Presence and distribution of FMRFamide-like immunoreactivity in the cyprid of the barnacle Balanus amphitrite (Cirripedia, Crustacea).

The presence and distribution of FMRFamide-like peptides (FLPs) in the cyprid larvae of the barnacle Balanus amphitrite were investigated using immunohistochemical methods. Barnacles are considered to be one of the most important constituents of animal fouling communities, and the cyprid stage is specialized for settlement and metamorphosis in to the sessile adult condition. FLPs immunoreactive (IR) neuronal cell bodies were detected in both the central and the peripheral nervous system. One bilateral group of neurons somata was immunodetected in the brain, and IR nerve fibers were observed in the neuropil area and optic lobes. Intense immunostaining was also observed in the frontal filament complex: frontal filament tracts leaving the optic lobes and projecting towards the compound eyes, swollen nerve endings in the frontal filament vesicles, and thin nerve endings in the external frontal filament. Thin IR nerve fibers were also present in the cement glands. Two pairs of neuronal cell bodies were immunodetected in the posterior ganglion; some of their axons appear to project to the cirri. FLPs IR neuronal cell bodies were also localized in the wall of the dilated midgut and in the narrow hindgut; their processes surround the gut wall and allow gut neurons to synapse with one another. Our data demonstrated the presence of FLPs IR substances in the barnacle cyprid. We hypothesize that these peptides act as integrators in the central nervous system, perform neuromuscular functions for thoracic limbs, trigger intestinal movements and, at the level of the frontal filament, play a neurosecretory role.

Gamma-aminobutyric acid and related molecules in the sea fan Eunicella cavolini (Cnidaria: Octocorallia): a biochemical and immunohistochemical approach.

The aim of this study has been the biochemical demonstration of the presence of gamma-aminobutyric acid (GABA) in the Mediterranean sea fan Eunicella cavolini by means of high-performance liquid chromatography, and the description of the distribution pattern of GABA and its related molecules, glutamic acid decarboxylase (GAD), vesicular GABA transporter (VGAT) and one of the GABA receptors (GABA(B) R) by immunohistochemical methods. The interrelationships of GABA, GAD and GABA receptor immunoreactivity have been established by using double-immunohistochemical methods and confocal microscopy. The immunodetection of monoclonal and/or polyclonal antibodies has revealed GABA immunoreactivity throughout the polyp tissue, both in neuronal and non-neuronal elements. GAD immunoreactivity has been mostly localized in the neuronal compartment, contacting epithelial and muscular elements. GABA(B) R immunoreactivity appears particularly intense in the nematocytes and in the oocyte envelope; its presence in GAD-immunoreactive neurons in the tentacles suggests an autocrine type of regulation. Western blot analysis has confirmed that a GABA(B) R, with a molecular weight of 142 kDa, similar to that of rat brain, is present in E. cavolini polyp tissue. The identification of the sites of the synthesis, vesicular transport, storage and reception of GABA strongly suggests the presence of an almost complete set of GABA-related molecules for the functioning of the GABAergic system in this simple nervous system. The distribution of these different immunoreactivities has allowed us to hypothesize GABA involvement in nematocyst discharge, in body wall and enteric muscular contraction, in neuronal integration and in male gametocyte differentiation.

First detection of olfactory marker protein (OMP) immunoreactivity in the olfactory epithelium of a cartilaginous fish.

Olfactory marker protein (OMP) is a protein expressed in the mature olfactory and vomeronasal neurons of many vertebrates, such as mammals, amphibians and bony fishes. Aim of this work was to investigate the OMP expression in the olfactory epithelium of the shark Scyliorhinus canicula (Linnaeus, 1758), by immunohistochemistry (IHC). Immunoreactivity was detected in the olfactory receptor neurons, in the crypt neurons and in the nerve fibers below the epithelium. Although very little is known about the OMP's function, its involvement in synaptogenesis, transduction cascade, neurogenesis and development of olfactory system has been suggested. The present work shows for the first time OMP's presence in a cartilaginous fish.

Distribution of choline acetyltransferase immunoreactivity in the alimentary tract of the barnacle Balanus amphitrite (Cirripedia, Crustacea).

