Alteration of orphanin FQ immunoreactivity and ppOFQ mRNA by combination of melatonin with electroacupuncture

The aim of the present study was to observe the alternation of central orph anin FQ (OFQ, also known as nociceptin) system while electroacupuncture (EA ) combined with melatonin (MEL). The experiments were carried out to invest igate the changes of OFQ-like immunoreactivity and prepro-orphanin FQ (ppOF Q) mRNA in some certain nuclei of the rat brain. Using immunohistochemical technique we found that the level of OFQ-like immunoreactivity was increase d significantly in some pain-modulation-related nuclei, such as ventromedia l hypothalamic nucleus, raphe magnus nucleus, dorsal raphe nucleus and peri aqueductal gray (PAG) after intraperitoneal (i.p.) injection of MEL 60 mg/k g, 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 sa me nuclei after the administration of MEL, and further decreased following the combination of EA and MEL. The results suggested that attenuating the r elease and synthesis of OFQ in the brain is one of the mechanisms that mela tonin promotes acupuncture analgesia.