An ultrastructural study of larval settlement in the sea anemone Urticina crassicornis (Cnidaria,Actiniaria)

Laboratory-reared larvae of the sea anemone Urticina (= Tealia) crassicornis have been examined by electron microscopy prior to and following settlement on algal substrata. At 18 days postfertilization, the free-swimming planula larva measures about 600 μm long. A stomodaeal invagination occurs at the narrow end of the larva and connects with a solid mass of endoderm in the core region. The endoderm possesses septa with well-developed myonemes and is situated subjacent to a thin sheet of mesoglea. The uniformly ciliated ectoderm that constitutes the outer layer of the larva contains: (1) spirocysts, (2) nematocysts, (3) mucus, (4) three types of membrane-bound granules, (5) a basiepithelial nerve plexus, and (6) a few nongranular cells that may represent sensory neurons. Within several minutes after the introduction of the algal substratum, the planula characteristically directs its broadened aboral end toward the alga and secretes a refractile sheet of material. As the aboral end attaches to the substratum, the larva becomes noticeably shorter along its oral-aboral axis, presumably owing to the contractions of myonemes that are located within the endodermal septa. All three types of granules and the ectodermal mucoid substances are exocytosed during settlement, but spirocysts and nematocysts characteristically remain undischarged. Ovoid, PAS⁺ granules are believed to be at least partly responsible for adhesion, since these granules are concentrated at the aboral end prior to settlement and are somewhat similar in ultrastructure to putative viscid granules produced by other species. Contrary to a previous report based on light microscopy, no discrete sensory organ is evident in serial sections of the aboral ectoderm. The ability of planulae to detect suitable substrata appears to depend instead on sparsely distributed sensory cells that occur throughout the larval ectoderm.     

Organization of cytoskeleton during the tentacle contraction and cytostome movement in the dinoflagellate Noctiluca scintillans McCartney

Summary Electron microscopy of Noctiluca scintillans reveals that the cytoskeleton of the tentacle involved in the motor action of the prey capture consists of three characteristic elements: a deformable peripheral fibrillo-granular ectosarc, abundant underlying microtubules organized in several rows on the convex side, and helicoid filaments about 8 nm in diameter organized into striated myonemes. Microtubules of the external row are crossed-linked with each other by fibrous elements 5 nm in diameter and 10–15 nm long, their links with the second row result in a Y-shaped binding. Bonds of the other rows are linked to each other irregularly between those of the same row. Striated myonemes are regularly inserted between the rows of microtubules on the ectosarc and between its pleats, joining together in a knot of disarrayed filaments with multidirectional orientation in the central axis of the tentacle. Striation of myonemes is based on an alternation of thick striae (TS) 40 nm wide with a periodicity of about 200 nm, and of some intermediary fine striae (FS) 10 nm wide. The events during tentacle contraction are: (1) Rotation of the tentacle, bringing the convex side to the inner side of it. Here, large numbers of microtubules have been visualized by optical immunocytochemistry after labelling with Paramecium antitubulin antiserum. (2) Increase of pleat amplitude (200–300 nm to 600 nm) in concomitance with a decrease of its period (500–700 nm to 250 nm). (3) Apparent modification of the microtubule orientation. (4) Transformation of some TS in several FS without modification of the striation periodicity.Near the cytostome, the cytoskeleton consists of a number quantity of microtubules underlying a non-pleated ectosarc and long tracts of contractile myonemes formed by 6-nm helicoid filaments linking the internal side of the cytostome of the supporting rod. Semirelaxed myonemes show an alternation of fine striae (FS) 35 nm wide between two clear areas (CA) with a periodicity of about 300 nm, plus an incipient dark area (DA) lying between them; together they are transformed into a thick stria (TS) during maximal contraction; the striation periodicity thus decreases by one half. These two systems are compared with one another and with other motile systems.     

