ULTRASTRUCTURAL-LOCALIZATION OF RFAMIDE-LIKE PEPTIDES IN NEURONAL DENSE-CORED VESICLES OF A CNIDARIAN PLANULA LARVA

The location of Arg-Phe-amide (RFamide)-like peptides in dense-cored v esicles in neurons of the planula larva of the marine hydrozoan Pennar ia tiarella was shown using immunogold electron microscopy. Expression of the peptide was detected as early as 16 h after fertilization. Gol d-labeled dense-cored vesicles ranging from 80 nm to 140 nm in diamete r were found in both cell bodies and neurites of ganglion cells (non-c iliated bipolar and multipolar neurons found at the base of the ectode rm just above the mesoglea) located in the aboral (anterior) and middl e regions of the planulae. Within the neurites, the labeled dense-core d vesicles were found in distinct clusters all along their lengths in close association with the cell membranes, a distribution which sugges ts that release of the peptide in planulae probably does not occur at specialized synaptic sites. Labeled cells also contained unlabeled den se-cored vesicles, unlabeled clear vesicles (60 nm to 100 nm in diamet er), and unlabeled electron-dense droplets (100 nm to 240 nm in diamet er). Localization of RFamide peptides to dense-cored vesicles of speci fic neurons in early planulae is significant because of growing eviden ce on the role of these substances in morphogenesis.