Jelena Radulovic, M.D., Ph.D - US grants

[unreadable] DESCRIPTION (provided by applicant): Anxiety disorders are thought to result from abnormal emotional responses associated with memories of aversive events. Most forms of anxiety are accompanied by generalized distress in response to threatening environments that can be modeled by context-dependent fear conditioning. Humans and rodents rapidly acquire fear responses to environmental contexts by classical conditioning procedures. A single pairing of a context with a stimulus perceived as harmful leads to the formation of long-term memory of the aversive episode persisting for years. Nevertheless, several re-exposures to the conditioning context without the harmful stimulus commonly lead to a decline of the fear response, a phenomenon termed extinction. In spite of its increasingly recognized significance in anxiety disorders, the molecular basis of extinction, in particular extinction of context-dependent fear is not well understood. The proposed research is designed to identify the key molecular mechanisms leading to extinction and delineate them from mechanisms underlying acquisition of contextual fear. Rodent models have been successfully employed to establish that hippocampal signaling encompassing protein phosphorylation and gene expression is essential for context- dependent fear conditioning. We hypothesize that altered coupling of these intracellular signaling pathways to gene responses contributes to extinction. By combining immunohistochemical and immunoblot approaches we expect to identify the main hippocampal substrates of the cAMP-dependent protein kinase, protein kinase C and mitogen-activated and extracellular signal regulated kinase during extinction. The role of these pathways in the regulation of gene responses and fear extinction of will be determined by combining pharmacological approaches with genetic mouse models. We expect to demonstrate that the hippocampus significantly contributes to the neuronal circuitry regulating extinction of contextual fear. The identified signal transduction pathways may serve as potential targets for the development of new therapeutic approaches that would eliminate persistent fear of threatening environmental contexts as observed in general anxiety and post-traumatic stress disorder. [unreadable] [unreadable] [unreadable]

DESCRIPTION (provided by applicant): Stressful experiences significantly facilitate the formation of aversive memories. Consequently, the recall of these memories triggers exaggerated and persistent fear responses. The effects of stress on aversive learning, observed in humans as well as experimental animals, have been implicated in the pathogenesis of posttraumatic stress disorder (PTSD). Here we put forward the hypothesis that key mechanisms triggered during acute stress, but activated with a delayed time course after cessation of the stressor, are the main mediators of enhanced aversive conditioning. If our hypothesis proves correct, the effects of acute traumatic events leading to psychopathology, such as PTSD, could be significantly prevented by poststress interventions. Because the occurrence of stressful situations is commonly unpredictable, the possibility of retrograde interference with brain neurotransmitter systems would be of particular significance for the prevention of stress-enhanced fear conditioning. Studies with rodents have shown that pharmacological blockade of glutamate receptors prior to stress exposure significantly attenuates the behavioral effects of stress. It is less clear whether similar manipulations can be effective after the stressor has terminated. The objective of this proposal is to characterize in detail the delayed effects of stress on fear conditioning and attempt to block these effects by poststress inactivation of glutamate receptors. We plan to employ the contextual fear conditioning as a model of robust aversive conditioning. Mechanistic questions addressed in this proposal will identify the glutamate receptor type (Aim 1), learning process (Aim 2) and downstream glutamatergic mechanisms (Aim 3) mediating the delayed and persistent stress effects on fear conditioning. The therapeutic implications of the findings will encompass novel options to retroactively and selectively alleviate stress-enhanced aversive conditioning by blocking specific glutamatergic mechanisms. Our long-term goal is to identify the mechanisms mediating the effects of stress on subsequent acquisition and persistence of endophenotypes relevant for PTSD. In susceptible individuals, a single stressful event is sometimes sufficient to trigger posttraumatic stress disorder (PTSD) and lasting fear. We propose that the development of such fear symptoms can be prevented by inhibition of glutamate receptors in the aftermath of stress. If this hypothesis is experimentally confirmed, the results will open new therapeutic options for the risk reduction and secondary prevention of fear symptoms associated with PTSD.

