Abstract
The aim of the present study was to observe the alternation of central orphanin FQ (OFQ, also known as nociceptin) system while electroacupuncture (EA) combined with melatonin (MEL). The experiments were carried out to investigate the changes of OFQ-like immunoreactivity and prepro-orphanin FQ (ppOFQ) mRNA in some certain nuclei of the rat brain. Using immunohistochemical technique we found that the level of OFQ-like immunoreactivity was increased significantly in some pain-modulation-related nuclei, such as ventromedial hypothalamic nucleus, raphe magnus nucleus, dorsal raphe nucleus and periaqueductal gray (PAG) after intraperitoneal (i.p.) injection of MEL 60 mg/kg, and it was further enhanced while MEL combined with EA. By using in situ hybridization, we found that ppOFQ mRNA expression was decreased in the same nuclei after the administration of MEL, and further decreased following the combination of EA and MEL. The results suggested that attenuating the release and synthesis of OFQ in the brain is one of the mechanisms that melatonin promotes acupuncture analgesia.
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