Antho‐RFamide‐containing neurons in the primitive nervous system of the anthozoan Renilla koellikeri

Abstract

The neuropeptide Antho-RFamide is extremely abundant in Renilla koellikeri (sea pansy), a representative of the cnidarians (octocorallians) considered to be closest to the stem ancestors of metazoans with nervous systems. Therefore, a knowledge of the distribution of Antho-RFamide-containing neurons in this species would contribute to our understanding of the early evolution of nervous systems. Using antisera raised against RFamide and FMRFamide, we detected immunostaining in numerous neurons throughout the nervous system of the sea pansy. The antisera revealed ectodermal nerve-nets on the upper and lower sides of the colony and on the oral side of tentacles, in the oral disk, and in the pharynx of feeding polyps. Neurons were immunostained also in the mesogleal nerve-net of feeding polyps and in the through-conducting mesogleal nerve-net of the colonial mass. Varying densities of stained neurons were observed in the different compartments of the endoderm: muscular walls of the feeding and water circulation polyps, mesenteric filaments and their derived follicles containing either ovocytes or spermatophores, in the endodermal channels connecting the different compartments of the colony, and in circular muscle of the peduncle. The distribution of immunostained neurons suggests that they play important roles in feeding, reproduction, neuromuscular transmission, and in neuro-neuronal transmission coordinating the different parts of the colony.

Fine structure of the ventral nerve centre and interspecific identification of individual neurons in the enigmatic Chaetognatha

“…A recent molecular analysis of the intraphyletic relationships has revealed the variability of this character (homoplasy) and highlighted the inXuence of the life style on chaetognath morphology, particularly for benthic species that adapt to a planktonic lifestyle (Papillon et al 2006). The functional signiWcance of RFamide peptides in metazoans is an intense Weld of research and one of the emerging themes is the remarkable conservation in control of feeding (Dockray 2004) and mating (Kriegsfeld 2006) behaviours both in Protostomia and Deuterostomia as well as in cnidarians (Pernet et al 2004). A thorough interspeciWc comparative analysis of RFir neurons is likely to provide more insights into how the variations in the organization of the muscular and nervous systems in Chaetognatha correlate with their diverging life styles as well as their feeding and mating behaviours.…”

Retinoic acid and nitric oxide promote cell proliferation and differentially induce neuronal differentiation in vitro in the cnidarian Renilla koellikeri

“…In hydra all neurons are associated with the epithelial monolayers (ectoderm and endoderm) and the mesogleal jelly, which is sandwiched by the two epithelial layers, is acellular. In contrast, the mesoglea of anthozoans such as the sea pansy is thicker and contains cells including neurons resembling the ganglion cells of hydra (Fautin and Mariscal, 1991;Pani et al, 1995;Pernet et al, 2004). Thus RA appears to specifically target interstitial cells for commitment to epithelium-associated cell lineages in the sea pansy, whereas NO selectively targets precursor cells of mesogleal neurons.…”

“…Values for analysis were cell numbers per mm 2 . Cell types were identified by matching their shape, size and, if applicable, intracellular characteristics with illustrated descriptions of sea pansy (Germain and Anctil, 1988;Pani et al, 1994;Pernet et al, 2004) and other anthozoan cells (Fautin and Mariscal, 1991). Elements failing to match these criteria were discarded from the counts.…”

“…5(D)]. These cells resemble the norepinephrine-and RFamide-immunoreactive neurons forming the nerve net in the mesoglea of the sea pansy, particularly near the endoderm (Pani et al, 1995;Pernet et al, 2004).…”

The neuroendocrine system of invertebrates: a developmental and evolutionary perspective

“…Neuropeptides in cnidarians act as transmitters mediating communication of neurons within the nerve net and stimulating effector organs (Grimmelikhuijzen & Westfall 1995, Holtmann & Thurm 2001, Pernet et al 2004. Peptides act as stimulators or inhibitors; no specific behavioral responses have been associated with any particular peptide.…”