Julian P. Meeks, PhD - US grants

[unreadable] DESCRIPTION (provided by applicant): Neuronal excitability and synaptic communication are depressed by mild increases in extracellular K+ ([K+]o). During stroke, brain trauma, and seizures, large [K+]o rises occur, causing neuronal deficits. Under normal and pathophysiological conditions, astrocytes in the CNS assist in buffering [K+]o by passive mechanisms that are not well understood. Inwardly-rectifying K+ channels (KIRs) are thought to be responsible for passive K+ homeostasis, and are expressed by hippocampal astrocytes. This proposal will answer fundamental questions concerning the endogenous function of astrocyte KIRs in the hippocampus. Astrocyte patch-clamp recordings will determine the physiological properties of barium-sensitive stimulus evoked K+ currents. Confocal microscopy and immunocytochemistry will be used to determine the localization of KIRs on hippocampal astrocyte membranes. Patch-clamp recordings from astrocyte somas and processes, along with K+ imaging techniques, will determine the capacity for KIRs to carry localized inward K+ currents in response to neuronal stimulation. These studies will determine the functional relevance of KIRs in hippocampal astrocytes and provide new insight into the role of KIRs in passive [K+]o buffering. [unreadable] [unreadable]

Description (provided by applicant): The vomeronasal or accessory olfactory system (AOS) detects and processes pheromone signaling information from the environment. In mice, pheromonal communication is involved in establishing dominance hierarchies in males, and plays roles in promoting, synchronizing, and maintaining fertility in females. The AOS remains poorly understood compared to other communicative sensory modalities, including olfaction through the main olfactory system. Despite key differences in the neural circuitry, most of our current thinking about the AOS derives from results obtained in the main olfactory system. This research plan is designed to increase our understanding of the first central brain structure in the AOS, the accessory olfactory bulb (AOB). This application focuses on the inhibitory granule cells (GCs), which modulate the principal mitral cells of the AOB through GABAergic dendro-dendritic synapses. There are no current published reports on GC tuning to natural pheromone stimulation, despite evidence for their involvement in lateral inhibition and learning. The first Specific Aim of this application is to determine whether sensory tuning of AOB GCs is broader or sharper than tuning of vomeronasal sensory neurons (VSNs). We will determine tuning by recording action potential responses in each cell type while stimulating with sulfated steroid compounds our lab has shown to activate VSNs. We will make single extracellular electrode recordings from GCs and multi-electrode array recordings from VSNs in acute, ex vivo preparations. The second Specific Aim investigates potential links between GC morphology and physiological function. The specific connectivity patterns between mitral cells and GCs in the AOB are likely to underlie the tuning properties of each cell. We will acquire 3-dimensional morphological information from physiologically- characterized AOB GCs after labeling each recorded cell with a cytoplasmic dye. We will quantify the position, span, and density of the cell processes using fluorescence microscopy. We will use these data to determine whether structural properties correlate with specific tuning qualities of the cells. The proposed studies will fill a substantial gap in our understanding of pheromone communication in vertebrates. Relevance: Mammalian behavior is informed strongly by pheromonal communication, but little is known about how neurons in the pheromone-associated areas of the brain process social cues. This research plan investigates the responsiveness of inhibitory granule neurons in pheromone-associated brain areas in mice in order to fill a substantial gap in our understanding of this sensory pathway.

PROJECT SUMMARY/ABSTRACT The overall goal of this research and training plan is to gain better understanding of the organization and function of the mouse accessory olfactory system (AOS). The AOS is a compact neural pathway that communicates directly with brain regions that govern so-called intrinsic social and reproductive behaviors. By increasing knowledge about sensory processing in the mouse AOS, this project will shed light on principles of mammalian olfaction, and will improve our understanding of links between sensation and behavior. The investigator, Dr. Julian Meeks, will gain up to two years of advanced postdoctoral training in the design and implementation of planar illumination microscopy and transgenic mice in support of an innovative approach using live neuronal calcium imaging to study inhibitory interneurons in the mouse accessory olfactory bulb. Two sponsors for this training were chosen, Dr. Timothy Holy and Dr. Daniel Kerschensteiner, that have strong experience in the fields of optical design and transgenic mouse production, respectively. Several hypotheses will be tested during the mentored and independent phases of this award. One main hypothesis links sensory receptive fields to axonal projection patterns in the brain. Testing several other hypotheses will identify specific sensory processing roles for the various interneuron populations in the accessory olfactory bulb. Testing these hypotheses will establish principles of mammalian social odor processing, and will help us to understand the functions that inhibitory neurons provide for sensory neural circuits. Through this research and mentored training plan, Dr. Meeks will produce valuable new data on AOS sensory processing, and will establish new experimental tools and approaches that will form a foundation for a career as an independent scientist.

