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.