Stacia I. Lewandowski

Abundant evidence indicates that repeated exposure to cocaine results in cellular and molecular adaptations in the mesolimbic dopamine (DA) reward system, which is comprised of dopaminergic projections from the ventral tegmental area (VTA) to the nucleus accumbens (NAc). Adaptations resulting from cocaine exposure reorients behavior towards drug seeking and drug use, making cocaine addiction a vicious cycle. Despite this knowledge, there are no FDA-approved pharmacotherapies for cocaine use disorder, suggesting that a more detailed understanding of the neurobiology that underlies cocaine addiction is needed. Cocaine exerts its addictive effects by blocking the dopamine transporter (DAT), leading to excess DA in the synaptic cleft, resulting in the euphoric “high” that is often sought-after during addiction. This leads to the activation of intracellular signaling pathways, such as the ERK1/2 Map Kinase signaling pathway. ERK1/2 signaling is abundantly distributed in the mesolimbic DA reward system, suggesting the importance of ERK1/2 signaling in the regulation of DA neurotransmission. This study describes the cell-specific modulation of the ERK1/2 pathway in vivo by expressing the ERK1/2 phosphatase MKP3 in dopaminergic neurons only. This is accomplished by generating adeno-associated viral (AAV) vectors with Cre recombinase (Cre)-dependent expression of MKP3. This construct is injected into the VTA of Long Evans rats expressing Cre in tyrosine hydroxylase positive cells (TH-Cre rats), thus achieving a decrease of the ERK1/2 signaling in DA neurons of the VTA. This study has found that cell-specific ERK1/2 inhibition results in the attenuation of cocaine-associated behaviors, which may be driven by observed changes in DA neurotransmission in the NAc. Using ex vivo brain slice biotinylation, this project has revealed that there are significant differences in cell surface levels of DAT in the striatum, suggesting ERK1/2 signaling may regulate DA tone by managing DAT surface availability as well as expression of key DA proteins. This demonstrates the importance of ERK1/2 signaling in the cellular and molecular adaptations associated with cocaine use. The goal of the proposed research is to identify specific downstream targets of this pathway to reveal novel therapeutic targets for treating cocaine use disorders.