Various animal models have been employed to understand the pathogenic mechanism of neuropathic pain. Nitric oxide (NO) is an important molecule in nociceptive transmission and is involved in neuropathic pain. However, its mechanistic actions remain unclear. The aim of this study was to better understand the involvement of neuronal and inducible isoforms of nitric oxide synthase (nNOS and iNOS) in neuropathic pain induced by chronic constriction injury (CCI) of the sciatic nerve in rats. We evaluated pain sensitivity (mechanical withdrawal thresholds using Randall and Selitto, and von Frey tests, and thermal withdrawal thresholds using Hargreaves test) prior to CCI surgery, 14 days post CCI and after intrathecal injections of selective nNOS or iNOS inhibitors. We also evaluated the distribution of NOS isozymes in the spinal cord and dorsal root ganglia (DRG) by immunohistochemistry, synthesis of iNOS and nNOS by Western blot, and NO production using fluorescent probe DAF-2 DA (DA). Our results showed higher number of nNOS and iNOS-positive neurons in the spinal cord and DRG of CCI compared to sham rats, and their reduction in CCI rats after treatment with selective inhibitors compared to non-treated groups. Western blot results also indicated reduced expression of nNOS and iNOS after treatment with selective inhibitors. Furthermore, both inhibitors reduced CCI-evoked mechanical and thermal withdrawal thresholds but only nNOS inhibitor was able to efficiently lower mechanical withdrawal thresholds using von Frey test. In addition, we observed higher NO production in the spinal cord and DRG of injured rats compared to control group. Our study innovatively shows that nNOS may strongly modulate nociceptive transmission in rats with neuropathic pain, while iNOS may partially participate in the development of nociceptive responses. Thus, drugs targeting nNOS for neuropathic pain may represent a potential therapeutic strategy.

中文翻译：

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选择性抑制nNOS和iNOS对大鼠神经性疼痛的影响。

已经采用各种动物模型来了解神经性疼痛的致病机理。一氧化氮（NO）是伤害性传递中的重要分子，并参与神经性疼痛。但是，其机械作用仍不清楚。这项研究的目的是更好地了解神经元和诱导型一氧化氮合酶（nNOS和iNOS）参与大鼠坐骨神经慢性压迫性损伤（CCI）引起的神经性疼痛。我们评估了CCI手术前，CCI后14天以及鞘内注射选择性nNOS或iNOS抑制剂后的疼痛敏感性（使用Randall和Selitto的机械性戒断阈值，以及von Frey测试，使用Hargreaves检验的热戒断阈值）。我们还通过免疫组织化学，通过蛋白质印迹法合成iNOS和nNOS以及使用荧光探针DAF-2 DA（DA）产生NO来评估脊髓和背根神经节（DRG）中NOS同工酶的分布。我们的研究结果显示，与假手术组相比，CCI的脊髓和DRG中nNOS和iNOS阳性神经元的数量更高，与非治疗组相比，用选择性抑制剂治疗后CCI大鼠的nNOS和iNOS阳性神经元数量减少。蛋白质印迹结果还表明，用选择性抑制剂处理后，nNOS和iNOS的表达降低。此外，两种抑制剂均降低了CCI诱发的机械和热撤离阈值，但只有von NOS抑制剂能够使用von Frey检验有效降低机械撤离阈值。此外，我们观察到，与对照组相比，受伤大鼠的脊髓和DRG中NO生成量更高。我们的研究创新地表明，nNOS可能强烈调节神经性疼痛大鼠的伤害性传递，而iNOS可能部分参与伤害性反应的发展。因此，针对nNOS的神经性疼痛靶向药物可能代表了一种潜在的治疗策略。