Cocaine-Mediated Modulation of Dopamine Transmission and Its Effects on Peripheral Immunity - Project Summary Midbrain expressing dopamine transporter (DAT), located in the ventral tegmental area (VTA) and substantia nigra pars compacta (SNpc), are involved in psychostimulant use disorders, psychiatric diseases, movement disorders, and HIV-associated neurocognitive disorder. Cocaine, a highly addictive psychostimulant, blocks DAT-mediated dopamine (DA) uptake, increasing extracellular DA levels in the CNS. Key to this proposal, activation or inhibition of DA neurons impacts peripheral immunity. For example, I have shown that peripheral immunity is dysregulated when DA neurons are lesioned, suggesting that midbrain DA can influence peripheral immunity, but the midbrain-to-peripheral circuitry is poorly understood. My pilot data suggest that midbrain DA neurons send projections to the dorsal vagal complex (DVC) and make synapses within the DVC. Neurons in the DVC express D1-like and D2-like dopamine receptors and change their activity in response to dopamine. The DVC projects to multiple organs, including the spleen via the celiac ganglion. My pilot data support the connection between midbrain-DVC-spleen, and that chemogenetic stimulation of midbrain DA neurons alters splenic immunity. I have also shown that immune cells express DAT, where in immune cells DAT activation is immune suppressive, highlighting distinct roles for DAT activity on peripheral immune cells versus DAT activity in the brain. Mice with global DAT deletion (DAT KO) exhibit heightened peripheral inflammatory responses to immune challenges, supporting an immune suppressive role for DAT in peripheral immunity. To study CNS DAT activity on peripheral immune cells independent of DAT's effects on peripheral immune cells, I generated mice chimeras with selective DAT deletion in the peripheral immune system (while keeping CNS DAT intact). Preliminary experiment in these chimeric mice shows immune cells DAT deletion causes distinct immunological changes compared to global DAT KO. My pilot data support the hypothesis that midbrain DA neuron activation affects peripheral immune responses via DA release in the DVC, regulating a midbrain-DVC-spleen circuit independent of immune cell DAT activity. In Aim 1, I will use viral tracing approaches to investigate whether midbrain DA neurons project to and make synapses within the DVC, whether these projections extend to the spleen in a multi-synaptic mechanism, and whether activation or inhibition of these neurons modulate splenic immunity. In Aim 2, I will investigate whether systemic cocaine versus locally applied cocaine in the CNS differentially affect splenic immunity. In Aim 3, I will test the hypothesis that DAT on peripheral immune cells modulates their immune response to immune stimulation. The results will provide novel insights into how DAT- expressing neurons influence the immune system and the independent role of DAT in immune cells, providing strong conceptual and methodological training under Drs. Khoshbouei and Okun, and under a mentoring team comprised of established professors, who are experts in the proposed approaches and are accomplished mentors, helping me to complete the proposed research and achieve career development goals of this proposal.
