Over the last years, the amphipod crustacean Parhyale hawaiensis has developed into an attractive marine animal model for evolutionary developmental studies that offers several advantages over existing experimental organisms. It is easy to rear in laboratory conditions with embryos available year-round and amenable to numerous kinds of embryological and functional genetic manipulations. However, beyond these developmental and genetic analyses, research on the architecture of its nervous system is fragmentary. In order to provide a first neuroanatomical atlas of the brain, we investigated P. hawaiensis using immunohistochemical labelings combined with laser-scanning microscopy, X-ray microcomputed tomography, histological sectioning and 3D reconstructions. As in most amphipod crustaceans, the brain is dorsally bent out of the body axis with downward oriented lateral hemispheres of the protocerebrum. It comprises almost all prominent neuropils that are part of the suggested ground pattern of malacostracan crustaceans (except the lobula plate and projection neuron tract neuropil). Beyond a general uniformity of these neuropils, the brain of P. hawaiensis is characterized by an elaborated central complex and a modified lamina (first order visual neuropil), which displays a chambered appearance. In the light of a recent analysis on photoreceptor projections in P. hawaiensis, the observed architecture of the lamina corresponds to specialized photoreceptor terminals. Furthermore, in contrast to previous descriptions of amphipod brains, we suggest the presence of a poorly differentiated hemiellipsoid body and an inner chiasm and critically discuss these aspects. Despite a general uniformity of amphipod brains, there is also a certain degree of variability in architecture and size of different neuropils, reflecting various ecologies and life styles of different species. In contrast to other amphipods, the brain of P. hawaiensis does not display any striking modifications or bias towards processing one particular sensory modality. Thus, we conclude that this brain represents a common type of an amphipod brain. Considering various established protocols for analyzing and manipulating P. hawaiensis, this organism is a suitable model to gain deeper understanding of brain anatomy e.g. by using connectome approaches, and this study can serve as first solid basis for following studies.

中文翻译：

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“amphi”——端足类动物的大脑：Parhyale hawaiensis 神经解剖学的新见解（Dana，1853）


在过去的几年里，片脚类甲壳类动物Parhyale hawaiensis已经发展成为一种有吸引力的海洋动物模型，可用于进化发育研究，与现有的实验生物相比具有多种优势。它很容易在实验室条件下培育，胚胎全年可用，并且适合多种胚胎学和功能遗传操作。然而，除了这些发育和遗传分析之外，对其神经系统结构的研究还很零散。为了提供第一个大脑神经解剖图谱，我们使用免疫组织化学标记结合激光扫描显微镜、X 射线微计算机断层扫描、组织学切片和 3D 重建来研究夏威夷 P. hawaiensis。与大多数片脚类甲壳类动物一样，大脑向背侧弯曲，偏离身体轴线，原大脑的外侧半球向下。它包括几乎所有突出的神经纤维网，这些神经纤维网是建议的软甲壳类甲壳类动物基本模式的一部分（除了小叶板和投射神经元束神经纤维网）。除了这些神经纤维网的总体一致性之外，夏威夷 P. hawaiensis 的大脑还具有复杂的中央复合体和修饰的薄片（一级视觉神经纤维），显示出有腔室的外观。根据最近对夏威夷 P. hawaiensis 光感受器投影的分析，观察到的叶片结构对应于专门的光感受器终端。此外，与之前对片脚类大脑的描述相反，我们建议存在分化差的半椭圆体和内部交叉，并批判性地讨论这些方面。 尽管片脚类动物的大脑总体上是一致的，但不同神经细胞的结构和大小也存在一定程度的差异，反映了不同物种的不同生态和生活方式。与其他片脚类动物相比，夏威夷对虾的大脑没有表现出任何显着的改变或偏向于处理一种特定的感觉方式。因此，我们得出结论，这个大脑代表了一种常见的端足类大脑类型。考虑到分析和操作夏威夷 P. hawaiensis 的各种已建立的协议，该生物体是一个合适的模型，可以通过使用连接组方法来更深入地了解大脑解剖学，并且这项研究可以作为后续研究的第一个坚实基础。