Fig. 7.

Expression of dominant-inhibitory CREB mutants inhibits the prosurvival effect of depolarization but not that of cpt-cAMP. SGNs were transfected with a 1:3 mixture of GFP plasmid and plasmid encoding either wild-type CREB (open bars), CREBm1 (light gray bars), or KCREB (dark gray bars); the latter two are dominant-inhibitory CREB mutants. The cultures were maintained in control (5K), depolarizing (25K), or 1 mm cpt-cAMP culture conditions, as indicated, for 48 hr. Surviving transfected SGNs were counted as in Figure 2 and normalized, in each experiment, to the number of surviving SGNs in the control 25K condition. Results shown are means of three separate experiments, each performed in duplicate. The ability of 25K to promote SGN survival was significantly (p < 0.005) reduced by either CREB mutant but was not affected by wild-type CREB. In contrast, the survival-promoting effect of cpt-cAMP was unaffected by the CREB mutants.