How we learn from social experiences and during social interactions is poorly understood, but it is thought to involve intricate changes to nerve cells in the brain and the connections between these cells. Cells involved in social learning are intermingled and intertwined with cells that may have completely different functions. Because of this complexity, identifying and studying the specific cells and networks involved in social learning remain a major challenge, and new methods are required to address this needle-in-a-hay-stack problem. This research will build a new set of genetic tools that allow researchers to mark cells in the brains of mice and zebra finches that are specifically involved in learning during social interactions, and will apply cutting-edge imaging, physiological, and genetic methods to dissect how the marked cells change during learning. This research is of fundamental importance because it will shed light on the brain mechanisms involved in social learning and build a new set of genetic tools that can be used by the scientific community to study brain mechanisms involved in learning and memory. The research also is of importance because developmental disorders and head injuries can severely compromise circuits in the brain and individuals' ability to learn from social encounters and navigate complex social interactions. The tools and methodologies developed in this research will be made freely available to other scientists through the world-wide web (http://www.utsouthwestern.edu/education/medical-school/departments/neuroscience/index.html) and through the Addgene public repository (http://www.addgene.org/). Funding for this research will also be used to educate and train young scientists in novel genetic, molecular, imaging and behavioral methodologies.

The proposed research will identify neuronal mechanisms involved in social learning from olfactory and auditory cues in mice and zebra finches, respectively. The proposal takes a highly interdisciplinary, collaborative approach involving four independent laboratories. The researchers will fluorescently "tag" neurons in mice and zebra finches that are selectively activated by olfactory and auditory social experiences using novel genetic strategies and viral tools that leverage the immediate-early gene c-Fos. Within brain regions of interest (olfactory and vocal learning circuits), these viral tools will differentially label neuronal populations depending on cellular activity and the specific social cues animals experience. In vivo Ca2+ imaging will be used to identify and map populations of neurons involved in processing and learning from social encounters. Novel optical methods will be used to map synaptic connectivity among tagged neuronal populations in vivo. Electrophysiological and transcriptomic analyses will be used to identify physiological and genetic factors unique to each tagged population, and identify neural subtypes and subpopulations responsible for social learning. These combined approaches will help reveal the network-level plasticity induced by social experiences. This collaborative, high-risk/high-impact research will generate novel in vivo molecular tools that allow fine and selective dissection of the network components of social learning.

Two major goals of neuroscience research are (1) to understand how sensory information guides behavior and (2) to understand how behaviors are modified by experience. In most sensory modalities, extracting salient information involves passing signals back-and-forth between multiple, highly-interconnected neural circuits, making it challenging to disentangle which computations are made by which neuronal populations. For this reason, there is a significant advantage to studying sensory processing in neural pathways that involve few interconnected circuits. In mice, a specialized chemosensory pathway called the accessory olfactory system strongly influences social behavior and utilizes just one small neural circuit for the majority of its information processing. This small neural circuit is called the accessory olfactory bulb (AOB), and the proposed research aims to determine how neurons in the AOB extract behaviorally-relevant chemosensory information from the environment and refine that information through experience. Information processing in the AOB critically depends on the function of several classes of inhibitory interneurons, and neural plasticity in AOB interneurons is thought to underlie forms of social learning. The proposed research will use electrophysiology, neuronal calcium imaging, and optogenetics to determine the specific sensory computations performed by three major classes of AOB interneurons. The proposal leverages a unique ex vivo preparation of the AOB that allows researchers to monitor and manipulate AOB neurons during naturalistic peripheral chemosensory stimulation, which is important for relating activity measurements to information content. Furthermore, the proposed experiments will determine how the computations made by these interneurons contribute to the expression of social behaviors. The final proposed experiments will investigate how experience-dependent plasticity in one of the AOB interneuron classes impacts forms of social learning. Overall, the proposed research will produce important insights into the neural mechanisms of sensory processing, social behaviors, and behavioral plasticity.

