Sensory and Autonomic Innervation of the Cervical Intervertebral Disc The Pathomechanics of Chronic Discogenic Neck Pain

KEY POINTS FROM DAN MURPHY 1) This study used rats. The authors note that prior studies have shown that ratsand humans have similar spinal innervation patterns. However, they also note thatthese findings should be reaffirmed on human specimens. 2) This study is an immunohistological analysis of the cervical intervertebral disc(IVD) to investigate its sensory and autonomic innervation. The authors used theneuro-tracer Fluoro-gold (FG) to stain ten C5 – C6 IVDs. They stained for thefollowing neurons: * Dorsal root ganglions (DRG) from level C1 – C8 [sensory {afferents} cellbodies; this would include pain afferents] * Stellate ganglion (SG) [inferior cervical sympathetic efferent ganglion] * Nodose ganglion (NG) [Vagus nerve parasympathetic sensory ganglion to thenucleus tractus solitarius]. 3) Several studies have reported that sympathetic nerves participate in chronicpain; sympathectomy procedures can effectively treat chronic pain. The DRGs, SG, and NG neurons were immune-stained for: * Calcitonin gene-related peptide (CGRP); found in inflammatory pain neurons. * Isolectin B4 (IB4); found in neuropathic (nerve injury) neurons. 4) Findings for the innervation of the C5-C6 IVD: * The neurons innervating the C5 – C6 IVD were derived from the C2 – C8 DRGs,but not from the C1 DRG. * 3% of the neurons were for neuropathic (nerve injury) pain: Isolectin B4 (IB4); [therefore pain afferents] * 21% of the neurons were for inflammatory pain: Calcitonin gene-related peptide (CGRP); [therefore pain afferents]