TY - JOUR
T1 - Electroacupuncture-induced analgesia in a rat model of ankle sprain pain is mediated by spinal α-adrenoceptors
AU - Koo, Sung Tae
AU - Lim, Kyu Sang
AU - Chung, Kyungsoon
AU - Ju, Hyunsu
AU - Chung, Jin Mo
N1 - Funding Information:
This work was supported by NIH Grants AT001474, NS031680, and NS011255. STK was supported, in part, by the Brain Korea 21 project and an Acupuncture Research Grant (K07120) from the Korea Institute of Oriental Medicine. We express our gratitude to Ms. Denise Broker for her excellent assistance in editing the manuscript.
PY - 2008/3
Y1 - 2008/3
N2 - In a previous study, we showed that electroacupuncture (EA) applied to the SI-6 point on the contralateral forelimb produces long-lasting and powerful analgesia in pain caused by ankle sprain in a rat model. To investigate the underlying mechanism of EA analgesia, the present study tested the effects of various antagonists on known endogenous analgesic systems in this model. Ankle sprain was induced in anesthetized rats by overextending their right ankle with repeated forceful plantar flexion and inversion of the foot. When rats developed pain behaviors (a reduction in weight-bearing of the affected hind limb), EA was applied to the SI-6 point on the contralateral forelimb for 30 min under halothane anesthesia. EA significantly improved the weight-bearing capacity of the affected hind limb for 2 h, suggesting an analgesic effect. The α-adrenoceptor antagonist phentolamine (2 mg/kg, i.p. or 30 μg, i.t.) completely blocked the EA-induced analgesia, whereas naloxone (1 mg/kg, i.p.) failed to block the effect. These results suggest that EA-induced analgesia is mediated by α-adrenoceptor mechanisms. Further experiments showed that intrathecal administration of yohimbine, an α2-adrenergic antagonist, reduced the EA-induced analgesia in a dose-dependent manner, whereas terazosin, an α1-adrenergic antagonist, did not produce any effect. These data suggest that the analgesic effect of EA in ankle sprain pain is, at least in part, mediated by spinal α2-adrenoceptor mechanisms.
AB - In a previous study, we showed that electroacupuncture (EA) applied to the SI-6 point on the contralateral forelimb produces long-lasting and powerful analgesia in pain caused by ankle sprain in a rat model. To investigate the underlying mechanism of EA analgesia, the present study tested the effects of various antagonists on known endogenous analgesic systems in this model. Ankle sprain was induced in anesthetized rats by overextending their right ankle with repeated forceful plantar flexion and inversion of the foot. When rats developed pain behaviors (a reduction in weight-bearing of the affected hind limb), EA was applied to the SI-6 point on the contralateral forelimb for 30 min under halothane anesthesia. EA significantly improved the weight-bearing capacity of the affected hind limb for 2 h, suggesting an analgesic effect. The α-adrenoceptor antagonist phentolamine (2 mg/kg, i.p. or 30 μg, i.t.) completely blocked the EA-induced analgesia, whereas naloxone (1 mg/kg, i.p.) failed to block the effect. These results suggest that EA-induced analgesia is mediated by α-adrenoceptor mechanisms. Further experiments showed that intrathecal administration of yohimbine, an α2-adrenergic antagonist, reduced the EA-induced analgesia in a dose-dependent manner, whereas terazosin, an α1-adrenergic antagonist, did not produce any effect. These data suggest that the analgesic effect of EA in ankle sprain pain is, at least in part, mediated by spinal α2-adrenoceptor mechanisms.
KW - Descending inhibitory system
KW - Electroacupuncture
KW - Naloxone
KW - Noradrenergic inhibitory system
KW - Phentolamine
KW - Weight-bearing force
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U2 - 10.1016/j.pain.2007.04.034
DO - 10.1016/j.pain.2007.04.034
M3 - Article
C2 - 17537577
AN - SCOPUS:38749101662
SN - 0304-3959
VL - 135
SP - 11
EP - 19
JO - Pain
JF - Pain
IS - 1-2
ER -