Dissecting the role of the gut microbiome on striatal chromatin conformation and drug-seeking behavior

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Project Summary Pathological substance use disorders are devastating psychiatric illnesses characterized by patterns of escalating and out of control drug use. These disorders account for profound disability, morbidity and mortality among patients, while also inflicting incalculable costs on their loved ones and society at large. Pathological use of stimulants, including cocaine, accounts for a significant proportion of morbidity and fatal overdose nationwide. Despite tremendous advances in elucidating the molecular changes underlying stimulant use disorders, there are no FDA-approved pharmacotherapies for their treatment. The largest obstacle to overcome in treating patients with psychostimulant use disorder is preventing relapse. In recent years, there has been a growing understanding that the resident population of bacteria in the gastrointestinal tract – collectively referred to as the gut microbiome – plays a critical role in regulating brain function and behavior. Extensive research now demonstrates that changes to the gut microbiome can support healthy brain function and also drive the development of pathological states. In our own lab, we have previously published that acute depletion of the microbiome can enhance the rewarding effects of cocaine and alter gene expression changes in the brain. In this proposal, I will investigate how antibiotic-induced depletion of the microbiome affects the persistence of drug-seeking behaviors in a mouse model of relapse, taking an integrative multi-level approach to examine changes in striatal reward centers at the epigenetic, transcriptional, and circuit levels. Preliminary data in Aim 1 (F99) demonstrate that microbiome-depleted mice exhibit increased cocaine-seeking behaviors following a period of prolonged abstinence. Full transcriptomic RNA-sequencing analysis from the nucleus accumbens demonstrates that these animals exhibit marked changes in gene expression in important gene networks known to affect DNA binding, synaptic plasticity, and behavior. Additional analyses demonstrate decreased permissive histone acetylation in microbiome-depleted mice following cocaine administration, suggesting that the microbiome affects chromatin structure. Aim 2 (F99) will delve more deeply into the microbial regulation of the epigenome in response to drugs of abuse by examining chromatin conformation in specific populations of striatal neurons. This will be accomplished via training in and application of Fluorescent- Activated Nuclear Sorting (FANS) and Assay for Transposase-Accessible Chromatin sequencing (ATAC-seq). These studies will be coupled with behavioral analyses to provide mechanistic insight into epigenetic remodeling underlying drug-seeking behaviors. For Aim 3 (K00) I will identify a postdoctoral mentor to support my professional development as well as my research examining the effects of the microbiome on firing activity in striatal neuronal subpopulations using in vivo calcium imaging techniques. These studies will provide important mechanistic insight into gut-brain signaling in a model of cocaine use disorder while simultaneously fostering my development into a successful independent investigator ready for a tenure-track faculty position.