Immunohistochemical observations on spinal tissue innervation: A review of hypothetical mechanisms of back pain

Immunohistochemical studies support earlier reports of a rich nerve supply to the posterior longitudinal ligament, a less developed innervation of the anterior ligament and the outermost annular ring, and a total lack of innervation in deeper parts of the intervertebral disc. Whether this pattern of innervation is altered when the disc becomes severely degenerated is presently uncertain. Recent studies have also revealed neuropeptide-immunoreactive nerves in the outermost parts of the annulus and adjacent peridiscal ligaments. These nerves are probably involved in discogenic back pain, and may become sensitized when disc tissue is injured. This sensitization appears to be coupled to an alteration of neuropeptide pools in the nearby dorsal root ganglion, the important site of neuropeptide production. Direct influences on the dorsal root ganglion, mechanical and/or chemical, may also be important, and may be involved in spinal segment degeneration.