Figure 6.  .

β-ionone, a rod opsin agonist, increases neuritic growth and CREB phosphorylation in rod cells. (A) Rod cells treated with β-ionone show increases of the longest neuritic length in all treatment groups (continuous treatment at noted concentrations for 3 days) and an increase in varicosities with pulse-treatment of 2.5 μM β-ionone (2.5 μM) (24-hour treatment followed by 2 days of control medium) (n = 500 cells; 10 cultures, 1 animal). (B) Cell death was induced by β-ionone. Rod cell number was reduced by 19.0% with 2.5 μM β-ionone, and by 37.2% with 10 μM β-ionone after 3 days. However, cells treated with pulsed-2.5 μM β-ionone did not show any cell death (n = 167 fields; 8 cultures, 1 animal). (C) The density of pCREB immunolabel of rod cells treated with 2.5, 10, or pulsed 2.5 μM β-ionone was higher than that of control group by 66.4%, 98.4%, and 92.0%, respectively (n = 500 cells; 10 cultures, 1 animal). (D, E) Rod cells treated with both β-ionone and 9-cis-retinal for 1 day and then cultured 2 more days in the dark show a decrease in neuritic outgrowth and varicosity formation compared with cultures treated with β-ionone alone. Treatment with 9-cis-retinal in the dark did not change neuritic development compared with the control (n = 734 cells; 20 cultures, 2 animals). (F, G) ABC-HRP immunocytochemistry for pCREB in control and in pulsed-2.5 μM β-ionone–treated rod cells show denser nuclear pCREB labeling and a longer neurite (triple arrows) with β-ionone than in control conditions. *P < 0.05; ***P < 0.001; Scale bar = 20 μm.