Effects of Sympathetic and Somatosensory Interaction to the Lumbar Radicular Pain –behavioral and Immunohistochemical Study-

Radicular pain is one of the most common complains handled by orthopedic surgeon. As the cause of sciatica, the mechanical compression of the nerve root and the chemical reactions induced by herniated disc containing nucleus pulposus have been reported, however, the pathological mechanism is still unknown. On the other hand, neuropathic pain followed by peripheral nerve injury is considered that there are two types of pain state: sympathetically independent pain (SIP) and sympathetically maintained pain (SMP) that is attenuated by sympathetectomy or sympathetic nerve block. Recent immunohistological studies in a peripheral nerve injury model have shown that sympathetic nerve fibers sprout the neurons in dorsal root ganglion (DRG). This abnormal sympathetic-somatosensory interaction seems to lead SMP. Also the sympathetic nervous system is suggested to be concerned in the radicular pain for the clinical effectiveness of the sympathetic block on radicular pain. The purpose of this study is to elucidate the pathological mechanism of radicular pain by investigating pain-related behavior of lumbar root constriction model in the rat. Furthermore, to assess the influences of sympathetic nerve fiber to radicular pain, we performed immunohistochemical analysis using antibodies to tyrosine hydroxylase.