Abstract

Three experiments were conducted with rhesus monkeys to assess some behavioral effects of the opium alkaloid, thebaine, in relation to its dependence liability. The concurrent intramuscular administration of naloxone did not antagonize the rate-decreasing effects of thebaine on a fixed-ratio (FR) schedule of food-reinforced responding. Animals trained to self-administer codeine (0.3 mg/kg/inj) on an FR 30 schedule did not self-administer thebaine (0.003-1.0 mg/kg/inj) at rates comparable to these of codeine. Rates were minimally above those of saline at 0.3 mg/kg inj. Monkeys given 23 hrs/day continuous access to 1.0 mg/kg/inj thebaine did, however, self-administer the drug at rates significantly higher than those maintained by saline, but not as high as those supported by 2.0 mg/kg/inj codeine. Two animals self-administering thebaine did not show any signs of withdrawal when injected with 0.1-1.0 mg/kg of naloxone or when saline was substituted for thebaine. A third monkey showed a severe reaction leading to death following an injection of 1.0 mg/kg naloxone.