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PubMed2007

Layer frustration, polar order and chirality in liquid crystalline phases of silyl-terminated achiral bent-core molecules.

A novel class of bent-core molecules with oligo(siloxane) or carbosilane units at both ends was synthesized and the self-organization of these molecules was investigated by polarizing microscopy, DSC, X-ray scattering, dielectric and electrooptical methods. Depending on the size of the silicon-containing segments, smectic and columnar liquid crystalline phases are formed. Most smectic phases are low birefringent and composed of macroscopic domains of opposite handedness (dark conglomerate phases). The switching process in these smectic phases is surface stabilized ferroelectric and, depending on the conditions, two distinct slow relaxation processes to nonpolar structures were observed. It is proposed that the smectic phases are built up by chiral and polar SmCsPF layer stacks which are separated by anticlinic interfaces. If the size of these layer stacks is sufficiently large a coupling to the substrate surfaces takes place and ferroelectric switching is observed. It is also suggested that the sponge-like layer distortion, occurring in the low birefringent mesophases, is due to an escape from the local polar order within these SmCsPF layer stacks. For compounds with larger silylated units a steric frustration arises, which leads to layer modulation (columnar ribbon phases) and this is associated with a transition from ferroelectric to antiferroelectric switching. All compounds show a switching of the molecules around the long axis which reverses the layer chirality.

Journal Article↗
PubMed2001

Laminar organization of the pyramidal cell layer of the subiculum in the rat.

The distribution of neurons in the subiculum of the rat that give rise to subcortical connections was studied using retrograde labeling with horseradish peroxidase conjugated to wheat germ agglutinin. Injections were made into the anteroventral thalamic nucleus, the medial mammillary nucleus, the nucleus accumbens, and the lateral septal nucleus. To facilitate the analysis, the hippocampal formation with adjacent cortices were "flattened," which allowed the cutting of sections perpendicular to the full septotemporal axis. Cells projecting to the anteroventral thalamic nucleus (AV cells), the medial mammillary body (MMB cells), and the nucleus accumbens (ACC cells) were observed consistently throughout the entire septotemporal (dorsoventral) and transverse extent of the subiculum (from field CA1 of the hippocampus to the presubiculum). In the transverse plane, the three kinds of projection cells were arranged in a laminar fashion: The AV cells were observed in the deepest portion of the subicular pyramidal cell layer, the ACC cells were observed in the most superficial portion of the layer, and the MMB cells were observed in the middle portion of the layer. Although this laminar arrangement was observed at all septotemporal levels of the subiculum, it was most apparent at the septal level. At more temporal levels, the "laminae" shifted such that the superficially located ACC cells were more prominent in the proximal half of the subiculum, whereas the AV cells were shifted toward the distal half of the subiculum. The average size of somata of the AV cells was 72.3 microm(2), that of the ACC cells was 105.2 microm(2), and that of the MMB cells was 121.8 microm(2). The connectional and cytoarchitectonic data indicate that there is a distinct sublamination of the subicular pyramidal cell layer, suggesting that the subiculum may be analogous to the infragranular layer (layers V and VI) of the isocortex.

Animals↗
PubMed2004

Target-specific differences in somatodendritic morphology of layer V pyramidal neurons in rat motor cortex.

Dendritic geometry has been shown to be a critical determinant of information processing and neuronal computation. However, it is not known whether cortical projection neurons that target different subcortical nuclei have distinct dendritic morphologies. In this study, fast blue retrograde tracing in combination with intracellular Lucifer yellow injection and diaminobenzidine (DAB) photoconversion in fixed slices was used to study the morphological features of corticospinal, corticostriatal, and corticothalamic neurons in layer V of rat motor cortex. Marked differences in the distribution of soma, somal size, and dendritic profiles were found among the three groups of pyramidal neurons. Corticospinal neurons were large, were located in deep layer V, and had the most expansive dendritic fields. The apical dendrites of corticospinal pyramidal neurons were thick, spiny, and branched. In contrast, nearly all corticostriatal neurons were small cells located in superficial layer V. Their apical dendritic shafts were significantly more slender, though spiny like those of corticospinal neurons. Corticothalamic neurons, which were located in superficial layer V and in layer VI, had small or medium-sized soma, slender apical dendritic shafts, and dendrites that were largely spine free. This study indicates that, in layer V of rat motor cortex, each population of projection neurons has a unique somatodendritic morphology and suggests that distinct modes of cortical information processing are operative in corticospinal, corticostriatal, and corticothalamic neurons.

