Electroacupuncture alleviates paradoxical sleep deprivation-induced postoperative hyperalgesia via a7nAChR mediated BDNF/TrkB-KCC2 signaling pathway in the spinal cord

Perioperative Paradoxical sleep deprivation (PSD) is associated with postoperative hyperalgesia. However, the clinical therapeutic strategies for PSD-induced postoperative hyperalgesia are limited. Electroacupuncture (EA) has been used for attenuating many types of pain, including neuropathic pain and inflammatory pain, but its effect on PSD-induced postoperative hyperalgesia is still unclear, and its analgesia mechanism should be further explored. In this study, we designed to investigate the possible mechanism of PSD-induced postoperative hyperalgesia and the effect of EA on PSD-induced postoperative hyperalgesia, and whether the mechanism is related to the BDNF/TrkB signaling pathway mediated by α7nAChR in the spinal cord. The paw withdrawal thermal latency (PWTL) and paw withdrawal mechanical threshold (PWMT) of rats were used to detect PSD-induced hyperalgesia. The expression of α7nAChR, BDNF, TrkB and KCC2 in the spinal cord were evaluated by Western blot and immunofluorescence. The results showed that preoperative 24 h PSD significantly decreased the PWTL and PWMT. The expression of α7nAChR and KCC2 significantly downregulated in the spinal cord of PSD-induced postoperative hyperalgesia rats, the opposite was observed for BDNF and TrkB expression. Moreover, intrathecal injection of alpha-bungarotoxin (α-BGT), a selective antagonist for α7nAChR, not only aggravated the pain hypersensitivity, but also demonstrated a further decrease of α7nAChR and KCC2 expression and a further increase of BDNF and TrkB expression. EA stimulation increased the PWTL and PWMT values of PSD-induced postoperative hyperalgesia rats, significantly upregulated α7nAChR and KCC2 expression, and significantly downregulated BDNF and TrkB expression. Moreover, intrathecal injection of α-BGT suppressed the analgesic effect of EA, inhibited the enhancement of α7nAChR and KCC2 expression and the reduction of BDNF and TrkB expression induced by EA. In conclusion, our study indicated that 24 h PSD can cause postoperative hyperalgesia, and the mechanism may be related to the disorder of α7nAChR mediated BDNF/TrkB-KCC2 signaling pathway. EA can alleviate postoperative hyperalgesia induced by PSD, which may be related to its effect in activating α7nAChR, inhibiting the expression of BDNF/TrkB, and up-regulating the expression of KCC2 in the spinal cord.