Striatal Microcircuit Dynamics of Ethanol Habits

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Project Summary The research proposal explores how a habit center in the brain, the dorsolateral striatum, is disinhibited by chronic alcohol exposure to foster habit formation. Understanding how this process works at molecular, neural circuit and behavioral levels is critical to devising novel therapeutic strategies targeting alcoholism, as well as comorbid habitual use of other substances of abuse. Dorsolateral striatum output is powerfully governed by the inhibitory fast-spiking interneuron (FSI) population. FSIs are in relatively high abundance in the dorsolateral striatum as compared to other striatal subregions, which positions these cells to be key modulators of dorslolateral striatum output and habit expression. As a minority population of neurons in the striatum, FSIs and their role in chronic ethanol exposure-induced habit formation is vastly understudied. This proposal seeks to understand how chronic ethanol exposure dampens FSI function to allow for dorsolateral striatum disinhibition and habitual action expression. This will be investigated in three specific experimental aims employing cutting-edge technology that allows for an unprecedented view into the function of these neurons in mice. In the first aim we test the hypothesis that chronic ethanol exposure depresses the release of the inhibitory neurotransmitter GABA from FSIs onto postsynaptic medium spiny neurons, which are the output neurons of the striatum. This will be accomplished using optogenetics coupled with brain slice electrophysiology. In the second aim we explore FSI synchrony. FSIs synchronize their activity to enhance their inhibitory authority over dorsolateral striatum output. Thus, we will test the hypothesis that FSIs desynchronize following chronic ethanol exposure. We will test this using slice electrophysiology and calcium imaging of FSI activity in awake behaving mice exposed to chronic alcohol. Finally, we will test the contribution of dampened FSI release of GABA and FSI asynchrony on alcohol drinking and generalized habit learning in mice. By examining how ethanol hijacks the neural circuitry of habit formation, the results of this study should significantly advance our knowledge toward novel therapeutic strategies targeting alcoholism and provide novel insight to myriad neuropsychiatric disorders involving striatal dysfunction.