Abstract Exposure to addictive drugs or alcohol modifies synaptic transmission, leading to drug-evoked aberrant synaptic plasticity, which is believed to control the reinforcement of drug or alcohol intake. The dorsal striatum, a crucial brain region for the expression of habit and goal-directed behaviors, has been linked to addiction. We recently reported that excessive alcohol intake caused long-lasting potentiation of glutamatergic transmission in striatal neurons expressing dopamine D1 receptors (D1-neurons), and sustained depression of glutamatergic activity in striatal neurons bearing D2 receptors (D2-neurons) (Wang et al., Journal of Neuroscience, 2015; Cheng et al., Biological Psychiatry, 2016). Although reversal of drug-evoked synaptic plasticity has been reported to reduce drug intake persistently, very little is known about which neuronal types are involved or whether this reversal alters alcohol intake. Thus, the goal of this application is to reverse alcohol-induced aberrant synaptic plasticity in striatal D1- and D2-neurons and thereby persistently reduce alcohol-seeking and relapse, with the long-term objective of determining how such reversal can be used to treat alcohol use disorder. Our hypothesis, based in part on our preliminary results, is that in vivo optogenetic induction of long-term depression (LTD) in striatal D1-neurons or long-term potentiation (LTP) in D2-neurons causes long- lasting reductions in operant alcohol seeking and relapse. We will test this hypothesis by pursuing the following three specific aims: 1) to determine whether induction of LTD and LTP in striatal slices from alcohol- drinking rats normalizes glutamatergic transmission; 2) to determine whether in vivo prefrontal cortical inputs and D1-neuron activity are enhanced by excessive alcohol intake and reversed by LTD induction; and 3) to determine whether optogenetic and pharmacological reversal of alcohol-evoked corticostriatal plasticity can persistently reduce alcohol seeking and relapse behaviors in rats. This application is highly innovative because it applies state-of-the-art approaches, including a combination of dual-channel optogenetics and in vivo fiber photometry calcium imaging, allowing us for the first time to determine how normalization of alcohol-evoked synaptic plasticity in specific neuronal populations alters their activities in vivo and thus decreases alcohol- drinking behavior persistently; these important questions cannot be addressed using conventional methodologies. Knowledge generated from this proposal will provide novel strategies for long-term treatment of alcohol use disorder.