Ultrastructure of the median eminence of the rat

Summary The ependymal cells bordering the median eminence to the third ventricle are characterised by many microvillus-like projections and bulbous cell processes of the luminal plasma membrane. The latter contain many vesicles 500–1,000 Å in diameter. Cilia with 9+2 fibrillar pattern are seen occasionally. Adhesive devices in the from of zonula adhaerens and zonula occludens are found in the apical part of the intercellular junction. Unmyelinated nerve fibres with a mean diameter of 1 and containing many electron dense granules of 830–1,330 Å are often seen between the ependymal cells.Two types of glial cells are found in the median eminence. One is characterised by a nucleus with dense blods of chromatin and dense cytoplasm, and it is associated chiefly with the nerve fibres in the region of the hypothalamo-hypophysial tract. The other type of glial cell is characterised by fine, uniformly distributed chromatin in the nucleus and a relatively pale cytoplasm and branched processes which terminate perivascularly in the base of the median eminence.Myelinated nerve fibres are seen only in the region of the hypothalamo-hypophysial tract. Only a part of them contain electron dense granules 1,330–2,330 Å in diameter.Three types of unmyelinated nerve fibres can be distinguished in the median eminence according to the size of the electron dense granules they contain: 1. Nerve fibres containing granules 1,330–2,330 Å in diameter. They are seen primarily in the hypothalamo-hypophysial tract, but also in the zona externa; 2. those containing granules with a mean diameter of 1,330 Å; and 3. those containing granules with a mean diameter of 1,000 Å. The last two types are both encountered in the hypothalamo-hypophysial tract, the zona externa and the perivascular region of the base of the median eminence. Under high magnification, the membrane of the granules show evidence of a trilaminar structure and the content of the granules with a low electron density appeares to consist of small microvesicles or globular components. Besides granules, these nerve fibres contain vesicles mostly 420 Å in diameter whose relative number increases towards the perivascular nerve endings. 53 per cent of the inclusions in the hypothalamo-hypophysial tract are granules and 47 per cent vesicles, while the corresponding percentages for the zona externa are 40 and 60 and for the perivascular nerve endings 20 and 80.The mean width of the pericapillary space is 1 , but it varies greatly. It containes many collagen fibrils and fibroblasts. The capillary endothelium is frequently fenestrated and contains many vesicles of various sizes.Two types of granules-containing cells are found in the pars tuberalis depending on the size of the electron dense granules: 1. cells containing granules with a mean diameter of 1,330 Å: and 2. cells containing granules with a mean diameter of 2,000 Å. In addition, there are occasional follicular cavities filled with amorphous material, microvilli and cilia of 9+2 fibrillar pattern.Aided by a grant from the Sigrid Jusélius Stifteise.     

Ultrastruktur der spinalen Liquorkontaktneurone beim Krallenfrosch (Xenopus laevis)

Zusammenfassung Zwischen und unter den Ependymzellen des Zentralkanals des Rückenmarkes von Xenopus laevis kommen Nervenzellen vor. Die intraependymalen Neurone sind rundlich und stehen mit dem Liquor cerebrospinalis durch eine breite Oberfläche in Berührung, von der sich längere und kürzere Fortsätze und ein Cilium (Typ 9+2) in das Lumen erheben. Die hypendymalen Neurone sind bipolar; ihr Dendrit verzweigt sich im Liquor ebenfalls in fingerförmige Fortsätze. Die Liquorkontaktfortsätze beider Zelltypen sind von feinen Filamenten ausgefüllt. Der Reissnersche Faden lagert sich manchen Fortsätzen an.In den intra- und hypendymalen Perikaryen findet man neben endoplasmatischem Retikulum, Golgi-Arealen und Mitochondrien kleine dense-core Vesikel (Durchmesser 600–900 Å). Der distale Fortsatz beider Neurontypen hat Neuritennatur. Axone, die synaptische und granulierte (Durchmesser 800–1200 Å) Vesikel enthalten, bilden relativ wenige Synapsen mit den Liquorkontaktneuronen. Im hypendymalen Neuropil findet man multipolare Nervenzellen, die 1000–1200 Å große granulierte Vesikel enthalten. Aufgrund des morphologischen Bildes wird die mögliche Rolle der Liquorkontaktfortsätze und des Ciliums bei der Funktion der Liquorkontaktneurone diskutiert.

