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

哺乳动物大脑中的丘脑皮质(TC)投射是一个具有新皮质环路板层特异性的系统。为了了解板层特异性TC轴突靶向的机制，在体外培养技术中研究了在发育中的皮质上层表达的细胞外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了靶层TC轴突的停止行为。在丘脑和皮质的器官型共培养中，还研究了TC轴突分支的活动依赖性。在体外培养的第二周，丘脑和皮质细胞自发放电增多时，TC轴突分支通过添加和消除动态形成。对放电或突触活动的药物阻断减少了重塑过程，特别是靶层中分支的增加。综上所述，这些发现表明，TC轴突靶向机制涉及多个板层特异性分子的调节和通过神经活动对分子机制的修改。

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.