To date only peptidergic innervation has been described in the alimentary tract of barnacles. In the present work the presence and distribution of choline acetyltransferase (ChAT), the acetylcholine (ACh) synthesizing enzyme, was investigated by immunohistochemistry in the alimentary tract of the adult barnacle Balanus amphitrite. Numerous ChAT-immunoreactive (IR) cells and a net of ChAT-IR cytoplasmic processes were localized inside the epithelium of the posterior midgut, close to the basement membrane; no IR nerve endings were detected in the midgut longitudinal and circular muscle bundles. Epithelial neurons or endocrine cells in the gut epithelium have been described in some invertebrate species belonging to different taxa and their peptidergic features are reported in the literature. Our results point out the presence of neuroepithelial cells also in the gut epithelium of barnacles; moreover, for the first time, a cholinergic feature is suggested for this cell type. These data seem to indicate the involvement of ACh in the gut functions of barnacle and suggest that the barnacle alimentary tract is more complex than previously thought and requires further study.

Distribution of FMRFamide-like immunoreactivity in the alimentary tract and hindgut ganglia of the barnacle Balanus amphitrite (Cirripedia, Crustacea).

In this study, the presence and distribution of FMRFamide-like immunoreactivity in the alimentary tract of barnacle Balanus amphitrite were investigated. A net of nerve fibers strongly immunoreactive to FMRFamide-like molecules was localized in the posterior midgut and hindgut. Positive varicose nerve terminals were also localized close to the circular muscle cells and, in the hindgut, close to the radial muscular fibers. Besides this nerve fibers network, one pair of contralateral ganglia was localized in the hindgut, each of them constituted by two strongly FMRFamide-labeled neurons and one nonlabeled neuron. Their immunoreactive axons directed toward the hindgut and posterior midgut suggest an involvement of FMRFamide-like substances in adult B. amphitrite gut motility. The hindgut associated ganglia of barnacles seem to correspond to the terminal abdominal ganglia of the other crustaceans. Since they are the only residual gut ganglia in the barnacle's reduced nervous system, we can hypothesize that gut motility needs a nervous system regulation partially independent of the central nervous system.

Observations of crypt neuron-like cells in the olfactory epithelium of a cartilaginous fish.

A new receptor neuron (RN) type was recently described in bony fish olfactory epithelium (OE): the crypt receptor neuron. This name is due to its main feature: the presence, at the apical part, of a deep invagination into which cilia protrude. The presence of this receptor neuron type is well documented in different species of bony fishes but it has never been described in cartilaginous fishes. In this study we demonstrate that crypt neuron-like cells are present in the olfactory epithelium of the elasmobranch Scyliorhinus canicula (Linnaeus, 1758). Histological observations allowed us to detect the presence of a few egg-shaped cells, characterized by a crypt like zone; alpha-tubulin immunoreactivity suggested the presence of cilia in the same area; fluorocrome conjugated lectin bindings suggested a distinctive mucus composition inside the presumptive crypt. The possible presence of crypt neuron-like cells in chondrichthyes would represent an interesting common feature between bony and cartilaginous fishes.

FMRFamide-like immunoreactivity in the sea-fan Eunicella cavolini (Cnidaria: Octocorallia).

The presence of FMRFamide-related peptides (FaRPs) was investigated, by immunohistochemical methods with a polyclonal FMRFamide antiserum, in the sea-fan Eunicella cavolini (Van Koch 1887), a representative of the cnidarians (octocorallians). The identification of FaRP-immunoreactive elements as neuronal cells and a nerve net was performed by double immunohistochemical methods with the monoclonal anti-beta-tubulin antibody. A strong and widely distributed FaRPs immunoreactivity was detected: FaRPs-immunoreactive nerve cells were observed among and underlying gastrodermal epithelial cells, epidermal cells lining tentacles, muscular septs and gonophores. A diffuse FaRPs-immunoreactive nerve net was also found between epithelia and mesoglea and in the stalk of the gonophore. These results improve our knowledge of the gorgonian nervous system and demonstrate that most of the immunoreactive cells belong to neural elements.