Interactions between narcotic agonists, partial agonists andd antagonists evaluated by punished an unpunished...

The effects of morphine, ketocyclazocine, cyclazocine, and SKF-10,047 were tested alone and in conjunction with naltrexone or naloxone, in rats responding under a multiple fixed-interval 3-min schedule of food presentation. Under this paradigm, electric shock was delivered on a fixed-ratio schedule for responses occurring during alternate schedule components. All of the drugs (except naltrexone and naloxone) decreased average rates of responding maintained by the unpunished component in a dose-dependent manner. The rate-decreasing effects of morphine and ketocyclazocine were antagonized by naltrexone. The rate-decreasing effects of cyclazocine were only slightly reversed by the antagonists, while those effects of SKF-10,047 were not affected by naltrexone. In some animals, certain doses of SKF-10,047 increased unpunished responding. This rate-increasing effect was antagonized by naltrexone. Morphine, ketocyclazocine, cyclazocine, and SKF-10,047 increased responding that was suppressed by electric shock, and these increases were antagonized by naltrexone and naloxone. Thus, the antagonism of opiate effects by narcotic antagonists depends in part on the behavior being evaluated.