Prolonged mechanical ventilation-induced neuroinflammation affects postoperative memory dysfunction in surgical mice

Introduction: Patients undergoing surgery frequently develop neuropsychological disturbances, including cognitive decline or memory impairment, and routine clinical procedures such as mechanical ventilation (MV) may affect acute-phase brain outcome. We aimed to investigate the effect of the prolonged MV on postoperative memory dysfunction in surgical mice. Methods: Male C57BL/6 mice were randomly divided into the following three groups: (1) The control group (group C) comprised anesthetized, unventilated animals; (2) the surgery group (subgroups S1h, S3h and S6h) was unventilated animals that underwent surgery under general anesthesia; and (3) the MV group (subgroups MV1h, MV3h and MV6h) was made up of animals under MV for 1 hour, 3 hours or 6 hours after surgery. Separate cohorts of animals were tested for memory function with fear conditioning tests or were killed at 6 hours, 1 day or 3 days postsurgery or post-MV to examine levels systemic and hippocampal interleukin (IL)-1 beta, IL-6 and tumor necrosis factor alpha (TNF alpha), and assessed synaptic structure and microglial activation. Nuclear factor kappa B (NF-kappa B) p65, cytochrome c, cleaved caspase-3 and cleaved poly(ADP-ribose) polymerase (PARP) activation were analyzed by Western blotting. Results: The MV6h group showed increased CD11b-immunopositive cells, synapse degeneration, cytochrome c release, cleaved caspase-3 and cleaved PARP-1 activation after surgery, as well as a decrease in freezing time after surgery. At 6 hours and 1 day post-MV, MV6h increased NF-kappa B activation and levels of systemic and hippocampal IL-1 beta, IL-6 and TNF alpha after surgery. Conclusions: Prolonged MV after surgery further aggravates cognitive decline that may stem from upregulation of hippocampal IL-1 beta, IL-6 and TNF alpha, partially via activation of gliocytes in the surgical mouse hippocampus.