Peripheral nerve lesions cause simultaneous alterations of substance P and enkephalin levels in the spinal cord.

The substance P and Met-enkephalin content were measured in the rat lumbar spinal cord after monolateral section of the sciatic nerve. The proximal stump of the lesioned nerve was either ligated, limiting the formation of neuroma, or sutured intraperitoneally, allowing the formation of a very large neuroma. Both types of lesion caused a similar peptide loss. Substance P and Met-enkephalin decreased by about 50% 10 days following the lesion. Such a loss was maintained even 30 days postoperatively and was not affected by the neuroma size. Immunohistochemical stainings showed that the loss of both peptides occurred in laminae I and II of the dorsal horn. It is suggested that pain sensation developing after peripheral nerve lesion may be due to the intraspinal loss of enkephalin rather than to the neuroma formation.