulant drugs to induce sensitization can be modulated by the circumstances surrounding drug administration.