Raju Metherate - US grants

Metherate 9510904 The brain seems to process information in special ways during times of behavioral arousal. One aspect of this arousal is secretion of the neurotransmitter acetylcholine (ACh) within the cerebral cortex. It has not yet been determined exactly how ACh modifies cortical function. With this award, Dr. Metherate will determine how ACh secretion activates the cortex, and in particular how it modifies information processing within cellular circuits within the cortex. The auditory cortex will be used as a model system for these studies. This work will uncover important cellular mechanisms of plasticity that are likely to be involved in shifts of attention, learning and memory. ***

Appropriate behavioral responses to acoustic stimuli involve coding of the physical properties of stimuli by the auditory system, as well as modification of coded information by diffuse neuromodulatory systems that are activated in specific behavioral states. Conversely, disruption of auditory pathways by injury, or degeneration of diffuse modulatory systems in pathological conditions (e.g., Alzheimer's disease) can disrupt appropriate responses. The long-term objectives of this research are to understand the cellular mechanisms and neuromodulatory regulation of information processing in auditory cortex. The experiments involve intracellular recordings to examine subthreshold synaptic integration of auditory inputs, and cholinergic modulation of tone-evoked synaptic potentials, in physiologically and morphologically identified neurons. Data is obtained using the whole-cell recording technique, which enables stable, high resolution intracellular recordings in vivo. Synaptic transmission is manipulated in single neurons via intracellular dialysis with pharmacological agents. Neurons are characterized electro- physiologically by determining intrinsic firing patterns, and morphologically by intracellular labeling with biocytin. Specific aims include determining how four synaptic potentials -- tow mediated by glutamate and two by gamma-aminobutyric acid (GABA) -- generate frequency receptive fields and rate-level functions. In part, contributions of GABAergic inhibition are revealed by intracellular blockade of membrane channels coupled to GABA receptors. Specific aims also include determining how cholinergic neuromodulation modifies synaptic interactions. Stimulation of nucleus basalis cholinergic neurons that project to auditory cortex, or selective lesion of these neurons using the novel immunotoxin 192 IgG-saporin, test the hypothesis that cholinergic inputs modify synaptic integration to "sharpen" frequency receptive fields. Neurons are thus characterized in terms of morphology, intrinsic membrane physiology, synaptic physiology, and acoustic responsiveness. This detailed, multifaceted characterization will promote an integrated, mechanistic understanding of auditory cortex function, and hence, lead to improved treatments for auditory cortex dysfunction.

DESCRIPTION (provided by applicant): Children of women who smoke during pregnancy exhibit higher-order auditory-cognitive deficits, but the relationship, if any, between developmental chronic nicotine exposure (CNE) and subsequent auditory deficits is unclear. Results from a newly-developed animal model indicate that CNE during development produces auditory-cognitive deficits, and reveal a potential cellular link: functional impairment of nicotinic acetylcholine receptors (nAChRs) in primary auditory cortex (A1). Studies also show that nAChRs normally enhance cortical processing in two ways: i) by increasing sensitivity to characteristic frequency (CF) stimuli, and ii) by reducing sensitivity to spectrally-distant stimuli. In other words, receptive fields become more sharply tuned. Preliminary studies on the auditory thalamocortical brain slice reveal a surprising cellular basis of the first effect: nAChRs facilitate responsiveness in A1 by enhancing axon excitability in thalamocortical relay neurons. This novel mechanism of nAChR function implies that a neurotransmitter (in this case acetylcholine) can regulate myelinated thalamocortical axons. The proposed studies test the hypothesis that nAChRs enhance thalamocortical axon excitability to increase sensitivity to CF stimuli, and excite cortical interneurons to reduce responses to spectrally-distant stimuli. The studies will exploit the thalamocortical brain slice to examine cellular mechanisms by which nAChRs differentially regulate thalamocortical and intracortical transmission. Parallel in vivo studies will determine how cellular mechanisms identified in the slice contribute to acoustic processing in the intact animal. Finally, the mechanism by which neonatal CNE produces lasting deficits in nAChR function will be examined by determining how CNE alters intracellular signal transduction activated by nicotine. The long-term goal of the proposed studies is an understanding of nAChR function in A1 and its disruption by CNE, which, in turn, may guide therapies for CNE-induced deficits. The effect of tobacco smoke on fetal brain development is a major public health issue, since most women who smoke continue to do so during pregnancy. Recent animal studies have confirmed a causal role for nicotine in producing long-lasting auditory-cognitive impairments, and the proposed studies will continue this work to identify the underlying cellular and molecular mechanisms, with the long-term goal of developing therapies to treat nicotine-induced cognitive impairments.

