RESUMO
Using immunohistochemistry and optical densitometry, substance P (SP) was investigated in the lumbar spinal cord of the frog Rana catesbeiana after sciatic nerve transection. In control animals, there was a high density of SP fibers in the Lissauer's tract and in the mediolateral band of the dorsal gray matter. Other SP immunoreactive fibers were observed in the dorsal part of the lateral funiculus and in the ventral horn. No SP label was found in any cell bodies. After axotomy, SP immunoreactive fibers decreased in the Lissauer's tract on the same side of the lesion. The other regions remained labeled. The changes were observed at 3 days following axonal injury and persisted at 5, 8 and 15 days. At 20 days, there was no significant difference between the axotomized side and the control one, thus indicating a recovery of the SP expression. These results indicate that the frog may be used as a model to study the effects of peripheral axotomy, contributing to elucidate the SP actions in the pain neuropath.