All ETDs from UAB

Advisory Committee Chair

Jeremy Day

Advisory Committee Members

Aurelio Galli

Brittany N Lasseigne

Erik D Roberson

Summer B Thyme

Document Type

Dissertation

Date of Award

2023

Degree Name by School

Doctor of Philosophy (PhD) Heersink School of Medicine

Abstract

The mesolimbic dopamine (DA) pathway, which consists of dopaminergic neurons that project from the ventral tegmental area (VTA) to the nucleus accumbens (NAc), is heavily implicated in drug addiction. Exposure to drugs of abuse results in increases in extracellular concentrations of DA in the NAc, which in turn activates an immediate early gene (IEG) expression program that primarily consists of activity-dependent transcription factors, such as the AP1 subunits Fos and JunB. IEGs engage a set of temporally and functionally distinct genes, termed the late response gene (LRG) expression program. While gene expression changes are critical for drug-dependent adaptations, two major questions remain. First, how does cell type heterogeneity contribute to drug-dependent transcriptional changes? Second, what is the molecular mechanism governing IEGdependent LRG activation? To answer the first question, I utilized single nucleus RNAsequencing (snRNA-seq) to comprehensively characterize transcriptionally distinct cell types in the rat VTA and NAc. In the VTA, we identified a cell type expressing the molecular machinery required for the synthesis and transport of multiple neurotransmitters. Differential expression analysis identified novel marker genes for both combinatorial and classically-defined DA neurons, which were validated with RNA fluorescence in situ hybridization (FISH). Interestingly, in the NAc we identified two populations of transcriptionally distinct Drd1-expressing medium spiny neurons (D1-MSNs). iv Interestingly, only one of these D1-MSN populations exhibited cocaine-induced IEG expression. Finally, to understand IEG-dependent LRG upregulation, I utilized primary rat embryonic striatal neurons to profile activity-dependent transcriptional and epigenetic changes. These experiments demonstrated that activity-dependent chromatin remodeling is dependent on protein synthesis and primarily occurs at genomic enhancers. Targeted analysis of enhancers undergoing chromatin remodeling identified a region upstream of the Pdyn TSS. CRISPR-based functional assays identified this region as a genomic enhancer that is necessary and sufficient for Pdyn transcription in both the rat and human genome. Together, the data within this thesis demonstrate that cell type heterogeneity significantly contributes to drug-dependent transcriptional changes within the NAc and identifies genomic enhancers as critical regulators of activity-dependent transcriptional responses that are important for drug-dependent cellular and behavioral adaptations.

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