[unreadable] DESCRIPTION (provided by applicant): The long-term objective of this research is to gain an understanding of the cellular mechanisms by which neurons in the auditory cortex (ACx) process spectrally complex information. The hypothesis to be tested is that individual ACx neurons receive converging, largely subthreshold, inputs subserving most of the audible spectrum, and that synaptic integration produces optimal responses to complex stimuli. The proposed underlying neural architecture involves thalamocortical projections to ACx layer 3/4 mediating characteristic frequency (CF) and near-CF responses, and intracortical projections outside of layer 4 mediating spectrally-distant nonCF responses. The precise synaptic architecture dictates that optimal synaptic integration occurs in response to specific, predictable, spectrotemporally complex stimuli. Three Specific Aims utilize in vivo intracellular recordings and a newly developed in vitro auditory thalamocortical preparation: 1) Determine if subthreshold receptive fields are much broader than spike-based receptive fields, using in vivo intracellular recordings in ACx. 2) Determine if thalamic stimulation in vitro activates ACx layer 3/4 followed by excitation in upper and lower layers of adjacent ACx. In parallel in vivo experiments, determine if CF stimuli activate synapses in layer 3/4 whereas spectrally-distant nonCF stimuli activate synapses outside of layer 4. 3) Determine in vitro how converging synaptic potentials are optimally integrated, and then determine in vivo if similar integration underlies optimal responses to complex stimuli. An understanding of these mechanisms will enhance treatments for conditions such as partial ACx lesions or cochlear implants, by guiding the design of stimuli to activate ACx optimally. [unreadable] [unreadable]

Address; Advisory Committees; Anatomic; Anatomical Sciences; Anatomy; Area; Arts; Auditory; Biological; Body Tissues; Brain; Cells; Chemicals; Collaborations; Construction; Data; Development; Discipline; Doctor of Philosophy; Encephalon; Encephalons; Facility Construction Funding Category; Fostering; Hearing; Image; Imaging technology; In Vitro; Individual; Instrumentation, Other; Investigators; Life; Method LOINC Axis 6; Methodology; Methods; Microscope; Microscopy; NRVS-SYS; Nervous System; Nervous System, Brain; Nervous system structure; Neurologic Body System; Neurologic Organ System; Olfaction; Olfactions; P-30; P-30 Protein; P30; P30 Protein; Ph.D.; PhD; Photons; Postdoc; Postdoctoral Fellow; Preparation; Qualifying; Rate; Recruitment Activity; Research; Research Associate; Research Personnel; Research Resources; Researchers; Resolution; Resources; Rosa; Rose; Science of Anatomy; Science of neurophysiology; Smell; Smell Perception; Specialist; Structure; Structure-Activity Relationship; Task Forces; Time; Tissues; Training; Training Support; Work; anatomy; base; chemical structure function; experience; experiment; experimental research; experimental study; hearing perception; imaging; improved; in vivo; innovate; innovation; innovative; instrument; instrumentation; member; neurophysiology; novel; post-doc; post-doctoral; ranpirnase; recruit; research study; sound perception; structure function relationship; tissue fixing; tool

DESCRIPTION (provided by applicant): Research in NIDCD mission areas is expanding at the University of California, Irvine (UCI). Since 2005, UCI has sponsored interactions and interdisciplinary collaborations among a group of over 20 faculty who comprise the Center for Hearing Research (CHR). The potential for interdisciplinary work is substantial, with faculty spanning 11 Departments in 5 Schools at UCI performing research in NIDCD mission areas. For these investigators, CHR has established a UC Irvine Core Center for Hearing and Communication Research to: 1) facilitate ongoing research by consolidating resources and providing access to state-of-the-art technology, 2) promote interdisciplinary work by educating users about Core facilities and providing expert assistance, and 3) recruit investigators from diverse backgrounds to research in NIDCD mission areas. There are two Core facilities: 1) The Imaging Core provides a 2-photon imaging system for visualizing neurons and real-time neural activity in live, including in vivo, or fixed, tissue. The system enables new kinds of Experiments, e.g., examining activity simultaneously in many neurons, or over time during development. An imaging specialist facilitates the integration of this technology into existing research programs and among users from multiple disciplines. 2) The Computing and Engineering Core provides signal processing and electronic systems support for physiological and behavior research. The Development of common signal processing algorithms will promote interdisciplinary collaborations (e.g., between physiological and behavioral projects) and facilitate data sharing. Core personnel conduct a lecture series to familiarize new researchers with the engineering technologies used in core users' laboratories. The two Cores interact with each other extensively, and with other P30 cores regionally and nationally. These shared facilities enhance ongoing research at UCI and accelerate the trend towards interdisciplinary research in NIDCD mission areas. The resulting synergy among disciplines is critical for a fuller understanding of communication and communication disorders.

