INHIBITORY ROLE OF ECDYSONE ON NEUROGENESIS AND POLYAMINE METABOLISM IN THE ADULT CRICKET BRAIN

Persistent neuroblasts that continue to produce interneurons were disc overed in the mushroom bodies of the adult house cricket, Acheta domes ticus (Cayre et al., 1994). In the present work, we examine the influe nce of ecdysone on this neurogenesis. In control females, the mitotic index decreased concomitantly to the rise of ecdysteroid titer, which accompanied oocyte maturation, whereas it remained unchanged in ovarie ctomized females. Furthermore, ecdysone injection into ovariectomized animals had a significant inhibitory action on neuroblast mitotic acti vity. Since cell proliferation and neuronal differentiation have been shown to be affected by polyamines, we also studied the action of ecdy sone on polyamine metabolism. Ovariectomy induced a decrease in polyam ine levels of fat body and markedly increased brain spermidine levels. In neural tissue, ecdysone injection into ovariectomized females redu ced spermidine levels to control values. Our results suggest that adul t cricket brain is a target for ecdysone action. Moreover, the tight c orrelation we demonstrated between neurogenesis and polyamine titers u nderlines the possible involvement of polyamines in neuroblast prolife ration. (C) 1997 Wiley-Liss, Inc.