ABSTRACT Opioids are the most commonly used and most effective analgesics, and are the first line of defense against acute and severe pain. However, this dramatic ability to mitigate pain comes with many side effects. These include constipation, nausea, sedation, dizziness, respiratory depression, dependence, and addiction. Among these, respiratory depression is the major driver of death by opioid overdose. According to the Center for Disease Control (CDC), nearly 50,000 people died in 2019 by opioid-induced respiratory depression (OIRD) in the United States, and the death rate is rising rapidly due to increased misuse and addiction to both prescription and illicit opioids. Thus, the US is currently experiencing a serious national public health crisis that is also taking a toll on social economic welfare. Despite these dire numbers, research elucidating the neural mechanisms of OIRD, which could identify therapeutic targets, has not been rigorously investigated. Animal studies have shown that OIRD and opioid analgesia are both mediated by the µ-opioid receptor (MOR), however the neural circuits and brain regions responsible for OIRD and opioid analgesia are not fully understood. The proposed research aims to dissect the neural circuits that selectively mediate OIRD or opioid analgesia using cutting-edge molecular, physiological, behavioral, and imaging techniques. Projection-specific single-cell transcriptomic analysis will then be used to identify functional markers expressed in the MOR- expressing neurons that specifically mediate OIRD, not opioid analgesia. Successful completion of the proposed research will identify novel therapeutic targets that selectively rescue OIRD without altering analgesic effects of opioids.

PROJECT NARRATIVE The proposed research will investigate the role played by specific neurons within the brainstem in opioid- induced respiratory depression (OIRD). Neuronal circuits within the brainstem are critical for maintaining breathing rhythms, and many of these neurons are severely impacted by opioid consumption, as they express opioid receptors. Identifying functional markers expressed in the MOR-expressing neurons that specifically mediate OIRD will provide a stepping stone to developing novel therapeutic interventions that selectively rescue OIRD without altering analgesic effects of opioids.