containing Cre recombinase, which is expressed in DAT+ neurons. For control, we studied the effect of injecting AAV DIO-eYFP, a similar virus that lacks SNX27b. In SNX27DA KO mice with either AAV DIO Snx27b-ires-GFP or AAV DIO-eYFP stereotaxically injected into the VTA, we observed GFP/YFP expression in midbrain sections after 12–20 days (Figure 5A). We then recorded baclofen-induced GABABR-activated GIRK currents (IBaclofen) in GFP/YFP positive neurons (Fig. 5A,B). Similar to uninjected SNX27DA KO mice (Figure 2B), IBaclofen was reduced by approximately 70% (66.2 ± 14.1 pA, n=6) for mice injected with AAV DIO-eYFP (Figure 5B). By contrast, IBaclofen was larger in DA neurons of SNX27DA KO mice injected with AAV DIO-Snx27b-ires-GFP (236.9 ± 47.7 pA, n=6) (Figure 5B), similar to wild-type IBaclofen (Figure 2B). Moreover, GABABR-dependent inhibition of neuronal firing in DA neurons of SNX27DA KO mice acutely expressing SNX27b was indistinguishable from wild-type neurons and significantly greater than in SNX27DA KO mice expressing eYFP (Figure 5C,D). Taken together, these results demonstrate that restoring SNX27 expression in DA neurons was sufficient to rescue GABABR-activated GIRK currents and inhibitory control of firing, making a developmental defect as the cause of reduced GABABR-activated GIRK currents highly unlikely.
