The extracellular matrix of the cuticle of Gordius panigettensis (Gordioiidae,Nematomorpha): observations by TEM,SEM and AFM

The cuticle of Gordius panigettensis (Sciacchitano, 1955) was studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and atomic force microscopy (AFM). The cuticle is composed of 30-50 compact layers. The number of the layers is higher in the central part of the animal's body and decreases at the extremities. Each layer is composed of parallel tightly packed fibres approximately 640 nm in diameter and of indefinite length. The fibres run strictly parallel within each layer, while in adjoining layers they run at a variable angle from 45 degrees in the central body to 90 degrees in the extremities. Each fibre shows a barely detectable filamentous inner structure and is enveloped in a thin highly regular net formed by hexagonal meshes. Our results suggested that these fibres should be proteinaceous although non-collagenous. Thinner radial fibres run among the large fibres and across all the layers and span the whole thickness of the cuticle from the epithelial layer located deep underneath the large fibres up to the epicuticle on the external surface of the animal.     

Structure and distribution of fibre types in the external eye muscles of the rat

Rat extraocular muscles are composed of two layers differing in muscle fibre diameter. In both layers multiply innervated fibres are found besides focally innervated ones. Significant differences in internal structure thus demand further subtyping. The global layer (predominantly larger fibres) contains 10" 'clear' fibres (multiple innervation, medium size) and a spectrum of focally innervated fibres, from small 'dark' fibres (30%, abundant mitochondria) over 'intermediate' fibres (30%) to large 'pale' fibres (30 %, few mitochondria). The orbital layer (exclusively small fibres) contains 80% focally innervated 'dark' fibres and 20% extremely small 'clear' fibres with multiple innervation. An ultrastructural characterization of the fibre types is given and possible functional implications are discussed.     

Layer-specific innervation of the dopamine-deficient frontal cortex in weaver mutant mice by grafted mesencephalic dopaminergic neurones

Summary The dopamine innervation of the frontal cortex originates in the A9 and A10 mesencephalic dopamine cell groups. In weaver mutant mice, there is a 77% frontocortical dopamine deficiency associated with losses of dopamine neurones in areas A9 and A10. The dopamine-depleted cortical areas of weaver mutant mice are receptive to reinnervation by afferent fibres originating in dopamine-containing mesencephalic grafts from normal donor embryos. In the anteromedial frontal lobe, reinnervation by tyrosine hydroxylase immunoreactive fibres is largely confined to the basal cortical layers whereas in the anterior cingulate cortex, tyrosine hydroxylase immunoreactive fibres also occupy superficial layers, including the molecular layer. Normally, the dopaminergic innervation of the anteromedial frontal lobe is distributed among the basal cortical layers (IV–VI), and the dopaminergic innervation of the cingulate cortex occupies both basal and superficial cortical layers. The pattern of innervation following transplantation indicates that, in repopulating dopamine-deficient cortical areas of recipient weaver mutants, graft-derived dopamine fibres show a preference for those layers which are normally invested by dopamine afferents.     

The larval development of lateral musculature in gilthead sea bream Sparus aurata and sea bass Dicentrarchus labrax

Fibre-type differentiation of the lateral musculature has been studied in Sparus aurata (L.) and Dicentrarchus labrax (L.) during larval development. Histochemical and ultrastructural techniques show two presumptive muscle layers and two germinative zones of presumptive myoblasts. At hatching, myotomal muscle consists of a monolayer of thin undifferentiated cells near the skin (first germinative zone) overlying another mono-layer of small diameter fibres extending hypaxially and epaxially away from the transverse septum. Below this, there is a much thicker, deep layer of fibres, generally large in diameter and polygonal in shape. The presumptive myoblasts are located between these two layers of fibres in the second germinative zone. Initially, the superficial and deep muscle fibres show high and low myosin ATPase activity, respectively. Both layers grow by generating new fibres from the two mentioned germinative zones. At the end of larval life, the superficial layer changes its histochemical profile from high to low myosin ATPase activity and, at the same time, intermediate or pink muscle fibres can be observed by oxidative activity (the NADH-TR reaction). Morphometric analysis shows a significant increase in mean fibre diameter during successive ages, as shown by the Student's t-test (hypertrophic growth). Skewness and kurtosis values of fibre diameters point to the generation of a new fibre population from the germinative zones (hyperplastic growth).     

