The excitatory amino acid transporter type 2 (EAAT2) represents the major mechanism for removal of extracellular glutamate. In the hippocampus, there is some EAAT2 in axon-terminals, whereas most of the protein is found in astroglia. The functional importance of the neuronal EAAT2 is unknown, and it is debated whether EAAT2-expressing nerve terminals are present in other parts of the brain. Here we selectively deleted the EAAT2 gene in neurons (by crossing EAAT2-flox mice with synapsin 1-Cre mice in the C57B6 background). To reduce interference from astroglial EAAT2, we measured glutamate accumulation in crude tissue homogenates. EAAT2 proteins levels were measured by immunoblotting. Although synapsin 1-Cre mediated gene deletion only reduced the forebrain tissue content of EAAT2 protein to 95.5 ± 3.4% of wild-type (littermate) controls, the glutamate accumulation in homogenates of neocortex, hippocampus, striatum and thalamus were nevertheless diminished to, respectively, 54 ± 4, 46 ± 3, 46 ± 2 and 65 ± 7% of controls (average ± SEM, n = 3 pairs of littermates). GABA uptake was unaffected. After injection of U-13C-glucose, lack of neuronal EAAT2 resulted in higher 13C-labeling of glutamine and GABA in the hippocampus suggesting that neuronal EAAT2 is partly short-circuiting the glutamate-glutamine cycle in wild-type mice. Crossing synapsin 1-Cre mice with Ai9 reporter mice revealed that Cre-mediated excision occurred efficiently in hippocampus CA3, but less efficiently in other regions and hardly at all in the cerebellum. Conclusions: (1) EAAT2 is expressed in nerve terminals in multiple brain regions. (2) The uptake catalyzed by neuronal EAAT2 plays a role in glutamate metabolism, at least in the hippocampus. (3) Synapsin 1-Cre does not delete floxed genes in all neurons, and the contribution of neuronal EAAT2 is therefore likely to be larger than revealed in the present study.

中文翻译：

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表达EAAT2（GLT-1; Slc1a2）的轴突末端在前脑中很常见，而不仅限于海马体。

2型兴奋性氨基酸转运蛋白（EAAT2）代表去除细胞外谷氨酸的主要机制。在海马中，轴突末端有一些EAAT2，而大多数蛋白质则存在于星形胶质细胞中。神经元EAAT2的功能重要性尚不明确，人们还在争论大脑其他部位是否存在表达EAAT2的神经末梢。在这里，我们选择性地删除了神经元中的EAAT2基因（通过在C57B6背景中将EAAT2-flox小鼠与突触素1-Cre小鼠杂交）。为了减少星形胶质EAAT2的干扰，我们测量了粗组织匀浆中谷氨酸的积累。EAAT2蛋白水平通过免疫印迹法测量。尽管突触蛋白1-Cre介导的基因缺失仅将EAAT2蛋白的前脑组织含量降低至野生型（同窝出生）对照的95.5±3.4％，新皮层，海马，纹状体和丘脑匀浆中谷氨酸的积累分别减少至对照组​​的54±4、46±3、46±2和65±7％（平均±SEM，n = 3对同窝仔） 。GABA吸收不受影响。注射U-13C-葡萄糖后，神经元EAAT2的缺乏导致海马中谷氨酰胺和GABA的13C标记较高，这表明神经元EAAT2部分地缩短了野生型小鼠的谷氨酸-谷氨酰胺循环。将突触蛋白1-Cre小鼠与Ai9报告基因小鼠杂交，发现Cre介导的切除在海马CA3中有效发生，但在其他区域效率较低，而在小脑中几乎完全没有。结论：（1）EAAT2在多个脑区的神经末梢表达。（2）神经元EAAT2催化的摄取至少在海马体中在谷氨酸代谢中起作用。（3）Synapsin 1-Cre不能在所有神经元中删除flox基因，因此神经元EAAT2的贡献可能大于本研究中揭示的。