1. 2021;24;E1099-E1108NLRP3-mediated Neuroinflammation Exacerbates Incisional Hyperalgesia and Prolongs Recovery After Surgery in Chronic Stressed Rats
   Animal Study
   Buwei Yu, MD, PhD, Jingwei Zhang, MD, Qingsheng Xue, MD, PhD, Lei Zhuang, MD, PhD, and Ying Meng, MD.

BACKGROUND: Postoperative pain management has increasingly become a public health problem worldwide. Psychological factors can be considered as independent risk factors for the intensity of postoperative pain and the occurrence of postoperative chronic pain.

OBJECTIVES: As stress events could facilitate NLR family pyrin domain-containing 3 (NLRP3) inflammasome activation in the central nervous system, we aimed to explore the role of perioperative NLRP3-mediated neuroinflammation in the exacerbation of incisional hyperalgesia in stressed rats.

STUDY DESIGN: Experimental trial in rats.

SETTING: Department of Anesthesiology, Shanghai, China.

METHODS: All animal experimental procedures were approved by the Animal Care and Use Committee of Shanghai Jiaotong University School of Medicine. This study was conducted in rat models of chronic restraint stress and hind paw incision model. Serum corticosterone level measurement and emotion-related behavioral tests were used to confirm that chronic restraint stress can cause depression-like behavior in rats. Pain behavior after surgery was assessed by withdrawal response to von Frey filament application. Immunofluorescence staining and  the Western blot test were used to evaluate the protein level of NLRP3, IL-1beta, C-fos in the basolateral amygdala (BLA) and GluN2B-containing N-methyl-D-aspartate (NMDA) receptors (GluN2B) expression in the central nucleus of the amygdala (CeA), respectively. Intra-BLA cannulation and microinjection of an NLRP3 specific inhibitor——MCC950 (0.5 µL, 2 µg/µL) were applied to the stressed rats for 4 days perioperatively to explore whether the stress-induced postoperative hyperalgesia and GluN2B expression in CeA can be altered.

RESULTS: The results showed that chronic restraint stress exposure led to depressive behavior in rats. Moreover, chronic restraint stress exposure increased NLRP3 and interleukin 1 beta (IL-1beta) expression in the basolateral amygdala (BLA), as well as exacerbated postoperative hyperalgesia and prolonged the recovery time of postoperative pain. Meanwhile, GluN2B expression in the CeA of the stressed group was higher than that of the control incision group. Inhibition of NLRP3 reversed the exacerbation of postoperative hyperalgesia by stress exposure, and down-regulated GluN2B expression in the CeA.

LIMITATIONS: The upstream mechanism by which NLRP3 is elevated in stressed rats was not explored.

CONCLUSION: These findings suggest that chronic restraint stress may influence postoperative hyperalgesia and NLRP3-mediated neuroinflammation, which may in turn contribute to stress-induced postoperative pain exacerbation.

KEY WORDS: Postoperative pain, NLRP3, chronic restraint stress, amygdala, neuroinflammation, rat, incision, depression