This is an application for funding of a study examining the neurobiology of fear and anxiety with a special emphasis on the role of synaptic ?2-containing GABAA receptors and extrasynaptic ?5- containing GABAA receptors. The ?2-containing GABAA receptors, which have been shown to mediate the anxiolytic-like action of diazepam in ethological tests of anxiety will be deleted from hippocampal principal neurons in the CA1, CA3, and DG subregions, respectively, and from the basolateral amygdala using cre- loxP-mediated recombination to elucidate subregion-specific functions and neuronal circuits (e.g. hippocampal trisynaptic and monosynaptic pathways) involved in modulation of anxiety. While the function of neurons in defined hippocampal subregions in learning and memory tasks has been extensively studied, the functions of these neurons in the regulation of emotions is still unknown. Preliminary results indicate a role for extrasynaptic ?5-containing GABAA receptors in extinction of conditioned fear, and based on this observation we propose experiments directed towards the development of a novel therapeutic strategy to promote extinction, which is a major goal in the treatment of posttraumatic stress disorder. Anxiety disorders are the most prevalent type of psychiatric disorders in the community, affecting approximately 10%-15% of the population. This proposal will investigate the functional role of GABAA receptor subtypes in defined neuronal circuits in the hippocampus and the amygdala for the modulation of anxiety-related behaviors. It is expected that the proposed research will identify the ?2- and the ?5- containing GABAA receptors as separate molecular targets for the treatment of distinct anxiety disorders, e.g. generalized anxiety disorder and posttraumatic stress disorder.