Contribution of the Parabrachial CGRP-Expressing Neurons to the Pathophysiology of Panic Disorder

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Project Summary/Abstract Panic disorder is a debilitating anxiety disorder that is characterized by sudden and recurrent attacks of intense, uncontrollable anxiety and fear. This psychiatric illness is unique among other anxiety-related disorders because individuals with panic disorder not only experience mental symptoms during an attack, but they also suffer acute physical symptoms, including cardiorespiratory, autonomic, and gastrointestinal symptoms. In addition, these panic attacks occur spontaneously, and are associated with innate unconditioned fear (i.e., fear that has not been learned through an aversive experience). To understand what causes these bouts of unconditioned fear and associated physiological symptoms in panic disorder, it is critical to characterize the neural circuitry underlying innate threat perception. The lateral parabrachial nucleus (PBN) within the brainstem regulates cardiorespiratory and autonomic functions, and also relays multimodal aversive sensory signals to the amygdala. Preliminary data show that factors that induce panic attack in panic disorder patients, such as caffeine, yohimbine or high CO2 levels, robustly activate neurons in the external lateral region of the PBN (PBel) that express a particular neuropeptide, Calcitonin gene-related peptide (CGRP), and activation of these neurons is necessary and sufficient for innate threat perception. However, little is known about the circuit mechanism of the PBel CGRP-expressing neurons in panic disorder pathogenesis. To address this problem, proposed experiments use state-of-the-art neural circuit dissection tools to MONITOR and MANIPULATE the activity of PBel CGRP neurons, as well as target neurons that express the CGRP receptor. The central objective of this proposal is to determine how PBel CGRP neurons respond to and encode innate sensory threats, and how these neurons contribute to the unique physical and emotional comorbidities in panic disorder. To achieve this objective, activity of PBel CGRP neurons will be monitored (via in vivo calcium imaging) as mice are exposed to multimodal sensory threats or panicogenic agents (Aim 1). PBel CGRP neurons will then be manipulated (inhibited or activated) using optogenetic and chemogenetic techniques to establish causal relationships between CGRP neuronal activity and physiological changes during innate threat perception (Aim 2). Lastly, activity of downstream neurons (those that express CGRP receptors in brain regions innervated by PBel CGRP neurons) will be monitored and manipulated to establish functional neural circuits involved in panic disorder pathogenesis (Aim 3). Contributions of the proposed research will be significant because it will advance the circuit-level understanding of panic disorder pathogenesis. The research plan is innovative because it investigates, for the first time, involvement of the PBel in panic disorder pathogenesis using cell type-specific circuit dissection tools. Successful completion of the proposed research will therefore provide neural circuit-based understanding of panic disorder symptoms, which may provide important insights toward developing therapeutic interventions for panic disorder.