Functional and Genomic Signatures of Escalated Fentanyl Use

Misuse of opioids represents a substantial public and economic burden in the US and worldwide. The existing pharmacological approaches to treatment of opioid use disorder (OUD) are most efficacious when coupled with behavioral therapies that target individual triggers to reduce or eliminate excessive drug consumption. While individual variability in opioid use have been acknowledged repeatedly in animal behavioral models, the genomic markers linked to neurobiological adaptations underlying such variability are not well understood. We argue that understanding the molecular background of individual differences in behavioral vulnerability to opioid use is critical for development of personalized pharmacogenomic approaches for OUD that may replicate clinical success of personalized cancer treatments. In line with this argument, we hypothesize that individual behavioral variability in escalation of fentanyl use is linked to systems level variability of genomic and functional networks within in the nucleus accumbens and prefrontal cortex. Escalation of drug intake is a central component of OUD diagnosis that can be modeled in animals trained to self-administer opioids under extended access conditions. Based on the published literature and preliminary data, we propose three complementary Aims to monitor development of escalated intake at behavioral, functional cellular/network, and genomic levels of analysis. Our Aim 1 hypothesizes that escalation of fentanyl intake emerges on the background of individual differences in sensitivity to non-drug (sucrose) reward. Finding evidence to support this aim has the potential to identify vulnerable individuals prior to initiation of opioid use. Aim 2 examines neuronal outcomes associated with escalated fentanyl intake. Specifically, we will evaluate whether individual profiles of escalated intake reflect altered regulation of cell excitability by four potassium channel families and the impact on neuronal output at single cell and network levels. The data collected as part of this aim will establish functional, neuronal drivers of vulnerability to escalated intake. Finally, Aim 3 compares the genomic landscape underlying variable fentanyl escalation in laboratory animals (rats) to human opioid use databases. In this aim, we take advantage of cell-type specific RNA sequencing to evaluate both neuronal and non-neuronal mechanisms of escalated intake in the nucleus accumbens and prefrontal cortex. This aim is expected to identify novel molecular pathways linked to fentanyl escalation and test the translational relevance of our preclinical findings to a human sample. To characterize interactions at the behavioral, functional, and genomic levels of analysis, a unifying statistical framework is developed based on linear mixed models to examine the strength of bi-directional relationships between behavioral escalation of intake and molecular outcomes.