Escalated oxycodone self-administration is associated with activation of specific gene networks in the rat dorsal striatum
The number of individuals diagnosed with opioid use disorder (OUD) has risen steeply because of the increased prescribing of opioid drugs like oxycodone for chronic pain relief. OUD is characterized by loss of control of drug taking, continued drug use in the presence of adverse consequences, and repeated relapses to drug taking. Repeated exposure to oxycodone self-administration can lead to addiction in certain rats while others remain unaffected. Understanding the molecular mechanisms between these two groups holds promise for developing strategies to combat addiction. To identify signaling pathways associated with oxycodone addition, this study used male Sprague-Dawley rats to self-administer oxycodone for 20 days according to short-(ShA, 3 h) and long-access (LgA, 9 h) paradigms. Animals were euthanized after 2 hours of self-administration cessation and their dorsal striata were used for RNA sequencing analysis. LgA rats escalated their oxycodone intake and developed into 2 phenotypes, named long-access high (LgA-H, addicted) and long-access lower (LgA-L, non-addicted) rats, based on the level of escalation and drug taken during the self-administration experiment. RNA sequencing revealed many differentially expressed genes in the oxycodone-addicted rats in comparison to other groups. DAVID analysis indicated that some of these genes were involved in potassium transport, ATP binding, and regulation of synaptic processes. Ingenuity pathway analysis (IPA) revealed previous involvement of some genes in OUD and cognitive processes. RNA sequencing and RT-PCR analysis of dorsal striatum samples unveiled a significant upregulation of potassium channel genes Kcnma1, Kcnk9, Kcnq1, Kcnd3, and Kcng3 in LgA-H rats, which was corelated with oxycodone intake. We also identified increased expression for Cldn3, Serping1, and Serpinh1 in ShA rats. Taken together, these observations identified potassium channels as potential targets for the treatment of oxycodone use disorder. Overall design: Herein we Long-access (LgA) and Sal rats were trained to self-administer for three sessions: one 3-h session during days 1–5, followed by two 3-h sessions during days 8–14, and then for three 3-h sessions during the rest of the study (days 15–20). Short-access (ShA) rats were trained to self-administer oxycodone for only one 3-h session for the entirety of the study (days 1–20).