DESCRIPTION (provided by applicant): Rooted in recent wars, displacement, and socio-economic instability, Serbia has established a 13.5% increase in the prevalence of post-traumatic stress disorder (PTSD) and major depression, making them the second largest public health problem in this LMIC country. In parallel, the health system has deteriorated, facing multiple challenges in areas of basic and clinical research. Most recently, a health care reform has started to address these problems at different levels. This proposal aims to join this initiatie by developing a collaborative program between Northwestern University (USA) and Vinca Institute (Serbia) in basic and translational research relevant for major affective disorders. The short-term goal of this collaboration is to initiate the discovery of molecular endophenotypes of PTSD by focusing on a newly proposed interaction between the glutamatergic and glucocorticoid (GC) systems. Our central hypothesis posits that the N-methyl-D-aspartate (NMDAR) subunit NR2A essentially contributes to PTSD- and depression-like behavior by regulating the nongenomic and genomic actions of GR. We will test this hypothesis by three specific aims designed to: (1) Establish the role of NR2A deficiency in fear regulation, depression, and GR signaling, (2) Determine whether the behavioral effects of NR2A deficiency can be rescued by nongenomic or genomic GR, and (3) Initiate collection of blood samples from PTSD patients to validate the preclinical findings. After completing the study, we expect to have determined that membrane- impermeant GC will rescue the glutamatergic deficits underlying PTSD-like behavior without exacerbating depression-like behavior. The resources will be used for building capacity for PTSD research in Serbia by training LMIC personnel, acquiring research equipment, and generating pilot data for a large-scale proposal aiming to identify novel treatment, diagnostic, and prognostic molecular targets of PTSD. The long-term goal is to develop a strong translational program in Serbia in the area of major affective disorders and initiate cross-cultural studies between the collaborating institutions. The research is primarily designed to establish the use of blood molecular phenotypes for the diagnosis, prognosis, and treatment of patients suffering from major emotional disorders.

ABSTRACT The highest cognitive functions such as reasoning, planning, and decision-making, are all, directly or indirectly, influenced by our past personal experiences, which are represented in hippocampal-cortical circuits as episodic memories. Dysfunction of these circuits has been linked to the most prevalent and challenging mental disorders of our time, ranging from dementia to anxiety, depression, and post-traumatic stress disorder. Understanding the neurobiological mechanisms of episodic memory formation and retrieval are therefore essential for the development of effective molecular and circuit-based therapies for such disorders. The current project focuses on systems consolidation, a process which, through sustained interactions between hippocampal and cortical circuits, leads to a lasting cortical representation of episodic memories. Based on existing evidence, including our own published and pilot data, we posit a key role of activity-dependent inflammatory signaling in discrete dorsohippocampal (DH) projections to the retrosplenial cortex (RSC) in systems consolidation, including tagging, activation, and deactivation of the DH-RSC circuit. Aim 1 is designed to determine the contributions of discrete DH-RSC projections to early tagging of RSC and sustained inflammatory signaling in DH and RSC. Aim 2 will focus on the direct contribution of hippocampal Toll-like receptors (Tlr) to memory consolidation and induction of TGFb1, and Aim 3 will examine the contribution of TGFb to the cortical dependence of memories and deactivation of inflammatory signaling in the DH-RSC circuit. These aims will be tested in mouse models of episodic-like memories by applying projection-specific manipulations of the DH-RSC circuit, cell-specific genetic manipulations of Tlr9 and TGFb receptors, and by monitoring circuit activity through virally expressed signaling reporters in vivo. We also plan to apply quantitative molecular biologic and biochemical approaches that will enable us to determine the concentration- dependent TGFb effects on gene expression patterns associated with activation and deactivation of the DH- RSC circuit. We believe that advancing our understanding of neuronal inflammation in the organization of memory circuits will advance our fundamental knowledge of systems consolidation. At the same time, we hope that circuit-specific Tlr9/TGFb signaling will emerge as candidate target for therapies for neuropsychiatric disorders rooted in episodic memory deficits.

