Xia Tianjiao, Cui Yin, Qian Yue, Chu Shuaishuai, Song Jia, Gu Xiaoping, Ma Zhengliang
From the Department of Anesthesiology, Affiliated Drum Tower Hospital of Medical Department, Nanjing University, Nanjing, Jiangsu, China.
Anesth Analg. 2016 Feb;122(2):542-52. doi: 10.1213/ANE.0000000000000991.
Numerous clinical investigations have revealed the circadian rhythm changes in the perception of chronic pain, and most clinical chronic pain types peak in the night. However, it is still undiscovered whether circadian rhythm of pain exists in rodents and the specific mechanism that may underlie it. Our study was conducted to investigate the rhythmic changes of hyperalgesia behavior in a chronic constrictive injury (CCI) model of rodents and to explore the role of the N-methyl-d-aspartate receptor 2B (NR2B)-cAMP response element binding protein (CREB)-CREB-regulated transcription coactivator 1 (CRTC1) signaling pathway in this pain rhythm.
A CCI operation was performed to mimic clinical chronic pain. Paw mechanical withdrawal threshold and paw withdrawal thermal latency were used to test pain behavior in rats; a von Frey cilia test was used to test mechanical hyperalgesia in mice at Zeitgeber time (ZT) 4, ZT10, ZT16, and ZT22 for 14 contiguous days. The relative mRNA and protein expression of NR2B, CREB and CRTC1 in the suprachiasmatic nuclei and the dorsal horn were measured by real-time polymerase chain reaction and Western blot. CRTC1 and CREB interference adenovirus vectors were injected intrathecally at 2 time points, respectively (ZT12 and ZT0), to further explore the proper time point for pain treatment.
During the period of chronic pain state, the pain behavior of CCI rodents showed a circadian rhythm with the peak at ZT4 or ZT10 daily. The pain thresholds were significantly different between the activity period and the rest period. The expressions of NR2B, CRTC1, and CREB at the spinal level were consistent with the pain rhythm. The intrathecal treatment with CRTC1 or CREB interference adenovirus from day 7 to day 9 after CCI surgery markedly improved pain behaviors. Nevertheless, when given at ZT0, they were both more effective at relieving peak pain than drugs given at ZT12.
Pain behavior in the chronic pain of CCI displayed circadian rhythm and was associated with circadian secretion of pain-related receptors. The NR2B-CREB-CRTC1 signaling pathway may play a crucial role in this rhythm. Moreover, our results suggest that measures to relieve pain should be taken before pain reaches its peak.
众多临床研究揭示了慢性疼痛感知中的昼夜节律变化，且大多数临床慢性疼痛类型在夜间达到峰值。然而，啮齿动物是否存在疼痛昼夜节律及其潜在的具体机制仍未被发现。我们开展本研究以探究啮齿动物慢性压迫性损伤（CCI）模型中痛觉过敏行为的节律变化，并探讨N-甲基-D-天冬氨酸受体2B（NR2B）-环磷酸腺苷反应元件结合蛋白（CREB）-CREB调节转录共激活因子1（CRTC1）信号通路在这种疼痛节律中的作用。
进行CCI手术以模拟临床慢性疼痛。用爪部机械性缩足阈值和爪部缩足热潜伏期来测试大鼠的疼痛行为；在授时时间（ZT）4、ZT10、ZT16和ZT22，连续14天用von Frey纤毛试验测试小鼠的机械性痛觉过敏。通过实时聚合酶链反应和蛋白质免疫印迹法测量视交叉上核和背角中NR2B、CREB和CRTC1的相对mRNA和蛋白表达。分别在两个时间点（ZT12和ZT0）鞘内注射CRTC1和CREB干扰腺病毒载体，以进一步探索疼痛治疗的合适时间点。
在慢性疼痛状态期间，CCI啮齿动物的疼痛行为呈现昼夜节律，每天在ZT4或ZT10达到峰值。活动期和休息期的疼痛阈值有显著差异。脊髓水平的NR2B、CRTC1和CREB表达与疼痛节律一致。CCI手术后第7天至第9天鞘内注射CRTC1或CREB干扰腺病毒可显著改善疼痛行为。然而，在ZT0给药时，它们在缓解疼痛峰值方面比在ZT12给药更有效。
CCI慢性疼痛中的疼痛行为表现出昼夜节律，且与疼痛相关受体的昼夜分泌有关。NR2B-CREB-CRTC1信号通路可能在这种节律中起关键作用。此外，我们的结果表明应在疼痛达到峰值之前采取缓解疼痛的措施。
