Sur C, Triller A, Korn H
INSERM U261, Département des Biotechnologies, Institut Pasteur, Paris, France.
J Comp Neurol. 1995 Jan 9;351(2):247-60. doi: 10.1002/cne.903510205.
Synapses are complex arrangements of pre- and postsynaptic differentiations involved in neural communication. A key element in this synaptic transmission is the presynaptic active zone where the release of neurotransmitter occurs. Active zones can be visualized and analyzed after staining with ethanolic phosphotungstic acid (EPTA) on semithin (0.5 micron) sections. This staining has been used in association with postembedding immunogold labeling for the neurotransmitters glycine or GABA, to investigate the organization of chemically defined inhibitory active zones, viewed in their full extent, on different regions of the goldfish Mauthner (M-) cell. With this approach, a marked variability in size and shape was observed for the release sites contacting the different parts of the postsynaptic neuron. In the axon cap and on the soma, glycinergic afferent terminals have small presynaptic grids (0.066 +/- 0.029 micron2, n = 30 and 0.076 +/- 0.037 micron2, n = 46, respectively). These grids are quite circular and they include 12 to 13 presynaptic dense projections (PDPs). The situation is different on the lateral dendrite, where glycinergic and GABAergic active zones display a greater variability in their surface areas (mean = 0.147 +/- 0.100 micron2, n = 115 and 0.139 +/- 0.080 micron2, n = 125, respectively), and their number of PDPs (mean = 19 +/- 9) per individual grid. Similarly, the shape of the release sites over the dendrite is more complex (annular, horseshoe-shaped) when compared to those on the soma. These differences of dendritic versus somatic release sites could represent a structural basis to maximize the shunting effect of glycinergic and GABAergic inhibitory junctions, i.e., close to excitatory inputs. We also observed that the proportion of endings containing 1 or more active zones also varies. More precisely, 96% and 82% of glycinergic terminals in the axon cap and on the soma, respectively, display only one active zone. On the dendrite, their proportion falls to 65.5% for both glycine- and GABA-containing boutons. The remaining inhibitory terminals contain 2 (30%) and 3 to 4 (4.5%) presynaptic grids. These results reveal a greater variability of morphology and organization of the inhibitory release sites at dendritic versus somatic locations. The functional significance of this observation for the synaptic transmission is discussed.
突触是参与神经通讯的突触前和突触后分化的复杂结构。这种突触传递中的一个关键要素是神经递质释放发生的突触前活动区。在半薄（0.5微米）切片上用乙醇磷钨酸（EPTA）染色后，活动区可以被可视化并进行分析。这种染色已与用于神经递质甘氨酸或GABA的包埋后免疫金标记相结合，以研究金鱼莫氏细胞（M细胞）不同区域上化学定义的抑制性活动区的完整组织结构。通过这种方法，观察到与突触后神经元不同部位接触的释放位点在大小和形状上有显著差异。在轴突帽和胞体上，甘氨酸能传入终末具有小的突触前网格（分别为0.066±0.029平方微米，n = 30和0.076±0.037平方微米，n = 46）。这些网格相当呈圆形，并且它们包含12到13个突触前致密突起（PDP）。在侧枝上情况不同，在那里甘氨酸能和GABA能活动区在其表面积（分别为平均0.147±0.100平方微米，n = 115和0.139±0.080平方微米，n = 125）以及每个单独网格的PDP数量（平均 = 19±9）方面表现出更大的变异性。同样，与胞体上的释放位点相比，树突上释放位点的形状更复杂（环形、马蹄形）。树突与胞体释放位点的这些差异可能代表了一种结构基础，以最大化甘氨酸能和GABA能抑制性连接的分流效应，即靠近兴奋性输入。我们还观察到含有1个或更多活动区的终末比例也有所不同。更确切地说，轴突帽和胞体中分别有96%和82%的甘氨酸能终末仅显示一个活动区。在树突上，对于含甘氨酸和含GABA的终扣，其比例降至65.5%。其余的抑制性终末含有2个（30%）和3至4个（4.5%）突触前网格。这些结果揭示了树突与胞体位置处抑制性释放位点在形态和组织上的更大变异性。讨论了这一观察结果对突触传递的功能意义。
