Visualizing subcellular modules for learning and memory: Axonal bouton-like specializations in Kenyon cells as functional units

学习信息在哪里以及如何在大脑中以记忆痕迹的形式表现出来，是神经科学中研究最深入的话题之一。昆虫大脑的蘑菇体代表了一个独特的模型系统来解决这个问题，因为神经元介导的联想气味学习，以及它们的连接，被很好地描述。使用Ca2+成像，我们可以证明，凯尼恩细胞的轴突终扣成为独立调制的过程中的联想学习，暗示这些终扣代表的功能单位，集体处理和存储的学习信息。这就提出了一个问题，即分子机制限制神经元信号，如Ca 2+和cAMP，轴突终扣。我们建议使用显微镜方法在亚细胞水平上分析这一点。首先，我们将使用高分辨率STED显微镜结合蛋白质标签定位cAMP合成腺苷酸环化酶rutabaga，cAMP降解磷酸二酯酶dunce，和Ca2+去除泵PMCA轴突凯尼恩细胞扣。第二，我们将使用功能性体内Ca2+和cAMP成像在轴突终扣的个别凯尼恩细胞，以确定其时空动态，他们的学习诱导的变化，以及如何这是受影响的下调芜菁甘蓝，dunce和PMCA。第三，我们将研究突触轴突终扣的可塑性如何介导复杂形式的联想学习。总的来说，该项目旨在揭示轴突终扣如何独立行动，以及它们如何集体获取和存储学习信息。

The question where and how learned information is physically manifested in the brain as memory traces is one of the most intensely studied topics in the neurosciences. The mushroom body of the insect brain represents a unique model system to address this question because neurons mediating associative odor learning, and their connectivity, are well described. Using Ca2+ imaging we could demonstrate that axonal boutons of Kenyon cells become independently modulated in the course of associative learning, implicating that these boutons represent functional units that collectively process and store learned information. This poses the question which molecular machineries confine neuronal signals, such as Ca2+ and cAMP, to axonal boutons. We propose to analyze this at the sub-cellular level using microscopic approaches. First, we will use high-resolution STED microcopy in combination with protein tagging to localize the cAMP-synthesizing adenylate cyclase rutabaga, the cAMP-degrading phosphodiesterase dunce, and the Ca2+-removing pump PMCA within axonal Kenyon cell boutons. Second, we will use functional in vivo Ca2+ and cAMP-imaging in axonal boutons of individual Kenyon cells to determine their spatio-temporal dynamics, their learning-induced change, and how this is affected by downregulating rutabaga, dunce and PMCA. Third, we will study how plasticity across synaptic axonal boutons mediates complex forms of associative learning. Overall, the project aims at uncovering how axonal boutons can act independently, and how they collectively acquire and store learned information.