Michael R. Drew, Ph.D. - US grants

[unreadable] DESCRIPTION (provided by applicant): This training and research award will prepare the candidate for an independent career as a molecular and behavioral neuroscientist using rigorous behavioral testing and genetic manipulations to analyze the brain circuits underlying learning and memory. The candidate is an experimental psychologist with significant experience in the area of animal learning. Training provided under the award take place at Columbia University's Departments of Psychiatry and Neuroscience and will enable the candidate to (1) develop laboratory skills in molecular genetics and quantitative microscopy; (2) expand his knowledge of molecular genetics and translational neuroscience so that he can independently develop novel scientific ideas, integrate his research findings with existing knowledge, and relate them to clinical practice; (3) receive mentorship in professional development; and (4) develop a strong understanding of the ethical issues inherent in the practice of science. The training goals will be accomplished through a program combining practical training, formal mentorship, and consultations with experienced independent researchers, coursework, seminar attendance, and professional scientific meetings. The research supported under the award will elucidate mechanisms through which adult hippocampal neurogenesis contributes to learning and memory. The adult hippocampus retains the ability to generate neurons, and a rapidly growing literature documents that adult-born neurons are functionally significant. The candidate has shown, for instance, that blocking hippocampal neurogenesis using irradiation or an inducible genetic method impairs contextual fear conditioning, a ubiquitous form of learning in which organisms acquire fear of environments that predict harm. Using contextual fear conditioning as a model system, the proposed research will use targeted irradiation and genetic manipulations to analyze how adult-born neurons contribute to acquisition, retention, and retrieval of memories. The proposed research will develop new tools for studying the role of adult-born neurons in learning and behavior, further our understanding of the biology of memory, and may give insight into how alterations in neurogenesis contribute to the etiology or treatment emotional disorders. [unreadable] [unreadable] [unreadable]

Program Director/Principal Investigator (Last, First, Middle): Drew, Michael R. PROJECT SUMMARY The hippocampus is one of a select few brain regions that retain the ability to generate neurons in adulthood. The conservation of adult neurogenesis across mammalian species from mice to humans suggests that neurogenesis contributes to hippocampal function in significant ways. Indeed, research in human patients and animal models suggests that changes in neurogenesis alter memory function and contribute to the etiology and treatment of emotional disorders. If we are to understand how the hippocampus mediates memory, emotion, and disorders thereof, we must understand the role of adult neurogenesis in hippocampal function. The main goal of this project is to identify mechanisms through which adult-born neurons contribute to hippocampal mechanisms of memory. We will focus on one well-studied model of neurogenesis-dependent learning: contextual fear conditioning, a ubiquitous form of learning in which animals acquire fear of a context paired with aversive stimulation. We have shown that arresting adult hippocampal neurogenesis impairs contextual fear conditioning, in that mice without neurogenesis exhibit less learned fear of a shock-paired context. However, the simple observation that arresting adult neurogenesis impairs CFC reveals very little about the role of adult neurogenesis in hippocampal memory mechanisms. Addressing mechanistic questions about the role of neurogenesis in memory processes requires new methods of manipulating neurogenesis with temporal and cellular precision. To this end we developed two new methods of manipulating neurogenesis with high temporal and cellular specificity. One is a novel transgenic mouse that enables reversible ablation of neural progenitor cells. The other is combined transgenic/viral approach that expresses an optogenetic neural silencer in defined cohorts of adult-born neurons. We propose to use these methods to reveal how neurogenesis contributes to underlying memory processes, such as acquisition, systems consolidation, and retrieval. Specifically, we will address these critical questions about the role of young, adult-born neurons in contextual fear memory: (1) Does the role of adult-born neurons in contextual fear conditioning relate to context representation, emotional learning, or expression of these forms of learning? (2) How does addition of neurons to the hippocampus affect maintenance of existing contextual fear memories? (3) What role do adult-born neurons play in long-term retention of the memories they help encode? These studies will elucidate fundamental mechanisms through which adult neurogenesis modulates memory, and, in doing so, will clarify mechanisms through which alterations in neurogenesis contribute to the treatment and etiology of emotional disorders, such as depression and anxiety disorders. 0925-0001/0002 (Rev. 08/12) Page Continuation Format Page

