EFFECT OF 5-HT ON PAIN MODULATION OF SUBSTANCE-P IN SPINAL-CORD OF RATS

AIM: To study the effect of serotonin (5-HT) on pain modulation of sub stance P (SP) in spinal cord of rats. METHODS: Using immunohisto-chemi stry and measurement of pain threshold. RESULTS: The c-fos expression evoked by intrathecal injection (it) SP 10 mu g and sc 5 % formaldehyd e (For) 150 mu L in the hindpaw was densely distributed in the laminae I, II, V, and VI of spinal dorsal horn. The pain threshold in the SP group was decreased while the pain intensity rating measured by behavi oral method in the For group was increased, The c-fos expression induc ed by it 5-HT 20 mu g was mostly distributed in the spinal dorsal horn in laminae III - IV and the pain threshold was increased. SP and For induced c-fos expressions in the spinal cord and the pain responses we re reduced by 5-HT and increased by 5-HT depletor fenclonine 300 mg . kg(-1). CONCLUSION: SP mainly played an algogenesia in the spinal cord . 5-HT inhibited the c-fos expression in the spinal cord evoked by SP and participated in pain modulation of SP.