Fig. 5. Photomicrographs of neuroblastoma cells (NBP2) in culture after treatment with RO20-1724, an inhibitor of cyclic nucleotide phosphodiesterase, and a polar carotenoid originally referred to as beta-carotene [52]. Control a) 4 days after plating (50,000 cells/60-mm dish) showing mostly round cells; polar carotenoid (20 µg/mL-treated cells; b) 4 days after treatment showing no significant change in morphology; RO20-1724 (200 µg/mL)-treated cells; c) 4 days after treatment revealing increased number of cells with neurites; cells treated with RO20-1724 plus polar carotenoid d) for a period of 4 days showing more differentiated cells than those produced by RO20-1724 treatment alone; cells treated with RO20-1724 plus polar carotenoid for a period of 8 days e) and f) 11 days showing extensive network of neurites [53] x200.