This study investigates the distinct neural circuits that trigger positive and negative fentanyl reinforcement in mice. Fentanyl, a potent opioid, induces euphoria and positive reinforcement, while also causing dependence and negative reinforcement through withdrawal symptoms. The research identifies that μ-opioid receptors (μORs) in the ventral tegmental area (VTA) and central amygdala (CeA) play critical roles in these processes. In the VTA, μORs on GABA neurons inhibit dopamine neurons, leading to increased dopamine in the nucleus accumbens (NAc), which drives positive reinforcement. Knockdown of μORs in the VTA abolished positive reinforcement but did not affect withdrawal, suggesting that VTA μORs are primarily involved in positive reinforcement. In contrast, μORs in the CeA are involved in negative reinforcement, as their knockdown reduced aversive withdrawal symptoms. Optogenetic stimulation of CeA μOR-expressing neurons induced place aversion, and mice learned to press a lever to stop this stimulation, indicating that these neurons mediate negative reinforcement. The study reveals that distinct populations of μOR-expressing neurons in the VTA and CeA are responsible for positive and negative reinforcement, respectively. These findings highlight the importance of specific neural circuits in the development of fentanyl addiction and suggest potential targets for interventions to reduce addiction and facilitate rehabilitation. The research also underscores the complex interplay between positive and negative reinforcement in the transition from controlled to compulsive opioid use.This study investigates the distinct neural circuits that trigger positive and negative fentanyl reinforcement in mice. Fentanyl, a potent opioid, induces euphoria and positive reinforcement, while also causing dependence and negative reinforcement through withdrawal symptoms. The research identifies that μ-opioid receptors (μORs) in the ventral tegmental area (VTA) and central amygdala (CeA) play critical roles in these processes. In the VTA, μORs on GABA neurons inhibit dopamine neurons, leading to increased dopamine in the nucleus accumbens (NAc), which drives positive reinforcement. Knockdown of μORs in the VTA abolished positive reinforcement but did not affect withdrawal, suggesting that VTA μORs are primarily involved in positive reinforcement. In contrast, μORs in the CeA are involved in negative reinforcement, as their knockdown reduced aversive withdrawal symptoms. Optogenetic stimulation of CeA μOR-expressing neurons induced place aversion, and mice learned to press a lever to stop this stimulation, indicating that these neurons mediate negative reinforcement. The study reveals that distinct populations of μOR-expressing neurons in the VTA and CeA are responsible for positive and negative reinforcement, respectively. These findings highlight the importance of specific neural circuits in the development of fentanyl addiction and suggest potential targets for interventions to reduce addiction and facilitate rehabilitation. The research also underscores the complex interplay between positive and negative reinforcement in the transition from controlled to compulsive opioid use.