第一部分 术中低体温对大鼠术后认知功能的影响及其可能机制，目的：术中低体温（Intraoperative hypothermia, IPH）是手术过程中常见并发症，并与多种不良事件相关。近年来，术后认知功能障碍（Postoperative cognitive dysfunction, POCD）与其不良后果受到越来越多的关注。目前尚无相关研究探讨IPH与POCD之间的相关性，本研究旨在评估IPH对剖腹探查大鼠术后认知功能的影响，并探讨可能的机制。方法：将SD大鼠随机分为低体温手术（Hypothermic）组，正常体温手术（Normothermic）组和对照（Control）组。对Hypothermic和Normothermic组的大鼠行剖腹探查术，术中将Hypothermic组大鼠的体温维持在33 ± 0.5 ℃，Normothermic组大鼠的体温维持在37 ± 0.5 ℃，Control组的大鼠对其进行正常喂养，不进行手术。我们用Y迷宫和莫里斯水迷宫（Morris Water Maze, MWM）测试评估大鼠术后的空间工作记忆能力、空间学习和记忆能力。行为学测试后，我们用苏木精-伊红（Haematoxylin-eosin, HE）染色观察大鼠海马区神经元形态学变化。用免疫印迹（Western blot, WB）分析测定大鼠海马区突触可塑性相关蛋白活性调节的细胞骨架相关蛋白（Activity-regulated cytoskeletal-associated protein, Arc）、环磷酸腺苷反应元件结合蛋白（Cyclic adenosine monophosphate-response element-binding protein, CREB）、S133-磷酸化的CREB（S133-phosphorylated CREB, p-CREB[S133]）、α-氨基-3-羟基-5-甲基-4-异恶唑丙酸受体1（α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptor 1, AMPAR1）和S831-磷酸化的AMPAR1（S831-phosphorylated AMPAR1, p-AMPAR1[S831]）的表达水平。结果：IPH与大鼠POCD之间存在相关性，IPH导致大鼠术后的空间工作记忆、空间学习和记忆损害。此外，我们还发现到IPH增加了大鼠海马齿状回（Dentate gyrus, DG）区的神经元损伤，抑制了大鼠海马区突触可塑性相关蛋白Arc、p-CREB（S133）和p-AMPAR1（S831）的表达水平。结论：IPH引起的大鼠POCD可能是由于海马DG区神经元损伤和突触可塑性相关蛋白Arc、p-CREB（S133）和p-AMPAR1（S831）表达降低所致。本研究初步探讨了IPH对大鼠POCD的影响机制；确切的机制需要进一步研究。

第二部分 术中低体温诱导海马CA1区血管功能障碍引起大鼠术后认知功能障碍，目的：术中低体温（Intraoperative hypothermia, IPH）在手术患者中很常见，可导致机体出现认知受损。海马负责记忆的形成和存储，海马阿蒙角（Cornu ammonis, CA）1区作为核心功能区，血供丰富，易受缺血影响，是记忆的关键区域。第一部分研究发现IPH可导致大鼠出现术后认知功能障碍（Postoperative cognitive dysfunction, POCD），在此基础上，本研究采用上述IPH诱导的大鼠POCD模型，旨在探索大鼠海马CA1区血管功能与神经元状态之间的关系。方法：成年雄性SD大鼠将其随机分为3组：低体温手术（Hypothermic, 33 ± 0.5 ℃）组，正常体温手术（Normothermic, 37 ± 0.5 ℃）组和对照（Control）组。对Hypothermic组和Normothermic组的大鼠行剖腹探查术，而Control组的大鼠进行正常喂养，不施行手术。用Y迷宫和莫里斯水迷宫（Morris Water Maze, MWM）测试评估大鼠术后认知功能变化，应用免疫组织化学（Immunohistochemistry, IHC）染色、二氢乙锭（Dihydroethidium, DHE）染色、苏木精-伊红（Haematoxylin-eosin, HE）染色和免疫荧光（Immunofluorescence, IF）染色检测大鼠海马区血管内皮细胞（Vascular endothelial cell, VECs）功能变化，血管平滑肌细胞（Vascular smooth muscle cells, VSMCs）表型转化，活性氧（Reactive oxygen species, ROS）物质的水平，海马CA1区神经元形态变化以及海马区记忆相关的活性调节的细胞骨架相关蛋白（Activity-regulated cytoskeletal-associated protein, Arc）的表达。结果：IPH导致大鼠术后空间工作记忆能力、空间学习和记忆能力损害，即大鼠出现POCD。本研究发现IPH扰乱大鼠海马CA1区VECs的功能，抑制了血管内皮生长因子（Vascular endothelial growth factor, VEGF）与内皮一氧化氮合酶（Endothelial nitric oxide synthase, eNOS）的表达。此外，大鼠海马的内皮完整性被破坏，并导致了活性氧（Reactive oxygen species, ROS）物质的积累。本研究还发现IPH使得大鼠海马CA1区VSMCs收缩表型标记物平滑肌肌球蛋白重链（Smooth muscle myosin heavy chain, SMMHC）的表达下降，合成表型标记物骨桥蛋白（Osteopontin, OPN）的表达增加，这进一步导致视黄醇结合蛋白（Retinol-binding protein 1, RBP1）过表达，表明VSMCs从生理状态的收缩表型转变为病理状态的合成表型。最后，我们发现血管功能障碍导致大鼠海马CA1区神经元受损，记忆相关蛋白Arc表达降低。结论：本研究在第一部分研究的基础上，对IPH诱导的大鼠POCD可能机制的进一步探索，发现IPH诱导的大鼠POCD可能是由于海马CA1区血管功能障碍导致的该区域神经元损伤引起。此研究可为探索IPH对海马和术后认知功能的影响提供新的认知，这可能有助于确定一个新的研究目标和治疗策略。

