Delineation of an Insula-BNST Circuit Engaged by Struggling Behavior that Regulates Avoidance
Stress is critical to every organism’s ability to adapt and survive. This dissertation reviews the history of stress research and reviews stress physiology across a variety of organ systems. Neurocircuitry that is involved in stress is examined, and special attention is given to the insula and the BNST. We explore animal models of stress and discuss different strategies for stress coping. We also describe motor efference copy and propose a possible mechanism by which motor efference copy could regulate affective circuitry. The research presented here focuses on active responses to stressors. Active responses to stressors involve motor planning, execution, and feedback. We identify an insular cortex to BNST (insula→BNST) circuit recruited during restraint stress-induced active struggling that modulates affective behavior. We demonstrate that activity in this circuit tightly follows struggling behavioral events and that the size of the fluorescent sensor transient reports the duration of the struggle event, an effect that fades with repeated exposure to the homotypic stressor. Struggle events are associated with enhanced glutamatergic- and decreased GABAergic signaling in the insular cortex, indicating the involvement of a larger circuit. We delineate the afferent network for this pathway, identifying substantial input from motor- and premotor cortex, somatosensory cortex, and the amygdala. To begin to dissect these incoming signals, we examine the motor cortex input, and show that the cells projecting from motor regions to insular cortex are engaged shortly before struggle event onset. This study thus demonstrates a role for the insula→BNST pathway in monitoring struggling activity and regulating affective behavior.