Environment-specific conditioning and sensitization with (+)-amphetamine.

Learning variables have an important role in determining the behavioral effects of some pharmacological treatments. Environmental control of sensitization and conditioning of the stimulant effects of (+)-amphetamine (AMPH) were studied in two experiments. Rats were given 6 1-hr habituation sessions in automated activity chambers conducted every second day. Two days later the 12 rats in the paired group in each study received AMPH (2.0 mg/kg) followed immediately by placement in the chambers for 1 hr whereas rats in the unpaired groups received saline. All rats were injected the following day and left in their home cages afterwards. At this time the paired groups received saline and the unpaired groups received AMPH. Three days later a second pairing and subsequent home cage injection was administered, using the same procedure. Immediately prior to the test session (4 days after the last pairing session) all rats in the sensitization experiment received AMPH and those in the conditioning study received saline. During pairing sessions AMPH treated rats exhibited more vertical activity than controls. On the saline test session in the conditioning study there was still a significant group difference demonstrating environment-specific conditioning. There was no evidence of sensitization on vertical activity; however, a significant difference in horizontal activity was seen on the AMPH test session. Results suggest that these two phenomena can be dissociated behaviorally and may not follow the same time-course.