Figure 6. Expression of SNX27-insensitive GIRK2a in VTA DA neurons of SNX27_DA KO mice restores GABA_BR-activated GIRK currents and inhibition.

(A) Schematic shows stereotaxic injection of AAV DIO-GIRK2a-eYFP into VTA of SNX27_DA KO mice. Fluorescence and DIC images of eYFP positive cell selected for recording from ex vivo midbrain section of SNX27_DA KO mice injected with AAV DIO-Girk2a-eYFP. (scale bar: 20 µm) (B) Top, whole-cell recordings from VTA DA neurons show baclofen-activated GIRK currents (I_Baclofen; 300 µM) from WT and SNX27_DA KO mice injected with AAV DIO-eYFP or AAV DIO-Girk2a-eYFP, and response to Ba²⁺ (1 mM). Scale bar is 100 s and 100 pA. Bottom, baclofen-induced currents in GIRK2a-eYFP positive cells are significantly increased from eYFP+ cells (**p<0.05, Student’s t test). Scatter plot of I_Baclofen for indicated DA neurons with average current indicated by solid black bar. (C,D) Input-output plots show firing frequency increases as a function of larger current injections in the absence (solid circles, ACSF) and presence of baclofen for DA neurons cells infected with eYFP (n=6) (C) or GIRK2a-eYFP (n=8) (D). Baclofen inhibits firing activity in GIRK2a-eYFP expressing DA neurons (D) but not in eYFP expressing neurons (C) of SNX27_DA KO mice (p<0.01 absence versus presence baclofen at 140–300pA, 2-way ANOVA with Bonferroni post hoc test).