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At least 721 records · Page 40Linked to original sources

PubMed1990

Preparing and analyzing fractured archaeological fibers.

A technique was developed to prepare archaeological fiber cross sections for electron microscopic examination and x-ray analysis. Use of this new method allows chemical and morphological information to be obtained from the interior of a single fiber or yarn. Fibers are fractured while frozen and then freeze dried. Following mounting and carbon coating, fibers are examined by scanning and backscatter electron microscopy and then analyzed by using energy-dispersive spectrometry. Elemental distribution is mapped by using image-processing software. In this report, the described technique is employed in the examination of ancient fibers from three different long-term storage environments (moist buried, dry buried, museum stored). Data obtained by examining the interior of fibers such as these provide insight into the conditions of a fiber's growth, the treatments applied during the fiber's processing and use, and the conditions in which the fiber was stored.

Archaeology↗

PubMed1981

Clinical performance of microporous polypropylene hollow-fiber oxygenator.

A newly developed polypropylene hollow-fiber oxygenator was used from June 1979, to July, 1980, in 100 patients undergoing open-heart operation. Adequate oxygenation and carbon dioxide elimination were observed throughout perfusion in spite of a relatively low ratio of oxygen flow to blood flow. Plasma hemoglobin level was maintained low after long hours of perfusion. There were no complications related to the oxygenator during or after the operation. Because of its highly efficient performance as well as small size and easy handling, this oxygenator is being used routinely during open-heart procedures in our hospital.

Adolescent↗

PubMedDate not supplied

Frequency selectivity in the auditory periphery: similarities between damaged and developing ears.

Single fiber tuning curves (stimulus frequency versus neural threshold curves) were obtained from 198 auditory nerve fibers in 24 kittens between birth and the 16th postnatal day and from 74 auditory nerve fibers in adult cats. Three developmental stages during which adult-like frequency-resolving capacity was acquired were identified. During the early stage of postnatal development, all auditory nerve fibers were essentially untuned and responded to a narrow range of low to middle frequency tone bursts presented at intensities exceeding 110 dB sound pressure level (SPL) re 20 muPa. In the intermediate stage, which occurred during the second postnatal week, auditory nerve fibers tuned to low- and mid-range frequencies acquired adult-like frequency-resolving capacity. Fibers tuned to high frequencies, which were recorded later in development than those tuned to lower frequencies, were as sharply tuned as their adult counterparts, but exhibited a low contrast between thresholds at characteristic frequency (tip) and lower (tail) frequencies (ie, low tip-to-tail ratios). Adult-like tuning curves were observed during the third stage, primarily as a consequence of the acquisition of adult-like tip-to-tail ratios. Our understanding of the cochlear mechanism(s) by which frequency selectivity is produced in adult animals has recently been enhanced by a combined anatomy and physiology investigation conducted by Liberman and Dodds, in which clear anatomic foci of cochlear damage were identified in cats with functionally characterized hearing loss. Similarly, descriptions of anatomic differentiation in the feline auditory end-organ correlate with functional measures of peripheral auditory system development. In this report, anatomic and physiologic similarities between developing and damaged ears are considered in an attempt to better characterized the process whereby normal frequency selectivities and thresholds are developed. Our findings support the notion that anatomic changes in the cochlea during development, primarily the development of adult-like anatomic relations between the tectorial membrane and sensory cells, underlie the acquisition of adult-like auditory nerve fiber tuning.

Age Factors↗

PubMed1999

The Dbl-related protein, Lfc, localizes to microtubules and mediates the activation of Rac signaling pathways in cells.

The possibility that the Dbl family member Lfc can activate Rac1 in cells is investigated in this study. Previously, we demonstrated that both Lfc and Lsc, like their closest relative Lbc, can act catalytically in stimulating the guanine nucleotide exchange activity of RhoA in vitro. Neither Lfc nor Lsc stimulated the in vitro exchange activity of Cdc42 or Rac1; however, Lfc was capable of forming a tight complex with Rac1 in vitro. We show here that Lfc stimulates c-Jun kinase (JNK) activity in COS-7 cells. This stimulation was blocked by a dominant negative mutant of Rac1 and somewhat less effectively by dominant negative RhoA, but not by dominant negative Cdc42. Overexpression of Lfc in NIH 3T3 cells induced the formation of actin stress fibers and membrane ruffles, consistent with the activation of both RhoA and Rac1 signaling pathways, whereas overexpression of Lsc led exclusively to well developed stress fibers. Using a recently developed assay for measuring the cellular activation of Rac, we did not find that expression of Lfc increased the levels of GTP-bound Rac1. However, an examination of the cellular localization of Lfc showed that it was localized to microtubules, similar to what has been reported for activated Rac1, the mixed lineage kinase (MLK) and JNK. Moreover, we have found that the Pleckstrin homology (PH) domain of Lfc specifically associates with tubulin. Taken together, these findings suggest a model where the PH domain-mediated localization of Lfc to microtubules enables the recruitment of Rac to a site proximal to its signaling targets, resulting in JNK activation and actin cytoskeletal changes.

