Agonist and antagonist effects of prototype opiate drugs in fentanyl dose-dose discrimination.
The experiments characterized the effects of fentanyl, morphine, naloxone, cyclazocine, nalorphine, ketocyclazocine and N-allylnormetazocine in rats that were trained to discriminate 0.04 mg/kg from 0.02 mg/kg fentanyl (dose-dose discrimination). The data are compared to results obtained previously in rats discriminating 0.04 mg/kg fentanyl from saline (drug-saline discrimination). In the dose-dose discrimination fentanyl and morphine produced responding appropriate to 0.04 mg/kg fentanyl at doses which were 3.0- and 1.6-fold higher, respectively, than in drug-saline discrimination. Naloxone antagonized the stimulus effects of 0.04 mg/kg fentanyl at 9.8-fold lower doses than in drug-saline discrimination. The dose-effect curves of fentanyl and naloxone in rats discriminating 0.04 mg/kg from 0.02 mg/kg fentanyl, were steeper than in rats discriminating 0.04 mg/kg fentanyl from saline. While cyclazocine, nalorphine and N-allylnormetazocine acted as mixed and partial agonists/antagonists in drug-saline discrimination, those compounds acted as pure and complete antagonists of 0.04 mg/kg fentanyl in dose-dose discrimination. The rank order of compounds in antagonizing the stimulus effects of 0.04 mg/kg fentanyl in dose-dose discrimination was naloxone greater than N-allylnormetazocine greater than cyclazocine greater than nalorphine. It is suggested that a greater magnitude of opiate activity is required for producing generalization with the same 0.04 mg/kg dose of fentanyl in dose-dose as compared with drug-saline discrimination. Dose-dose discrimination may afford a more accurate method of the discriminative stimulus properties of drugs.(ABSTRACT TRUNCATED AT 250 WORDS)
D000818:Animals; D004193:Discrimination Learning / Q000187:drug effects; D004192:Discrimination, Psychological / Q000187:drug effects*; D004305:Dose-Response Relationship, Drug; D005283:Fentanyl / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D005795:Generalization, Stimulus / Q000187:drug effects; D008297:Male; D009020:Morphine / Q000494:pharmacology; D009270:Naloxone / Q000494:pharmacology; D009294:Narcotics / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains
D009294:Narcotics; D009270:Naloxone; D009020:Morphine; D005283:Fentanyl