Evolution of a Molluscan Cardioregulatory Neuropeptide

SYNOPSIS. The cardioexcitatory neuropeptide FMRFamide was firstidentified from a clam, but has now been demonstrated in severalother molluscs. It is probably present throughout the molluscanphylum though co-existing with related peptides in some species.For example, I report here the finding of the peptide phenylalanyl-leucyl-arginyl-phenylalanineamide (FLRFamide) in the mesogastropod Pomacea paludosa whereit accounts for 10–20% of the total FMRFamide-like activity.This peptide may be a minor component of the FMRFamide-likeactivity in other species as well. The pulmonate snails haveseveral, closely-related, heptapeptide analogs of FLRFamidethat are unique to them, such as pyroglutamyl-aspartyl-prolyl-phenylalanyl-leucyl-arginyl-phenylalanineamide (pQDPFLRFamide) which was isolated from Helix aspersa.Two additional pulmonate heptapeptides that have been isolatedprobably differ from pQDPFLRFamide only in their N-terminalamino acid residues. The heptapeptides account for most of theFMRFamidelike activity in the species in which they occur. Though the tetrapeptides FMRFamide and FLRFamide have virtuallyidentical activities on various molluscan tissues, the heptapeptideshave activity that is distinct from the tetrapeptides on somepulmonate muscles. 1 have attempted to explain the evolutionof this diversity of peptide structure and function found inthe modern pulmonates by postulating a gene duplication in thegastropod line leading to them.     

Cellular Neuronal Control of Molluscan Heart

Bivalve and gastropod molluscs undergo large changes in externalenvironmental conditions, as well as in internal state. Cardiacresponses to these changing conditions have been recorded ina variety of species. There is a general tendency for heartrate, and presumably cardiac output, to increase in responseto situations that would increase the load on respiratory andexcretory systems. Changes in molluscan heart function in manycases appear not to be mediated directly by cardiac nerves,but rather by such indirect mechanisms as changes in blood constituentsor mechanical, hemodynamic effects on heart muscle. Three typesof cardiac response in Aplysia have been shown to be mediated,at least in part, by the heart regulator nerves. The neural circuits that regulate heart rate in Aplysia andin Helix have been partially described in cellular detail. InMercenaria, Aplysia and other molluscan species there is evidencethat cyclic adenosine monophosphate has a role in mediatingthe excitatory effects of serotonin on heart muscle. There appearsto be, in fact, a general tendency in the Aplysia nervous systemfor neurons that exert tonic, modulatory effects within neuralnetworks that control a variety of behaviors to use serotoninfor a transmitter. In each case there is evidence to suggestthat changes in cyclic adenosine monophosphate levels may mediatesome of the modulatory effects of serotonin.     

XXXV.—Obituary

T he Union, and everybody interested in bird-life, will be deeply affected by the death, of such, a personality as Mr. Hubert Delaval Astley, President of the Avicultural Society, which occurred at his home, Brinsop Court, near Hereford, after a long and painful illness, on 26 May last.