Steroid regulation of the peptide-mediated increase in cyclic GMP in the nervous system of the hawkmoth, Manduca sexta

The action of the peptide, eclosion hormone (EH) on the CNS of Manduca sexta appears to be mediated via the second messenger cGMP. Injections of EH or release of endogenous EH cause a rapid increase in cGMP in the CNS. Cyclic GMP, 8-bromo-cGMP and the phosphodiesterase inhibitors IBMX and theophylline mimic the action of EH in triggering premature ecdysis behavior. The CNS is only sensitive to EH just before ecdysis, both in triggering ecdysis and increasing endogenous cGMP levels. The development of the ability to increase cGMP levels occurs earlier than the behavioral sensitivity and the relative timing of these events is discussed in terms of the likely site for the block in behavioral sensitivity. The steroid hormone 20-hydroxyecdysone is shown to regulate the ability of EH to elevate cGMP levels in the CNS.