Journal Article

Atp1a2 and Kcnj9 Are Candidate Genes Underlying Sensitivity to Oxycodone‐Induced Locomotor Activation and Withdrawal‐Induced Anxiety‐Like Behaviors in C57BL/6 Substrains

Reed, Eric R., Jenkins, David F., Mulligan, Megan K., Luong, Alexander M., Goldberg, Lisa R., Luttik, Kimberly P., Johnson, W. Evan, Kirkpatrick, Stacey L., Cox, Jiayi, Yao, Emily J., Kelliher, Julia C., Bryant, Camron D., Ferris, Martin T., Baskin, Britahny M., Yazdani, Neema, Beierle, Jacob A., Scotellaro, Julia A., Drescher, Timothy A., Adla, Yahia, Crotts, Sydney B.

2025

Overview

Opioid use disorder is heritable, yet its genetic etiology is largely unknown. C57BL/6J and C57BL/6NJ mouse substrains exhibit phenotypic diversity in the context of limited genetic diversity which together can facilitate genetic discovery. Here, we found C57BL/6NJ mice were less sensitive to oxycodone (OXY)‐induced locomotor activation versus C57BL/6J mice in a conditioned place preference paradigm. Narrow‐sense heritability of OXY‐induced locomotor activity traits ranged from 0.22 to 0.31, implicating suitability for genetic analysis. Quantitative trait locus (QTL) mapping in an F2 cross identified a chromosome 1 QTL explaining 7%–12% of the variance in OXY locomotion and anxiety‐like withdrawal in the elevated plus maze. A second QTL for EPM withdrawal behavior on chromosome 5 near Gabra2 (alpha‐2 subunit of GABA‐A receptor) explained 9% of the variance. To narrow the chromosome 1 locus, we generated recombinant lines spanning 163–181 Mb, captured the QTL for OXY locomotor traits and withdrawal, and fine‐mapped a 2.45‐Mb region (170.16–172.61 Mb). Transcriptome analysis identified five, localized striatal cis‐eQTL transcripts and two were confirmed at the protein level (KCNJ9, ATP1A2). Kcnj9 codes for a potassium channel (GIRK3) that is a major effector of mu opioid receptor signaling. Atp1a2 codes for a subunit of a Na+/K+ ATPase enzyme that regulates neuronal excitability and shows functional adaptations following chronic opioid administration. To summarize, we identified two candidate genes underlying the physiological and behavioral properties of opioids, with direct preclinical relevance to investigators employing these widely used substrains and clinical relevance to human genetic studies of opioid use disorder. We exploited near‐isogenic C57BL/6 substrains to fine‐map a 2.45‐Mb region containing DNA variants underlying oxycodone behaviors. We mapped a genomic region on distal chromosome 1 and identified genotype‐driven, differentially expressed mRNAs and proteins within this region and DNA variants. Atp1a2 and Kcnj9 as two likely candidate genes underlying oxycodone behavior.

• Publisher: Blackwell Publishing Ltd,John Wiley & Sons, Inc
• Subject: addiction / Analgesics, Opioid - pharmacology / Animals / Anxiety / Anxiety - chemically induced / Anxiety - genetics / Chromosome 1 / Chromosome 5 / Chromosomes / Drug abuse / Drug addiction / Drug withdrawal / Excitability / Female / fentanyl / G Protein-Coupled Inwardly-Rectifying Potassium Channels - genetics / G Protein-Coupled Inwardly-Rectifying Potassium Channels - metabolism / Genetic analysis / Genetic diversity / gwas / Heritability / Locomotion / Locomotion - drug effects / Locomotion - genetics / Locomotor activity / Male / Mice / Mice, Inbred C57BL / Na+/K+-exchanging ATPase / Narcotics / Neostriatum / opiate / opioid / Opioid receptors (type mu) / Original / Oxycodone / Oxycodone - pharmacology / Place preference conditioning / Potassium channels (inwardly-rectifying) / qtl / quantitative trait / Quantitative Trait Loci / rats / Receptors, GABA-A - genetics / reduced complexity cross / Sodium-Potassium-Exchanging ATPase - genetics / Sodium-Potassium-Exchanging ATPase - metabolism / Substance use disorder / Substance Withdrawal Syndrome - genetics / systems genetics / Transcriptomes / γ-Aminobutyric acid