Distribution of peptide-containing neurons and endocrine cells in the rabbit gastrointestinal tract,with particular reference to the mucosa

Summary The distribution patterns of peptide-containing neurons and endocrine cells were mapped in sections of oesophagus, stomach, small intestine and large intestine of the rabbit, by use of standard immunohistochemical techniques. Whole mounts of separated layers of ileum were similarly examined. Antibodies raised against vasoactive intestinal peptide (VIP), substance P (SP), somatostatin (SOM), neuropeptide Y (NPY), enkephalins (ENK) and gastrin-releasing peptide (GRP) were used, and for each of these antisera distinct populations of immunoreactive (IR) nerve fibres were observed. Endocrine cells were labelled by the SP, SOM or NPY antisera in some regions.VIP-IR nerve fibres were common in each layer throughout the gastrointestinal tract. With the exception of the oesophagus, GRP-IR nerve fibres also occurred in each layer of the gastrointestinal tract; they formed a particularly rich network in the mucosa of the stomach and small intestine. Fewer nerve fibres containing NPY-IR or SOM-IR were seen in all areas. SOM-IR nerve fibres were very scarce in the circular and longitudinal muscle layers of each area and were absent from the gastric mucosa. The SP-IR innervation of the external musculature and ganglionated plexuses in most regions was rather extensive, whereas the mucosa was only very sparsely innervated. ENK-IR nerve fibres were extremely rare or absent from the mucosa of all areas, although immunoreactive nerve fibres were found in other layers.These studies illustrate the differences in distribution patterns of peptide-containing nerve fibres and endocrine cells along the gastrointestinal tract of the rabbit and also show that there are some marked differences in these patterns, in comparison with other mammalian species.     

Carapace and plastron sensitivity to touch and vibration in the tortoise (Testudo hermanni and T. graeca)

Neural impulses in response to tactile stimulation of the shell were recorded from afferent nerve fibres in tortoises ( T. graeca and T. hermanni). It was found that there is a mechanoreceptive innervation in the superficial layers of the shell which is sensitive to transient stimuli, particularly to vibration at frequencies up to 100 Hz. Receptive fields pertaining to single and small groups of individual afferent fibres were mapped: the fields were sharply circumscribed and distributed in relation to the scutes of the shell. The tactile innervation that was found would be consistent with a capacity for recognition and accurate localization of innocuous stimuli and may play a central role in courtship and mating behaviour.     

Distribution of GABA-like immunoreactive neurons in the optic lobes of Periplaneta americana

Summary Specific antisera against protein-conjugated -aminobutyric acid (GABA) were used in immunocytochemical staining procedures to study the distribution of the putative GABA-like immunoreactive neurons in the optic lobes of Periplaneta. GABA-like immunoreactive structures are evident in all three optic neuropil regions. Six different populations of GABAergic neurons, whose perikarya are grouped around the medulla, are found within the optic lobe. The number of these immunoreactive cells varies greatly and corresponds to the number of ommatidia of the eye. In the proximal part of the lamina, a coarse network of GABA-positive fibres is recognizable. These are the processes of large field tangential cells whose fibres pass through the distal surface of the medulla. A second fibre population of the lamina is made up of the processes of the centrifugal columnar neurons whose perikarya lie proximally to the medulla. The medulla contains 9 layers with GABAergic elements of variable immunoreactivity. Layers 1, 3, 5, 7 and 9 exhibit strong labelling, as a result of partial overlapping of the processes of centrifugal and centripetal columnar neurons, tangential fibres and/or lateral processes of perpendicular fibres and (possibly) processes of amacrines. A strong immunoreactivity is found in the proximal and distal layers of the lobula.     

Sexual dimorphism in the visual system of flies: The divided brain of male Bibionidae (Diptera)

Summary The mapping of the compound eyes onto the visual neuropils and the cell types in the lamina and the lobula complex of Bibionidae (Diptera) were studied by means of extracellular cobalt injections and Golgi impregnations. Dorsal and ventral eyes in males map into separate dorsal-and ventral neuropils up to the level of the lobula complex. The dorsal-eye lamina is unilayered, while the ventral-eye lamina in males and the lamina in females are multilayered: layers A and C are invaded by en-passant terminals of long visual fibres, layer B by the terminals of short visual fibres. Long visual fibres have a short and a long terminal in the ventral medulla with terminal specialisations in three distinct layers. Only one type of receptor ending exists in the dorsal medulla, the terminal branches of which are restricted to one layer only. Arrays of contralateral neurones are found in the medial part of the dorsal lobula, which receives input from the zone of binocular vision of the ipsilateral dorsal eye, and in the posterior dorsal lobula and lobula plate. The dorsal lobula plate contains large tangential neurones, the dendritic arborisations of which are revealed by cobalt injection into the thoracic ganglia. The divided brain of male bibionids offers the opportunity to investigate separately the nervous systems involved in sex-specific visually guided flight behaviour and in general visually guided flight control.     

