Pentazocine-like discriminative stimulus effects of morphine are blocked by the dopamine D-1 antagonist SCH23390, but not by the dopamine D-2 antagonist sulpiride.
The effects of selective dopamine antagonists on the pentazocine-like discriminative stimulus effects of morphine were investigated in the rat trained to discriminate 3.0 mg/kg of pentazocine from vehicle. Morphine (3.0 mg/kg), a mu-selective agonist, produced stimulus effects in common with pentazocine (3.0 mg/kg), indicating that the stimulus effects are mediated through mu opioid receptors. The pentazocine-like stimulus effects of morphine (3.0 mg/kg) were clearly inhibited by the dopamine D-1 antagonist SCH23390 (0.03-0.56 mg/kg) but not by the dopamine D-2 antagonist sulpiride (20.0-80.0 mg/kg). The results suggest that the pentazocine-like discriminative stimulus effects of morphine are mediated via dopamine D-1 receptors.
Ukai
M
M
Department of Chemical Pharmacology, Faculty of Pharmaceutical Sciences, Meijo University, Nagoya, Japan.
Hiraiwa
E
E
Kameyama
T
T
D000818:Animals; D001552:Benzazepines / Q000494:pharmacology*; D018492:Dopamine Antagonists; D004305:Dose-Response Relationship, Drug; D008297:Male; D009020:Morphine / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D010423:Pentazocine / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains; D017447:Receptors, Dopamine D1; D017448:Receptors, Dopamine D2; D013469:Sulpiride / Q000494:pharmacology*
D001552:Benzazepines; D018492:Dopamine Antagonists; D017447:Receptors, Dopamine D1; D017448:Receptors, Dopamine D2; D009020:Morphine; D013469:Sulpiride; D010423:Pentazocine