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     

Biogene Amine im Nervensystem von Lineus sanguineus Rathke (Nemertini)

Zusammenfassung Mit Hilfe der von Carlsson, Falck und Hillarp entwickelten Methode zur fluoreszenzmikroskopischen Lokalisation biogener Amine werden im Nervensystem von Lineus sanguineus erstmalig primäre Catecholamine nachgewiesen, von denen auf Grund ihres Verteilungsmusters angenommen wird, daß sie als Transmitterstoffe wirken. Nur wenige Ganglienzellen innerhalb der Nervenzellschicht des Gehirns sind catecholaminerg. Sie versorgen über das Neuropilem von Ganglien und lateralen Nervensträngen im wesentlichen drei periphere, terminale Fasersysteme, die im Bereich der Frontalorgane, des Rüssels und im Mund-Vorderarm-Bereich liegen.Die intraneuronale Verteilung biogener Amine entspricht weitgehend derjenigen im Wirbeltier-Neuron. Wahrscheinlich ist das catecholaminerge Nervensystem im Bereich der Frontalorgane sensibel, im Rüssel und in der Mund-Vorderdarm-Region motorisch. Möglicherweise hat es auch senso-motorischen Charakter. Das Verteilungsmuster der terminalen catecholaminergen Nervenfasernetze wird hinsichtlich einer etwaigen biologischen Bedeutung, die es beim Erwerb der Beute haben könnte, diskutiert.

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Primary catecholamines in the nervous system of lineus sanguineus Rathke (Nemertini)

Summary By the aid of the histochemical fluorescence method of Carlsson, Falck and Hillarp primary catecholamines which might act as transmitters are demonstrated in the nervous system of Lineus sanguineus. There are only a few catecholaminergic cells within the layer of nerve cells of the brain. Via the neuropile of the ganglia and the lateral nerve cords, they mainly supply three peripheric nets of nerve fibers, situated in the frontal organs, in the proboscis and in the mouth-foregut-region.The intraneuronal distribution of the biogenic amines is almost identical with the one in vertebrate neurons. Probably the catecholaminergic nervous system in the frontal organs is a sensory one, and it might be motoric in the proboscis and in the mouth-foregut-region. Possibly its character is both sensory and motoric. The pattern of the distribution of the three terminal nervous plexus is discussed in view of its possible biological relevance during the act of taking the prey.

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Mit Unterstützung durch die Deutsche Forschungsgemeinschaft     

Die Erregungsübertragung bei Lineus sanguineus Rathke (Nemertini)

Zusammenfassung Mit histochemischer Methodik läßt sich in den Geweben von Lineus sanguineus (Nemertini) Acetylcholinesterase (ACHE; Spezifitätskontrolle: Eserin- und iso-OMPA-Test) nachweisen. Das Enzym kommt im zentralen und peripheren Nervensystem (Ganglienzellen, Neuropilem, Nervenfasern) vor. Daneben sind die Epithelien der Frontalorgane und Kopfspalten, die Cerebralorgane, die Muskulatur und die Blutzellen ACHE-reaktiv. Die Enzymverteilung läßt auf einen cholinergen Transmittermechanismus schließen.Die Befunde werden in Zusammenhang mit Befunden am aminergen Nervensystem von Lineus (Reutter, 1969) besprochen. Möglicherweise werden doppelt innervierte Sinnesorgane (z.B. Frontalorgane) cholinerg erregt und aminerg kontrolliert, analog zum Parasympathicus-Sympathicus-System der Wirbeltiere. Die ACHE-Aktivität im Bereich der Muskulatur, die frei von aminergen Fasern ist, läßt darauf schließen, daß sie cholinerg erregt wird.

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Impulse transmission in Lineus sanguineus Rathke (Nemertini)II. The cholinergic nervous system

Summary With histochemical methods acetylcholinesterase (ACHE; the specifity of which was tested with eserine and iso-OMPA) was demonstrated within several tissues of Lineus sanguineus (Nemertini). The enzyme is mainly located in the central and in the peripheral nervous system (neurons, neuropileme, and nerve fibers). The epithelia of the frontal organs and of the lateral head folds, the cerebral organs, the musculature and the blood cells are ACHE-reactive, too. The distribution of the enzyme may indicate cholinergic neurotransmission.The results are discussed in view to the adrenergic nervous system of Lineus (Reutter, 1969). Possibly double innervated organs (i.e. the frontal organs) are stimulated cholinergically and are controlled aminergically. This will be in analogy to the parasympathetic-sympathetic system of vertebrates. The activity of ACHE within the musculature, where no aminergic nerve fibers are found, indicates its cholinergic stimulation.

