BackgroundReduced dopamine D2 receptor (D2R) ligand binding has repeatedly been demonstrated in the striatum of humans with alcohol use disorder (AUD). The attenuated D2R binding has been suggested to reflect a reduced D2R density, which in turn has been proposed to drive craving and relapse. However, results from rodent studies addressing the effects of alcohol drinking on D2R density have been inconsistent.MethodsA validated alcohol drinking model (intermittent access to 20% alcohol) in Wistar rats was used to study the effects of voluntary alcohol drinking (at least 12 weeks) on the D2R in the striatum compared to age‐matched alcohol‐naïve control rats. Reverse transcriptase quantitativePCRwas used to quantify isoform‐specificDrd2gene expression levels. Using bisulfite pyrosequencing,DNAmethylation levels of a regulatory region of theDrd2gene were determined. In situ proximity ligation assay was used to measure densities of D2R receptor complexes: D2R‐D2R, adenosine A2A receptor (A2AR)‐D2R, and sigma1 receptor (sigma1R)‐D2R.ResultsLong‐term voluntary alcohol drinking significantly reducedmRNAlevels of the long D2R isoform in the nucleus accumbens (NAc) but did not alter CpG methylation levels in the analyzed sequence of theDrd2gene. Alcohol drinking also reduced the striatal density of D2R‐D2R homoreceptor complexes, increased the density of A2AR‐D2R heteroreceptor complexes in theNAc shell and the dorsal striatum, and decreased the density of sigma1R‐D2R heteroreceptor complexes in the dorsal striatum.ConclusionsThe present results on long‐term alcohol drinking might reflect reduced D2R levels through reductions in D2R‐D2R homoreceptor complexes and gene expression. Furthermore, based on antagonistic interactions between A2ARand D2R, an increased density of A2AR‐D2R heteroreceptor complexes might indicate a reduced affinity and signaling of the D2R population within the complex. Hence, both reduced striatal D2R levels and reduced D2R protomer affinity within the striatal A2AR‐D2R complex might underlie reduced D2R radioligand binding in humans withAUD. This supports the hypothesis of a hypodopaminergic system inAUDand suggests the A2AR‐D2R heteroreceptor complex as a potential novel treatment target.