Distribution of catecholamine-containing,serotonin-like and neuropeptide FMRFamide-like immunoreactive neurons and processes in the nervous system of the actinotroch larva ofPhoronis muelleri (Phoronida)

Summary Glyoxylic-acid-induced fluorescence of catecholamines and antibodies against serotonin and FMRFamide were used to study the distribution of putative neurotransmitters in the actinotroch larva ofPhoronis muelleri Selys-Longchamps, 1903. Catecholamines occur in the neuropile of the apical ganglion, in the longitudinal median epistome nerves, in the epistome marginal nerves, and in the nerve along the bases of the tentacles. The tentacles have laterofrontal and latero-abfrontal bundles of processes that form two minor nerves along the lateral ciliary band of the tentacles, and a medio-frontal bundle of processes. Monopolar cells are located on the ventro-lateral part of the mesosome. Processes are located along the posterior ciliary band and as a reticulum in the epidermis. Serotonin-like immunoreactive cells and processes are located in the apical ganglion, in the longitudinal median epistome nerves, and as a dorsal and ventral pair of bundles along the tentacle bases. Processes from the latter extend into the tentacles as the medioabfrontal processes. The latero-abfrontal processes form a minor nerve along the ciliary band. The dorsal bundles forms the major nerve ring along the tentacles and processes extend from it to the metasome. Processes are located along the posterior ciliary band. FMRFamide-like immunoreactive cells and processes are found in the apical ganglion, in the longitudinal median epistome nerves and as a pair of lateral epistome processes projecting towards the ring of tentacles. In the tentacles, a pair of latero-frontal processes are found; these form a minor nerve along the ciliary band. A band of cells can be seen along the tentacle ring.     

A waterborne behavioral cue for the actinotroch larva of Phoronis pallida (Phoronida) produced by Upogebia pugettensis (Decapoda: Thalassinidea)

Phoronis pallida (Phoronida) occurs as a commensal within the burrow of Upogebia pugettensis (Decapoda: Thalassinidea). Upogebia-conditioned seawater (UCSW) induced an exploratory swimming behavior in competent larvae of P. pallida in a dosage-dependent manner. This behavior included a significant increase in swimming speed that was directed downward, along with the repeated probing of the bottom with the sensory portion of the oral hood. The waterborne cue from the shrimp was present in the gut effluent, and the swimming behavior was not the result of the elevated ammonia concentration. Molecular weight separation of the UCSW estimated that the cue was between 10 and 50 kDa. Enzymatic treatments showed that the cue's activity could be eliminated by arginase and significantly reduced by lipase. Competent larvae were also induced to metamorphose when exposed to 20 mM CsCl for 30 min. Larvae did not respond to CsCl when cultured about 4 weeks past the onset of competence. Compared with actinotroch larvae of other phoronid species, P. pallida larvae exhibit greater behavioral specificity and neuronal differences within the hood sense organ. These anatomical and behavioral differences may have been maintained through a coevolutionary process among P. pallida and species of thalassinid shrimps that share Upogebia life-history characteristics.     

Podocytes in the blood vessel linings of Phoronis muelleri (Phoronida,Tentaculata)

Summary In several metasomal blood vessels of Phoronis muelleri myofilament-containing podocytes are the predominant cell-type. In some regions the podocytes can build a labyrinth resembling e.g. the glomerular epithelium of Enteropneusta and the axial organ of Asteroidea.Financially supported by DFG (Sto 75/4)     

Ultrastructure and relationship between protonephridia and metanephridia in Phoronis muelleri (Phoronida)

Summary The actinotrocha of Phoronis muelleri has one pair of ectodermally derived, monociliated protonephridia. The duct runs mainly between the epidermis and the lining of the hyposphere coelom, pierces the septum and extends into the blastocoel. The proximal part is branched and closed up by terminal complexes consisting of two morphologically different cells which both serve filtration. During metamorphosis, the terminal complexes and the branches of the duct are cast off. The cells degenerate, pass into the remaining duct and are endocytosed by the duct cells. After metamorphosis the remaining part of the protonephridial duct is U-shaped, blindly closed and borders on the prospective lophophoral vessel. In a later stage the duct receives a ciliated funnel, which consists of monociliated epithelio-muscle cells and is a derivative of the lining of the metacoel. Thus, a part of the protonephridial duct of the larva and the whole metanephridial duct of the adult are identical. Aspects of a possible homology between phoronid nephridia and such organs in other bilaterians are discussed.     

