Girk ablation had no impact on apparent capacitance, input resistance, Ih current amplitude, or action potential duration in putative VTA DA neurons (not shown). Genotype-dependent differences in spontaneous rates, however, were evident. Surprisingly, VTA DA neurons from Girk2−/− mice exhibited lower rates than wild-type, Girk1−/−, and Girk3−/− counterparts (Fig. 2C). Firing rates of VTA DA neurons from wild-type slices were consistently and reversibly lowered in the presence of the Girk channel blocker tertiapin, suggesting that the lower firing rates observed in DA neurons from Girk2−/− mice were largely attributable to the loss of Girk channel function (Fig. 2C). Indeed, tertiapin application had no effect on firing rates of VTA DA neurons in slices from Girk2−/− mice (not shown).
