It has been known for over a century that the hippocampus, the center for learning and memory in the brain, is selectively vulnerable to ischemic damage, with the CA1 being more vulnerable than the CA3. It is also known that leucine enkephalin, or YGGFL, is neuroprotective. We hypothesized that the extracellular hydrolysis of YGGFL may be greater in the CA1 than the CA3, which would lead to the observed difference in susceptibility to ischemia. In rat organotypic hippocampal slice cultures, we estimated the Michaelis constant and the maximum velocity for membrane-bound aminopeptidase activity in the CA1 and CA3 regions. Using electroosmotic push–pull perfusion and offline capillary liquid chromatography, we inferred enzyme activity based on the production rate of GGFL, a natural and inactive product of the enzymatic hydrolysis of YGGFL. We found nearly 3-fold higher aminopeptidase activity in the CA1 than the CA3. The aminopeptidase inhibitor bestatin significantly reduced hydrolysis of YGGFL in both regions by increasing apparent K_m. Based on propidium iodide cell death measurements 24 h after oxygen–glucose deprivation, we demonstrate that inhibition of aminopeptidase activity using bestatin selectively protected CA1 against delayed cell death due to oxygen–glucose deprivation and that this neuroprotection occurs through enkephalin-dependent pathways.

中文翻译：

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通过电渗推挽灌注确定的更高的氨肽酶活性有助于海马CA1区对缺氧葡萄糖的选择性脆弱性

一个多世纪以来，人们已经知道海马体（大脑中学习和记忆的中心）有选择地易受缺血性损伤的侵害，其中CA1比CA3更加脆弱。还已知亮氨酸脑啡肽或YGGFL具有神经保护作用。我们假设，CA1中YGGFL的细胞外水解可能比CA3大，这将导致观察到的对缺血的敏感性差异。在大鼠器官型海马切片培养物中，我们估计了CA1和CA3区的Michaelis常数和膜结合的氨肽酶活性的最大速度。使用电渗推挽式灌注和离线毛细管液相色谱法，我们根据GGFL的产率推断了酶的活性，GGFL是YGGFL酶促水解的天然和非活性产物。我们发现CA1中的氨肽酶活性比CA3高近3倍。氨基肽酶抑制剂Bestatin通过增加表观表达来显着降低两个区域中YGGFL的水解ķ_米。根据氧-葡萄糖剥夺后24 h碘化丙啶的细胞死亡测量，我们证明使用Bestatin抑制氨基肽酶活性可选择性保护CA1免受由于氧-葡萄糖剥夺引起的延迟细胞死亡，并且这种神经保护作用是通过脑啡肽依赖性途径发生的。