An Ultrastructural Study of the Thalamic Input to Layer 4 of Primary Motor and Primary Somatosensory Cortex in the Mouse
An Ultrastructural Study of the Thalamic Input to Layer 4 of Primary Motor and Primary Somatosensory Cortex in the Mouse
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DOI：
10.1523/jneurosci.2557-16.2017
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发表时间：
2017-03-01
影响因子：
5.3
通讯作者：
Schuhknecht, Gregor F. P.
中科院分区：
文献类型：
--
作者：
Bopp, Rita;Holler-Rickauer, Simone;Schuhknecht, Gregor F. P.
初级运动皮质(M1)作为无颗粒区的传统分类最近受到了挑战，因为在M1中发现了功能层4(L4)。L4是丘脑在感觉区域输入的主要靶点，这提出了一个问题，即小鼠M1区的丘脑皮质突触与邻近感觉皮质(S1)的突触相比是如何形成的。我们通过对囊泡谷氨酸转运蛋白2(VGluT2)的免疫反应性来识别丘脑突起，并从电子显微镜中进行无偏向的折射物计数。我们发现，与S1相比，丘脑对M1中L4局部回路的突触数量的贡献比例只有一半。此外，M1中的丘脑突起仅针对刺状树突，而与9%的突触类似，S1中的突触与光滑神经元的树突形成。M1的VGluT2(+)突触较小，平均每头形成的突触数比S1少(1.3vs2.1vs2.1)，但M1的VGluT2(+)突触大于s1(突触后致密面积中位数分别为0.064微米(2)和0.042微米(2))。在M1和S1中，丘脑突触仅占L4中所有不对称突触的一小部分(分别为12.1%和17.2%)。丘脑传入M1的L4的功能作用在很大程度上被忽略了，但我们的数据表明，与S1一样，丘脑的输入被L4回路的经常性兴奋性连接放大。丘脑缺乏对M1抑制性神经元的直接输入，可能表明M1和S1的L4抑制性门控在时间上存在差异。
The traditional classification of primary motor cortex (M1) as an agranular area has been challenged recently when a functional layer 4 (L4) was reported in M1. L4 is the principal target for thalamic input in sensory areas, which raises the question of how thalamocortical synapses formed in M1 in the mouse compare with those in neighboring sensory cortex (S1). We identified thalamic boutons by their immunoreactivity for the vesicular glutamate transporter 2 (VGluT2) and performed unbiased disector counts from electron micrographs. We discovered that the thalamus contributed proportionately only half as many synapses to the local circuitry of L4 in M1 compared with S1. Furthermore, thalamic boutons in M1 targeted spiny dendrites exclusively, whereas similar to 9% of synapses were formed with dendrites of smooth neurons in S1. VGluT2(+) boutons in M1 were smaller and formed fewer synapses per bouton on average (1.3 vs 2.1) than those in S1, but VGluT2(+) synapses in M1 were larger than in S1 (median postsynaptic density areas of 0.064 mu m(2) vs 0.042 mu m(2)). In M1 and S1, thalamic synapses formed only a small fraction (12.1% and 17.2%, respectively) of all of the asymmetric synapses in L4. The functional role of the thalamic input to L4 in M1 has largely been neglected, but our data suggest that, as in S1, the thalamic input is amplified by the recurrent excitatory connections of the L4 circuits. The lack of direct thalamic input to inhibitory neurons in M1 may indicate temporal differences in the inhibitory gating in L4 of M1 versus S1.