Mit Unterstützung durch die Deutsche Forschungsgemeinschaft.     

Ultrastructure of the nephridio-circulatory connections in Tubulanus annulatus (Nemertini,Anopla)

Summary The protonephridial terminal organs in the nemertean Tubulanus annulatus form an integral part of the blood vessel wall. Both endothelial and muscle-cell layers of the vessel's wall are discontinued at the site of each terminal organ. The terminal organs are usually composed of from one to three terminal cells enclosing a central lumen provided with many microvilli and separated from the blood vessel's lumen by a membranous filtration area. The latter is perforated by numerous winding clefts formed by interdigitation of minute cytoplasmic pedicels arising from processes issued by each of the involved terminal cells. Ultrafiltration of blood plasma takes place across a filtration membrane which spans the cleft system and the basal lamina of the terminal cells. Fluid is propelled into the lumen of the terminal organs through the activity of ciliary bundles, one for each terminal cell involved, perhaps supplemented by vascular turgor. All efferent conduits of the protonephridium have profuse infoldings of the luminal cell surfaces and/or numerous pinocytotic pits suggestive of reabsorption of substances from the primary urine.Abbreviations BL basal lamina - C cilium - CP coated pit - CT collecting tubule - CV inzcoated vesicle - D dictyosome - E endothelial cell - F fenestration of endothelial cell - FA filtration area - FM filtration membrane - G glycogen granule - LV lateral vessel - M mitochondrion - MC muscle cell - MV microvillus - N nucleus of terminal cell - NE nucleus of endothelial cell - NP nephridiopore - PC protonephridial capillary cell - PT protonephridial tubule - R rootlet - TC terminal cell     

Ultrastructure and development of the rhabdomeric eyes in Lineus viridis (Heteronemertea, Nemertea)

Nemerteans are undoubtedly members of the Spiralia, although their phylogenetic relationships are still a matter of debate. The apparently acoelomate organization suggests a relationship with the platyhelminths, whereas the blood-vascular system has been interpreted as an equivalent to coelomic cavities of annelids, indicating a close relation between annelids and nemerteans. Like other spiralians, most nemertean species are known to have one or several pairs of rhabdomeric and subepidermally situated eyes when adult. The development of these eyes as well as the mode in which the eyes are multiplied is as yet unknown. This is the first attempt to investigate eye formation in a nemertean. In the heteronemertean Lineus viridis (Müller, 1774) the everse rhabdomeric eyes are located deeply underneath the epidermis and consist of a few pigment cells that form a cup-like structure with interdigitating processes that contain numerous pigment granules. In hatchlings, the optical cavity contains processes of 12 sensory cells, each bearing a single cilium and various microvilli. The perikarya of these cells are located distally from the pigment cup. During further development the number of cells increases. Eye development starts with a small anlage situated underneath the epidermis, irrespective of whether this is the first eye or any additional one. The anlage consists of five unpigmented cells and three dendritic processes, each bearing apical microvilli and a single cilium. There is no evidence for an epidermal origin of the eyes. In L. viridis eye formation resembles that described in platyhelminths in which eyes also develop as cerebral derivatives. Although this result has the potential to influence the discussion on the position of Nemertea, the data have to be interpreted with care, since development of L. viridis is derived within the Nemertea.     

Das Verhalten des aminergen Nervensystems während der Regeneration des Vorderdarms von Lineus sanguineus Rathke (Nemertini)

Znsammenfassung An 1–16 Tagen alten Regeneraten wurde mit der OsO₄-KJ- und OsO₄-NaJ-Fixierung sowie einer fluoreszenzmikroskopischen Methode zur Erfassung biogener Amine die Innervation des regenerierenden Vorderdarms histologisch untersucht.Die Vorderdarmanlage entsteht ab dem 4. Regenerationstag. Sie wird von Blastocyten aufgebaut, die dem Mitteldarm und dem Mesenchym entstammen. Im Bereich der Vorderdarmanlage werden Nervenfasern erst ab dem 6. Regenerationstag nachweisbar; ab dem 11. Regenerationstag enthalten sie frühestens ein Catecholamin. Bis zum 16. Regenerationstag entsteht ein aminerger Nervenfaserplexus fast normalen Umfangs. Zu diesem Zeitpunkt können die regenerierten Individuen erstmals Nahrung aufnehmen.Das aminerge Nervensystem beeinflußt das Regenerationsgeschehen nicht. Es ist aber für die Funktionsaufnahme des Vorderdarms sicher von Bedeutung.

