Project Summary/Abstract Traumatic brain injury (TBI) affects millions of Americans annually and has been linked to development of psychopathology such as increased alcohol use and anxiety. Stress is also a risk factor for alcohol abuse and anxiety, and TBI is often preceded by stress (e.g., in military combat); therefore it is critical to understand how stress impacts TBI neuropathology and risk for post-TBI psychiatric comorbidities. Addressing this gap in knowledge will provide the basis for development of therapeutic interventions for TBI in stressed individuals, and more specifically the combined impact of TBI and stress on post-injury alcohol drinking and anxiety. The amygdala, which mediates anxiety and influences alcohol motivation and craving, is hyper-responsive in patients with alcohol use disorder (AUD), anxiety disorders, and posttraumatic stress disorder (PTSD), and amygdala responsivity is positively correlated with symptom severity. Evidence from our lab and others suggests that stress and TBI each increase basolateral amygdala (BLA) excitability, which may underlie increases in anxiety-like behavior and operant alcohol self-administration after each of these insults. BLA excitatory transmission is modulated by endocannabinoids (ECs), and increasing EC tone with systemic drug injections prevents behavioral effects of stress or TBI. Collectively, these findings support the hypothesis that stress exacerbates post-TBI alcohol drinking, anxiety-like behavior, and EC-modulated BLA hyperexcitability. Therefore we predict that increasing BLA EC tone will reduce post-TBI/stress alcohol drinking and anxiety-like behavior. This hypothesis will be tested in male and female rats using a fluid percussion model of TBI. The specific aims will test the predictions that (1) traumatic stress exacerbates TBI-induced neurobehavioral impairment; (2) traumatic stress exacerbates TBI-induced increases in BLA excitability and decreases in EC signaling; and (3) increasing BLA EC tone reduces alcohol self-administration and anxiety-like behavior after stress and TBI. Rats will be exposed to predator odor 24 h prior to receiving mild TBI to the somatomotor cortex and then tested for alcohol self-administration and anxiety-like behavior over the 10 days following injury. Brains will be excised 24 h after behavioral testing to examine changes in BLA excitability via slice electrophysiology and changes in cannabinoid receptor type 1 (CB1R) expression via immunohistochemistry. Pharmacological manipulation of BLA EC tone 30 min post-injury will be used to test potential attenuation of post-TBI/stress escalation of alcohol drinking and anxiety-like behavior. Completion of this project will contribute to our understanding of the impact of prior stress exposure to the neuropathophysiology of TBI and may identify novel treatment targets for TBI and comorbid psychiatric illnesses like AUD and PTSD. This research proposal and the associated professional development ac...