Abstract: Cocaine is a widely abused psychostimulant that acts primarily by elevating extrasynaptic dopamine levels through the inhibition of dopamine transporter function. At the present time, there are no viable and effective treatment options available for cocaine use disorders. A detailed understanding of the regulation of downstream molecular substrates mediating the physiologic adaptations that occur following cocaine exposure and how they contribute to the pathophysiology of cocaine abuse is of critical importance for identifying potential therapeutic strategies for treating cocaine use disorders and thus for public health. In vitro studies have demonstrated a central role for the intracellular ERK1/2 kinase signaling pathway in the regulation of key proteins within dopaminergic neurons. However, gaps remain in our understanding of how these results translate into ex vivo and in vivo models of cocaine use disorders. We propose to employ a novel approach enabling temporally and anatomically precise control over ERK1/2 signaling in dopamine neurons. This approach involves a viral construct developed in our laboratories with Cre recombinase-dependent expression of a blue-light inducible activator of this signaling pathway. The viral construct will be employed in combination with transgenic rats that express Cre recombinase in dopaminergic neurons to specifically target intracellular ERK1/2 signaling in dopamine neurons. In support of our approach, we have observed increased ERK1/2 activation following blue light exposure and that ERK1/2 activation of DA terminals in the NAc disrupts DA neurotransmission. We will use this targeted genetic approach to further our understanding of the role of intracellular ERK1/2 signaling in dopaminergic cells in regulating dopamine neurotransmission. We will use biochemical assays to determine changes in expression, phosphorylation, and subcellular localization of key dopaminergic proteins (Aim 1) and employ in vivo fast scan cyclic voltammetry (Aim 2) to study alterations in DA neurotransmission resulting from the activation of ERK1/2 signaling in dopaminergic neurons We believe the successful completion of this project will lead to novel insights into the regulation of cellular and molecular changes involved in the development of cocaine use disorder. We anticipate that the experiments described in this application will facilitate future studies to identify unique downstream targets of these pathways that mediate cocaine-associated behaviors. We expect this will ultimately lead to novel therapeutic avenues for treating this disorder.