title: Gabapentin activates spinal noradrenergic activity in rats and humans and reduces hypersensitivity after surgery.
abstract: BACKGROUND
  Gabapentin has been reported to inhibit various acute and chronic pain conditions in animals and humans. Although the efficacy of gabapentin depends on the alpha2delta subunit of voltage-gated calcium channels, its analgesic mechanisms in vivo are still unknown. Here, the authors tested the role of spinal noradrenergic inhibition in gabapentin's analgesia for postoperative pain.
  
  
  METHODS
  Gabapentin was administered orally and intracerebroventricularly to rats on the day after paw incision, and withdrawal threshold to paw pressure was measured. The authors also measured cerebrospinal fluid concentration of norepinephrine and postoperative morphine use after surgery in patients who received oral placebo or gabapentin.
  
  
  RESULTS
  Both oral and intracerebroventricular gabapentin attenuated postoperative hypersensitivity in rats in a dose-dependent manner. This effect of gabapentin was blocked by intrathecal administration of the alpha2-adrenergic receptor antagonist idazoxan and the G protein-coupled inwardly rectifying potassium channel antagonist tertiapin-Q, but not by atropine. In humans, preoperative gabapentin, 1,200 mg, significantly increased norepinephrine concentration in cerebrospinal fluid and decreased morphine requirements.
  
  
  CONCLUSIONS
  These data suggest that gabapentin activates the descending noradrenergic system and induces spinal norepinephrine release, which produces analgesia via spinal alpha2-adrenoceptor stimulation, followed by activation of G protein-coupled inwardly rectifying potassium channels. The authors' clinical data suggest that gabapentin activates the descending noradrenergic system after preoperative oral administration at the time of surgery. These data support a central mechanism of oral gabapentin to reduce postoperative pain and suggest that this effect could be magnified by treatments that augment the effect of norepinephrine release.
authors.affiliation: Department of Anesthesiology and Center for Study of Pharmacologic Plasticity in the Presence of Pain, Wake Forest University School of Medicine, North Carolina 27157-1009, USA.
authors.forename: Ken-Ichiro
authors.initials: K
authors.lastname: Hayashida
authors.forename: Sophia
authors.initials: S
authors.lastname: DeGoes
authors.forename: Regina
authors.initials: R
authors.lastname: Curry
authors.forename: James C
authors.initials: JC
authors.lastname: Eisenach
mesh_terms: D000317:Adrenergic alpha-Antagonists / Q000008:administration & dosage; D000588:Amines / Q000008:administration & dosage / Q000494:pharmacology*; D000700:Analgesics / Q000008:administration & dosage / Q000494:pharmacology*; D000701:Analgesics, Opioid / Q000008:administration & dosage; D000818:Animals; D001514:Bee Venoms / Q000008:administration & dosage; D001522:Behavior, Animal / Q000187:drug effects; D003509:Cyclohexanecarboxylic Acids / Q000008:administration & dosage / Q000494:pharmacology*; D004195:Disease Models, Animal; D004305:Dose-Response Relationship, Drug; D000077206:Gabapentin; D006801:Humans; D006930:Hyperalgesia / Q000517:prevention & control*; D019329:Idazoxan / Q000008:administration & dosage; D008297:Male; D009020:Morphine / Q000008:administration & dosage; D009638:Norepinephrine / Q000134:cerebrospinal fluid*; D010149:Postoperative Pain / Q000517:prevention & control*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013116:Spinal Cord / Q000187:drug effects; D013126:Spinal Nerve Roots / Q000187:drug effects; D013997:Time Factors; D005680:gamma-Aminobutyric Acid / Q000008:administration & dosage / Q000494:pharmacology*
chemical_list: D000317:Adrenergic alpha-Antagonists; D000588:Amines; D000700:Analgesics; D000701:Analgesics, Opioid; D001514:Bee Venoms; D003509:Cyclohexanecarboxylic Acids; C029738:tertiapin; D005680:gamma-Aminobutyric Acid; D000077206:Gabapentin; D009020:Morphine; D009638:Norepinephrine; D019329:Idazoxan