Potentiation of the NMDA receptor-mediated responses through the activation of the glycine site by microglia secreting soluble factors
Potentiation of the NMDA receptor-mediated responses through the activation of the glycine site by microglia secreting soluble factors
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DOI：
10.1002/glia.20322
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发表时间：
2006-04-15
期刊：
影响因子：
6.2
通讯作者：
Nakanishi, H
中科院分区：
文献类型：
--
作者：
Hayashi, Y;Ishibashi, H;Nakanishi, H
我们以前曾报道过，无论是转移的小胶质细胞和小胶质细胞条件培养基（MCM）加强N-甲基-D-天冬氨酸（NMDA）受体介导的突触反应在皮层神经元。为了阐明小胶质细胞增强NMDA受体介导的反应的机制，我们研究了MCM对NMDA诱导的内向电流在机械分离的海马CA 1神经元全细胞膜片钳记录下的影响。MCM以剂量依赖性方式增强NMDA诱导电流的幅度高达10倍，并且MCM的这种作用即使在煮沸或切断分子量大于3 kDa的分子后仍然存在。在浓度足以饱和NMDA受体甘氨酸位点的甘氨酸存在下，MCM未能进一步增强NMDA诱导的电流。甘氨酸位点拮抗剂5，7-二氯犬尿烯酸可明显抑制MCM的作用。即使在用D-丝氨酸降解酶D-氨基酸氧化酶处理后，仍然观察到MCM的效果。另一方面，MCM对NMDA受体的电压依赖性Mg 2+阻断没有显著影响。此外，MCM还能促进Schaffer侧支通路-CA 1锥体细胞突触长时程增强的形成。使用高效液相色谱系统，我们发现MCM中的甘氨酸和L-丝氨酸的水平显着高于对照培养基中的水平。还注意到，在神经元损伤的急性期，在海马中观察到小胶质细胞的甘氨酸产量增加。这些观察结果强烈表明，甘氨酸是一个主要的致病分子释放的小胶质细胞，加强NMDA诱导的电流。(c)2006 Wiley-Liss，Inc.
We have previously reported that both transferred microglia and microglia-conditioned medium (MCM) potentiated the N-methyl-D-aspatate (NMDA) receptor-mediated synaptic responses in cortical neurons. To elucidate the mechanism underlying the potentiation of NMDA receptor-mediated responses by microglia, we examined the effects of MCM on NMDA-induced inward currents in mechanically dissociated hippocampal CA1 neurons under whole-cell patch recordings. MCM potentiated the amplitude of NMDA-induced currents up to 10-fold in a dose-dependent manner, and this effect of MCM remained even after boiling or cutting off molecules with a molecular mass more than 3 kDa. In the presence of glycine with a concentration sufficient to saturate the NMDA receptor glycine site, MCM failed to further potentiate the NMDA-induced currents. The glycine site antagonist 5, 7-dichrolokynurenic acid, significantly inhibited the effects of MCM. The effect of MCM was still observed even after treatment with D-amino acid oxidase, a D-serine degrading enzyme. On the other hand, MCM had no significant effect on the voltage-dependent Mg2+ blockade of NMDA receptors. Furthermore, MCM enhanced the formation of the long-term potentiation in the Schaffer collateral pathway-CA1 pyramidal cell synapses. Using a high performance liquid chromatography system, we found the levels of both glycine and L-serine in MCM to be significantly higher than those in the control medium. It was also noted that an increased glycine productivity of microglia was observed in the hippocampus in the acute phase of neuronal injury. These observations strongly suggest that glycine is a major causative molecule released from microglia that potentiates the NMDA-induced currents. (c) 2006 Wiley-Liss, Inc.