Elizabeth P. Bauer - US grants

DESCRIPTION (provided by applicant): There is a growing realization that human subjects with anxiety disorders exhibit abnormalities in how they acquire and/or extinguish conditioned fear responses. Thus, understanding how anxiety and conditioned fear interact at the neuronal level has direct clinical relevance. The neuropeptide corticotropin-releasing factor (CRF) is released throughout the brain under conditions of stress and anxiety. The amygdala contains particularly dense concentrations of CRF receptors whose activation leads to anxious behaviors. Yet the modulation of fear learning by this neuropeptide and indeed the interaction between anxiety and fear learning has not been comprehensively explored. We propose to examine this question by using multiple complementary methods. We will first analyze the anatomical distribution of CRF receptors within the basolateral nucleus of the amygdala (BLA), determining whether these receptors are located on the principal excitatory neurons of the BLA and/or on subsets of inhibitory interneurons. We will next examine behaviorally how CRF modulates fear learning and expression. Finally, using in vitro electrophysiology, we will study how CRF affects electrophysiological properties of BLA neurons and synaptic plasticity. Together, the experiments in this proposal represent an important step in understanding how CRF modulates Pavlovian fear conditioning. Thus, the results of this project may yield fundamental insights into the causes of anxiety disorders and provide a foundation for clinical investigation and pharmaceutical development. PUBLIC HEALTH RELEVANCE: Many anxiety disorders can be characterized by abnormalities in acquiring or extinguishing conditioned fear. This project will explore the relationship between a key neuropeptide associated with anxiety and the ability to learn and express conditioned fear responses.

? DESCRIPTION (provided by applicant): The major aim of this proposal is to investigate the interactions between two brain regions involved in fearful and anxious behaviors. The bed nucleus of the stria terminalis (BNST) has been implicated in processing adaptive and pathological anxiety. The central nucleus of the amygdala (CE) contributes to both anxious behaviors and fear learning. These two structures have similar cell types, are interconnected and share almost identical patterns of efferent targets. Despite their anatomical and functional similarities, the interaction between these two structures is poorly understood. We propose to examine the BNST-CE pathway using multiple complementary methods. We will characterize the neurons in the oval nucleus of the BNST that project to the CE by retrogradely labeling BNST neurons and using immunofluorescent analysis of neuropeptide markers. We will also characterize neurons in the CE which receive input from BNST neurons. We will then use optogenetic techniques to specifically activate those neurons in the oval BNST which connect with the CE. An AAV vector expressing Cre recombinase fused to a transcellular tracer protein will be infused into the CE. Cre-recombinase would be transported along with the tracer to cell bodies in the BNST as well as other areas which project to the CE. Second, a Cre-dependent virus expressing the rhodopsin derivative channel-rhodopsin will be placed in the oval nucleus of the BNST. Thus, opsin expression will be Cre-dependent and will be limited to those neurons in the BNST which are anatomically connected to the CE. Success of this dual viral strategy will be verified using immunofluorescence and in vitro electrophysiology. Finally, we will examine behaviorally how the BNST-CE pathway modulates anxiety-like behavior, fear learning, fear generalization and fear extinction using optogenetic techniques to activate this pathway. Together, the experiments in this proposal represent an important step in understanding the functional significance of the BNST-CE pathway. Many anxiety disorders in humans can be characterized by abnormalities in acquiring and/or extinguishing conditioned fear responses. Thus, understanding how anxiety and fear learning interact at the neuronal level has clear translational significance.

PROJECT SUMMARY: The major aim of this proposal is to investigate the interactions between two brain regions involved in fearful and anxious behaviors. The ventral subiculum (vSUB), the main output of the ventral hippocampus, has been implicated in both anxiety-like behaviors and fear expression. The bed nucleus of the stria terminalis (BNST) processes both adaptive and pathological anxiety. The vSUB contributes a significant input to the BNST, yet the interaction between these two structures is poorly understood. We propose to examine the vSUB-BNST pathway using multiple complementary methods. We will first characterize the neurons in the vSUB that project to the BNST by retrogradely labeling vSUB neurons and using immunofluorescent analysis of neuropeptide markers. We will then determine whether the vSUB-BNST pathway contributes to context fear conditioning, fear reinstatement and anxiety behaviors: three behaviors which are well-known to be involve the BNST. We will use FOS immunohistochemistry to characterize the contribution of this pathway to these three behaviors. We will then use optogenetic techniques to examine the behavioral effects of modulating neuronal activity in this pathway. Our results will reveal which behaviors recruit the vSUB-BNST pathway, and how modulation of this pathway can affect fear- and anxiety-like behaviors. Finally, we will use in vivo electrophysiology to record from vSUB neurons during context and cued fear conditioning, fear reinstatement, and anxiety tasks. The use of optogenetic tools will allow us to specifically identify and record from neurons within the vSUB which project to the BNST. Together, the experiments in this proposal represent an important step in understanding the functional significance of the vSUB-BNST pathway. Our working hypothesis is that activity in the vSUB-BNST is reduced in threatening contexts. Many anxiety disorders in humans can be characterized by an inability to reduce fear responses in a non-threatening environment. Thus, understanding how anxiety and fear learning are mediated by specific neuronal circuits has clear translational significance.