Fyn kinase in the dorsomedial striatum (DMS) of rodents plays a central role in mechanisms underlying excessive alcohol intake. The DMS is comprised of medium spiny neurons (MSNs) that project directly (dMSNs) or indirectly (iMSNs) to the substantia nigra. Here, we examined the cell-type specificity of Fyn's actions in alcohol use. First, we knocked down Fyn selectively in DMS dMSNs or iMSNs of mice and measured the level of alcohol consumption. We found that downregulation of Fyn in dMSNs, but not in iMSNs, reduces excessive alcohol but not saccharin intake. D1Rs are coupled to Gαs/olf, which activate cAMP signaling. To examine whether Fyn's actions are mediated through cAMP signaling, DMS dMSNs were infected with GαsDREADD, and the activation of Fyn signaling was measured following CNO treatment. We found that remote stimulation of cAMP signaling in DMS dMSNs activates Fyn and promotes the phosphorylation of the Fyn substrate, GluN2B. In contract, remote activation of GαsDREADD in DLS dMSNs did not alter Fyn signaling. We then tested whether activation of GαsDREADD in DMS dMSNs or iMSNs alters alcohol intake and observed that CNO-dependent activation of GαsDREADD in DMS dMSNs but not iMSNs increases alcohol but not saccharin intake. Finally, we examined the contribution of Fyn to GαsDREADD-dependent increase in alcohol intake, and found that systemic administration of the Fyn inhibitor, AZD0503 blocks GαsDREADD-dependent increase in alcohol consumption. Our results suggest that the cAMP-Fyn axis in the DMS dMSNs is a molecular transducer of mechanisms underlying the development of excessive alcohol consumption.

A prominent aspect of drug addiction is the ability of drug-associated cues to elicit craving and facilitate relapse. Understanding the factors that regulate cue reactivity will be vital for improving treatment of addictive disorders. Low availability of dopamine (DA) D2 receptors (D2Rs) in the striatum is associated with high cocaine intake and compulsive use. However, the role of D2Rs of nonstriatal origin in cocaine seeking and taking behavior and cue reactivity is less understood and possibly underestimated. D2Rs expressed by midbrain DA neurons function as autoreceptors, exerting inhibitory feedback on DA synthesis and release. Here, we show that selective loss of D2 autoreceptors impairs the feedback inhibition of DA release and amplifies the effect of cocaine on DA transmission in the nucleus accumbens (NAc) in vitro. Mice lacking D2 autoreceptors acquire a cued-operant self-administration task for cocaine faster than littermate control mice but acquire similarly for a natural reward. Furthermore, although mice lacking D2 autoreceptors were able to extinguish self-administration behavior in the absence of cocaine and paired cues, they exhibited perseverative responding when cocaine-paired cues were present. This enhanced cue reactivity was selective for cocaine and was not seen during extinction of sucrose self-administration. We conclude that low levels of D2 autoreceptors enhance the salience of cocaine-paired cues and can contribute to the vulnerability for cocaine use and relapse.

The mammalian target of rapamycin complex 1 (mTORC1), a transducer of local dendritic translation, participates in learning and memory processes as well as in mechanisms underlying alcohol-drinking behaviors. Using an unbiased RNA-seq approach, we identified Prosapip1 as a novel downstream target of mTORC1 whose translation and consequent synaptic protein expression are increased in the nucleus accumbens (NAc) of mice excessively consuming alcohol. We demonstrate that alcohol-dependent increases in Prosapip1 levels promote the formation of actin filaments, leading to changes in dendritic spine morphology of NAc medium spiny neurons (MSNs). We further demonstrate that Prosapip1 is required for alcohol-dependent synaptic localization of GluA2 lacking AMPA receptors in NAc shell MSNs. Finally, we present data implicating Prosapip1 in mechanisms underlying alcohol self-administration and reward. Together, these data suggest that Prosapip1 in the NAc is a molecular transducer of structural and synaptic alterations that drive and/or maintain excessive alcohol use.