The goal of this proposal is the continued characterization of fundamental and distinctive features of GABA receptor function and synapses of the mammalian CNS. In light of the known alterations of GABAergic inhibition in several neurological and psychiatric disorders, and of the GABA-related mechanism of action of numerous clinically used drugs such as anxiolytics, anesthetics and anticonvulsants, the proposed studies will considerably contribute to the understanding of inhibition and its alteration by drugs or neuronal activity. Each specific aim addresses a critical issue related to the regulation of GABAergic inhibition. These aims are: (1) to establish the specifics of the inhibitory control of interneurons, leading to understanding of the synchronous activation of GABA neuronal networks responsible for the timing of high frequency oscillations in the brain; (2) to gain insight into the cellular and molecular mechanisms which regulate GABA release and govern its synchrony; and (3) to uncover molecular alterations affecting the function of synaptic GABA-A receptors during tolerance and withdrawal after chronic BZ treatment. First, recordings from individual anatomically identified hippocampal interneurons will provide the first comprehensive combined physiological and anatomical fingerprinting of these cells. The findings are expected to explain the precise synaptic control of the interneuronal network, known as the critical clock for the high-frequency (gamma) oscillations in the cortex, in turn thought to underlie higher cortical function. Second, the study will probe pre- and postsynaptic factors, including GABA-B receptors and synaptic vesicle proteins, involved in the synchrony of GABA release. These factors are crucial for translating the high frequency discharges of interneurons into a precisely timed GABA release which tightly controls the activity of other interneurons and principal cells. The third part of the proposal will address BZ tolerance and withdrawal, a topic of considerable clinical relevance. We will examine the hypothesis that synaptic GABA receptor function is controlled by phosphorylation, and that alterations in this process may underlie BZ tolerance and withdrawal. The resulting insights into critical aspects of the short and long-term functioning of GABA synapses will lead to a better grasp of many clinical problems associated with alterations in inhibitory function including those of cognitive processes. A thorough understanding of the regulation of GABAergic inhibition may open novel therapeutical approaches aimed at devastating psychiatric and neurodegenerative disorders including anxiety, stress, stroke, and epilepsy.