The cuticle of the hoplocarid crustacean Squilla desmaresti Risso

The cuticle of Squilla desmaresti does not show a well-defined Balken structure as described by Krishnakumaran (1956) in S. holoschista . Parallel fibres follow curved courses of differing orientation in the horizontal plane, and successive layers of fibres are separated by laminar membranes of different chemical composition from the remainder of the cuticle.     

The ultrastructure of the cuticle of adult female Mermis nigrescens (Nematoda)

The ultrastructure of the cuticle of the adult female nematode Mermis nigrescens has been described. There is an epicuticle and three-layered membrane covering the cuticle. The cortex is penetrated by canals which extend from the surface of the cuticle to the matrix of the layer beneath the cortex. Beneath the cortex are two layers of giant fibres which spiral around the nematode, a thick layer containing a network of fibres and a basal layer containing a vacuolated matrix material. it is thought that the epicuticle is secreted from the canals in the cortex. The possible functions of the layers in the cuticle have been discussed and similarities with the cuticle of the Acanthocephala have been noted.     

The study of chromatin and chromosome structure on preparations of interphase nucleus derivatives resulting from nuclear wall removal.III Structural heterogeneity of chromatin and argyrophilic zone of the nucleolus in stretched membrane-free nuclei and chromatin bodies from human peripheral lymphocytes

Viewed by light microscopy, the majority of lymphocytes in smears of human peripheral blood display a deep staining (with any chromatin- or DNA-specific dye) of the nucleus consisting of densely aggregated chromatin in addition to one or several small nucleoli with a dot- or spot-like argyrophilic zone. Amembraneous nuclei and "free chromatin" structures were isolated from intact lymphocytes gently treated with Triton X-100. Surface stretching of both these nuclei and structures, shortly fixed in methanol--glacial acetic acid (3:1), resulted in spatial separation of thin and thick chromatin or argyrophilic fibres, nucleoli, intranuclear bodies, polymorphous aggregations of chromatin or argyrophilic fibres and incidentally observed splitted or beaded thick chromatin fibres and the chromocenter. The light microscopic pattern of chromatin fibres of stretched amembraneous nuclei, isolated from peripheral lymphocytes, well compares with that of deconvolved images of intact lymphocyte nucleus obtained with optical tomography.     

Serotonin-like immunoreactivity in the optic lobes of three insect species

The cellular localization of 5-HT in the optic lobes of three insect species was assayed with the use of antibodies raised against 5-HT. In Schistocerca, Periplaneta, and Calliphora all neuropil regions of the optic lobe, the lamina, medulla and lobula, contain 5-HT-immunoreactive varicose fibres in different patterns, like columns and layers. Such fibres also connect the lobula to neuropil in the lateral protocerebrum. In Calliphora also 5-HT-positive fibres of the medulla and lobula plate have projections to the lateral protocerebrum, whereas the origin of the lamina fibres is not certain. In all species the processes displaying 5-HT-like immunoreactivity appear to be derived from a relatively small number of cell bodies, each neuron thus having processes over a large volume of the neuropil of the optic lobe in different layers.     

Structure,composition and mechanical properties of the silk fibres of the egg case of the Joro spider, <Emphasis Type="Italic">Nephila clavata</Emphasis> (Araneae,Nephilidae)

The silk egg case and orb web of spiders are elaborate structures that are assembled from a number of components. We analysed the structure, the amino acid and fibre compositions, and the tensile properties of the silk fibres of the egg case of Nephila clavata. SEM shows that the outer and inner covers of the egg case consist of thick, medium and thin silk fibres. The silk fibres of the outer cover of the egg case are probably produced by the major and minor ampullate glands. The silk fibres of the inner cover of the egg case from cylindrical glands appears to be distinct from the silk fibres of the major ampullate glands based on their micro-morphology, mole percent amino acid composition and types, and tensile behaviour and properties. Collectively, our investigations show that N. clavata uses silk fibres from relatively few glands in varying combinations to achieve different physical and chemical properties (e.g., color, diameter, morphology and amino acid composition) and functional and mechanical properties in the different layers of the egg case.     

