Electron microscopic immunocytochemical detection of PSD-95, PSD-93, SAP-102, and SAP-97 at postsynaptic, presynaptic, and nonsynaptic sites of adult and neonatal rat visual cortex
Electron microscopic immunocytochemical detection of PSD-95, PSD-93, SAP-102, and SAP-97 at postsynaptic, presynaptic, and nonsynaptic sites of adult and neonatal rat visual cortex
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DOI：
10.1002/syn.1047
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发表时间：
2001-06-15
期刊：
影响因子：
2.3
通讯作者：
Bredt, DS
中科院分区：
文献类型：
--
作者：
Aoki, C;Miko, I;Bredt, DS
膜相关鸟苷酸激酶（MAGUKs）在细胞-细胞接触位点组装蛋白质复合物。在大脑兴奋性突触中，MAGUKs定位于突触后致密物（postsynaptic density，PSD）并与N-甲基-D-天冬氨酸（N-methyl-D-aspartate，NMDA）谷氨酸受体和下游信号蛋白相互作用。然而，NMDA受体并不局限于PSD，因为电子显微镜免疫细胞化学（EM-ICC）结果表明，NMDA受体也出现在树突的非突触部分，可能作为储备快速插入突触膜，以响应适当的突触活动。NMDA受体也存在于轴突中，至少部分地支持谷氨酸依赖性的递质释放增强。在本研究中，进行了系统的EM-ICC调查，以确定四种神经元MAGUKs-PSD-95，PSD-93，SAP-102和SAP-97-的分布是否类似于NMDA受体。定量分析表明，PSD-95的密度超过不对称轴-棘突触连接的厚PSD是2 - 3倍的水平，直接相邻的细胞质的棘和终端，而对称的突触没有显示与PSD-95的关联。类似地，所有四种MAGUK都发生在脊柱的PSD上。然而，我们也检测到MAGUK免疫反应，虽然更弥漫，沿着突触前膜和轴突和树突状细胞的细胞质。事实上，PSD-95在神经元内的总体分布是沿着沿着质膜（包括突触部分）与在细胞质中一样普遍，远离质膜。这些结果表明，MAGUKs具有双重作用：维持受体在突触和调节受体之间的非突触和突触网站的穿梭。Synapse 40：239 - 257，2001，（C）2001 Wiley-Liss，Inc.
Membrane-associated guanylate kinases (MAGUKs) assemble protein complexes at sites of cell-cell contact. At excitatory synapses in brain, MAGUKs localize to the postsynaptic density (PSD) and interact with N-methyl-D-aspartate (NMDA) glutamate receptors and downstream signaling proteins. However, NMDA receptors are not restricted to the PSDs, as electron microscopic immunocytochemical (EM-ICC) results indicate that NMDA receptors also occur at nonsynaptic portions of dendrites, perhaps functioning as reserves for rapid insertion into synaptic membranes in response to appropriate synaptic activity. NMDA receptors also occur in axons, at least in part to support glutamate-dependent enhancement of transmitter release. In this study, a systematic EM-ICC survey was performed to determine whether the distributions of four neuronal MAGUKs-PSD-95, PSD-93, SAP-102, and SAP-97-resemble that of NMDA receptors. Quantitative analysis revealed that the density of PSD-95 over thick PSDs of asymmetric axo-spinous synaptic junctions is 2-3-fold the level in the immediately adjacent cytoplasm of spines and terminals, while symmetric synapses show no association with PSD-95. Similarly, all four MAGUKs occur over PSDs of spines. However, we also detected MAGUK immunoreactivity, albeit more diffusely, along presynaptic membranes and in the cytoplasm of axons and dendritic shafts. In fact, the overall distribution of PSD-95 within the neuropil is equally prevalent along plasma membranes (including synaptic portions) as in the cytoplasm, away from plasma membranes. These results suggest that MAGUKs have dual roles: to maintain receptors at synapses and to regulate shuttling of receptors between nonsynaptic and synaptic sites. Synapse 40:239-257, 2001, (C) 2001 Wiley-Liss, Inc.