Tamamaki N, Nojyo Y
Department of Anatomy, Fukui Medical School, Japan.
J Comp Neurol. 1995 Mar 13;353(3):379-90. doi: 10.1002/cne.903530306.
In order to examine whether the entorhinal-hippocampal-entorhinal circuit is reciprocal and topographic, the connections between the subiculum, the CA1 field, and the entorhinal cortex were studied with the carbocyanine dye (Dil), which moves in both retrograde and anterograde directions. We investigated the organization of reciprocal connections revealed by injections of Dil in the entorhinal cortex along the rhinal sulcus. Anterograde fluorescent labeling showed the same pattern reported in previous studies of the dorsal hippocampus. When the injection site of DiI extended into the deep layers (IV-VI) of the same cortical column, the anterograde labeling of the perforant path was accompanied by retrograde labeling of the subicular neurons and the CA1 neurons. The distribution of labeled cells overlapped the distribution of labeled fibers, and the distribution of labeled cells paralleled that of the labeled fibers in the CA1 field. DiI injection into the medial entorhinal cortex revealed fewer retrogradely labeled subicular neurons than injection into the lateral entorhinal cortex, whereas the number of labeled CA1 neurons was not dependent on the injection site. The number of labeled CA1 neurons was always several times greater than the number of subicular neurons. Thus, the amount of information conveyed by the CA1 projection might be higher than that conveyed by the subicular projection. These results indicate that the entorhinal cortex, CA1, and the subiculum are connected reciprocally and topographically. We believe that the framework of the major hippocampal circuit proposed in previous studies should be reconsidered. We propose that the CA1 projection, rather than the subicular projection, is the main projection that feeds back information from the hippocampus to the entorhinal cortex.
为了研究内嗅-海马-内嗅回路是否是相互的且具有拓扑结构，我们使用了在逆行和顺行方向都能移动的羰花青染料（Dil）来研究海马下脚、CA1区和内嗅皮质之间的连接。我们沿着嗅沟在内嗅皮质注射Dil，研究由此揭示的相互连接的组织情况。顺行荧光标记显示出与先前关于背侧海马的研究所报道的相同模式。当DiI的注射部位延伸到同一皮质柱的深层（IV-VI层）时，穿通通路的顺行标记伴随着海马下脚神经元和CA1神经元的逆行标记。标记细胞的分布与标记纤维的分布重叠，并且在CA1区标记细胞的分布与标记纤维的分布平行。向内嗅皮质内侧注射DiI所显示的逆行标记的海马下脚神经元比向外侧内嗅皮质注射时少，而标记的CA1神经元的数量不依赖于注射部位。标记的CA1神经元的数量总是比海马下脚神经元的数量多几倍。因此，由CA1投射传递的信息量可能高于由海马下脚投射传递的信息量。这些结果表明，内嗅皮质、CA1区和海马下脚是相互且按拓扑结构连接的。我们认为先前研究中提出的主要海马回路框架应该重新考虑。我们提出，从海马向内嗅皮质反馈信息的主要投射是CA1投射，而不是海马下脚投射。
