title: Electroacupuncture inhibition of hyperalgesia in an inflammatory pain rat model: involvement of distinct spinal serotonin and norepinephrine receptor subtypes.
abstract: BACKGROUND
  Although acupuncture analgesia is well documented, its mechanisms have not been thoroughly clarified. We previously showed that electroacupuncture (EA) activates supraspinal serotonin- and norepinephrine-containing neurones that project to the spinal cord. This study investigates the involvement of spinal alpha(2)-adrenoceptors (α2-ARs) and 5-hydroxytryptamine (serotonin) receptors (5-HTRs) in EA effects on an inflammatory pain rat model.
  
  
  METHODS
  Inflammatory hyperalgesia was induced by injecting complete Freund's adjuvant (CFA, 0.08 ml) into the plantar surface of one hind paw and assessed by paw withdrawal latency (PWL) to a noxious thermal stimulus. The selective α2a-AR antagonist BRL-44408, α2b-AR antagonist imiloxan hydrochloride, 5-HT2B receptor (5-HT2BR) antagonist SB204741, 5-HT3R antagonist LY278584, or 5-HT1AR antagonists NAN-190 hydrobromide, or WAY-100635 were intrathecally administered 20 min before EA or sham EA, which was given 2 h post-CFA at acupoint GB30.
  
  
  RESULTS
  EA significantly increased PWL compared with sham [7.20 (0.46) vs 5.20 (0.43) s]. Pretreatment with α2a-AR [5.35 (0.45) s] or 5-HT1AR [5.22 (0.38) s] antagonists blocked EA-produced anti-hyperalgesia; α2b-AR, 5-HT2BR, and 5-HT3R antagonist pretreatment did not. Sham plus these antagonists did not significantly change PWL compared with sham plus vehicle, indicating that the antagonists had little effect on PWL. Immunohistochemical staining demonstrated that α2a-ARs are on primary afferents and 5-HT1ARs are localized in N-methyl-d-aspartic acid (NMDA) subunit NR1-containing neurones in the spinal dorsal horn.
  
  
  CONCLUSIONS
  The data show that α2a-ARs and 5-HT1ARs are involved in the EA inhibition of inflammatory pain and that the NMDA receptors are involved in EA action.
authors.affiliation: Center for Integrative Medicine, School of Medicine,  University of Maryland, 685 W. Baltimore St. MSTF, Rm 8-22, Baltimore, MD 21201,  USA.
authors.forename: Y
authors.initials: Y
authors.lastname: Zhang
authors.forename: R X
authors.initials: RX
authors.lastname: Zhang
authors.forename: M
authors.initials: M
authors.lastname: Zhang
authors.forename: X Y
authors.initials: XY
authors.lastname: Shen
authors.forename: A
authors.initials: A
authors.lastname: Li
authors.forename: J
authors.initials: J
authors.lastname: Xin
authors.forename: K
authors.initials: K
authors.lastname: Ren
authors.forename: B M
authors.initials: BM
authors.lastname: Berman
authors.forename: M
authors.initials: M
authors.lastname: Tan
authors.forename: L
authors.initials: L
authors.lastname: Lao
mesh_terms: D058669:Adrenergic alpha-2 Receptor Antagonists / Q000494:pharmacology; D000818:Animals; D004195:Disease Models, Animal; D015671:Electroacupuncture / Q000379:methods*; D005620:Freund's Adjuvant; D006358:Hot Temperature; D006930:Hyperalgesia / Q000139:chemically induced / Q000378:metabolism / Q000517:prevention & control*; D008297:Male; D010147:Pain Measurement / Q000379:methods; D051381:Rats; D017207:Rats, Sprague-Dawley; D011930:Reaction Time / Q000187:drug effects / Q000502:physiology; D018341:Receptors, Adrenergic, alpha-2 / Q000378:metabolism / Q000502:physiology*; D044263:Receptors, Serotonin, 5-HT1 / Q000378:metabolism / Q000502:physiology*; D058829:Serotonin 5-HT1 Receptor Antagonists / Q000494:pharmacology; D013116:Spinal Cord / Q000378:metabolism
chemical_list: D058669:Adrenergic alpha-2 Receptor Antagonists; D018341:Receptors, Adrenergic, alpha-2; D044263:Receptors, Serotonin, 5-HT1; D058829:Serotonin 5-HT1 Receptor Antagonists; D005620:Freund's Adjuvant