Dopamine/D2 Receptor and HD Figure 3. D2 receptor stimulation potentiates neuritic retraction and growth cone collapse induced by ExpHtt in striatal neurons. A) Immunohistochemical detection of MAP2 protein (red) was performed on striatal neurons transfected with either Htt or ExpHtt (GFP) and treated or not for 14 hours with quinpirole (10 mM). Nuclei were labelled using Hoechst (blue). The white arrow in the merge panel points to a neurite in transfected neurons. B) Phalloidin labelling of F-actin was assayed to visualize growth cone on Htt and ExpHtt-expressing striatal neurons. White arrows and insert in the merge panel depict a growth cone in a transfected neuron. C) Quantification of mean neuritic length in transfected neurons was determined from MAP2 staining using ImageJ software in Htt (white bars) and ExpHtt (black bars)-expressing neurons, treated or not with dopamine (DA, 100 mM), quinpirole (Quin, 10 mM) or DA plus raclopride (1 mM) for 14 hours. D) Quantification of growth cone collapse was determined on phalloidin staining in Htt (white bars) and ExpHtt (black bars)- transfected neurons treated or not with quinpirole (10 mM) for 14 hours. C and D) Data were analyzed from at least 3 independent experiments (100 transfected neurons per condition and per experiment) and expressed as mean6SEM.(***P,0.001, ns: non significant). doi:10.1371/journal.pone.0008287.g003 PLoS ONE | www.plosone.org 4 December 2009 | Volume 4 | Issue 12 | e8287