The stomatogastric
ganglion (STG) and the cardiac
ganglion (CG) of decapod crustaceans are modulated by neuroactive substances released locally and by circulating
hormones released from neuroendocrine structures including the pericardial organs (POs). Using nanoscale liquid chromatography electrospray ionization quadrupole-time-of-flight tandem mass spectrometry and direct tissue matrix-assisted
laser desorption/ionization Fourier transform mass spectrometry we have identified and sequenced a novel
neuropeptide,
GAHKNYLRFamide (previously misassigned as KHKNYLRFamide in a study that did not employ
peptide derivatization), from the POs and/or the stomatogastric nervous system (STNS) of the crabs,
Cancer borealis,
Cancer productus and
Cancer magister. In C. borealis, exogenous application of
GAHKNYLRFamide increased the burst frequency and number of spikes per burst of the isolated CG and re-initiated bursting activity in non-bursting ganglia, effects also elicited by the
FMRFamide-like
peptides (FLPs)
SDRNFLRFamide and
TNRNFLRFamide. In the intact STNS (which contains the STG), exogenous application of
GAHKNYLRFamide increased the frequency of the pyloric rhythm and activated the gastric mill rhythm, effects also similar to those elicited by
SDRNFLRFamide and
TNRNFLRFamide. FLP-like immunoreactivity in the POs and the STNS was abolished by pre-adsorption with the synthetic
GAHKNYLRFamide. Different members of the FLP family exhibited differential degradation in the presence of extracellular
peptidases. Taken collectively, the amino acid sequence of
GAHKNYLRFamide, the blocking of FLP-like immunostaining, and its physiological effects on the CG and STNS suggest that this
peptide is a novel member of the FLP superfamily.