Escalated Oxycodone Self-Administration Is Associated with Activation of Specific Gene Networks in the Rat Dorsal Striatum

Abstract

The diagnosis of opioid use disorder (OUD) is prevalent due to increased prescribing of opioids. Long-term oxycodone self-administration can lead to addiction-like behavioral responses in rats. Herein, we sought to identify molecular pathways consequent to long-term exposure to oxycodone self-administration. Towards that end, we used male Sprague Dawley rats that self-administered oxycodone for 20 days according to short-(ShA, 3 h) and long-access (LgA, 9 h) paradigms. LgA rats escalated their oxycodone intake and developed into 2 phenotypes, labeled Long-access High (LgA-H) and Long-access Low (LgA-L) rats, based on their escalation. RNA sequencing analysis revealed the LgA-H has significantly different DEGs in comparison to other groups. DAVID analysis revealed the participation of LgA-H DEGs in potassium transport. RT-PCR analysis of striatal samples validated the increased levels of potassium channels. Since these increases correlated with oxycodone intake, we believe potassium channels are potential targets for the treatment of oxycodone use disorder.

Keywords: RNA sequencing; dorsal striatum; oxycodone; potassium channels; self-administration.

Figure 1

Insights into oxycodone self-administration: Experimental timeline, behavioral data, RNA sequencing analysis (A) Experimental timeline, Saline (n = 8), Short-access (ShA) (n = 10) rats, and Long-access (LgA) (n = 18). (B) Oxycodone intake by LgA and ShA groups. (C) LgA rats show two distinct intake phenotypes, high (LgA-H) (n = 11) and low (LgA-L) (n = 7), based on their drug intake. Volcano plots (D) LgA-L vs. Sal, (E) LgA-L vs. Sal, (F) ShA vs. Sal, (G) LgA-H vs. ShA, (H) LgA-L vs. ShA, (I) LgA-H vs. LgA-L illustrating the number of significant genes (p  <  0.05) between each pairwise comparison. (J) Hierarchical clustering for DEGs that met the criterion of 1.5-fold change and p  <  0.05, with blue indicating downregulated genes, and red indicating upregulated genes. Key to statistics: ### = p < 0.001, comparison of LgA-H to ShA rats; !!! p < 0.001, comparison of LgA-H to LgA-L rats; $$$ p < 0.001, comparison of LgA-L to ShA rats.

Figure 2

Identification of gene and molecular network in the LgA-H animals in comparison to LgA-L. (A) The Venn diagram shows significant upregulated genes (p  <  0.05, fold change 1.5 F). (B) This Venn diagram shows significant downregulated genes (p  <  0.05, fold change 1.5 F). Sankey diagrams (Sankeymatic.com/build) reveal molecular functions for genes that were (C) upregulated and (D) downregulated in the LgA-H vs. LgA-L comparison. (E) Ingenuity Pathway Analysis (IPA, https://digitalinsights.qiagen.com/products-overview/discovery-insights-portfolio/analysis-and-visualization/qiagen-ipa/, accessed on 26 July 2025) shows the molecular networks for DEGs in the LgA-H vs. LgA-L comparison. The red color represents upregulated genes, whereas the green color represents downregulated genes, and the blue color represents interacting partners.

Figure 3

Identification of altered molecular networks in the LgA-H rats in comparison to Sal, ShA, and LgA-L. (A) Sankey diagrams revealed molecular functions of genes that were upregulated. (B) represents IPA gene networks in the LgA-H vs. Sal comparison. (C) Sankey diagrams revealed molecular functions of genes that were upregulated. (D) IPA illustrates gene networks in the LgA-H vs. ShA comparison. (E) Sankey diagrams revealed molecular function of genes that were upregulated. (F) IPA shows gene networks in the LgA-H vs. LgA-L comparison. The red color represents upregulated genes, whereas the green color represents downregulated genes, and the blue color illustrates interacting partners.

Figure 4

Potassium channels showed increased expression in the dorsal striatum of LgA-H rats. (A) Kcnma1, (C) Kcnd3, (E) Kcnk9, (G) Kcng3, (I) Kcnq1, and (L) Slc24a3. This increased expression of potassium channels was found to positively correlate with oxycodone intake (B) Kcnma1, (D) Kcnd3, (F) Kcnk9, (H) Kcng3, (J) Kcnq1, and (K) Slc24a3. Key to statistics: *, **, *** = p < 0.05, 0.01, 0.001, comparison LgA-H, LgA-L, or ShA to saline rats; #, ## = p < 0.05, 0.01, comparing LgA-H to ShA rats; !, !!! = p < 0.05, 0.001 comparing LgA-H to LgA-L rats.

Figure 5

Real-time quantitative PCR of DEGs of other genes. (A) Cldn3, (C) Serping1, and (E) Serpinh1, showed changed expression, which was not correlated with oxycodone intake, illustrated in (B) Cldn3, (D) Serping1, and (F) Serpinh1 in ShA rats. (G) Fmo2, and (I) Nectin4 showed decreased expression in the dorsal striatum of LgA-L rats, with (H) Fmo2 but not (J) Nectin4 showing negative correlation with oxycodone intake. (K,L) Expression of Slc19a3 was decreased in all oxycodone-exposed rats, without any correlation with oxycodone intake. Key to statistics: *, ** = p < 0.05, 0.01, comparison of LgA-H, LgA-L, or ShA to saline rats; #, ##, ### = p < 0.05, 0.01, 0.001 comparing LgA-H rats to ShA rats; $ = p < 0.05, comparison of LgA-L rats to ShA rats; !!! = p < 0.001, comparison of LgA-H rats to LgA-L rats.