Structural determinants of transmission at large hippocampal mossy fiber Synapses
Structural determinants of transmission at large hippocampal mossy fiber Synapses
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DOI：
10.1523/jneurosci.1946-07.2007
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发表时间：
2007-09-26
影响因子：
5.3
通讯作者：
Luebke, Joachim H. R.
中科院分区：
文献类型：
--
作者：
Rollenhagen, Astrid;Saetzler, Kurt;Luebke, Joachim H. R.
突触是大脑中信号处理和可塑性的关键元件。为了确定海马苔藓纤维突触的独特功能特性的结构因素，完整的定量几何形状进行了研究，使用电子显微镜连续切片，然后计算机辅助三维重建。特别是，相关参数的发射器释放和突触可塑性进行了检查。两个膜专业化被发现：活动区（AZ），发射机释放网站，和点adherentia，假定的粘附复合物。单个的钮扣平均有25个AZ（范围，7-45），形状和大小各不相同（平均，0.1 μ m（2）;范围，0.07-0.17 μ m（2））。个体AZ之间的平均距离为0.45 μ m。苔藓纤维终扣和它们的靶结构大多被星形胶质细胞包裹，但精细的胶质细胞过程从未到达活动区。两个结构因素可能促进突触串扰：AZs之间的短距离和AZs处没有精细的胶质细胞过程。因此，突触串扰可能有助于海马苔藓纤维突触的功效。平均而言，一个终扣包含20，400个突触囊泡;近似900个囊泡位于距活动区60 nm内，近似4400个位于60 nm至200 nm之间，其余超过200 nm，这表明大的易于释放，回收和储备池。不同池的组织可能是在这个突触突触的突触前可塑性的关键结构相关。因此，苔藓纤维终扣在结构和功能上与Held的花萼和其他中央突触有根本的不同。
Synapses are the key elements for signal processing and plasticity in the brain. To determine the structural factors underlying the unique functional properties of the hippocampal mossy fiber synapse, the complete quantitative geometry was investigated, using electron microscopy of serial ultrathin sections followed by computer-assisted three-dimensional reconstruction. In particular, parameters relevant for transmitter release and synaptic plasticity were examined. Two membrane specializations were found: active zones (AZs), transmitter release sites, and puncta adherentia, putative adhesion complexes. Individual boutons had, on average, 25 AZs ( range, 7-45) that varied in shape and size ( mean, 0.1 mu m(2); range, 0.07-0.17 mu m(2)). The mean distance between individual AZs was 0.45 mu m. Mossy fiber boutons and their target structures were mostly ensheathed by astrocytes, but fine glial processes never reached the active zones. Two structural factors are likely to promote synaptic cross talk: the short distance between AZs and the absence of fine glial processes at AZs. Thus, synaptic cross talk may contribute to the efficacy of hippocampal mossy fiber synapses. On average, a bouton contained 20,400 synaptic vesicles; similar to 900 vesicles were located within 60 nm from the active zone, similar to 4400 between 60 and 200 nm, and the remaining beyond 200 nm, suggesting large readily releasable, recycling, and reserve pools. The organization of the different pools may be a key structural correlate of presynaptic plasticity at this synapse. Thus, the mossy fiber bouton differs fundamentally in structure and function from the calyx of Held and other central synapses.