Hyolith-type microstructure in a mollusc-like fossil from the Early Cambrian of Yunnan, China

A phosphatized bilaterally symmetrical, spirally coiled conch from the Lower Cambrian phosphates of the Meishucunian Stage of eastern Yunnan, China, is composed of two well-preserved layers. The outer one is built of longitudinal mineralized fibres not strictly parallel to each other, but may anastomose or branch. The fibres form comarginal ribs with transversal grooves between them, corresponding to growth stages. In the ribs, the fibres are arranged closely and are steeply inclined towards the apex, while in the grooves the fibres are subparallel to the conch surface and more loosely packed. Small elliptic and triangular holes are situated within and between the fibres of the outer layer. The inner layer consists of transversal fibres running around the conch. They are almost parallel to each other but partly separated by narrow discontinuous slits. Despite overall morphological similarity of the conch to shells of some early Cambrian molluscs, the observed orthogonal configuration of longitudinally oriented fibrous structures of the outer layer and transversal fibres of the inner layer is found in orthothecid hyoliths, phosphatized microstuctures of which have been described from the Lower Cambrian of the Siberian Platform. The new material from the Yangtze Platform supports a conclusion of a distinctive type of microstructure available in hyoliths different from molluscan microstructures available from the Lower Cambrian.     

A unique cross section through the skin of the dinosaur Psittacosaurus from China showing a complex fibre architecture

This paper reports on a unique preservation of soft tissues in the ventrolateral region of the plant-eating dinosaur Psittacosaurus from the Jehol biota of China. The preservation is of a deep cross section through the dermis, which includes multiple layers of collagenous fibres in excess of 25, among the highest recorded in vertebrates, with a further 15 more layers (poorly preserved) estimated for the entire height of the section. Also, for the first time in a dinosaur two fibre layers parallel to the skin surface are preserved deep within the dermis at the base of the cross section. These fibre layers comprise regularly disposed fibres arranged in left- and right-handed geodesic helices, matching the pattern at the surface and reasonably inferred for the entire section. As noted from the studies on modern-day animals, this fibre structure plays a critical part in the stresses and strains the skin may be subjected to and is ideally suited to providing support and protection. Psittacosaurus gives a remarkable, unprecedented understanding of the dinosaur skin.     

A scanning and transmission electron microscopic study of the membranes of chicken egg.

Questions regarding the structure of the inner and outer shell membranes of the chicken egg were addressed in this study by correlating observations from light microscopy and scanning and transmission electron microscopy. The egg membrane had a limiting membrane, which measured .9 to .15 microns in thickness and appeared to be a continuous and an impervious layer, but the shell membrane did not. Under the SEM, each membrane was seen to be made up of several fibre layers. In the tear preparations viewed under the SEM two layers were observed in the egg membranes and three to five layers in the shell membrane, with an apparent plane of cleavage between each layer. Each fibre was made up of a central core and an outer mantle layers. The central core was perforated by channels which measured .08 to 1.11 microns in diameter and ran longitudinally along the length of the fibre. Between the mantle layer and the fibre core was a gap or cleft measuring between .03 to .07 microns. The diameter of the fibres of the inner layer of the egg membrane ranged between .08 to .64 microns, whereas those of the outer layer of the same membrane ranged from .05 to 1.11 microns. Fibres in the shell membrane ranged from .11 to 4.14 microns diameter.     

Fibre organization and reorganization in the retinotectal projection of Xenopus

This study concerns the retinotopic organization of the ganglion cell fibres in the visual system of the frog Xenopus laevis. HRP was used to trace the pathways taken by fibres from discrete retinal positions as they pass from the retina, along the optic nerve and into the chiasma. The ganglion cell fibres in the retina are arranged in fascicles which correspond with their circumferential positions of origin. Within the fascicles the fibres show little age-related layering and do not have a strict radial organization. As the fascicles of fibres pass into the optic nerve head there is some exchange of position resulting in some loss of the retinal circumferential organization. The poor radial organization of the fibres in the retinal fascicles persists as the fibres pass through the intraocular part of the nerve. At a position just behind the eye there is a major fibre reorganization in which fibres arising from cells of increasingly peripheral retinal locations are found to have passed into increasingly peripheral positions in the nerve. Thus, fibres from peripheral-most retina are located at the nerve perimeter, whilst fibres from central retina are located in the nerve core. It is at this point that the radial, chronotopic, ordering of the ganglion cell axons, found throughout the rest of the optic pathway, is established. This annular organization persists along the length of the nerve until a position just before the nerve enters the brain. Here, fibres from each annulus move to form layers as they pass into the optic chiasma. This change in the radial organization appears to be related to the pathway followed by all newly growing fibres, in the most superficial part of the optic tract, adjacent to the pia. Just behind the eye, where fibres become radially ordered, the circumferential organization of the projection is largely lost. Fibres from every circumferential retinal position, which are of similar radial position, are distributed within the same annulus of the nerve. At the nerve-chiasma junction where each annulus forms a single layer as it enters the optic tract, there is a further mixing of fibres from all circumferential positions. However, as the fibres pass through the chiasma some active pathway selection occurs, generating the circumferential organization of the fibres in the optic tract. Additional observations of the organization of fibres in the optic nerve of Rana pipiens confirm previous reports of a dual representation of fibres within the nerve. The difference in the organization of fibres in the optic nerve of Xenopus and Rana pipiens is discussed.     

