Epigenetic Control of Reward Learning

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DESCRIPTION (provided by applicant): The ability to form and maintain associations between environmental cues, actions, and rewarding stimuli is an elementary yet fundamental aspect of learned behavior that is necessary for survival. Multiple lines of research have identified that such reward-related learning is mediated by a distributed network of brain nuclei centered upon the nucleus accumbens and its innervation from dopamine neurons located in the midbrain. Both dopamine and nucleus accumbens neurons encode stimulus-reward relationships, and impaired processing in either area inhibits reward learning. Within the nucleus accumbens, dopamine operates through several well- defined intracellular signaling cascades to direct synaptic plasticity and alter neuronal output. Recent studies indicate that dopamine transmission within the nucleus accumbens induces epigenetic remodeling that is associated with both brief and prolonged changes in gene expression. However, the role that epigenetic changes play in reward learning is unclear. This proposal will examine whether two different types of epigenetic alteration (histone modification and DNA methylation) are induced by classical stimulus-reward conditioning. These changes will be investigated using a variety of cutting-edge techniques, including chromatin immunoprecipitation, direct bisulfite sequencing of DNA, and quantitative RT-PCR. These assays will allow us to determine not only whether reward learning is associated with epigenetic modification in the nucleus accumbens, but will also reveal which genes such changes are affecting. Furthermore, the ability of epigenetic changes to functionally modulate learning will be examined by blocking specific histone modifications or DNA methylation in the nucleus accumbens during conditioning. The results will provide novel insight into the epigenetic control of reward learning and enhance our understanding of the molecular pathways that regulate motivated behavior. PUBLIC HEALTH RELEVANCE: Reward-related learning is critical to adaptive as well as maladaptive motivated behavior, and the neural processes that regulate such learning for natural and drug rewards share considerable features, both at the systems and molecular level. Therefore, while this study will elucidate the molecular mechanisms that contribute to normal formation and maintenance of reward-related behaviors, it will also provide a better understanding of how such mechanisms may contribute to drug addiction. In the long term, this improved understanding will equip us to develop more effective treatment and prevention strategies for drug addiction and improve quality of life for addicted individuals, and will also lead to a better understanding of adaptive learning in general.