Reviews of the Computing and Engineering Core were strongly positive, noting its usefulness for a large number of users. However, the resume cites the lack of a plan to prioritize use of resources, and the lack of details regarding the innovative lecture series. In addition, the summary notes concern over the ability to recruit a qualified engineer. We have addressed each concern. First, we are pleased to have recruited Dr. Thomas Lu to be the Core engineer. Dr. Lu has an engineering degree and a Ph.D. in auditory neurophysiology from Johns Hopkins. He currently is a postdoctoral fellow with Dr. Fan-Gang Zeng and has extensive training in psychophysics, cochlear implants, and DSP programming. His background and interests are ideal for this position. Second, an Advisory Committee consisting of Dr. Lu and two users will assist the Core director in setting priorities, including evaluating new requests and user feedback, during quarterly meetings. The P30 Director and Executive Committee will provide guidance for setting priorities and evaluating use of resources. For the Computing and Engineering Core, priority will be determined by two guiding principles: (1) relevance and (2) broad impact. The "relevance" principle will give the highest priority to the R01 projects that qualify the present P30 application, second priority to other Federallyfunded projects (RO3, NSF) in NIDCD mission areas, followed by other grants (e.g., internal campus funds). The "broad impact" principle will give priority to software and hardware design that best serves the maximum number of users while considering effective use of Core resources and time. Finally, we provide a syllabus and other details for the lecture series (Biomed. Eng. 298: Auditory Science and Engineering). The course will be co-taught annually by Drs. Zeng and Lu.

The Director of the P30 will be Dr. Raju Metherate. Dr. Metherate also is Director of CHR, an advantageous arrangement since a close relationship between the P30 and CHR will maximize the effectiveness of both groups. Dr. Metherate was a founding member and Associate Director of the IRU for Hearing and Speech Science, and assumed responsibility for IRU activities in 2003 when Dr. Len Kitzes became acting chair of the Department of Anatomy and Neurobiology. When the IRU transitioned to CHR in 2005, Dr. Metherate was elected Director. Dr. Metherate joined UCI as an assistant professor in 1995, and currently is an associate professor in the Dept. of Neurobiology and Behavior. He is PI on two NIH R01 grants, from NIDCD and NIDA, and has maintained continuous funding from NIH and NSF for over 13 years to study cellular mechanisms in the auditory cortex. Since CHR is a UCI "Campus Center," its director reports directly to his own Dean (Biological Sciences) and the Vice Chancellor for Research, from whose office the mandate and funding for CHR originates. The line of communication with the Vice Chancellor for Research is important since the P30 and CHR involve faculty from eleven Departments in five Schools across the UCI campus. The P30 and CHR administrative structures are such that no single department carries undue weight or influence. (See the Appendix for a list of P30 faculty and their Department and School affiliations.) The P30 Executive Committee will comprise the Director, both Core Directors, and a rotating representative of the P30 investigators. Note that the Core Directors are from different Schools (Biological Sciences and Medicine). The Executive Committee will meet regularly, at least quarterly, to ensure that the needs of each Core and its users are met and that all facilities are being managed efficiently. Core Directors can voice concerns brought up at internal meetings of each Core's users and Advisory Committees. In addition, the Executive Committee as a group will solicit and evaluate feedback from all users at regular intervals, at least annually, and make recommendations to the Director for changes to P30 procedures and priorities. Important issues will include how the P30 is able to enhance ongoing research and promote interdisciplinary collaborations. Note that each Core director, in consultation with the Core's Advisory Committee, will be responsible for prioritizing usage of his or her core. In general, the highest priority for use of Core facilities will be to provide support for ongoing, R01-funded, NIDCD-related research. Secondary priority will be for research supported by other Federal funding (e.g., NIH-R03, NSF). Additional priorities (e.g., attracting new investigators to NIDCD-related topics) will be pursued when possible. Proper distribution of each Core's resources will be reviewed by the Executive Committee at quarterly meetings, and procedures to resolve inequities formulated. Administrative support for the P30 will be provided through Dr. Metherate's home department, the Dept. of Neurobiology and Behavior (Chair, Dr. Thomas J. Carew). Department staff will assist with personnel, purchasing, scheduling meetings, preparing progress reports and other administrative tasks. The department is familiar with the needs of interdisciplinary research centers, having a close relationship with three major research institutes directed by department faculty: the Center for the Neurobiology of Learning and Memory (Dr. Michael D. Rugg, Director), the Institute for Brain Aging and Dementia (Dr. Carl W. Cotman, Director), and the Reeve-Irvine Research Center (Dr. Oswald Steward, Director). Administrative effort for the P30 is expected to be minimal: 10% effort each for the Director and Core Directors, and 25% effort for an Administrative Assistant in the Dept. of Neurobiology and Behavior.

