Structural and biochemical alterations in the dorsal horn of the spinal cord caused by peripheral nerve lesions

Substance P and Met-enkephalin were detected by radioimmunoassay and immunocytochemistry in the rat lumbar spinal cord. The sciatic nerve was lesioned by resecting a piece and the proximal stump was either ligated, for limiting neurite outgrowth, or intraperitoneally sutured, allowing the formation of a large neuroma. Ten days post lesioning both peptide levels dropped approximately 50% and the punctate immunoreactivity decreased in the dorsal horn. Lesioning both sciatic nerves did not accelerate nor increase the extent of peptide loss compared to monolateral lesions. Immunocytochemistry showed that after bilateral lesioning also the punctate immunoreactivity in the dorsal horn decreased less drastically. However, FRAP staining of the dorsal horn decreased according to the lesion paradigms, mono- and bilaterally with the same intensity. Therefore nerve lesions trigger the process, but the peptidergic loss seems intraspinally regulated. In addition, both kinds of abnormal neurite outgrowth similarly altered peptide levels and distribution in the spinal cord. Our data suggest that pain states related to peripheral nerve lesions may be due to opiate peptide loss rather than to neuroma.