Impact of stress-induced circuit-specific changes in locus coeruleus opioid signaling on anxiety-like behavior

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Project Summary Anxiety disorders interfere with daily life and are amongst the most prevalent psychiatric conditions in the United States. Poor outcomes in patient populations likely arise in part due to missing knowledge of how these conditions develop. Given the personal, public health, and economic costs of anxiety disorders, gaining a thorough understanding of the mechanisms by which chronic anxiety-like behavior develops will aid in the development of novel more effective treatments for these conditions and is in the national interest. The locus coeruleus (LC) is a brainstem nucleus involved in a wide array of central nervous system functions. Stress activates LC and promotes hypervigilant anxiety-like behavior. Although many studies in the past have investigated how stress affects the function of the LC at short intervals, less is known about how stressor exposure causes long term changes in the nucleus that are associated with a chronically altered behavioral state. Recent observations from our laboratory show that an acute traumatic stressor can produce long-lasting elevations in anxiety-like behavior and LC activity, and furthermore, these effects may be related to decreased expression and sensitivity of LC opioid receptors. Recognition of an anxiolytic role for opioid receptors in LC, particularly within anatomically defined subsets of LC neurons, will be informative of cellular and circuit mechanisms through which chronic anxiety-like behavior develops. Understanding how stressor exposure produces long-term changes in LC gene expression, function and opioid signaling may provide insights towards therapeutic approaches to counteract some of the abnormal behaviors seen in anxiety disorder patient populations. An important consideration in this proposal is the unique roles of LC cells that interact with two other brain regions that mediate distinct aspects of anxiety-like behavior, the medial prefrontal cortex and the central nucleus of the amygdala. By demonstrating that stress induces opposing genetic and physiological changes in LC cells that communicate with each of these areas, we will gain insights to cellular and circuit mechanisms of the genesis of anxiety-like behavior which becomes persistent and maladaptive in several mood disorders. Furthermore, recognizing unique roles for LC cells innervating each of these areas in mediating stress susceptibility or resilience will provide an important backdrop against which new experiments can be designed to test the hypothesis that these neurons have causal roles in mounting a behavioral response to stress. The goals of this project are first to identify the genetic and physiological changes that occur in these cells in response to stress to drive anxiety like behavior. We will then genetically modify these classes of neurons to either manipulate their level of activation during stress, or to increase and decrease their sensitivity to endogenous opioids. These studies will reveal that changes in LC neuronal activity and opioid receptor function are important contributors to behaviors seen in anxiety disorders. These experiments will clarify the role that the central noradrenergic system plays in mediating the emotional and behavioral limb of the stress response, how it adapts following stressor exposure, and how these changes might lead to chronic changes in behavior that manifest as anxiety disorder-like symptoms.