INTRODUCTION: Low back pain and neck pain often become wide‐ranging and chronic, and many clinicians are challenged when treating this chronic pain. Several authors have reported that sympathetic nerves participate in chronic pain. Furthermore, various sympathectomy procedures have been reported to be effective for chronic pain. The purpose of the current study is to investigate sensory and autonomic innervation of the intervertebral disk (IVD) in rats.
METHODS: In this study, we performed surgery at the cervical IVD, because the stellate ganglion and nodose ganglion can be unambiguously identified. Ten Sprague‐Dawley rats were used. The neuro‐tracer fluoro‐gold (FG) was applied to the surfaces of the C5/6 IVD to label the innervating DRG, stellate ganglion (SG), and nodose ganglion (NG) neurons. Seven days postsurgery, DRGs from C1‐C8, SG, and NG neurons were harvested and sectioned. Harvested DRGs were immunostained for the pain marker (CGRP). The proportions of CGRP‐immunoreactive (IR) FG‐labeled DRG neurons, non‐CGRP‐IR FG‐labeled DRG neurons, FG‐labeled SG neurons, and FGlabeled NG neurons among all FG‐labeled neurons were calculated.
RESULTS: FG‐labeled neurons innervating the C5/6 IVD were distributed throughout C2‐C8 DRGs. The proportions of CGRP‐IR FG‐labeled DRG neurons, non‐CGRP‐IR FGlabeled DRG neurons, FG‐labeled SG neurons, and FG‐labeled NG neurons among all FG‐labeled neurons were 21.7%, 56.8%, 9.3%, and 12.1%, respectively.
DISCUSSION: The C5/6 IVD was innervated multisegmentally from the C2‐C8 DRG, SG, and NG neurons. Overall, 78.5% of the nerve fibers innervating the IVD were sensory nerves and 21.4% were autonomic nerves. Furthermore, 21.7% of the nerve fibers innervating the IVD were afferent sensory pain‐related nerves, 9.3% were efferent sympathetic nerves, and 12.1% were efferent parasympathetic nerves. These findings may explain the wide‐ranging and chronic diskogenic pain that occurs via somatosensory and autonomic nervous system.