David Henry Gire, Ph.D. - US grants

[unreadable] DESCRIPTION (provided by applicant): Project Summary The main goal of the studies within this application is to define the role that a specific class of GABAergic neurons, called periglomerular (PG) cells, has in mediating information transfer in the olfactory bulb. The main hypothesis to be tested is that PG cells, through a feed-forward inhibitory mechanism onto output mitral cells, function to gate signals of different strengths, favoring strong signals over weak signals. Such a mechanism may be functionally important for enhancing differences between closely related odors. Each aim of this application will test a specific hypothesis that follows from this mechanism. The first aim will examine the general response profile of mitral cells, testing the specific hypothesis that "modules" of mitral cells engage in all-or-none responses to sensory input that occur simultaneously throughout the modular network. The second aim will then test the hypothesis that PG cells gate the generation of these mitral cell network responses. Experiments in aims 1 and 2 will primarily be done using electrophysiological techniques combined with pharmacological manipulations in rat in vitro olfactory bulb slices. The 3rd aim will test exactly how PG cells modulate mitral cell network responses, testing the specific hypothesis that PG cells inhibit mitral cells through a feed-forward mechanism. This hypothesis will be tested using calcium imaging of PG cells and electrophysiological recording of mitral cells in rat olfactory bulb slices. Taken together, the studies within this application will establish a role for PG cells in regulating information transfer through the first central relay of the olfactory system, the olfactory bulb. Relevance The studies described within this application will define mechanisms that inhibitory interneurons use to influence the excitability of neuronal circuits. Throughout the brain, dysfunction of this type of inhibition can lead to human disorders, perhaps the most notable being epilepsy. These studies will thus provide information that will aide in the understanding and treatment of neurological disorders, in addition to basic information about sensory processing. [unreadable] [unreadable] [unreadable] [unreadable]

DESCRIPTION (provided by applicant): A chief goal of sensory neuroscience is to understand how neural activity forms perception and guides behavior in awake, behaving subjects. A main component of sensory processing in awake animals involves the filtering of sensory information based upon behavioral context. The first goal of this proposal is to use neural recordings from the olfactory bulbs of awake, behaving mice to ascertain the degree of behavioral filtering present in the early stages of the olfactory system. The second goal is to examine the roles that feedback centrifugal projections from the cortex play in controlling this filtering. The second goal will be achieved using viral transduction of light-activated proteins to selectively block feedback from the olfactory (piriform) cortex during olfactory-based behaviors in mice. The olfactory system has been chosen for these studies based upon its clear ethological relevance for mice, as well as its well-defined corticofugal feedback from the piriform cortex to the olfactory bulb. Since these olfactory feedback projections resemble cortico-thalamic feedback seen in other sensory systems, our studies will be applicable to general mechanisms of sensory filtering across modalities, and will have particular relevance to disorders that impact sensory filtering, such as schizophrenia and autism spectrum disorders. PUBLIC HEALTH RELEVANCE: The studies within this proposal will investigate the role that behavioral context plays in sensory filtering, as well as possible neural mechanisms through which this filtering occurs. These studies will have applicability to psychiatric disorders that involve deficits in sensory filtering, such as schizophrenia and autism spectrum disorders.

