Pairings of a Circular Alley with Apomorphine Produce Conditioned Hyperactivity

During training trials, some rats were injected with apomorphine as the unconditioned stimulus immediately before (Group Forward) or 15 min before (Group Backward) exposure to the conditioned stimulus, a circular alley where locomotor activity was measured for 30 min. Rats in the control condition (Group Unpaired) were not injected until 15 min after their removal from the alley. When the rats were later tested in the circular alley without prior administration of the drug, both Groups Forward and Backward were more active than Group Unpaired and thus showed conditioned hyperactivity. During a final test in which all the rats were injected with apomorphine prior to placement in the circular alley, Groups Forward and Backward showed greater apomorphine-induced hyperactivity than Group Unpaired. Although Group Forward was more active than Group Backward during both tests, these differences were not significant. These findings provide further evidence for the modulation of drug effects by Pavlovian conditioning.