G protein-coupled receptor signal transduction and Ca signaling pathways of the allatotropin/orexin system in Hydra.

Allatotropin is a pleiotropic peptide originally characterized in insects. The existence of AT neuropeptide signaling was proposed in other invertebrates. In fact, we previously proposed the presence of an AT-like system regulating feeding behavior in Hydra sp. Even in insects, the information about the AT signaling pathway is incomplete. The aim of this study is to analyze the signaling cascade activated by AT in Hydra plagiodesmica using a pharmacological approach. The results show the involvement of Ca and IP signaling in the transduction pathway of the peptide. Furthermore, we confirm the existence of a GPCR system involved in this pathway, that would be coupled to a G subfamily of Gα protein, which activates a PLC, inducing an increase in IP and cytosolic Ca. To the best of our knowledge, this work represents the first in vivo approach to study the overall signaling pathway and intracellular events involved in the myoregulatory effect of AT in Hydra sp.