Sargent P B
J Physiol. 1983 Oct;343:85-104. doi: 10.1113/jphysiol.1983.sp014882.
The relationship between the size of parasympathetic neurones and the number of synaptic boutons terminating upon them has been studied in the cardiac ganglion of Xenopus laevis. Synaptic boutons were visualized by impregnation with zinc iodide and osmium (ZIO), which by electron microscopy was shown to stain heavily all synaptic boutons in six preparations. Light microscopic examination of the unipolar ganglion cells in intact tissue reveals that larger neurones have more synaptic boutons. The number of boutons terminating on the cell body is significantly correlated with its surface area. By statistical means it was possible to demonstrate that the relation between bouton number and surface area is linear and that the regression line has a y-intercept not significantly different from zero. Therefore the density of synaptic boutons, one per 127 micron2 of cell body surface, is independent of cell size. The size of synaptic boutons, measured as the area of apposition between bouton and cell body, is similar for small and for large ganglion cells; thus a constant fraction (2%) of the cell body on average is covered by synaptic boutons, regardless of cell size. The correlation between bouton number and cell body surface area is not the result of interaction between boutons. The frequency distribution of boutons per normalized cell was found to be similar to that expected from the Poisson distribution. Thus the probability that a bouton will be 'assigned' to a particular cell is independent of how many other boutons are present. The only factor that appears to influence the number of boutons on the cell body is its size.
在非洲爪蟾的心脏神经节中，研究了副交感神经元大小与终止于其上的突触终扣数量之间的关系。通过用碘化锌和锇（ZIO）浸渍来观察突触终扣，电子显微镜显示在六个标本中ZIO能使所有突触终扣强烈染色。对完整组织中的单极神经节细胞进行光镜检查发现，较大的神经元具有更多的突触终扣。终止于细胞体上的终扣数量与其表面积显著相关。通过统计学方法可以证明，终扣数量与表面积之间的关系是线性的，并且回归线的y轴截距与零无显著差异。因此，突触终扣的密度为每127平方微米细胞体表面一个，与细胞大小无关。以终扣与细胞体之间的贴附面积来衡量，小神经节细胞和大神经节细胞的突触终扣大小相似；因此，无论细胞大小如何，平均有恒定比例（2%）的细胞体被突触终扣覆盖。终扣数量与细胞体表面积之间的相关性并非终扣之间相互作用的结果。发现每个标准化细胞的终扣频率分布与泊松分布预期的相似。因此，一个终扣“分配”到特定细胞的概率与其他终扣的数量无关。唯一似乎影响细胞体上终扣数量的因素是其大小。
