Signal integration and interpretation by the DARPP-32 system in dendrites of medium spiny neurons in the striatum. The membrane of spiny neurons (solid curved line) contains receptors for the neurotransmitters dopamine and glutamate, which had been released by other neurons into the synaptic cleft. Diamonds show molecular binding, while arrows with plus signs designate activation or enzymatic reactions and dash-dotted lines with bars indicate inhibition. Shaded boxes in green color represent phosphorylated forms of DARPP-32, with labels indicating the specific phosphorylated site, and arrows showing possible transitions between the different phosphorylation states. Open block arrows indicate possible multiple-site phosphorylation. Please refer to the Figure 2 for a detailed map of all possible transitions between different phosphorylation forms. Abbreviations are: dopamine receptor of D1 subtype (D1), dopamine receptor of D2 subtype (D2), G protein and subunits (Gαβγ, Gα), adenylate cyclase (AC5), cyclic AMP (cAMP), phosphodiesterases (PDE1, PDE4), protein kinase A (PKA, PKAc), alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA), N-methyl-D-aspartate (NMDA), protein phosphatase 2B (PP2Bi, PP2B), protein phosphatase-1 (PP1), protein phosphatase 2A (PP2A), cyclin-dependent kinase 5 (CDK5), casein kinase 2 (CK2), casein kinase 1 (CK1), protein phosphatase 2C (PP2C), dopamine- and cAMP-regulated phosphoprotein with 32 kDa molecular weight (DARPP-32). Phosphorylation of DARPP-32 is indicated by the corresponding amino acid and location, such as DARPP-32Thr34. See Figure 2 for multiple-site phosphorylation.