Fentanyl, a potent painkiller, elicits both positive and negative reinforcement, leading to addiction in a significant portion of users. μ-opioid receptors play a crucial role in these reinforcing effects, but the specific neural circuits involved remain unclear. This study used optogenetic and genetic approaches to identify the neuronal populations responsible for positive and negative reinforcement in the ventral tegmental area (VTA) and central amygdala (CeA), respectively. In VTA, μ-opioid receptor knockdown abolished dopamine transients and positive reinforcement but did not affect withdrawal symptoms. In CeA, μ-opioid receptor knockdown eliminated aversive symptoms during withdrawal, suggesting its role in negative reinforcement. Optogenetic stimulation of μ-opioid receptor-expressing neurons in CeA caused place aversion, and mice learned to press a lever to pause this stimulation, indicating the presence of a disinhibition mechanism involving μ-opioid receptors in VTA for positive reinforcement. These findings provide insights into the neural circuits underlying fentanyl addiction and suggest potential targets for interventions to reduce addiction and facilitate rehabilitation.Fentanyl, a potent painkiller, elicits both positive and negative reinforcement, leading to addiction in a significant portion of users. μ-opioid receptors play a crucial role in these reinforcing effects, but the specific neural circuits involved remain unclear. This study used optogenetic and genetic approaches to identify the neuronal populations responsible for positive and negative reinforcement in the ventral tegmental area (VTA) and central amygdala (CeA), respectively. In VTA, μ-opioid receptor knockdown abolished dopamine transients and positive reinforcement but did not affect withdrawal symptoms. In CeA, μ-opioid receptor knockdown eliminated aversive symptoms during withdrawal, suggesting its role in negative reinforcement. Optogenetic stimulation of μ-opioid receptor-expressing neurons in CeA caused place aversion, and mice learned to press a lever to pause this stimulation, indicating the presence of a disinhibition mechanism involving μ-opioid receptors in VTA for positive reinforcement. These findings provide insights into the neural circuits underlying fentanyl addiction and suggest potential targets for interventions to reduce addiction and facilitate rehabilitation.