Many Operation Iraqi Freedom/Operation Enduring Freedom/Operation New Dawn (OIF/OEF/OND) veterans experience chronic pain, which is worsened by co-morbid conditions such as post-traumatic stress disorder (PTSD) and depression. Significantly, there is an unmet clinical need to provide effective treatments for chronic pain. One hurdle for the development of new therapies is a lack of understanding which neurotransmitters and brain circuits are responsible for the persistence of chronic pain. Thus, this career development application will provide the necessary training to develop an independent VA scientist capable of researching novel brain circuitry responsible for the development of stress-induced chronic pain. OBJECTIVES: The objective of this study is to identify the brain circuitry responsible for persistent stress- induced pain and comorbid behaviors using targeted brain manipulations, including optogenetic techniques. The overarching hypothesis is that stress induces imbalanced signaling within the limbic brain circuitry to produce persistent pain hypersensitivity. RESEARCH PLAN: This project will utilize two interrelated, independent specific aims. Specific Aim 1 will test the hypothesis that stress-induced increases corticotropin-releasing factor signaling in the medial prefrontal cortex leads to persistent visceral and somatic pain-like behaviors. Specific Aim 2 will test the hypothesis that an imbalance in signaling between limbic brain regions, regulated by corticotropin-releasing factor and glutamatergic receptors, is responsible for chronic stress-induced hypersensitivity. We will use a combination of targeted stereotaxic surgeries, cannula implantations, drug microinfusions, and laser stimulation to modify nociceptive, anxiety-like, and depression-like behaviors in conscious, freely moving rats. TRAINING PLAN: Through his mentoring team and consultants, the candidate will receive training on how to conduct the optogenetic, electrophysiological, and behavioral studies needed to address the research plan. Additionally, the candidate will take formal courses to promote his professional development, including responsible conduct of research, statistical analysis, and laboratory management. With formal mentorship to improve his written and oral communication, the candidate will be able to present the findings of this research at national and international meetings and publish the results in quality journals. ANTICIPATED OUTCOMES: The research in Aim 1 will demonstrate that stress-induces increases in corticotropin-releasing factor expression within the medial prefrontal cortex leading to enhanced visceral and somatic sensitivity, which signals through corticotropin-releasing factor receptors in the bed nucleus of the stria terminalis to produce the behaviors. Specific Aim 2 will show using optogenetic activation that activation of amygdala terminals or inhibition of medial prefrontal cortex terminals in the bed nucleus of the stria terminalis will produce visceral and somatic hypersensitivity in non-stressed rats. The experiments will also demonstrate that inhibiting amygdala signaling (corticotropin-releasing factor) while stimulating medial prefrontal cortex signaling (glutamate) in chronically stressed rats will inhibit pain-like behaviors. Completion of these Specific Aims, along with the proposed mentoring and training, will ensure that the candidate develops his research skills to submit a future VA Merit grant and eventually becomes a life-long VA Research Career Scientist. SIGNIFICANCE TO VETERANS HEALTH: Scientifically, the results from this project will identify a novel stress-associated brain circuit, along with the specific neurotransmitters, that modulates chronic pain. Identification of the mechanisms and circuitry involved in chronic stress-induced pain could lead to new targets for therapies to treat veterans experiencing chronic pain, which is a significant unmet healthcare burden. Professionally, this career development award will produce an independent scientist with the capability of investigating chronic pain mechanisms to provide additional tools to improve the quality-of-life for veterans.