ABSTRACT
OBJECTIVE Trigeminal pain is mostly uni-lateral orofacial,but pain sensitization often spreads to contralateral orofacial or distal body regions.Widespread trigeminal pain has more severe intensity,longer dura-tion,and wider distribution,accompanied by more serious comorbid emotional syndrome.Unfortunately,the first-line analgesics for neuropathic pain has limited effect on widespread pain along with unavoidable side effects.In-depth understanding of the pathogenesis of wide-spread trigeminal pain is urgently needed.METHODS Trigeminal pain was induced by partial transection of the infraorbital nerve(p-IONX)and evaluated by measur-ing nociceptive thresholds to mechanical or heat stimula-tion.Neuronal activity was evaluated by single-unit and patch clamp recordings.HMGB1 expression was mea-sured by immunohistochemistry.Antagonism of HMGB1 was achieved by injecting anti-HMGB1 monoclonal anti-body(mAb)intracerebrally or intraperitoneally.RESULTS P-IONX model induced not only orofacial algesia but also somatic algesia in hind paw.Spontaneous firing frequency of glutamatergic neurons in the ventral posteromedial tha-lamic nucleus(VPMGlu)as well as the amplitude and fre-quency of sEPSCs significantly increased after p-IONX.Moreover,calcium signal recording showed that VPMGlu became to be activated by the noxious mechanical stimu-lation given on the hind paw,suggesting that VPMGlu recruited somatic afferents after p-IONX.We further explored the upstream brain regions of VPMGlu by virus retrograde tracing.We found the afferents from the grac-ile nucleus/cuneate nucleus(Gr/Cu),which are involved in the conduction of somatic sensation,markedly increased.And chemogenetical inhibiting Gr/Cu-VPM circuit alleviated the widespread neuropathic pain.In addition,the expression of HMGB1 in the VPM was sig-nificantly increased after p-IONX.Local administration of anti-HMGB1 mAb in the VPM relieved widespread neuro-pathic pain in mice receiving p-IONX.CONCLUSION These results demonstrate that the remodeling of affer-ent neurons in VPM underlie the spreading of wide-spread trigeminal neuropathic pain.Highly expressed HMGB1 in VPM plays an important role in these patho-logical changes after nerve injury and systemic adminis-tration of anti-HMGB1 mAb concurrently relieves wide-spread pain.