The Role of Dopamine Transporter Trafficking in Psychostimulant Addiction

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DESCRIPTION (provided by applicant): Psychostimulant addiction is a widespread problem in the United States that affects millions of individuals at a substantial cost in both lost wages and medical expenses. Amphetamines and cocaine act primarily by blocking monoamine reuptake facilitated by sodium- and chloride-dependent plasma membrane transporters for serotonin, norepinephrine and dopamine. Although these psychostimulants have equimolar affinity for the monoamine transporters, the reinforcing properties of these drugs are thought to be largely mediated by their interaction with the dopamine transporter (DAT). Recent in vitro and in vivo studies demonstrate that, in addition to inhibiting DAT function, amphetamines and cocaine also modulate DAT cell surface levels via membrane trafficking. Preliminary studies from our laboratory demonstrate that amphetamine- induced loss of cell surface DAT occurs via enhancing DAT internalization rates. However, it is unknown whether psychostimulant-induced changes in DAT surface expression are integral to the addictive process. This is due to a lack of available animal models to test this hypothesis. We recently identified a ten amino acid region spanning residues 587-596 in the DAT carboxy terminus that is necessary for basal and protein kinase C-stimulated DAT endocytosis. We propose to test whether psychostimulant- mediated DAT trafficking is required for the rewarding properties of psychostimulants. To this end, we aim to generate DAT "knock in" mice expressing endocytic-defective DATs. The resulting mice will be assessed for amphetamine self-administration, conditioned place preference and sensitization, to test whether DAT trafficking plays a role in the rewarding properties of psychostimulants. Moreover these animals will be an invaluable tool for future studies examining the role of DAT trafficking in synaptic transmission and dopaminergic plasticity. Psychostimulant abuse and addiction is a growing problem in the United States, reaching near epidemic proportions over the past several years. Despite numerous investigations into the mechanisms underlying psychostimulant addiction, there are still large gaps in our knowledge. The current proposal aims to develop an animal model in which the targets of amphetamine in the brain are modified, to determine whether the actions of amphetamine on these target proteins contribute to the addictive process.