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Front. Neurosci. | doi: 10.3389/fnins.2018.00902

The expressing patterns of opioid peptides, anti-opioid peptides and their receptors in the central nerve system are involved in electroacupuncture tolerance

 Juan Wan1, Zhengying Qiu2, Yi Ding1, Sha Nan1 and  Ming-Xing Ding1*
  • 1Huazhong Agricultural University, China
  • 2Lanzhou Institute of Husbandry and Pharmaceutical Sciences (CAAS), China

To investigate dynamic processes of enkephalin (ENK), cholecystokinin octapeptide (CCK-8), orphanin FQ (OFQ) and their receptors (µ opioid receptor, MOR; CCK B type receptor, CCKBR and opioid receptor-like 1 receptor, OPRL1) in the central nerve system during electroacupuncture (EA) tolerance, EA of Sixty Hz was used to stimulate goats for 6 h. Pain threshold was measured using potassium iontophoresis. The expression levels of ENK, CCK-8 and OFQ and their receptors were determined with ELISA and qPCR, respectively. The results showed that the change rates of pain threshold in EA-treated goats decreased from 89.9 ± 11.7% at 0.5 h to –11.4 ± 8.9% at 6 h. EA induced the decreased ENK and increased CCK-8 and OFQ in the most measured nuclei. EA caused decreased preproenkephalin mRNAs in ACB, CAU, PVH and PAG at 4 h, and decreased or unchanged MOR mRNAs at 2 to 6 h, but increased CCK mRNAs in CAU, PVT, PVH, PAG and SCD at 4 to 12 h. Increased prepronociceptin mRNAs and fluctuated CCKBR and OPLR1 mRNAs were found in the most measured nuclei. ENK levels were positively correlated (p < 0.01) with the change rates of pain thresholds in the measured nuclei or areas while CCK-8 levels (or OFQ levels) were negatively correlated (p < 0.01) with the pain thresholds in CAU (or CAU and ACB). These results suggest that the development and recovery of EA tolerance may be associated with the specific expression patterns of opioid peptides, anti-opioid peptides and their receptors in the analgesia-related nuclei or areas.

Keywords: electroacupuncture tolerance (EAT), enkephalin (ENK), cholecystokinin octapeptide (CCK-8), Orphanin FQ (OFQ), µ- opioid receptor (MOR), CCKB receptor, Opioid receptor-like1 receptor (OPRL1)

Received: 03 Aug 2018; Accepted: 19 Nov 2018.

Edited by:

Mitsuhiro Kawata, Kyoto Prefectural University of Medicine, Japan

Reviewed by:

Balazs Gaszner, University of Pécs, Hungary
Kenzo Kumamoto, Meiji University of Integrative Medicine, Japan  

Copyright: © 2018 Wan, Qiu, Ding, Nan and Ding. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Prof. Ming-Xing Ding, Huazhong Agricultural University, Wuhan, 430070, Hubei Province, China, dmx@mail.hzau.edu.cn