Effects of adolescent oxycodone exposure on adult remifentanil self-administration and gene expression in male and female mice

Introduction The Opioid Epidemic is a public health crisis in the United States, contributing to an estimated 54,000 deaths in 2024. A major contributing factor is prescription and recreational use of painkillers such as oxycodone. Adolescent painkiller use predicts later-life transition to more potent opioids, but the causal relationship and its neurobiological mechanisms are not fully understood. Methods Adolescent male and female mice were exposed to oxycodone (OXY) or saline (SAL), then tested for intravenous self-administration (IVSA) of remifentanil, a potent synthetic opioid, in adulthood. RNA sequencing (RNA-seq) was performed on reward-related brain regions, the nucleus accumbens (NAc) and ventral tegmental area (VTA), from adult mice that underwent adolescent OXY or SAL with or without subsequent IVSA. Results Adolescent OXY increased adult remifentanil IVSA in females but not males. In contrast to the behavior, adolescent OXY induced modest differential gene expression in adulthood, though several interesting candidate genes were identified for future study, particularly in the male NAc. We further found that adolescent OXY induced differential splicing in all comparisons, with a potentially greater response in the female VTA post-IVSA. Gene-Set Enrichment Analysis (GSEA) showed that adolescent OXY treatment (vs. SAL) produced gene-set enrichment in the adult male NAc, which was similar whether or not animals later underwent IVSA. In the female NAc, gene-set enrichment was minimal with OXY treatment alone, while the IVSA cohort showed substantial enrichment. In contrast, adolescent OXY exposure alone was associated with similar patterns of gene-set enrichment in the male and female VTA, which was absent in the IVSA cohort. Complementary Rank-Rank Hypergeometric Overlap (RRHO) analysis identified patterns of gene expression concordance that recapitulated the GSEA results. Discussion Considering the IVSA and RNA-seq together, these data lead us to new hypotheses that male mice mount a gene expression response in the NAc following adolescent OXY associated with a lack of long-term increases in volitional drug taking. In contrast, females may exhibit an alternative splicing response in the VTA during adult IVSA which is associated with increased drug taking. These analyses have provided valuable targets for future validation and mechanistic investigation of these new hypotheses.