A study of target recognition and axon branching m hanisms in the thalamomrocalpmjection

在哺乳动物大脑的丘脑皮质（TC）投影是一个很好的表征系统的层流特异性的新皮层电路。为了了解层特异性TC轴突靶向的机制，在体外培养技术中研究了发育中的皮层上层表达的细胞外分子和细胞表面分子的作用。结果表明，多个上层分子协同作用产生靶层TC轴突的停止行为。在丘脑和皮层的器官型共培养中也研究了TC轴突分支的活性依赖性。体外培养第2周，丘脑和皮质细胞自发放电增加，TC轴突分支以添加和消除的方式动态形成。药物阻断放电或突触活动可减少重塑过程，特别是靶层中的分支增加。综上所述，这些发现表明TC轴突的靶向机制涉及多个层特异性分子的调控以及通过神经活动对分子机制的修饰。

The thalamocortical (TC) projection in the mammalian brain is a well characterized system in terms of laminar specificity of neocortical circuits. To understand the mechanisms that underlie lamina-specific TC axon targeting, the role of extracellular and cell surface molecules which are expressed in the upper layers of the developing cortex was studied in vitro culture techniques. The result demonstrated that multiple upper layer molecules cooperated to produce stop behavior of TC axons in the target layer. Activity dependency of TC axon branching was also investigated in organotypic cocultures of the thalamus and cortex. TC axon branches were formed dynamically by addition and elimination during the second week in vitro, when spontaneous firing increased in thalamic and cortical cells. Pharmacological blockade of firing or synaptic activity reduced the remodeling process, in particular, branch addition in the target layer. Together, these findings suggest that TC axon targeting mechanisms involve the regulation with multiple lamina-specific molecules and modification of the molecular mechanisms via neural activity.