Expression of ORL1 mRNA in some brain nuclei in neuropathic pain rats

The present study was designed to investigate changes of opioid receptor like 1 receptor (ORL(1), NOP) mRNA expression in some pain-related brain nuclei of neuropathic pain rats using in situ hybridization technique. Nociceptin/orphanin FQ (N/OFQ), the endogenous ligand of ORL(1), plays an important role in neuropathic pain through its receptor. There are ORL(1) mRNA expression in the nucleus of raphe magnus (NRM), ventrolateral periaqueductal gray (vlPAG) and dorsal raphe nucleus (DRN) of rat mesencephalon. In the sciatic nerve chronic constriction injury (CCI)-induced neuropathic pain model, a significant increase of ORL(1) mRNA expression was observed in these three regions on the 7th day after operation, and the changes lasted for 2 weeks. The result indicated that ORL(1) synthesis was increased in NRM, vlPAG and DRN of neuropathic pain rats, suggesting that ORL(1) was involved in nociceptive transmission of neuropathic pain.