Molecular determinants of ensemble recruitment by drugs of abuse

ABSTRACT While a large amount of work has focused on how stimuli are encoded in the transcriptional and physiological activity patterns within genetically defined neuronal populations, emerging evidence has clearly shown that stimuli activate only a small percentage of neurons in any given brain region. Therefore, understanding how specific functionally defined subsets of neurons within reward-related brain regions – such as the nucleus accumbens (NAc) - contribute to the progression of addiction will be important in finding more specific treatment strategies. We focus on how cocaine-activated ensembles are recruited initially and how these ensembles undergo changes over time to drive behaviors associated with cocaine use disorder. Epigenetic mechanisms - in which stimuli trigger long-lasting changes in transcription - have emerged as a mediator of drug-induced adaptation within the brain. Epigenetic regulation occurs at the nucleosome: DNA wrapped around an octamer of histone proteins, which constitutes a platform for epigenetic marks that dynamically regulate chromatin architecture and transcription. We identified a cocaine-induced epigenetic regulator in the NAc: lysine acetyltransferase 2a (KAT2a/Gcn5), showing that KAT2a is a critical regulator of cocaine reinforcement, cocaine-induced plasticity, and is expressed within cocaine-activated ensembles in the NAc. Building upon our strong preliminary data, we will probe how KAT2a regulates cocaine ensemble recruitment and maintenance by asking the following questions: 1. Does KAT2a expression dictate initial recruitment into cocaine-activated ensembles 2. Does KAT2a within recruited ensembles determine the cocaine-induced plasticity that occurs over time? Using single nucleus RNA sequencing (snRNAseq), ensemble-specific epigenetic profiling, and cellular resolution imaging in awake and behaving animals we will track the same cells over time to understand how KAT2a is involved in ensemble selection and maintenance and whether it is the initial cocaine ensemble that undergoes plasticity following cocaine self-administration or whether an entirely new ensemble is recruited by repeated drug exposure. Critically, this proposal goes beyond simply generating large quantities of multidimensional data – of which there are already many in the context of drug exposure. The next frontier of using these high-density approaches will be using them to ask targeted questions that were intractable before the advent of this technology.