1 Department of Physiology and Brain Korea 21 PLUS Project for Medical Science, Yonsei University College of Medicine, Seoul, Republic of Korea.
2 Division of Bio and Health Sciences, Mokwon University, Daejeon, Republic of Korea.
Mol Pain. 2018 Jan-Dec;14:1744806918814345. doi: 10.1177/1744806918814345. Epub 2018 Oct 31.
The insular cortex is an important region of brain involved in the processing of pain and emotion. Recent studies indicate that lesions in the insular cortex induce pain asymbolia and reverse neuropathic pain. Endogenous cannabinoids (endocannabinoids), which have been shown to attenuate pain, are simultaneously degraded by fatty acid amide hydrolase (FAAH) that halts the mechanisms of action. Selective inhibitor URB597 suppresses FAAH activity by conserving endocannabinoids, which reduces pain. The present study examined the analgesic effects of URB597 treatment in the insular cortex of an animal model of neuropathic pain. Under pentobarbital anesthesia, male Sprague-Dawley rats were subjected to nerve injury and cannula implantation. On postoperative day 14, rodents received microinjection of URB597 into the insular cortex. In order to verify the analgesic mechanisms of URB597, cannabinoid 1 receptor (CB1R) antagonist AM251, peroxisome proliferator-activated receptor alpha (PPAR alpha) antagonist GW6471, and transient receptor potential vanilloid 1 (TRPV1) antagonist Iodoresiniferatoxin (I-RTX) were microinjected 15 min prior to URB597 injection. Changes in mechanical allodynia were measured using the von-Frey test. Expressions of CB1R, N-acyl phosphatidylethanolamine phospholipase D (NAPE-PLD), and TRPV1 significantly increased in the neuropathic pain group compared to the sham-operated control group. Mechanical threshold and expression of NAPE-PLD significantly increased in groups treated with 2 nM and 4 nM URB597 compared with the vehicle-injected group. Blockages of CB1R and PPAR alpha diminished the analgesic effects of URB597. Inhibition of TRPV1 did not effectively reduce the effects of URB597 but attenuated expression of NAPE-PLD compared with the URB597-injected group. In addition, optical imaging demonstrated that neuronal activity of the insular cortex was reduced following URB597 treatment. Our results suggest that microinjection of FAAH inhibitor into the insular cortex causes analgesic effects by decreasing neural excitability and increasing signals related to the endogenous cannabinoid pathway in the insular cortex.
岛叶皮层是大脑中参与处理疼痛和情绪的重要区域。最近的研究表明，岛叶皮层的损伤会导致疼痛失认症和神经性疼痛的逆转。内源性大麻素（内源性大麻素）被证明可以减轻疼痛，同时也被脂肪酸酰胺水解酶（FAAH）降解，从而阻止其作用机制。选择性抑制剂 URB597 通过保留内源性大麻素来抑制 FAAH 的活性，从而减轻疼痛。本研究在神经性疼痛动物模型的岛叶皮层中检查了 URB597 治疗的镇痛效果。在戊巴比妥麻醉下，雄性 Sprague-Dawley 大鼠接受神经损伤和套管植入。术后第 14 天，动物接受 URB597 微注射到岛叶皮层。为了验证 URB597 的镇痛机制，在注射 URB597 前 15 分钟，注射大麻素 1 型受体（CB1R）拮抗剂 AM251、过氧化物酶体增殖物激活受体α（PPARα）拮抗剂 GW6471 和瞬时受体电位香草素 1（TRPV1）拮抗剂碘树脂毒素（I-RTX）。使用 von-Frey 测试测量机械性痛觉过敏的变化。与假手术对照组相比，神经性疼痛组中 CB1R、N-酰基磷酯酰乙醇胺磷脂酶 D（NAPE-PLD）和 TRPV1 的表达显著增加。与载体注射组相比，用 2 nM 和 4 nM URB597 处理的组中机械阈值和 NAPE-PLD 的表达显著增加。CB1R 和 PPARα 的阻断减弱了 URB597 的镇痛作用。抑制 TRPV1 不能有效降低 URB597 的作用，但与 URB597 注射组相比，它降低了 NAPE-PLD 的表达。此外，光学成像显示，URB597 治疗后岛叶皮层神经元活动减少。我们的结果表明，将 FAAH 抑制剂微注射到岛叶皮层中会通过降低神经兴奋性和增加岛叶皮层内源性大麻素途径的信号来引起镇痛作用。
