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 substance P (SP) in spinal cord of rats.

METHODS

Using immunohisto-chemistry and measurement of pain threshold.

RESULTS

The c-fos expression evoked by intrathecal injection (it) SP 10 micrograms and sc 5% formaldehyde (For) 150 microL 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 behavioral method in the For group was increased. The c-fos expression induced by it 5-HT 20 micrograms 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 were 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.