Vaughn J E, Henrikson C K
Brain Res. 1976 Jul 16;110(3):431-45. doi: 10.1016/0006-8993(76)90856-8.
Focal surface specializations occur upon axons, axon growth cone filopodia and, somewhat less frequently, upon dendrites as well as dendritic growth cones in embryonic mouse spinal cord. These surface specializations are observed during the early synaptogenic period (embryonic days 12-16) when the axons of the marginal zone are forming synaptic junctions with motor neuron dendrites growing into their domain. At relatively low electron microscopic magnifications, the specializations appear as discrete patches of electron-dense material located just outside the plasma membrane. Higher resolution and an optimum section plane reveal the following ultrastructural characteristics of these specializations. There is a narrow (approximately 5 nm) less dense layer between the outer surface of the plasms membrane and the thicker (approximately 11.5-15 nm) electron-dense, distal layer of the specializations. The dense layer contains spherical profiles (approximately 10-15 nm in diameter) which have relatively clear centers and non-laminar, opaque perimeters. The surface specializations are commonly associated with an accumulation of dense, fibrillar cytoplasmic material that undercoats the cytoplasmic surface of the plasma membrance directly opposite to the external specializations. Furthermore, some of these surface specializations appear to be forming or merging with the cleft material of protosynaptic junctions and primitive puncta adhaerentia-like contacts. We have also examined the pattern of concanavalin A-peroxidase staining on the cell surfaces in embryonic spinal cord. At embryonic day 13, the earliest stage examined in the concanavalin A-peroxidase experiments, there is already an ubiquitous staining around all the cellular processes in the marginal zone as well as around the perikarya and processes of cells located in the intermediate and ventricular zones. No selective enhancement of neurite surfaces occurred which might have correlated with the surface specializations described above. Finally, the possibility is discussed that the neurite surface specializations might play some role in intercellular recognition phenomena leading to the formation of synaptic junctions and puncta adhaerentia.
在胚胎期小鼠脊髓中，局灶性表面特化出现在轴突、轴突生长锥丝状伪足上，在树突以及树突生长锥上出现的频率稍低。这些表面特化在早期突触形成期（胚胎第12 - 16天）被观察到，此时边缘区的轴突正在与长入其区域的运动神经元树突形成突触连接。在相对较低的电子显微镜放大倍数下，这些特化表现为位于质膜外侧的离散电子致密物质斑块。更高的分辨率和最佳的切片平面揭示了这些特化的以下超微结构特征。在质膜外表面与特化的较厚（约11.5 - 15纳米）电子致密远端层之间有一个狭窄（约5纳米）的较低密度层。致密层包含球形轮廓（直径约10 - 15纳米），其中心相对清晰，周边为非层状、不透明。表面特化通常与致密的纤维状细胞质物质的积累相关，这些物质在质膜细胞质表面与外部特化相对的位置形成衬里。此外，这些表面特化中的一些似乎正在形成或与原突触连接和原始黏着斑样接触的裂隙物质融合。我们还研究了胚胎脊髓细胞表面伴刀豆球蛋白A - 过氧化物酶染色的模式。在胚胎第13天，即伴刀豆球蛋白A - 过氧化物酶实验中检查的最早阶段，边缘区所有细胞突起周围以及位于中间区和室管膜区细胞的胞体和突起周围已经存在普遍的染色。未观察到可能与上述表面特化相关的神经突表面的选择性增强。最后，讨论了神经突表面特化可能在导致突触连接和黏着斑形成的细胞间识别现象中发挥某种作用的可能性。
