Anxiety and stress-related disorders, including panic disorder (PD), generalized anxiety disorder (GAD), and posttraumatic stress disorder (PTSD), are among the most disabling neuropsychiatric conditions in the United States. A core feature of these disorders is pathological anxiety (i.e., maladaptive arousal and fear). Animal models point strongly towards shared mechanisms underlying pathological anxiety to involve the locus coeruleus (LC), the primary source of norepinephrine in the CNS, and modulator of the regulation of arousal and response to threat. However, the specific role of the LC in human pathological anxiety is not known, due in part to past technical limitations of non-invasive imaging for small nuclei such as the LC. Thus, despite the prevailing hypothesis of the role of the LC, the pathophysiology of anxiety disorders remains largely undiscovered. This gap impedes translational research aimed at developing more biologically based models of human anxiety and stress-related disorders, precluding precision medicine for these disorders. In order to address this gap, we propose to the first transdiagnostic in vivo study of LC in anxiety, leveraging cutting-edge 7 Tesla (7 T) MRI in patients with PD, PTSD, GAD. Our central hypothesis is that LC dysregulation underlies shared dimensions of psychopathology across neuropsychiatric disorders that are characterized by pathological anxiety. Here we develop and apply MRI innovations for 7 T structural, connectomic, and functional characterization of the LC in terms of drivers of pathological anxiety across diagnostic boundaries. Our 7 T MRI approach affords on the order of three-fold higher resolution and sensitivity over 3 T MRI for multi- modal imaging the LC in patient populations. Our preliminary 7 T MRI data demonstrate the neuroanatomical and functional architecture of LC and connected cortico-subcortical circuitry robustly characterized in both patients and controls. Using quantitative magnetization transfer (MT) imaging and neurite orientation dispersion density imaging (NODDI), our proposal will allow for the precise localization, quantification and microstructural characterization of the LC in humans. Building on our pilot data, Aim 1 will establish the role of LC microstructure in pathological anxiety.
Aim 2 will establish the relationship between LC functional and anatomical connectivity and pathological anxiety.
Aim 3 will establish the role of LC in functional response to threat in pathological anxiety. In each case, co-variance between imaging measures of the LC and dimensional measures of anxiety will be examined trans-diagnostically across four study groups [PTSD (n=30), PD (n=30), GAD (n=30), healthy controls (N=30)] in a cross-sectional design. Secondarily, between-group differences will be examined. Finally, in Aim 4, we will use a data-driven approach to explore how specific measures of LC microstructure, connectivity, and function relate to specific dimensional clinical features across diagnoses.
Anxiety and stress-related disorders, including panic disorder (PD), generalized anxiety disorder (GAD), and posttraumatic stress disorder (PTSD), are among the most disabling neuropsychiatric conditions in the United States. Given the successful completion of this research, we will provide the first in vivo characterization of the human locus coeruleus system in patients with anxiety across clinical diagnoses. We anticipate this work will enhance diagnostic strategies for anxiety disorders, elucidate novel targets in LC circuits for new therapies, and build a translational bridge from animal models of pathological anxiety to human disease.
