Project Summary/Abstract Substances of abuse alter neural circuitry that result in the progression towards a substance use disorder (SUD) in a subset of individuals. Currently, the United States is faced with an epidemic of SUD causing immense human suffering and high overdose rates. Understanding the changes in neural circuitry that underlie the transition to SUD-like behaviors, particularly in behaviors that have high risk such as escalated drug intake, is key to designing and implementing new therapeutic techniques to combat this epidemic. The midbrain dopaminergic system and particularly its projection to the Nucleus Accumbens (NAc) has been heavily implicated in drug consumption and is believed to be involved in the addictive liability of drugs and the progression to compulsive drug taking. Importantly, previous results from the Phillips lab demonstrated that escalation of drug intake results from a decrement of the phasic dopamine signal to drug associated cues. The driving force behind this degradation of phasic dopamine response related to drug consumption is unknown. However, other neuromodulatory systems have also been implicated in drug consumption, such as corticotropin releasing factor (CRF), and are capable of modulating the dopamine system. The overarching hypothesis of this proposal is that CRF receptors in specific subpopulations of the NAc contributes to escalation of drug intake through negatively modulating dopamine signaling. This hypothesis will be addressed through two independent aims. Aim 1 will test the necessity of CRF receptor 1 in the NAc in the escalation of drug taking via bilaterally knocking out CRF receptor 1 in NAc subpopulations using CRISPR/SaCas9 technology prior to a long access self-administration regime. Aim 2 will test the modulation of phasic dopamine response via CRF receptor 1 in the NAc during escalation of drug taking via unilaterally knocking out CRF receptor 1 and bilaterally measuring dopamine signaling in the NAc during long access self-administration via fiber photometry coupled with a dopamine sensor. The results from this proposal will 1) outline the role of NAc CRF receptors and 2) further investigate the contribution of dopamine modulation, both in the progression of SUD-like phenotypes. Uncovering the neural mechanisms that drive SUD-like drug consumption will provide therapeutic targets to combat SUD and related harms.