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Intrathecal TRPM8 blocking attenuates cold hyperalgesia via PKC and NF-κB signaling in the dorsal root ganglion of rats with neuropathic pain

Authors Cao S, Li Q, Hou J, Li Z, Cao X, Liu X, Qin B

Received 5 December 2018

Accepted for publication 27 February 2019

Published 18 April 2019 Volume 2019:12 Pages 1287—1296

DOI https://doi.org/10.2147/JPR.S197168

Checked for plagiarism Yes

Review by Single-blind

Peer reviewer comments 2

Editor who approved publication: Dr Katherine Hanlon


Song Cao,1,2* Qingmei Li,3* Jingfeng Hou,1 Zhourui Li,1 Xinya Cao,1 Xiaohong Liu,4 Bangyong Qin1

1Department of Pain Medicine, Affiliated Hospital of Zunyi Medical University, Zunyi 563000, People’s Republic of China; 2Guizhou Key Laboratory of Anesthesia and Organ Protection, Zunyi Medical University, Zunyi 563000, People’s Republic of China; 3Department of Anesthesiology, Affiliated Hospital of Zunyi Medical University, Zunyi 563000, People’s Republic of China; 4Department of Physiology, Zunyi Medical University, Zunyi 563000, People’s Republic of China
 
*These authors contributed equally to this work 


Background: TRPM8 channel plays central roles in the sensitization of nociceptive transduction and is thought as one of the potential targets for the treatment of neuropathic pain. However, the specific molecular mechanisms are still less clear.
Methods: Sciatic chronic constriction injury (CCI) rats were intrathecally administered with AMTB (TRPM8-selective antagonist) or PDTC (nuclear factor-kappa B (NF-κB) inhibitor). Cold-, thermal- and mechanical-pain thresholds were examined in CCI and sham-operated rats before and after intrathecal administration of AMTB or PDTC. Protein expression levels of TRPM8 and NF-κB p65, p-PKC/PKC value and p-PKA/PKA value in the CCI ipsilateral L4-6 dorsal root ganglions (DRGs) were analyzed. In addition, the co-expression of TRPM8 and NF-κB was evaluated in DRG.
Results: Intrathecal injection of AMTB decreased the cold hypersensitivity and aggravated the thermal-hyperalgesia in the next 2 weeks after CCI surgery. The protein expression of TRPM8 and NF-κB p65 in the ipsilateral DRGs significantly increased after CCI surgery, which can be reversed by intrathecal administration of AMTB. The PKC, PKA, p-PKC/PKC and p-PKA/PKA values showed significantly increase after CCI surgery, while intrathecal AMTB administration offset the expression increase of PKC, p-PKC and p-PKC/PKC but PKA or p-PKA/PKA in the DRG. NF-κB inhibitor not only efficiently increased the cold-, thermal-pain threshold of CCI rats, but also enhanced AMTB’s anti-cold pain effect although exerted no anti-thermal hyperalgesia effect compared with TRPM8 blockade group. Immunofluorescence results showed co-expression of TRPM8 and NF-κB in DRG neurons.
Conclusion: TRPM8 channels in DRGs participate in the pathogenesis of cold and thermal hyperalgesia (not mechanical allodynia) in rats with neuropathic pain, which could be regulated by PKC (not PKA) and NF-κB signaling. TRPM8 channel, PKC and NF-κB are potential targets for cold hyperalgesia treatment in neuropathic pain patients.

Keywords: TRPM8, neuropathic pain, dorsal root ganglia, PKC, NF-κB

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