title: Innervation of the lumbar intervertebral disc by nerve growth factor-dependent neurons related to inflammatory pain.
abstract: METHODS
  We used anatomic tracers and immunoreactivity in rats to define dorsal root ganglion neuron populations innervating the lumbar discs in physiologic and inflammatory states.
  
  
  OBJECTIVE
  To investigate the percentages of calcitonin gene-related peptide-immunoreactive (CGRP-ir) and isolectin B4 (IB4)-binding neurons innervating lumbar discs.
  
  
  BACKGROUND
  Small neurons are classified into two types. One contains CGRP and expresses the nerve growth factor receptor. The other binds IB4 and expresses the glial cell line-derived neurotrophic factor receptor.
  
  
  METHODS
  A neurotracer, Fluoro-Gold, was applied to the L5-L6 disc in rats. Five days later, 50-microL saline (control group: n = 8) or Complete Freund's adjuvant (inflammatory group: n = 8) was applied to the disc. Seven days after the second operation, T13-L5 dorsal root ganglions were processed for double staining of CGRP and IB4.
  
  
  RESULTS
  Of the Fluoro-Gold-labeled neurons, 50.1 +/- 4.6% (mean +/- SEM) were positive for CGRP and 0.7 +/- 0.6% positive for IB4 in the control group, while 65.6 +/- 4.7% were positive for CGRP and 1.0 +/- 1.0% positive for IB4 in the inflammatory group. The percentage of CGRP-ir neurons was significantly higher than that of IB4-binding neurons in both groups (P < 0.001, each). The percentage of CGRP-ir neurons in the inflammatory group was significantly higher than in the control group (P < 0.05).
  
  
  CONCLUSIONS
  We found that most small neurons innervating the disc were CGRP-ir. Furthermore, disc inflammation caused an increase in CGRP-ir neurons but not IB4-binding neurons, suggesting that CGRP-ir, nerve growth factor-dependent neurons are more responsible for discogenic pain.
authors.affiliation: Department of Orthopedic Surgery, Graduate School of Medicine, Chiba University, Chiba, Japan. yasuaoki@h6.dion.ne.jp
authors.forename: Yasuchika
authors.initials: Y
authors.lastname: Aoki
authors.forename: Seiji
authors.initials: S
authors.lastname: Ohtori
authors.forename: Kazuhisa
authors.initials: K
authors.lastname: Takahashi
authors.forename: Hidetoshi
authors.initials: H
authors.lastname: Ino
authors.forename: Yuzuru
authors.initials: Y
authors.lastname: Takahashi
authors.forename: Tanemichi
authors.initials: T
authors.lastname: Chiba
authors.forename: Hideshige
authors.initials: H
authors.lastname: Moriya
mesh_terms: D000818:Animals; D001370:Axonal Transport; D015740:Calcitonin Gene-Related Peptide / Q000032:analysis*; D048429:Cell Size; D004396:Coloring Agents; D015299:Discitis / Q000503:physiopathology*; D005456:Fluorescent Dyes; D005727:Ganglia, Spinal / Q000166:cytology*; D051100:Glial Cell Line-Derived Neurotrophic Factor; D006023:Glycoproteins / Q000032:analysis*; D007403:Intervertebral Disc / Q000294:innervation*; D037102:Lectins / Q000032:analysis*; D008159:Lumbar Vertebrae; D008297:Male; D009414:Nerve Growth Factors / Q000502:physiology*; D009437:Neuralgia / Q000503:physiopathology*; D009475:Neurons, Afferent / Q000737:chemistry / Q000145:classification / Q000648:ultrastructure*; D037121:Plant Lectins / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D017475:Receptors, Nerve Growth Factor / Q000502:physiology*; D012585:Sciatica / Q000503:physiopathology; D013266:Stilbamidines; D053675:Versicans
chemical_list: C049774:2-hydroxy-4,4'-diamidinostilbene, methanesulfonate salt; D004396:Coloring Agents; D005456:Fluorescent Dyes; C495041:Gdnf protein, rat; D051100:Glial Cell Line-Derived Neurotrophic Factor; D006023:Glycoproteins; C045475:Griffonia simplicifolia lectins; D037102:Lectins; D009414:Nerve Growth Factors; D037121:Plant Lectins; D017475:Receptors, Nerve Growth Factor; D013266:Stilbamidines; C508324:Vcan protein, rat; D053675:Versicans; D015740:Calcitonin Gene-Related Peptide