Animals↗
PubMed1976

Early formation of synapses in the molecular layer of the fetal rat cerebellum.

The initial phase of synaptogenesis in the molecular layer of the albino rat cerebellum has been studied quantitatively and qualitatively with the electron microscope. Using both aldehyde-osmium (AL-OS) and ethanolic phosphotungstic acid (E-PTA) preparations, synapses were observed as early as embryonic day 19 throughout the entire rostro-caudal extent of the vermal molecular layer. The undeveloped nature of the elements participating in the formation of these synapses precluded their identification, for at this stage of cerebellar development, the Purkinje cells have not developed characteristic dendrites and both the massive production of cells within the external granule layer and the migration of neuroblasts through the molecular layer are in their initial phases. Evidence of synapse formation at this early stage of molecular layer development indicates that the rudiments of neuronal systems are present before the bulk of the molecular layer has come into existence and before most of the constituent elements of the cerebellum have differentiated. From embryonic day 19 to embryonic day 22, the number of E-PTA synaptic contacts was always less than the number of AL-OS synapses. This decrepancy and the variations observed in the morphology of the presynaptic components of E-PTA stained synaptic contacts, indicate that E-PTA morphology, and particularly the development of presynaptic dense projections, represents a late stage of synapse formation.

Animals↗
PubMed1977

Aging of the rat olfactory bulb: growth and atrophy of constituent layers and changes in size and number of mitral cells.

A quantitative study of the rat olfactory bulb during aging was carried out by directly measuring or calculating the following parameters at 3, 12, 24, 27, and 30 months: The volume of the glomerular, external plexiform, and internal granular layers, a relative measure of the size of the olfactory nerve layer, the mean volume of mitral cell nuclei and perikarya, a relative measure of the mean volume of the mitral cell dendritic tree as well as the total length and mean cross-sectional area of its constituent dendrites, and number of mitral cells. In addition, measurements of the size and number of mitral cells in the accessory olfactory bulb were performed. Data were analyzed with analysis of variance, multiple range tests for differences means at the various ages, and simple, partial, and multiple product-moment correlations. From 3 to 24 months a linear increase of approximately 50% occurs in all layers of the olfactory bulb. During this time the mean perikaryal volume and dendritic volume of mitral cells increases, also in a linear fashion, approximately 100%. No significant change occurs in the number of mitral cells. From 24 to 30 months a significant decrease occurs in the volume of the layers. Although the total volume of mitral cell dendritic trees decreases slightly from 24 to 27 months, the volume of individual mitral cell dendritic treess, as well as perikaryal and nuclear size, increases sharply during this period, apparently in compensation for a sharp decrease in the number of mitral cells which occurs at this time. From 27 to 30 months no further decrease in mitral cell number occurs, but the size of mitral cell perikarya, and especially dendritic trees, decreases sharply. The coordinated increase in olfactory bulb size from 3 to 24 months appears to be a comtinuation into adult life of earlier postnatal increases. The atrophy from 24 to 30 months appears not to be associated with peripheral rhinitis, since the glomerular and olfactory nerve layers do not show greater atrophy than the other layers, and atrophy also occurs in the accessory olfactory bulb, which is supplied by nerves from the vomeronasal organ, a structure not normally subject to rhinitis.

Aging↗
PubMed1985

Derivation of cerebellar Golgi neurons from the external granular layer: evidence from explantation of external granule cells in vivo.

