Lack of Molecular-Anatomical Evidence for GABAergic Influence on Axon Initial Segment of Cerebellar Purkinje Cells by the Pinceau Formation
Lack of Molecular-Anatomical Evidence for GABAergic Influence on Axon Initial Segment of Cerebellar Purkinje Cells by the Pinceau Formation
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DOI：
10.1523/jneurosci.1651-12.2012
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发表时间：
2012-07-04
影响因子：
5.3
通讯作者：
Watanabe, Masahiko
中科院分区：
文献类型：
--
作者：
Iwakura, Atsushi;Uchigashima, Motokazu;Watanabe, Masahiko
小脑浦肯野细胞(PC)的轴突起始段(AIS)被称为Pinceau结构的GABA能篮子细胞(BCS)的分支轴突所包围。这种独特的结构被认为是一种通过电和/或GABA能抑制来调制PC输出的装置。丰富的钾通道、不存在钠通道以及BC轴突之间发育的隔膜状连接支持电抑制。然而，GABA能抑制的神经化学基础还没有得到很好的研究。在这里，我们使用C56BL/6小鼠解决了这个问题。首先，我们证实了之前的观察结果，即典型的突触接触是罕见的，仅限于轴突近端，其余部分大多被星形细胞突起覆盖。然后，我们检测了GABA合成酶谷氨酸脱羧酶(GAD)、囊泡GABA转运体囊泡抑制性氨基酸转运体(VIAAT)、Cytomatrix活动区蛋白基管、GABA受体GABA(A)Rα1和细胞黏附分子Neu-linin-2等参与GABA能信号转导的分子的表达。这些分子被招募来在周边体BC-PC突触以及沿着海马和新皮质锥体细胞的AIS形成功能组装。GAD和VIAAT免疫金标记物在Pinceau结构中的标记比在骨周BC终末低5倍，并且没有向AIS聚集。此外，巴松管、神经连接素-2和GABA(A)Rα1在Ankyrin-G阳性的AIS上没有形成可检测到的簇。这些发现表明，在Pinceau结构中，GABA能信号机制组织松散，甚至不完全。总之，BCS似乎没有对AIS施加GABA能突触抑制，尽管针状结构的作用模式仍有待探索。
The axon initial segment (AIS) of cerebellar Purkinje cells (PCs) is embraced by ramified axons of GABAergic basket cells (BCs) called the pinceau formation. This unique structure has been assumed to be a device for the modulation of PC outputs through electrical and/or GABAergic inhibition. Electrical inhibition is supported by enriched potassium channels, absence of sodium channels, and developed septate-like junctions between BC axons. The neurochemical basis for GABAergic inhibition, however, has not been well investigated. Here we addressed this issue using C56BL/6 mice. First, we confirmed previous observations that typical synaptic contacts were rare and confined to proximal axonal portions, with the remaining portions being mostly covered by astrocytic processes. Then we examined the expression of molecules involved in GABAergic signaling, including GABA synthetic enzyme glutamic acid decarboxylase (GAD), vesicular GABA transporter vesicular inhibitory amino acid transporter (VIAAT), cytomatrix active zone protein bassoon, GABA receptor GABA(A)R alpha 1, and cell adhesion molecule neuroligin-2. These molecules were recruited to form a functional assembly at perisomatic BC-PC synapses and along the AIS of hippocampal and neocortical pyramidal cells. GAD and VIAAT immunogold labeling was five times lower in the pinceau formation compared with perisomatic BC terminals and showed no accumulation toward the AIS. Moreover, bassoon, neuroligin-2, and GABA(A)R alpha 1 formed no detectable clusters along the ankyrin-G-positive AIS proper. These findings indicate that GABAergic signaling machinery is organized loosely and even incompletely in the pinceau formation. Together, BCs do not appear to exert GABAergic synaptic inhibition on the AIS, although the mode of action of the pinceau formation remains to be explored.