Deller T, Drakew A, Heimrich B, Förster E, Tielsch A, Frotscher M
Institute of Anatomy, University of Freiburg, Freiburg, D-79001, Germany.
Exp Neurol. 1999 Apr;156(2):254-67. doi: 10.1006/exnr.1999.7021.
Area CA1 of the rodent hippocampus is characterized by a highly lamina-specific and nonoverlapping termination of afferent fiber tracts. Entorhinal fibers terminate in stratum lacunosum-moleculare and commissural/associational fibers terminate in strata radiatum and oriens. It has been hypothesized that this fiber lamination depends on specific signals for the different afferent fiber tracts that are located on distinct dendritic segments of the postsynaptic neuron. In order to test this hypothesis, entorhinal and commissural/associational afferents to Ammon's horn were investigated in the adult reeler mutant mouse, in which developmental cell migration defects have disrupted the normal array of cells. Golgi staining revealed a deep and a superficial principal cell layer in the mutant. The morphology of the cells located in the deep pyramidal cell layer was considerably abnormal, whereas most cells located in the superficial pyramidal cell layer showed an almost normal cellular and dendritic morphology. Anterograde tracing with Phaseolus vulgaris leukoagglutinin revealed that the duplication and disorganization of the pyramidal cell layer in area CA1 are mirrored by the duplication and disruption of afferent fiber termination zones. In the zone above the abnormal deep pyramidal cell layer, i.e., between the two cell layers, entorhinal fibers as well as commissural/associational fibers terminate and intermingle. In contrast, in the zone above the fairly normal superficial pyramidal cell layer, entorhinal and commissural/associational fibers retain their normal fiber segregation. These data suggest that the normal laminar organization of the murine hippocampus depends on positional cues presented by their target cells.
啮齿动物海马体的CA1区具有传入纤维束高度分层特异性且不重叠的终止特征。内嗅纤维终止于腔隙-分子层，连合/联合纤维终止于放射层和原层。据推测，这种纤维分层依赖于位于突触后神经元不同树突节段上的不同传入纤维束的特定信号。为了验证这一假设，在成年reeler突变小鼠中研究了通向海马角的内嗅和连合/联合传入纤维，在该突变小鼠中，发育性细胞迁移缺陷破坏了正常的细胞排列。高尔基染色显示突变体中有一个深层和一个浅层主细胞层。位于深层锥体细胞层的细胞形态明显异常，而位于浅层锥体细胞层的大多数细胞显示出几乎正常的细胞和树突形态。用菜豆白细胞凝集素进行顺行追踪显示，CA1区锥体细胞层的重复和紊乱反映在传入纤维终止区的重复和破坏上。在异常深层锥体细胞层上方的区域，即两层细胞之间，内嗅纤维以及连合/联合纤维终止并相互交织。相反，在相当正常的浅层锥体细胞层上方的区域，内嗅纤维和连合/联合纤维保持其正常的纤维分离。这些数据表明，小鼠海马体的正常分层组织依赖于其靶细胞提供的位置线索。
