REINFORCING AND DISCRIMINATIVE STIMULUS PROPERTIES OF MIXED AGONIST-ANTAGONIST OPIOIDS

  • 1 January 1984
    • journal article
    • research article
    • Vol. 229  (1) , 118-126
Abstract
Nine mixed agonist-antagonist opioids were evaluated in macaque monkeys [Macaca mulatta] for their ability to serve as positive reinforcers and for their discriminative stimulus similarity to etorphine and ethylketazocine. For tests of reinforcing properties, various doses of each drug were substituted for codeine under a fixed-ratio 30 time-out 600 se schedule of i.v. delivery. Discriminative properties were assessed in separate groups of monkeys for which etorphine and saline, or ethylketazocine and saline, were established as discriminative stimuli for responses maintained under a fixed-ratio 20 schedule of food delivery. Two patterns of reinforcing and discriminative stimulus properties were observed. Buprenorphine, butorphanol, GPA-1657 [.beta.-[l]-5-phenyl-9-methyl-2''-hydroxy-2-methyl-6,7-benzomorphan], nalbuphine, propiram and WY-16225 (dezocine) functioned as positive reinforcers and occasioned etorphine-appropriate but not ethylketazocine-appropriate responses. dl-Profadol also functioned as a positive reinforcer; its stereoisomers occasioned etorphine-appropriate but not, in general, ethylketazocine-appropriate responses. Levallorphan and oxilorphan did not function as positive reinforcers and occasioned ethylketazocine-appropriate but no more than 30% etorphine-appropriate responses. Under these experimental conditions, the reinforcing and discriminative stimulus profiles of the mixed agonist-antagonist opioids paralleled those of etorphine-like (.mu.) or ethylketazocine-like (.kappa.) opioid agonists.