The present report provides evidence to challenge the traditional view that cerebellar Golgi cells are derived from the ventricular neuroepithelium, postulating instead that they originate from external granule cells. Supporting evidence for this assertion comes from three sources: 1) Typical Golgi cells are found in ectopic granule cell colonies, both outside the cerebellum (in the subarachnoid space) and also within the cerebellar cortex between fused folia. Because ectopic granule cell colonies are derived from external granule cells, which become displaced after treatment with 6-hydroxydopamine (6-OHDA), it was assumed that the ectopic Golgi cells also stem from such displaced external granule cells. 2) In order to demonstrate that Golgi cell precursors migrate from the external granular layer into the Purkinje cell plate, the development of the cerebellar cortex was studied over the period of Golgi cell genesis. On E19 the external granular layer in the rat is subdivided into an outer proliferative and an inner subproliferative zone. At the inner margin of the external granular layer, and in the marginal zone, radially oriented, darkly staining cells are present that exhibit all the characteristics of migrating neurons possessing a leading process oriented toward the Purkinje cell plate, a somatic cilium, and a close association with radial glia fibers. In later stages, these cells are also found deep to the Purkinje cell plate. Because Golgi cells arise during the period between E19 and postnatal day 2 in the rat (Altman and Bayer, '77, '78) and as the basket cells, the first neurons of proven origin from the external granular layer, are not produced before the second postnatal day (Altman, '72), the earlier migrating neurons are presumed to be Golgi cells. 3) Available data from cell kinetic 3H-thymidine studies show that there is no unequivocal evidence for Golgi cell genesis from the ventricular neuroepithelium, because, at the time of Golgi cell birth, ventricular and external granular stem cell populations are proliferating, and with the present methods it is not possible to decide which of these are the precursors of Golgi cells. Thus, taken together, the findings of this study show that Golgi cells are more likely to arise from the external granular layer than from the ventricular neuroepithelium. This concept would unify cerebellar histogenesis by proposing that projection neurons arise from the ventricular neuroepithelium, whereas all interneurons of the cerebellar cortex are descendants of the external granular layer.

Animals↗
PubMed1985

Commissural neurons in layer III of cat primary auditory cortex (AI): pyramidal and non-pyramidal cell input.

The types of layer III neurons in cat primary auditory cortex (AI) projecting to the contralateral AI were studied with horseradish peroxidase or horseradish peroxidase conjugated to wheat germ agglutinin. Injections between the anterior and posterior ectosylvian sulci retrogradely labeled both pyramidal and non-pyramidal somata in contralateral cortical layers III, V, and VI in AI, and in the ventral nucleus of the ipsilateral medial geniculate body. Three-quarters (72%) of the retrogradely labeled cells were found in layer III and one-quarter (28%) lay in layers V and VI. Every part of AI was innervated by commissural neurons. The topographical distribution of the labeled cells varied systematically. Injections in the caudal part of AI labeled cells in the caudal part of the opposite AI, while more rostral injections labeled cells in the contralateral, rostral AI. Injections covering the rostro-caudal extent of AI labeled cells throughout the opposite AI. Each part of AI thus projects most strongly to a contralateral, homotypic area, and less strongly to other, adjacent sectors of AI. The types of labeled cells were distinguished from one another on the basis of size, somatic and dendritic morphology, laminar distribution, and nuclear membrane morphology. Their somatodendritic profiles were compared to, and correlated with, those in Golgi-impregnated material from adult animals. Among the pyramidal cells of origin were small, medium-sized, and large neurons, and star pyramidal cells. The non-pyramidal cells of origin included bipolar and multipolar cells. Thus, at least six of the 12 kinds of neurons, as defined by morphological methods, participate in the interhemispheric pathway. Pyramidal cells comprised 65% of the cells of origin, 14% of the labeled cells in layer III were non-pyramidal, and 21% of the neurons could not be classified. It is unknown if these different types of commissural neurons have the same laminar or cytological targets in AI, or if they represent more than one functional or parallel pathway within AI. In any case, cytologically diverse layer III neurons contribute to the commissural system.

Animals↗
PubMed1987

Connections between pyramidal neurons in layer 5 of cat visual cortex (area 17).

