A factor causing stable stimulation of juvenile hormone synthesis by Diploptera punctata corpora allata in vitro

Co-incubation of corpora allata (GA) from the cockroach, Diploptera puncta, with ovaries, fat body or muscle but not brain or testis, leads to a subst antial increase in juvenile hormone synthesis. Incubation of the glands in medium pre-conditioned with ovaries also stimulates JH synthesis. The ovary was used as a convenient source of stimulatory factor for a detailed analy sis of its physiological effects on the CA. The increase in JH synthesis is stable, maintained over 24 h after exposure to the stimulatory factor. Sti mulation is dose-dependent, and the corpora allata show an exquisite relati onship between sensitivity to this factor and developmental stage. Day 0 an d day 1 glands, as well as glands from post-vitellogenic females, are sensi tive to stimulation, whereas glands from vitellogenic females are not sensi tive. Corpora allata attached to the brain do not respond to the stimulator y factor, and denervation in vivo leads to an increase in JH synthesis by t he glands and a loss in sensitivity to the factor. These data suggest that glands from pre- and post-vitellogenic females are inhibited by their nervo us connection to the brain. In contrast, glands from vitellogenic females a re normally responding to the endogenous stimulatory factor and are thus no longer stimulated in vitro. Coincubation of CA with allatostatin and condi tioned medium still leads to a stimulation of JH synthesis, suggesting that the restraining effect of the nervous connections to the brain is not caus ed by allatostatin. The CA cell number increases between emergence and day 2, then remains stable until after oviposition. The stimulatory factor acce lerates the increase in cell number in young adult females. The results are interpreted as providing evidence for a constitutive change in CA activity caused by a humoral factor produced by various tissues including the ovary , and modulated by nervous connections to the brain. (C) 1998 Elsevier Scie nce Ltd. All rights reserved.