Fig. 4.

Strong NMDA stimulation specifically results in dephosphorylation of CREB in 14 DIV neurons, which is refractory to further rephosphorylation by forskolin or KCl. Top, The figure illustrates the protocol used for sequential stimulation by NMDA and forskolin/KCl. Middle, Shown are representative immunoblotting experiments for CREB phosphorylation (left) and Erk1/2 phosphorylation (right) for cultures at 7 and 14 DIV, as indicated. Bottom, Histograms quantify the relative levels of phospho-CREB or phospho-Erk1/2 for each condition/lane from several experiments (n = 5). Asterisk indicates significance at p < 0.01 in an unpaired, two-tailed Student's t test when compared with the value obtained in neurons stimulated additionally with KCl for 5 min or forskolin for 5 min at 7 DIV.