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）是其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，例如定位食物来源（例如，合适的植物）和可能鉴定产卵（产卵）的理想场所。虽然相当多的研究集中在如何获得有关CO2的感觉信息，但对中枢神经系统（CNS）如何处理这些信息知之甚少。为了解决这一问题，本项目将利用一种在实验上有利的、经过广泛研究的食草昆虫模式蛾-天蛾，使用本实验室已经开发和实践的方法。导致这个项目的试点研究表明，一组特殊的感觉感受器细胞，位于感觉器官（唇须坑器官，LPO）中，位于成年蛾的每个唇须（口器）的深内陷中，专门用于检测和定量评估该器官周围空气中的CO2。解剖学证据表明，虽然LPO受体细胞位于该口器中，但它们将轴突发送到昆虫大脑中的触角叶（AL），即类似于脊椎动物嗅球的初级嗅觉中心。此外，我们的初步工作清楚地表明，在AL中的一些中央神经元接收和处理突触输入，因此有关CO2的信息，从LPO受体细胞。因此，该项目的重点是记录由LPO受体细胞和AL中接收来自LPO感觉细胞的输入的响应神经元产生的电信号（关于CO2的编码感觉信息）。此外，这些AL神经元的形态进行了研究，通过细胞内染色，以揭示类型和模式的分支的神经元有助于处理的CO2信息。这项研究是第一次研究环境CO2信息的中央处理，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。CO2、温度和湿度是昆虫重要的环境变量，这三种刺激的感觉系统具有某些生理特性。因此，CO2信息的处理可能与温度和/或湿度信息的处理有共同之处，因此大脑中信息处理的一般原理可以从拟议的项目中出现。这些研究预计将导致了解有关环境CO2的信息是如何首先在昆虫大脑的AL中处理的。烟草天蛾是一种很好的实验动物，因为它：（a）具有高度发达的CO2检测器官;（B）体型大，因此是神经生理学研究的理想动物，易于在实验室饲养，有利于分子、生理和生物水平的实验;（c）已经产生了关于昆虫嗅觉的神经生物学和气味引导行为的神经行为学的大量信息，其中大部分是通过本实验室以前的研究完成的;和（d）是一种农业害虫，尽管在经济上不是很重要，但表现出与重要的食草害虫相似的行为和感觉机制。因此，该项目的发现，补充了该实验室正在进行的其他研究，将有利于正在进行的基础研究，旨在了解神经系统如何分析，识别和响应气味，也应该产生的见解，将是有用的农业竞技场设计新的策略，保护作物免受昆虫捕食。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助理（主要研究者）的研究培训，并涉及一名或多名本科生的研究。

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.