D-1 dopamine receptor activation reduces GABA(A) receptor currents in neostriatal neurons through a PKA/DARPP-32/PP1 signaling cascade

Dopamine is a critical determinant of neostriatal function, but its impact on intrastriatal GABAergic signaling is poorly understood The role of D-1 d opamine receptors in the regulation of postsynaptic GABA(A) receptors was c haracterized using whole cell voltage-clamp recordings in acutely isolated, rat neostriatal medium spiny neurons. Exogenous application of GABA evoked a rapidly desensitizing current that was blocked by bicuculline. Applicati on of the D-1 dopamine receptor agonist SKF 81297 reduced GABA-evoked curre nts in most medium spiny neurons. The D-1 dopamine receptor antagonist SCH 23390 blocked the effect of SKF 81297. Membrane-permeant cAMP analogues mim icked the effect of D-1 dopamine receptor stimulation, whereas an inhibitor of protein kinase A (PKA; Rp-8-chloroadenosine 3',5' cyclic monophosphothi oate) attenuated the response to D-1 dopamine receptor stimulation or cAMP analogues. Inhibitors of protein phosphatase 1/2A potentiated the modulatio n by cAMP analogues. Single-cell RT-PCR profiling revealed consistent expre ssion of mRNA for the beta 1 subunit of the GABA(A) receptor-a known substr ate of PKA-in medium spiny neurons. Immunoprecipitation assays of radiolabe led proteins revealed that D-1 dopamine receptor stimulation increased phos phorylation of GABA(A) receptor beta 1/beta 3 subunits. The D-1 dopamine re ceptor-induced phosphorylation of beta 1/beta 3 subunits was attenuated sig nificantly in neostriata from DARPP-32 mutants. Voltage-clamp recordings co rroborated these results, revealing that the efficacy of the D-1 dopamine r eceptor modulation of GABA(A) currents was reduced in DARPP-32-deficient me dium spiny neurons. These results argue that D-1 dopamine receptor stimulat ion in neostriatal medium spiny neurons reduces postsynaptic GABA(A) recept or currents by activating a PKA/DARPP-32/protein phosphatase 1 signaling ca scade targeting GABA(A) receptor beta 1 subunits.