Neocortical inhibitory terminals innervate dendritic spines targeted by thalamocortical afferents
Neocortical inhibitory terminals innervate dendritic spines targeted by thalamocortical afferents
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DOI：
10.1523/jneurosci.3846-06.2007
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发表时间：
2007-01-31
影响因子：
5.3
通讯作者：
Kawaguchi, Yasuo
中科院分区：
文献类型：
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作者：
Kubota, Yoshiyuki;Hatada, Sayuri;Kawaguchi, Yasuo
皮层的快速抑制主要发生在gaba能突触上，这些突触是由局部中间神经元形成的，连接到突触后目标。虽然gaba能输入到新皮质锥体神经元的躯体和轴突初始段与动作电位产生的直接抑制有关，但gaba能输入到远端树突节段（包括脊柱）的作用尚未得到很好的表征。由于抑制输入的很大一部分发生在远端树突和棘上，因此确定这些gaba能突触是否由某些类型的突触前细胞选择性地形成于特定的突触后元件将是很重要的。通过电镜观察不同亚型非锥体细胞形成的突触，我们发现惊人的大比例（33.4 +/- 9.3%）的末端形成对称突触连接到皮质棘的一个子集上，而皮质棘主要由一个不对称的末端共同神经支配。利用谷氨酸囊泡转运蛋白VGLUT1和VGLUT2异构体免疫组化，我们发现双神经支配的脊髓选择性地接受表达VGLUT2的丘脑皮质传入信号，但几乎不接受表达VGLUT1的皮质内输入信号。通过比较差异神经支配的脊髓体积及其突触连接区，我们发现vglut2阳性末梢神经支配的脊髓体积明显大于vglut1阳性末梢神经支配的脊髓体积，并且这些脊髓的突触比vglut1阳性传入神经支配的脊髓体积更大，穿孔次数更多。这些结果表明，锥体细胞棘的抑制性输入可能优先减少丘脑皮质突触传递，而不是皮质内突触传递，因此定位于选择性地阻断皮质外信息。
Fast inhibition in the cortex is gated primarily at GABAergic synapses formed by local interneurons onto postsynaptic targets. Although GABAergic inputs to the somata and axon initial segments of neocortical pyramidal neurons are associated with direct inhibition of action potential generation, the role of GABAergic inputs to distal dendritic segments, including spines, is less well characterized. Because a significant proportion of inhibitory input occurs on distal dendrites and spines, it will be important to determine whether these GABAergic synapses are formed selectively by certain classes of presynaptic cells onto specific postsynaptic elements. By electron microscopic observations of synapses formed by different subtypes of nonpyramidal cells, we found that a surprisingly large fraction (33.4 +/- 9.3%) of terminals formed symmetrical synaptic junctions onto a subset of cortical spines that were mostly coinnervated by an asymmetrical terminal. Using VGLUT1 and VGLUT2 isoform of the glutamate vesicular transporter immunohistochemistry, we found that the double-innervated spines selectively received thalamocortical afferents expressing the VGLUT2 but almost never intracortical inputs expressing the VGLUT1. When comparing the volumes of differentially innervated spines and their synaptic junction areas, we found that spines innervated by VGLUT2-positive terminal were significantly larger than spines innervated by VGLUT1-positive terminal and that these spines had larger, and more often perforated, synapses than those of spines innervated by VGLUT1-positive afferent. These results demonstrate that inhibitory inputs to pyramidal cell spines may preferentially reduce thalamocortical rather than intracortical synaptic transmission and are therefore positioned to selectively gate extracortical information.