Staiger Jochen F, Sachkova Alexandra, Möck Martin, Guy Julien, Witte Mirko
Institute for Neuroanatomy, Universitätsmedizin Göttingen, Georg-August-Universität Göttingen, Göttingen, Germany.
Front Neuroanat. 2022 Oct 28;16:1000107. doi: 10.3389/fnana.2022.1000107. eCollection 2022.
Reelin is a large extracellular glycoprotein that is secreted by Cajal-Retzius cells during embryonic development to regulate neuronal migration and cell proliferation but it also seems to regulate ion channel distribution and synaptic vesicle release properties of excitatory neurons well into adulthood. Mouse mutants with a compromised reelin signaling cascade show a highly disorganized neocortex but the basic connectional features of the displaced excitatory principal cells seem to be relatively intact. Very little is known, however, about the intrinsic electrophysiological and morphological properties of individual cells in the reeler cortex. Repetitive burst-spiking (RB) is a unique property of large, thick-tufted pyramidal cells of wild-type layer Vb exclusively, which project to several subcortical targets. In addition, they are known to possess sparse but far-reaching intracortical recurrent collaterals. Here, we compared the electrophysiological properties and morphological features of neurons in the reeler primary somatosensory cortex with those of wild-type controls. Whereas in wild-type mice, RB pyramidal cells were only detected in layer Vb, and the vast majority of reeler RB pyramidal cells were found in the superficial third of the cortical depth. There were no obvious differences in the intrinsic electrophysiological properties and basic morphological features (such as soma size or the number of dendrites) were also well preserved. However, the spatial orientation of the entire dendritic tree was highly variable in the reeler neocortex, whereas it was completely stereotyped in wild-type mice. It seems that basic quantitative features of layer Vb-fated RB pyramidal cells are well conserved in the highly disorganized mutant neocortex, whereas qualitative morphological features vary, possibly to properly orient toward the appropriate input pathways, which are known to show an atypical oblique path through the reeler cortex. The oblique dendritic orientation thus presumably reflects a re-orientation of dendritic input domains toward spatially highly disorganized afferent projections.
Reelin是一种大型细胞外糖蛋白，在胚胎发育过程中由Cajal-Retzius细胞分泌，以调节神经元迁移和细胞增殖，但在成年后它似乎也能调节兴奋性神经元的离子通道分布和突触小泡释放特性。Reelin信号级联受损的小鼠突变体表现出高度紊乱的新皮层，但移位的兴奋性主细胞的基本连接特征似乎相对完整。然而，关于Reeler皮层中单个细胞的内在电生理和形态学特性，我们所知甚少。重复爆发式放电（RB）是野生型Vb层大型、厚簇状锥体细胞独有的特性，这些细胞投射到几个皮层下靶点。此外，它们还具有稀疏但延伸范围广的皮层内回返侧支。在这里，我们比较了Reeler初级体感皮层中神经元与野生型对照神经元的电生理特性和形态特征。在野生型小鼠中，RB锥体细胞仅在Vb层被检测到，而在Reeler小鼠中，绝大多数RB锥体细胞位于皮层深度的浅三分之一处。内在电生理特性没有明显差异，基本形态特征（如胞体大小或树突数量）也保存良好。然而，在Reeler新皮层中，整个树突树的空间取向高度可变，而在野生型小鼠中则完全是刻板的。似乎Vb层注定要成为RB锥体细胞的基本定量特征在高度紊乱的突变新皮层中保存良好，而定性形态特征则有所不同，可能是为了正确地朝向适当的输入通路，已知这些通路在Reeler皮层中呈现非典型的斜向路径。因此，倾斜的树突取向大概反映了树突输入域向空间高度紊乱的传入投射的重新定向。