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Ultrastructure of the spinal liquor contacting neurons in the clawed toad (Xenopus laevis)

Summary Nerve cells are situated between and below the ependymal cells of the central canal of the spinal cord of Xenopus laevis. The intraependymal neurons are round-shaped; they contact the cerebrospinal fluid by a large surface from which longer and shorter processes and a cilium (type 9+2) arise into the lumen. The hypendymal neurons are bipolar; their dendrite ramifies also into finger-like processes in the cerebrospinal fluid. The liquor contacting processes of both cell types contain fine filaments. The Reissner's fibre contacts some of the processes.In the intra- and hypendymal perikarya, small dense-core vesicles (diameter 600–900 Å) are found besides of endoplasmic reticulum, Golgi-areas and mitochondria. The distal process of both neuron types has neurite character. Axons containing synaptic and granulated (diameter 800–1200 Å) vesicles, form relatively few synapses with the liquor contacting neurons. In the hypendymal neuropile, multipolar nerve cells occur that contain granulated vesicles with a diameter of about 1000–1200 Å. On the basis of the morphological picture, the possible role of the liquor contacting processes and of the cilium in the function of the liquor contacting neurons are discussed.

     

Intracytoplasmic filaments in pulmonary lymphatic endothelial cells

Summary The cytochemistry and ultrastructure of intracytoplasmic filaments of pulmonary lymphatic endothelial cells of neonatal rabbits were studied by comparison with myofilaments of the peribronchial and pulmonary vascular smooth muscle cells. Two types of endothelial filaments were observed: thin filaments (diameter: 50 Å) which lie close to the abluminal cell membrane; and thick filaments (diameter: 90 Å) which are dispersed throughout the cell cytoplasm.Following heavy meromyosin (HMM) treatment, characteristic arrowhead complexes formed in the thin lymphatic endothelial filaments as well as in the actin filaments of the smooth muscle cells. There was no detectable reaction of HMM with the thick filaments.After incubation with EDTA, the thin filaments were labile, and the thick filaments became the major filamentous component in the endothelial cells. In smooth muscle cells, the actin myofilaments were also labile while the 100 Å filaments were stable.These observations support the hypothesis that the actin-like thin endothelial lymphatic filaments form part of a contractile system, while the thick filaments constitute a plastic cell skeleton. The significance of the contractile system in lymphatic endothelial cells might lie in a mechanism for the active regulation of the endothelial intercellular junctions and gaps and hence the permeability of the lymphatic endothelial cell lining.This study was supported by The Council for Tobacco Research—U.S.A. The authors thank Professor Robert C. Rosan, M.D. (Saint-Louis University—U.S.A.) for expert advice. R. Renwart, B. Emanuel and R. Jullet for technical, G. Pison and St. Ons for photographical and N. Tyberghien for secretarial assistance.     

Vesicle and granule content of sympathetic ganglion cells during limb regeneration of the newt Triturus

Summary Fine structural observations were made on the vesicle and granule content of ganglion cells in the posterior subclavian ganglion and peripheral nerve fibers of the upper forelimb of the newt Triturus. The populations of vesicles and granules in normal ganglion cells and nerve fibers were compared with those observed after limb transection. In normal neurons, clear vesicles range in size from 250 to 1000 Å in diameter, but are most frequently 400–500 Å. Vesicles with dense contents (granules) also vary greatly in size, but most are 450–550 Å in diameter and correspond to dense-core vesicles. Large granules that contain acid phosphatase activity are thought to be lysosomes. During limb regeneration, in both the ganglion cells and peripheral nerves, the ratio of dense vesicles to clear vesicles increases. There is a large increase in number of dense granules with a diameter over 800 Å, particularly in the peripheral regenerating fibers. This study shows that regenerating neurons differ from normal in their content of vesicular structures, especially large, membrane-bounded granules.This work was supported by grants from the National Science Foundation (GB 7912) and from the National Cancer Institute (TICA-5055), National Institutes of Health, United States Public Health Service.     

Zur Ultrastruktur der Chromatophorenmuskelzellen von Loligo vulgaris

Zusammenfassung Die Innervation der braunen, roten und gelben Chromatophoren von Loligo vulgaris ist quantitativ und qualitativ verschieden. In den begleitenden Nervenbündeln finden sich stets Axone mit hellen (etwa 300 Å Ø), gelegentlich auch solche mit dense-core-Vesikeln (etwa 600 Å Ø).Die Myofilamente der kontraktilen Rinde sind gegeneinander versetzt und um die Längsachse spiralig gewunden. Im axialen Sarkoplasma treten gebündelte, in Längsrichtung zur Muskelzelle orientierte Filamente auf (jedes etwa 70 Å Ø), die möglicherweise eine Funktion bei der tonischen Kontraktion erfüllen.

