扩散性三叉神经病理性疼痛中VPM感觉传入环路重构及HMGB1的作用研究

Widespread trigeminal neuropathic pain (TNP) is notorious for being refractory to common management, which makes it urgent to investigate the underlying mechanisms and search for specific therapeutic drugs. Recently, it has been revealed that remodeling of neural circuit in the brain may take place following peripheral nerve injury. However, its relationship with the spread of neuropathic pain and how it develops are still unclear. Previously, we established the mouse model of widespread TNP by partially transecting the infraorbital nerve and found that neuroinflammation mediated by TLR4-MyD88 signaling pathway and HMGB1 in the central nervous system were involved in the spread of pain abnormality. Our pilot experiment also found that HMGB1 expression was significantly elevated in the VPM and the glutamatergic neurons were remarkably sensitized following p-IONX. Moreover, these neurons may recruit new afferents from the dorsal column nuclei which relay the body sensation, indicating the possible remodeling of VPM afferent circuit. Taking advantage of electrophysiology in vivo and in vitro, optogenetics and neuron subtype-specific tracing techniques, this study aims to study whether the remodeling of VPM afferent circuit occurs and its role in widespread TNP, and further to study the roles of HMGB1 in the remodeling and involving pathway(s). This study will reveal the cerebral mechanisms of widespread TNP for the first time and provide experimental evidence for identifying the new therapeutic target for this disease, thus is of great significance both theoretically and clinically.

扩散性三叉神经病理性疼痛（trigeminal neuropathic pain, TNP）的临床治疗非常困难，迫切需要深入研究其发生机制并开发针对性的治疗药物。外周神经损伤可诱导脑内神经环路重构，但与神经病理性疼痛扩散的关系及其发生机制都不清楚。课题组前期首次成功建立了眶下神经部分切断（p-IONX）诱导的扩散性TNP小鼠模型，并发现TLR4-MyD88和HMGB1介导的中枢神经炎症反应参与了异常疼痛的扩散。预实验还发现，p-IONX后VPM内HMGB1表达增加，谷氨酸能神经元被显著致敏，而且可能募集了新的躯体感觉传入。本研究拟采用在体和离体电生理、光遗传学和神经元特异性病毒追踪技术，研究VPM的感觉传入神经环路重构在异常疼痛扩散中的作用，并进一步研究HMGB1在其中的作用和机制。研究将首次揭示扩散性TNP的脑内机制，为发现新的药物作用靶点提供实验依据，具有重大的理论和临床意义。

三叉神经病理性疼痛（TNP），是多种原因损伤了三叉神经或其中枢传导通路导致的慢性神经痛，是最让人痛苦的疾病之一。扩散性TNP疼痛强度更强，持续时间更长，分布区域更广泛，伴随有更严重的慢性疼痛综合征。然而，扩散性TNP的临床治疗是非常棘手的问题。本研究采用小鼠眶下神经部分性切断（partial infraorbital nerve transection, p-IONX）诱导扩散性TNP，研究了VPM感觉传入神经环路重构在扩散性TNP发生中的作用及促炎因子HMGB1的贡献。结果发现，p-IONX 后VPM中谷氨酸能神经元（VPMGlu）的兴奋性增加，并能被后爪的伤害性刺激激活。追踪实验发现，VPMGlu传入神经网络在p-IONX后发生重构，其中薄束核和楔束核（Gr/Cu）神经元到VPMGlu的投射增加明显。这些传入神经到达VPMGlu可进一步投射到颗粒状岛叶皮层（AI）。用化学遗传学方法选择性抑制VPMGlu-AI神经环路可缓解扩散性神经痛。同时，p-IONX后VPM内HMGB1表达显著增加。全身拮抗HMGB1可阻断p-IONX引起的VPMGlu神经元对后爪刺激的反应，而在VPM局部拮抗HMGB1可缓解p-IONX小鼠的扩散性神经痛。以上结果表明，p-IONX后被致敏的VPMGlu传入神经发生重构，接受躯干和四肢的感觉信息传入，并进一步传入至AI，导致了痛敏的扩散，HMGB1在其中发挥了促进作用。此外，我们还发现，p-IONX后小鼠出现了早发性焦虑。内侧前额叶皮层（mPFC）中的HMBG1表达上调与焦虑发作同步。在术后早期和晚期拮抗mPFC的 HMGB1可缓解焦虑及厌恶情绪，而在mPFC局部给与外源性ds-HMGB1会提高正常小鼠的焦虑水平并诱导厌恶情绪。p-IONX后mPFC中2/3层锥体神经元的兴奋性增加，全身性拮抗HMGB1抑制了2/3层锥体神经元的过度兴奋，可同时缓解扩散性神经痛和焦虑。以上结果表明，p-IONX后mPFC中HMGB1增加了2/3层锥体神经元的兴奋性，促使了焦虑的形成和维持。综上，本研究结果表明HMGB1介导的神经炎症反应在TNP的痛敏扩散和情感障碍共病中均发挥重要作用，可能是药物治疗的潜在靶点。