Similar but different: Comparative neuroanatomy of the chemo- and mechanosensory pathways in scorpion pectines

化学感觉是几乎所有生命形式的一种不可或缺的形式。关于节肢动物门，最多样化的动物门，许多代表具有初级化学感受器官-触角I -与第二头节相关。下颚纲（六足纲、甲壳纲和多足纲）的嗅觉通路非常相似，它们的初级嗅觉中心甚至在几个方面类似于脊椎动物的嗅球。剩下的真节肢动物分类群，Chelicerata，不具有专门的化学感觉附属物与第二头节。在蝎子身上观察到一个特别有趣的解决方案来弥补触角的缺乏。这些动物拥有所谓的果胶作为专门的化学感觉附属物，也实现机械感觉功能，就像下颌动物中的天线I一样。有趣的是，栉齿位于身体的腹侧，就在行走腿和生殖器盖的后面。它们是梳状的器官，布满了成千上万的机械和化学感受器，排列在每个牙齿或钉的腹侧。果胶被认为在扫描基板作为接触化学感受器的重要作用。感觉传入纤维投射到中枢神经的许多隔室（小叶到肾小球）。这些区室让人联想到下颌动物嗅觉中心的球状组织。最初的回填实验揭示了PEG感器，这是相当罕见的化学感受系统，虽然通常在mechanosensory neuropils中观察到的躯体定位投影。这就提出了一个问题，如何化学和mechanosensory输入集成在果胶neuropils.The目前的项目着手研究蝎子果胶neuropils和他们的预测详细的神经解剖组织。我们将专注于这一途径的所有组成部分：从外周到中枢神经系统的化学感觉神经元的投射，中枢神经系统中假定肾小球的结构和解剖，局部中间神经元及其神经递质的特征，以及投射神经元与高级脑中心的连接。我们将比较由此产生的数据集的mechanosensory果胶预测，从而表征两种感觉方式的整合模式。发展方面将在所有项目部分中得到解决，重点是感觉结构及其主要投射。这将扩大我们对化学和机械感觉神经柱及其交织组织中潜在功能必要性的理解。

The chemical sense is an integral modality for virtually all forms of life. Regarding Arthropoda, the most diverse animal phylum, many representatives possess primary chemosensory organs – the antennae I - associated with the second head segment. Olfactory pathways of the Mandibulata (Hexapoda, Crustacea, and Myriapoda) are markedly similar, and their primary olfactory centers even resemble vertebrate olfactory bulbs in several respects. The remaining euarthropod taxon, the Chelicerata, do not possess dedicated chemosensory appendages associated with the second head segment. A particularly fascinating solution to compensate the lack of antennae is observed in scorpions. These animals possess so-called pectines as dedicated pairs of chemosensory appendages that also fulfil a mechanosensory function, much like the antenna I in Mandibulata. Intriguingly, the pectines are located on the ventral side of the body, just behind the walking legs and the genital operculum. They are comb-shaped organs studded with many thousands of mechano- and chemosensory sensilla that are arranged on the ventral sides of each tooth, or peg. Pectines have been suggested to play an important role in scanning the substrate as contact chemoreceptive organs. The sensory afferents project into numerous (lobular to glomerular) compartments of the central nervous pectine neuropil. These compartments are reminiscent of the glomerular organization of the olfactory centers in Mandibulata. Initial backfill experiments revealed a somatotopic projection of peg sensilla, which is quite uncommon for chemoreceptive systems, though typically observed in mechanosensory neuropils. This raises the question of how chemo- and mechanosensory inputs are integrated in the pectine neuropils.The present project sets out to investigate the neuroanatomical organization of the scorpion pectine neuropils and their projections in detail. We will focus on all components of this pathway: Projections of chemosensory neurons from the periphery into the CNS, structure and anatomy of putative glomeruli in the central nervous system, characteristics of local interneurons and their neurotransmitters, and connectivity to higher brain centers by projection neurons. We will compare the resulting data set to the mechanosensory pectine projections and thus characterize the mode of integration of the two sensory modalities. Developmental aspects will be addressed in all project parts, focusing on sensory structures and their primary projections. This will expand our understanding of potential functional necessities in the organization of the chemo- and mechanosensory neuropils and their interlacing.