海马CA1区Somatostatin中间神经元活性恢复延迟介导全麻后记忆损害的机制探究

Postoperative cognitive impairment (POCD) is a severe problem in anesthesiology, and learning and memory deficits are the core symptoms of POCD. In the past, brain stress and inflammation were considered to be the mechanisms of memory deficit after general anesthesia. Recent studies illustrated that the imbalance of excitatory-inhibitory homeostasis between hippocampal pyramidal neurons and interneurons was the key cause of memory deficit after general anesthesia. However, the specific mechanism, especially the effect of general anesthesia on hippocampal interneurons, remained to be clarified. Previously, we found that general anesthesia by isoflurane induced a sustained inhibition of Sst interneurons in hippocampal CA1, and caused delayed recovery after the termination of anesthesia. The recovery phase of Sst interneurons was paralleled with the reconstruction of memory function. Specifically activating Sst interneurons by DREADDs technique could accelerate the recovery of memory function after general anesthesia, suggesting that it was the cause of memory deficit after general anesthesia. Thus, we hypothesized that the excitatory of Sst interneurons in hippocampal CA1 recovered lingeringly after general anesthesia, which induced the imbalance of excitatory-inhibitory homeostasis and impairment of synaptic plasticity, so that memory function damaged after general anesthesia. This project aims to explore the role of Sst interneurons in hippocampal CA1 in memory recovery after general anesthesia and its regulatory mechanism on pyramidal neurons by combining optogenetic and calcium imaging techniques, and to provide novel therapeutic targets for the prevention and treatment of POCD.

术后认知功能障碍（POCD）是麻醉领域重大科学问题，麻醉后记忆功能受损是POCD的核心症状。以往认为脑内炎症反应是全麻后记忆损害的机制。近年研究指出，海马锥体神经元与中间神经元构成的兴奋-抑制稳态失衡是该病的关键成因，但其具体机制，尤其全麻对中间神经元的影响，仍有待阐明。申请人前期发现，异氟烷全麻引起海马CA1区Sst中间神经元兴奋性持续受抑制，麻醉终止后活性恢复延迟，其恢复时相与记忆功能重建同步。利用DREADDs技术全麻后特异性提高该类神经元兴奋性，可加速记忆功能恢复，提示Sst中间神经元功能异常是全麻后记忆受损的原因。故提出假说：全麻后海马CA1区Sst中间神经元兴奋性恢复延迟，兴奋-抑制稳态失衡，介导突触可塑性受损，诱发全麻后记忆功能损害。本项目拟结合光遗传、钙成像等技术，探究海马CA1区Sst中间神经元在全麻后记忆恢复中的作用及其对锥体神经元调控机制，为POCD的防治提供新靶点。

术后认知功能障碍（POCD）的发病机制解析是麻醉学重大科学问题，记忆功能受损是POCD的核心症状。本项目在课题假说中提出：全麻后海马CA1区Sst中间神经元兴奋性恢复延迟，兴奋-抑制稳态失衡，介导突触可塑性受损，诱发全麻后记忆功能损害。为证实该假说本项目完成如下三部分研究内容：①观察全麻-觉醒中海马CA1区Glu、Sst、Pv三种神经元兴奋性动态变化特征。②明确调控Sst神经元兴奋性对全麻后学习记忆功能重建影响。③明确全麻后海马Sst神经元对Glu神经元兴奋性、突触可塑性及集群电活动特性调节机制，及其对认知功能影响。研究发现：①麻醉后情景记忆的获取能力减退，且CA1区Sst神经元c-Fos表达显著减少，Sst神经元活性恢复与认知重建时相一致。钙成像结果表明全麻后CA1区Glu神经元和Sst神经元活性降低，但觉醒后Glu神经元活性快速恢复而Sst神经元持续抑制。双光子观测显示CA1区Glu、Pv神经元以非同步化模式发放，Sst神经元以同步化模式发放，术后Sst神经元呈现间歇同步化爆发。②运用DREADDs技术在麻醉终止后即刻兴奋海马CA1区Sst神经元活性可显著逆转麻醉后情景记忆能力减退，加速记忆功能恢复。③生理条件下特异性抑制海马Sst神经元介导LFP8Hz以上振荡能量减弱，而激活Sst神经元CA1区LFP呈现慢波/Ripple振荡交替现象，与术后LFP特性变化一致。过度激活海马Sst神经元使得71%Glu神经元广泛抑制而编码负性应激的印迹神经元集群激活，并以同步化模式在Ripple振荡期间发放，增强印迹Glu神经元的突触连接强度，导致负性记忆巩固增强而新记忆无法形成。④拓展研究发现，中脑VTA区SST阳性GABA神经元感受多种类型应激，抑制下游LH区介导恢复性睡眠，从而缓解焦虑情绪和躯体应激水平，为理解术后情绪异常、术后睡眠紊乱等其他POCD主要表征提供证据。本研究为解答POCD的发病机制奠定丰富的理论基础。