Evidence for thoracolumbar spinal cord processing of inflammatory, but not acute colonic pain.

The lower bowel is innervated by visceral afferents projecting to the lumbosacral and thoracolumbar spinal segments. The present study tested the hypothesis that sensory processing from the normal colon occurs in the lumbosacral spinal cord with little or no activity in the thoracolumbar segments. Following colonic inflammation, viscerosensory processing in the thoracolumbar spinal cord is recruited, contributing to visceral hyperalgesia. A baseline visceromotor reflex to colorectal distention recorded in intact rats was eliminated following bilateral L6-S3 dorsal rhizotomies. The visceromotor reflex recovered to 29% of baseline following colonic inflammation. These results suggest that visceral hyperalgesia and referred pain in patients with lower bowel disorders partly result from novel viscerosensory processing in the thoracolumbar spinal cord.