Tools for dissecting neural circuits of interoception and autonomic regulation

Behavioral states and physiological states are often linked, and concurrently perturbed in disease processes such as anxiety and panic disorder, but the bottom-up influence of internal physiological signals on behavior is complex. Physiological theories of emotion were proposed over a century ago, hypothesizing that rapid heartbeats alone could give rise to fear responses and are not merely a consequence of subjective emotional processing, but direct testing of such hypotheses has been infeasible. Investigation of the roles of afferent, interoceptive signaling in behavioral regulation requires spatial and temporal dissection of the interactions between autonomic and central circuits, but to date such studies have been limited, in part due to challenges both in observing multi-organ neural systems in their anatomically intact states, as well as in manipulating relevant physiological signals on rapid time-scales in awake, freely moving animals. To enable further studies of interactions between physiological states and behavior, in my thesis I describe a series of tools addressing these challenges. First, I built upon the hydrogel tissue chemistry technique CLARITY to enable rapid volumetric imaging of cleared peripheral organs in their intact state, enabling direct visualization of autonomic innervation throughout diverse tissue types. Second, I worked collaboratively to develop a computational tool enabling registration of cleared mouse brains to common reference atlases, enabling quantification of brain-wide activity changes under different physiological conditions. Finally, I developed a non-invasive optogenetic pacemaker to precisely control cardiac rhythms in freely-moving mice, utilizing the recently discovered red-shifted and ultra-photosensitive marine opsin, ChRmine, in conjunction with wearable micro-LED optics. Using the optical pacemaker, I directly tested the behavioral impact of cardiac palpitations on anxiety-like and apprehensive behavior, and found that intermittent tachyarrhythmia enhanced anxiety-like behavior and apprehension in stressful settings, but those same cardiac rhythms did not generate such behaviors in the absence of external stressors. Using whole brain activity mapping and tissue clearing, I then mapped regions of the brain that were preferentially activated by aberrant cardiac rhythms, and identified numerous anatomical regions -- including regions well known to be part of a "Central Autonomic Network" -- as potential mediators of bottom-up cardiac signal processing. Simultaneous optogenetic inhibition of posterior insula cortex, but not other regions within the Central Autonomic Network, during optical cardiac pacing was sufficient to reverse the induced behaviors, indicating that this region is one necessary site mediating cardiogenic anxiety-like and apprehensive behavior. Taken together, these findings offer insights into the neural mechanisms by which visceral signals can causally influence complex behaviors, and further present simple and generalizable tools for both volumetric mapping of diverse tissues, as well as non-invasive, temporally precise control of genetically-targeted organs throughout the body

Advisor: Deisseroth Karl
Chen Xiaoke
Kaltschmidt Julia
McNab Jennifer (Jennifer A.)