The structural features of two physiologically-characterised pyramidal neurons (PC1 and PC2) closely situated in layer 5b in the visual cortex (area 17) of a single cat were studied using a combination of electrophysiological and anatomical techniques. Both PC1 and PC2 had exceptionally large somata (30-40 microns in diameter). On the basis of this and other morphological features cell PC1 was classified as a Meynert cell. PC1 possessed a very large (2.75 degrees X 4.50 degrees) binocularly driven standard complex receptive field. PC2 was also binocularly driven with a small, B-type receptive field. Both cells had the same preference for the direction and orientation of visual stimuli. PC1 and PC2 could be antidromically activated from stimulating electrodes positioned above the dorsal lateral geniculate nucleus with a response latency indicating that these cells probably innervated the visual tectum or pretectum. In addition to corticoefferent axons, the two neurons possessed extensive intracortical axon arbors that ramified extensively in layers 5 and 6 of the medial and lateral banks of the lateral gyrus in area 17. Axon collaterals from both PC1 and PC2 also innervated a small common target region in area 18. A total of 313 boutons from the axonal arbors of PC1 and PC2 were examined in the electron microscope. All of the identified synaptic junctions were found to establish Gray type 1 asymmetrical contacts. The combined ultrastructural data for both neurons indicated that 80% of boutons were onto dendritic spine heads, with 14%, 6%, and 1% onto small-, medium-, and large-calibre dendritic shafts, respectively. The spectrum of postsynaptic targets showed little variation with respect to lamina, distance from somata, or cortical area. Other large pyramidal neurons in layer 5 and spiny neurons in layer 6 were identified as receiving synaptic input from either PC1 or PC2. Using a computer graphics system, rotations of the bouton distributions revealed the existence of a clustered innervation of layers 5 and 6 in areas 17 and 18 derived from the two identified neurons. The bouton distributions strongly resembled the tangential pattern described previously for the functional slab-like organisation of the cortex. The results provide a morphological basis for the clustered intrinsic connectivity of pyramidal cells in layers 5 and 6 of the cat visual cortex. Furthermore, the results indicate the widespread excitatory influence of large pyramidal neurons on other cells projecting subcortically to sites dealing with visually guided behavior.

Animals↗
PubMed1990

Intermediate and deep layers of the macaque superior colliculus: a Golgi study.

We studied the intermediate and deep layers of the macaque superior colliculus by means of the Golgi technique in an attempt to better understand the structural features of this important oculomotor center. For this study, we examined the optic (stratum opticum, SO), intermediate gray (stratum griseum intermedium, SGI), intermediate white (stratum album intermedium, SAI), and deep gray (stratum griseum profundum, SGP) layers. These are the four layers in which neurons having saccade-related activity are localized. We identified eight neuronal types on the basis of differences in somatic and dendritic morphologies: large multipolar neurons (Type I); large pyramidal neurons (Type II); large fusiform neurons (Type III); medium fusiform neurons with spiny, radially oriented dendrites (Type IV); medium round neurons with fan-shaped dendritic trees (Type V); medium stellate neurons with varicose dendrites (Type VI); medium multipolar neurons with robust, spiny dendrites (Type VII); and local interneurons (Type VIII). Most neuronal types possessed features that are homologous to presynaptic dendritic features in other brain centers. With the exception of the medium stellate neurons (Type VI), which are aspinous, and the local interneurons (Type VIII), which are sparsely spinous, all other types had a moderate number of spines on their dendrites. Dendrites that terminated in the optic layer had specializations not observed elsewhere, suggesting that these tips may sample a tectal afferent that is not present in the more ventral layers. These eight types comprise all the neuronal morphologies observed in a large number of Golgi-impregnated macaque brains (n = 50). We suggest that they represent the full range of neuron types in the saccade-related layers of the macaque tectum.

Animals↗
PubMed1990

Retinal vasculature of the fovea of the squirrel monkey, Saimiri sciureus: three-dimensional architecture, visual screening, and relationships to the neuronal layers.

