PROJECT SUMMARY/ABSTRACT – OVERALL PPG Our Program Project Grant (PPG) exploits advances in transcriptional biology to fundamentally increase our knowledge of the lasting abnormalities in brain that underlie stimulant and opioid addiction. We focus on specific cell types in nucleus accumbens and dorsal striatum, key brain regions implicated in addiction. The PPG is composed of four Projects and three Cores all at Mount Sinai. The PIs are leaders in their fields, with an established history of effective collaboration, and use their complementary expertise to chart a multi- disciplinary course in the proposed research. Project 1 (Eric Nestler) focuses on transcription factors induced in brain reward regions by self-administered (SA) stimulants and opioids. Project 2 (Paul Kenny) characterizes specific neuronal microRNAs, which control gene expression in these regions and drug SA behavior, and which are regulated by microglia. Project 3 defines subpopulations of microglia in striatum—including a subset that expresses the D1 dopamine receptor—that modulate neuronal transcription and behavioral responses to drug exposure including SA. Project 4 (Yasmin Hurd) concentrates on the influence of genomic enhancer regions, and their transcriptional and chromatin mediators, in governing molecular and behavioral adaptations to drugs of abuse. All four projects validate findings from animals in human postmortem brain tissue, while discoveries in humans are fed back to animal models to explicate the underlying mechanisms involved. The PPG is supported by three Cores, an Administrative Core (Eric Nestler) to oversee and coordinate PPG operations; an Animal Models Core (Paul Kenny, Richard O’Connor) to provide animal models of addiction and other advanced tools (e.g., viral gene transfer, inducible mutant mice, opto- and chemogenetics, and fiber photometry) to manipulate individual genes of interest in specific cell types of the targeted brain regions and thereby provide causal evidence linking molecular-cellular plasticity to addiction-related phenomena; and a Gene and Chromatin Analysis Core (Li Shen) to provide state-of-the-art methods and bioinformatics to characterize genome-wide regulation of gene expression and chromatin modifications in addiction. This pioneering investigation of transcriptional mechanisms of drug addiction is driving major advances in the field.