? DESCRIPTION (provided by applicant): A central goal in neuroscience is to identify cellular ensembles supporting mental and behavioral states, but these ensembles cannot be defined a priori. The dentate gyrus (DG), for example, contains more than 1M granule cells, which are essentially indistinguishable from each other, but less than 5% of these seemingly identical neurons are active during any one behavioral event, suggesting that the associated mental states are each mediated by a small subset of neurons. We propose to develop a novel method for identifying and gaining genetic access to such transient, behaviorally-relevant assemblies of neurons in awake animals. The key unique features of our approach are (1) its temporal precision is unprecedented because it is the first neuronal tagging technique that matches the timescale of naturalistic behavior; and (2) its ability to label multiple cell populations in the sme animal enables the comparison of state-specific cell ensembles. Our novel molecular-genetic technique first identifies activated neurons on the basis of elevated intracellular calcium and then tags them using light. Light application is especially attractive because it is temporally precise: just as other optogenetic methods have aided neuronal circuit analysis by approximating the timescale of cell activity, so too will a light-dependent labeling technique illuminate functional cell assemblies. The technique will be entirely virus-based, so it is usable across species without relying on transgenic animals. Under this award we will establish the technique by developing and testing two critical innovations: (1) a synthetic bidirectional promoter system, and (2) caging chemistry for multi-wavelength visible light regulation of promoter function. Ultimately this technique will be used to elucidate the neuronal substrates of diverse mental states, such as fear, hunger, depression, anxiety, and addiction, thereby advancing the exploration of critical brain networks. This high-risk, high-reward project comprises multiple innovative features. Elements of the nascent reporter system described here, such as promoter strength, mechanism for regulating gene expression, choice of activating ligand, caging chemistry, and in vivo ligand and light delivery represent starting point that will benefit from extensive optimization. Once existing reporter components have been sufficiently refined, we envision replacing fluorescent reporters with recombinases, so that actuators can be expressed in identified cells for testing neuronal function. Other features, including the development of novel caged ligands, as well as additional methods for brain-wide activity reporting will also be addressed following achievement of our Aims. Despite the inherent risks, we are confident that our proposed system represents a fundamental and much-needed departure from existing techniques. We believe that our approach will evolve from its present status as a promising endeavor into a widely-used tool with the support of the BRAIN Initiative.

Project Summary/Abstract The hippocampus is one of a select few brain regions that retain the ability to generate neurons in adulthood. Research in human patients and animal models suggests that increases and decreases in neurogenesis alter memory function and contribute to the etiology and treatment of emotional disorders. Despite almost 15 years of research linking adult neurogenesis to memory and emotional regulation, almost nothing is known about the circuit and coding mechanisms through which adult neurogenesis influences these processes. The recent development (with BRAIN Initiative support) of head-mounted minimicroscopes provides an unprecedented opportunity to image activity of adult-born neurons as animals learn and behave. Under this award, we will acquire equipment and training that will enable our lab to sustainably incorporate miniscope imaging into our research program on adult neurogenesis. In addition, we will perform calcium imaging experiments in freely moving mice as they explore contexts and undergo contextual fear conditioning, a model learning paradigm that is sensitive to perturbations of adult neurogenesis. Using optogenetic silencing of adult-born neurons, we will characterize how adult-born neurons influence coding of context memory in dentate gyrus, a region required for context memory. These experiments will provide new and previously unattainable insights into the mechanisms through which adult-born neurons regulate hippocampal memory, and they will enable our lab to integrate miniscope technology in a sustainable way in multiple ongoing research streams.

Project Summary: The primary clinical treatment for maladaptive fear is extinction?repeated exposure to a fearful stimulus in the absence of threat. Extinction does not permanently eliminate maladaptive fear. Extinguished fear resurfaces with the passage of time or if a new trauma is experienced. The transience of extinction suggests that it does not erase learned fear but, instead, establishes a new memory that competes with the fear memory for expression. To understand why fear returns, we must know more about the mechanisms controlling the retrieval or expression of extinction. Here we propose a highly novel approach to elucidate these mechanisms. Our proposal focuses on the dentate gyrus (DG), a region of the hippocampus that plays a critical role in acquisition of context fear memory?fear of a place in which an aversive experience occurred. We recently discovered that DG neural activity is also required for context fear extinction. Under this award, we will use using activity-dependent neural tagging, a technique that allows us to tag (and later manipulate) neural ensembles that are active during a behavioral experience, to investigate how neural ensembles in DG orchestrate the expression of fear and extinction memories. Our central hypothesis is that extinction causes DG to generate a new context representation, and activation of this extinction representation suppresses fear. Consistent with this hypothesis, our preliminary studies indicate (1) that fear learning and fear extinction activate distinct ensembles of ?fear neurons? and ?extinction neurons? in DG in mice, and (2) the activity of these ensembles modulates expression of fear and extinction. The proposed studies will leverage these findings to (1) test the hypothesis that the recovery of fear after extinction reflects changes in the activity of DG fear and extinction ensembles, (2) identify mechanisms through which these ensembles modulate fear, and (3) visualize the processing of fear and extinction memory in real-time using in vivo imaging with head-mounted miniature microscopes. We anticipate that the proposed research will uncover mechanisms controlling the expression of fear and extinction, reveal why fear recovers after extinction, and identify strategies for making extinction more durable.