Ultrastructure and formation of the body cavity lining in Phoronis muelleri (Phoronida, Lophophorata)

Among other characteristics a trimeric coelomic compartmentation consisting of an anterior protocoel, followed by a mesocoel and a posterior metacoel is traditionally believed to substantiate the sister-group relationship between Lophophorata and Deuterostomia, together forming the Radialia. As molecular data cannot support this hypothesis a reanalysis of the coelomic cavities in Phoronida is undertaken, because corresponding coelomic compartmentation is widely accepted to support the Radialia hypothesis. A coelomic cavity can be recognized on the ultrastructural level because its lining is a true epithelium with polarized cells interconnected by apical adherens junctions. This study reveals that neither in larval nor adult Phoronis muelleri (Phoronida) an anterior cavity with such a lining is present. What on the light microscopic level leads to the impression of a cavity inside the larval episphere, actually is an enlarged subepidermal extracellular matrix with an amorphous, presumably gel-like filling, into which several muscle cells are embedded. Larvae, thus, possess only one coelomic cavity, the large trunk coelom of the larva which is adopted in the adult organization. The second coelomic cavity of adult P. muelleri, the lophophore coelom, develops as a double-layer of epithelialized mesodermal cells at the base of the adult tentacle buds and becomes fluid filled during metamorphosis. Like the larval episphere, larval tentacles and most parts of the blastocoel are filled by an amorphous matrix. Reanalysis of the literature and comparison with Brachiopoda and Bryozoa allows the hypothesis that a protocoel is lacking in all Lophophorata, and that merely two unpaired coelomic cavities, one tentacle and one trunk coelom, can be assumed for the ground pattern of this taxon. These results do not provide further evidence for the Radialia hypothesis, but also do not contradict it. Accepted: 28 August 2000     

Structure and metamorphic remodeling of the larval nervous system and musculature of Phoronis pallida (Phoronida)

The structure of the larval nervous system and the musculature of Phoronis pallida were studied, as well as the remodeling of these systems at metamorphosis. The serotonergic portion of the apical ganglion is a U-shaped field of cell bodies that send projections into a central neuropil. The majority of the serotonergic cells are (at least) bipolar sensory cells, and a few are nonsensory cells. Catecholaminergic cell bodies border the apical ganglion. The second (hood) sense organ develops at competence and is composed of bipolar sensory cells that send projections into a secondary neuropil. Musculature of the competent larva includes circular and longitudinal muscle fibers of the body wall, as well as elevators and depressors of the tentacles and hood. The juvenile nervous system and musculature are developed prior to metamorphosis and are integrated with those of the larva. Components of the juvenile nervous system include a diffuse neural net of serotonergic cell bodies and fibers and longitudinal catecholaminergic fibers. The juvenile body wall musculature consists of longitudinal fibers that overlie circular muscle fibers, except in the cincture regions, where this pattern is reversed. Metamorphosis is initiated by the larval neuromuscular system but is completed by the juvenile neuromuscular system. During metamorphosis, the larval nervous system and the musculature undergo cell death, and the larval tentacles and gut are remodeled into the juvenile arrangement. Although the phoronid nervous system has often been described as deuterostome-like, these data show that several cytological aspects of the larval and juvenile neuromuscular systems also have protostome (lophotrochozoan) characteristics.     

Fine Structure of the Tentacles of Phoronis australis Haswell (Phoronida,Lophophorata)

The epidermis of the tentacles of Phoronis australis consists of six cell types: supporting cells, choanocyte-like sensory cells, both types monociliated, secretory A-cells with a mucous secretion, and three kinds of B-cells with mucoprotein secretions. On cross-sections of the tentacle, one can distinguish four faces: the frontal one, heavily ciliated and located between the two frontolateral rows of sensory cells, the lateral and the abfrontal ones. The orientation of the basal structures of the cilia is related to the direction of their beat. The basiepidermal nervous system is grouped mainly at the frontal and abfrontal faces. The basement membrane is thickest on the frontal face and consists of circular collagen fibrils near the epidermis and longitudinal ones near the peritoneum. All peritoneal cells surrounding the mesocoel are provided with smooth longitudinal myofibrils, and isolated axons are situated between these cells and the basement membrane. The wall of the single blood capillary in each tentacle consists of epitheliomuscular cells with circular myofilaments, lying on a thin internal basal lamina; there is no endothelium.     

