青藤碱抑制丘脑腹后外侧核神经元兴奋性缓解小鼠慢性炎性痛

Sinomenine alleviates Chronic inflammatory pain Via inhibiting neuronal excitability of the Ventral Posterolateral Thalamus in mice

关键词:  慢性炎性痛  青藤碱  丘脑腹后外侧核  神经元兴奋性

Key words:  Chronic inflammatory pain  Sinomenine  Ventral posterolateral thalamic nucleus  Neuronal excitability

摘要:

目的 探究青藤碱（Sinomenine，Sino）对慢性炎性痛小鼠的痛行为学影响及中枢机制。方法 注射完全弗氏佐剂（Complete Freund’s adjuvant，CFA）以构建慢性炎性痛模型。将小鼠随机分为对照（Control）+生理盐水（Normal Saline , NS）组，CFA + NS组，Control + Sino组，CFA + Sino组。机械缩足阈值和热缩足潜伏期评估小鼠慢性炎性痛，免疫荧光化学实验标记小鼠VPL脑区小清蛋白（Parvalbumin, PV）神经元以及神经元活性标志物c-Fos。离体电生理记录VPL内神经元兴奋性变化情况。脑立体微量注射在体水平观察Sino对小鼠慢性炎性痛行为学的影响。结果 慢性炎性痛状态下VPL脑区c-Fos标记神经元数目增加，VPL内神经元兴奋性显著增加，具体表现为：静息膜电位向去极化方向移动，动作电位阈值向超极化方向移动，静息膜电位和动作电位阈值差值减小，动作电位振幅显著增加，去极化电流刺激诱发的动作电位发放频率增高。CFA小鼠腹腔注射青藤碱可明显改善机械痛敏和热痛敏，且VPL脑区c-Fos标记神经元数量显著减少。离体灌流青藤碱可降低VPL内神经元兴奋性，表现为呈剂量依赖性抑制VPL内神经元动作电位发放，半数有效抑制浓度为1715 μmol·L-1。VPL内局部微量注射青藤碱4 mmol·L-1可有效缓解CFA小鼠机械痛敏和热痛敏。结论 青藤碱通过抑制丘脑腹后外侧核神经元的兴奋性，从而缓解CFA诱导的慢性炎性痛。

Abstract:

To investigate the analgesic effect of sinomenine (Sino) on chronic inflammatory pain in mice and its underlying central mechanisms. METHODS A chronic inflammatory pain model was established by intraplantar injection of Complete Freund's adjuvant (CFA). mouse were randomly divided into control + Normal saline (NS) group, CFA + NS group, Control + Sino group, CFA + Sino group. Mechanical allodynia and thermal hyperalgesia were assessed by measuring the paw withdrawal threshold and paw withdrawal latency, respectively. Immunofluorescence staining was performed to label parvalbumin (PV)-positive neurons and the neuronal activity marker c-Fos within the ventral posterolateral thalamic nucleus(VPL). Whole-cell patch-clamp recordings were performed on VPL neurons to observe changes in neuronal excitability. In Vivo assessment of Sinomenine on pain behaviors in chronic inflammatory pain mice by stereotaxic microinjection. RESULT Under chronic inflammatory pain conditions, the number of c-Fos-positive neurons was markedly elevated in the VPL, Besides, the excitability of VPL neurons was significantly increased which mainly manifested as follows: more depolarized resting membrane potential (RMP), more hyperpolarized action potential (AP) threshold, decreased difference value between RMP and AP threshold, increased AP amplitude, and raised firing frequency evoked by depolarizing current injection. Intraperitoneal injection of sinomenine significantly alleviated mechanical and thermal hyperalgesia of CFA mice, and markedly reduced the number of c-Fos-positive neurons in the VPL. In vitro bath application of sinomenine significantly reduced the excitability of VPL neurons and showed a dose-dependent inhibition of AP spikes in VPL neurons, with a half-maximal inhibitory concentration (IC??) of 1715 μmol·L?1. Furthermore, local microinjection of sinomenine at 4 mmol·L?1 into the VPL could effectively alleviated mechanical and thermal hyperalgesia in CFA mice. CONCLUSION Sinomenine alleviates CFA-induced chronic inflammatory pain by suppressing neuronal excitability in the VPL. KEY WORDS: Chronic inflammatory pain; Sinomenine; Ventral posterolateral thalamic nucleus; Neuronal excitability