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Melatonin enhances the expression of β-endorphin in hypothalamic arcuate nucleus of morphine-dependent mice

WEI Yi-Ming, XU Ying, YU Chang-Xi, HAN Jing

Department of Pharmacology； Department of Physiology and Pathophysiology, College of Preclinical Medicine, Fujian Medical University, Fuzhou 350004, China

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.

Key words: Melatonin; morphine dependence; hypothalamic arcuate nucleus; β-endorphin; proopiomelanocortin

Received: 2008-08-22　　Accepted: 2009-04-15

Corresponding author: 俞昌喜　　E-mail: changxiyu@mail.fjmu.edu.cn

Citing This Article：

WEI Yi-Ming, XU Ying, YU Chang-Xi, HAN Jing. Melatonin enhances the expression of β-endorphin in hypothalamic arcuate nucleus of morphine-dependent mice. Acta Physiol Sin 2009; 61 (3): 255-262 (in Chinese with English abstract).