The existence of referred pain and ectopic paresthesia caused by tooth pulp inflammation may make definitive diagnosis difficult and cause misdiagnosis or mistreatment; thus, elucidation of that molecular mechanism is urgent. In the present study, we investigated the mechanisms underlying ectopic pain, especially tongue hyperalgesia, after tooth pulp inflammation. A rat model with mandibular first molar tooth pulp exposure was employed. Tooth pulp exposure-induced heat and mechanical-evoked tongue hypersensitivity was measured, and immunohistochemical staining for Iba1, a marker of active macrophages, IL-1β, IL-1 type I receptor (IL-1RΙ), and toll-like receptor 4 in the trigeminal ganglion was performed. In addition, we investigated the effects of injections of liposomal clodronate Clophosome-A (LCCA), a selective macrophage depletion agent, lipopolysaccharide from Rhodobacter sphaeroides (LPS-RS, a toll-like receptor 4 antagonist), IL-1β, or heat shock protein 70 (Hsp70, a selective agonist of toll-like receptor 4), to examine changes in tongue hypersensitivity and in the regulation of IL-1RΙ, toll-like receptor 4, and transient receptor potential vanilloid 1 (TRPV1) biosynthesis. At day 1 after tooth pulp exposure, obvious tooth pulp inflammation was observed. Tooth pulp exposure-induced heat and mechanical tongue hypersensitivity was observed from days 1 to 3 after tooth pulp exposure. The production of IL-1β in activated macrophages and toll-like receptor 4 and IL-1RΙ expression were significantly increased in trigeminal ganglion neurons innervating the tongue following tooth pulp exposure. Intra-trigeminal ganglion injection of LCCA significantly suppressed tongue hypersensitivity; however, toll-like receptor 4 and IL-1RΙ expression in trigeminal ganglion neurons innervating the tongue was not significantly altered. Intra-trigeminal ganglion injection of LPS-RS significantly suppressed tongue hypersensitivity and reduced IL-1RΙ expression in the trigeminal ganglion neurons innervating the tongue following tooth pulp exposure. Intra-trigeminal ganglion injection of recombinant Hsp70 significantly promoted tongue hypersensitivity and increased IL-1RI expression in trigeminal ganglion neurons innervating the tongue in naive rats. Furthermore, intra-trigeminal ganglion injection of recombinant IL-1β led to tongue hypersensitivity and enhanced TRPV1 expression in trigeminal ganglion neurons innervating the tongue in naive rats. The present findings suggest that the neuron-macrophage interaction mediated by toll-like receptor 4 and IL-1RI activation in trigeminal ganglion neurons affects the pathogenesis of abnormal tongue pain following tooth pulp inflammation via IL-1RI and TRPV1 signaling in the trigeminal ganglion. Further research may contribute to the establishment of new therapeutic and diagnostic methods.

中文翻译：

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巨噬细胞介导的 Toll 样受体 4–interleukin-1R 信号在与牙髓炎症相关的异位舌痛中的作用

牙髓炎症引起的牵涉痛和异位感觉异常的存在，可能使明确诊断变得困难，造成误诊或误治；因此，阐明该分子机制迫在眉睫。在本研究中，我们研究了牙髓炎症后异位痛的潜在机制，尤其是舌痛觉过敏。采用具有下颌第一磨牙牙髓暴露的大鼠模型。测量牙髓暴露诱导的热和机械诱发的舌头过敏反应，并对 Iba1、IL-1β、IL-1 I 型受体 (IL-1R1) 和 Toll 样受体 4 的免疫组织化学染色三叉神经节被执行。此外，我们研究了注射脂质体氯膦酸盐 Clophosome-A (LCCA) 的效果，这是一种选择性巨噬细胞消耗剂，来自球状红杆菌（LPS-RS，toll​​ 样受体 4 拮抗剂）、IL-1β 或热休克蛋白 70（Hsp70，toll​​ 样受体 4 的选择性激动剂）的脂多糖，以检查舌头过敏和IL-1R1、toll 样受体 4 和瞬时受体电位香草素 1 (TRPV1) 生物合成的调节。在牙髓暴露后第1天，观察到明显的牙髓炎症。在牙髓暴露后的第 1 至 3 天观察到牙髓暴露引起的热和机械舌过敏。激活的巨噬细胞中 IL-1β 的产生和 Toll 样受体 4 和 IL-1R1 表达在牙髓暴露后支配舌头的三叉神经节神经元中显着增加。三叉神经节内注射LCCA显着抑制舌过敏；然而，支配舌头的三叉神经节神经元中的toll样受体4和IL-1R1表达没有显着改变。LPS-RS 的三叉神经节内注射显着抑制了舌超敏反应并降低了在牙髓暴露后支配舌头的三叉神经节神经元中的 IL-1R1 表达。三叉神经节内注射重组 Hsp70 显着促进舌头过敏，并增加了支配幼稚大鼠舌头的三叉神经节神经元中 IL-1RI 的表达。此外，三叉神经节内注射重组 IL-1β 导致舌头过敏，并增强了支配幼稚大鼠舌头的三叉神经节神经元中 TRPV1 的表达。目前的研究结果表明，由三叉神经节神经元中的 toll 样受体 4 和 IL-1RI 激活介导的神经元-巨噬细胞相互作用通过三叉神经节中的 IL-1RI 和 TRPV1 信号传导影响牙髓炎症后异常舌痛的发病机制。进一步的研究可能有助于建立新的治疗和诊断方法。