Collaborative Research: Higher-order processing in a peripheral neural structure of a nudibranch mollusc

在神经科学和更广泛的生物学中，普遍原则是通过比较各种不同的生物体来确定的。神经科学的一个原则是，高阶计算是由中枢神经系统(CNS)的神经回路执行的，而不是由外周神经系统(PNS)执行的。然而，这可能并不适用于所有类型的动物。这个项目研究软体动物的嗅觉处理回路是否在三叉神经节而不是中枢神经中发现，就像在脊椎动物和昆虫等其他动物门中一样。该项目使用裸枝软体动物Berghia stephanieae，这是一种有魅力的实验室培育物种，是许多其他神经科学实验室物种的廉价替代品，从而增加了学生进行研究的机会。像其他腹足软体动物一样，Berghia在其中枢神经系统中有巨大的、可单独识别的神经元。然而，像它的远亲章鱼一样，它的三叉神经节中也有更多的小神经元，其中包括外周神经节和亚上皮下神经元。偏向中心论使研究人员偏向于认为大脑比外围设备更重要。然而，这可能并不适用于所有类型的神经系统。确定软体动物的外周系统在多大程度上执行被认为是为大脑保留的计算，可能会改变我们对大脑实际构成的看法。该项目的目标是阐明外周鼻孔复合体的神经结构和功能，该复合体由鼻孔、用于远程化学接收的背侧头部附件以及相关的鼻孔神经节组成。将使用连接学和转录学的方法来确定鼻孔复合体中是否存在类似于脊椎动物嗅球和昆虫触角叶中的嗅球的肾小球。它有三个目标：1)将使用机器学习算法从体积连续的电子显微镜图像中构建鼻浮体神经节的连接体，以确定它所包含的神经回路基元。机器学习算法对Berghia超微结构特征的定制将促进其他软体动物的连接学研究。2)将汇编一份神经元类型的图谱，其中将包括鼻孔复合体中的神经元和向其输入的神经元。通过单细胞RNA测序确定的神经基因表达将使用原位杂交链式反应(HCR)、免疫组织化学(IHC)和轴突追踪来定位。一个门户网站将提供对带注释的连接体和神经元图谱的访问，使研究人员和学生能够探索Berghia的基因、神经元和神经电路。3)将利用伯吉亚的再生能力，通过行为分析和选择性损伤来探索鼻浮体复合体在导航行为中的作用。使用Berghia开发的实验室课程将允许本科生使用HCR和IHC标记神经元并为其成像，并使用自动跟踪进行行为实验。这将使学生能够与实验室研究人员的发现并行地发现和测试关于神经元和神经回路的假设。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

In neuroscience and in biology more broadly, universal principles are determined by comparing a wide variety of different organisms. A tenet of neuroscience is that higher-order computations are performed by neural circuits in the central nervous system (CNS), not the peripheral nervous system (PNS). However, this might not be universally true for all types of animals. This project examines whether olfactory processing circuitry in a mollusc is found in the PNS rather than the CNS, as it is in other animal phyla such as vertebrates and insects. The project uses the nudibranch mollusc, Berghia stephanieae, which is a charismatic lab-grown species that is an inexpensive alternative to many other neuroscience laboratory species, thereby increasing access to research for students. Berghia, like other gastropod molluscs has large, individually identifiable neurons in its CNS. However, like its distant cousin, the octopus, far more small neurons are located in its PNS, which contains peripheral ganglia and sub-epithelial neurons. Anthro¬po¬centricism has biased researchers to believe that the brain is more important than the periphery. However, this might not be true for all types of nervous systems. Determining the extent to which peripheral systems in molluscs perform computations that were thought to be reserved for the brain could transform our view of what actually constitutes a brain.The goal of the project is to elucidate the neural architecture and function of the peripheral rhinophore complex, which consists of the rhinophore, a dorsal cephalic appendage used for distance chemoreception, and the associated rhinophore ganglion. A connectomics and transcriptomics approach will be used to determine whether there are glomeruli in the rhinophore complex that are organized like olfactory glomeruli in the olfactory bulb of vertebrates and the antennal lobe of insects. There are three objectives: 1) A connectome of the rhinophore ganglion will be constructed from volume serial electron microscopic images using machine-learning algorithms to determine the neural circuit motifs that it contains. Customization of machine-learning algorithms to the ultrastructural features of Berghia will facilitate connectomics research in other molluscs. 2) An atlas of neuronal types will be assembled, which will include neurons in the rhinophore complex and neurons that input to it. Neural gene expression, determined from single cell RNA sequencing, will be mapped using in situ hybridization chain reaction (HCR), immunohistochemistry (IHC), and axon tracing. A web portal will provide access to the annotated connectome and neuronal atlas, allowing researchers and students to explore genes, neurons, and neural circuitry in Berghia. 3) The role of the rhinophore complex in navigational behavior will be explored with behavioral assays and selective lesions, taking advantage of Berghia’s regenerative abilities. Laboratory courses developed using Berghia will allow undergraduate students to label and image neurons with HCR and IHC and perform behavioral experiments with automated tracking. This will enable students to make discoveries and test hypotheses regarding neurons and neural circuits in parallel to the discoveries made by laboratory researchers.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.