Reinforcing effects of enantiomers of N,N-dimethylamphetamine in squirrel monkeys

Reinforcing effects of the (+)- and (-)-enantiomers of N,N-dimethylamphetamine, a drug that is abused in humans, were studied in squirrel monkeys (Siamiri sciureus) trained under schedules of intermittent cocaine reinforcement. During training, each 30th response produced an injection of cocaine (fixed-ratio schedule), which was followed by a 1-min period during which lights were out and responses had no scheduled consequences (timeout). Sessions in which cocaine injections were scheduled alternated in an irregular sequence with sessions in which saline injections were scheduled. After training, response rates were well maintained by cocaine (response rates approximated 1.4 responses per second) but occurred relatively infrequently during sessions in which saline was injected (response rates approximated 0.3 responses per second). Doses of 10 to 56 micrograms/kg/injection of (+)-N,N-dimethylamphetamine maintained rates of responding significantly higher than those maintained by saline. The (-)-enantiomer did not maintain rates of responding that were higher than those maintained by saline when tested at doses up to 100 micrograms/kg/injection. These findings support previous results indicating that N,N-dimethylamphetamine will function as a reinforcer in laboratory animals. Further, they suggest that the significant reinforcing activity of this drug is restricted to the (+)-enantiomer.