? DESCRIPTION (provided by applicant): Progress towards understanding mechanisms of hearing, and the treatment of hearing deficits, requires an integrated effort from multiple disciplines within the field of hearing research. The Center for Hearing Research (CHR) at the University of California, Irvine (UCI) maintains an interdisciplinary training program that takes advantage of the breadth and depth of hearing research at UCI to train new scientists broadly across multiple disciplines as well as deeply in one. The 17 training faculty in CHR span six departments in four Schools (Biological Sciences, Engineering, Medicine and Social Sciences) with research interests that cover a broad range of levels (genes, molecules, cells, systems and behavior) and experimental approaches (cell and molecular biology, neurophysiology, psychoacoustics, computation, human imaging, medical devices). Thus, CHR is well-positioned to offer interdisciplinary training. We request support for three predoctoral students and two postdoctoral researchers including medical residents from Otolaryngology. The didactic core of the training program is a course in Auditory Neuroscience, which covers the auditory system from cells to psychoacoustics, the cochlear to the cortex, and basic and clinical aspects. Mandatory features of the training program that encourage interdisciplinary interactions are participation in all CHR activities (e.g., seminar series, journal club and two annual conferences) required oral and poster presentations to scientifically diverse audiences on three occasions per year, and regular meetings with basic and clinical scientists. The normal period of support is two years for pre- and post-doctoral trainees (1-2 years for residents). Predoctoral trainees normally enter the program in their second year of graduate study and are required to take a course on grant writing and submit an NRSA proposal. The program is managed by the Program Director and an Executive Committee, and will foster development of trainees' intellectual, technical and professional skills needed to pursue successful careers in hearing research.

The Administrative Shell is closely tied to administration of the Center for Hearing Research (CHR)?i.e., Core Center administrators also form the leadership and most active members of CHR?so that facilitating interactions among users and promoting collaborative, interdisciplinary efforts is easily accomplished. The Core Center will be administered by Core Center Director, Raju Metherate, Core Directors Karina Cramer (Imaging Core) and Fan-Gang Zeng (Computing and Engineering Core) and a rotating representative of the P30 users (currently, John Middlebrooks). Individually and as a group, the administrators will ensure that the needs of each Core and its users are met and that facilities are being managed efficiently, thereby ensuring that the Core Center meets its objectives. Administrative support for the P30 is provided through the home department of Dr. Metherate, the Dept. of Neurobiology and Behavior. Department staff handle personnel issues, purchasing, monthly budget reports, annual progress reports and other administrative tasks.

PROJECT SUMMARY / ABSTRACT For hearing, as for other senses, higher-level processing improves with attention-related release of the neurotransmitter acetylcholine and activation of nicotinic acetylcholine receptors (nAChRs) in the brain. Similarly, auditory-cognitive function is enhanced by systemic administration of nicotine to activate nAChRs, impaired by pharmacological blockade of nAChRs, and progressively diminished by disease-induced loss of nAChRs (e.g., in Alzheimer?s disease) that reduces the efficacy of endogenous acetycholine. It is widely agreed, therefore, that nAChRs are important for sensory-cognitive function. As a result, selective nicotinic agonists are being developed as treatments for cognitive disorders; however, to date these are only moderately successful and further progress requires a better understanding of how nAChRs regulate cortical processing. This project will test the hypothesis that nicotine produces its cognitive-enhancing effects by ?sharpening? neural representations in two key regions, primary auditory (A1) and prefrontal (PFC) cortex, and that nicotine?s effects depend on activating a2 nAChRs located on inhibitory neurons that can be identified by the protein marker, vasoactive intestinal peptide (VIP). Aim 1 will determine how nAChRs regulate neural circuits in mouse A1 and PFC using in vitro brain slices and in vivo electrophysiological recordings. The use of transgenic mouse lines will enable recordings from identified neurons, including VIP neurons, and recordings from mice with a2 nAChRs ?knocked out? or made hypersensitive. Aim 2 will determine how nicotine alters the activity of A1 and PFC neurons during auditory-cued behavior using high-density single-cell recordings in rats and mice performing a novel auditory-sequence memory task. Again, nicotine effects will be compared across wild-type, a2 knock-out and a2 hypersensitive mice. Aim 3 will use chemogenetic techniques to determine if suppression of VIP neurons or a2 nAChRs blocks nicotine?s effects on neural processing, in vitro and in vivo, and behavioral performance. This project will advance the understanding of nAChRs in auditory-cognitive function and the specific involvement of VIP interneurons and a2 nAChRs in A1 and PFC. Confirmation of an important role will guide development of more effective and selective drug therapies to enhance auditory- cognitive function.

