Comparison of the Reinforcing and Rate-Decreasing Actions in the Rhesus Monkey*

Abstract. N-ethyl amphetamine HCI (NEA) and fenfluramine HC1 (meta-trifluoromethyl N-ethyl amphetamine) were evalu-ated as reinforcers inrhesus monkeys that had been previously trained to press a lever using food presentations and cocaine HC1 injections as reinforcers. Each daily session consisted of episodic opportunities to obtain reinforcers under a fixed-ratio schedule of 30. A drug period was interpolated be-tween two periods in which lever-press responding was main-tained by food presentations. Compared to saline, none of the drugs altered the rate of responding in the food periods which preceded the drug sessions, indicating the absence of residual response-disrupting drug actions from previous es-sions. However, NEA and fenfluramine self-injection resulted in dose-related decreases in response rates during the food periods which immediately followed the drug sessions. Cocaine HCI (30 gg/kg/injection) maintained high response rates at over one response/second during the drug periods, as did the same dose of NEA. Doses of 10 and 100 gg/kg/injection of NEA as well as all doses of fenfluramine HC1 (10 through 300 gg/kg/injection) maintained rates that were not different from those associated with saline injections. These results substantiate and extend earlier findings with fenfluramine and indicate that its failure to act as a reinforcer is attributable to its meta-trifluoromethyl group