Daniel A. Llano - US grants

[unreadable] DESCRIPTION (provided by applicant): Project Summary: The objective of the proposed studies is to understand the functional relationships between the auditory cortex and thalamus, and ultimately to uncover the neural substrates for auditory cognition. This work will test the hypothesis that the nonlemniscal portions of the auditory thalamus act as a link in an alternate information route between auditory cortical areas: a cortico-thalamocortical route, with layer 5 auditory corticothalamic projections providing feedforward driving input to the nonlemniscal thalamic nuclei while layer 6 corticothalamic projections provide feedback to all areas of the auditory thalamus. To test this idea, the reciprocity patterns and synaptic morphologies of laminar-specific corticothalamic projection systems in the mouse will be studied using injections of tracers into both the auditory cortex and thalamus. In addition, the physiologic signatures of driver or modulator responses in the thalamus will be studied in the auditory corticothalamic slice preparation by using laser-uncaging of glutamate to stimulate auditory corticothalamic neurons in layers 5 and 6, respectively, while recording from neurons in the subnuclei of the auditory thalamus. Finally, pairs of connected auditory cortical and thalamic neurons will be recorded from to better define the detailed circuitry of corticothalamic systems. The proposed experiments should shed light on the role(s) of the massive, heterogeneous corticothalamic projection systems as well as help to clarify the role of the nonlemniscal thalamus in shaping auditory cortical function. In addition, this work will be the focus of an intensive laboratory training experience designed to prepare the investigator for a research career dedicated to the study of auditory thalamocortical function. This will be coupled with training in clinical aphasiology and cognitive neurology to enable the investigator to develop strategies to address problems of higher cortical function that depend upon the integrity of thalamocortical networks. Relevance: The goal of the proposed research is to better understand the brain mechanisms underlying the perception of sound. It is hoped that this work will lead to a better understanding of speech perception and to new ways to diagnose and treat patients who have lost their ability to use language. [unreadable] [unreadable] [unreadable]

DESCRIPTION (provided by applicant): Hearing loss is a major cause of morbidity and social disengagement in the aging population. Unfortunately, hearing aids, which compensate for the peripheral deficits, do not adequately enhance the intelligibility of speech in real-world situations. This is because a major cause of age-relating hearing loss is the dysfunction of central mechanisms that allow the brain to selectively attend to particular streams of auditory input. One hypothesis to explain the breakdown in this selective attention process is the particular vulnerability of cortical inhibition in the aging brain. We propose to examine the role of age-related loss of inhibition in one neural system that has been implicated in selective auditory attention: the auditory corticothalamic system. We have previously shown that auditory corticothalamic neurons in young adult mice are under substantial inhibitory control and that multiple distinct inhibitory microcircuits exist within the corticothalamic system. We hypothesize that there is an age-associated loss of particular elements within this inhibitory microcircuitry. We will investigate age-related changes in the inhibitory circuitry onto identified auditory corticothalamic neurons using laser scanning photostimulation of caged glutamate in the slice preparation. Specifically, based on our previous work, we will study three particular sets of inhibitory inputs: GABAAergic inputs from layers 2/3 and 5 onto layer 5 corticothalamic neurons and layer 6-derived GABAAergic inputs onto layer 6 corticothalamic neurons. We will also investigate age-related changes in the functional mapping of cortical inputs onto thalamic neurons. We hypothesize that decreases in cortical inhibition will produce a broadening of cortical input onto thalamic cells, and that this may be responsible for the selective auditory attention deficits described above. We will record from individual thalamic neurons in the auditory corticothalamic slice preparation and construct cortical input maps using laser scanning photostimulation. Maps will be compared between young and aged mice and it is expected that aging will broaden these inputs. Our longer term goals are to extend this work to the in vivo preparation to correlate potential age-associated changes in corticothalamic mapping to particular auditory attention deficits. The proposed work will lead to a greater understanding of the mechanisms responsible for age-associated central auditory dysfunction, and may ultimately provide therapeutic targets for amelioration of this highly prevalent condition. PUBLIC HEALTH RELEVANCE: Age-associated hearing loss affects approximately one third of older adults and the proposed work will examine the brain mechanisms of this hearing loss. Specifically, we believe that the root of these difficulties is the inability to suppress distracting sounds and that this is caused by dysfunction of particular sets of brain cells. We will test this idea by examining changes in the brain circuitry of the auditory system in aging animal models.

