title: The effects of electroacupuncture on the extracellular signal-regulated kinase 1/2/P2X3 signal pathway in the spinal cord of rats with chronic constriction injury.
abstract: BACKGROUND
  Electroacupuncture (EA), as a traditional clinical method, is widely accepted in pain clinics, but the analgesic effect of EA has not been fully demonstrated. In the present study, we investigated the effect of EA on chronic pain and expression of P2X3 receptors in the spinal cord of rats with chronic constriction injury (CCI).
  
  
  METHODS
  The study was conducted in 2 parts. In part 1, Sprague Dawley rats were divided into 6 groups (n = 10): sham-CCI, CCI, LEA; CCI + 2 Hz EA at acupoints), HEA; CCI + 15 Hz EA at acupoints), NA-LEA (CCI + 2 Hz EA at nonacupoints), and NA-HEA (CCI + 15 Hz EA at nonacupoints). EA treatment was performed once a day on days 4 to 9 after CCI. Nociception was assessed using von Frey filaments and a hotplate apparatus. The protein and the messenger RNA (mRNA) levels of P2X3 receptors in the spinal cord were assayed by Western blotting and real-time polymerase chain reaction, respectively. In part 2, rats were divided into 5 groups (n = 10): sham-CCI, CCI, EA (CCI + EA at acupoints), NA-EA (CCI + EA at nonacupoints), and U0126 (CCI + intrathecal injection of U0126). EA treatment was conducted similar to part 1. Rats were given 5 µg U0126 in the U0126 group and 5% dimethyl sulfoxide intrathecally. Ten microliters was used as a vehicle for the other 4 groups twice a day on days 4 to 9 after CCI. Extracellular signal-regulated kinase 1/2 (ERK1/2) and ERK1/2 phosphorylation in the spinal cord were also assayed by Western blotting.
  
  
  RESULTS
  EA treatment exhibited significant antinociceptive effects and reduced the CCI-induced increase of both protein and mRNA expression of P2X3 receptors in the spinal cord. Furthermore, 2 Hz EA had a better analgesic effect than 15 Hz EA, and the protein and mRNA level of P2X3 receptor in spinal cord were lower in rats treated with 2 Hz EA at acupoints than 15 Hz EA at acupoints. Either EA at acupoints or intrathecal injection of U0126 relieved allodynia and hyperalgesia and reduced the expression of P2X3 receptors and ERK1/2 phosphorylation in the spinal cord.
  
  
  CONCLUSIONS
  The data demonstrated that EA alleviates neuropathic pain behavior, at least in part, by reducing P2X3 receptor expression in spinal cord via the ERK1/2 signaling pathway. Low frequency EA has a better analgesic effect than high frequency HEA on neuropathic pain.
authors.affiliation: Department of Anesthesiology, Tianjin Nankai Hospital, Tianjin Medical University, Sanwei Road 122, Nankai District, Tianjin, People's Republic of China 300100. yujianbo11@126.com
authors.forename: Jianbo
authors.initials: J
authors.lastname: Yu
authors.forename: Cong
authors.initials: C
authors.lastname: Zhao
authors.forename: Xiaoqin
authors.initials: X
authors.lastname: Luo
mesh_terms: D000818:Animals; D001522:Behavior, Animal / Q000502:physiology; D015153:Blotting, Western; D002070:Butadienes / Q000008:administration & dosage / Q000494:pharmacology; D003251:Constriction, Pathologic / Q000503:physiopathology*; D015671:Electroacupuncture; D004791:Enzyme Inhibitors / Q000008:administration & dosage / Q000494:pharmacology; D006358:Hot Temperature; D007278:Injections, Spinal; D008297:Male; D019950:Mitogen-Activated Protein Kinase 1 / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D048052:Mitogen-Activated Protein Kinase 3 / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D009570:Nitriles / Q000008:administration & dosage / Q000494:pharmacology; D010147:Pain Measurement / Q000379:methods; D010812:Physical Stimulation; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics; D051381:Rats; D017207:Rats, Sprague-Dawley; D060888:Real-Time Polymerase Chain Reaction; D058477:Receptors, Purinergic P2X3 / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D020426:Sciatic Neuropathy / Q000503:physiopathology; D015398:Signal Transduction / Q000502:physiology*; D013116:Spinal Cord / Q000502:physiology*
chemical_list: D002070:Butadienes; D004791:Enzyme Inhibitors; D009570:Nitriles; D012333:RNA, Messenger; D058477:Receptors, Purinergic P2X3; C113580:U 0126; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3