ISOLATION, LOCALIZATION, AND BIOACTIVITY OF THE FMRFAMIDE-RELATED NEUROPEPTIDES GYIRFAMIDE AND YIRFAMIDE FROM THE MARINE TURBELLARIAN BDELLOURA-CANDIDA

Two FMRFamide-related neuropeptides, GYIRFamide and YIRFamide, were is olated from the marine turbellarian Bdelloura candida. The peptides el icited a dose-dependent contraction of isolated turbellarian muscle fi bers, and both were more potent than FMRFamide. Structure-activity stu dies, using a range of analogues of the tetrapeptide amide, indicated that the structure of the endogenous peptides was optimal for peak act ivity. Immunocytochemistry, using an autologous antiserum, revealed a widespread distribution of peptide immunoreactivity within central and peripheral neurons and their processes. This study indicates an impor tant role for GYIRFamide and YIRFamide in the control of neuromuscular function in turbellarians.