Sensory Processing of Environmental -CO2 Information in the Insect Brain

大多数生物呼吸产生的二氧化碳（CO2）是它们气味的基本组成部分。许多昆虫可以感知周围空气中的二氧化碳浓度，它们被认为在重要任务中使用这些信息，如寻找食物来源（例如，合适的植物）和可能确定理想的产卵地点（产卵）。尽管大量的研究都集中在二氧化碳的感觉信息是如何获得的，但对于中枢神经系统（CNS）如何处理这些信息却知之甚少。为了解决这一问题，本项目将利用一种实验上有利且被广泛研究的模式食植物昆虫——Manduca sexta，使用本实验室已经开发和实践的方法。导致这个项目的初步研究表明，一组特殊的感觉受体细胞位于一个感觉器官（唇-触须窝器官，LPO），它位于成年蛾的每个唇触须（口器）的深凹处，专门用于检测和定量评估该器官周围空气中的二氧化碳。解剖学证据表明，尽管LPO受体细胞位于该口器，但它们将轴突发送到触角叶（AL），这是昆虫大脑中类似脊椎动物嗅球的初级嗅觉中心。此外，我们的试点工作清楚地表明，人工神经中的一些中枢神经元接收和处理来自LPO受体细胞的突触输入，从而接收有关二氧化碳的信息。因此，该项目的重点是记录由LPO受体细胞和人工智能中接收LPO感觉细胞输入的响应神经元产生的电信号（关于二氧化碳的编码感觉信息）。此外，通过细胞内染色研究这些AL神经元的形态，以揭示参与CO2信息处理的神经元分支的类型和模式。这项研究是首次对环境二氧化碳信息的中央处理进行研究，它有望大大增加我们对昆虫中枢神经系统嗅觉机制的理解。二氧化碳、温度和湿度对昆虫来说是重要的环境变量，这三种刺激的感觉系统具有一定的生理特性。因此，对二氧化碳信息的处理可能与对温度和/或湿度信息的处理有一些共同之处，因此，大脑中信息处理的一般原则可能会从拟议的项目中出现。这些研究预计将有助于了解有关环境二氧化碳的信息是如何在昆虫大脑的AL中首先处理的。对于这项研究来说，淫蛛是一种很好的实验动物，因为它：(a)拥有高度发达的二氧化碳探测器官；(b)体积大，因此是神经生理学研究的理想选择，易于在实验室中饲养，并且有利于在分子，生理和有机体水平上进行实验；(c)在昆虫嗅觉的神经生物学和气味引导行为的神经行为学方面获得了丰富的信息，其中大部分是通过本实验室先前的研究获得的；(d)是一种农业害虫，虽然在经济上不是很重要，但其行为和感觉机制与重要的草食性害虫相似。因此，这个项目的发现，补充了实验室正在进行的其他研究，将有利于正在进行的旨在了解神经系统如何分析、识别和响应气味的基础研究，也应该在农业领域为设计保护作物免受昆虫捕食的新策略提供有用的见解。最后，除了其科学影响和对农业的潜在利益外，该项目还将有助于博士后（关键研究者）的研究培训，并使一名或多名本科生参与研究的各个方面。

The carbon dioxide (CO2) produced by the respiration of most organisms is a fundamental constituent of their odor. Many insects can sense the concentration of CO2 in the air around them, and they are thought to use that information in vital tasks such as locating food sources (e.g., appropriate plants) and possibly identifying desirable sites for oviposition (egg laying). Whereas considerable research has focused on how the sensory information about CO2 is acquired, little is known about how that information is processed in the central nervous system (CNS). In order to address this issue, this project will take advantage of an experimentally favorable and extensively studied model plant-eating insect, the moth Manduca sexta, using methods already developed and in practice in this laboratory. Pilot studies that led to this project suggested that a particular group of sensory receptor cells, situated in a sensory organ (the labial-palp pit organ, LPO) recessed in a deep invagination on each labial palp (a mouthpart) of the adult moth, are specialized to detect and quantitatively assess CO2 in the air around that organ. Anatomical evidence shows that although the LPO receptor cells are located in that mouthpart, they send their axons to the antennal lobe (AL), the primary-olfactory center resembling the vertebrate olfactory bulb, in the insect's brain. Furthermore, our pilot work clearly shows that some of the central neurons in the AL receive and process synaptic inputs, and thus information about CO2, from the LPO receptor cells. Thus, the project centers on recording of the electrical signals (coded sensory information about CO2) generated by LPO receptor cells and the responding neurons in the AL that receive inputs from the LPO sensory cells. In addition, the morphology of those AL neurons is studied by means of intracellular staining in order to reveal the types and patterns of branching of neurons contributing to processing of CO2 information. This research is the first study of central processing of environmental-CO2 information, and it promises to add significantly to our understanding of CNS olfactory mechanisms in insects. CO2, temperature, and humidity are environmental variables of importance to insects, and the sensory systems for those three kinds of stimuli share certain physiological properties. Therefore it may be that the processing of CO2 information has aspects in common with the processing of information about temperature and/or humidity, such that general principles of information processing in the brain could emerge from the proposed project. These studies are expected to lead to understanding of how information about environmental CO2 is first processed in the AL of the insect brain. Manduca sexta is an excellent experimental animal for this research because it: (a) possesses a highly developed CO2-detecting organ; (b) is large and hence ideal for neurophysiological studies, easily reared in the laboratory, and favorable for experimentation at the molecular, physiological, and organismal levels; (c) has yielded a wealth of information about the neurobiology of insect olfaction and the neuroethology of odor-guided behavior, much of it through previous research done in this laboratory; and (d) is an agricultural pest which, although not very important economically, exhibits behavior and sensory mechanisms that are similar to those of important, herbivorous pest insects. Thus, the findings from this project, complementing other research under way in this laboratory, will benefit ongoing basic research aimed at understanding how nervous systems analyze, recognize, and respond to odors, and should also yield insights that will be useful in the agricultural arena for designing new strategies for protection of crop plants from insect predation. Finally, in addition to its scientific impact and potential benefit to agriculture, this project will contribute to the research training of a postdoctoral associate (the key investigator) and also involve one or more undergraduate students in aspects of the studies.