Comparative aspects of structure and action of molluscan neuropeptides.

A number of neuropeptides were isolated from the ganglia and muscles of molluscs, and their actions were examined. Diverse neuropeptides, in addition to several classical neurotransmitters, were suggested to be involved in the regulation of the anterior byssus retractor muscle of Mytilus. A wide structural variety of members of the Mytilus inhibitory peptide family was observed in each of the genera Mytilus, Achatina and Helix. Gly-Trp-NH2, the C-terminal dipeptide fragment of the neuropeptide AGPWamide, showed a more potent action than the parent peptide in all of the muscles examined. Peptides related to some molluscan neuropeptides were found to be distributed interphyletically. Some neuropeptides containing a D-amino acid residue were found in Achatina and Mytilus. These aspects of molluscan neuropeptides are thought not to be exceptional.