Development of the nervous system in Phoronopsis harmeri (Lophotrochozoa, Phoronida) reveals both deuterostome- and trochozoan-like features

Background

Inferences concerning the evolution of invertebrate nervous systems are often hampered by the lack of a solid data base for little known but phylogenetically crucial taxa. In order to contribute to the discussion concerning the ancestral neural pattern of the Lophotrochozoa (a major clade that includes a number of phyla that exhibit a ciliated larva in their life cycle), we investigated neurogenesis in Phoronopsis harmeri, a member of the poorly studied Phoronida, by using antibody staining against serotonin and FMRFamide in combination with confocal microscopy and 3D reconstruction software.

Results

The larva of Phoronopsis harmeri exhibits a highly complex nervous system, including an apical organ that consists of four different neural cell types, such as numerous serotonin-like immunoreactive flask-shaped cells. In addition, serotonin- and FMRFamide-like immunoreactive bi- or multipolar perikarya that give rise to a tentacular neurite bundle which innervates the postoral ciliated band are found. The preoral ciliated band is innervated by marginal serotonin-like as well as FMRFamide-like immunoreactive neurite bundles. The telotroch is innervated by two neurite bundles. The oral field is the most densely innervated area and contains ventral and ventro-lateral neurite bundles as well as several groups of perikarya. The digestive system is innervated by both serotonin- and FMRFamide-like immunoreactive neurites and perikarya. Importantly, older larvae of P. harmeri show a paired ventral neurite bundle with serial commissures and perikarya.

Conclusions

Serotonin-like flask-shaped cells such as the ones described herein for Phoronopsis harmeri are found in the majority of lophotrochozoan larvae and therefore most likely belong to the ground pattern of the last common lophotrochozoan ancestor. The finding of a transitory paired ventral neurite bundle with serially repeated commissures that disappears during metamorphosis suggests that such a structure was part of the ??ur-phoronid?? nervous system, but was lost in the adult stage, probably due to its acquired sessile benthic lifestyle.     

Fine structure of the epistome in Phoronis ovalis: significance for the coelomic organization in Phoronida

Abstract. The hypothesis of a common ancestry of the lophophorate taxa Brachiopoda, Bryozoa, Phoronida, and the Deuterostomia can be traced back to the late 19th century when Masterman recognized a tripartite organization of the body consisting of pro-, meso-, and metasome, along with coelomic body cavities in each compartment, as characteristic for Echinodermata, Pterobranchia, Phoronida, and Brachiopoda. This idea became quite popular under the name archicoelomate concept. The organization of the phoronids, and especially of their transparent actinotroch larva, has for a long time been used as a touchstone for the validity of this concept. As a coelomic lining can reliably be recognized only on the ultrastructural level, this technique has been applied for adults of Phoronis ovalis , which is assumed to be a sister species to all other phoronids. Phoronis ovalis contains only two coelomic compartments, a posterior coelom inside the trunk (metasoma), occupying the space between the trunk epidermis and the digestive epithelium, and an anterior lophophoral coelom inside and basal to the tentacular crown (mesosoma). There is no coelomic cavity inside the epistome (prosoma). This part of the body is filled with myoepithelial cells, which are continuous with the epithelial lining of the lophophore cavity. These cells form a lumenless bilayer and possess long, tiny myofilamentous processes, which are completely embedded in an extracellular matrix. A comparison with data on P. muelleri shows that there is no need to assume three different coelomic cavities in Phoronida, in contrast to the predictions of the archicoelomate concept. At least for this taxon, a correspondence to the situation in deuterostomes can hardly be found.     

The structure of the nervous system of the pluteus larva of Strongylocentrotus purpuratus

Summary Tissues that have the ultrastructural characteristics of nervous tissues are associated with ciliary and muscular elements of the pluteus larva of Strongylocentrotus purpuratus. The nerve cells are found along the margins of the ciliary bands, which are composed predominantly of spindle-shaped ciliated cells. The nerve cells contribute axonal processes to a tract of axons, which runs at the base of the ciliary band throughout its length. Axonal tracts, in the esophagus, lie beneath the circumesophageal muscles. Branched microvilli, which have been interpreted as sensory receptors, are located on the oral side of the main ciliary band and connect with the nerve cells in the ciliary band. The nervous structures described here, and other tissues of the pluteus that have been previously described as nervous, are compared on the basis of their association with receptor and effector organs, and their ultrastructural characteristics.     