The retinal vasculature of the fovea of squirrel monkeys was studied in retinal whole mounts and in sections of the same retinas. At the center of the fovea there is an approximately circular avascular zone surrounded by a set of terminal capillaries in the inner nuclear layer. Within the foveal depression, four capillary planes that bear a precise relationship to the neuronal organization appear in a specific sequence with increasing eccentricity. The first plane to be established is the dominant, most voluminous one, located closest to the photoreceptors at the deep (sclerad) border of the inner nuclear layer. A second major plane appears next at the sclerad border of the ganglion cell layer. The two remaining, less voluminous planes occur at a slightly greater eccentricity. One of these, located at the shallow (vitread) border of the inner nuclear layer, often drains into the ganglion cell plane. The fourth plane is initially situated at the vitread border of the ganglion cell layer; with increasing eccentricity it moves into the nerve fiber layer. These capillaries are oriented like the nerve fibers with which they travel. Both the shallow inner nuclear and nerve fiber planes of capillaries show marked regional variations. The capillary planes are within or adjacent to regions of high cytochrome oxidase activity. The retinal vascular network is an unrecognized contributor to the optical filtering properties of the eye. In much of the central retina, a photon has a 40-50% chance of encountering one or more capillaries before it reaches a photoreceptor.

Animals↗
PubMed1992

Genesis of neurons in the retinal ganglion cell layer of the monkey.

We have analyzed the genesis of various neuronal classes and subclasses in the ganglion cell layer of the primate retina. Neurons were classified according to their size and the time of their origin was determined by pulse labeling with 3H-thymidine administered to female monkeys 38 to 70 days pregnant. All offspring were sacrificed postnatally, and their retinas processed for autoradiography. The somata of cells in the retinal ganglion cell layer generated on embryonic day (E) 38 ranged from 9 to 14 microns in diameter. Between E40 and E56, the minimum soma diameter remained around 8-9 microns, while the maximum gradually increased to 22 microns. As a consequence, the means of the distributions of labeled cells also increased with age, from 11.8 microns diameter for cells generated on E38 to 14.6 microns diameter at E56. Over this period the percentage of labeled cells in the 10.5-16.5 microns and greater than 16.5 microns diameter range gradually increased. The proportion of the labeled cells in the less than 10.5 microns diameter range decreased from E38 to E45, but subsequently increased rapidly. At the end of neurogenesis in the retinal ganglion cell layer, around E70, most labeled cells were considerably smaller (7-9 microns) than those generated earlier. Our results indicate that within the ganglion cell layer of the macaque, neurons of small caliber are generated first, followed successively by medium sized cells. Large, putative P alpha cells are generated late. The production between E56 and E70 of cells with the smallest somata suggests that the last-generated neurons in the ganglion cell layer are predominantly displaced amacrine cells. Within the same sector of retina, different classes of neurons in the ganglion cell layer of the rhesus monkey appear to have a sequential schedule of production.

Animals↗
PubMed1994

Pyramidal neurons in layer 5 of the rat visual cortex. III. Differential maturation of axon targeting, dendritic morphology, and electrophysiological properties.

