Organization and somatotopy of corticothalamic projections from L5B in mouse barrel cortex
Organization and somatotopy of corticothalamic projections from L5B in mouse barrel cortex
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DOI：
10.1073/pnas.1704302114
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发表时间：
2017-08
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影响因子：
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通讯作者：
Anton Sumser;Rebecca A. Mease;B. Sakmann;Alexander Groh
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作者：
Anton Sumser;Rebecca A. Mease;B. Sakmann;Alexander Groh
在体感觉系统中，信号以地形方式从外周传感器传递到大脑皮层，这意味着感觉受体的相对空间组织由皮层中的地图表示。由于体感觉皮层不是感觉信号的终端，我们研究了地形图是否通过厚簇层5B （L5B）神经元的皮层输出通路维持在皮层之外。我们发现，体感觉皮层中的L5B神经元以特定区域的投射强度、映射方向和地形精度靶向6个单独的皮质下核。因此，地形组织通过L5B通路在初级皮层之外持续存在，具有特定目标的精度。皮层5B层（L5B）的神经元连接皮层和许多皮层下区域。研究得最好的L5B皮质-皮质下连接可能是啮齿动物桶状皮质（BC）和丘脑后内侧核（POm）中的L5B神经元之间的连接。然而，L5B巨扣在POm和其他皮质下靶点的空间组织尚不清楚，因此尚不清楚这条下行通路是否保留了躯体形态，即体图组织，这是上升体感觉通路的标志。我们通过双色顺行标记研究了BC的下行L5B通路的组织。我们在三维空间中重建并量化了来自BC中相邻L5B柱的钮扣云。L5B细胞作用于中脑前部和丘脑的6个核，包括丘脑后部、中间带和前顶盖。L5B皮层下神经支配在钮扣数量、密度和投射体积方面具有特异性。这里所研究的所有靶核的共同点是维持BC中不同桶柱的投影拓扑，尽管具有特定目标的精度。我们估计低皮质-皮质下收敛和发散，表明L5B皮质丘脑通路是稀疏和高度并行的。最后，钮扣的空间组织和须状图的组织揭示了丘脑后群被细分为四个亚核（前、外侧、内侧和后）。总之，皮质L5B神经元通过稀疏和体位组织的平行通路建立了广泛的皮质-皮质下网络。
Significance In the somatosensory system, signals are transduced from peripheral sensors up to the cerebral cortex in a topographic manner, meaning that the relative spatial organization of the sensory receptors is represented by a map in the cortex. Because the somatosensory cortex is not the terminus of sensory signals, we investigated whether topographic maps are maintained beyond the cortex via cortical output pathways from thick-tufted layer 5B (L5B) neurons. We found that L5B neurons in the somatosensory cortex topographically target six separate subcortical nuclei with area-specific projection strength, map orientation, and topographic precision. Thus topographic organization persists beyond the primary cortex via the L5B pathway with target-specific precision. Neurons in cortical layer 5B (L5B) connect the cortex to numerous subcortical areas. Possibly the best-studied L5B cortico–subcortical connection is that between L5B neurons in the rodent barrel cortex (BC) and the posterior medial nucleus of the thalamus (POm). However, the spatial organization of L5B giant boutons in the POm and other subcortical targets is not known, and therefore it is unclear if this descending pathway retains somatotopy, i.e., body map organization, a hallmark of the ascending somatosensory pathway. We investigated the organization of the descending L5B pathway from the BC by dual-color anterograde labeling. We reconstructed and quantified the bouton clouds originating from adjacent L5B columns in the BC in three dimensions. L5B cells target six nuclei in the anterior midbrain and thalamus, including the posterior thalamus, the zona incerta, and the anterior pretectum. The L5B subcortical innervation is target specific in terms of bouton numbers, density, and projection volume. Common to all target nuclei investigated here is the maintenance of projection topology from different barrel columns in the BC, albeit with target-specific precision. We estimated low cortico–subcortical convergence and divergence, demonstrating that the L5B corticothalamic pathway is sparse and highly parallelized. Finally, the spatial organization of boutons and whisker map organization revealed the subdivision of the posterior group of the thalamus into four subnuclei (anterior, lateral, medial, and posterior). In conclusion, corticofugal L5B neurons establish a widespread cortico–subcortical network via sparse and somatotopically organized parallel pathways.