Massive amounts of brain imaging data open an unprecedented window into the structure and function of the brain, yet the tools to aid the understanding of the data are lagging. The main goal of this research project is to understand the dynamics of brain function, particularly in the auditory system, through global yet very high spatial and temporal resolution imaging techniques and using the state-of-the-art analytical tools developed for analysis of dynamic social networks. The interdisciplinary neuroscience and computational team, building on promising initial results, will work to adapt these tools developed for understanding human and animal behavior to the context of brain networks and the processes that happen over them. Using this innovative approach, the team will study a particular brain pathway that connects two brain regions that are critical for normal hearing. The project will not only lead to a greater understanding of brain function, but will also bring a new technique to the neuroscience toolbox which may help other investigators to study network properties of the brain. Graduate students and postdocs in computer science and neuroscience will collaborate across disciplinary boundaries, building new scientific approaches and insights.

Top-down projections are ubiquitous in sensory systems and are poorly understood. In the current proposal, a model descending system, the auditory corticothalamic projection in the mouse, will be examined. The research team will take advantage of recent methodological developments in the study of this system and ask: What is the impact of corticothalamic projections on network interactions across populations of thalamic neurons? To answer this, a novel dynamic network analysis method known as Community Dynamic Analysis, or CommDy, will be used to analyze imaging data from a brain slice preparation that retains connectivity between the auditory cortex, auditory thalamus, and other related structures in the mouse. Both calcium imaging data and flavoprotein autofluoresence imaging data will be used for this analysis. Since this study represents the first use of CommDy in neuroscience, validation studies will be done in a simplified brain slice preparation containing bilateral motor cortices and the corpus callosum.

? DESCRIPTION (provided by applicant): The ability to extract meaning from sounds, even when degraded, is critical for normal hearing. A key strategy employed by the auditory system during acoustically-challenging situations is the use of contextual cues to disambiguate cluttered signals. Importantly, many patients with language-related disorders, such as aphasia, autism and dyslexia, have difficulties harnessing such contextual cues. The neural mechanisms by which high-level information can be used to shape lower-level sensory processing are not yet known. A potential substrate for this type of processing is the massive top-down projection system emanating from virtually every level of the auditory system. In this project, we will provide a functional characterization of one of the largest of these projections: the auditory corticocollicular system. The corticocollicular system can rapidly and profoundly change the tuning of neurons in the inferior colliculus, but key aspects about its organization are not known. We hypothesize that this system comprises at least two functionally distinct sub- systems; one from cortical layer 5 and another from cortical layer 6. Using the mouse model, the cortical distribution of layer 5 and 6 neurons that project to small regions of the inferior colliculus willbe reconstructed and compared. Our early data suggest that input from layer 6 emanates from a more widespread area than layer 5 and tends to predominate in the non-primary parts of the auditory cortex. In addition, we will combine in vivo transcranial flavoprotein autofluoresence imaging with quantitative neuronal reconstructions to compare the projection patterns of layer 5 vs. layer 6 cortical projections to the inferior colliculus. Finally, using a novel corticocolliculr brain slice preparation and laser photostimulation, we will compare the synaptic properties of layer 5 and 6 corticocollicular synapses. Successful completion of this project will provide the first circuit-level characterization of this important pathway and will lay the groundwork for a greater understanding of how top-down modulatory systems break down during disorders of communication.

? DESCRIPTION (provided by applicant): The thalamic reticular nucleus (TRN) is a capsule of GABAergic neurons that partially envelops the thalamus and has been speculated to play a role in normal cognitive functions, such as selective attention, and in pathological states, such as tinnitus and schizophrenia. Therefore, understanding the function of the auditory portion of the TRN will unlock secrets not only about normal hearing, but also provide insights about how thalamocortical systems become dysfunctional in disease. Unfortunately, the impact of the TRN on sensory processing has been particularly inscrutable because of its small size and deep location. Until now, there has not been an experimental preparation that permitted measurement of thalamic and cortical activity at the cellular level while allowing simultaneous manipulation of the TRN and afferent input to the thalamus. We have recently overcome this hurdle by developing a brain slice preparation in the mouse that contains robust connectivity between the inferior colliculus, auditory thalamus, auditory TRN and the auditory cortex (Llano et al. J Neurophysiology 2014, 111(1):197). Herein, we combine the use of this new preparation with a range of optical, electrophysiological and pharmacological tools to test a novel hypothesis: that the TRN produces paradoxical rate- dependent enhancement of the transmission of neural signals as they pass through the colliculo-thalamocortical pathway. This hypothesis is based upon recent findings that the auditory TRN receives non-reciprocal input from wide-ranging neural structures, such as the frontal cortex and amygdala, and that GABAergic input from the TRN produces short windows of hyperexcitability in thalamic neurons by de-inactivating T-type calcium currents. Successful completion of this work will open the doors to future studies that examine the impact of the frontal cortex and amygdala on auditory thalamocortical systems through the TRN, and therefore will shed light on how cognitive and emotional states influence acoustic processing.