3T3 Cells↗

PubMed2006

Fiber-guided CO2 laser surgery in an animal model.

OBJECTIVE: This study tested a newly developed flexible fiber for CO(2) laser surgery. BACKGROUND DATA: The lack of a flexible delivery system with the current CO(2) laser has limited its surgical application. We conducted in vitro and in vivo studies by using the skin tissue model of animals to test a new laser fiber system. METHODS: In an in vitro study, the acute thermal effect of laser surgery using this new fiber was tested and compared on fresh porcine skin at 3.0-5.0-W laser power and at 0.3-0.5-mm spot size. In the in vivo experiments, the healing process of the skin incisions and wounds was followed microscopically in 16 rats, at post-operative days 2, 6, 12, and 21 after the laser surgery with 3.0-W power and 0.5-mm spot size. RESULTS: The results from the in vitro tissue showed limited thermal damage to neighboring tissue. In the in vivo study, there was rapid postoperative healing. CONCLUSION: Our findings indicate that this fiber system, at least with the laser parameters used in this study, appears to be an effective and feasible alternative for CO(2) laser surgery. It has great potential for development of office-based surgery under local anesthesia.

Animals↗

PubMed1991

Effects of prenatal stress and ethanol on cerebellar fiber tract maturation in B6D2F2 mice: an image analysis study.

Two studies were carried out to evaluate the role of prenatal stress in the outcome of prenatal ethanol exposure on central nervous system maturation in offspring. B6D2F1 mice were paid-fed liquid diets containing either 25% ethanol-derived calories or an isocaloric amount of maltose-dextrin on days 12 to 17 of gestation. During this period, half of the dams in each dietary condition also underwent two daily one-hour periods of restraint stress. A fifth group, provided with lab chow and water ad lib, was left undisturbed throughout pregnancy. At birth, all pups were fostered to untreated dams. Neither prenatal ethanol nor prenatal stress affected the maturation of cerebellar fiber tracts as indicated by membrane lipid staining either on day 32 post-conception or at weaning, nor was there an interactive effect of ethanol and stress combined. On the other hand, fiber tract maturation was significantly retarded on both days by prenatal undernutrition caused by treatment-induced reductions in maternal food intake. In the second study, pregnant dams were divided into three groups, all of which were fed lab chow and water. One group underwent the same stressing procedure as in the first study while a second group was unrestrained but pair-fed to the stressed group. A third group was undisturbed and allowed food and water ad lib. The offspring of both prenatally stressed and pair-fed dams did not differ from each other in terms of cerebellar fiber tract maturation, but both groups exhibited immature fiber tract development relative to the offspring of ad lib-fed dams. These data suggest that alterations in maternal nutritional status due to the ethanol and stress treatments can affect cerebellar fiber tract maturation in developing offspring.

Animals↗

PubMed1983

Alterations in the Ca2+ sensitivity of tension development by single skeletal muscle fibers at stretched lengths.

The apparent length dependence in the calcium sensitivity of tension development in skeletal muscle has been investigated in the present study. At sarcomere lengths of 2.46-2.62 micron, the Hill plot of tension-pCa data is well fit by not one but two straight lines, suggesting the possible involvement of more than a single class of Ca2+-binding site in tension development. On the other hand, increasing the sarcomere length to 3.00-3.25 micron yielded Hill plots that were described by a single straight line, which indicates that at long lengths tension might be regulated by the binding of Ca2+ to a single class of Ca2+-binding sites, presumably the low affinity sites of TnC. This length-dependent transformation of the tension pCa relation occurred at free Mg2+ concentrations of both 0.05 and 3.2 mM. Although the mechanism of this effect is uncertain, plausible explanations for the biphasic Hill plot at the shorter lengths include the possible involvement of Ca2+ activation of the thick filaments and/or myosin LC2 phosphorylation in the process of tension development.

