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Evidence-Based Complementary and Alternative Medicine
Volume 2014, Article ID 659343, 12 pages
http://dx.doi.org/10.1155/2014/659343
Research Article

Comparison of Electroacupuncture and Morphine-Mediated Analgesic Patterns in a Plantar Incision-Induced Pain Model

1Graduate Institute of Clinical Medicine, College of Medicine, China Medical University, Taichung, Taiwan
2Department of Anesthesiology, School of Medicine, China Medical University, Taichung, Taiwan
3Department of Anesthesiology, China Medical University Hospital, No. 2, Yuh-Der Road, North District, Taichung 40447, Taiwan
4Graduate Institute of Acupuncture Science, College of Chinese Medicine, China Medical University, Taichung, Taiwan
5Department of Acupuncture, China Medical University Hospital, Taipei Branch, Taipei, Taiwan
6Acupuncture Research Center, China Medical University, Taichung 40447, Taiwan
7Department of Pediatrics, School of Medicine, Taipei Medical University, Taipei, Taiwan
8Guang Li Biomedicine, Inc., Xizhi, New Taipei City, Taiwan
9Pain Management and Research Center, China Medical University Hospital, Taichung 40447, Taiwan
10Department of Anesthesiology, Shin-Kong Memorial Hospital, Taipei, Taiwan
11Research Center for Chinese Medicine and Acupuncture, China Medical University, Taichung 40447, Taiwan

Received 5 May 2014; Revised 12 September 2014; Accepted 29 September 2014; Published 2 November 2014

Academic Editor: Lixing Lao

Copyright © 2014 Yen-Jing Zeng et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Electroacupuncture (EA) is a complementary therapy to improve morphine analgesia for postoperative pain, but underlying mechanism is not well-known. Herein, we investigated EA-induced analgesic effect in a plantar incision (PI) model in male Sprague-Dawley rats. PI was performed at the left hind paw. EA of 4 Hz and high intensity or sham needling was conducted at right ST36 prior to PI and repeated for another 2 days. Behavioral responses to mechanical and thermal stimuli, spinal phospho-ERK, and Fos expression were all analyzed. In additional groups, naloxone and morphine were administered to elucidate involvement of opioid receptors and for comparison with EA. EA pretreatment significantly reduced post-PI tactile allodynia for over 1 day; repeated treatments maintained analgesic effect. Intraperitoneal naloxone could reverse EA analgesia. Low-dose subcutaneous morphine (1 mg/kg) had stronger inhibitory effect on PI-induced allodynia than EA for 1 h. However, analgesic tolerance appeared after repeated morphine injections. Both EA and morphine could equally inhibit PI-induced p-ERK and Fos inductions. We conclude that though EA and morphine attenuate postincision pain through opioid receptor activations, daily EA treatments result in analgesic accumulation whereas daily morphine injections develop analgesic tolerance. Discrepant pathways and mechanisms underlying two analgesic means may account for the results.