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The ultrastructure of chromatophore muscle cells in Loligo vulgaris

Summary The innervation of the brown, red and yellow chromatophore muscle cells in Loligo vulgaris shows quantitative and qualitative differences. The nerve bundles regularly contain axons with electronlucent vesicles of about 300 Å diameter, and occasionally axons with dense core vesicles of about 600 Å diameter. The myofibrils of the contractile cortex show a staggered arrangement and are wound in a spiral with respect to the axis of the muscle cell. In the axial sarcoplasm there is additionally a bundle of thin filaments of about 70 Å thickness. The bundle is orientated in parallel with the longitudinal axis of the muscle cell. Its function may be to maintain tonic contractions.

Mit Unterstützung durch die Deutsche Forschungsgemeinschaft.     

Fine structure of smooth muscle and neuromuscular junctions in the foot of Helix aspersa

Summary The smooth muscle cells in the foot of Helix aspersa are arranged in bundles which interweave to form a complex mesh. In the peripheral cytoplasm of the muscle cells there is a system of interconnected obliquely and longitudinally orientated tubules. The full extent of this system has not been determined; its possible function in relation to Ca⁺⁺ storage and excitation-contraction coupling is discussed. Longitudinal tubules are present among the myofilaments and in association with mitochondria. Distributed throughout the myofilaments are elliptically shaped dense bodies, the fine structure of which resembles an accumulation of thin filaments. Located on the plasma membrane of the muscle cells are dense areas; the fine structure and relationships of these cellular elements resemble desmosomes. They may serve as attachment points for thin, cytoplasmic filaments (not necessarily myofilaments). The muscle cells are innervated by axons which diverge from a coarse, neural plexus (the sole plexus). The axons initially come into close contact with the muscle cells and then pass over their surfaces for up to 35 before being gradually enveloped by flange-like protrusions of the muscle cells. These axons contain either, (i) agranular vesicles (600 Å in diameter), (ii) agranular and very dense granular vesicles (1000 Å in diameter) or (iii) agranular and less dense, granular vesicles (1000 Å in diameter). The possible role of these inclusions as sites of excitatory and inhibitory transmitters is discussed.I wish to thank Professor G. Burnstock for making laboratory facilities available. This work has been supported by the Australian Research Grants Committee.     

Filaments and microtubules in the cytoplasm of the granulosa cells from the human follicle

Summary The cytoplasm of granulosa cells in human primordial follicles from normal women shows a system of filaments and microtubules. Filaments about 70–150 Å in diameter and several m in length can be seen as bundles or irregularly distributed. Microtubules about 200 Å in diameter are predominantly oriented in paranuclear regions. The relationships between cytoplasmic filaments and microtubules in granulosa cells and those of Sertoli cells are briefly discussed.     

Electron microscopical observations on the brush border of proximal tubule cells of mammalian kidney

Summary The ultrastructure of the plasma membrane and the core of microvilli of proximal tubule cells has been investigated by electron microscopy using sectioned and negatively stained material. By the technique of negative staining, a particulated coat is disclosed on the outside of the plasma membrane of microvilli of brush borders isolated from rat, rabbit and ox. This coat is composed of 30 to 60 Å particles and is 150 to 300 Å thick and appears to be a distinguishing feature for the luminal plasma membrane (brush border) of proximal tubule cells. The plasma membrane of the basal part of tubule cells is found to be smooth. By thin sectioning, an axial bundle of 50 to 70 Å diameter filaments regularly arranged in an 1+6 configuration, one axially located filament being surrounded by a ring of six, is disclosed. The distance from the ring of filaments to the inner surface of the plasma membrane is 250–300 Å, the diameter of the ring 300 Å and the center-to-center distance between filaments 120 Å. Negative staining also discloses 60 Å filaments in microvilli of isolated brush borders. Broken off, single microvilli (fingerstalls) are observed with thin filaments projecting from their broken ends. Filaments up to 1 in length are seen. At high magnification, the filaments appear beaded and show strong resemblance with actin filaments isolated from skeletal muscle. Based on present evidence, it is postulated that microvilli constituting renal brush borders possess contractile properties, which may play a role in the absorption process operating at the luminal part of the cells.The authors are indebted to Miss Kirsten Sjöberg for skilled technical assistance, and to the Danish State Research Foundation and the Tuborg Foundation for financial support.     

