• Katsumasa Tanimoto, Tsuneo Takebayashi, Takeshi Kobayashi, Noritsugu Tohse, and Toshihiko Yamashita.
• Department of Orthopaedic Surgery, Sapporo Medical University School of Medicine, South 1, West 16, Chuo-ku, Sapporo 060-8543, Japan. tanimoto@sapmed.ac.jp
• Clin. Orthop. Relat. Res. 2011 Sep 1;469(9):2568-76.

BackgroundPostganglionic 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 unclearQuestions/PurposesWe 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.MethodsThe 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.ResultsThe 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.ConclusionsOur observations suggest NE plays an important role in generating lumbar radicular pain mainly via α(2)-adrenoceptors.Clinical RelevanceAn α(2)-antagonist may be an appropriate agent for trials to treat lumbar radicular pain.

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