Opioid use disorder (OUD) is a chronic, relapsing condition driven by maladaptations in critical reward and aversion circuits that perpetuate drug-seeking behavior and exacerbate negative affective states upon cessation of opioid exposure. While mu-opioid receptors (MORs) in the ventral tegmental area (VTA) are central to opioid reinforcement, the remodeling of their structural connectivity during chronic morphine-seeking behavior and their role in negative affect during protracted withdrawal - the weeks to months following opioid cessation – remain unclear. This dissertation seeks to investigate the contribution of VTA MOR neurons to chronic morphine-seeking behavior, acute withdrawal, and negative affective behaviors during protracted withdrawal. Using an oral morphine administration model, we observed that chronic morphine exposure increases lateral hypothalamus (LH) monosynaptic inputs to VTA MOR neurons and induces elevated social deficit-, anxiety-, and despair-related behaviors during a 4-week withdrawal period. VTA MOR neurons exhibit increased neuronal activation at the onset of withdrawal and are connected to prominent reward and aversion structures. Additionally, VTA MORs were identified as critical modulators of withdrawal-induced low sociability and neuronal activation in the anterior cingulate cortex (ACC) in response to an acute morphine challenge dose during protracted withdrawal. These findings underscore the critical role of VTA MOR neurons and their associated circuits in driving opioid-seeking behavior and low sociability during protracted withdrawal, positioning them as potential mechanistic targets for alleviating negative affective states during opioid withdrawal.