Project Summary Progress towards understanding mechanisms of hearing, and the treatment of hearing deficits, requires an integrated effort from multiple disciplines. The Center for Hearing Research (CHR) at the University of California, Irvine (UCI) maintains an interdisciplinary training program that takes advantage of the breadth and depth of hearing research at UCI to train new scientists broadly across multiple disciplines and deeply in one. The 21 training faculty in CHR span six departments in five Schools (primary appointments in Biological Sciences, Medicine, Social Sciences and Education; joint appointments in Engineering) with research interests that cover a broad range of levels (genes, molecules, cells, systems and behavior) and experimental approaches (cell and molecular biology, neurophysiology, psychoacoustics, computation, human imaging, human learning, medical device engineering). Thus, CHR is ideally positioned to offer interdisciplinary training. We request support for three predoctoral students and two postdoctoral researchers including medical residents. The didactic core of the training program is a course in Auditory Neuroscience, which covers the auditory system from cells to psychoacoustics, cochlea to cortex, and basic to clinical sciences. Mandatory features of the training program that encourage interdisciplinary interactions are participation in all CHR activities (e.g., seminar series, journal club and annual conferences), presentations to scientifically diverse audiences, and regular meetings with basic and clinical scientists. The normal period of support for trainees is two years. Predoctoral trainees normally enter the program in their second year of graduate study and are required to take a course on grant writing and prepare an NRSA proposal. The program is managed by the Program Director and an Executive Committee, and will foster development of trainees? intellectual, technical and professional skills needed to pursue successful careers in hearing research.

Age-related decline in central auditory function significantly affects quality of life in the elderly, with impaired speech perception leading to increased risk for depression, social isolation and cognitive decline. A 2017 Lancet Commission report cites hearing loss as the largest modifiable risk factor for developing cognitive decline, exceeding smoking, high blood pressure, lack of exercise and social isolation. Remarkably, a 2019 large-scale study found that even mild hearing loss, i.e., still within the normal range, produced an even closer association with cognitive decline. Currently, there is no effective therapy for age-related central auditory decline?hearing aids only address audibility?and no drug treatment. Ideally, a combination of drug treatment with hearing aids and behavioral training could restore auditory function, but the development of pharmacological treatments requires a better understanding of the mechanisms by which candidate drugs improve hearing. The goals of this proposal are to develop biomarkers of altered auditory processing in aging mice and humans, and using these biomarkers, to test the hypothesis that nicotine can normalize these age-related central auditory deficits. Because nicotine enhances cortical and cognitive function, pharmaceutical companies are developing nicotine-like drugs to target cognitive deficits in aging. These drugs are non-addictive (unlike nicotine in tobacco), yet nicotine also is non-addictive when given topically or orally. However, its clinical benefits have not been exploited except as an aid to stop smoking. We hypothesize that: 1) acute nicotine compensates for the age-related decline in inhibition by exciting the remaining inhibitory neurons; 2) chronic nicotine exposure (CNE) upregulates nicotinic acetylcholine receptors (nAChRs); and, as a result, 3) acute nicotine and/or CNE will reduce or reverse the age-related auditory decline. We will test these hypotheses in both mouse and human at the level of cells (mouse in vitro brain slice), neural systems (mouse in vivo physiology; human brain imaging and EEG) and behavior (human psychoacoustics). Aim 1 will determine in mouse whether age-related decline in auditory spectrotemporal processing is reversed by acute nicotine or CNE, and characterize the associated cellular mechanisms. Aim 2 will identify, in humans, age-related changes in receptive field properties in auditory cortex using novel fMRI techniques and determine if nicotine reverses these changes using psychoacoustics, fMRI and EEG. This project features a multifaceted, parallel approach in mouse and human. Each Aim will: 1) examine auditory processing at multiple adult ages; 2) use similar acoustic stimuli in both species, accounting for species differences in hearing, to target common mechanisms; 3) test the effects of nicotine. A successful outcome will promote an integrated understanding across levels, from cellular mechanisms to perception, and facilitate translation of nicotine-based therapeutic treatments to clinical populations.