title: Endomorphins 1 and 2 induce amnesia via selective modulation of dopamine receptors in mice.
abstract: The involvement of dopamine receptors in the amnesic effects of the endogenous micro-opioid receptor agonists endomorphins 1 and 2 was investigated by observing step-down type passive avoidance learning in mice. Although the dopamine D1 receptor agonist R(+)-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine-7,8-diol hydrochloride (R(+)-SKF38393) (0.05 and 0.1 mg/kg), the dopamine D1 receptor antagonist R(+)-7-chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine hydrochloride (R(+)-SCH23390) (2.5 and 5 microg/kg) or the dopamine D2 receptor agonist N-n-phenethyl-N-propylethyl-p-(3-hydroxyphenyl)-ethylamine (RU24213) (0.3 and 1 mg/kg) had no significant effects on the endomorphin-1 (10 microg)- or endomorphin-2 (10 microg)-induced decrease in step-down latency of passive avoidance learning, (-)-sulpiride (10 mg/kg), a dopamine D2 receptor antagonist, significantly reversed the decrease in step-down latency evoked by endomorphin-2 (10 microg), but not by endomorphin-1 (10 microg). Taken together, it is likely that stimulation of dopamine D2 receptors results in the endomorphin-2-but not endomorphin-1-induced impairment of passive avoidance learning.
authors.affiliation: Department of Chemical Pharmacology, Faculty of Pharmacy, Meijo University, 468-8503, Nagoya, Japan. ukai@ccmfs.meijo-u.ac.jp
authors.forename: Makoto
authors.initials: M
authors.lastname: Ukai
authors.forename: Hui Ping
authors.initials: HP
authors.lastname: Lin
mesh_terms: D015647:2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-benzazepine / Q000494:pharmacology; D000647:Amnesia / Q000378:metabolism* / Q000523:psychology; D000818:Animals; D001362:Avoidance Learning / Q000187:drug effects; D001552:Benzazepines / Q000494:pharmacology; D018491:Dopamine Agonists / Q000494:pharmacology; D018492:Dopamine Antagonists / Q000494:pharmacology; D008297:Male; D008568:Memory / Q000187:drug effects; D051379:Mice; D009842:Oligopeptides / Q000378:metabolism* / Q000494:pharmacology; D010627:Phenethylamines / Q000494:pharmacology; D011954:Receptors, Dopamine / Q000187:drug effects*; D017447:Receptors, Dopamine D1 / Q000187:drug effects; D017448:Receptors, Dopamine D2 / Q000187:drug effects; D013237:Stereoisomerism; D013469:Sulpiride / Q000494:pharmacology
chemical_list: D001552:Benzazepines; D018491:Dopamine Agonists; D018492:Dopamine Antagonists; D009842:Oligopeptides; D010627:Phenethylamines; D011954:Receptors, Dopamine; D017447:Receptors, Dopamine D1; D017448:Receptors, Dopamine D2; C105293:endomorphin 1; C105294:endomorphin 2; D015647:2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-benzazepine; C016868:N-n-propyl-N-phenylethyl-4(3-hydroxyphenyl)ethylamine hydrochloride; D013469:Sulpiride