DESCRIPTION (provided by applicant): One of the primary functions of the brain is to integrate and process sensory input into a form that can guide the behavior of an animal within its environment. Combining sensory information in such a way that the source of a given stimulus can be located is a key aspect of this function. I propose to study the integration and processing of bilateral sensory information as it applies to odor localization in mice. Mice are macrosmotic creatures, and employ their sense of smell to detect conspecifics, food, and predators at a distance. Odor source localization is thus a vital ability for mice. Despite its ethological importance, the neural mechanisms that support odor localization are largely unknown. Research in this proposal will focus upon a cortical structure, the anterior olfactory nucleus (AON), which has been hypothesized to play a central role in odor localization by processing bilateral olfactory information and transmitting this information across the two hemispheres of the brain. First, work performed during the mentored phase will define a functional role for inter-hemispheric feedback projections from the AON to earlier olfactory structures. This will be accomplished by both monitoring the odor responses of these neurons and controlling their activity during odor localization tasks. Selective monitoring of AON feedback projections will be accomplished through cutting edge multiphoton imaging techniques, and the role of these neurons in odor localization will be directly tested using optogenetic strategies. Training in these two techniques will greatly contribute to the experimental repertoire of the candidate. After obtaining this information, work during the independent phase will employ these techniques to elucidate the mechanisms through which bilateral input is processed in the AON, focusing upon the role of inhibitory neurons. Taken together, the results of these studies will define how feedback from the cortex and local cortical inhibitory processing work together to combine bilateral sensory information in such a way that the source of an odor can be identified. By defining the mechanisms used to integrate sensory information in support of an ethologically relevant function, this work will provide a firm basis fr the general understanding of information processing within neural circuits as it occurs during natural sensory-driven behavior. Defining such fundamental mechanisms of neural circuit processing will be instrumental for the understanding and treatment of disorders that alter sensory integration, such as schizophrenia and autism spectrum disorders. Candidate's immediate and long-term career goals The candidate, Dr. David Gire, has experience with research in the olfactory system at both the circuit and systems level, providing a solid background in the methods and concepts related to this proposal. The long term goal of Dr. Gire's career is to define the neural circuit mechanisms used by animals as they process odor cues to obtain information about their environment. To conduct this work, in addition to his current experience, Dr.Gire will need to obtain training in techniques that will allow him to study neural circuit dynamics with high specificity and resolution while these circuits are used to process sensory information in awake, behaving animals. The research training provided in this proposal will involve methods designed to monitor and control specific neural circuit elements in behaving animals. These techniques include multi-photon imaging, head-restrained behavior, precise odor stimulation, and optogenetics. Combined training in these techniques will provide the final set of tools necessary for Dr. Gire to begin an independent research career with a focus upon neural circuit operation in awake, behaving animals. Key elements of the research career development plan The research described in the mentored phase of this proposal will be carried out in the laboratory of Dr. Venkatesh Murthy at Harvard University. The Murthy lab has demonstrated excellence in key areas of the proposal, including multiphoton imaging and optogenetic investigation of the olfactory system. The candidate has also assembled an Advisory Committee to support the successful completion of the training and research in this proposal. This committee includes Drs. Ed Boyden (MIT), Naoshige Uchida (Harvard), and Rachel Wilson (Harvard Medical School). Each committee member will provide specific research expertise and training to the candidate, including direct training in each of the committee members' laboratories. While in the mentored phase, the candidate will meet frequently with his mentor and committee in order to ensure progress with regard to both the research goals of the proposal as well as the candidate's advancement towards becoming an independent investigator. As the candidate begins his independent career, his Advisory Committee will continue to offer support and advice regarding early career issues, which will further support the transition of the candidate to independence.

PROJECT SUMMARY While the existence of multiple memory systems in the brain is generally accepted, it is not known how these different systems interact to result in continuously adaptive memory-guided behaviors and decisions. Recent results clearly show that particular combinations of memory-related brain systems show synchronized neural activity (at the population level, for example at the theta frequency) in a task-dependent way. Yet the informational and behavioral significance of such co-modulation of neural activity in not known perhaps in part because such measures are not temporally or informationally refine enough to reveal the significance of this interaction. This proposal aims to develop a novel paradigm for determining whether a specific type of information in one brain area can provide a signal to a connected memory structure to engage or disengage in its well-known memory-related function. Specifically, Aim 1 will test the causal relationship between neural signatures of planned behaviors in hippocampus and the regulation of working memory/action selection by the medial prefrontal cortex. Also, the subsequent impact of this neural directive on future action selection, as well as on future hippocampal place field integrity, will be examined. It is postulated that prefrontal cortex normally stabilizes place fields which in turn should enable rats to more quickly adapt to changing task conditions. Disruption of such prefrontal function, especially during the operation of working memory, should destabilize place fields and EEG phenomena that rely on fully function place fields. In addition, impaired choice accuracy is predicted. Aim 2 proposes to build on the exciting idea that hippocampal theta oscillates between periods of memory encoding and memory retrieval. The same open loop system that was developed in Aim 1 will be used to disrupt selectively working memory encoding or retrieval functions of the medial prefrontal cortex when encoding or retrieval are detected in hippocampus. The general prediction is that disrupting encoding in the prefrontal cortex will disproportionately impair the initial learning behavioral and neural processes relative to behavioral and neural processes that go on after learning has taken place. The combined results will provide new insight into the informational nature of communication between hippocampus and the prefrontal cortex. Also the closed loop paradigm can serve as an innovative and new model for studying the functional interactions between other memory and behavioral systems of the brain, which in turn can have tremendous clinical and therapeutic benefits. It may be possible to interfere with (in cases of unwanted specific associations) or facilitate (in cases of deficient desired associations) specific types of learning or learned associations that characterize a number of mental disorders.

