Abstract
Dopamine receptor signaling exhibits prominent plasticity that is important for the pathogenesis of both addictive and movement disorders. Psychoactive stimulants that activate the dopamine D(1) receptor (Drd1a) induce the rapid phosphorylation and activation of extracellular signal-regulated kinase 1/2 (ERK1/2) in neurons of the nucleus accumbens and ventral striatum. This response is known to be dependent on the phosphatase inhibitor dopamine- and cAMP-regulated phosphoprotein-32 (DARPP-32) and appears critical for the sensitization of Drd1a responses that contributes to addiction. Loss of dopamine input to the striatum, as in models of Parkinson's disease (PD), also results in a sensitization of responses to dopamine agonists that is manifest by increased activation of ERK1/2 in the dorsal striatum. Here, we test whether DARPP-32 is required for sensitization of Drd1a responses in a PD model. In the normal dorsal striatum, there is minimal Drd1a-mediated activation of ERK1/2; however, in the PD model there is robust Drd1a-mediated activation of ERK1/2. In both wild-type and DARPP-32 knock-out mice, Drd1a robustly induces pERK1/2 throughout the dopamine-depleted striatum. These findings indicate that Drd1a sensitization relevant for PD occurs by a novel mechanism that does not require DARPP-32.