ABSTRACT

Nociceptor sensitization following nerve injury or inflammation leads to chronic pain. An increase in the nociceptor hyperpolarization-activated current, I_h, is observed in many models of pathological pain. Pharmacological blockade of I_h prevents the mechanical and thermal hypersensitivity that occurs during pathological pain. Alterations in the Hyperpolarization-activated Cyclic Nucleotide-gated ion channel 2 (HCN2) mediate I_h-dependent thermal and mechanical hyperalgesia. Limited knowledge exists regarding the nature of these changes during chronic inflammatory pain. Modifications in HCN2 expression and post-translational SUMOylation have been observed in the Complete Freund’s Adjuvant (CFA) model of chronic inflammatory pain. Intra-plantar injection of CFA into the rat hindpaw induces unilateral hyperalgesia that is sustained for up to 14 days following injection. The hindpaw is innervated by primary afferents in lumbar DRG, L4-6. Adjustments in HCN2 expression and SUMOylation have been well-documented for L5 DRG during the first 7 days of CFA-induced inflammation. Here, we examine bilateral L4 and L6 DRG at day 1 and day 3 post-CFA. Using L4 and L6 DRG cryosections, HCN2 expression and SUMOylation were measured with immunohistochemistry and proximity ligation assays, respectively. Our findings indicate that intra-plantar injection of CFA elicited a bilateral increase in HCN2 expression in L4 and L6 DRG at day 1, but not day 3, and enhanced HCN2 SUMOylation in ipsilateral L6 DRG at day 1 and day 3. Changes in HCN2 expression and SUMOylation were transient over this time course. Our study suggests that HCN2 is regulated by multiple mechanisms during CFA-induced inflammation.

摘要

神经损伤或发炎后伤害感受器致敏导致慢性疼痛。在许多病理性疼痛模型中均观察到伤害感受器超极化激活电流I _h的增加。I _h的药理学阻断作用可防止在病理性疼痛期间发生机械和热超敏反应。超极化激活的环核苷酸门控离子通道2（HCN2）的变化介导I _h依赖的热和机械痛觉过敏。关于慢性炎性疼痛期间这些变化的性质的知识有限。在慢性炎症性疼痛的完全弗氏佐剂（CFA）模型中已观察到HCN2表达和翻译后SUMOylation的修改。足底内注射CFA到大鼠后爪会引起单侧痛觉过敏，注射后可持续长达14天。腰DRG L4-6的主要传入神经支配后爪。在CFA诱发的炎症的前7天中，L5 DRG的HCN2表达和SUMOylation的调节已得到充分证明。在这里，我们检查了CFA后第1天和第3天的双边L4和L6 DRG。使用L4和L6 DRG冷冻切片，通过免疫组织化学和邻近结扎法检测HCN2表达和SUMOylation，分别。我们的发现表明，足底内注射CFA在第1天而不是第3天引起L4和L6 DRG中HCN2表达的双侧增加，并在第1天和第3天增强同侧L6 DRG中HCN2 SUMOylation的变化。和SUMOylation在这段时间内是短暂的。我们的研究表明，HCN2在CFA诱导的炎症过程中受多种机制调控。