School of Biological Sciences, University of Utah, Aline Skaggs Wilmot Biology Building, 257 South 1400 East, Salt Lake City, UT 84112, USA; Neuroscience Program, University of Utah, Salt Lake City, UT 84112, USA.
Center for Theoretical Neuroscience, Columbia University, Jerome L Greene Science Center, 3227 Broadway, New York, NY 10027, USA.
Curr Biol. 2022 Sep 26;32(18):4000-4012.e5. doi: 10.1016/j.cub.2022.07.055. Epub 2022 Aug 16.
Associative brain centers, such as the insect mushroom body, need to represent sensory information in an efficient manner. In Drosophila melanogaster, the Kenyon cells of the mushroom body integrate inputs from a random set of olfactory projection neurons, but some projection neurons-namely those activated by a few ethologically meaningful odors-connect to Kenyon cells more frequently than others. This biased and random connectivity pattern is conceivably advantageous, as it enables the mushroom body to represent a large number of odors as unique activity patterns while prioritizing the representation of a few specific odors. How this connectivity pattern is established remains largely unknown. Here, we test whether the mechanisms patterning the connections between Kenyon cells and projection neurons depend on sensory activity or whether they are hardwired. We mapped a large number of mushroom body input connections in partially anosmic flies-flies lacking the obligate odorant co-receptor Orco-and in wild-type flies. Statistical analyses of these datasets reveal that the random and biased connectivity pattern observed between Kenyon cells and projection neurons forms normally in the absence of most olfactory sensory activity. This finding supports the idea that even comparatively subtle, population-level patterns of neuronal connectivity can be encoded by fixed genetic programs and are likely to be the result of evolved prioritization of ecologically and ethologically salient stimuli.
关联脑区，如昆虫的蘑菇体，需要以有效的方式来表示感觉信息。在黑腹果蝇中，蘑菇体的肯尼恩细胞整合来自随机一组嗅觉投射神经元的输入，但一些投射神经元——即那些被少数具有进化意义的气味激活的神经元——比其他神经元更频繁地与肯尼恩细胞连接。这种偏向的随机连接模式是有利的，因为它使蘑菇体能够将大量气味表示为独特的活动模式，同时优先表示少数特定的气味。这种连接模式是如何建立的，在很大程度上仍然未知。在这里，我们测试了连接肯尼恩细胞和投射神经元的机制是否取决于感觉活动，或者它们是否是硬连线的。我们在部分嗅觉缺失的果蝇（缺乏必需的气味共受体 Orco 的果蝇）和野生型果蝇中绘制了大量蘑菇体的输入连接。对这些数据集的统计分析表明，在没有大多数嗅觉感觉活动的情况下，观察到的肯尼恩细胞和投射神经元之间的随机和偏向的连接模式正常形成。这一发现支持了这样一种观点，即即使是相对微妙的神经元连接的群体水平模式也可以由固定的遗传程序来编码，并且可能是对生态和进化有意义的刺激进行优先排序的结果。
