Sensory Processing of Environmental -CO2 Information in the Insect Brain

大多数生物体呼吸产生的二氧化碳是其气味的基本成分。许多昆虫可以感觉到它们周围空气中二氧化碳的浓度，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(例如适当的植物)，以及可能确定产卵的合适地点。虽然相当多的研究集中在关于二氧化碳的感觉信息是如何获得的，但对这些信息在中枢神经系统(CNS)中是如何处理的知之甚少。为了解决这一问题，该项目将利用实验上有利的和广泛研究的食草性昆虫模型--六色飞蛾，利用本实验室已经开发和实践的方法。导致这一项目的初步研究表明，位于成虫每个唇瓣(口部)深凹陷的感觉器官(唇瓣凹陷器官，LPO)中的一组感觉感受器细胞，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受体细胞位于口部，但它们将轴突发送到昆虫大脑中的触角叶(AL)，触角叶是类似于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，AL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，从而处理有关二氧化碳的信息。因此，该项目的中心是记录由LPO受体细胞和AL中的反应神经元产生的电信号(关于二氧化碳的编码感觉信息)，这些神经元从LPO感觉细胞接收输入。此外，用细胞内染色的方法研究了这些AL神经元的形态，以揭示参与CO_2信息处理的神经元的分支类型和模式。这项研究是对环境二氧化碳信息的中央处理的第一次研究，它有望极大地增加我们对昆虫中枢嗅觉机制的理解。二氧化碳、温度和湿度是昆虫重要的环境变量，对这三种刺激的感觉系统具有一定的生理特性。因此，二氧化碳信息的处理可能与温度和/或湿度信息的处理有共同之处，从而可以从拟议的项目中得出大脑信息处理的一般原理。这些研究有望引导人们理解有关环境二氧化碳的信息最初是如何在昆虫大脑的AL中处理的。六叶树是这项研究的优秀实验动物，因为它：(A)具有高度发达的二氧化碳探测器官；(B)体型大，因此非常适合进行神经生理学研究，易于在实验室饲养，有利于在分子、生理和生物水平上进行实验；(C)已获得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丰富信息，其中大部分是通过本实验室以前进行的研究；以及(D)是一种农业害虫，虽然在经济上不是非常重要，但表现出与重要的草食性害虫相似的行为和感觉机制。因此，该项目的发现，作为该实验室正在进行的其他研究的补充，将有助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，并将产生在农业领域有用的见解，以设计保护作物免受昆虫捕食的新策略。最后，除了对农业的科学影响和潜在益处外，该项目还将有助于博士后助理(主要研究人员)的研究培训，并使一名或多名本科生参与研究方面的工作。

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.