PROJECT SUMMARY This application seeks to renew the Neurobiology of Information Storage Training Program (NISTP), which is devoted to preparing exceptional predoctoral students for research-intensive careers in the science of learning and memory. Active since 2003, the program is focused on training in fundamental mechanisms of information storage in animals and humans, acting as a central organizer for research in this area at Northwestern. With the recent shift in mental health research toward dimensional, systems-based frameworks there is unprecedented need for training of the kind offered through this program, which provides training at multiple levels of analyses for understanding mechanisms of learning and memory and their relevance to mental health. The NISTP is based in the Northwestern University Interdepartmental Neuroscience (NUIN) program, emerging from a multidisciplinary group of 29 interactive investigators who have successfully engaged in collaborative research on molecular/genetic, cellular/circuit, and systems/behavioral determinants of information storage. NISTP preceptors have strong track records in predoctoral training and well-funded research programs, and can impart both basic and clinical perspectives to a group of outstanding developing scientists. Training components of the NISTP will include: 1) an advanced course in the latest research in information storage neurobiology, taught by NISTP preceptors; 2) two trainee-hosted lecture series featuring leading investigators in the field of information storage; 3) mock study sections for trainees preparing NRSA applications; and 4) quarterly NISTP meetings including a) ?research in progress? trainee talks, b) ?bench to bedside? translational discussions, c) ?computational modeling and memory? interactive discussions, and d) the annual NISTP retreat. NISTP also serves to educate students in the ethics of science and to recruit students from underrepresented groups to study learning and memory. Continuous evaluation of the program will be accomplished using qualitative mechanisms, such as evaluations by trainees, and quantitative measures, such as tracking the research productivity, funding, and career trajectories of former trainees. An internal Steering Committee and an External Advisory Committee will conduct additional assessment processes.Trainees are drawn primarily from a pool of NUIN students who have completed most of the required coursework and have We r equest continued support for five trainee slots, which will be supplemented with one institutionally funded ?affiliate? slot . With the value added by the NISTP, we are confident that NISTP trainees will emerge from their graduate training poised to advance research in fundamental biological mechanisms of learning and memory and well positioned to develop novel translational applications. made significant progress in their thesis research.

Opioid drugs are widely prescribed to patients suffering from chronic pain despite the fact that we still know very little about the impact of opioids, chronic pain, and both conditions on brain function. The main goals of this project are to (i) provide novel evidence for the functional interaction between reward-, pain-, and memory-processing circuits, (ii) determine how this interaction is affected by chronic pain, and (iii) show whether restoring the function of these circuits can reduce pain and opioid addiction. Based on our recent and pilot studies, we posit that functional changes in projections from the mesolimbic ventral tegmental area (VTA) to DH, carrying information on pain and reward, alter hippocampal plasticity and enable the DH-RSC memory circuit to gain excessive control over both chronic pain and opioid craving. Dissecting the role of individual neurotransmitter circuits is essential for the better understanding of sex-specific differences in opioid seeking, showing higher susceptibility of females to aversive triggers and higher susceptibility of males to rewarding triggers. Specific Aim 1 is designed to determine the role of VTA-DH projections in chronic pain and opioid craving using chemogenetic inactivation of glutamatergic, GABAergic, dopaminergic pathways. Specific Aim 2 will use similar approaches to determine the role of glutamatergic DH-RSC and RSC-VTA projections. Specific Aim 3 will show whether sex-specific activity of discrete VTA-DH-RSC projections is sufficient to induce pain and opioid craving. Specific Aim 4 will integrate key findings of Project 3 with findings of the other projects of the Center by examining the relationship between memory and reward circuits (Project 2), the relationship between transcriptional changes in the VTA and the reorganization of VTA-DH circuits (Project 4), the impact of individual VTA-DH-RSC pathways on whole brain activity and connectivity (Project 1), and the relevance of our findings for patient populations (Project 1). We expect to show that originally distinct pathways processing pain, reward, and memory, alter their stimulus specificity during chronic pain and addiction, causing changes of DH plasticity and reorganization of the VTA-DH-RSC circuit. The circuit, transcriptional, and synaptic mechanisms identified in this project will serve as a basis for development of new treatments for chronic pain and addiction. !