Selected opioids and responding for intracranial reinforcement.
Rats fixed with chronically indwelling electrodes for intracranial stimulation (ICS) of the lateral hypothalamus pressed a lever during daily sessions for a fixed intensity of ICS. Before some sessions, they were given placebo, or ethylketocyclazocine (EKC) in racemic or isomeric forms [either (+)EKC or (-)EKC]. Naloxone (NX) was also given with the agents. The racemate facilitated pressing across a narrow range of small doses (centered about 0.02 mg/kg). At no dose did (-)EKC, a potent analgesic, facilitate pressing and typically depressed it. (+)EKC, at doses of 0.04 and 0.08 mg/kg, facilited pressing. These data provide further confirmation that opioid analgesia and ability to enhance pressing are separable. When NX was given with a large dose of the racemate, paradoxically pressing for ICS was facilitated. Apparently, NX selectively blocked the effects of (-)EKC. SKF 10047 was also administered in racemic and isomeric forms. All three forms produced some facilitation of pressing at small doses (e.g., 0.75 mg/kg) and depressed pressing at large doses (e.g., 5.0 mg/kg).
D000818:Animals; D003496:Cyclazocine / Q000031:analogs & derivatives* / Q000494:pharmacology; D016314:Ethylketocyclazocine; D007026:Hypothalamic Area, Lateral / Q000187:drug effects; D009270:Naloxone / Q000494:pharmacology*; D010620:Phenazocine / Q000031:analogs & derivatives* / Q000494:pharmacology; D051381:Rats; D012054:Reinforcement, Psychology; D012653:Self Stimulation / Q000187:drug effects*; D013237:Stereoisomerism
D009270:Naloxone; D016314:Ethylketocyclazocine; C012134:SK&F 10047; D010620:Phenazocine; D003496:Cyclazocine