Ventral tegmental area neuromedin s expression and signaling in opioid responses - Summary Opioid use and abuse are a major health and economic concern, with reduction of abused prescription opioids shifted to cheaper, illicit opioids like fentanyl. Thus, development of non-opioid treatments is crucial, but requires additional understanding of the neurobiological underpinnings. Dysregulation of the reward circuitry contributes to opioid-induced plasticity and addictive-like behavior, including altered function of ventral tegmental area (VTA) dopamine (DA) neurons. Given the powerful and unique roles that activity of these neurons play in a multitude of behaviors, it is unsurprising that VTA DA neurons are heterogenous and can be parsed into functional subsets based on inputs, projection-target, co-transmitter expression, and activity. To this end, we have recently defined a novel subset of VTA DA neurons based on their expression of the neuropeptide neuromedin s (NMS). Morphine increases Nms expression in VTA DA neurons, and chemogenetic activation and inhibition of VTA NMS neurons promotes and inhibits morphine-elicited behavior, respectively, without altering cocaine responses. However, whether VTA NMS signaling drives these effects is unclear, as chemogenetic manipulation also increases DA release. Knowledge of NMS function in the brain has been limited by the lack of specific tools, so we have generated a floxed NMS (NMSFlx) mouse and CRISPR-based viral vectors to manipulate NMS in cell-, circuit-, and temporally-specific manners. Our preliminary data show that knockout of NMS from VTA neurons decreases morphine conditioned place preference (CPP), suggesting that the morphine-induced increase in VTA Nms promotes morphine responses. Our data show that the main output region of VTA NMS neurons is the nucleus accumbens (NAc), which expresses the receptor for NMS, NMUR2. We also show that knockdown of NMUR2 in the NAc reduces morphine locomotor sensitization, consistent with our VTA NMS KO data and supporting a functional VTA-NAc NMS-NMUR2 circuit. Thus, in this application we seek to characterize how opioids engage VTA DA NMS neurons and whether VTA DA NMS expression and NAc NMUR2 signaling promote opioid behavior via three specific aims: 1) determine whether VTA NMS expression and NAc NMUR2 signaling are required for Mor-induced activity changes of NAc MSNs, 2) determine how morphine promotes Nms expression in VTA DA neurons and associated neuronal activity, and 3) determine if VTA NMS KO mice have reduced morphine CPP and fentanyl self-administration. Our studies will utilize novel genetic tools to KO NMS from VTA DA neurons and assess the physiological and behavioral impact in adult mice using in vivo calcium imaging and multiple opioid behavioral paradigms. These studies are expected to define the role of a specific VTA-NAc NMS-NMUR2 circuit, its activity during behavior, and thereby investigate its potential as a target for therapeutic intervention.
