Wernitznig Stefan, Rind Frances Claire, Pölt Peter, Zankel Armin, Pritz Elisabeth, Kolb Dagmar, Bock Elisabeth, Leitinger Gerd
Institute of Cell Biology, Histology and Embryology, Research Unit Electron Microscopic Techniques, Medical University of Graz, 8010, Graz, Austria.
J Comp Neurol. 2015 Feb 1;523(2):298-312. doi: 10.1002/cne.23682. Epub 2014 Oct 25.
The small size of some insects, and the crystalline regularity of their eyes, have made them ideal for large-scale reconstructions of visual circuits. In phylogenetically recent muscomorph flies, like Drosophila, precisely coordinated output to different motion-processing pathways is delivered by photoreceptors (R cells), targeting four different postsynaptic cells at each synapse (tetrad). Tetrads were linked to the evolution of aerial agility. To reconstruct circuits for vision in the larger brain of a locust, a phylogenetically old, flying insect, we adapted serial block-face scanning electron microscopy (SBEM). Locust lamina monopolar cells, L1 and L2, were the main targets of the R cell pathway, L1 and L2 each fed a different circuit, only L1 providing feedback onto R cells. Unexpectedly, 40% of all locust R cell synapses onto both L1 and L2 were tetrads, revealing the emergence of tetrads in an arthropod group present 200 million years before muscomorph flies appeared, coinciding with the early evolution of flight.
一些昆虫体型微小，且眼睛具有晶体状的规则结构，这使得它们成为大规模重建视觉回路的理想选择。在系统发育较近的蝇类（如果蝇）中，光感受器（R细胞）向不同的运动处理通路传递精确协调的输出，每个突触（四联突触）针对四个不同的突触后细胞。四联突触与空中敏捷性的进化有关。为了重建蝗虫（一种系统发育古老的飞行昆虫）较大大脑中的视觉回路，我们采用了连续块面扫描电子显微镜（SBEM）技术。蝗虫的板层单极细胞L1和L2是R细胞通路的主要靶点，L1和L2各自为不同的回路提供输入，只有L1向R细胞提供反馈。出乎意料的是，蝗虫所有R细胞与L1和L2形成的突触中，40%是四联突触，这表明四联突触在蝇类出现前两亿年的一个节肢动物类群中就已出现，与飞行的早期进化相吻合。
