SUMMARY Substance use disorder (SUD), including use of the psychostimulant amphetamine (AMPH) and its congeners, is on the rise, especially in the Covid-19 pandemic era. There are no effective medications available for psychostimulant SUD, likely because of the lack of thorough understanding of the complex neurobiology underlying the disease. Noradrenergic neurotransmission in the mesolimbic circuit plays a critical role in SUD. AMPH inhibits norepinephrine (NE) transporter (NET) activity promoting its behavioral effects. NET, a principal mediator of NE signaling, is regulated by post-translational modifications, such as phosphorylation and protein- protein interactions. These regulators of NET are impacted by psychostimulants, including amphetamine, in turn impacting the stimulant and rewarding effects of these drugs. However, to date, post-translational modifications have not been a focus of investigation in the SUD field. Our published studies over several years demonstrate that the The258/Ser259 motif, a phospho-site in the NET, plays a pivotal role in regulating AMPH-evoked behaviors. In this proposal, we explore this novel finding using cutting-edge techniques, including a phosphorylation-defective NET-Thr258Ala/Ser259Ala mutant mouse model (NET-T258A/S259A), a viral- mediated brain region-specific blockade of NET-T258/S259 phosphorylation, and recordings of extracellular NE dynamics in vivo using high-speed chronoamperometry and microdialysis. With these new models and tailored biochemical, neurochemical, and behavioral studies, the current proposal aims to fill critical gaps in our understanding of the central role of NET phosphorylation in AMPH-evoked NE dynamics and animal behavior. As a key mechanism, we have discovered that NET-T258A/S259A mice exhibit genotype- and sex-specific alterations in AMPH sensitivity in addition to brain-region specific variations in NET function and expression. Here, we will expand and test our overarching hypothesis that brain region-specific T258/S259-dependent NET phosphorylation and regulation contributes to sex-specific AMPH-induced behaviors relevant to addiction and reward. Aim 1 will investigate NET regulatory phenomena including NET phosphorylation and NET subcellular distribution and protein-protein interactions in the prefrontal cortex and nucleus accumbens to determine the relationship between T258A/S259A mutant-dependent dysfunction in AMPH-mediated NET regulation and in AMPH-evoked behaviors. Aim 2 will evaluate brain-region specific roles of T258/S259-dependent NET regulation in AMPH reward using adult DBH-Cre mice expressing the NET-T258/S259 motif in a NE-terminal specific manner. Aim 3 will examine the impact of T258/S259-dependent NET phosphorylation and regulation on NE dynamics (release and clearance as well as extracellular levels) modulated by AMPH in vivo. Outcomes from proposed studies will provide novel insights into the mechanisms of SUD, open new avenues for examining T258/S259-p...