Mitogenic effects of 20-hydroxyecdysone on neurogenesis in adult mushroom bodies of the cockroach, Diploptera punctata

The purpose of this study was to examine the mitogenic effects of 20-hydroxyecdysone on neurogenesis in mushroom bodies of the adult cockroach, Diploptera punctata. The occurrence of neurogenesis was studied immunocytochemically after in vivo labeling with 5-bromo-2'-deoxyuridine (BrdU). The number of BrdU-labeled cells in the mushroom bodies was high shortly after adult ecdysis, then gradually decreased, and proliferation ceased on day 8. 20-Hydroxyecdysone injection during the early adult stages significantly delayed the decrease in mitotic activity. Moreover, 20-hydroxyecdysone injection during the late stage stimulated quiescent mushroom body neuroblasts to initiate their mitotic activity in a dose-dependent manner. These results indicated that the mushroom body neuroblasts of this insect become quiescent in the maturing central nervous system, but retain the capacity for proliferation if exposed to appropriate environmental signals. We conclude that 20-hydroxyecdysone has a mitogenic effect on neurogenesis in mushroom bodies of this insect.