N17Rac1 and N17Cdc42 can prevent NGF withdrawal-induced neuronal death. (A) SCG neurons, cultured for 5–7 days, were microinjected with increasing concentrations of N17Rac1 (hatched bars), N17Cdc42 (solid bars), 1.0 mg/ml pRK5 (negative control, open bar), or 0.05 mg/ml of Bcl-2 (positive control, striped bar). Twenty-four hours later the cells were withdrawn from NGF and left for an additional 48 hr. Cell survival was assessed by calcein staining as described in Material and Methods. The results are the means of four independent experiments ± SEM. #, the P value of N17Cdc42 at 0.1 mg/ml is <0.01. (B) Sympathetic neurons (SCG neurons), cultured for 5–7 days in the presence of NGF, were coinjected with 0.1 mg/ml V12Cdc42 (solid bar) and increasing concentrations of N17Rac1 (hatched bars) or 0.4 mg/ml pRK5 (open bar). Forty-eight hours later, the percentage of surviving cells was assessed as described in Material and Methods. In each experiment, 200 cells were injected. The results are the means of three independent experiments ± SEM.