LFRFamides: a novel family of parasitation-induced -RFamide neuropeptides that inhibit the activity of neuroendocrine cells in Lymnaea stagnalis

We report the characterization of a cDNA encoding a novel -RFamide neuropeptide precursor that is up-regulated during parasitation in the snail Lymnaea stagnalis. Processing of this precursor yields five structurally related neuropeptides, all but one ending with the C-terminal sequence -LFRFamide, as was confirmed by direct mass spectrometry of brain tissue. The LFRFamide gene is expressed in a small cluster of neurons in each buccal ganglion, three small clusters in each cerebral ganglion, and one cluster in each lateral lobe of the cerebral ganglia. Application of two of the LFRFamide peptides to neuroendocrine cells that control either growth and metabolism or reproduction induced similar hyperpolarizing K+-currents, and inhibited electrical activity. We conclude that up-regulation of inhibitory LFRFamide neuropeptides during parasitation probably reflects an evolutionary adaptation that allows endoparasites to suppress host metabolism and reproduction in order to fully exploit host energy recourses.