The Role of Parabrachial CGRP Neurons in Opioid Reinforcement

PROJECT SUMMARY Opioid Use Disorder (OUD) is a chronic, relapsing disease that, despite our best efforts to understand and mitigate the disease, has become a worsening public health crisis. 1,2 Currently, the medications to treat OUD interact directly with opioid receptors. 3 While this helps patients decrease the use of more dangerous opioids, the mechanism of action of the currently available drugs continues to perpetuate the substance abuse cycle. Exploring novel non-opioid targets is necessary to overcome this current standstill. One specific alternative population we are interested in investigating is calcitonin gene-related peptide (CGRP) expressing neurons within the parabrachial nucleus (CGRPPBN). These neurons have been well studied in itch and pain fields and are known to project to the central amygdala (CeA) 4,5, a brain region directly implicated in processing the negative emotional valence associated with alcohol and opioid withdrawal. The objective of this proposal is to assess the functional role of CGRPPBN in opioid reinforcement and to determine the gene expression and epigenetic changes associated with opioid taking and opioid withdrawal. Our preliminary results show that CGRPPBN activity decreases during opioid taking and increases during opioid withdrawal. We have also found that this population of neurons robustly expresses the µ-opioid receptor along with glutamatergic markers, positioning this population as a potential direct activator of the CeA during opioid withdrawal. To further probe these results, I will inhibit CGRPPBN neurons using molecular and pharmacological approaches and determine the behavioral consequences of these interventions. One of the pharmacological approaches we will be testing is an FDA-approved CGRP inhibitor currently used for migraine treatment. We will then establish the molecular profile of these neurons using nuclear RNAseq and Cleavage Under Tagmentation (CUT&Tag) at baseline, as well as during morphine taking and protracted abstinence. By integrating transcriptomic data with epigenetic information on post-translational histone modifications, I will be able to build a comprehensive map of the active and inactive chromatin regions with their corresponding differentially expressed genes, which can be used to detect epigenetic targets critical to the identity of CGRPPBN neurons. The results of this study will allow us to establish the feasibility of targeting these neurons to treat OUD via currently FDA-approved medications or through novel epigenetic targets identified in this study. These results will broaden our understanding of withdrawal and help expand our therapeutic arsenal for the long-term maintenance of opioid abstinence and prevention of relapse.