Juang J L, Carlson S D
Department of Entomology, University of Wisconsin, Madison 53706.
J Comp Neurol. 1992 Oct 15;324(3):343-52. doi: 10.1002/cne.903240305.
Using scanning and transmission electron microscopy, we studied basic ultrastructure, membrane specializations, and blood-brain barrier properties of the ventral ganglion and abdominal nerves of the last (third) instar larva of a dipteran fly, Delia platura. Both ganglion and nerves are covered with a non-cellular neural lamella. A monolayer of flattened perineurial cells lies beneath the neural lamella. Perineurial cells contain stores of metabolites and nutrients and these cells extensively interdigitate with one another. An extensive extracellular series of channels pervades perineurial cells. Glial cells beneath the perineurium envelope but do not entwine axons. In a minority of cases, adjacent axons in nerve and neuropil appear to be contiguous without glial intervention. Extensive (pleated) septate junctions with triangular septa are present between perineurial cells. Hemidesmosomes, half desmosomes (a first report for invertebrates), and desmosomes were also observed. Although no tight junctions were discovered, an effective blood-brain barrier exists, and tracer (ionic lanthanum) in no case reached neuronal surfaces. Extracellular tracer halted within the extensive septate junctions between perineurial cells. We postulate that in the absence of tight junctions the functional blood-brain barrier is effected by the septate junctions in the central nervous system of the Delia larva.
我们利用扫描电子显微镜和透射电子显微镜，研究了双翅目昆虫韭蛆（Delia platura）末龄（第三龄）幼虫腹神经节和腹神经的基本超微结构、膜特化以及血脑屏障特性。神经节和神经均覆盖有一层无细胞的神经膜。神经膜下方是一层扁平的围神经细胞。围神经细胞含有代谢物和营养物质储备，且这些细胞彼此广泛交错。围神经细胞中有一系列广泛的细胞外通道。神经膜下方的神经胶质细胞包裹着轴突，但并不缠绕。少数情况下，神经和神经纤维网中相邻的轴突在没有神经胶质细胞干预的情况下似乎是相邻的。围神经细胞之间存在大量带有三角形隔膜的（褶皱）分隔连接。还观察到了半桥粒、半个桥粒（无脊椎动物的首次报道）和桥粒。尽管未发现紧密连接，但存在有效的血脑屏障，示踪剂（离子镧）在任何情况下都未到达神经元表面。细胞外示踪剂在围神经细胞之间广泛的分隔连接内停止。我们推测，在没有紧密连接的情况下，功能性血脑屏障是由韭蛆幼虫中枢神经系统中的分隔连接实现的。
