Wnt1 protects primary mesencephalic dopaminergic (DA) neurons against cell death induced by serum deprivation (SD), 6-hydroxydopamine (6-OHDA) and MPP+. Enriched neuronal cultures derived from the mesencephalon of E14 rat embryos maintained for 9-12 days in vitro (DIV) were shifted to a medium without serum and growth factors (A, 12-72 h) or to increasing concentrations (5-50 μM) of 6-OHDA or MPP+ (B) in the absence or the presence of a treatment with Wnt1 (100 ng/ml). Differences were analyzed by ANOVA followed by Newman-Keuls test, and considered significant when p < 0.05. A-B: DA neuron survival assessed by counting TH+ neurons over the DAPI+ nuclei, and expressed as percent (%) of PBS-treated control. C: [3H]dopamine incorporation was assessed 48 h after SD or 24 h after 6-OHDA or MPP+ (25 μM), the values expressed as % of control. D: Caspase activity was determined by measuring DEVD-AFC hydrolysis. Enzymatic determinations were performed in lysates from cell cultures deprived of serum or challenged with 6-OHDA or MPP+ for 6 h. *p < 0.05 when compared to control (PBS); ° p < 0.05 when compared to sister cultures exposed the cytotoxic insult (within each experimental group). E-J: Representative images showing TH+ neurons (in red, E) and DAPI nuclear counterstaining (blue) 24 h after PBS, after 48 h of SD (F), or 24 h after 6-OHDA (G), in absence or the presence of Wnt1 pre-treatment (H,I,J). MPP+ sharply decreases TH neurite length, an effect efficiently counteracted by Wnt1.