Nociceptin (also named Orphanin FQ)

plays a very important role in spinal pain modulation. The present study was designed to explore the effect of nociceptin o n neuropathic pain in rats with chronic constrictive injury (CCI). Paw withdrawl latency (PWL) was measured by the stimulation of radiant heat on the foot pad o f rats. It was observed that 3 days after CCI

the PWL of the operated lateral w as significantly shorter than that of the contralateral

indicating the existenc e of hyperalgesia. The hyperalgesia remained for no less than 30 days. It was sh owed that significant decrease of the number of OFQ LI neurons in the dorsal ho rn of spinal cord (L 4～6 ) 4 or 7 days after CCI. The changes of expression of prepronociceptin mRNA in the spinal dorsal horn after t he thermal hyperalgesia were also investigated. The integral optical density (I OD) and mean optical den sity (OD) of the stained spinal cord sections were measured using the image proc essing following in situ hybridizationon (DIG oligonucleotide tailing test). It was showed that the values of IOD and OD in the spinal dorsal horn in constri ction injury treatment groups were increased significantly (from day 7 after CCI to day 14). The above results suggested that the OFQ in the spinal dorsal horn may be involved in neurophathic pain.