Deller T, Nitsch R, Frotscher M
Institute of Anatomy, University of Freiburg, Germany.
J Comp Neurol. 1995 Jan 30;352(1):55-68. doi: 10.1002/cne.903520105.
Numerous studies have shown a lamina-specific termination of commissural fibers to the dentate gyrus in the inner molecular layer. However, the exact course and arborization pattern of individual fibers remained unknown. In this study, the commissural fiber tract to the dentate gyrus of the rat has been studied using the anterograde tracer Phaseolus vulgaris-leucoagglutinin (PHA-L), which labels individual axons and their collaterals. Following iontophoretic application of the tracer, anterogradely labeled fibers were followed through the posterior basal fornix and medial fimbria where they formed a dense fiber bundle. Labeled fibers then entered the dentate gyrus close to the medial blade of the granule cell layer where they separated and traversed the hilus. Only in those cases where the injection also involved CA3 pyramidal cells could axons arborizing in the hilus be observed. Typically, fibers that continued into the molecular layer did not arborize in the hilus. Upon their entrance into the molecular layer, these fibers changed direction, gave off several collaterals, and followed a new path parallel to the granule cell layer where they preferentially formed en passant contacts. These commissural fibers to the inner molecular layer terminated in a wide septotemporal (longitudinal) extension. However, a considerable number of fibers reached the outer molecular layer where some of them formed extensive arborizations. Moreover, these commissural fibers to the outer molecular layer appeared to be restricted to the hippocampal lamella, corresponding to the level of the contralateral injection site. These data suggest the existence of three commissural projections to the rat dentate gyrus: (1) commissural fibers to the hilus arising from CA3 neurons, (2) commissural fibers to the inner molecular layer, and, (3) commissural fibers to the outer molecular layer.
大量研究表明，连合纤维在齿状回内分子层存在层特异性终止。然而，单个纤维的确切走行和分支模式仍不清楚。在本研究中，利用顺行示踪剂菜豆白细胞凝集素（PHA-L）对大鼠齿状回的连合纤维束进行了研究，该示踪剂可标记单个轴突及其侧支。在离子导入示踪剂后，追踪顺行标记的纤维，它们穿过后基底穹窿和内侧伞，在那里形成密集的纤维束。标记纤维随后进入靠近颗粒细胞层内侧叶片的齿状回，在那里它们分开并穿过门区。只有在注射也涉及CA3锥体细胞的情况下，才能观察到在门区分支的轴突。通常，继续进入分子层的纤维不在门区分支。进入分子层后，这些纤维改变方向，发出几个侧支，并沿着与颗粒细胞层平行的新路径走行，在那里它们优先形成沿途接触。这些到内分子层的连合纤维在宽的颞中隔（纵向）延伸范围内终止。然而，相当数量的纤维到达外分子层，其中一些在外分子层形成广泛的分支。此外，这些到外分子层的连合纤维似乎局限于海马板层，与对侧注射部位的水平相对应。这些数据表明存在三条投射到大鼠齿状回的连合纤维：（1）由CA3神经元发出的到门区的连合纤维，（2）到内分子层的连合纤维，以及（3）到外分子层的连合纤维。
