title: Does norepinephrine influence pain behavior mediated by dorsal root ganglia?: a pilot study.
abstract: BACKGROUND
  Postganglionic neurons in the sympathetic nervous system reportedly are involved in lumbar radicular pain and release norepinephrine (NE), a neurotransmitter. Increased numbers of sympathetic nerve fibers have been found in dorsal root ganglion (DRG) neurons in a root constriction model. Whether this is a reasonable model for pain, however, is unclear
  
  
  OBJECTIVE
  We asked whether: (1) painful behaviors occurred in the root constriction model; (2) NE enhanced the excitability of DRG neurons in the root constriction model; and (3) which adrenoceptors were related to the mediation of the NE effects.
  
  
  METHODS
  The L5 root was sutured proximal to the DRG as the root constriction model. Behavioral tests were performed until 28 days after surgery. At 10 to 14 days after the root constriction, DRG neurons were quickly excised and digested with collagenase for electrophysiologic studies. Action potentials were recorded from single DRG neurons using a whole-cell patch clamp technique. NE (10 μmol/L) was directly applied to the DRG neurons. The adrenergic sensitivity was examined in combination with antagonists.
  
  
  RESULTS
  The rats with root constriction exhibited painful behavior. NE increased the excitability of DRG neurons in the root constriction model. The effects of NE were inhibited by pretreatment with an α-antagonist and α(2)-antagonist but not an α(1)-antagonist.
  
  
  CONCLUSIONS
  Our observations suggest NE plays an important role in generating lumbar radicular pain mainly via α(2)-adrenoceptors.
  
  
  CONCLUSIONS
  An α(2)-antagonist may be an appropriate agent for trials to treat lumbar radicular pain.
authors.affiliation: Department of Orthopaedic Surgery, Sapporo Medical University School of Medicine, South 1, West 16, Chuo-ku, Sapporo 060-8543, Japan. tanimoto@sapmed.ac.jp
authors.forename: Katsumasa
authors.initials: K
authors.lastname: Tanimoto
authors.forename: Tsuneo
authors.initials: T
authors.lastname: Takebayashi
authors.forename: Takeshi
authors.initials: T
authors.lastname: Kobayashi
authors.forename: Noritsugu
authors.initials: N
authors.lastname: Tohse
authors.forename: Toshihiko
authors.initials: T
authors.lastname: Yamashita
mesh_terms: D000200:Action Potentials; D058668:Adrenergic alpha-1 Receptor Antagonists / Q000494:pharmacology; D058669:Adrenergic alpha-2 Receptor Antagonists / Q000494:pharmacology; D000704:Analysis of Variance; D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects; D004195:Disease Models, Animal; D005727:Ganglia, Spinal / Q000187:drug effects / Q000378:metabolism* / Q000503:physiopathology / Q000601:surgery; D008297:Male; D009638:Norepinephrine / Q000378:metabolism*; D010146:Pain / Q000209:etiology / Q000378:metabolism* / Q000503:physiopathology / Q000517:prevention & control; D017288:Pain Threshold; D018408:Patch-Clamp Techniques; D010865:Pilot Projects; D051381:Rats; D017207:Rats, Sprague-Dawley; D011930:Reaction Time; D018341:Receptors, Adrenergic, alpha-2 / Q000187:drug effects / Q000378:metabolism*; D013536:Suture Techniques; D013997:Time Factors
chemical_list: D058668:Adrenergic alpha-1 Receptor Antagonists; D058669:Adrenergic alpha-2 Receptor Antagonists; D018341:Receptors, Adrenergic, alpha-2; D009638:Norepinephrine