INVESTIGATING NUCLEUS ACCUMBENS ASTROCYTE CELLULAR PROCESSES AFFECTED BY COCAINE SELF-ADMINISTRATION

Despite considerable strides in addiction research over recent decades, there remain no FDA-approved pharmacotherapeutic interventions for psychostimulant use disorders. Dysregulation in glutamate homeostasis in the nucleus accumbens (NAc) contributes to cocaine-seeking behaviors and has been accordingly proposed as a candidate mechanism to target for relapse prevention. Because glutamate homeostasis is largely mediated by astrocytes, it is important to understand how cocaine use affects astrocyte structure and function. Work from a number of labs has demonstrated that NAc astrocytes are significantly altered in structure following rat self-administration of cocaine and subsequent homecage abstinence. Specifically, astrocytes are smaller and show less colocalization with synaptic markers. However, the underlying mechanisms that produce these morphological changes and how they affect functional roles of astrocytes remain unknown. Therefore, the experiments performed within this dissertation use both hypothesis-driven and discovery-based approaches to investigate the mechanism(s) driving the effects of cocaine self-administration on NAc astrocytes. Specifically, the first aim investigates the effects of cocaine self-administration and extended abstinence on expression of the cytoskeletal regulator protein, ezrin, which is abundant in fine processes of astrocytes. Significant differences in ezrin expression or NAc astrocyte structure were not observed between saline controls and cocaine-administering rats, suggesting that there are likely multiple factors that modulate cocaine-induced morphological changes in NAc astrocytes. The second aim utilizes RNA sequencing of astrocyte-specific mRNA to broadly investigate changes in the astrocyte transcriptome and translatome that may be altered following cocaine self-administration. This experiment revealed minimal differences in gene expression of astrocytes between saline controls and cocaine-administering rats, but substantial changes in gene expression within cocaine-administering rats across abstinence, suggesting an effect of time on astrocyte gene expression. In particular, pathway analysis revealed decreases in genes associated with cholesterol synthesis and metabolism across time in the cocaine-abstinent groups, but not the saline abstinent groups. In summary, this dissertation demonstrates the complexities of regulatory mechanisms of astrocyte structural changes induced by cocaine and indicate a potential aging effect on astrocyte gene expression and function prompted by cocaine self-administration.