Opiate antagonists reduce cocaine but not nicotine self-administration

Psychopharmacology (Berl). 1991;104(2):167-70. doi: 10.1007/BF02244173.


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.

Publication types

  • Comparative Study

MeSH terms

  • Animals
  • Cocaine / antagonists & inhibitors*
  • Cocaine / pharmacology
  • Conditioning, Operant / drug effects
  • Male
  • Naloxone / pharmacology
  • Naltrexone / pharmacology
  • Narcotic Antagonists / pharmacology*
  • Nicotine / antagonists & inhibitors*
  • Nicotine / pharmacology
  • Rats
  • Reinforcement Schedule
  • Self Administration


  • Narcotic Antagonists
  • Naloxone
  • Naltrexone
  • Nicotine
  • Cocaine