CHANGES OF SPINAL SUBSTANCE-P, CALCITONIN-GENE-RELATED PEPTIDE, SOMATOSTATIN, MET-ENKEPHALIN AND NEUROTENSIN IN RATS IN RESPONSE TO FORMALIN-INDUCED PAIN

Changes of substance P (SP)-, calcitonin gene-related peptide (CGRP)-, somatostatin (SS)-, Met-enltephalin (Met-Enk)- and neurotensin (NT)- immunoreactive materials on two sides of the lumbar dorsal horn were i nspected microscopically and quantified with a computer-assisted image processing system in rats with intact or totally transected spinal co rd 2 h after injection of 0.2 ml of 0.5% formalin into the right hindp aw subcutaneously. The results showed that the SP-like immunoreactivit y (SP-LI), CGRP-LI, SS-LI, Met-Enk-LI, and NT-LI were significantly hi gher in fibers and terminals in superficial laminae of the dorsal horn ipsilateral to the formalin injection in both of the experimental gro ups. It is supposed that the increased contents of these peptides refl ect an increased biosynthesis, transport, and release of these peptide s in primary afferents and spinal intrinsic neurons in response to the long-lasting inflow of noxious messages, and that these changes seem to be produced even in the condition when the supraspinal effects have been excluded.