Discriminative stimulus effects of nalbuphine in nontreated and morphine-treated pigeons.
In the present study, the stimulus effects of the low efficacy agonist nalbuphine were examined under two conditions: nontreated and morphine treated. In the first experiment, five pigeons were trained to discriminate among 3.2 mg/kg morphine, 5.6 mg/kg nalbuphine, and saline. Nalbuphine produced nalbuphine-like responding. Low doses of morphine produced nalbuphine-like responding, whereas high doses produced morphine-like responding. Naltrexone produced saline-like responding and reversed the stimulus effects produced by the training doses of morphine and nalbuphine. Five different pigeons were treated daily with 10 mg/kg morphine (i.m.) and trained 6 h later to discriminate among 10 mg/kg morphine, 1.0 mg/kg nalbuphine and saline. In these pigeons, morphine produced morphine-like responding and nalbuphine produced nalbuphine-like responding. Morphine abstinence produced nalbuphine-like responding that was reversed by morphine. Additionally, naltrexone produced nalbuphine-like responding. These data suggest that the discrimination between morphine and nalbuphine in the nontreated and morphine-treated pigeons may be based on the relative efficacy differences between morphine, a higher efficacy mu-agonist, and nalbuphine a lower efficacy mu-agonist.
Walker
E A
EA
Department of Psychology, University of North Carolina at Chapel Hill, 27599, USA.
Hawkins
E R
ER
Tiano
M J
MJ
Picker
M J
MJ
Dykstra
L A
LA
D000701:Analgesics, Opioid / Q000494:pharmacology*; D000818:Animals; D010856:Columbidae; D003463:Cues; D004193:Discrimination Learning / Q000187:drug effects; D004192:Discrimination, Psychological / Q000187:drug effects*; D009020:Morphine / Q000494:pharmacology*; D009266:Nalbuphine / Q000494:pharmacology*; D009271:Naltrexone / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000494:pharmacology*; D012193:Reversal Learning / Q000187:drug effects
D000701:Analgesics, Opioid; D009292:Narcotic Antagonists; D009271:Naltrexone; D009020:Morphine; D009266:Nalbuphine