Endomorphins 1 and 2 induce amnesia via selective modulation of dopamine receptors in mice

• Published in: European journal of pharmacology Vol. 446; no. 1; pp. 97 - 101
• Main Authors: Ukai, Makoto, Lin, Hui Ping
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 20-06-2002; Elsevier
• Subjects: 2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-benzazepine - pharmacology; Amnesia - metabolism; Amnesia - psychology; Animals; Avoidance Learning - drug effects; Benzazepines - pharmacology; Biological and medical sciences; Dopamine Agonists - pharmacology; Dopamine Antagonists - pharmacology; Dopamine receptor; Drug toxicity and drugs side effects treatment; Endomorphin-1; Endomorphin-2; Male; Medical sciences; Memory - drug effects; Mice; Mouse; Oligopeptides - metabolism; Oligopeptides - pharmacology; Passive avoidance learning; Pharmacology. Drug treatments; Phenethylamines - pharmacology; Receptors, Dopamine - drug effects; Receptors, Dopamine D1 - drug effects; Receptors, Dopamine D2 - drug effects; Stereoisomerism; Sulpiride - pharmacology; Toxicity: nervous system and muscle; μ-Opioid receptor; μ-Opioid receptor; Endomorphin-1; Mouse; Dopamine receptor; Passive avoidance learning; Endomorphin-2; Memory disorder; Nervous system diseases; Endomorphin 2; Dopamine; Endomorphin 1; Cognitive disorder; Toxicity; Rodentia; μ Opioid receptor; Central nervous system; Cerebral disorder; Vertebrata; Mammalia; D2 Dopamine receptor; Learning disability; Animal; Central nervous system disease; Amnesia; Neurological disorder; Mechanism of action; Brain (vertebrata)
• ISSN: 0014-2999; 1879-0712
• DOI: 10.1016/S0014-2999(02)01760-0

The involvement of dopamine receptors in the amnesic effects of the endogenous μ-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-1
H-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-1
H-3-benzazepine hydrochloride (
R(+)-SCH23390) (2.5 and 5 μg/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 μg)- or endomorphin-2 (10 μg)-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 μg), but not by endomorphin-1 (10 μg). 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.