A NOVEL NEUROPEPTIDE-ENDOCRINE INTERACTION CONTROLLING ECDYSTEROID PRODUCTION IN IXODID TICKS

Ixodid (hard) ticks are blood-feeding arthropods that require a blood meal to complete each stage of development. However, the hormonal even ts coordinating aspects of feeding and development are only poorly und erstood. We have delineated a new neuropeptide-endocrine interaction i n the adult tick, Amblyomma hebraeum, that stimulates the synthesis of the moulting hormones, the ecdysteroids. In adult female ticks, ecdys teroid synthesis could be demonstrated in integumental tissue incubate d in vitro with a synganglial (central nervous system) extract, but no t in its absence. Stimulation by the synganglial extract is both time- and dose-dependent, but is completely abolished by trypsin treatment, suggesting that the activity is due to a peptide/protein. Integumenta l tissue ecdysteroidogenesis is also stimulated by elevation of the cA MP concentration using forskolin and 3-isobutyl-1-methyl-xanthine, or by 8-bromo-cAMP. This suggests the involvement of at least a cAMP seco nd messenger system in the neuropeptide-ecdysteroidogenesis axis, with out precluding a role for other second messengers as well. Despite inv olving a quite different steroidogenic tissue, the foregoing system ha s some parallels with the known prothoracicotropic hormone (neuropepti de)-prothoracic gland endocrine axis of insects.