Steward O, Falk P M
Department of Neuroscience, University of Virginia Health Sciences Center, Charlottesville 22908.
J Comp Neurol. 1991 Dec 15;314(3):545-57. doi: 10.1002/cne.903140311.
Previous studies have revealed that polyribosomes are selectively localized beneath post-synaptic sites on central nervous system (CNS) neurons, and are particularly prominent during periods of synapse growth. The present study evaluates whether polyribosomes are most prominent at a consistent time in the developmental history of the synapse, or instead at a consistent time in the life of the organism regardless of the state of synaptic maturation (suggesting a globally acting factor). We compare the time course of synaptogenesis and the association between polyribosomes and developing synapses in three regions that develop at different rates: the external and internal blades of the dentate gyrus, and the CA1 region of the hippocampus proper. Each region was examined electron microscopically at 1, 4, 7, 10, 15, 20, 28 and over 120 days of age, evaluating: (1) synapse density (the number of synaptic profiles/area of neuropil), (2) the width of the neuropil layers, (3) the proportion of synapses with underlying polyribosomes, and (4) the number of polyribosome-containing synapses/area of neuropil. As anticipated on the basis of the differences in cytogenesis, the time course of synaptogenesis was different in the three regions. In the external blade of the dentate gyrus, synapse density increased in a nearly linear fashion between birth and 15 days of age, and then continued to increase at a somewhat slower rate until 28 days of age. Synapse development in the internal blade was delayed by several days in comparison to the external blade. In CA1, synapse density increased slowly between 1 and 7 days, and then at a rapid rate between 7 and 28 days of age. In all three regions, the proportion of synapses with underlying polyribosomes was highest between 1 and 7 days of age, and then decreased as synapse density increased. However, the peak in the number of polyribosome-containing synapses/unit area of neuropil occurred at different times in the three regions (4-7 days of age in the external blade of the dentate gyrus and in CA1, and 20 days of age in the internal blade). In addition to further defining the relationship between polyribosomes and developing synapses, the present study provides a data base on the time course of synapse development in the hippocampus and dentate gyrus, which will be useful for comparisons with other measures.
以往的研究表明，多核糖体选择性地定位于中枢神经系统（CNS）神经元突触后位点的下方，并且在突触生长期间尤为显著。本研究评估多核糖体是在突触发育历史中的某个一致时间最为显著，还是在生物体生命中的某个一致时间最为显著，而与突触成熟状态无关（这表明存在一个全局作用因子）。我们比较了三个以不同速率发育的区域中突触发生的时间进程以及多核糖体与发育中突触之间的关联：齿状回的外叶和内叶，以及海马体本身的CA1区域。在1、4、7、10、15、20、28日龄及超过120日龄时，对每个区域进行电子显微镜检查，评估：（1）突触密度（突触轮廓数/神经毡面积），（2）神经毡层的宽度，（3）具有多核糖体的突触比例，以及（4）含多核糖体的突触数/神经毡面积。基于细胞发生差异的预期，三个区域中突触发生的时间进程不同。在齿状回的外叶，突触密度在出生至15日龄之间以近乎线性的方式增加，然后以稍慢的速率持续增加直至28日龄。与外叶相比，内叶的突触发育延迟了几天。在CA1区，突触密度在1至7日龄之间缓慢增加，然后在7至28日龄之间快速增加。在所有三个区域中，具有多核糖体的突触比例在1至7日龄之间最高，然后随着突触密度的增加而降低。然而，每单位神经毡面积中含多核糖体的突触数量的峰值在三个区域中出现在不同时间（齿状回外叶和CA1区为4至7日龄，内叶为20日龄）除了进一步明确多核糖体与发育中突触之间的关系外，本研究还提供了海马体和齿状回中突触发育时间进程的数据库，这将有助于与其他测量方法进行比较。
