Transcriptional response to chronic fentanyl self-administration in rat amygdala and habenula

The current preponderance of fentanyl involvement in opioid and polysubstance overdose deaths is overwhelming. It is imperative to understand how properties that set fentanyl apart from other opioids interact with local circuit molecular adaptations in brain regions linked to the mesolimbic dopamine system and known to influence compulsive drug seeking and use. To study this, we turned to a long-access drug self-administration (SA) model in rats to produce escalating volitional fentanyl intake (n=8 fentanyl, n=11 saline). Brain tissue samples from the habenula (Hb) and amygdala (Amyg) were immediately extracted after the last long-access session to study transcriptomic changes following chronic escalating fentanyl use using bulk RNA-sequencing in these regions enriched in mu-opioid receptors. Fentanyl vs. saline differentially expressed genes (DEGs) were identified (453 in Hb; 3041 in Amyg; FDR < 0.05). Enrichment of chronic fentanyl use related DEGs in regional cell type-specific marker gene sets were assessed to identify candidate cell types as potential biological substrates for future translational investigation into opioid use disorder. MAGMA analyses revealed that the identified downregulated DEGs in the amygdala in particular overlap with genes associated with substance use disorders (SUDs) GWAS data. These findings provide a foundation to understand how two brain regions heavily implicated in reward processing and the development of SUDs are impacted at the molecular level following chronic escalating intake of the potent synthetic opioid fentanyl, thereby providing biological leads for more effective therapeutic interventions for patients at higher risk for overdosing.