This paper describes the early morphological and physiological development of pyramidal neurons in layer 5 of the rat visual cortex in relation to the targets chosen by their axons. Cells were prelabeled by retrograde transport from the superior colliculus or the contralateral visual cortex and intracellularly injected either in fixed slices or after recording in living slices. In the adult, corticotectal cells have thick apical dendrites with an extensive terminal arborization extending into layer 1, and fire characteristic bursts of action potentials when injected with a depolarizing current; interhemispheric cells have slender apical dendrites that terminate without a terminal tuft, usually in layer 2/3, and they display a more regular firing pattern (Kasper et al.: J Comp Neurol, this issue, 339:459-474). At embryonic day E18 (when axons of the two classes of cells are already taking different routes towards their targets) and E21, pyramidal-like cells throughout the cortical plate all have similar soma-dendritic morphology, with spindle-shaped cell bodies and few, short basal dendrites but apical dendrites that all end in distinct tufts in the marginal zone. At postnatal day P3, after the axons of both cell classes have reached their targets, all pyramidal neurons in layer 5 still have distinct terminal arborizations in layer 1, though they vary in complexity and extent. The somata are now more mature (round to ovoid in shape), and the basal dendritic tree has extended. As early as P5, all cells studied could be clearly classified as tufted or untufted (considerably earlier than previously reported; Koester and O'Leary: J Neurosci 12:1382, '92), and these features correlated precisely with the projection target, as in the adult. Measurement showed that although interhemispheric cells lose their terminal tufts, in general the trunks of their apical dendrites do not withdraw but continue to grow, at roughly the same rate as those of corticotectal cells. The two classes of layer 5 pyramidal neurons differentiate from each other in three distinct phases: pathway selection by axons precedes the loss of the apical tuft by interhemispheric cells, and these morphological characteristics are established 10 days before the onset of burst-firing in corticotectal cells. These three steps may be guided by different molecular signals.

Action Potentials↗
PubMed1990

Dark-rearing retards the maturation of astrocytes in restricted layers of cat visual cortex.

The cat visual cortex develops its mature appearance, i.e., its circuitry and neuronal morphology, during a limited period of postnatal development under the influence of visual experience. The critical period for cortical plasticity, which normally extends from the third to seventh postnatal week, can be prolonged by raising animals in total darkness. The prolongation of the critical period by dark-rearing is restricted to the cortical layers except layer IV. Besides the influence of afferent activity on the physiology of cortical cells and on the interconnectivity of thalamo-cortical afferents, visual experience has also been shown to affect the development of glial cells. The present study investigates the effects of dark-rearing on astroglial characteristics as determined by immunostaining for glial fibrillary acidic protein (GFAP) and the S-100 protein. The data reveal a retardation of astrocytic maturation in dark-reared animals, shown by a reduced presence of GFAP immunoreactivity compared to light-experienced animals. The density of astrocytic cell bodies positive for S-100 is unaffected by dark-rearing, suggesting that astroglial proliferation does not rely on afferent activity. However, punctate S-100 staining in the neuropil, which has been shown to reflect astrocytic processes, was also reduced in certain cortical layers in dark-reared animals. The effects of dark-rearing on the expression of GFAP and S-100 were restricted to the cortical layers except layer IV, i.e., those layers that reveal a prolongation of the critical period for cortical plasticity following dark-rearing. It is concluded that astrocytic maturation in the visual cortex is influenced by neuronal activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Formation of the myelinated nerve fiber layer in the chicken retina.

Oligodendrocytes in the ganglion cell layer, the myelinating cells in the chicken retina, were investigated morphologically and quantitatively. Oligodendroblasts divided in the inner retinal layer around the 14th day of incubation and differentiated into oligodendrocytes. The oligodendrocytes started sheathing an axon in the nerve fiber layer at the 14th day of incubation. The number of myelin lamellae increased rapidly during the first week after chicks had hatched. An immunological reaction of anti-myelin basic protein was observed on the myelin sheaths in the nerve fiber layer and on the oligodendrocytes in the ganglion cell layer. These results suggest that the oligodendrocytes form the myelinated nerve fiber layer of the chicken and that they act independently of the Müller cells during myelination.

Age Factors↗
PubMed1993

Projection of the entorhinal layer II neurons in the rat as revealed by intracellular pressure-injection of neurobiotin.

A component of the perforant path, projection of the entorhinal layer II neurons, was investigated by recovering intracellularly labeled layer II neurons from the medial or intermediate entorhinal cortex in rats. The labeled layer II spiny stellate neurons had axon collaterals in layers I, II, and III of the entorhinal cortex as well as some axon collaterals in the subiculum. The stem axons gave rise to terminal axon branches that covered the entire extent (suprapyramidal blade, crest, and infrapyramidal blade) of the dentate gyrus and the CA2-3 fields in the transverse plane, forming a sheet-like formation. The axon arbor in the hippocampal formation spread up to 2 mm wide in a septotemporal direction. The sheet-like formation of the axon arbors was a narrow layer in the suprapyramidal blade and in the stratum lacunosum-moleculare of the CA2-3 fields. The layer became wider in the crest and infrapyramidal blade of the dentate gyrus. This study shows that the entorhinohippocampal circuit is not a simple circle from single cells level.

