Synaptic Circuit Organization of Motor Corticothalamic Neurons
Synaptic Circuit Organization of Motor Corticothalamic Neurons
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DOI：
10.1523/jneurosci.4023-14.2015
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发表时间：
2015-02
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影响因子：
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通讯作者：
N. Yamawaki;G. Shepherd
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作者：
N. Yamawaki;G. Shepherd
皮质丘脑（CT）神经元在第6层构成了一个大的，但神秘的皮质投射神经元类。它们是如何整合到皮质内和丘脑-皮质-丘脑回路中的还不完全清楚，特别是在感觉皮质之外。在这里，我们研究了CT电路在小鼠前肢运动皮层（M1）使用多种电路分析方法。从CT，端脑内（IT）和锥体束（PT）投射神经元刺激和记录，我们发现了强CT参与CT和CT参与IT连接;然而，CT→IT连接仅限于第6层的IT神经元，而不是5 B。CT参与性兴奋性连接非常少。在这些通路中，双突触抑制系统地伴随着兴奋，根据突触前（类特异性）和突触后（细胞-细胞）因素，兴奋的幅度按比例缩放。特别是，CT神经元诱发比例更多的抑制相对于兴奋（I/E比）比IT神经元。此外，抑制的幅度被调整到与单个神经元水平的兴奋量相匹配;在极端情况下，没有接受兴奋的神经元也没有受到抑制。扩展这些研究，解剖皮质和丘脑之间的连接，我们发现，M1-CT神经元和丘脑皮质神经元的腹外侧（VL）核显着不连接在任何方向。相反，皮质中的VL轴突兴奋IT和PT神经元，丘脑中的CT轴突兴奋其他丘脑神经元，包括后核中的神经元，这些神经元还接受PT兴奋。这些研究结果，在几个方面与以前的观察在感觉区，照亮了M1内的CT神经元的基本电路组织和M1和丘脑之间。
Corticothalamic (CT) neurons in layer 6 constitute a large but enigmatic class of cortical projection neurons. How they are integrated into intracortical and thalamo-cortico-thalamic circuits is incompletely understood, especially outside of sensory cortex. Here, we investigated CT circuits in mouse forelimb motor cortex (M1) using multiple circuit-analysis methods. Stimulating and recording from CT, intratelencephalic (IT), and pyramidal tract (PT) projection neurons, we found strong CT↔ CT and CT↔ IT connections; however, CT→IT connections were limited to IT neurons in layer 6, not 5B. There was strikingly little CT↔ PT excitatory connectivity. Disynaptic inhibition systematically accompanied excitation in these pathways, scaling with the amplitude of excitation according to both presynaptic (class-specific) and postsynaptic (cell-by-cell) factors. In particular, CT neurons evoked proportionally more inhibition relative to excitation (I/E ratio) than IT neurons. Furthermore, the amplitude of inhibition was tuned to match the amount of excitation at the level of individual neurons; in the extreme, neurons receiving no excitation received no inhibition either. Extending these studies to dissect the connectivity between cortex and thalamus, we found that M1-CT neurons and thalamocortical neurons in the ventrolateral (VL) nucleus were remarkably unconnected in either direction. Instead, VL axons in the cortex excited both IT and PT neurons, and CT axons in the thalamus excited other thalamic neurons, including those in the posterior nucleus, which additionally received PT excitation. These findings, which contrast in several ways with previous observations in sensory areas, illuminate the basic circuit organization of CT neurons within M1 and between M1 and thalamus.