PKCγ in Vc and C1/C2 is Involved in Trigeminal Neuropathic Pain

The aim of the present study was to clarify the involvement of protein kinase C gamma (PKC gamma) in the facial neuropathic pain following infraorbital nerve injury. We analyzed the change in PKC gamma expression in the trigeminal spinal subnucleus caudalis (Vc) and upper cervical spinal cord (C1/C2) following chronic constriction injury of the infraorbital nerve (ION-CCI). We also studied ION-CCI-mediated mechanical nocifensive behavior in rats. The mechanical head-withdrawal threshold significantly decreased 1 to 14 days after ION-CCI compared with that before ION-CCI and in sham rats. The expression of PKC gamma was significantly larger in the ipsilateral Vc compared with the contralateral side in ION-CCI rats 3, 7, and 14 days after ION-CCI. Intrathecal (i.t.) administration of the PKC gamma inhibitor chelerythrine prevented an increase in the PKC gamma expression in the ipsilateral Vc. Moreover, i.t. administration of chelerythrine annulled ION-CCI-mediated reduction in the head-withdrawal threshold. Taken together, these findings suggest that PKC gamma expression in the Vc played an important role in the mechanism of orofacial static mechanical allodynia following trigeminal nerve injury.