(A) Immunoblot analysis of expression and phosphorylation on serine 133 of endogenous and overexpressed CREB in uninfected hippocampal neurons and in neurons infected with rAAV-hrGFP, rAAV-CREB and rAAV-mCREB. CREB expression and CREB phosphorylation on serine 133 (pCREB) was assessed using antibodies to CREB and antibodies specific for the serine 133 phosphorylated form of CREB, respectively. (B) Quantitative analysis of the levels of CREB and CREB phosphorylated on serine 133 (pCREB). In uninfected hippocampal neurons and in neurons infected with rAAV-hrGFP, the ratio of pCREB to CREB (pCREB/CREB) was calculated for endogenous CREB; for hippocampal neurons infected with rAAV-CREB and rAAV-mCREB, the ratios were determined for overexpressed CREB and mCREB. Bars represent means ± SEM (n = 3). Statistical significance was determined by One-way ANOVA, Bonferroni post hoc test; statistically significant differences are indicated with an asterisk (***p < 0.001 versus rAAV-hrGFP; N.S., not significant).