Figure 4.

Electrophysiological characterization of SNc and VTA neurons of D2R^{floxflox/En1Cre/+} mice. A, Loss of presynaptic D2 autoreceptor-mediated inhibition of firing in SNc and VTA of D2R^{floxflox/En1Cre/+} mice compared with control mice. B, Normal GABA_B-mediated inhibition of firing in both genotypes (representative examples). C, Percentage of firing inhibition by quinpirole (2 μm) in SNc (left) and VTA (right) in D2R^floxflox (black bars) and D2R^{floxflox/En1Cre/+} (white bars) (n = 4 for each condition; for both regions: p < 0.05 D2R^floxflox vs D2R^{floxflox/En1Cre/+}, ranked sum test). D, Percentage of firing inhibition by baclofen (2 μm) in SNc (left; n = 4 D2R^{floxflox/En1Cre/+}, n = 3 D2R^floxflox) and VTA (right; n = 4 for both genotypes) [not significant D2R^floxflox (black bars) vs D2R^{floxflox/En1Cre/+} (white bars) in either region].