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Effect of melatonin on the content of #beta#--endorphin in the hypothalamic arcuate nucleus and periaqueductal grey of midbrain in morphine withdrawal mice

Wei Yiming, Xu Ying, Yu Changxi

Department of Pharmacology,Fujian Medical University.Fuzhou 350004,Fujian

Abstract

The present study was undertaken to investigate the effect of melatonin on the level of #beta#-endorphin (#beta#-EP) in the arcuate nucleus hypothalamus (Arc) and periaqueductal grey (PAG) of midbrain in mice with morphine abstinence. Male Kunming strain mice were injected subcutaneously (s.c.) with an increasing dose of morphine continuously for 8 d to establish dependence model. Withdrawal response was induced by naloxon (3 mg/kg, s.c.). The potency of withdrawal response was evaluated according to the jumping times and body weight loss. Ninty minutes prior to the precipitation of naloxone, 80 mg/kg of melatonin (MEL) was injected intraperitoneally (i.p.) to observe its antagonistic effect on the withdrawal response of morphine-dependent mice. After behavioral observation, radioimmunoassay was used to determine the content of #beta#-EP in the PAG of midbrain, and immunohistochemical assay was used to observe the intensity of #beta#-EP-like immunoreactivity in the Arc in mice. It was shown that melatonin (i.p., 80 mg/kg) inhibited the naloxone-precipitated withdrawal responses in mice significantly (P<0.05). In the meantime, melatonin increased the content of #beta#-EP in the PAG of midbrain significantly (P<0.05) and attenuated the intensity of #beta#-EP-like immunoreactivity in the Arc in mice (P<0.05). The results suggest that melatonin increases the level of #beta#-EP in the PAG of midbrain, decrease the level of #beta#-EP in the Arc in mice with morphine abstinence.

Key words: Melatonin;morphine dependence;withdrawal response;Hypothalamic arcuate nucleus;periaqueductal grey of midbrain;#beta#-endorphin

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Citing This Article：

Wei Yiming, Xu Ying, Yu Changxi. Effect of melatonin on the content of #beta#--endorphin in the hypothalamic arcuate nucleus and periaqueductal grey of midbrain in morphine withdrawal mice. Acta Physiol Sin 2007; 59 (6): 765-769 (in Chinese with English abstract).