Electron microscope researches on the ultrastructure of nucleoli in animal tissues

Summary On the basis of electron microscopy of nucleoli in various physiological stages of similar and different cells, it is assumed that the nucleolonemata appear for the first time in the pre-mitotic stage and subsequently the nucleolus-associated body makes its appearance.The nucleolonema is composed of helically coiled filaments 50 Å in diameter.The nucleolus-associated body comprises tightly packed filaments about 15–30 Å thick which are helically coiled.     

Ultrastructure of the neurohaemal region of the toad median eminence

Summary According to the internal structure and size of the granules, six types of nerve endings can be distinguished in the toad median eminence: 1. Endings containing mostly dense granules of 600 Å in diameter; 2. Endings containing dense granules of about 800 Å in diameter; 3. Endings which contain dense granules 1,000–2,000 Å in diameter, with the peak at 1,200–1,400 Å; 4. Endings containing granules with a characteristic structure, which differentiate them from the other three types; 5. Scarce endings containing granules 2,000 to 3,800 Å in diameter; and 6. Endings containing only vesicles 400–500 Å in diameter. Types 3 and 4 endings are mainly found in the outer pericapillary zone, and are probably responsible for the strong Gomori-positive reaction observed in this zone. The other four types of endings occur mainly in the inner pericapillary zone, and appear to be Gomori-negative.The probable origins of the different types of endings, and their possible relations with the different releasing factors is discussed.The subendothelial basement membrane has numerous long processes which form a complicated network in contact with all the nerve endings, some nerve fibres and glial cells.Two types of glial cells are described. Pinocytotic vesicles are frequently seen at the points where these cells contact the basement membrane. All the ultrastructural features suggest that these cells are carrying out transport functions.Fellow of the Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina.The author is very grateful to Professor H. Heller for his continued encouragement and criticism and to Mr. J. Lane and Mr. P. Heap for their valuable help.     

Ultrastructural Studies of the Development of Nerves in Hydra

Three types of mature epidermal neurons and several of theirdifferentiating stages aie presented in this ultrastructuralstudy. Each of the three types, neurosensory, neurosecretory,and ganglionic cells, is derived from interstitial cells, (i)Mature neurosensory cells contain elongated nuclei, a well-developedcilium in each cell, and membrane-bounded neurosecretory droplets(700–1300 A in diameter). There may be two or more neuritesin which are numerous microtubules, glycogen particles, ribosomesand many neurosecretory droplets, (ii) Mature neurosecretorycells closely resemble neurosensory cells, except that no ciliumis present. The perikarya contain small, dense nuclei, neurosecretorydroplets (850–1300 A in diameter), mitochondria, glycogenparticles, and microtubules. Active Golgi complexes are presentin both cell types. The nemites are similar to those describedfor neurosensory cells, (iii) Mature ganglionic cells are bipolaror multipolar. The small, dense nuclei are surrounded by a smallamount of cytoplasm. The neurites contain mostly microtubules;a few mitochondria, ribosomes, and glycogen particles are alsopresent, but there are no secretory droplets. To date, only neurosensory and neurosecretory cells have beenobserved in the gastiodermis. They are structurally indistinguishablefrom their epideimal counterparts. A significant finding is that three types of synapses—neuromuscular,neuronematocyte, and interneuronal—are identified in boththe epidermal and gastrodermal neurons.     

