Chi C, Carlson S D
J Neurocytol. 1980 Aug;9(4):451-69. doi: 10.1007/BF01204836.
Membrane specializations between the three types of glial cells in the first optic neuropil (lamina ganglionaris) of the housefly were determined from thin sections and freeze-fracture replicas. Three strata of glia cells are present in the lamina. A relatively thin layer of satellite glia covers the distal (perikaryal) rind of the lamina and these cells wrap retinular axons that enter the lamina. The central synaptic fields of the lamina neurons are enclosed by epithelial glia, while the proximal surface of the lamina is capped by marginal glial cells. Satellite glia bond to each other via desmosomes, septate and gap junctions. Freeze-fracture replicas show gap junctions as aggregations of E face particles and P face pits on the intramembranous surfaces. Parallel rows of P face particles are indicative of septate junctions. Angulated, intersecting, P face particle ridges are arranged in circumferential bands around retinular axons at the glia-axon interface. Thin section correlates of these junctions are presented. Epithelial glia are characterized by elaborate series of parallel membranes which appear to be suspended in the cytoplasm but may be the invaginated plasma membranes of a neighbouring glial cell. An intermembranous cleft of 40-50 A is noted and this area has an appreciable electron density which give the appearance of a gap junction. When cleaved, these membranes show plaques of particles on the P face. The marginal glial cells are relatively large and are joined by a newly discovered junction which is characterized (from freeze-fracture data) by numerous, undulating, uninterrupted, parallel P face ridges which sometimes become circular and form enclosures. In thin section, electron-dense material fills the membrane appositional areas and in tangential sections faint diffuse parallel striae are seen. This specialized cell contact may be a variant of a continuous junction although, based on fracture replicas, there are obvious similarities to tight junctions. These membranes specializations are related, in the three dimensions of the optic cartridges, to functions in a possible blood-eye barrier system.
通过薄切片和冷冻蚀刻复制品确定了家蝇第一视神经节（神经纤维层）中三种神经胶质细胞之间的膜特化。神经纤维层中有三层神经胶质细胞。一层相对较薄的卫星神经胶质细胞覆盖着神经纤维层的远端（胞体）外皮，这些细胞包裹着进入神经纤维层的视网膜轴突。神经纤维层神经元的中央突触区域被上皮神经胶质细胞包围，而神经纤维层的近端表面则由边缘神经胶质细胞覆盖。卫星神经胶质细胞通过桥粒、分隔连接和缝隙连接相互连接。冷冻蚀刻复制品显示缝隙连接为E面颗粒和膜内表面P面孔穴的聚集。平行排列的P面颗粒表示分隔连接。在神经胶质细胞与轴突的界面处，有角状、交叉的P面颗粒脊围绕视网膜轴突呈圆周带排列。展示了这些连接的薄切片相关性。上皮神经胶质细胞的特征是有一系列精致的平行膜，这些膜似乎悬浮在细胞质中，但可能是相邻神经胶质细胞的内陷质膜。观察到膜间裂隙为40 - 50埃，该区域有明显的电子密度，呈现出缝隙连接的外观。当劈开时，这些膜在P面上显示出颗粒斑。边缘神经胶质细胞相对较大，通过一种新发现的连接相连，从冷冻蚀刻数据来看，这种连接的特征是有许多起伏、不间断的平行P面脊，这些脊有时会变成圆形并形成封闭结构。在薄切片中，电子致密物质填充膜贴合区域，在切向切片中可见微弱的弥漫性平行条纹。这种特殊的细胞接触可能是连续连接的一种变体，尽管基于断裂复制品，它与紧密连接有明显的相似之处。在视柱的三维结构中，这些膜特化与可能的血眼屏障系统中的功能相关。
