G protein-coupled receptor signal transduction and Ca2+ signaling pathways of the allatotropin/orexin system in Hydra

•Pharmacological inhibition of ligand binding shows that AT activity is mediated by a GPCR.•The complete signaling pathway of an AT peptide is found in Hydra.•The lack of response after PLC inhibition shows the involvement of the IP3 pathway.•The use of an IP3R inhibitor confirms the involvement of IP3 in the activity of AT.