Effect of morphine on P-CREB, PC1/3 or PC2 protein levels in the hypothalamus in rats treated with morphine or placebo for 24 h or seven days. Rats were implanted with a placebo (open bars) or morphine (filled bars) pellet for 24 h (A, C, E) or seven days (B, D, F). Western blot measuring the level of P-CREB (A, B), PC1/3 (C, D) or PC2 (E, F) in hypothalamic extracts of the rats was performed. The same membranes were stripped and then immunoblotted with GAPDH antibody as a control. Densitometry of the bands expressing P-CREB, PC1/3 or PC2 was compared to GAPDH for quantitation. The data are expressed in arbitrary units as the mean +/- SEM. *p<0.05, **p<0.01, ***p<0.001.