Figure 7.

Lipid rafts enhance the survival-promoting activity of GDNF by protecting Ret from degradation. Sympathetic neurons were maintained in NGF, deprived of NGF for 24 h, or deprived of NGF in the presence of GDNF (50 ng/ml). Some neurons that were treated with GDNF were concurrently treated with the proteasome inhibitor epoxomicin (Epox; 5 μm) or were depleted of cholesterol by treatment with lovastatin (Lova; 5 μm) for 12 h before GDNF treatment in the continued presence of the inhibitor. As a control, NGF-deprived neurons were saved with potassium depolarization alone (KCl; 25 mm) or in the presence of lovastatin. The neurons were then fixed, Nissl stained, and the number of surviving neurons in each condition counted. These experiments were plotted as the mean ± SEM. The asterisks indicate statistically significant differences (p < 0.05) from the two indicated conditions and GDNF or GDNF and lovastatin treatments, respectively.