New vertebrate brain–gut peptide related to a molluscan neuropeptide and an opioid peptide

Abstract

Peptides related to mammalian hormones and neuropeptides are known to occur widely in invertebrate nervous systems^1–11. It seems plausible to suppose that peptides which have hitherto been found only in invertebrate nervous systems might also have representatives that function as hormones or neuroregulators in vertebrates. However, this idea has yet to be rigorously tested. Recently, Boer et al.¹² described immunohistochemical studies in which antisera to a peptide isolated from molluscan ganglia, Phe-Met-Arg-Phe-NH₂ (FMRFamide)¹³, revealed nerve fibres in the brain of the mouse and a teleost fish. This tetrapeptide is of particular interest in that its amino acid sequence is related to that of the C-terminal tetrapeptide of cholecystokinin (CCK) and gastrin (Trp-Met-Asp-Phe-NH₂), and is identical to the primary sequence of the C-terminal tetrapeptide of an enke-phalin-related heptapeptide, Tyr-Gly-Gly-Phe-Met-Arg-Phe-OH, recently isolated from bovine adrenal medulla and striatum and known to be a potent opioid agonist^14–16. It is not known whether the material identified by Boer et al. corresponds to these previously identified vertebrate peptides. We present here evidence from radioimmunoassay and immunohistochemical studies that FMRFamide-like material occurs in central nervous system and gut endocrine cells of vertebrates. The material is distinguishable in properties and distribution from presently known peptides related to CCK or Met-enkephalin, and we propose that it be added to the list of substances thought to have dual roles as gut hormones and central neuroregulators^17,18.