FIGURE 8.

Release of HB-EGF induced by D2R stimulation. A, HB-EGF and EGF mRNA expression was amplified by RT-PCR. B, mesencephalic neuronal cells from WT (n = 4) and D2R^−/−(n = 4) mice were treated with PMA (100 ng/ml) or quinpirole (10 μm) for 10 min. C, siGFP- or siADAM10/17-transfected mesencephalic neuronal cells from WT (n = 6) and D2R^−/− (n = 7) mice were treated with quinpirole. D, mesencephalic neuronal cells from WT mice (n = 6) were treated with quinpirole for 30 min to 12 h (left). Concentrations of HB-EGF in culture supernatants were measured by ELISA. Mesencephalic neuronal cells from D2R^−/− mice were treated with or without control concentrated conditioned media and quinpirole-treated concentrated conditioned media (right). Mean values ± S.E. (error bars) are shown. *, p < 0.05; **, p < 0.01; ***, p < 0.001 for control versus drug-treated cells. &&, p < 0.01; ANOVA followed by a Bonferroni test for siGFP- versus siADAM10/17-transfected cells. Quin, quinpirole; CM, conditioned media. E, proposed mechanism for D2R-dependent dopaminergic neuronal development, involving ADAM10, ADAM17, HB-EGF, and EGFR signaling coupled with ERK activation. Activated D2R can phosphorylate ERK, resulting in EGFR transactivation through HB-EGF. This signaling can promote dopamine neuron development.