The neuronal architecture of the mushroom body provides a logic for associative learning.
The neuronal architecture of the mushroom body provides a logic for associative learning.
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DOI：
10.7554/elife.04577
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发表时间：
2014-12-23
期刊：
影响因子：
7.7
通讯作者：
Rubin GM
中科院分区：
文献类型：
--
作者：
Aso Y;Hattori D;Yu Y;Johnston RM;Iyer NA;Ngo TT;Dionne H;Abbott LF;Axel R;Tanimoto H;Rubin GM
我们确定了组成果蝇蘑菇体（MB）的神经元，无脊椎动物大脑中的一个联想中心，并提供了一个全面的地图，描述他们的潜在连接。21 MB输出神经元（MBON）类型中的每一种都沿着2000个Kenyon细胞的平行轴突详细阐述了分离的树突状乔木，形成了15个隔室，共同平铺MB叶。MBON轴突投射到MB外部的五个离散神经柱，并且三种MBON类型在叶中形成前馈网络。20种多巴胺能神经元（DAN）类型中的每一种将轴突投射到一个或至多两个MBON隔室。DAN轴突在区室化的凯尼恩细胞-MBON突触上的会聚创建了一个高度有序的单位，可以支持学习对感觉表征施加效价。MB的神经元的补充的阐明提供了一个全面的解剖基板，从中可以推断出联想嗅觉学习和记忆的功能逻辑。DOI：http://dx.doi.org/10.7554/eLife.04577.001神经科学的关键目标之一是了解脑细胞的特定回路如何使动物对周围不断变化的世界做出最佳反应。这样的过程在简单的大脑中更容易研究，果蝇体积小，生命周期短，基因工具箱发达，被广泛用于研究基因和神经回路，这些都是学习和行为的基础。果蝇可以学会接近以前与食物配对的气味，也可以避免任何与电击配对的气味，大脑中称为蘑菇体的部分在这个过程中起着核心作用。当气味分子与苍蝇触角上的受体结合时，它们会激活大脑触角叶中的神经元，进而激活蘑菇体内的凯尼恩细胞。然后，凯尼恩细胞激活输出神经元，将信号传递到大脑的其他部分。已知相对较少的凯尼恩细胞被任何给定的气味激活。此外，似乎一种特定的气味会激活不同果蝇体内不同的凯尼恩细胞。由于气味和它激活的凯尼恩细胞之间的联系对每只苍蝇来说都是独一无二的，每只苍蝇都需要通过自己的经验来学习凯尼恩细胞激活的特定模式意味着什么。阿索等人现在已经将复杂的分子遗传学和解剖学技术应用于数千种不同的转基因果蝇，以识别蘑菇体的神经元。由此产生的地图显示，蘑菇体包含大约2200个神经元，包括7种类型的凯尼恩细胞和21种类型的输出细胞，以及20种使用神经递质多巴胺的神经元。此外，该地图提供了对支持基于气味的学习的电路的见解。例如，它揭示了蘑菇体可以分为15个解剖学隔室，每个隔室由一组特定的输出和多巴胺能神经元细胞类型的存在来定义。由于多巴胺能神经元有助于塑造苍蝇的气味反应的基础上，以前的经验，这种组织表明，这些隔间可能是半自主的信息处理单元。与昆虫大脑的其他部分相比，蘑菇体具有类似于哺乳动物大脑的灵活组织。因此，阐明果蝇中支持联想学习的回路应该可以更容易地识别脊椎动物中的等效机制。DOI：http://dx.doi.org/10.7554/eLife.04577.002网站
We identified the neurons comprising the Drosophila mushroom body (MB), an associative center in invertebrate brains, and provide a comprehensive map describing their potential connections. Each of the 21 MB output neuron (MBON) types elaborates segregated dendritic arbors along the parallel axons of ∼2000 Kenyon cells, forming 15 compartments that collectively tile the MB lobes. MBON axons project to five discrete neuropils outside of the MB and three MBON types form a feedforward network in the lobes. Each of the 20 dopaminergic neuron (DAN) types projects axons to one, or at most two, of the MBON compartments. Convergence of DAN axons on compartmentalized Kenyon cell–MBON synapses creates a highly ordered unit that can support learning to impose valence on sensory representations. The elucidation of the complement of neurons of the MB provides a comprehensive anatomical substrate from which one can infer a functional logic of associative olfactory learning and memory. DOI: http://dx.doi.org/10.7554/eLife.04577.001 One of the key goals of neuroscience is to understand how specific circuits of brain cells enable animals to respond optimally to the constantly changing world around them. Such processes are more easily studied in simpler brains, and the fruit fly—with its small size, short life cycle, and well-developed genetic toolkit—is widely used to study the genes and circuits that underlie learning and behavior. Fruit flies can learn to approach odors that have previously been paired with food, and also to avoid any odors that have been paired with an electric shock, and a part of the brain called the mushroom body has a central role in this process. When odorant molecules bind to receptors on the fly's antennae, they activate neurons in the antennal lobe of the brain, which in turn activate cells called Kenyon cells within the mushroom body. The Kenyon cells then activate output neurons that convey signals to other parts of the brain. It is known that relatively few Kenyon cells are activated by any given odor. Moreover, it seems that a given odor activates different sets of Kenyon cells in different flies. Because the association between an odor and the Kenyon cells it activates is unique to each fly, each fly needs to learn through its own experiences what a particular pattern of Kenyon cell activation means. Aso et al. have now applied sophisticated molecular genetic and anatomical techniques to thousands of different transgenic flies to identify the neurons of the mushroom body. The resulting map reveals that the mushroom body contains roughly 2200 neurons, including seven types of Kenyon cells and 21 types of output cells, as well as 20 types of neurons that use the neurotransmitter dopamine. Moreover, this map provides insights into the circuits that support odor-based learning. It reveals, for example, that the mushroom body can be divided into 15 anatomical compartments that are each defined by the presence of a specific set of output and dopaminergic neuron cell types. Since the dopaminergic neurons help to shape a fly's response to odors on the basis of previous experience, this organization suggests that these compartments may be semi-autonomous information processing units. In contrast to the rest of the insect brain, the mushroom body has a flexible organization that is similar to that of the mammalian brain. Elucidating the circuits that support associative learning in fruit flies should therefore make it easier to identify the equivalent mechanisms in vertebrate animals. DOI: http://dx.doi.org/10.7554/eLife.04577.002