Project Summary We recently demonstrated that dorsolateral striatum fast-spiking interneurons (FSIs) are necessary for compulsive alcohol drinking, which is a cardinal feature of alcohol use disorder. This proposal seeks to understand the impact of ethanol on this critical interneuron population at molecular, neural circuit, and behavioral levels to advance novel therapeutic strategies targeting compulsive alcohol use. While chronic intermittent ethanol exposure exerts little effect on excitatory inputs to FSIs and FSI intrinsic excitability, it dramatically downregulates inhibitory synaptic control of FSIs – positioning FSIs to activate without regulation to underlie pathological compulsive drinking behavior. Our substantial preliminary data points to a framework wherein ethanol acutely potentiates GABAergic input to FSIs and, following repeated intermittent exposure to ethanol, GABAergic inputs are homeostatically downregulated by a degradation of the extracellular matrix that surrounds FSIs, the so-called perineuronal nets that stabilize inhibitory input onto FSIs. Thus, we herein hypothesize that this dramatic loss of GABAergic input to FSIs is mediated by a degradation of perineuronal nets. This will be tested with three interrelated yet fully independent experimental aims using cutting-edge approaches. Aim 1 will examine circuit-specific synaptic mechanisms governing the acute ethanol potentiation of GABAergic input to FSIs using molecular tools and whole-cell patch clamp electrophysiology. Aim 2 will determine the fate of GABAergic inputs to FSIs that are downregulated by chronic intermittent ethanol using a suite of advance cellular and molecular imaging techniques. Aim 3 will explore the causal interaction of acute ethanol potentiation of GABAergic input and the perineuronal net-mediated downregulation of these inputs following chronic intermittent ethanol exposure using a powerful combination of slice electrophysiology, perineuronal net imaging, in vivo chemogenetics, and compulsive alcohol drinking analyses. This multilevel, orthogonal experimental approach positions this project to yield vertical advances toward novel therapeutics targeting compulsive alcohol consumption and insight to myriad neuropsychiatric disorders involving dorsal striatal dysfunction.