Sieve structure of slit diaphragms of podocytes and pore cells of gastropod molluscs

Summary The ultrastructure of the slit diaphragms between the pedicels of the podocytes of the prosobranch Viviparus viviparus and between the cytoplasmic tongues of the haemocyanin producing pore cells of the pulmonate Lymnaea stagnalis was investigated. In both cell types 2 diaphragms are present in the slits. They form a 3-dimensional sieve structure with holes of respectively 90 × 110 Å (podocyte) and 200 × 220 Å (pore cell). Injection experiments showed that the size of the holes of the pore cell sieve matches that of particles which can be ingested by this cell type. The substructure of the sieves of the molluscs is compared to that of the 2-dimensional sieve of the podocytes of the mouse and the rat.The authors thank Mrs. J.E. Vlugt-van Dalen for technical assistance and Mr. G.W.H. van der Berg for drawing the diagrams. Thanks are furthermore due to Miss B.E.C. Plesch for correcting the English text     

Ultrastructure of the neurosecretory system of the Colorado potato beetle,Leptinotarsa decemlineata (Say)

Summary The ultrastructure of seven types of neurosecretory cells (NSC) in the medial and lateral groups of the protocerebrum is described. The differences among cell types established earlier by light microscopy parallel differences in size and appearance of the neurosecretory particles observed in electron micrographs. No relationship was found between the affinity for Gomori's paraldehyde fuchsin stain and the nature of the particles.The secretions of the A-, A₁-, and C-types of NSC of the medial group are characterized by electron-dense neurosecretory granules of 1250 Å dia., medium-dense granules of 2100 Å, and electron-lucent vesicles of 1700 Å, respectively. The L-type NSCof the lateral group contain smaller (1300 Å) or larger (1700 Å) neurosecretory granules. The medial B- and E-types of NSC and the lateral L_B-type contain granulated vesicles (1200 Å) of the same appearance. These cell types differ in other respects and most likely have separate functions.The author wishes to thank the Laboratory of Virology of the Agricultural University for the use of the electron microscope, Mr. J. Groenewegen and Miss J. van Rinsum for technical assistance, and Professor J. Lattin for correcting the English text. Part of the work has been done while the author was in the service of the Netherlands Organization for the Advancement of Pure Research (ZWO, grant 942-48), and the National Council for Agricultural Research (TNO).     

The fine structure of the hypothalamic secretory neurons of the White-crowned Sparrow,Zonotrichia leucophrys gambelii (Passeriformes: Fringillidae)

Summary The fine structures of the neurons and neuropils of the magnocellular supraoptic nucleus and the parvocellular nuclei of the rostral hypothalamus, including the suprachiasmatic and medial, lateral and periventricular preoptic nuclei, and the neuronal apparatus of the organum vasculosum laminae terminalis, have been examined in the male White-crowned Sparrow, Zonotrichia leucophrys gambelii, by correlated light and electron microscopy.The magnocellular supraoptic nucleus is characterized by large neurosecretory perikarya which contain a well developed Golgi complex and densecored granules 1,500–2,200 Å in diameter. The neuropil displays axons, dendrites and glial fibers. Some axonal profiles contain dense-cored vesicles 800–1,000 Å in diameter and clear vesicles 500 Å in diameter. Axo-somatic and axo-dendritic synapses are conspicuous in this nuclear region.The suprachiasmatic nucleus is characterized by an accumulation of small neurons with moderately developed cellular organelles and some dense-cored granules, approximately 1,000 Å in diameter. The profiles of axons within the neuropil contain dense-cored granules 800–1,000 Å in diameter and clear vesicles 500 Å in diameter.The neurons of the medial preoptic nucleus are relatively large and exhibit well developed cellular organelles and dense-cored granules 1,300 to 1,500 Å in diameter. Granular materials are formed within the Golgi complex. The medial preoptic nucleus is rich in secretory perikarya.Occasionally, neurons with granules 1,500–2,200 Å in diameter are encountered in the lateral preoptic and periventricular preoptic nuclei. They may be considered as scattered elements of the magnocellular (supraoptic and paraventricular) system.The organum vasculosum laminae terminalis consists of three layers, i.e., ependymal, internal and external zones, and exhibits a vascular arrangement similar to that of the median eminence. The perikarya of the parvocellular neurons and their axons in the internal zone contain numerous secretory granules ranging from 1,300 to 1,500 Å in diameter.This investigation was supported by Grant No. 5R040 Japan-U.S. Cooperative Science Program of the Japan Society for the Promotion of Science to Professor H. Kobayashi and Professor S.-I. Mikami, by a Scientific Research Grant No. 56019 from the Ministry of Education of Japan to S.-I. Mikami, by support from the Deutsche Forschungsgemeinschaft (Schwerpunktprogramm Biologie der Zeitmessung) to Prof. A. Oksche and by Grant No. GF 33334, U.S.-Japan Cooperative Science Program of the National Science Foundation to Prof. D.S. Farner.Herrn Professor Dr. Dres h.c. Wolfgang Bargmann zu seinem 70. Geburtstag am 27. Januar 1976 gewidmet.     

