Abstract
Studies in animal models of Parkinson's disease have revealed that degeneration of noradrenaline neurons is involved in the motor deficits. Several types of adrenoceptors are highly expressed in neostriatal neurons. However, the selective actions of these receptors on striatal signaling pathways have not been characterized. In this study, we investigated the role of adrenoceptors in the regulation of dopamine/dopamine- and cAMP-regulated phosphoprotein of M(r) 32 kDa (DARPP-32) signaling by analyzing DARPP-32 phosphorylation at Thr34 [protein kinase A (PKA)-site] in mouse neostriatal slices. Activation of beta(1)-adrenoceptors induced a rapid and transient increase in DARPP-32 phosphorylation. Activation of alpha(2)-adrenoceptors also induced a rapid and transient increase in DARPP-32 phosphorylation, which subsequently decreased below basal levels. In addition, activation of alpha(2)-adrenoceptors attenuated, and blockade of alpha(2)-adrenoceptors enhanced dopamine D(1) and adenosine A(2A) receptor/DARPP-32 signaling. Chemical lesioning of noradrenergic neurons mimicked the effects of alpha(2)-adrenoceptor blockade. Under conditions of alpha(2)-adrenoceptor blockade, the dopamine D(2) receptor-induced decrease in DARPP-32 phosphorylation was attenuated. Our data demonstrate that beta(1)- and alpha(2)-adrenoceptors regulate DARPP-32 phosphorylation in neostriatal neurons. G(i) activation by alpha(2)-adrenoceptors antagonizes G(s)/PKA signaling mediated by D(1) and A(2A) receptors in striatonigral and striatopallidal neurons, respectively, and thereby enhances D(2) receptor/G(i) signaling in striatopallidal neurons. alpha(2)-Adrenoceptors may therefore be a therapeutic target for the treatment of Parkinson's disease.