Sciatic nerve transection produces death of dorsal root ganglion cells and reversible loss of substance P in spinal cord

Sciatic nerve section has been shown to reduce substance P (SP) in the dorsal horn of the spinal cord, but the mechanism which underlies the reduction is not understood. Whether SP levels subsequently recover as they do after dorsal rhizotomy has also been unknown. To test the hypothesis that transganglionic degeneration of primary afferents contributes to the reduction of SP, we have studied the changes in SP which result from section of the cat sciatic nerve and determined the extent of dorsal root ganglion (DRG) cell death. Sciatic nerve section resulted in DRG cell death, but the amount was variable and not seen in all animals. Reduction in dorsal horn and DRG SP was seen in all animals, and in the spinal cord it was followed by recovery. These sequelae resemble the changes which follow dorsal rhizotomy. After sciatic nerve section, the reduction in dorsal horn SP is small than after rhizotomy, the recovery more complete, and both the reduction and the recovery proceed more slowly. Evidence is presented that similar mechanisms may contribute to depletion of intraspinal SP after sciatic nerve section and after dorsal rhizotomy. The mechanisms contributing to recovery of spinal cord SP after sciatic nerve section may resemble known mechanisms of recovery that occur when the lesion is central.