Anterolateral Motor Cortex Connects with a Medial Subdivision of Ventromedial Thalamus through Cell Type-Specific Circuits, Forming an Excitatory Thalamo-Cortico-Thalamic Loop via Layer 1 Apical Tuft Dendrites of Layer 5B Pyramidal Tract Type Neurons
Anterolateral Motor Cortex Connects with a Medial Subdivision of Ventromedial Thalamus through Cell Type-Specific Circuits, Forming an Excitatory Thalamo-Cortico-Thalamic Loop via Layer 1 Apical Tuft Dendrites of Layer 5B Pyramidal Tract Type Neurons
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DOI：
10.1523/jneurosci.1333-18.2018
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发表时间：
2018-10-10
影响因子：
5.3
通讯作者：
Shepherd, Gordon M. G.
中科院分区：
文献类型：
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作者：
Guo, KuangHua;Yamawaki, Naoki;Shepherd, Gordon M. G.
前外侧运动皮层（ALM）和腹内侧（VM）丘脑在功能上是相连的，以支持运动规划期间的持续活动。我们在小鼠（雌性/雄性）中使用光遗传学和电生理学分析了潜在的突触互连。在皮层，来自VM丘脑的丘脑皮质（TC）轴突兴奋ALM 5 B层的VM投射锥体束（PT）神经元。这些轴突也强烈地激发第2/3层神经元（其强烈地激发PT神经元，如前所示），但不激发第6层中的VM投射皮质丘脑（CT）神经元。VM -> PT回路中最强的连接定位于PT神经元的顶簇树突，在第1层。阻断超极化激活的环核苷酸门控（HCN）通道后，这些簇输入选择性增强。在丘脑中，来自ALM PT神经元的轴突兴奋位于VM内侧的ALM投射VM神经元。这些轴突向内侧背核的神经元提供弱的输入，而向丘脑GABA能网状核的神经元或向VM投射到初级运动皮层（M1）的神经元提供很少或没有输入。相反，MI PT轴突兴奋MI -但不是ALM-投射VM神经元。我们的发现表明，首先，一组细胞类型特异性连接形成一个兴奋性丘脑-皮质-丘脑回路的ALM VM通信和电路水平的基板，用于支持在这个系统中的混响活动。第二，这个循环的一个关键特征是顶树突上的I层突触的显著参与，顶树突是具有不同信号传导特性的亚细胞区室，包括HCN介导的增益控制。第三，ALM VM环路与VM的M1相关回路的分离为运动系统中的平行通路组织的概念增加了细胞水平的支持。
The anterolateral motor cortex (ALM) and ventral medial (VM) thalamus are functionally linked to support persistent activity during motor planning. We analyzed the underlying synaptic interconnections using optogenetics and electrophysiology in mice (female/male). In cortex, thalamocortical (TC) axons from VM thalamus excited VM-projecting pyramidal tract (PT) neurons in layer 5B of ALM. These axons also strongly excited layer 2/3 neurons (which strongly excite PT neurons, as previously shown) but not VM-projecting corticothalamic (CT) neurons in layer 6. The strongest connections in the VM -> PT circuit were localized to apical tuft dendrites of PT neurons, in layer 1. These tuft inputs were selectively augmented after blocking hyperpolarization-activated cyclic nucleotide-gated (HCN) channels. In thalamus, axons from ALM PT neurons excited ALM-projecting VM neurons, located medially in VM. These axons provided weak input to neurons in mediodorsal nucleus, and little or no input either to neurons in the GABAergic reticular thalamic nucleus or to neurons in VM projecting to primary motor cortex (M1). Conversely, MI PT axons excited MI - but not ALM-projecting VM neurons. Our fmdings indicate, first, a set of cell type-specific connections forming an excitatory thalamo-cortico-thalamic loop for ALM VM communication and a circuit-level substrate for supporting reverberant activity in this system. Second, a key feature of this loop is the prominent involvement of layer I synapses onto apical dendrites, a subcellular compartment with distinct signaling properties, including HCN-mediated gain control. Third, the segregation of the ALM VM loop from M1-related circuits of VM adds cellular-level support for the concept of parallel pathway organization in the motor system.