GPR88 in A(2A)R Neurons Enhances Anxiety-Like Behaviors

GPR88 is an orphan G-protein-coupled receptor highly expressed in striatal dopamine D(1) (receptor) R- and D2R-expressing medium spiny neurons. This receptor is involved in activity and motor responses, and we previously showed that this receptor also regulates anxiety-like behaviors. To determine whether GPR88 in D2R-expressing neurons contributes to this emotional phenotype, we generated conditional Gpr88 knock-out mice using adenosine A(2A)R (A(2A)R)-Cre-driven recombination, and compared anxiety-related responses in both total and A(2A)R-Gpr88 KO mice. A(2A)R-Gpr88 KO mice showed a selective reduction of Gpr88 mRNA in D2R-expressing, but not D(1)R-expressing, neurons. These mutant mice showed increased locomotor activity and decreased anxiety-like behaviors in light/dark and elevated plus maze tests. These phenotypes were superimposable on those observed in total Gpr88 KO mice, demonstrating that the previously reported anxiogenic activity of GPR88 operates at the level of A(2A)R-expressing neurons. Further, A(2A)R-Gpr88 KO mice showed no change in novelty preference and novelty-suppressed feeding, while these responses were increased and decreased, respectively, in the total Gpr88 KO mice. Also, A(2A)R-Gpr88 KO mice showed intact fear conditioning, while the fear responses were decreased in total Gpr88 KO. We therefore also show for the first time that GPR88 activity regulates approach behaviors and conditional fear; however, these behaviors do not seem mediated by receptors in A(2A)R neurons. We conclude that Gpr88 expressed in A(2A)R neurons enhances ethological anxiety-like behaviors without affecting conflict anxiety and fear responses.