Orexinergic神经系统部分失活在老年大鼠麻醉觉醒延迟中的作用

The delay of emergence in elder paitients could induce cognitive dysfunction and increase the morbidity of Alzheimer's disease, the problem of which has confused the anesthetists for a long time. Decrease of metabolism in the aged patients was considered to be the main cause of emergence delay. However, the new evidence has been shown that the arousal-related neurons changed their activity during this process. Our previous studies have shown that orexinergic neurons played a positive pro-emergence role after anesthesia. Clinically, even higher content of orexin in plasma was found in the elder than in younger people, the emergence was still later in the aged, which was a contradictory to the expectation. Recently, it has been reported that the aged rats had fewer orexin receptors although with higher orexin level. Thus the hypothesis of current study is that partial inactivation of orexinergic system could be the key reason for the delay of emergence from anesthesia in the aged. This study will make use of in vivo microdialysis, neuropharmacology and other technologies to explore the changes of projection fibers and receptors in tuberomammillary nuclear (TMN) which is the main projection area of orexinergic neurons. We also observe the effect of orexin projections on the histaminergic neuron activities and function, to clarify its role in the delayed emergence. The study will provide a new interpretation for the emergence delay in the aged patients and is helpful to find new targets for the interventions.

老年患者麻醉后觉醒延迟可诱发认知功能障碍，增加Alzheimer's 发病率，是困扰麻醉医生的难题。传统观点认为药物代谢减慢是麻醉觉醒延迟的原因，但新证据显示与觉醒相关的神经元活动性变化可能起重要作用。我们前期研究证实，神经肽orexin在麻醉终止后起主动促醒作用。进一步临床研究发现，虽然老龄患者血浆orexin水平较中青年患者升高，但其麻醉觉醒时间却延长，这与预期结果相反。动物实验发现老年大鼠orexin水平增高同时伴有受体数目减少。由此我们推测，老龄个体 orexinergic神经系统部分失活是导致觉醒延迟的重要原因。本项目将利用在体微透析、神经药理学等技术研究老年动物orexinergic神经系统主要投射区-结节乳头体核（TMN）的投射纤维和受体变化，观察其对组胺神经元活动和功能影响，阐明其在觉醒延迟中的作用。研究成果将有助于对老年患者麻醉觉醒延迟原因作出新的解释和寻找新的干预靶点。

背景：目前，老年患者与全身麻醉术后相关风险的发生已经被学者们广泛研究，但是其相关机制并未清楚的阐明。以往基础研究证明，orexin在全身麻醉苏醒期起促觉醒作用。然而老年大鼠血浆orexin水平增高，但并未在老年患者麻醉觉醒中没有发挥促觉醒作用。本实验旨在探索orexin-1受体降低是参与调节老年大鼠麻醉觉醒延迟的机制之一。方法：采用翻正反射消失和恢复时间记录老年大鼠和青年大鼠在1.4%异氟醚麻醉下的麻醉的诱导和觉醒时间；通过免疫荧光染色和细胞计数确定老年大鼠和青年大鼠神经元数目变化，并采用放射免疫检测血浆orexin-A含量的变化；用Western blot、PCR和免疫荧光染色检测老年大鼠和青年大鼠 orexin-1和-2受体含量变化；采用慢病毒侧脑室注射法上调orexin -1受体的含量，四周转染成功后，观察生理盐水对照组,空病毒组和病毒实验组老年大鼠麻醉觉醒时间的变化,并且与青年大鼠组作比较。结果：老年大鼠组异氟醚介导的麻醉觉醒时间为18.12±0.72分钟，明显长于青年大鼠麻醉觉醒时间14.65±0.29分钟（P=0.0017）；同时，老年大鼠orexin能神经元的数目并没有发生明显变化，但血浆orexin-A含量（34.93±1.15pg/ml）显著高于青年大鼠（26.58±2.95 pg/ml）（p=0.03）；继而Western blot和PCR结果显示，老年大鼠orexin-1受体在蛋白质表达或核酸转录水平中均明显低于青年大鼠（P=0.04），而orexin-2受体的表达两者无统计学差异；应用慢病毒上调老年大鼠的orexin-1受体，老年大鼠的觉醒时间缩短到与青年大鼠相同的水平上，明显低于普通老年大鼠（P=0.004）。结论：异氟醚麻醉下，老年大鼠的觉醒时间延迟机制可能与orexin-1受体的降低有密切关联。