Joseph M. Stujenske, M.D., Ph.D. - US grants

? DESCRIPTION (provided by applicant): Fear is an adaptive mechanism for interacting with an uncertain environment. Fear should be evoked at times when danger is likely and suppressed when safety is perceived. Neural activity of fear and safety circuits are believed to underlie these dynamic shifts in fear expression. In particular, circuits in the basolateral amygdala (BLA) are believed to be an important hub for meditating these switches. The BLA integrates diverse input from sensory cortices, frontal cortices, and the thalamus, which carries direct sensory information from sensory organs. Output structures of the BLA ultimately control physiological reactions to stress: changes in heart rate, respiratory rate, and other systems controlled by the hypothalamic-pituitary axis. Thus, if fear circuits in the BLA were activated inappropriately, all f the physiological effects associated with stress would be triggered, though the environment would otherwise be perceived to be safe. This could also arise if safety circuits were unable to properly suppress fear-related signaling. Dysfunction in safety circuits are hypothesized to underlie fear and anxiety disorders, especially post- traumatic stress disorder (PTSD), in which exaggerated and inappropriate fear responses are elicited. Brain imaging studies have identified two prominent changes in patients with PTSD: hyperactivity of the amygdala and hypoactivity of the prefrontal cortex (PFC); thus, it was hypothesized that the amygdala mediates fear, while the PFC mediates safety by a suppression of amygdala activity. This model is of course oversimplified. It remains unclear how the amygdala and PFC interact to mediate switches between fear and safety. To investigate this question, we have previously recorded simultaneously from the BLA and PFC using microelectrodes while mice were exposed to aversive and safe cues. Our results revealed that safety was associated with directional transfer of information from the PFC to the BLA and that directional communication led to a strengthening of fast gamma (70-120 Hz) oscillations in the BLA. This proposal aims to take advantage of this identified neural correlate to probe the specific circuit elements underlying safety signaling using optogenetic approaches simultaneously with in vivo electrophysiology. Oscillatory activity is believed to relate to the activity of inhibitory cells, and indeed, disrupton of inhibition in the amygdala has been shown to infere with the proper suppression of fear in animal models. However, there are many classes of inhibitory interneurons, and we thus seek to further dissect this microcircuitry to identify the neural underpinnings of fear suppression and mPFC-BLA communication. This will be accomplished by separately manipulating the two main classes of interneurons in the BLA, parvalbumin and somatostatin-positive cells.

Project Summary/Abstract This proposal is for a four-year research career development program, focused on the study of the neurophysiology of fear and safety discrimination, which has relevance to anxiety disorders and post-traumatic stress disorder. By the start of the project, the candidate will have been appointed an Instructor in the Department of Psychiatry at Weill Cornell Medical Center. The proposal is a natural extension of the candidate's previous research and clinical training on safety signals in the medial prefrontal cortex (mPFC) and basolateral amygdala (BLA). It outlines a plan for the candidate to achieve his goal of becoming an expert in the circuit mechanisms of fear and anxiety disorders, extending the training of the candidate in two dimensions, which are reflected in the mentorship of Drs. Conor Liston and Joshua Levitz: 1. Encoding of fear and safety- related information in large, distributed mPFC and BLA ensembles and 2. Cell-surface receptors that modulate prefrontal output to the BLA for successful fear discrimination and represent promising pharmacological targets for treating generalized fear. The proposed experiments and multi-faceted training plan will impart the candidate with a unique combination of skills that will position him to transition into a successful independent career as a physician-scientist studying the neurophysiology of fear and anxiety in psychiatric disorders. Anxiety disorders are the most prevalent mental disorders, affecting one-fifth to one-third of the adult US population, and the disorders are typically chronic, associated with high disease burden and significant healthcare cost. While effective treatments exist, a substantial proportion of patients are minimally responsive, underpinning the need to develop therapeutics that work through different cellular mechanisms. Anxiety disorders are highly co-morbid with each other and with other psychiatric disorders, highlighting the value of research into common neurocircuit mechanisms with trans-diagnostic relevance. Patients with PTSD or anxiety disorders have both been found to exhibit the overgeneralization of conditioned fear, which is associated with abnormal reactivity of the mPFC and BLA. The goal of my proposal is to investigate the encoding of fear and safety discrimination in interconnected mPFC and BLA neurons. Specifically, this proposal investigates the role of metabotropic glutamate receptor 2 (mGluR2) in controlling mPFC-to-BLA output by: 1. Defining high- dimensional fear and safety encoding mechanisms in mGluR2+ and mGluR2- mPFC-BLA projectors; 2. Elucidating fear discrimination learning-related changes in connectivity between mGluR2+ and mGluR2- mPFC cells and functionally-distinct downstream BLA ensembles; 3. Dissecting the role of mGluR2 signaling specifically at mPFC-BLA presynaptic terminals in fear discrimination learning. Collectively, these experiments provide novel insight into the neurophysiology of fear and safety discrimination in the mPFC-BLA circuit and investigate mGluR2 as a potential therapeutic target for anxiety disorders and PTSD.