Animals↗
PubMed2002

Preparation of TiO(2) layers on cp-Ti and Ti6Al4V by thermal and anodic oxidation and by sol-gel coating techniques and their characterization.

The excellent biocompatibility of titanium and its alloys used, for example, for medical devices, is associated with the properties of their surface oxide. For a better understanding of the tissue reaction in contact with the oxide layer, knowledge of the chemical and physical properties of this layer is of increasing interest. In this study, titania films were produced on cp-Ti and Ti6Al4V substrates by thermal oxidation, anodic oxidation, and by the sol-gel process. The thickness and structure of the films produced under different conditions were determined by ellipsometry, infrared spectroscopy, and X-ray diffraction measurements. The corrosion properties of these layers were investigated by current density-potential curves under physiological conditions. The oxide layers produced on cp-Ti and Ti6Al4V by thermal oxidation consist of TiO(2) in the rutile structure. For the anodized samples the structure of TiO(2) is a mixture of amorphous phase and anatase. The structure of the coatings produced by the sol-gel process for a constant annealing time depends on the annealing temperature, and with increasing temperature successively amorphous, anatase, and rutile structure is observed. Compared to the uncoated, polished substrate with a natural oxide layer, the corrosion resistance of cp-Ti and Ti6Al4V is increased for the samples with an oxide layer thickness of about 100 nm, independent of the oxidation procedure.

Alloys↗
PubMed2005

Effect of hybrid layer on stress distribution in a premolar tooth restored with composite or ceramic inlay: an FEM study.

The aim of this finite elemental stress analysis study was to evaluate the effect of hybrid layer on distribution and amount of stress formed under occlusal loading in a premolar tooth restored with composite or ceramic inlay. The mandibular premolar tooth was selected as the model based on the anatomical measurements suggested by Wheeler. The analysis is performed by using a Pentium II IBM compatible computer with the SAP 2000 structural analysis program. Four different mathematical models including the following structures were evaluated: 1) composite inlay, adhesive resin, and tooth structure; 2) composite inlay, adhesive resin, hybrid layer, and tooth structure; 3) ceramic inlay, adhesive resin, and tooth structure; 4) ceramic inlay, adhesive resin, hybrid layer, and tooth structure. Loading was applied from the occlusal surface of the restoration, and shear stresses under loading were evaluated. The findings were drawn by the Saplot program, and the results were analyzed by graphical comparison method. The output indicated that the hybrid layer acts as a stress absorber in models 2 and 4. The hybrid layer has also changed mathematical values of stress on cavity floors in both restoration types. Ceramic inlay collected the stress inside the body of the material, but the composite inlay directly transferred the stress through dental tissues. As a result, it was concluded that the hybrid layer has an effect on stress distribution under loading in a premolar tooth model restored with composite or ceramic inlay.

Acrylic Resins↗
PubMed1988

Ultrasonographic diagnosis of submucosal tumors of the stomach: the "bridging layers" sign.

The ultrasonic findings in 14 cases with submucosal tumors and one case with extragastric lymphoma using the fluid-filled stomach method were reviewed to determine the appearance of the stomach wall in submucosal tumors. Two characteristic ultrasound features of submucosal tumors were demonstrated in all 14 lesions except in two located high in the fundus of the stomach. One feature was mucosal bridging layers, i.e., three layers could be seen on the mucosal side of the tumors, and at least two of them continued to layers 1 and 2 of the normal gastric wall. The other was a serosal bridging layer, i.e., layer 5 of the normal gastric wall ran toward the serosal side of the tumor. On the basis of a "bridging layers" sign, we believe a definite diagnosis of submucosal tumor can be obtained from ultrasound images.

Diagnosis, Differential↗