Opiate antagonists reduce cocaine but not nicotine self-administration.
Rats were trained to self-administer cocaine in 1-h sessions on a fixed ratio 5 (FR5) schedule of reinforcement. Acquisition was carried out at a unit dose of 0.3 mg/kg and responding was then stabilized at cocaine doses of 0.1, 0.3, and 1.0 mg/kg/infusion. Pretreatments with naltrexone (0.1-10 mg/kg, SC) 20 min prior to the start of self-administration sessions resulted in decreases in cocaine self-administration at doses of 0.1 and 0.3 mg/kg/infusion, but not at 1.0 mg/kg/infusion. Decreases depended on the dose of naltrexone used, with greater decreases in self-administration occurring at higher antagonist doses. In addition, treatment with the opiate antagonist naloxone also reduced cocaine self-administration at a unit dose of 0.3 mg/kg. A group of rats trained to self-administer nicotine at a dose of 0.03 mg/kg/infusion on the same schedule of reinforcement was unaffected by naltrexone treatment. These results may indicate that an endogenous opiate system plays a role in cocaine reinforcement.
Corrigall
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Addiction Research Foundation, Toronto, Ontario, Canada.
Coen
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D000818:Animals; D003042:Cocaine / Q000037:antagonists & inhibitors* / Q000494:pharmacology; D003216:Conditioning, Operant / Q000187:drug effects; D008297:Male; D009270:Naloxone / Q000494:pharmacology; D009271:Naltrexone / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000494:pharmacology*; D009538:Nicotine / Q000037:antagonists & inhibitors* / Q000494:pharmacology; D051381:Rats; D012055:Reinforcement Schedule; D012646:Self Administration
D009292:Narcotic Antagonists; D009270:Naloxone; D009271:Naltrexone; D009538:Nicotine; D003042:Cocaine