Analgesic and discriminative stimulus properties of U-62,066E, the selective kappa-opioid receptor agonist, in the rat.
The analgesic and discriminative stimulus properties of U-62,066E, a selective kappa-opioid receptor agonist, were investigated in the rat and compared with those of morphine. In the hot-plate test, U-62,066E produced a potent analgesic effect almost comparable to that of morphine. U-62,066E-induced analgesia was far less sensitive to antagonism by naloxone than was morphine-induced analgesia, but was potently reversed by MR-2266, a kappa-receptor antagonist. Although tolerance occurred to both U-62,066E and morphine analgesia, there was no cross-tolerance between these drugs. U-62,066E did show cross-tolerance to U-50,488H, another selective kappa-receptor agonist. Rats were trained to discriminate either 1.0 mg/kg U-62,066E or 3.2 mg/kg morphine from saline in a two-level food-reinforced procedure. The stimulus effect of U-62,066E was substituted for by U-50,488H and E-2078 a stable dynorphin derivative, but not by morphine. None of the kappa-agonists substituted for the morphine stimulus. Although U-62,066E stimulus by itself was not antagonized by MR-2266 or naloxone up to as high a dose as 10 mg/kg, the U-62,066E-like stimulus effect of U-50,488H was markedly blocked by MR-2266. The dopamine antagonists haloperidol and sulpiride substituted for the U-62,066E stimulus cue that was, however, not attenuated by the dopamine agonist lisuride. Lisuride reversed the U-62,066E-like stimulus induced by U-50,488H.(ABSTRACT TRUNCATED AT 250 WORDS)
Department of Pharmacology, Faculty of Pharmaceutical Sciences, Kyushu University, Fukuoka, Japan.
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Ohno
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Yamamoto
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Ueki
D000700:Analgesics / Q000494:pharmacology*; D000818:Animals; D001575:Benzomorphans / Q000494:pharmacology; D003463:Cues; D004192:Discrimination, Psychological / Q000187:drug effects*; D004298:Dopamine / Q000502:physiology; D018492:Dopamine Antagonists; D004399:Dynorphins / Q000031:analogs & derivatives / Q000494:pharmacology; D008297:Male; D009020:Morphine / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000494:pharmacology; D010446:Peptide Fragments / Q000494:pharmacology; D011759:Pyrrolidines / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains; D011957:Receptors, Opioid / Q000187:drug effects*; D017473:Receptors, Opioid, kappa; D017450:Receptors, Opioid, mu
D000700:Analgesics; D001575:Benzomorphans; D018492:Dopamine Antagonists; D009292:Narcotic Antagonists; D010446:Peptide Fragments; D011759:Pyrrolidines; D011957:Receptors, Opioid; D017473:Receptors, Opioid, kappa; D017450:Receptors, Opioid, mu; C061285:E 2078; C027247:MR 2266; D004399:Dynorphins; D009020:Morphine; C051272:spiradoline; D004298:Dopamine