Vertebrate brain-gut peptides related to FMRFamide and Met-enkephalin Arg6Phe7.

Many mammalian brain-gut peptides are known to be represented in invertebrate nervous systems; we have now examined the possibility that an invertebrate neuropeptide occurs in vertebrates. Antisera were raised in rabbits to the molluscan neuropeptide. Phe-Met-Arg-Phe-NH2 (FMRFamide). The antiserum used for radioimmunoassay and immunocytochemistry is highly specific for the C-terminus of the tetrapeptide. In radioimmunoassays of tissue extracts of brain, gut and pancreas of various vertebrates (chicken, frog, dog, rat) concentrations of immunoreactive material up to about 200 pmol/g have been recorded. The immunoreactive material in chicken pancreas behaves on gel filtration and ion exchange chromatography as a molecule that is larger and less basic peptide that FMRFamide. Immunocytochemical studies have demonstrated an endocrine cell origin for FMRFamide-like material in chicken pancreas, and in dog ileum. In brain, FMRFamide can be localised to nerve cell bodies (frog) and nerve fibres (frog and rat). Synthetic FMRFamide has been shown to have excitatory actions on brain stem neurons in the rat. It is suggested that neurons in the rat central nervous system have receptors for FMRFamide that normally bind endogenous material with FMRFamide immunoreactivity.