Animals↗

PubMed1999

IFL1, a gene regulating interfascicular fiber differentiation in Arabidopsis, encodes a homeodomain-leucine zipper protein.

Arabidopsis inflorescence stems develop extraxylary fibers at specific sites in interfascicular regions. The spatial specification of interfascicular fiber differentiation is regulated by the INTERFASCICULAR FIBERLESS1 (IFL1) gene because mutation of that gene abolishes the formation of normal interfascicular fibers in Arabidopsis stems. To understand further the role of IFL1 in the specification of fiber differentiation, we cloned the IFL1 gene by using a positional cloning strategy. Sequence analysis showed that the IFL1 gene encodes a transcription factor that has the same features as a family of homeodomain-leucine zipper (HD-ZIP) proteins found only in plants. The predicted IFL1 protein is composed of three distinct domains, including a 60-amino acid HD at the N terminus followed by a 28-amino acid ZIP motif and a 724-amino acid C-terminal region. A nuclear targeting assay showed that IFL1 is able to direct a beta-glucuronidase fusion protein into the nucleus, which is consistent with IFL1's presumed function as a transcription factor. Gene expression analysis demonstrated that the IFL1 gene is expressed in the interfascicular regions in which fibers differentiate, which is consistent with its role in the control of interfascicular fiber differentiation. Furthermore, the IFL1 gene was shown to be expressed in the vascular regions, indicating its possible role in the regulation of vascular tissue formation. This possibility is supported by the observation that differentiation of both xylary fibers and vessel elements is altered in the vascular bundles of ifl1 mutants. Our results provide direct evidence that an HD-ZIP protein plays a role in the spatial control of fiber differentiation.

Amino Acid Sequence↗

PubMed1984

Force response to width and length perturbations in compressed skinned skeletal muscle fibers.

Previous studies have shown that radial compression of calcium-activated skinned skeletal muscle fibers, with attendant reduction of filament lattice spacing, reduces isometric force generation. In relaxed skinned fibers, radial compression produces a marked increase in axial elastic modulus, and the response to a small amplitude length perturbation resembles that of a muscle in rigor. We interpret these results as indicating that radial compression of the myofilament lattice produces "hindered" cross-bridges which are load bearing but not force generating. The experiments reported here were designed to study the effect(s) of "hindered" cross-bridges on both the time course of isometric force responses following Ca2+ activation and fiber width and length perturbations. The experiments were carried out at room temperature on radially compressed skinned single rabbit soleus fibers. Force development following step-wise Ca2+ activation and step-wise changes of fiber width was "slow" (60-90 sec) compared to that in normal width fibers (approximately 1 sec), and could be approximated by a single exponential curve. Force redevelopment following a length release in compressed fibers was both more rapid and more complicated than force development following activation and width steps, and required a double exponential curve for an adequate description. The results are consistent with the notion that hindered cross-bridges form as a result of lattice compression, and that the hindered bridges affect the force responses following width and length perturbations.

Adenosine Diphosphate↗

PubMed1987

[Development of different types of muscle fiber in the postnatal ontogeny of guinea pigs].

As demonstrates estimation of myosin ATPase and SDG activity, the guinea pig is already born with differentiated muscle fibers (MF), and the first histochemical differences between them take place in the uterine 10 days before birth. Tonic oxidative fibers of the first type, arranging hexagonally, develop especially quickly at early stages of postnatal ontogenesis. Their relative contents up to the end of the observations (185 days) do not change, and area of their transversal section increases but slightly in comparison to the phasic fibers. The main age changes of the muscle tissue are connected with formation and rearrangement of the phasic fibers. The most intensive reconstructions of the phasic fibers coincide with the period of game activity and sex maturation. In mixed muscles the part of the glycolytic fibers increase during the postnatal ontogenesis. In the process of ontogenesis the soleus muscle fully consists of oxidative fibers. The definitive level of the MF development is established after the guinea pigs have reached their sex maturation. Comparing the results of the given investigation with the previous data on development of MF in rats, it is possible to conclude that term and premature animals have various rates in development of the muscle system, however, main stages of myogenesis coincide, though they are connected with various phases of ontogenesis.

Aging↗

PubMed2002

HRP injection in lobule VI-VII of the cerebellar cortex reveals a bilateral inferior olive projection in granuloprival rats.

