Surgery Upregulates High Mobility Group Box-1Causing Cognitive Dysfunction In Aged Rats

Aim:1.To explore the impact of anesthesia and surgery on cognitive function in aged rats.2. We sought to determine the relationship between cognitive decline and inflammation, namely high mobility group box-1(HMGB1), after surgery in aged rats.Methods:(1) The first part of the experiment:①Female Sprague Dawley (SD) aged rats (22-23months) were randomly divided into seven groups:control (C,n=15)、anesthesia only (A1、A3、A7anesthesia at days1、3and7, n=15/group), anesthesia plus surgery (S1、S3、S7surgery at days1、3and7, n=15/group). Rats were exposed to isoflurane anesthesia (3%isoflurane for induction followed by2%for maintenance) for2h with endotracheal intubation in anesthesia group, monitoring of vital signs and gas concentration. Animals in the anesthesia plus surgery groups underwent splenectomy. Rats in the control group were exposed to oxygen for2h in a gas chamber.②Spatial learning and memory were evaluated in the MWM, rats were trained for6days with three trials per day, On day7, animals underwent surgery and/or general anesthesia; on posttreatment days1,3and7, rats were subjected to a reversal test. The time to reach the platform (latency)、 distance and speed was recorded by smart junior system.(2) The second part of the experiment:5rats in each group were randomly used for one indicator.①.After MWM test, blood samples were collected, the Levels of HMGB1、TNF-a and IL-1β in the serum were measured by ELISA.②. After perfused, the brain was removed. BBB permeability was measured by IgG immuno-histochemistry, expression of HMGB1in the hippocampus was measured using immunofluorescenc, the morphology and number of the neurons were measured by nissl staining③. BBB ultrastructure was measured by transmission electron microscope (TEM).④. The hippocampi were quickly dissected and frozen in liquid nitrogen, the mRNA levels of HMGB1、TNF-α IL-1β and RAGE were measured by PT-PCR.⑤.The protein levels of HMGB1. TNF-α、IL-1β and RAGE were measured by western blot. All statistical data were analyzed using SPSS17.0.Results:The first part of the experiment:surgical trauma resulted in impairments in distance (732.97±157.38cm at day1,613.17±175.63cm at day3,P<0.001respectively) and latency(44.54±6.63s at day1,38.3±6.25s at dya3,P<0.001respectively) on postoperative day1and3in aged rats compared with control group (distance:322±116.88cm latency:24.7±8.63s). Distance (557.93±187.42cm P=0.003) and latency(35.99±7.70s P=0.001) were impaired at day1after anesthesia.The second part of the experiment:①HMGB1was significantly upregulated after surgery on postoperative day1(0.204±0.023ug/L,P=0.003), before returning to baseline,No changes from baseline were observed in TNF-α and IL-1β at all time points.②Immunohistochemistry and TEM showed BBB disruption induced by surgery and anesthesia.③Levels of HMGB1、TNF-α、IL-1β and the RAGE were significantly upregulated in the hippocampus of operated animals (P<0.001), and significantly increased after exposure to anesthesia at day1(P<0.001).④The number of neurons in the hippocampal CA1region was not decreased by surgery, and no statistically significant difference compared with the control group.Conclusions:The first part of the experiment:Anesthesia and surgical trauma, appears to contribute to the cognitive dysfunction in aged rats, and more severely in surgery group.The second part of the experiment:①The proinflammatory cytokines HMGB1was upregulated by surgical trauma contribute to the cognitive dysfunction in aged rats.②HMGB1in the peripheral may contribute to the BBB dysfunction and neuroinflammation.③HMGB1and RAGE signaling appear pivotal mediators of surgery-induced cognitive decline after peripheral surgical trauma.