Part I: The Effects of Intraoperative Hypothermia on Postoperative Cognitive Function in the Rat and Its Possible Mechanisms, Aims: Intraoperative hypothermia (IPH) is a common complication during operations and is associated with several adverse events. Postoperative cognitive dysfunction (POCD) and its adverse consequences have drawn increasing attention in recent years. There are currently no relevant studies investigating the correlation between IPH and POCD. The aim of this study was to assess the effects of IPH on postoperative cognitive function in rats undergoing exploratory laparotomies and to investigate the possible related mechanisms. Methods: Adult male Sprague-Daweley rats were randomly assigned to Hypothermic group, Normothermic group and Control group. Hypothermic and Normothermic group received exploratory laparotomies. The body temperatures of rats in Hypothermic group were maintained at 33 ± 0.5 ℃ and the Normothermic group were maintained at 37 ± 0.5 ℃. The Control group was fed normally without operation. We used the Y-maze and Morris Water Maze tests to assess postoperative spatial working memory ability, spatial learning, and memory ability. Following the behavioral tests, the morphological changes in hippocampal neurons were examined by haematoxylin-eosin staining. Subsequently, western blot analysis was performed to measure the hippocampal synaptic plasticity-related protein expression levels of activity-regulated cytoskeletal-associated protein (Arc), cyclic adenosine monophosphate-response element-binding protein (CREB), S133-phosphorylated CREB (p-CREB [S133]), α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptor 1 (AMPAR1), and S831-phosphorylated AMPAR1 (p-AMPAR1 [S831]). Results: Our results suggest a correlation between IPH and POCD in rats and that IPH may lead to POCD regarding impairments in spatial working memory, spatial learning, and memory. Moreover, we also observed that IPH increased the damage of neurons in the dentate gyrus (DG) region of the hippocampus, inhibited the expression of hippocampal synaptic plasticity-related proteins Arc, p-CREB (S133) and p-AMPAR1 (S831). Conclusions: POCD induced by IPH might be due to neurons damage in the DG region of the hippocampus and decreased expression of hippocampal synaptic plasticity-related proteins Arc, p-CREB (S133), and p-AMPAR1 (S831). This study was only a preliminary exploration of the mechanisms underlying intraoperative hypothermia effect on POCD; the precise mechanism requires further investigation.

Part II: Intraoperative Hypothermia-induced Vascular Dysfunction in Hippocampal CA1 Region Causes Postoperative Cognitive Dysfunction in Rats, Aims: Intraoperative hypothermia (IPH) is very common among patients undergoing surgery and can lead to cognitive impairment. The hippocampus is responsible for memory formation and retention. As a functional core area, the cornu ammonis 1 (CA1) region of hippocampus contains abundant blood vessels and is susceptible to ischemia and critical for memory. The part I suggests that IPH may lead to postoperative cognitive dysfunction (POCD). On this basis, using a rat model of POCD induced by IPH, the present study was undertaken to explore the relationship between vascular function and neuronal state in the CA1 region of hippocampus. Methods: Adult male Sprague-Daweley rats used for this study were randomly divided into three groups: Hypothermic group (33 ± 0.5 ℃), Normothermic group (37 ± 0.5 ℃) and Control group. The rats in groups Hypothermic and Normothermic were subjected to exploratory laparotomies, while the rats in group Control were fed normally without operation. The postoperative cognitive function of rats was evaluated using the Y-maze and Morris Water Maze (MWM) tests. The immunohistochemistry (IHC) staining, Dihydroethidium (DHE) staining, haematoxylin-eosin staining (HE) and immunofluorescence (IF) staining were performed to detect vascular endothelial cell (VECs) function changes, vascular smooth muscle cells (VSMCs) phenotypic transformation, reactive oxygen species (ROS) levels, the neuronal morphological change in the hippocampal CA1 region and memory-related activity-regulated cytoskeletal-associated protein (Arc) expression. Results: IPH leads to impairments of spatial working memory, spatial learning, and memory after surgery, that is, POCD occurred in rats. Furthermore, this research indicated that IPH disturb VECs function in hippocampal CA1 region, inhibit the expressions of vascular endothelial growth factor (VEGF) and endothelial nitric oxide synthase (eNOS). Subsequently, the destruction of endothelial integrity led to reactive oxygen species (ROS) accumulation. Additionally, IPH reduced the expression of VSMCs contractile phenotypic marker smooth muscle myosin heavy chain (SMMHC) and increased the expression of VSMCs synthetic phenotypic marker osteopontin (OPN) in hippocampal CA1 region, which eventually led to the overexpression of retinol-binding protein 1 (RBP1). This indicated that VSMCs transformed from contractile phenotype in physiological state to synthetic phenotype in pathological state. Ultimately, this study suggested that vascular dysfunction cause the damage of neurons in the hippocampal CA1 region and reduce the expression level of memory-related protein Arc. Conclusions: Based on the research in the part I, the study further explored the possible mechanism of IPH-induced POCD in rats, and revealed it may be caused by neuronal damages induced by vascular dysfunction in the hippocampal CA1 region. This study could provide novel insights into exploring the effects of IPH on the hippocampus and postoperative cognitive function, which might allow the identification of a new research target and treatment strategy.