Actin filaments: the main components of the scolopale in insect sensilla

Summary Two types of insect sensilla, mechanosensitive scolopidia and thermo-/hygrosensitive poreless sensilla contain a scolopale, which consists of numerous microtubules embedded in bundles of filaments (7–10 nm in diameter). The bundles are readily seen in the electron microscope in cryofixed (high-pressure freezing and rapid injection) and substituted samples. The filaments can be identified as actin filaments by using fluorescent phalloidins. Both electron microscopy and Triton-extraction exeriments reveal mechanical linkage between the main components in both types of sensilla. Since myosin appears to be absent in the scolopale, the actin filaments are unlikely to be involved in any contraction mechanism; these filaments more probably provide mechanical stability. The functional properties of the scolopale are discussed.     

Entstehung und Ultrastruktur der Biondi-Körper in den Plexus chorioidei des Menschen (Biopsiematerial)

Zusammenfassung Bei 50–60jährigen Menschen enthält das Plexusepithel Einschlüsse (Biondi-Körper), die als Zeichen einer Alterung gelten. Elektronenmikroskopisch bestehen sie aus einer fibrillären Komponente und verschiedenartigen tropfigen (Lipid) oder granulären (u.a. Lipofuszin) Strukturen. Nach Frühstadien solcher Komplexe wurde im Seitenventrikel-plexus (Biopsiematerial) 20–30 Jahre alter Personen gefahndet. In dieser Altersgruppe haben wir nur Lipidtropfen, Lysosomen, stark osmiophile Partikel und Konglomerate dieser Einschlüsse beobachtet; die für ältere Menschen charakteristischen Filamentbündel (Fasern) ließen sich bisher nicht nachweisen. Das Plexusepithel einer 54jährigen Frau war reich an verschiedenen Entwicklungsstadien fibrillärer Biondi-Strukturen. Aus 80–100 Å starken Filamenten bestehende Bündel können frei im Grundplasma der Plexuszelle liegen; ähnliche Filamente trifft man auch innerhalb von großen lysosomenartigen Körpern an. Solchen Fasern bzw. Lysosomenkomplexen lagern sich Lipidtropfen, kleinere elektronendichte Cytosomen und Lipofuszingranula an. Einzelne Filamente sind quergestreift, mit einer Periode von etwa 40–50 Å und globulären Untereinheiten (Durchmesser etwa 25 Å). Nach Färbung mit Kongorot sind die Biondi-Fasern stark doppelbrechend; ein Teil dieses Materials leuchtet grün, andere Faserstrukturen zeigen einen gelben Farbton. Diese Merkmale entsprechen den Strukturcharakteristika von Amyloidfasern. Auf den Amyloidcharakter der Biondi-Einschlüsse haben bereits Divry (1955) und Schwartz (1970) hingewiesen; immunbiologische Aspekte ihrer Entstehung sind zu diskutieren. Einzelne Biondi-Einschlüsse können auch in den Liquor cerebrospinalis austreten. Gebilde, die an die nichtfibrilläre Komponente der Biondi-Körper erinnern, wurden auch im Endothel und in den Pericyten der Plexusgefäße dargestellt.

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Formation and ultrastructure of Biondi bodies in the human choroid plexus (biopsy material)