Project Summary/Abstract The goal of this exploratory research project is to improve understanding about the mechanisms by which mammalian neural circuits decode environmental chemosensory information and use that information to support survival and reproduction. Specifically, the proposed research will investigate cell type-specific neural codes in the parallel brain pathways of the mouse accessory olfactory system (AOS). The AOS possesses a single neural circuit, the accessory olfactory bulb (AOB), that links the peripheral sensory neurons in the nose to powerful regions in the limbic system, but it remains unclear how information about naturally-occurring blends of social chemosignals is extracted through the AOB and its downstream targets. The exploratory research plan will utilize existing ex vivo approaches and collaboratively develop in vivo multi-site multielectrode AOS recording methods to investigate neuronal ensemble in the AOB and its downstream targets. This research will produce data linking sensory experience to ?mission critical? mammalian behavioral states, and improve our understanding of mammalian physiology. The gains made by these studies and the establishment of new experimental and analytical tools will ultimately benefit human health.

Project Summary/Abstract The overall goal of this research plan is to improve understanding about mammalian bile acid chemosignaling through the accessory olfactory system (AOS). Bile acids ? well known regulators of fat digestion and metabolism ? also serve as external chemosignals for the AOS. In most mammals, the AOS directly influences brain regions that control anxiety and social behaviors, and understanding this brain pathway is likely to provide insights into mammalian sexual/reproductive drive, social anxiety, and moods. New knowledge about AOS function may be utilized to help control rodent populations, including those that harbor harmful microorganisms. The mechanisms of peripheral bile acid sensation, the mechanisms of bile acid information processing in the brain, and the behavioral impacts of bile acids are currently unknown. The proposed research will combine new calcium imaging techniques with transcriptome analysis to identify the peripheral AOS receptor(s) sensitive to bile acids. Other proposed experiments will investigate network properties in accessory olfactory bulb (AOB), where bile acid and other steroid information is integrated. Finally, behavioral assessment will be coupled to brain-wide immediate early gene mapping to determine the overall impacts of bile acid chemosensation on brain activity and behavior. The proposed research will investigate these topics in order to improve understanding of this important class of mammalian chemosignals. The results of the proposed experiments will ultimately benefit human health by linking mammalian gut physiology to brain function.

Two major goals of neuroscience research are (1) to understand how sensory information guides behavior and (2) to understand how behaviors are modified by experience. In most sensory modalities, extracting salient information involves passing signals back-and-forth between multiple, highly-interconnected neural circuits, making it challenging to disentangle which computations are made by which neuronal populations. For this reason, there is a significant advantage to studying sensory processing in neural pathways that involve few interconnected circuits. In mice, a specialized chemosensory pathway called the accessory olfactory system strongly influences social behavior and utilizes just one small neural circuit for the majority of its information processing. This small neural circuit is called the accessory olfactory bulb (AOB), and the proposed research aims to determine how neurons in the AOB extract behaviorally-relevant chemosensory information from the environment and refine that information through experience. Information processing in the AOB critically depends on the function of several classes of inhibitory interneurons, and neural plasticity in AOB interneurons is thought to underlie forms of social learning. The proposed research will use electrophysiology, neuronal calcium imaging, and optogenetics to determine the specific sensory computations performed by three major classes of AOB interneurons. The proposal leverages a unique ex vivo preparation of the AOB that allows researchers to monitor and manipulate AOB neurons during naturalistic peripheral chemosensory stimulation, which is important for relating activity measurements to information content. Furthermore, the proposed experiments will determine how the computations made by these interneurons contribute to the expression of social behaviors. The final proposed experiments will investigate how experience-dependent plasticity in one of the AOB interneuron classes impacts forms of social learning. Overall, the proposed research will produce important insights into the neural mechanisms of sensory processing, social behaviors, and behavioral plasticity.