Environment-dependent sensitization to amphetamine-induced circling behavior

Sensitization to amphetamine-induced circling behavior in nonlesioned, female rats was studied. Experiments were designed to determine the effects of time spent in the test environment prior to and following the administration of amphetamine and of the time between injections of amphetamine on the environment-dependent nature of the sensitization process. One group of rats was allowed to habituate to the test apparatus prior to injection of the drug. In this group, the drug was administered in the apparatus and the rats remained there for the duration of drug action. Another group of rats was placed in the apparatus only during the time of peak drug action. These rats were administered amphetamine in their home cages and were not allowed time to habituate to the test apparatus. Amphetamine was administered 2 times and injections were separated by either 1 or 7 days. To determine if the sensitization was dependent on the environment in which the drug was previously experienced, one-half of each of these groups of rats were kept in their home cages following the first injection of amphetamine and experienced the effects of the second injection of amphetamine in the test apparatus. The other half experienced the effects of both injections of amphetamine in the test apparatus. Sensitization was found to occur only in rats that experienced the effects of the first drug injection in the test environment.