Dually innervating nociceptive networks in the rat lumbar posterior longitudinal ligaments.
METHODS
The present study investigated the distribution of sensory and autonomic nerves to the posterior longitudinal ligament of the rat lumbar vertebra.


OBJECTIVE
The results were analyzed to provide a new insight into the pathogenesis of low back pain.


BACKGROUND
Previous studies that have descriptively reported on posterior longitudinal ligament innervation have attributed important roles to the sinuvertebral nerve as an output of nociceptive sensation. Meanwhile, development of immunohistochemistry has made it possible to identify numerous neurotransmitters, and thus various suggested pathophysiologic roles of the nerve fibers in the posterior longitudinal ligament. However, such microscopic identification of the nerve fibers has not been able to reveal comprehensive distributions of the various fibers, which are presumed to be derived from the sinuvertebral nerve.


METHODS
Rat posterior longitudinal ligaments of whole thickness was immunohistochemically stained for calcitonin gene-related peptide and tyrosine hydroxylase, which have been considered markers of nociceptive and noradrenergic fibers respectively. Light-microscopic and electron-microscopic observation was reinforced with another experimental study in which resection of the dorsal root ganglia induced characteristic denervation patterns to the rat posterior longitudinal ligament.


RESULTS
The present study revealed that the lumbar. PLL was dually innervated by two distinctive systems of nociceptive fibers. One of the systems was polysegmentally innervated and closely associated with autonomic innervation, whereas the other was unisegmentally innervated and not associated with autonomic fibers.


CONCLUSIONS
Pathogenesis of low back pain can be better understood if the presence of the two distinctive nerve systems innervating the posterior longitudinal ligament is taken into account.
Imai
S
S
Department of Orthopaedic Surgery. Shiga University of Medical Science, Otsu-shi, Japan.
Hukuda
S
S
Maeda
T
T
D000818:Animals; D015740:Calcitonin Gene-Related Peptide / Q000032:analysis; D007124:Immunoenzyme Techniques; D017846:Longitudinal Ligaments / Q000294:innervation*; D017116:Low Back Pain / Q000209:etiology; D008159:Lumbar Vertebrae / Q000033:anatomy & histology; D008297:Male; D008854:Microscopy, Electron; D009412:Nerve Fibers / Q000737:chemistry / Q000648:ultrastructure; D009619:Nociceptors / Q000737:chemistry / Q000648:ultrastructure*; D051381:Rats; D011917:Rats, Inbred Lew; D017208:Rats, Wistar; D013127:Spinal Nerves / Q000033:anatomy & histology; D014446:Tyrosine 3-Monooxygenase / Q000032:analysis
D014446:Tyrosine 3-Monooxygenase; D015740:Calcitonin Gene-Related Peptide