Discriminative stimulus effects of spiradoline, a kappa-opioid agonist.
This study represents the initial step in assessing the discriminative effects of spiradoline (U62,066), a potent congener of the selective kappa-opioid agonist, U50,488. Separate groups of rats were trained to discriminate between SC injections of saline and either 3.0 mg/kg spiradoline or 3.0 mg/kg morphine in a discrete-trial shock-avoidance/escape procedure. Spiradoline-trained rats generalized completely to U50,488 (ED50S for spiradoline and U50,488 were 0.66 and 8.71 mg/kg, respectively), but selected the choice lever appropriate for saline in generalization tests with graded doses of morphine, phencyclidine, and agonist-antagonist opioids with varying degrees of kappa activity, ethylketocyclazocine, nalorphine, and butorphanol. Morphine-trained rats did not generalize to spiradoline. Naltrexone (0.01 or 0.1 mg/kg) blocked surmountably the discriminative effects of both spiradoline and morphine, but was approximately 10-fold less potent against spiradoline. These results indicate that the discriminative effects of spiradoline are mediated by kappa-opioid receptors; meaningful mu-opioid and PCP/sigma components of action were not in evidence. The potency and apparent pharmacological selectivity of spiradoline suggest the potential value of this drug for studying kappa-opioid-mediated stimulus control of behavior.
Holtzman
S G
SG
Department of Pharmacology, Emory University School of Medicine, Atlanta, GA 30322.
Cook
L
L
Steinfels
G F
GF
D019900:3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; D000818:Animals; D002077:Butorphanol / Q000494:pharmacology; D004192:Discrimination, Psychological / Q000187:drug effects* / Q000502:physiology; D016314:Ethylketocyclazocine / Q000494:pharmacology; D005795:Generalization, Stimulus; D008297:Male; D009020:Morphine / Q000494:pharmacology; D009269:Nalorphine / Q000494:pharmacology; D010622:Phencyclidine / Q000494:pharmacology; D011759:Pyrrolidines / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains; D011930:Reaction Time; D011957:Receptors, Opioid / Q000187:drug effects*; D017473:Receptors, Opioid, kappa; D017450:Receptors, Opioid, mu
D011759:Pyrrolidines; D011957:Receptors, Opioid; D017473:Receptors, Opioid, kappa; D017450:Receptors, Opioid, mu; D016314:Ethylketocyclazocine; D019900:3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; D009020:Morphine; D010622:Phencyclidine; C051272:spiradoline; D002077:Butorphanol; D009269:Nalorphine