Summary The choroid epithelium of 50–60-year old persons contains inclusions known as Biondi bodies. These inclusions have been presumed to be signs of aging. Electron microscopic studies have shown that mature Biondi bodies contain filaments, various droplets, and dense granular structures. The vesicular inclusions are identified as lipid droplets; lipofuscin pigment may be associated with lysosomes. In the present studies, in order to analyse the early stages of formation of Biondi bodies, we investigated biopsy material from 20–30-year old persons. In this age group, we observed lipid bodies, lysosomes, osmiophilic particles, and complexes of these structures, but not the filament bundles that were characteristically present in older persons. In a 54-year-old female, the choroid epithelium contained different forms and stages of Biondi fibers. Some groups of filaments of 80–100 Å mean diameter were seen in cytoplasm; others were located in large lysosome-like bodies. Both types of inclusions were associated with lipid droplets, small electron-dense cytosomes and lipofuscin pigment granules. Some filaments showed cross-striation with about 40–50 Å periodicity and globular subunits measuring about 25 Å in diameter. In sections stained with Congo red, the Biondi fibers were strongly birefringent and displayed green or yellow colors. These data are in agreement with the morphological and physical characteristics of human amyloid fibrils and filaments. It has been suggested by Divry (1955) and Schwartz (1970) that Biondi bodies contain amyloid deposits. Immunobiological aspects should therefore be considered in relation to the formation of Biondi bodies. Evidence has been found in our material that single Biondi bodies may be extruded into the cerebrospinal fluid. Further, structures resembling the vesicular and granular components of Biondi bodies were observed in the endothelium and pericytes of the choroid vessels.

Mit Unterstützung durch die Deutsche Forschungsgemeinschaft.     

Ultrastruktur glycerinextrahierter Dünndarmmuskelzellen der Ratte vor und nach Kontraktion

Zusammenfassung Die Tunica muscularis des Dünndarms der Ratte wurde elektronenmikroskopisch vor und nach Glycerinextraktion und nach verschieden lang andauernder ATP-Behandlung untersucht. Vor und nach der Extraktion sind nur 50–80 Å breite F-Actin-Filamente in den glatten Muskelzellen nachzuweisen. Die extrahierten glatten Muskelzellen kontrahieren sich nach Zugabe von ATP. Gleichzeitig treten in der Längsrichtung der Zelle verlaufende 150–200 Å dicke Myosinfilamente auf. Während langanhaltender Inkubation mit ATP trennen sich Actin- und Myosinfilamente zunächst voneinander durch eine Art Gleitmechanismus, da die Actinfilamente noch an der Zellmembran verhaftet bleiben, die Myosinfilamente sich aber verschieben. Dann lösen sich die Actinfilamente von der Zellmembran und Actin- und Myosinfilamente bilden ein dichtes Netzwerk im Zentrum der Zelle. In der Umgebung dieses Netzwerkes verbleiben feine Filamente mit einem Durchmesser von 20–30 Å.

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Ultrastructure of glycerinated small intestine muscle cells of the rat before and after contraction

Summary Tunica muscularis of the rat's small intestine was studied electron microscopically before and after glycerol-extraction and at various times after ATP treatment. Before and after extraction only F-actin-filaments with a diameter of 50–80 Å could be found in smooth muscle cells. Dense bodies disappear during extraction. Glycerinated smooth muscle cells contract when ATP is added. At the same time thick filaments with a diameter of 150–200 Å appear, which probably represent myosin filaments, running longitudinally within the cells. During prolonged ATP treatment actin and myosin filaments first separate from each other by a sort of sliding mechanism because actin filaments are still bound to the cell membrane while myosin filaments move. Then actin filaments are drawn off from the cell membrane and actin and myosin filaments assemble in an intricate network of filaments in the central part of the cell. Around this network fine filaments with a diameter of 20–30 Å remain.

Für die technische Mithilfe danke ich Frau Karla Struwe.     

Tubuläre intranukleäre Einschlußkörper beiLinaria vulgaris,L. alpina (Scrophulariaceae) undIncarvillea variabilis (Bignoniaceae)

The epidermal nuclei of the ovary inLinaria vulgaris andL. alpina, and the nuclei in leaves ofIncarvillea variabilis often contain crystalloid, tubular inclusions. The tubuli in bothLinaria species have an average diameter of 200 Å with a width of 70 Å in the clear and are arranged in a higly organized manner: Parallel tubuli form layers which build up a crystal lattice. There are three directions of tubuli in each inclusion: In each layer they are aligned in an angle of 60° to those of the next, so that the tubuli of the fourth layer are in the same direction as those of the first one. InIncarvillea the tubuli (each with an average diameter of 220 Å, and 70 Å width in the clear) also exhibit compact packing, but their arrangement is not so highly ordered as inLinaria.