Impact of chronic, voluntary fentanyl intake on single-cell gene expression and brain-wide neuronal activity patterns

Abstract/Project Summary Opioid use disorder is defined as chronic, maladaptive opioid use despite negative consequences. Prolonged opioid exposure can induce long-lasting changes to neural circuitry involved with reward and motivation, leading to drug cravings and tolerance to the drug’s rewarding effects over time. One brain region known to play a key role in opioid reward processing is the nucleus accumbens, which contains two subpopulations of GABAergic medium spiny neurons that express either the D1 or D2 dopamine receptor, as well as a variety of interneuron cell types and glia. Medium spiny neurons project to multiple brain regions, and µ-opioid receptors are also expressed on many neurons throughout the brain. Thus, it is reasonable to predict that chronic opioid exposure will be associated with global alterations in neuronal activity patterns. Improving our understanding of both the molecular and circuit-level mechanisms underlying opioid use disorder is crucial to facilitating the development of more effective treatments. To address this gap in knowledge, I plan to leverage a rodent model of chronic, voluntary oral fentanyl intake that I have developed and implemented. My goal for this training proposal is to use this paradigm to specifically assess what changes occur to gene expression and neural circuitry over periods of sustained opioid self-administration. In Aim 1, we plan to conduct single nuclei RNAseq in the nucleus accumbens of mice after chronic fentanyl intake and withdrawal. Aim 2 will utilize transgenic mice to visualize expression of the early immediate gene cFOS, a marker of neuron activity. Whole-brain clearing and light-sheet microscopy will be used to quantify the neural activation patterns associated with long-term fentanyl escalation and withdrawal. Together, these aims will lead to a more complete understanding of the impact of chronic opioid exposure, which may inform the development of novel therapeutic interventions for opioid use disorder.