Background. Visceral hypersensitivity is a common occurrence of gastrointestinal diseases such as irritable bowel syndrome (IBS), wherein early-life stress (ELS) may have a high predisposition to the development of visceral hypersensitivity in adulthood, with the specific underlying mechanism still elusive. Herein, we assessed the potential effect of small-conductance calcium-activated potassium channel subtype 2 (SK2) in the spinal dorsal horn (DH) on the pathogenesis of visceral hypersensitivity induced by maternal separation (MS) in mice. Methods. Neonatal mice were subjected to the MS paradigm, an established ELS model. In adulthood, the visceral pain threshold and the abdominal withdrawal reflex (AWR) were measured with an inflatable balloon. The elevated plus maze, open field test, sucrose preference test, and forced swim test were employed to evaluate the anxiety- and depression-like behaviors. The expression levels of SK2 in the spinal DH were determined by immunofluorescence and western blotting. The mRNA of SK2 and membrane palmitoylated protein 2 (MPP2) were determined by quantitative real-time polymerase chain reaction (qRT-PCR). Electrophysiology was applied to evaluate the neuronal firing rates and SK2 channel-mediated afterhyperpolarization current (). The interaction between MPP2 and SK2 was validated by coimmunoprecipitation. Results. In contrast to the naïve mice, ethological findings in MS mice revealed lowered visceral pain threshold, more evident anxiety- and depression-like behaviors, and downregulated expression of membrane SK2 protein and MPP2 protein. Moreover, electrophysiological results indicated increased neuronal firing rates and decreased in the spinal DH neurons. Nonetheless, intrathecal injection of the SK2 channel activator 1-ethyl-2-benzimidazolinone (1-EBIO) in MS mice could reverse the electrophysiological alterations and elevate the visceral pain threshold. In the naïve mice, administration of the SK2 channel blocker apamin abated and elevated spontaneous neuronal firing rates in the spinal DH neurons, reducing the visceral pain threshold. Finally, disruption of the MPP2 expression by small interfering RNA (siRNA) could amplify visceral hypersensitivity in naïve mice. Conclusions. ELS-induced visceral pain and visceral hypersensitivity are associated with the underfunction of SK2 channels in the spinal DH.

中文翻译：

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通过下调小鼠小电导钙激活钾通道亚型 2 (SK2) 对新生儿母体分离对内脏超敏反应的易感性

背景。内脏超敏反应是肠易激综合征（IBS）等胃肠道疾病的常见表现，其中早期生活压力（ELS）可能很容易在成年期发生内脏超敏反应，具体机制尚不清楚。在此，我们评估了脊髓背角 (DH) 中小电导钙激活钾通道亚型 2 (SK2) 对母体分离 (MS) 诱导的小鼠内脏超敏反应发病机制的潜在影响。方法. 新生小鼠接受 MS 范式，即已建立的 ELS 模型。在成年期，内脏痛阈和腹部缩回反射 (AWR) 是用充气气球测量的。采用高架十字迷宫、野外测试、蔗糖偏好测试和强迫游泳测试来评估焦虑和抑郁样行为。通过免疫荧光和蛋白质印迹测定脊柱DH中SK2的表达水平。通过定量实时聚合酶链反应 (qRT-PCR) 测定 SK2 和膜棕榈酰化蛋白 2 (MPP2) 的 mRNA。应用电生理学评估神经元放电率和 SK2 通道介导的超极化后电流 ( )。MPP2 和 SK2 之间的相互作用通过免疫共沉淀验证。结果。与幼稚小鼠相比，MS 小鼠的行为学发现显示内脏痛阈降低，焦虑和抑郁样行为更明显，膜 SK2 蛋白和 MPP2 蛋白的表达下调。此外，电生理结果表明神经元放电率增加，脊髓 DH 神经元减少。尽管如此，在 MS 小鼠中鞘内注射 SK2 通道激活剂 1-乙基-2-苯并咪唑啉酮 (1-EBIO) 可以逆转电生理改变并提高内脏痛阈。在幼稚小鼠中，SK2 通道阻滞剂 apamin 的给药减弱并提高了脊髓 DH 神经元中的自发神经元放电率，从而降低了内脏痛阈。最后，通过小干扰 RNA (siRNA) 破坏 MPP2 表达可以放大幼稚小鼠的内脏超敏反应。结论。ELS 诱导的内脏疼痛和内脏超敏反应与脊柱 DH 中 SK2 通道的功能不足有关。