小剂量氯胺酮减轻老龄大鼠七氟醚麻醉后认知功能障碍的机制：内嗅皮质神经元树突棘的可塑性

Mechanism of low-dose ketamine-induced reduction of cognitive dysfunction following sevoflurane anesthesia in aged rats ： plasticity of dendritic spines in entorhinal cortical neurons

目的探讨内嗅皮质神经元树突棘的可塑性与小剂量氯胺酮减轻老龄大鼠七氟醚麻醉后认知功能障碍的关系。方法清洁级健康雄性SD大鼠36只，18月龄，体重500～600 g，采用随机数字表法分为3组（n＝12）：对照组（C组）、七氟醚麻醉组（Sev组）和氯胺酮组（K组）。C组不进行任何处理；Sev组吸入空气（流量1 L/min）和3.6%七氟醚的混合气体3 h；K组腹腔注射氯胺酮10 mg/kg，5 min后吸入空气（流量1 L/min）和3.6%七氟醚的混合气体3 h。麻醉后3 d进行旷场实验和水迷宫实验，随后取脑组织，采用NISSL染色、高尔基银浸染色和免疫组化的方法分别测定内嗅皮质Ⅱ-Ⅲ层神经元密度、树突棘密度以及突触后密度蛋白（PSD-95）和突触素（SY38）的表达水平。结果与C组比较，Sev组中央区停留时间缩短，逃避潜伏期延长，内嗅皮质神经元树突棘的密度减少，PSD-95和SY38表达下调（P〈0.05）；与Sev组比较，K组中心区停留时间延长，逃避潜伏期缩短，内嗅皮质神经元树突棘的密度增加，PSD-95和SY38表达上调（P〈0.05）。3组内嗅皮质神经元密度差异无统计学意义（P〉0.05）。结论小剂量氯胺酮减轻七氟醚麻醉诱发老年大鼠认知功能障碍的机制可能与增强内嗅皮质神经元树突棘的可塑性有关。

Objective To investigate the relationship between the plasticity of dendritic spines in entorhinal cortical neurons and mechanism of low-dose ketamine-induced reduction of cognitive dysfunction following sevoflurane anesthesia in aged rats. Methods Thirty-six pathogen-free healthy male Sprague- Dawley rats, aged 18 months, weighing 500-600 g, were divided into 3 groups （n= 12 each） using a random number table： control group （group C）, sevoflurane anesthesia group （group Sev） and ketamine group （group K）. Group C received no treatment. Group Sev inhaled the mixture of air （flow rate 1 L/min） and 3.6% sevoflurane for 3 h. In group K, ketamine 10 mg/kg was injected intraperitoneally, and 5 min later the mixture of air （flow rate 1 L/min） and 3.6% sevoflurane was inhaled for 3 h. Open field test and Morris water maze test were performed 3 days after anesthesia. After the behavioral tests, the animals were sacrificed, and their brains were removed and cut into sections for determination of the density of neurons, density of dendritic spines, and expression of postsynaptic density protein-95 （PSD-95） and synaptophysin （SY38） in superficial laminaes （ II -m ） of entorhinal cortex using Nissl＇s staining, Golgi staining and immunohistochemistry, respectively. Results Compared with group C, the time of staying at the central region was significantly shortened, the escape latency was prolonged, the density of dendritic spines was decreased, and the expression of PSD-95 and SY38 was down-regulated in group Sev （P〈0.05）. Compared with group Sev, the time of staying at the central region was significantly prolonged, the escape latency was shortened, the density of dendritic spines was increased, and the expression of PSD-95 and SY38 was upregulated in group K （P〈0.05）. There were no significant differences in the density of neurons in entorhinal cortex between the three groups （P〉0.05）. Conclusion The mechanism by which low-dose ketamine attenuates cognitive dysfunction induced by sevoflurane anesthesia may be related to the enhanced plasticity of dendritic spines in entorhinal cortical neurons of aged rats.