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The aminergic nervous system in the regenerating foregut of Lineus sanguineus Rathke (Nemertini)

Summary The aminergic innervation of the regenerating foregut of Lineus sanguineus regenerates, aged 1–16 days, was studied by using OsO₄-KJ and OsO₄-NaJ fixation and fluorescence microscopic methods.The foregut anlage is first observed on the 4th day of regeneration, and consists of blastocytes which originate from the midgut and mesenchyme. Nerve fibers are first detected near the foregut anlage on the 6th day of regeneration. The aminergic nerve plexus are formed from the 11th day onwards and attains a nearly normal size on the 16th day of regeneration; at this time the animals does first able to take in food.The aminergic nervous system did not influence the process of regeneration, but appears to be of importance in the commencement of the foregut function.

Mit Unterstützung durch die Deutsche Forschungsgemeinschaft.     

Ultrastructure of sperm and male reproductive system in Lineus viridis (Heteronemertea, Nemertea)

Nemerteans possess serially arranged gonads that lie between the midgut pouches. In both sexes the gonads are lined with an epithelium. During maturity, they gain contact to the exterior by a ciliated duct, which is generally assumed to be a derivative of the gonad. Gonad lining and sperm ultrastructure are little known in heteronemerteans, a group of nemerteans belonging to the Anopla, one of the two large nemertean subgroups. Reproduction biology in heteronemertean Lineus viridis allows predicting a modified sperm type, so-called introsperm for this taxon. Nothing is known on the fate of the testes at the end of the reproductive period of this perennial species. In order to test the predictions and to broaden the data base, males of L. viridis were collected at different times of the year. Histological and ultrastructural data show that the gonad wall is lined with different aciliated endothelial cells and germ cells, while the gonoduct is formed by densely ciliated cells. The testes are completely filled with sperm cells during maturity; there is no hint at ongoing spermiogenesis at this time. The sperm consists of head, midpiece and tail. Externally, head and midpiece cannot be discriminated. The acrosome is cup-shaped and lies anterior to the nucleus which contains 6–8 lateral ridges. Three long mitochondria mark the midpiece. They line the posterior section of the nucleus and extend up to the level of the ciliary basal structures. The sperm morphology corroborates the predictions derived from the mode of reproduction. At the end of the reproductive period the male gonads change cellular composition, while the gonoduct degenerates. Provided that both sexes show the same growth rate, male offspring acquire sexual maturity earlier than female offspring, since L. viridis males are always smaller than the females. In contrast to the males, females keep their gonads and gonoducts during most time of the year. Since large males were never found within the studied population, these data indicate that L. viridis might be a consecutive hermaphrodite.     

Ultrastructure of potential photoreceptor organs in the larva ofScrupocellaria bertholetti (bryozoa)

Summary Pigmented spots have been implicated as potential photoreceptors in many bryozoan larvae which display phototactic behavior. Larvae ofScrupocellaria bertholetti, initially photopositive on release from the brood chambers, have a pair of identical posterolateral pigmented spots and a third morphologically different spot in the anteromedian line. The presumed photoreceptoral organelle in each is composed of numerous unmodified cilia which have the typical 9+2 arrangement of microtubules with electron-dense arms extending from thea-microtubule of each peripheral pair. The posterolateral pigmented spot is composed of two modified coronal cells and a basal sensory cell. Cilia arising from the apical part of this basal cell are aligned vertically. Densely packed pigment vesicles in the three cells form a shield that restricts light entry to one direction. The anteromedian pigmented spot is composed of four cells, two lateral and two posterior. Cilia of the opposing lateral cells are horizontally aligned, whereas cilia of the posterior cells are vertical and curve outward from the oral margin of the pigmented spot. Pigment vesicles are present in all four cells to form a complete shield. Extensions of the larval nervous system are in direct contact with the four cells of the anteromedian spot and the basal cells of the posterolateral spots. The posterolateral pigmented spots share structural and topological similarities with the pigmented spots ofBugula neritina, the only other supposed photoreceptors in lophophorates which have been studied at the ultrastructural level. It is not yet possible to homologize these potential photoreceptors with those of other groups.     

