Synapse-Dependent and Independent Mechanisms of Thalamocortical Axon Branching Are Regulated by Neuronal Activity
Synapse-Dependent and Independent Mechanisms of Thalamocortical Axon Branching Are Regulated by Neuronal Activity
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DOI：
10.1002/dneu.22317
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发表时间：
2016-03-01
影响因子：
3
通讯作者：
Yamamoto, Nobuhiko
中科院分区：
文献类型：
--
作者：
Matsumoto, Naoyuki;Hoshiko, Maki;Yamamoto, Nobuhiko
轴突分支和突触形成是建立精确电路连接的关键过程。这些过程受到神经活动的严格调控，但它们之间的关系在很大程度上仍不清楚。我们使用器官型共培养制剂，以检查突触形成的作用，在活动依赖性轴突分支丘脑皮质（TC）的预测。为了使TC轴突及其突触前位点可视化，将编码DsRed和EGFP标记的突触素（SYP-EGFP）的两种质粒共转染到少量丘脑神经元中。单个TC轴突的延时成像显示，大多数分支出现SYP-EGFP斑点，表明突触形成先于轴突分支的出现。我们还研究了神经元活动对轴突分支和突触形成的影响，通过操纵自发放电活动的丘脑细胞。内向整流钾通道Kir2.1和细菌电压门控钠通道NaChBac分别用于抑制和促进放电活性。我们发现抑制神经活动会减少轴突分支和突触形成。相反，增加神经活动只促进轴突分支的形成。NaChBac表达细胞的延时成像进一步揭示，新的分支经常出现在SYP-EGFP斑点以外的位置，表明增强活性促进轴突分支形成，这是由于在非突触位点出现的分支增加。这些结果表明，突触前位置是分支出现的热点，频繁的放电活动可以将分支出现转变为突触独立的过程。(C)2015 Wiley Periodicals，Inc.
Axon branching and synapse formation are critical processes for establishing precise circuit connectivity. These processes are tightly regulated by neural activity, but the relationship between them remains largely unclear. We use organotypic coculture preparations to examine the role of synapse formation in the activity-dependent axon branching of thalamocortical (TC) projections. To visualize TC axons and their presynaptic sites, two plasmids encoding DsRed and EGFP-tagged synaptophysin (SYP-EGFP) were cotransfected into a small number of thalamic neurons. Time-lapse imaging of individual TC axons showed that most branches emerged from SYP-EGFP puncta, indicating that synapse formation precedes emergences of axonal branches. We also investigated the effects of neuronal activity on axon branching and synapse formation by manipulating spontaneous firing activity of thalamic cells. An inward rectifying potassium channel, Kir2.1, and a bacterial voltage-gated sodium channel, NaChBac, were used to suppress and promote firing activity, respectively. We found suppressing neural activity reduced both axon branching and synapse formation. In contrast, increasing neural activity promoted only axonal branch formation. Time-lapse imaging of NaChBac-expressing cells further revealed that new branches frequently appeared from the locations other than SYP-EGFP puncta, indicating that enhancing activity promotes axonal branch formation due to an increase of branch emergence at nonsynaptic sites. These results suggest that presynaptic locations are hotspots for branch emergence, and that frequent firing activity can shift branch emergence to a synapse-independent process. (C) 2015 Wiley Periodicals, Inc.