Localization of FMRFamide-like peptides in the snail Helix aspersa

The distribution of FMRFamide-like material in the gastropod mollusc, Helix aspersa, was studied by radioimmunoassay (RIA) and immunocytochemistry. Most of the RIA activity was concentrated in the central nervous system, the male reproductive tract, the tentacles and the posterior digestive system (Table 1). The density of FMRFamidergic perikarya, nerves and nerve varicosities in the muscle tissue of all these regions, as indicated immunocytochemically (Fig. 2), was well correlated with the distribution as determined by RIA. Gel chromatography of each extract resolved two peaks of FMRFamide-like immunoreactivity (Fig. 3). The first of these was further analysed by high-pressure liquid chromatography (HPLC), and the components included two major immunoreactive peaks identifiable, both by their retention times and their effects on the radula protractor muscle of Busycon contrarium, as the known peptides FMRFamide and pQDPFLRFamide (Figs 4–6). The second peak from gel chromatography gave only a single peak, distinct from that of FMRFamide and pQDPFLRFamide, in two HPLC systems (Fig. 7), but it did not behave like a competitive ligand in the FMRFamide RIA. Moreover, its immunoreactivity, unlike any peptides we tested, was not affected by carboxypeptidase Y (Fig. 8), and it was not active on the radula protractor muscle. Thus, it is certainly not an FMRFamide-like peptide. We conclude that Helix aspersa contains at least two FMRFamide-like peptides, FMRFamide and pQDPFLRFamide. These peptides appear to act both as neurohormones and as neurotransmitters or modulators in the central ganglia, reproductive, digestive, muscular and circulatory systems.