Ultrastructure of the lycophora larva ofGyrocotyle urna (Cestoda,Gyrocotylidea)

Summary The fine structure of the glands of the lycophora larva ofGyrocotyle urna is described. There are four pairs of different glands which can be differentiated by the ultrastructure of their vesicles, their location and their gland pores. Their cell bodies are located at the transition from the median to the posterior third of the larva. Gland ducts formed by extensions of the gland cells run anteriorly and terminate at the anterior tip of the larva. In the cytoplasm of the terminal duct regions peripheral microtubules are found. The structure and function of the glands inGyrocotyle is discussed with regard to the evolution of cestodes and other Neodermata.     

The invention of the pilidium larva in an otherwise perfectly good spiralian phylum Nemertea

One of the most remarkable larval types among spiralians, and invertebrates in general, is the planktotrophic pilidium. The pilidium is found in a single clade of nemerteans, called the Pilidiophora, and appears to be an innovation of this group. All other nemerteans have either planktotrophic or lecithotrophic juvenile-like planuliform larvae or have direct development. The invention of the pilidium larva is associated with the formation of an extensive blastocoel that supports the delicate larval frame and elaborate ciliary band. Perhaps the most striking characteristic of the pilidium is the way the juvenile worm develops inside the larva from a series of isolated rudiments, called the imaginal discs. The paired cephalic discs, cerebral organ discs, and trunk discs originate as invaginations of larval epidermis and subsequently grow and fuse around the larval gut to form the juvenile. The fully formed juvenile ruptures the larval body and, more often than not, devours the larva during catastrophic metamorphosis. This review is an attempt to examine the pilidium in the context of recent data on development of non-pilidiophoran nemerteans, and speculate about the evolution of pilidial larval development. The author emphasizes the difference between the planuliform larvae of Palaeonemerteans and Hoplonemerteans, and suggest a new name for the hoplonemertean larvae--the decidula.     

Ultrastructure of the lycophora larva of Gyrocotyle urna (Cestoda,Gyrocotylidea)

Summary The fine structure of the ciliated epidermis, the body musculature and the neodermis anlage cells of the free-swimming lycophora larva of Gyrocotyle urna Grube and Wagener, 1852, is described. The epidermis is syncytial and covers the whole body including a caudal cavity into which the larval hooks protrude. It contains several types of vesicles, mitochondria and membrane whorls but lacks nuclei, dictyosomes and endoplasmic reticulum. The locomotory cilia exhibit single rostrally directed rootlets. The body musculature consists of about 25 longitudinal and 42 circular muscles. Their nuclei are located proximally to the contractile elements. The neodermis anlage cells show numerous dictyosomes, elaborated cisternae of endoplasmatic reticulum, typical coated vesicles and membranous bodies. Extrusions of these cells do not penetrate the epidermis but contact it by desmosoms.The evolution of epidermal and neodermal structures of Gyrocotyle and other parasitic Platyhelminthes is discussed. The probable consequences of the lack of some types of organelles in the epidermis of Neodermata are considered.Abbreviations bb basal body - bl basal lamina - ci locomotory cilia - Ce epidermis of the caudal cavity - cr ciliary rootlet - di dictyosome - Ep epidermis - er endoplasmic reticulum - Hm hook musculature - ld lipid droplet - Lh larval hook - Lm longitudinal musculature - mi mitochondria - mt microtubule - mv microvilli - mw membrane whorl - Ne neodermis anlage cell - nu nucleus - Re receptor - Rm circular musculature - ve vesicles     

Ultrastructure of the lycophora larva of Gyrocotyle urna (Cestoda,Gyrocotylidea)