The intermediate filament protein peripherin is a marker for cerebellar climbing fibres

Immunocytochemical staining with antibodies to the class III intermediate filament protein peripherin reveals discrete subpopulations of neurons and nerve fibres throughout the rat central nervous system. Some of these fibres enter the cerebellar granular and molecular layers. Here we use light and electron microscopic immunocytochemistry and confocal fluorescence microscopy to identify the peripherin positive fibres in the molecular layer of the cerebella of various mammals. 1) The peripherin positive fibres in the molecular layer have morphological attributes of climbing fibres, and peripherin positive fibres are also detected in the olivo-cerebellar tract. Furthermore peripherin positive neurons can be seen in the inferior olive, from which climbing fibres originate. (2 ) The peripherin positive molecular layer fibres rapidly degenerate in rats treated with 3-acetylpyridine (3-AP), a reagent which destroys neurons in the inferior olive, and the time course of degeneration of these mirrors that previously described for 3-AP induced destruction of climbing fibres. (3) Cerebella of other mammal species tested (mouse, rabbit, pig, cow and human) revealed a similar peripherin staining pattern in the cerebellum, including fibres in the molecular layer with the morphology of climbing fibres. (4) We also noted peripherin positive spinocerebellar and vestibulocerebellar mossy fibres in the cerebellar granular layer of folia known to receive these inputs. (5) A subset of perivascular nerve fibres are also peripherin positive. These results show that peripherin is a useful marker for mammalian cerebellar climbing fibres, and that a subset of morphologically distinct cerebellar mossy fibres are also peripherin positive.     

The ultrastructure and vascular supply of the different fibre types in the axial muscle of the sturgeon Acipenser stellatus,Pallas

Summary The ultrastructure and vascular supply of the different fibre types in the lateral muscles of the sturgeon Acipenser stellatus were studied by light- and electron microscopy and morphometry. Three fibre types form separate layers without intermingling. The red fibres are superficial, the white fibres deep and the intermediate fibres between them. From morphometric analyses, the mitochondrial volume fraction in red fibres is 30%, in intermediate fibres 3.7% and in white fibres 0.7%. Z lines are most fuzzy in the red fibres. Triads of the sarcotubular system are always situated at the level of the Z discs. In red fibres the three elements are arranged in a series along the myofibrils, whereas in white fibres they are arranged transversely and in the intermediate fibres they are aligned obliquely. The number of capillaries surrounding each fibre is 2.3, 0.9 and 0.2 for the red, intermediate and white fibres, respectively. In red fibres 16% of the surface is directly covered by capillaries. The corresponding percentages for intermediate and white fibres are 5 and 1, respectively. Per unit volume of the fibre, the directly vascularised fibre surface in red fibres is about ten times larger than that of white fibres.The degree of vascularisation of the fibre types is directly related to the volume fraction of mitochondria, and thus to their aerobic capacities.     

Alcuni Aspetti Della Variabilità Del Legno Secondario Di Un Esemplare Di Prunus Persica Stokes

Abstract

Some aspects of the variability in wood structure of a specimen of PRUNUS PERSICA Stokes. — The secondary xylem of a young stem of Prunus persica Stokes has been investigated under three main headings: 1) vessel and fibre length; 2) intrusive fibre growth; 3) relative amount of libriform fibres, fibretracheids and tracheids.

Vessel members and fibres have been reckoned from single rings and from the whole wood body.

The relation between the above mentioned dimensions and the position within the wood body and the width of the growth layers has been calculated.

No remarkable variation has been found along the axis of the stem; on the contrary there is a decrease in both fibres and vessels length along the radius of the stem from inside outwards. Such behaviour having never been recorded before, the possible causes are suggested.

A positive correlation has been found between the width of the growth layers and 1) vessel members and fibres length, 2) fibre intrusive growth, 3) percentage of libriform fibres. In addition a relative correlation between percentage of libriform fibres and age of the cambium has been put in evidence.