SPECIFIC CONTRIBUTION OF LUMBAR SPINAL MECHANISMS TO PERSISTENT NOCICEPTIVE RESPONSES IN THE FORMALIN TEST

To determine whether a lumbar spinal mechanism mediates the late phase of the nociceptive response in the formalin test, we compared the eff ects of intrathecal (i.t.) lidocaine given pre- or post-formalin at th e lumbar or thoracic level. Pre- but not post-formalin administration of lidocaine to the lumbar level significantly attenuated late. phase nociceptive responses. In contrast, neither pre- nor post-formalin adm inistration of lidocaine to the mid-thoracic level altered nociceptive responses. In rats chronically spinalized at the mid-thoracic level, nociceptive responses to formalin were observed which were blocked by i.t. pre-treatment with lidocaine at the lumbar level. These results s uggest that a specific lumbar spinal mechanism is involved in the init iation of persistent nociception in the formalin test.