Caballero-Bleda M, Witter M P
Department of Morphological Sciences, Faculty of Medicine, University of Murcia, Spain.
Exp Brain Res. 1994;101(1):93-108. doi: 10.1007/BF00243220.
The relations between the inputs from the presubiculum and the parasubiculum and the cells in the entorhinal cortex that give rise to the perforant pathway have been studied in the rat at the light microscopical level. Projections from the presubiculum and the parasubiculum were labeled anterogradely, and, in the same animal, cells in the entorhinal cortex that project to the hippocampal formation were labeled by retrograde tracing and subsequent intracellular filling with Lucifer Yellow. The distribution and the number of appositions between the afferent fibers and hippocampal-projection neurons in the various layers of the entorhinal cortex were analyzed. The results show that layers I-IV of the entorhinal cortex contain neurons that give rise to projections to the hippocampal formation. The morphology of these projection neurons is highly variable and afferents from the presubiculum and the parasubiculum do not show a preference for any specific morphological cell type. Both inputs preferentially innervate the dendrites of their target cells. However, presubicular and parasubicular projections differ with respect to the layer of entorhinal cortex they project to. The number of appositions of presubicular afferents with cells that have their cell bodies in layer III of the entorhinal cortex is 2-3 times higher than with cells in layer II. In contrast, afferents from the parasubiculum form at least 2-3 times as many synapses on the dendrites of cells located in layer II than on neurons that have their cell bodies in layer III. Cells in layers I and IV of the entorhinal cortex receive weak inputs from the presubiculum and parasubiculum. Not only is the presubiculum different from the parasubiculum with respect to the distribution of projections to the entorhinal cortex, they also differ in their afferent and efferent connections. In turn, cells in layer II of the entorhinal cortex differ in their electrophysiological characteristics from those in layer III. Moreover, layer II neurons give rise to the projections to the dentate gyrus and field CA3/CA2 of the hippocampus proper, and cells in layer III project to field CA1 and the subiculum. Therefore, we propose that the interactions of the entorhinal-hippocampal network with the presubiculum are different from those with the parasubiculum.
在大鼠中，已在光学显微镜水平研究了来自内嗅前区和内嗅旁区的输入与产生穿通通路的内嗅皮质细胞之间的关系。对内嗅前区和内嗅旁区的投射进行了顺行标记，并且在同一只动物中，通过逆行追踪以及随后用路西法黄进行细胞内填充，标记了投射至海马结构的内嗅皮质中的细胞。分析了传入纤维与内嗅皮质各层中向海马投射的神经元之间并置的分布和数量。结果表明，内嗅皮质的I-IV层包含向海马结构发出投射的神经元。这些投射神经元的形态高度可变，来自内嗅前区和内嗅旁区的传入纤维对任何特定形态的细胞类型均无偏好。两种输入均优先支配其靶细胞的树突。然而，内嗅前区和内嗅旁区的投射在它们所投射到的内嗅皮质层方面有所不同。内嗅前区传入纤维与胞体位于内嗅皮质III层的细胞之间的并置数量比与II层细胞之间的并置数量高2-3倍。相反，来自内嗅旁区的传入纤维在位于II层的细胞树突上形成的突触数量至少是胞体位于III层的神经元上突触数量的2-3倍。内嗅皮质I层和IV层中的细胞从内嗅前区和内嗅旁区接收微弱的输入。内嗅前区不仅在投射至内嗅皮质的分布方面与内嗅旁区不同，它们在传入和传出连接方面也有所不同。反过来，内嗅皮质II层中的细胞在电生理特性上与III层中的细胞不同。此外，II层神经元向齿状回以及海马本部的CA3/CA2区发出投射，而III层中的细胞投射至CA1区和下托。因此，我们提出内嗅-海马网络与内嗅前区的相互作用不同于与内嗅旁区的相互作用。
