Inhibition of Parabrachial CGRP Neurons Reduces Morphine Reinforcement and Withdrawal

Abstract ID 92395 Poster Board 511 Opioid Use Disorder (OUD) is a chronic, relapsing disease that, despite our best research efforts, has become a worsening public health crisis. Currently, the medications to treat OUD belong to the opioid class of drugs and, therefore, continue to interact directly with opioid receptors. While these medications are safe and effective for the cessation of opioids with higher abuse potentials, there is still a need for effective non-opioid receptor-targeting therapeutics. Exploring novel non-opioid targets is necessary to overcome this barrier. One such non-opioid target we are currently investigating is the calcitonin gene-related peptide (CGRP) system, particularly CGRP-expressing neurons in the parabrachial nucleus (CGRPPBN). These neurons have been well studied in itch and pain and are known to project to brain regions implicated in opioid reward and withdrawal. Previous studies in our lab have found that CGRPPBN activity decreases during opioid taking and increases during opioid withdrawal. To further characterize the behavioral role of CGRPPBN neurons in opioid withdrawal, Calca-Cre transgenic mice received viral injections into the PBN containing an inhibitory DREADD (hm4Di), and two weeks later, mice were implanted with 2x25 mg morphine pellets. After five days, morphine withdrawal was induced by removing the pellets. Mice were administered either clozapine-N-oxide (CNO) (3 mg/kg, I.P.) or vehicle (saline, I.P.) 5.5 hours post pellet removal, and behavior was recorded at 6 and 24 hours post pellet removal. Two experimenters scored videos for jumping and wet dog shakes. Those mice injected with CNO showed fewer wet-dog shakes at the 6-hour time than vehicle-injected controls. We next sought to characterize the behavioral role of CGRPPBN neurons in opioid taking. In this experiment, morphine intravenous self-administration (IVSA) was used. Calca-Cre transgenic mice received viral injections into the PBN containing either an inhibitory DREADD (hm4Di) or a control mCherry vector and, two weeks later, were implanted with jugular catheters. Subsequently, operant responding for intravenous morphine was established. After 12 daily sessions, mice were administered CNO (3 mg/kg, I.P.) or vehicle (saline, I.P.) and allowed to respond for morphine. CGRPPBN inhibition reduced morphine intake in hm4Di-injected animals, while those with a control virus maintained their previous levels of morphine intake. Decreases in morphine intake were maintained 24 hours after CNO administration but returned to previous baseline levels at 48 hours. These results suggest that CGRPPBN neurons play a role in the behavioral consequences of both opioid reinforcement and withdrawal. CGRP receptor inhibitors are FDA-approved for the treatment of migraine and exist in both short and long-lasting formulations. By leveraging these available medications for the off-label purpose of treating OUD, we may be able to determine the translational potential of these preclinical findings and, therefore, expand our therapeutic arsenal for long-term maintenance of opioid abstinence and relapse.