Figure 5.

A, Left, Diagram showing effect of DA on DARPP-32 phophorylation (for details, see Svenningsson et al., 2004; Bateup et al., 2008; Yger and Girault, 2011). D₁ receptor stimulation increases c-AMP production and protein kinase A (PKA) activity, which phosphorylates DARPP-32 to yield pDARPP-32(Thr34). D₂ receptor stimulation decreases c-AMP production and protein kinase A activity, which decreases the dephosphorylation of pDARPP-32(Thr75) by protein phosphatase 2A (PP-2A) and therefore increases pDARPP-32(Thr75) expression. Right, Tetrabenazine, which depletes DA, was hypothesized to have the opposite effect of DA, increasing pDARPP-32(Thr75) in substance-P-positive neurons and pDARPP-32(Thr34) in encephalin-positive neurons. B, C, Immunofluorescence double labeling of different forms of phosphorylated DARPP-32. B, pDARPP-32(Thr34) immunofluorescence is localized in encephalin-positive neurons (yellow/orange areas of cells in merged photo), whereas pDARPP-32(Thr75) immunofluorescence activity is colocalized with substance P (yellow/orange areas of cells in merged photo). C, pDARPP-32(Thr34) is not present in substance-P-positive neurons (separate green and red cells in merged photo) and pDARPP-32(Thr75) is not colocalized with enkephalin immunofluorescence activity (separate green and red cells in merged photo).