PPP1R1B and fragile X syndrome: To determine whether the proportion of D1- and D2-SPNs in the NAc is preserved between the WT and FXS mice, the percentage of tdTomato-positive cells co-expressing the dopamine- and cAMP-regulated phosphoprotein Mr∼32,000 (DARPP-32), a marker of all SPNs, was estimated in the NAc Core and Shell (Figures 2A, B).