NAc Circuits Underlying Opioid Taking and Seeking

Abstract Overdose deaths are on the rise, with 107,941 reported overdose deaths in the US in 2022 alone. Strikingly, 73,838 of those deaths were associated with synthetic opioids, most of which involved fentanyl. Drugs of abuse are thought to “hijack” synaptic plasticity mechanisms and drive molecular, synaptic, and circuit remodeling within the ventral tegmental area (VTA)-nucleus accumbens (NAc) mesolimbic dopamine system. These neuroadaptive responses are hypothesized to underlie the development of addictive behaviors and to promote negative emotional and motivational states during withdrawal through strengthening anti-reward systems. Evidence suggests that there are dissociable circuits within the striatum and NAc that mediate distinct aspects of opioid reward, seeking, somatic withdrawal, and dependence and that each of these may be associated with their own forms of drug-induced plasticity mechanisms. NAc medium spiny neurons (MSNs) are typically characterized by their expression of dopamine receptors, however, the standard dopamine receptor (D)1/D2 classifications do not fully capture the role of MSNs in addiction. Manipulations to these populations based on dopamine receptor expression has led to conflicting and ambiguous results. Single cell transcriptomic data has identified several novel classes of MSNs, however, limited studies on these cell types exist, especially in the context of opioid use. Additionally, single cell sequencing is unable to capture key features of these newly identified subtypes, including topography and input-output organization. This proposal seeks to utilize “Barcoded Anatomy Resolved by Sequencing” (BARseq) to address these technical challenges while elucidating the active cells and circuits during remifentanil taking and seeking. BARseq provides a means to trace thousands of single neurons, providing gene expression and topographical information of the cells in the injection site(s), and producing brain-wide projection patterns. In a diverse, heterogeneous, and anatomically indistinct region with multiple output projection pathways such as the NAc, this technique is essential to characterize the multiple distinct subclasses of MSNs and begin to understand their function in addiction. The studies proposed will provide novel mechanistic insights into the cells, circuits, and neuroadaptive mechanisms that mediate the progression of addiction, with greater precision than previously available, resulting in novel opportunities for developing treatments for addiction.