Blasco-Ibáñez J M, Freund T F
Institute of Experimental Medicine, Hungarian Academy of Sciences, Budapest, Hungary.
Hippocampus. 1997;7(3):307-20. doi: 10.1002/(SICI)1098-1063(1997)7:3<307::AID-HIPO6>3.0.CO;2-H.
Hilar mossy cells of the mouse were shown recently to display calretinin immunoreactivity (Liu et al. [1996] Exp Brain Res 108:389-403). The morphological and connectional characteristics of these cells are poorly understood. In the present study, we used immunohistochemical, electron microscopic, and neuronal tracing techniques to describe their distribution, morphology, and connectivity. The distribution of calretinin-immunoreactive mossy cells varied significantly along the dorsoventral axis of the hilus. At dorsal levels, calretinin immunoreactivity was limited largely to a subpopulation of interneurons. At mid-dorsoventral and ventral levels, however, most if not all mossy cells displayed calretinin immunoreactivity. We found that most hilar mossy cells are calretinin immunoreactive but lack gamma-aminobutyric acid, as demonstrated by postembedding immunostaining of alternate semithin sections. Calretinin-immunoreactive mossy cells typically had two to three thick dendrites covered with complex spines (thorny excrescences). Electron microscopy revealed that these spines received multiple asymmetric contacts from mossy fibres. Axons arising from these cells formed a strong belt of calretinin immunoreactivity restricted to the inner third of the dentate molecular layer. This immunoreactivity was equally dense throughout the dorsoventral length of the dentate gyrus, suggesting that axons of calretinin-immunoreactive mossy cells located in the ventral levels diverge greatly and are capable of innervating distant regions of the dentate gyrus. Ultrastructural examination showed that calretinin-immunoreactive boutons made asymmetric synaptic contacts primarily on spines and, occasionally, on dendritic shafts of granule cells and accounted for the majority of asymmetrical synapses in the inner molecular layer. Injections of the retrograde tracer wheatgerm agglutinin-gold into the dentate gyrus demonstrated that calretinin-immunoreactive mossy cells concentrated in the ventral hilus project massively to both the dorsal and ventral aspect of the contralateral dentate gyrus. A small proportion of retrogradely labelled cells showed immunoreactivity for neuropeptide Y or somatostatin. If mossy cells of the ventral hilus receive the majority of their input from ventral granule cells, one may expect ventral granule cells to be more efficient in recruiting large numbers of granule cells during synchronous activity patterns than dorsal granule cells. Spontaneous activity originating from granule cells in the ventral dentate gyrus can be propagated throughout the dorsoventral length of the dentate gyrus bilaterally via the dorsoventrally divergent and contralaterally projecting axons of the mossy cells. This organization may explain why the ventral dentate gyrus is frequently involved in pathological phenomena.
最近研究表明，小鼠的门区苔藓细胞显示钙视网膜蛋白免疫反应性（Liu等人，[1996]《实验脑研究》108:389 - 403）。然而，对这些细胞的形态和连接特征了解甚少。在本研究中，我们使用免疫组织化学、电子显微镜和神经元追踪技术来描述它们的分布、形态和连接性。钙视网膜蛋白免疫反应性苔藓细胞的分布在门区的背腹轴上有显著差异。在背侧水平，钙视网膜蛋白免疫反应性主要局限于中间神经元的一个亚群。然而，在背腹中间和腹侧水平，大多数（如果不是全部）苔藓细胞显示钙视网膜蛋白免疫反应性。我们发现，大多数门区苔藓细胞具有钙视网膜蛋白免疫反应性，但缺乏γ-氨基丁酸，交替半薄切片的包埋后免疫染色证明了这一点。钙视网膜蛋白免疫反应性苔藓细胞通常有两到三根粗树突，表面覆盖着复杂的棘（棘状赘生物）。电子显微镜显示，这些棘接受来自苔藓纤维的多个不对称接触。这些细胞发出的轴突在齿状分子层的内三分之一形成了一条强烈的钙视网膜蛋白免疫反应性带。这种免疫反应性在齿状回的背腹长度上同样密集，表明位于腹侧水平的钙视网膜蛋白免疫反应性苔藓细胞的轴突广泛发散，能够支配齿状回的远处区域。超微结构检查显示，钙视网膜蛋白免疫反应性终扣主要在棘上形成不对称突触接触，偶尔也在颗粒细胞的树突干上形成，并且在分子层内侧占不对称突触的大多数。将逆行示踪剂麦胚凝集素 - 金注射到齿状回表明，集中在腹侧门区的钙视网膜蛋白免疫反应性苔藓细胞大量投射到对侧齿状回的背侧和腹侧。一小部分逆行标记的细胞显示对神经肽Y或生长抑素的免疫反应性。如果腹侧门区的苔藓细胞大部分输入来自腹侧颗粒细胞，那么可以预期腹侧颗粒细胞在同步活动模式中比背侧颗粒细胞更有效地募集大量颗粒细胞。源自腹侧齿状回颗粒细胞的自发活动可以通过苔藓细胞背腹发散和对侧投射的轴突在双侧齿状回的背腹长度上传播。这种组织方式可能解释了为什么腹侧齿状回经常参与病理现象。