The Ultrastructure of the Protonephridium of the Actinotroch Larva (Phoronida)

The actinotroch larva of Phoronis muelleri has a pair of protonephridia located beneath the tentacle ring and draining the blastocoel; each protonephridium is composed of about 25 solenocytes and a nephroduct which opens in a nephropore on the ventral side of the metasome. The neck of the solenocytes consists of bars, mutually interconnected by a fenestration lamina. Inside the neck microvilli originate proximally in the proximal intrachoanal field and extend through the neck into the nephroduct. There is no canal cell. In cross section the nephroduct is composed of 5–7 monociliary cells, with the cilium protruding through a border of microvilli and extending into the nephroduct. The whole protonephridium is surrounded by a basal lamina. Comparisons of the actinotroch protonephridium with those of other groups have not revealed any convincing homologies. The protonephridia of the protostomians are all considered to be of ectodermal origin, while the cyrtopodocytes of Branchiostoma are mesodermal. The protonephridium of the actinotroch is ectodermal.     

柞蚕幼虫期神经系统一氧化氮合酶的NADPH-d组织化学

运用NADPH-d组织化学整体染色方法研究柞蚕Antheraea pernyi Gu rin-Meneville幼虫神经系统中一氧化氮合酶阳性细胞的分布、数量及形态特征。结果表明,柞蚕各龄期幼虫中枢神经的脑及各神经节中都有一氧化氮合酶阳性反应,阳性神经元根据其形态大小和染色特性可分为A,B,C3种类型:A型细胞沿神经节中线分布,阳性反应较强,胞体长径约30~70μm,各神经节中的数量恒定。B型细胞多分布于神经节周边部分,阳性反应较弱,胞体长径约8~20μm,各神经节中的数量变化较大,随着龄期增加有减少的趋势。C型细胞分布于咽下神经节和第8腹神经节,在3种细胞中阳性反应最强,胞体长径约16~50μm。     

Serotonin immunoreactivity in the nervous system of the Pandora larva, the Prometheus larva, and the dwarf male of Symbion americanus (Cycliophora)

Cycliophora is a recently described phylum of enigmatic metazoans with a very complex life cycle that includes several sexual and asexual stages. Symbion pandora and Symbion americanus are the only two cycliophoran species hitherto described, of which morphological and genetic knowledge is still deficient to clarify the phylogenetic position of the phylum. Aiming to increase the database on the cycliophoran neural architecture, we investigated serotonin immunoreactivity in the free swimming Pandora larva, the Prometheus larva, and the adult dwarf male of S. americanus. In the larval forms, serotonin is mainly expressed in a ring-shaped pattern at the periphery of the antero-dorsal cerebral ganglion. Additionally, several serotonergic perikarya emerge from both sides of the cerebral ganglion. Thin neurites project anteriorly from the cerebral ganglion, while a pair of ventral longitudinal neurites emerges laterally and runs along the anterior-posterior body axis. Posteriorly, the ventral neurites fuse and extend as a posterior projection. In the dwarf male, serotonin is found mainly in the commissural neuropil of the large anterior cerebral ganglion. In addition, serotonin immunoreactivity is present in the most anterior region of the ventral neurites. Comparative analysis of spiralian nervous systems demonstrates that the neuroanatomy of the cycliophoran larval stages resembles much more the situation of adult rather than larval spiralians, which may be explained by secondary loss of larval structures and heterochronic shift of adult components into the nervous system of the Pandora and the Prometheus larva, respectively.     

Development of the nervous system of the pluteus larva of Strongylocentrotus droebachiensis

Summary Development of the nervous system of the pluteus larva of Strongylocentrotus droebachiensis was investigated using indirect immunofluorescence with antibodies against dopamine, GABA, and serotonin, and glyoxylic acid-induced fluorescence of catecholamines. Serotonergic cells first appear in full gastrulae; dopaminergic and GABAergic cells are present in early four-arm plutei. The number of neurons and the complexity of the nervous system increases through development of the pluteus. In the pluteus the dopaminergic component of the nervous system includes a ganglion in the lower lip of the mouth and a pair of ganglia at the base of the post-oral arms which extend axons along the base of the circumoral ciliary band. The distribution of cells visualized by glyoxylic acid-induced fluorescence is similar to that of dopaminergic cells. GABAergic neurons occur in the upper lip and in the wall of the esophagus. Serotonergic neurons are present in the lower lip; the pre-oral hood contains an apical ganglion which extends axons along the base of the epidermis overlying the blastocoel. The dopaminergic and GABAergic components of the nervous system are associated with effectors involved in feeding and swimming. The serotonergic component is not associated with any apparent effectors but may have a role in metamorphosis.     

