Suppression of neuropathic pain by peripheral electrical stimulation in rats: mu-opioid receptor and NMDA receptor implicated.
Peripheral electrical stimulation (PES) has been utilized to manage chronic pain associated with nerve injury. However, the data on clinical effectiveness are conflicting and the neurophysiological mechanism is not well known. This study was designed to assess whether PES relieved neuropathic pain and its possible mechanisms. The neuropathic pain model was made with lumbar 5th (L5) and 6th (L6) spinal nerve ligations in rats. Nociceptive responses of the rats were assessed by the cold plate test (the number and duration of paw lifts that occurred in 5 min on a 5 +/- 1 degrees C cold plate). PES with a frequency of 2 Hz and at increasing strengths was given for 30 min via stainless-steel needles inserted into standard acupoints on the leg and back, respectively. Immunochemistry was used to examine the immunoreactivity of the NMDA receptor 1 (NR1) subunit in the spinal cord dorsal horn. The results are as follows: (1) PES relieved neuropathic pain and the effect was blocked by 1.0 mg/kg naloxone. (2) The effect of one session of PES lasted up to 12 h. (3) Repetitive PES showed a cumulative effect and no tolerance was observed. (4) There was a significant increase of NR1 immunoreactivity in the superficial laminae of the spinal cord of neuropathic pain rats as compared with naive rats. This increase could be reversed by repetitive 2 Hz PES. These results suggest that PES can relieve neuropathic pain, and that mu-opioid receptors and NMDA receptors are involved in the effect of PES.
Sun
Rui-Qing
RQ
Neuroscience Research Institute and Key Laboratory of Neuroscience, Ministry of Education, Peking University, Beijing 100083, PR China.
Wang
He-Chun
HC
Wan
You
Y
Jing
Zheng
Z
Luo
Fei
F
Han
Ji-Sheng
JS
Wang
Yun
Y
D000818:Animals; D004195:Disease Models, Animal; D004599:Electric Stimulation Therapy; D008026:Ligation; D008297:Male; D009270:Naloxone / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000494:pharmacology; D009437:Neuralgia / Q000473:pathology / Q000503:physiopathology* / Q000628:therapy*; D010147:Pain Measurement / Q000187:drug effects; D020671:Posterior Horn Cells / Q000378:metabolism / Q000473:pathology; D051381:Rats; D017207:Rats, Sprague-Dawley; D016194:Receptors, N-Methyl-D-Aspartate / Q000378:metabolism*; D017450:Receptors, Opioid, mu / Q000037:antagonists & inhibitors / Q000378:metabolism*
C409466:NR1 NMDA receptor; D009292:Narcotic Antagonists; D016194:Receptors, N-Methyl-D-Aspartate; D017450:Receptors, Opioid, mu; D009270:Naloxone