Department of Anesthesiology, Tri-Service General Hospital and National Defense Medical Center, Taipei, Taiwan.
Neuroscience. 2009 Dec 1;164(2):435-43. doi: 10.1016/j.neuroscience.2009.08.015. Epub 2009 Aug 12.
Pertussis toxin (PTX) treatment results in ADP-ribosylation of Gi-protein and thus in disruption of mu-opioid receptor signal transduction and loss of the antinociceptive effect of morphine. We have previously demonstrated that pretreatment with ultra-low dose naloxone preserves the antinociceptive effect of morphine in PTX-treated rats. The present study further examined the effect of ultra-low dose naloxone on mu-opioid receptor signaling in PTX-treated rats and the underlying mechanism. Male Wistar rats implanted with an intrathecal catheter received an intrathecal injection of saline or PTX (1 microg in 5 microl of saline), then, 4 days later, were pretreated by intrathecal injection with either saline or ultra-low dose naloxone (15 ng in 5 microl of saline), followed, 30 min later, by saline or morphine (10 microg in 5 microl of saline). Four days after PTX injection, thermal hyperalgesia was observed, together with increased coupling of excitatory Gs-protein to mu-opioid receptors in the spinal cord. Ultra-low dose naloxone pretreatment preserved the antinociceptive effect of morphine, and this effect was completely blocked by the mu-opioid receptor antagonist CTOP, but not by the kappa-opioid receptor antagonist nor-BNI or the delta-opioid receptor antagonist naltrindole. Moreover, a co-immunoprecipitation study showed that ultra-low dose naloxone restored mu-opioid receptor/Gi-protein coupling and inhibited the PTX-induced mu-opioid receptor/Gs-protein coupling. In addition to the anti-neuroinflammatory effect and glutamate transporter modulation previously observed in PTX-treated rats, the re-establishment of mu-opioid receptor Gi/Go-protein coupling is involved in the restoration of the antinociceptive effect of morphine by ultra-low dose naloxone pretreatment by normalizing the balance between the excitatory and inhibitory signaling pathways. These results show that ultra-low dose naloxone preserves the antinociceptive effect of morphine, suppresses spinal neuroinflammation, and reduces PTX-elevated excitatory Gs-coupled opioid receptors in PTX-treated rats. We suggest that ultra-low dose naloxone might be clinically valuable in pain management.
百日咳毒素（PTX）治疗导致 Gi 蛋白的 ADP-核糖基化，从而破坏 μ-阿片受体信号转导并丧失吗啡的镇痛作用。我们之前已经证明，超低剂量纳洛酮预处理可保留 PTX 处理大鼠中吗啡的镇痛作用。本研究进一步研究了超低剂量纳洛酮对 PTX 处理大鼠中 μ-阿片受体信号的影响及其潜在机制。雄性 Wistar 大鼠植入鞘内导管，接受鞘内注射生理盐水或 PTX（1μg 在 5μl 生理盐水中），然后，4 天后，通过鞘内注射生理盐水或超低剂量纳洛酮（15ng 在 5μl 生理盐水中）预处理，30 分钟后，用生理盐水或吗啡（10μg 在 5μl 生理盐水中）处理。PTX 注射后 4 天，观察到热痛觉过敏，同时脊髓中兴奋性 Gs 蛋白与 μ-阿片受体的偶联增加。超低剂量纳洛酮预处理可保留吗啡的镇痛作用，该作用完全被 μ-阿片受体拮抗剂 CTOP 阻断，但不被 κ-阿片受体拮抗剂 nor-BNI 或 δ-阿片受体拮抗剂纳曲吲哚阻断。此外，共免疫沉淀研究表明，超低剂量纳洛酮恢复了 μ-阿片受体/Gi 蛋白偶联，并抑制了 PTX 诱导的 μ-阿片受体/Gs 蛋白偶联。除了在 PTX 处理大鼠中观察到的抗神经炎症作用和谷氨酸转运体调节作用外，通过恢复 μ-阿片受体 Gi/Go 蛋白偶联来重建吗啡的镇痛作用，涉及到兴奋性和抑制性信号通路之间的平衡。这些结果表明，超低剂量纳洛酮通过抑制脊髓神经炎症和降低 PTX 升高的兴奋性 Gs 偶联阿片受体来保留吗啡的镇痛作用。我们建议，超低剂量纳洛酮在疼痛管理中可能具有临床价值。
