CHARACTERIZATION OF FRONTAL CORTICAL CIRCGRIN2B_011731 IN OPIOID-INDUCED NEUROADAPATIONS

Opioid use disorder (OUD) is chronic relapse neurological disorder, best characterized by profound drug-induced neuroadaptations which drive drug-seeking phenotypes and persist in the absence of drug. In this dissertation we will examine circular RNA (circRNA) dysregulation following a rodent model of heroin self-administration and characterize a novel circRNA pathway regulating opioid induced neuroadaptations. We identified 76 circRNAs regulated by heroin self-administration, of these we selected circGrin2b_011731 (circGrin2b) for further characterization. circGrin2b is derived from exon 3 of linear Grin2b, which encodes the regulatory subunit of the NMDA receptor, GluN2b, a protein essential for opioid learning and memory paradigms. First, using a custom small-interfering RNA (siRNA) targeting the backsplice junction of circGrin2b, we show that knock-down of orbitofrontal cortex (OFC) circGrin2b significantly reduces heroin intake during self-administration, while only non-significantly reducing heroin-seeking phenotypes. This suggests that OFC circGrin2b is functionally relevant to heroin self-administration phenotypes. Next, we utilized an in vitro primary cortical culture morphine exposure model to interrogate putative upstream biogenesis mechanisms and examine expression of potential circGrin2b microRNA (miRNA)-sponge targets. We validated circGrin2b interactions with miR-26b-3p and miR-100-3p utilizing a luciferase binding assay. Sponging of these 2 miRNA targets can have extensive impact of translation of miRNA-repressed genes, as both miRNAs are involved in regulation of messenger RNAs involved in opioid signaling. Taken together, this dissertation characterized the behavioral and molecular role of a novel circRNA species in mediating opioid-induced neuroadaptations and expands upon the current understanding of the role of circRNAs in regulating synaptic plasticity.