Project Summary In this proposal, we request funding for the purchase of a multiphoton microscope system to be housed in the Beckman Institute for Advanced Science and Technology at the University of Illinois. The state-of-the-art microscopy system will permit deep-tissue imaging into fixed and live tissues and serve as a shared resource for multiple investigators at the University of Illinois. The microscope will be outfitted with an extended infrared laser, optogenetic stimulation capability and an easily moveable stage to permit in vitro as well as in vivo electrophysiology experimentation. In addition, the microscope will be supported and managed by the Beckman Institute Microscopy Suite, for which there is already dedicated space and full-time Ph.D.-level staff to manage the instrument. The microscopy suite is a unit that is fully supported by the Beckman Institute, with paid staff who have extensive experience in managing high-end laser- based microscopy systems. The Microscopy Suite also has infrastructure to ensure maximal utilization of the microscope by NIH-funded users. Eleven major users and one minor user have been identified, and their diverse interests represent the interdisciplinary nature of the Beckman Institute. The major users come from 8 different departments and use of a multiphoton microscope will support their NIH-supported research, with funding coming from 8 different institutes (NCI, NIAID, NIBIB, NIDA, NIDCD, NIMH, NIGMS and NINDS). The major users have research interests in developing novel technology platforms for cancer diagnosis, for understanding the biological underpinnings of inherited cognitive disorders, for understanding invertebrate neurobiology, studying glial-neuronal interactions and others. Therefore, the multiphoton microscope would support both basic and translational research across a variety of disciplines, and support ongoing NIH-funded research at Illinois.

Aging-related hearing loss is growing at an alarming rate. Unfortunately, simple peripheral amplification devices, such as hearing aids, do not adequately treat this problem because they do not address the changes that occur at the level of the central nervous system. Although many previous investigators have examined the individual changes in tuning function, neurotransmitter pharmacology, temporal properties, etc., in the aging auditory system, what has been missing is an understanding of a unifying mechanism that ties these changes together. Herein, we propose to test the hypothesis that mitochondrial dysfunction underlies aging-related changes in physiological function, and that there may be metabolic ?hubs? in the auditory system that are particularly vulnerable during aging. To answer this question, we will employ an endurance exercise intervention in a population of mice that have been genetically engineered to age prematurely and examine the impact of exercise on brain metabolism at multiple levels of the central auditory system simultaneously. We hypothesize that particular portions of the central auditory system will be selectively vulnerable to aging-related changes, and that 1) endurance exercise will mitigate these changes and 2) upregulation of PGC1?, a transcriptional coactivator critical for mitochondrial biogenesis, is associated with the protective effects of exercise. Successful completion of this work will not only shed light on basic mechanisms involved in aging, but will also reveal new therapeutic targets to augment the beneficial effects of endurance exercise on the central auditory system.

ABSTRACT Healthy subjects rapidly shift their attention in response to a dynamic sensory environment and changing cognitive demands. Failure to quickly shift perceptual resources between auditory and other modalities has been hypothesized to be a core deficit in both dyslexia and autism. Precisely how the brain shuttles information between sensory systems is not known, but recent work suggests that the thalamus contains circuits that have the capacity to rapidly transition between different sensory modalities. Specifically, the thalamic reticular nucleus (TRN), a thin shell of GABAergic neurons surrounding the thalamus, may serve as a link to allow communication between different areas of the sensory thalamus, a phenomenon we refer to as thalamic ?cross- talk.? Based on recent data and our preliminary findings, we hypothesize that thalamo-TRN- thalamic circuits provide critical connections between thalamic nuclei and therefore permit rapid switching between auditory and other thalamocortical pathways. We propose to test this hypothesis using a novel combination of anatomical, chemogenetic, optical stimulation and optical imaging approaches in the mouse, using both slice and in vivo approaches. Specifically, we will determine which of multiple potential circuit pathways is/are used to permit auditory, visual and auditory thalamic nuclei to communicate with each other. Next, we will determine whether and how such thalamic cross-talk influences synaptic responses at the level of the auditory cortex. Finally, the impact of the TRN on cross-modal processing will be directly examined by optically modulating the TRN while imaging cortical responses to combined sensory stimulation in awake mice. Successful completion of this project will provide the first circuit-level characterization of the role of the TRN in communication between the auditory thalamus and other thalamic regions. In addition, this work will lay the groundwork for a greater understanding of how thalamoreticular systems break down in disorders of communication.