The presence and distribution of RFamide-like immunoreactive nerve fibers in scyphistomae of Aurelia aurita

Abstract

The presence of Arg-Phe-NH 2 (RFamide)-immunoreactive material in a large number of neurons in nerve nets of scyphomedusae has been demonstrated previously. However, the organization of RFamide-containing nerves in the scyphistoma (the scyphozoan polyp) has not been examined. In this study, nerve fibers in scyphistomae (polyps) of Aurelia aurita were examined immunocytochemically with antisera against RFamide. RFamide-immunoreactive neurites could be visualized on whole-mount preparations. The antisera stained nerve fibers in the tentacles, the oral disc and the body column. The immunoreactive nerve fibers were dense on the adaxial side (oral disc side) of the tentacles and absent on the abaxial side (external body wall side). The nerve net of the tentacles was continuous with that of the oral disc. A dense plexus of nerve fibers in the oral disc projected mostly radially from the mouth toward the bases of the tentacles. At the outer edge of the oral disc, some fibers ran circumferentially. The circumoral fibers became concentrated at peristomial pits and then projected under the nerve fiber bundles into the septa of the body column. Four interradial nerve fiber bundles ran longitudinally in four interradial septa. These results indicate that RFamide-containing nerves are a prominent feature of the nervous system of scyphistomae.