Our long-term goal is to understand GABAergic inhibition in neurological disorders. GABAA receptors (GABAA-Rs) mediate the majority inhibition in the brain. Synaptically localized GABAA-Rs mediate fast inhibitory neurotransmission. Extrasynaptic GABAA-Rs can be activated by a low concentration of ambient GABA to mediate tonic inhibition, which plays an important role in regulating neuronal excitability. Extrasynaptic GABAA-Rs play important roles in learning and memory, anxiety and depression, alcoholism, epilepsy, and sleep disorders. Despite our increasing understanding of the functional significance of extrasynaptic GABAA-Rs, the molecular mechanisms underlying extrasynaptic targeting of GABAA-Rs are poorly understood. The specific objective of this proposal is to unravel the targeting mechanisms of d subunit-containing GABAARs, which is the major subtype of extrasynaptically localized GABAARs. Based on a strong set of preliminary data, we propose a novel hypothesis that in addition to ?2 and d subunits, a subunits also carry critical targeting signals governing synaptic versus extrasynaptic localization of GABAARs. This hypothesis will be tested with a unique model system of molecularly reconstituted functional GABAergic synapses. With precise control of the postsynaptic compositions in model synapses, we will investigate how synaptic and extrasynaptic GABAARs interact with neuroligin-2/gephyrin/collybistin complex. Immuno-electron microscopy and quantum dot-based time lapse imaging will be used to visualize the localization and dynamic movement of d-GABAARs. Finally, ?2-/- and d-/- neurons will be used to investigate functional rescue of chimeric and mutant d-GABAARs and ?2-GABAARs. Our studies will gain fundamental understanding of the extrasynaptic targeting mechanisms of d-GABAA-Rs, which is pivotal for molecular designing of new drug therapy to treat neurological disorders that are associated with extrasynaptic GABAA-Rs. PUBLIC HEALTH RELEVANCE: Project Narrative Extrasynaptic GABAA receptors play important roles in learning and memory, anxiety and depression, alcoholism, epilepsy, and sleep disorders. However, very little is known about these extrasynaptically localized GABAA receptors. Our research employs an array of multidisciplinary approaches to unravel the molecular mechanisms underlying extrasynaptic targeting of GABAA receptors. Such molecular understanding will identify novel drug targets for therapeutic intervention of neurological disorders.