PROJECT SUMMARY When searching for resources such as food animals accumulate information over time. How this is accomplished by the olfactory system is largely unknown due to two constraints. First, the sensory cues used for odor-guided searches (odor plumes) are notoriously complex and unable to be completely predicted by computational models. Second, the current technology for detecting odor plumes is too large to use with freely moving animals. These limitations mean that our understanding of how animals search with odors, an ability seen across numerous diverse species, is still in its infancy. This is especially true for mice, animals that are one of the major biomedical model species and that rely on odors to find food. This proposal will use new head-mounted odor sensors to accurately detect odor plume encounters by mice while they are using these sensory cues to search. We will combine these sensors with Neuropixels probes to record from hundreds of neurons simultaneously and chart the flow of information through the olfactory system and to cortical decision- making structures. Specifically, we will test the relationship between neural signatures of odor encounters in the olfactory cortex and the guidance of search behavior by the orbitofrontal cortex. We will assess how information is transmitted between these two connected structures as well as how the orbitofrontal cortex accumulates odor evidence. These goals will be accomplished by training mice to find the source of a volatile organic compound, ethanol, which will be detected by miniature sensors that we have altered to become fast response and head-mountable. While animals search for the source of this odor, the sensor will transmit any contact that they make with the odor plume. We will then reconstruct the information obtained by the animal during its search to ascertain how this information guides decisions. Using Neuropixels probes we will extend this analysis into the large-scale neural circuits that support this complex behavior. By recording neural activity simultaneously in the olfactory and orbitofrontal cortices we will test how odor information is routed from sensory to decision-making areas under multiple odor-guided search conditions. These conditions will include searches in complex environments with background odors. We will functionally test this circuit by targeted optogenetic inactivation of the feedback pathway from the oribitofrontal cortex to the olfactory cortex. We will measure the impact of this inactivation both behaviorally and neurophysiologically and quantify changes in odor information in both structures. We postulate that orbitofrontal cortex will accumulate information during odor-guided search and that feedback from the orbitofrontal to the olfactory cortex will suppress background odor input, enhancing search effectiveness. The successful development of this paradigm can serve as an innovative new model for studying the interactions between sensory and decision-making systems of the brain, enhancing understanding of how the brain accumulates information from complex sensory signals.

PROJECT SUMMARY All animals use sensory cues to find their way through complex environments and locate vital resources such as food or mates. From simple organisms such as worms finding nutrient-rich soil at centimeter-scale distances to polar bears following their noses across kilometers to feed upon seal carcasses, the ability to navigate an environment using odors is one of the most evolutionarily ancient and widespread examples of this complex behavior. Interest in the ability to navigate with odors has spanned decades and resulted in numerous models suggesting how animals can accomplish this feat. Testing these models is extremely difficult because in nearly all terrestrial environments odors are transported as fluctuating plumes by turbulent air flow. This necessitates either the use of simplifying models for odor flow or complex three-dimensional computational fluid dynamics simulations. In both cases, only statistical connections can be made between the performance of a simulated searcher and the behavior and neural processing of an animal. This limitation rules out the ability to combine moment-to-moment neural recordings with the sensory input guiding an animal?s behavior. This proposal represents a cross-disciplinary effort between experts in fluid dynamics, olfactory systems neuroscience, and neurophysiology to directly establish the algorithms used for odor-guided navigation and the neural implementation of these algorithms in the early olfactory system of mice. We will use newly developed, miniature odor sensors to record odor plumes at the mouse nose during odor-guided navigation. By combining these sensor readings with computational models of odor flow we will directly test the behavioral algorithms used by mice to navigate with odor plumes. To establish the neural implementation of these algorithms we will perform large-scale neural imaging and electrophysiology recordings from the early olfactory system while monitoring odor plume input at the nose. We will also use viral labeling techniques to selectively record neural activity from cells that send output to specific downstream cortical structures. By recording neural activity from olfactory bulb cells with specific cortical targets we will test how odor information is routed from sensory to decision-making areas to support odor-guided navigation. Finally, we will combine these levels of analysis to generate a complete model of odor-guided navigation that connects behavioral algorithms to neural implementation.