BNST circuitry to hypothalamic regions in stress-induced avoidance

PROJECT SUMMARY: Stress can induce long-lasting behavioral changes that result in psychiatric illnesses, such as post-traumatic stress disorder (PTSD). Some of these changes include avoidance of future situations that may be stress- inducing or ignoring one’s own basic needs, such as eating. In mice, stress can manifest in similar ways: after a stress-inducing experience, mice will not explore for food or eat in a novel, brightly lit environment in spite of hunger. This phenomenon of avoidant behavior is known as novelty-suppressed feeding or hyponeophagia. The bed nucleus of the stria terminalis (BNST) is a region of the extended amygdala that regulates behavioral responses to stress. BNST neural activity is also enhanced in response to uncontrollable stress in humans. Using a mouse model of stressor controllability, our preliminary data establishes that both GABA and glutamate neuron activity within the BNST is increased during uncontrollable stress, extending the previously aforementioned finding in humans to specific BNST neurons. We have also found that BNST neurons form synapses onto key hypothalamic brain regions that play a role in feeding and stress regulation: the arcuate nucleus (ARC) and the paraventricular nucleus of the hypothalamus (PVH). Using RNAscope in situ hybridization, we discovered that the majority of glutamatergic BNST neurons co-express the genetic machinery to vesicularly package both GABA and glutamate. The goal of this proposed project is to determine the synaptic functionality of GABA and glutamate co-transmission from BNST neurons to ARC and PVH in the context of stress-induced avoidance. The principal hypothesis is that there is an increase in co-transmission of GABA and glutamate after uncontrollable stress on downstream ARC and PVH neurons. Therefore, we hypothesize that the GABA-glutamate BNST to hypothalamus pathways are necessary for uncontrollable stress to cause avoidant behavior. A combination of optogenetics, whole-cell electrophysiology, behavioral analyses of stress, and intersectional viral strategies will be used to target and investigate the BNST circuitry to ARC and PVH. In Aim 1, we will evaluate stress-induced changes in GABA and glutamate release from BNST neurons to ARC and PVH. In Aim 2, we will manipulate GABA and glutamate transmission from BNST to ARC and PVH during uncontrollable stress and identify changes in novelty-suppressed feeding. The data generated from this proposed project may identify novel mechanisms of neurotransmitter co-transmission that may be used to reduce the effects of stress on avoidance.