Summary The ultrastructure of the protonephridial system of the lycophore larva of Gyrocotyle urna Grube and Wagener, 1852, is described. It consists of six terminal cells, at least two proximal canal cells, two distal canal cells and two nephridiopore cells. The terminal cells and the proximal canal cell build up the filtration weir with its two circles of weir rods. The proximal canal cell constitutes a solid, hollow cylinder without a cell gap and desmosome. The distal canal cell is characterized by a strong reduction of the canal lumen by irregularly shaped microvilli. The nephridiopore region is formed by a nephridiopore cell; its cell body is located at some distance proximally within the larva. The connection among different canal cells is brought about by septate desmosomes. Morphological, evolutionary and functional aspects of the protonephridial system within Platyhelminthes are discussed. The structure of the proximal canal cells without a desmosome is considered an autapomorphy of Cestoda.Abbreviations ci cilia of the terminal cell - Co distal canal cell - col lumen of the distal canal cell - Ep epidermis - er outer rods of the filtration weir - il inner leptotriches - ir inner rods of the filtration weir - ld lipid droplets - mt microtubule - mv microvilli - Nc nephridiopore cell - Ne neodermis anlage cells - nu nucleus - pC proximal canal cell - ro ciliary rootlets - sd septate desmosome - Tc terminal cell     

Zur Nahrungsaufnahme vonTetrastemma melanocephalum (Nemertini)

The proboscis of hoplonemerteans is armed with a stylet apparatus, which is used for capturing prey.Tetrastemma melanocephalum (Johnston) is a common hoplonemertean in the littoral of the Baltic Sea and the North Sea. It lives in the phytal and on sand- and mudflats and occurs in large numbers in theCorophium belts in the waddenseas.T. melanocephalum feeds on arthropods, mainly on copepods and amphipods. The prey is caught with the proboscis, penetrated by the stylet and grows weak (reduction of movements) within a few seconds; it is then sucked out. During the summer, a 15–35 mm long nemertean captures about 3 specimens ofCorophium volutator of 3.5–6 mm length per day. In theCorophium belt at Sahlenburg, German Bight, North Sea, 29 nemerteans/0.25m² were found; they feed mainly onC. volutator, so that on average more than 10 000 specimens ofC. volutator/m²/month are sucked out by these nemerteans. Hence,T. melanocephalum is an important consumer ofCorophium.     

Ultrastructure of the rectum of the soil-spraying larva in Bittacus cirratus (Mecoptera: Bittacidae)

Protoplasma - The larvae of Bittacidae have an interesting behavior of spraying soil particles on their body surface through the anus. However, the hindgut specialization associated with this...     

Cyclin O (Ccno) functions during deuterosome-mediated centriole amplification of multiciliated cells

Mucociliary clearance and fluid transport along epithelial surfaces are carried out by multiciliated cells (MCCs). Recently, human mutations in Cyclin O (CCNO) were linked to severe airway disease. Here, we show that Ccno expression is restricted to MCCs and the genetic deletion of Ccno in mouse leads to reduced numbers of multiple motile cilia and characteristic phenotypes of MCC dysfunction including severe hydrocephalus and mucociliary clearance deficits. Reduced cilia numbers are caused by compromised generation of centrioles at deuterosomes, which serve as major amplification platform for centrioles in MCCs. Ccno-deficient MCCs fail to sufficiently generate deuterosomes, and only reduced numbers of fully functional centrioles that undergo maturation to ciliary basal bodies are formed. Collectively, this study implicates CCNO as first known regulator of deuterosome formation and function for the amplification of centrioles in MCCs.     

The morphology of the apical organ and adjacent epithelium of pilidium prorecurvatum, a pelagic larva of an unknown heteronemertean (Nemertea)

The morphology of pilidia ex gr. recurvatum from Peter the Great Bay (Sea of Japan) was studied by confocal laser scanning and transmission-electron microscopy. The studied pilidium larvae differ from pilidium recurvatum in lacking a posterior ciliary ring and by the presence of a caudal tuft. On this basis, pilidium prorecurvatum is proposed as a new name for the lavae. The apical organ of pilidium prorecurvatum is represented by a thickened epithelium, which consists of uniform columnar monociliary collar cells and is innervated by a pair of serotonergic intraepithelial neurons. The bodies of the serotonergic neurons are located outside of the apical organ, but occasional axons were found at the organ base. The rest of the pilidial epithelium is represented by flattened polygonal multiciliated cells with sparse microvilli; the bodies of two neurons lie in the helmet epithelium immediately adjacent to the apical organ. Morphologically, the apical organ of the pilidium corresponds well to that of other lophotrochozoan larvae, but their homology remains unclear.