Abstract: Acute stress and threat produce physiological anxiety to facilitate planning and allow for organisms to tune behavior for exploration of the environment, thus serving to promote hyperarousal, anxiogenic-like behavior and avoidance (i.e. aversive responses). Stress is also directly linked to numerous mental health diseases and these disorders currently affect ~30% of the US population. The locus coeruleus (LC) noradrenergic (NE) system and its related GPCRs have been implicated in numerous stress-related affective disorders including, anxiety, hyperarousal and negative affect. The LC-NE system is a critical component for integration of stress-induced avoidance. Our recent evidence and the literature suggests that LC-NE neurons exhibit more molecular, cellular, circuit and functional diversity (i.e. are polymorphic) than previously thought. It is hypothesized that through these various modes of LC-NE operation, output to downstream circuits, GPCRs, and behavior are tightly regulated. We propose to isolate and define the unique molecular-cellular, physiological and neuropharmacological mechanisms regulating LC-NE function in response to salient stimuli and stress. Recent evidence from our group and others also suggests that LC-NE soperational modes are tightly regulated by a local GABAergic neuron population alongside a host of unknown molecular and neuropharmacological components. In the next five years we will focus on a comprehensive alignment of molecular-cellular, neuropharmacological, imaging, and behavioral approaches to better define converging characteristics of the LC-NE system in avoidance, arousal and “anxiety-like” responses. Here we use a multi-disciplinary approach that includes molecular-cellular approaches, neuropharmacology, NE- biosensors, optogenetics, and in vivo 2p/1p calcium imaging approaches to define the specific cells, circuits, and receptors within the LC system that mediate stress-induced behavioral avoidance and “anxiety-like” behaviors. Our central hypothesis to be tested is that the LC-NE system and it’s distinct neurons have diverse stress/stimuli-responsive molecular and physiological modes in vivo. We predict that LC-NE neuron activity - in part - determines release NE in BLA and HPC; and unique LC cell types, and discrete neuropeptide/GPCRs, tightly regulate LC-NE operation and behavioral avoidance. We propose 3 aims: 1) To determine how stress- induced activation of LC-NE neurons alters encoding and norepinephrine release in the hippocampus and BLA 2) To define the dynamic role of peri-LC GABAergic neurons in the control of LC-NE neuron activity during acute stress and avoidance. 3) To utilize molecular profiling alongside electrophysiology, sensors, and neuropharmacology, to decipher genetically defined LC cell types impacted by stress. This confluence of molecular-cellular, neuropharmacological, physiological and behavioral analysis of LC-NE function will provide a valuable framework for understanding...