(A) Immunoblot analysis of expression and phosphorylation on serine 133 of endogenous CREB (endo-CREB; endo-pCREB) and overexpressed CREB (exo-CREB; exo-pCREB) in uninfected hippocampal neurons and in neurons infected with rAAV-hrGFP or rAAV-CREB at the indicated times after treatment with 20 μM NMDA. Expression of endogenous and overexpressed CREB was analyzed with an antibody to CREB; overexpressed CREB was also detected using an anti-Flag antibody. CREB phosphorylation on serine 133 (pCREB) was assessed using antibodies specific for the serine 133 phosphorylated form of CREB. CREB degradation products are indicated by an asterisk. (B) Quantitative analysis of the pCREB/CREB ratios of the immunoblot analyses shown in (A). Means ± SEM are given (n = 4).