Despite numerous approaches to the resolution of euarthropod phylogeny, mainly based on modern sequence information and traditional external morphology, the resulting hypotheses are often contradictory and leave many questions about euarthropod evolution unanswered. The comparison of developmental and structural aspects of the nervous system has shown to be a valuable contribution to the assessment of current phylogenetic hypotheses. One promising approach for the generation of new character sets is the morphology of transmitter systems and the discovery of individually identifiable neurons, which allow phylogenetic comparisons on the single cell level. In this context, the serotonin transmitter system has been investigated to a considerable degree. Studies to date have yielded important stimuli to our understanding of euarthropod relationships and the evolution of their nervous systems. However, data on other transmitter systems remain fragmented, and their value with respect to phylogenetic questions remains speculative. The biogenic amine histamine is a promising transmitter; a substantial amount of data has been reported in the literature and the homology of some histaminergic neurons has been suggested. Here, we present a comprehensive review of histaminergic neurons in the ventral nerve cord of Euarthropoda. Using immunocytochemical labeling of histamine combined with confocal laser-scanning microscopy, we investigated the transmitter system in phylogenetically relevant taxa, such as Zygentoma, Remipedia, Diplopoda, and Arachnida. By reconstructing ground patterns, we evaluated the significance of this specific character set for euarthropod phylogeny. With this approach, we identified a set of neurons, which can be considered homologous within the respective major taxon. In conclusion, the histaminergic system contains useful information for our understanding of euarthropod phylogeny, supporting the proposed clades Tetraconata and Mandibulata. Furthermore, this character set has considerable potential to help resolve relationships within the major clades at a deeper level of taxonomy, due to the considerable variability in neurite morphology.

中文翻译：

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腹神经索中的组胺能神经元：评估其对节肢动物系统发育的价值。

尽管主要基于现代序列信息和传统的外部形态学来解决真肢节肢动物系统发育的方法很多，但由此产生的假说常常是矛盾的，并没有回答关于真肢节肢动物进化的许多问题。神经系统发育和结构方面的比较已显示出对评估当前系统发育假说的宝贵贡献。产生新字符集的一种有前途的方法是发射机系统的形态和发现可单独识别的神经元，这使得可以在单细胞水平上进行系统发育比较。在这种情况下，已经对5-羟色胺递质系​​统进行了相当程度的研究。迄今为止的研究对我们了解人肢节肢动物的关系及其神经系统的演变产生了重要的刺激作用。但是，其他发射机系统上的数据仍然是零散的，它们在系统发育问题上的价值仍然是推测性的。生物胺组胺是一种有前途的递质。文献中已经报道了大量数据，并且已经暗示了某些组胺能神经元的同源性。在这里，我们提出了在真肢动物腹神经索中的组胺能神经元的全面综述。使用组胺的免疫细胞化学标记与共聚焦激光扫描显微镜相结合，我们研究了系统发育相关类群（如Zygentoma，Remipedia，Diplopoda和Arachnida）中的递质系统。通过重建地面图案，我们评估了该特定字符集对真人节肢动物系统发育的意义。通过这种方法，我们确定了一组神经元，这些神经元在相应的主要分类单元内可以被认为是同源的。总之，组胺能系统包含有用的信息，有助于我们了解真人节肢动物的系统发育，支持拟议的四足纲（Tetraconata）和下颌纲（Mandibulata）。此外，由于神经突形态的巨大差异，该字符集在更深层次的分类学上具有巨大的潜力，可帮助解决主要进化枝之间的关系。组织胺能系统包含有用的信息，有助于我们了解真人节肢动物的系统发育，支持拟议的四足纲和下颌纲。此外，由于神经突形态的巨大差异，该字符集在更深层次的分类学上具有巨大的潜力，可帮助解决主要进化枝之间的关系。组织胺能系统包含有用的信息，有助于我们了解真人节肢动物的系统发育，支持拟议的四足纲和下颌纲。此外，由于神经突形态的巨大差异，该字符集在更深层次的分类学上具有巨大的潜力，可帮助解决主要进化枝之间的关系。