title: Melatonin enhances the expression of β-endorphin in hypothalamic arcuate nucleus of morphine-dependent mice.
abstract: The study was conducted to investigate the effect of melatonin (MEL) on the expression of β-endorphin (β-EP) in the hypothalamic arcuate nucleus (ARH) of morphine-dependent mice. For a period of 8 consecutive days, male Kunming strain mice were injected subcutaneously (s.c.) with normal saline or increasing doses (10-80 mg/kg) of morphine, and intraperitoneally (i.p.) with MEL (10, 20 or 40 mg/kg) or vehicle (5% ethanol saline) simultaneously. Withdrawal response was induced by naloxone (3 mg/kg, s.c.) at 2 h after final morphine injection on the 8th day. The potency of withdrawal response was evaluated according to the jumping times and the body weight loss. After that, the expressions of β-EP and proopiomelanocortin (POMC) mRNA in ARH were examined by immunohistochemistry and RT-PCR, respectively. The results showed that MEL (i.p., 20 mg/kg) decreased the naloxone-precipitated withdrawal responses in morphine-dependent mice significantly (P<0.05). Meanwhile, MEL increased the intensity of β-EP-like immunoreactivity and enhanced the expression of POMC mRNA in ARH (P<0.05). These results suggest that MEL increases the expression of β-EP in ARH of morphine-dependent mice, which may partly contribute to the action of MEL to inhibit the development of morphine dependence.
authors.affiliation: Department of Pharmacology, Fujian Medical University, Fuzhou, China.
authors.forename: Yi-Ming
authors.initials: YM
authors.lastname: Wei
authors.forename: Ying
authors.initials: Y
authors.lastname: Xu
authors.forename: Chang-Xi
authors.initials: CX
authors.lastname: Yu
authors.forename: Jing
authors.initials: J
authors.lastname: Han
mesh_terms: D000818:Animals; D001111:Arcuate Nucleus of Hypothalamus / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D008550:Melatonin / Q000494:pharmacology*; D051379:Mice; D009020:Morphine / Q000494:pharmacology; D009021:Morphine Dependence / Q000378:metabolism*; D009270:Naloxone / Q000494:pharmacology; D011333:Pro-Opiomelanocortin / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D013375:Substance Withdrawal Syndrome / Q000378:metabolism; D001615:beta-Endorphin / Q000378:metabolism*
chemical_list: D012333:RNA, Messenger; D009270:Naloxone; D001615:beta-Endorphin; D011333:Pro-Opiomelanocortin; D009020:Morphine; D008550:Melatonin