Figure 4. St. John’s Wort and hypericin inhibit extracellular signal-regulated kinase activation in retina. Retinas were harvested from eyes of mice following gavage administration of vehicle, 15 mg/kg/day St. John’s Wort (SJW) or 45 µg/kg/day hypericin from P12 through P17. Levels of phosphorylated ERK (P-ERK), total ERK, and actin were determined by western blot analysis. Representative blots from three experiments are shown. Phosphorylation levels of ERK were quantified by NIH image analysis. Immunoblots were normalized to total loaded protein. Data are presented as mean ± SEM. Asterisk (*) indicates p<0.01 versus vehicle treatment.