PROJECT SUMMARY/ABSTRACT Alcohol directly stimulates the hypothalamic-pituitary-adrenal (HPA) axis, a primary stress system, initiating the release of glucocorticoid hormones. Preclinical work indicates that chronic alcohol exposure increases both brain and peripheral corticosterone in rodents, with some studies suggesting greater increases in the brain. These increases in rodent brain glucocorticoid levels are prolonged and persist long after plasma corticosterone returns to baseline. Thus, brain glucocorticoid dysfunction may underlie long-lasting, persistent alcohol use. Studies of HPA axis dysregulation in humans with alcohol use disorder (AUD) have only examined peripheral cortisol in relation to alcohol and with mixed results. Chronic alcohol use is associated with both elevated and blunted levels of peripheral cortisol in response to alcohol and stress in individuals with AUD. So, what we know about HPA dysregulation in AUD is based solely on peripheral cortisol, and results are inconsistent and incomplete because we have not been able to study a marker of brain cortisol - forming a significant gap in the existing literature. Translating preclinical findings in the brain to human AUD and examining the relationship between brain-peripheral cortisol is a critical next step in understanding HPA dysfunction in this population. Levels of glucocorticoids in the brain are dependent on the enzyme 11β- Hydroxysteroid dehydrogenase type 1 (11β-HSD1), which catalyzes the conversion of cortisone to cortisol (or corticosterone in rodents). 11β-HSD1 is expressed in brain regions critical to alcohol addiction, including the amygdala and prefrontal cortex (PFC). Using a novel radiotracer called [18F]FMOZAT together with Positron Emission Tomography (PET) brain imaging, we can now measure levels of 11β-HSD1 in the living human brain. Using these methods, we have exciting preliminary data (obtained through K01AA025670) suggesting that individuals with AUD (n=9) have higher 11β-HSD1 availability compared to healthy controls (n=12) in prefrontal-limbic regions. Preliminary data also demonstrate that 11β-HSD1 availability in ventromedial PFC is associated with drinks per week, quantity of drinks per drinking episode, and AUD severity. However, we do not know how 11β-HSD1 availability in brain corresponds to peripheral cortisol in humans, and whether brain vs. periphery predicts drinking behavior. This proposal will derive critical foundational information on brainperiphery HPA axis dysregulation by: fully characterizing both availability of 11β-HSD1, a cortisol regenerating enzyme, in brain and peripheral cortisol in those with AUD vs. healthy controls, and determining whether brain vs. periphery predicts drinking behavior (Primary Aim 1). We will also evaluate whether 11β-HSD1 availability vs. peripheral cortisol predict stress-related drinking using EMA and a biosensor system in individuals with AUD compared to healthy controls (Exploratory Aim 2). This will...