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

Abstract

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 1hour, 3hours or 6hours after surgery. Separate cohorts of animals were tested for memory function with fear conditioning tests or were killed at 6hours, 1day or 3days postsurgery or post-MV to examine levels systemic and hippocampal interleukin (IL)-1β, IL-6 and tumor necrosis factor α (TNFα), and assessed synaptic structure and microglial activation. Nuclear factor KB (NF-KB) 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 6hours and 1day post-MV, MV6h increased NF-KB activation and levels of systemic and hippocampal IL-1β, IL-6 and TNFα after surgery. Conclusions: Prolonged MV after surgery further aggravates cognitive decline that may stem from upregulation of hippocampal IL-1β, IL-6 and TNFα, partially via activation of gliocytes in the surgical mouse hippocampus.