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

学习到的信息在哪里以及如何在大脑中作为记忆痕迹在物理上表现出来的问题，是神经科学中最热门的研究课题之一。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，因为介导联想气味学习的神经元及其连接性得到了很好的描述。利用钙离子成像，我们可以证明，在联想学习过程中，Kenyon细胞的轴突连接子变得独立调制，这意味着这些连接子代表着共同处理和存储学习信息的功能单位。这就提出了一个问题，是什么分子机制将神经元信号，如钙离子和cAMP，限制在轴突上。我们建议使用微观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记来定位cAMP合成腺苷环化酶rutabaga、cAMP降解磷酸二酯酶Dunce和钙清除泵PMCA在轴突Kenyon细胞胞核内。其次，我们将使用体内功能性钙离子和单个Kenyon细胞轴突周围的cAMP成像来确定它们的时空动态，它们在学习中诱导的变化，以及下调Rutabaga、Dunce和PMCA的影响。第三，我们将研究跨突触轴突的可塑性如何调节复杂形式的联想学习。总体而言，该项目旨在揭示轴突如何独立运作，以及它们如何集体获取和存储学习到的信息。

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.