Characterization of D2S−/− mice. (A) RT-PCR analyses of D2R expression in striatal mRNAs from WT, D2S−/−, and D2L−/− mice. The upper band (245 bp) corresponds to D2L, whereas the lower (158 bp) to D2S, as indicated by arrows. (B) qRT-PCR–based quantifications of D2R expression in striatal extracts of WT, D2S−/−, and D2L−/− mice, using primers common to both isoforms (exon 2), using GAPDH as control. Bars are mean ± SEM of D2R/GAPDH ratios (n = 4 per genotype). (C) Saturation isotherm analyses for binding of the D2R antagonist [3H]-Spiperone to striatal membranes from WT (circles) (Bmax = 720 ± 85 fmol/mg protein; Kd = 30 ± 2 pM) and D2S−/− mice (diamonds) (Bmax = 600 ± 67 fmol/mg protein; Kd = 28 ± 1 pM) (n = 3 per genotype).