Dopamine/D2 Receptor and HD Figure 5. DA and quinpirole activate Rho/ROCK pathway on striatal neurons. A) Western-blot detection of Rho-GTP (top) along with Total Rho (middle) and b-tubulin (bottom) after 15 minutes of treatment with DA (100 mM) and quinpirole (10 mM) in non-transfected striatal neurons. B) Quantification of Rho-GTP activity from 3 independent experiments. Total Rho was expressed as Arbitrary Unit (AU). Note the significant increase of Rho-GTP/Total Rho after 15 minutes of DA (Grey bar) and quinpirole (Black bars) treatment (*P,0.05). C) Immunocytochemical detection of P-Cofilin (green) and MAP2 (red) proteins 20 minutes after quinpirole treatment (10 mM, lower panel) and in Control conditions (upper panel). Nuclei were labelled using Hoechst (blue). D and E) Quantification of P-Cofilin positive neurons (n = 3 independent experiments, 100 neurons per experiment) using Metamorph software after quinpirole treatment alone or in the presence (D) of pharmacological inhibitors of ROCK, Hydroxyfasudil (10 mM) and Y-27632 (10 mM) or (E) after transfection of siRNA ROCK-II. B, D and E, Data are expressed as mean6SEM (***P,0.001, **P,0.005, *P,0.05). doi:10.1371/journal.pone.0008287.g005 mediated effects on aggregate formation. Thus, altogether, these findings suggest that D2 receptor stimulation plays a key role in GABAergic/MSN vulnerability to ExpHtt, via potentiation of neuropil aggregates and axonal poisoning. Other deleterious effects of D2 receptor stimulation on ExpHtt induced neuronal dysfunctions were recently unraveled (41). In an elegant study, the authors showed that D2 receptor stimulation increased ExpHtt- induced deficiency of mitochondrial complex II protein activity, which plays a key role in oxidative energy metabolism. In cellular models expressing the full length mutant Htt, immortalized mutant STHdhQ111, striatal neuronal progenitor cell lines or striatal neurons from YAC128 mice, D1R stimulation but not D2R is involved in DA-mediated cell death and potentiation of glutamate toxicity [23,25]. In these studies, D1R-mediated effects were critically linked to increased calcium influx. Thus, depending on the expression of the full length or the cleaved fragment of PLoS ONE | www.plosone.org 7 December 2009 | Volume 4 | Issue 12 | e8287