Coexistence of D3R typical and atypical signaling in striatonigral neurons during dopaminergic denervation. Correlation with D3nf expression changes

Dopamine D₃R are widely expressed in basal ganglia where interact with D₁R. D₃R potentiate cAMP accumulation and GABA release stimulated by D₁R in striatonigral neurons through “atypical” signaling. During dopaminergic denervation, D₃R signaling changes to a “typical” in which antagonizes the effects of D₁R, the mechanisms of this switching are unknown. D₃nf splice variant regulates membrane anchorage and function of D₃R and decreases in denervation; thus, it is possible that D₃R signaling switching correlates with changes in D₃nf expression and increases of membranal D₃R that mask D₃R atypical effects. We performed experiments in unilaterally 6-hydroxydopamine lesioned rats and found a decrease in mRNA and protein of D₃nf, but not of D₃R in the denervated striatum. Proximity ligation assay showed that D₃R-D₃nf interaction decreased after denervation, whereas binding revealed an increased B_max in D₃R. The new D₃R antagonized cAMP accumulation and GABA release stimulated by D₁R; however, in the presence of N-Ethylmaleimide (NEM), to block G_i protein signaling, activation of D₃R produced its atypical signaling stimulating D₁R effects. Finally, we investigated if the typical and atypical effects of D₃R modulating GABA release are capable of influencing motor behavior. Injections of D₃R agonist into denervated nigra decreased D₁R agonist-induced turning behavior but potentiated it in the presence of NEM. Our data indicate the coexistence of D₃R typical and atypical signaling in striatonigral neurons during denervation that correlated with changes in the ratio of expression of D₃nf and D₃R isoforms. The coexistence of both atypical and typical signaling during denervation influences motor behavior.