CODEINE- AND COCAINE-REINFORCED RESPONDING IN RHESUS MONKEYS: EFFECTS OF DOSE ON RESPONSE RATES UNDER A FIXED-RATIO SCHEDULE

¹ Department of Pharmacology University of Michigan Medical School Ann Arbor, Michigan

Over a wide range of doses, codeine (0.001-1.0 mg/kg/injection) and cocaine (0.001-0.3 mg/kg/injection) both maintained lever-press responding when 30 responses were required for each intravenous injection. Rate of responding for each drug increased to a maximum and then decreased as dose (milligrams per kilogram per injection) increased. Maximum response rate for cocaine (0.003 mg/kg/injection) was over 3 times greater than the maximum response rate for codeine (0.03 mg/kg/injection). For both drugs, greatest stability of response rates across sessions was obtained at the higher doses, and changes in dose generally produced immediate changes in response rates. Injections of codeine were usually distributed in a negatively accelerated pattern within sessions while injections of cocaine were more evenly distributed. History of cocaine exposure appeared to increase response rates for low doses of cocaine in some monkeys.

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