FMRP in the striatum: mechanisms of early drug reward

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Project Summary/Abstract Substance use disorders, affecting approximately 20.1 million individuals in the U.S., are characterized by a shift in voluntary drug-taking to compulsive drug-seeking and -taking behaviors, which persist despite negative consequences and remain prone to relapse after periods of abstinence. Though environmental influences have been identified as risk factors, there are major gaps in understanding of biological factors that contribute to the development of substance use disorders, limiting our ability to provide effective and lasting treatments. Previous work suggests that the fragile X mental retardation protein (FMRP), an RNA-binding protein that regulates synaptic plasticity, is required for cocaine-induced synapse elimination in the striatum, a brain region critical to reward function. Moreover, loss of FMRP, either broadly or in the ventral striatum (nucleus accumbens; NAc), is capable of dampening cocaine-induced behaviors that are considered indicative of higher addiction-related risk. The main objective of this R36 application is to determine the mechanism by which FMRP facilitates operant self-administration of intravenous cocaine and reinstatement of drug-seeking behavior. The central hypothesis, based on published and preliminary data, is that FMRP positively mediates cocaine intravenous self-administration and reinstatement of drug-seeking via its regulation of the activity- regulated cytoskeleton-associated protein (Arc) in D1-receptor (D1R) expressing cells of the NAc. This hypothesis will be tested in two specific aims, each utilizing conditional knockdown approaches and an extensive self-administration assay that includes cue- and drug-induced reinstatement paradigms. Aim 1 will determine whether FMRP mediates these phenotypes via its function in specifically D1R or D2R cells of the NAc, while Aim 2 will determine whether FMRP’s regulation of Arc contributes to these phenotypes. This work will complete the applicant’s dissertation, as part of her training for a career in addiction-related science, provide insight into the mechanism by which FMRP mediates drug-related behaviors, providing critical direction for future studies aimed at identifying downstream targets for therapeutic intervention.