The peripheral nervous system supports blood cell homing and survival in the Drosophila larva

Interactions of hematopoietic cells with their microenvironment control blood cell colonization, homing and hematopoiesis. Here, we introduce larval hematopoiesis as the first Drosophila model for hematopoietic colonization and the role of the peripheral nervous system (PNS) as a microenvironment in hematopoiesis. The Drosophila larval hematopoietic system is founded by differentiated hemocytes of the embryo, which colonize segmentally repeated epidermal-muscular pockets and proliferate in these locations. Importantly, we show that these resident hemocytes tightly colocalize with peripheral neurons and we demonstrate that larval hemocytes depend on the PNS as an attractive and trophic microenvironment. atonal (ato) mutant or genetically ablated larvae, which are deficient for subsets of peripheral neurons, show a progressive apoptotic decline in hemocytes and an incomplete resident hemocyte pattern, whereas supernumerary peripheral neurons induced by ectopic expression of the proneural gene scute (sc) misdirect hemocytes to these ectopic locations. This PNS-hematopoietic connection in Drosophila parallels the emerging role of the PNS in hematopoiesis and immune functions in vertebrates, and provides the basis for the systematic genetic dissection of the PNS-hematopoietic axis in the future.     

Catecholamine-containing,serotonin-like and neuropeptide FMRFamide-like immunoreactive cells and processes in the nervous system of the pilidium larva (Nemertini)

Summary Pilidium larvae at different developmental stages have been investigated for the occurrence of glyoxylic acid induced fluorescence in catecholamines (CA), and serotonin-like (5-HT) and neuropeptide FMRFamide-like (FMRFamide) immunoreactivity (ir). The distribution of CA, 5-HT-ir and FMRFamide-ir cells and processes was compared with the location of nerve processes as found by transmission electron microscopy (TEM). In the pilidium larvae the marginal and oral nerves contain CA and 5-HT-ir processes and 5-HT-ir unipolar cells. The posterior suboral nerve contain CA and 5-HT-ir processes, whereas in the anterior suboral nerve neither CA nor 5-HT-ir and FMRFamide-ir were observed. The lateral helmet nerve contains FMRFamide-ir processes and unipolar cells. In the epidermis CA and 5-HT-ir multipolar cells were found. The juvenile worm that develops inside the pilidium larva was found to contain only 5-HT-ir. A pair of lateral cords extent the whole length of the juvenile and anteriorly they form the anterior ventral cerebral commissure. Also, from the anterior part of the lateral cords projects a pair of circumrhynchodeal processes which dorsally form the dorsal cerebral commissure. A pair of proboscis processes originate from the circumrhynchodeal processes and extend the whole length of the probosics. From the dorsal cerebral commissure cephalic processes project rostrally and ventrally. Only unipolar 5-HT-ir cells were observed, and they were located along the lateral cords into which their processes extend.Abbreviations AEC 3-amino-9-ethylcarbazole - ap apical plate - arp anterior accessory ridge processes - ason anterior suboral nerve - CA catecholamines - cd cephalic discs - cp cephalic processes - crp circumrhynchodeal processes - DAB 3,3'-diaminobenzidine - dc dorsal cerebral commissure - epi epidermis - es oesophagus - fl fore lobe - FMRFamide phe—met—arg—phe—NH₂ - Go goat - GS goat serum - hl hind lobe - int intestine of the juvenile - lhn lateral helmet nerve - lhp lateral helmet processes - ll lateral lobe - lp lateral processes of the juvenile - mcb marginal ciliary band - me mesoderm - mn marginal nerve - moc monociliary cell - mp marginal processes - mu muscle - muc multiciliary cell - n 1, n 2, n 3 division of marginal nerve - on oral nerve - op oral processes - pb proboscis - pp proboscis processes - pson posterior suboral nerve - psop posterior suboral processes - Ra rabbit - sd stomodeum - st stomach - td trunk discs - tr trunk - TRITC tetramethylrhodamine isothiocyanate - vc ventral cerebral commissure - z 1, z 2 ciliary zones of marginal ciliary band - 5-HT serotonin