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.