Morphine promotes neuroinflammation after NOD-like receptor protein 3 (NLRP3) oligomerization in glial cells, but the capacity of other opioids to induce neuroinflammation and its relationship to the development of analgesic tolerance is unknown. We studied the effects of morphine and fentanyl on NLRP3 inflammasome activation in glial and neuronal cells in the dorsal raphe nucleus (DRN), a region involved in pain regulation. Male Wistar rats received i.p. injections of morphine (10 mg/kg) or fentanyl (0.1 mg/kg) 3 × daily for 7 days and were tested for nociception. Two hours after the last (19th) administration, we analyzed NLRP3 oligomerization, caspase-1 activation and gasdermin D-N (GSDMD-N) expression in microglia (CD11b positive cells), astrocytes (GFAP-positive cells) and neurons (NeuN-positive cells). Tolerance developed to both opioids, but only fentanyl produced hyperalgesia. Morphine and fentanyl activated NLRP3 inflammasome in astrocytes and serotonergic (TPH-2-positive) neurons, but fentanyl effects were more pronounced. Both opioids increased GFAP and CD11b immunoreactivity, caspase-1 and GSDMD activation, indicating pyroptotic cell death. The opioid receptor antagonist (−)-naloxone, but not the TLR4 receptor antagonist (+)-naloxone, prevented microglia activation and NLRP3 oligomerization. Only (+)-naloxone prevented astrocytes’ activation. The anti-inflammatory agent minocycline and the NLRP3 inhibitor MCC950 delayed tolerance to morphine and fentanyl antinociception and prevented fentanyl-induced hyperalgesia. MCC950 also prevented opioid-induced NLRP3 oligomerization. In conclusion, morphine and fentanyl differentially induce cell-specific activation of NLRP3 inflammasome and pyroptosis in the DRN through TLR4 receptors in astrocytes and through opioid receptors in neurons, indicating that neuroinflammation is involved in opioid-induced analgesia and fentanyl-induced hyperalgesia after repeated administrations.

吗啡在胶质细胞中 NOD 样受体蛋白 3 (NLRP3) 寡聚化后促进神经炎症，但其他阿片类药物诱导神经炎症的能力及其与镇痛耐受性发展的关系尚不清楚。我们研究了吗啡和芬太尼对中缝背核 (DRN) 中的神经胶质细胞和神经元细胞中 NLRP3 炎性体激活的影响，DRN 是一个参与疼痛调节的区域。雄性 Wistar 大鼠接受 ip 注射吗啡 (10 mg/kg) 或芬太尼 (0.1 mg/kg) 每天 3 次，持续 7 天，并测试伤害感受。在最后一次（第 19 次）给药后两小时，我们分析了小胶质细胞（CD11b 阳性细胞）、星形胶质细胞（GFAP 阳性细胞）和神经元（NeuN 阳性细胞）中的 NLRP3 寡聚化、caspase-1 活化和 gasdermin DN (GSDMD-N) 表达）。对两种阿片类药物产生耐受性，但只有芬太尼产生痛觉过敏。吗啡和芬太尼可激活星形胶质细胞和 5-羟色胺能（TPH-2 阳性）神经元中的 NLRP3 炎性体，但芬太尼的作用更为明显。两种阿片类药物均增加 GFAP 和 CD11b 免疫反应性、caspase-1 和 GSDMD 活化，表明细胞焦亡。阿片受体拮抗剂 (-)-纳洛酮，而非 TLR4 受体拮抗剂 (+)-纳洛酮，可阻止小胶质细胞活化和 NLRP3 寡聚化。只有 (+)-纳洛酮能阻止星形胶质细胞的活化。抗炎药米诺环素和 NLRP3 抑制剂 MCC950 延迟了对吗啡和芬太尼镇痛的耐受性，并预防了芬太尼引起的痛觉过敏。MCC950 还阻止了阿片类药物诱导的 NLRP3 寡聚化。综上所述，