In immature rats, Purkinje cells receive synapses from multiple climbing fibers. During development, this multi-innervation regresses and only one climbing fiber innervates each Purkinje cell in the adult. The multi-innervation of immature rats is maintained in the adult if the precursors of the cerebellar granule cells are destroyed by early postnatal X-irradiation. The present study was undertaken to determine the origin of climbing fibers projecting to lobule VI-VII of the cerebellum in X-irradiated granuloprival rats. Olivary neurons were labelled by retrograde transport of wheat germ agglutinin conjugated to horseradish peroxidase, which was injected by iontophoresis in the right vermis of lobule VI-VII. Three-dimensional reconstructions of the inferior olive were made for granuloprival and control rats. No significant variation in the shape and dimension of the olive was observed between the two groups. Labeled cells were found in the middle part of the median accessory olive (MAO). In control rats, stained cells were found only in the contralateral MAO, whereas in the granuloprival rats they were located in both the contralateral and the ipsilateral MAO. Homologous zones were marked in control and granuloprival rats in the middle part of MAO. In granuloprival rats, there was a symmetry in the distribution of the stained cells in the ipsi- and contralateral MAO along the three axes. Therefore, polyinnervation involves homologous regions of both inferior olivary nuclei.

Animals↗

PubMed1994

Utilization of myoblasts from transgenic mice to evaluate the efficacy of myoblast transplantation.

A possible treatment for Duchenne muscular dystrophy is the injection of normal myoblasts into dystrophic muscles to induce the formation of new, healthy, and dystrophin-positive muscle fibers. To develop this therapy, it is important to identify the muscle fibers formed by the injected myoblasts in the host muscles. In this study, we used myoblasts from transgenic mice which have a gene expressing beta-galactosidase under the control of the promoter of quail fast skeletal muscle troponin I. This transgene is expressed in myotubes and muscle fibers, but not in myoblasts. Twenty-eight days after myoblast transplantation in nude and in mdx mice, muscle fibers containing of beta-galactosidase were identified by x-gal staining. In mdx mice, most of the beta-galactosidase-positive muscle fibers resulting from the myoblast transplantation were also dystrophin positive. This technique could make it possible to follow the success of myoblast transplantation even in mice that are not depleted of dystrophin.

Animals↗

PubMed2002

Capsaicin-sensitive adrenal sensory fibers participate in compensatory adrenal growth in rats.

Compensatory adrenal growth, in which one gland undergoes hyperplasia after removal of the other, is mediated by a neural reflex. In the present studies, a method employing capsaicin to selectively remove adrenal sensory fibers was developed and applied to determine whether adrenal capsaicin-sensitive fibers participate in compensatory adrenal growth. The splanchnic nerves of anesthetized male rats were treated with capsaicin or vehicle. Capsaicin treatment selectively removed adrenal calcitonin gene-related peptide-positive fibers. One week after drug treatment, rats underwent left adrenalectomy or sham surgery and recovered for 5 days. Capsaicin treatment bilaterally or to the left splanchnic nerve alone (i.e., the afferent nerve in the reflex) impaired compensatory adrenal growth at 5 days compared with vehicle controls, whereas capsaicin treatment to the right splanchnic nerve alone did not affect growth. Moreover, left adrenalectomy induced c-Fos immunolabeling in ipsilateral dorsal spinal cord that was prevented by capsaicin treatment. These data suggest that adrenal capsaicin-sensitive afferent nerves participate in compensatory adrenal growth and that this effect is primarily on the afferent limb of the reflex.

Adaptation, Physiological↗

PubMed2001

Lung tissue mechanics and extracellular matrix composition in a murine model of silicosis.

The dynamic mechanical properties of lung tissue and its contents of collagen and elastic fibers were studied in strips prepared from mice instilled intratracheally with saline (C) or silica [15 (S15) and 30 days (S30) after instillation]. Resistance, elastance, and hysteresivity were studied during oscillations at different frequencies on S15 and S30. Elastance increased from C to silica groups but was similar between S15 and S30. Resistance was augmented from C to S15 and S30 and was greater in S30 than in S15 at higher frequencies. Hysteresivity was higher in S30 than in C and S15. Silica groups presented a greater amount of collagen than did C. Elastic fiber content increased progressively along time. This increment was related to the higher amount of oxytalan fibers at 15 and 30 days, whereas elaunin and fully developed elastic fibers were augmented only at 30 days. Silicosis led not only to pulmonary fibrosis but also to fibroelastosis, thus assigning a major role to the elastic system in the silicotic lung.

Algorithms↗

PubMedDate not supplied

[Ultrastructure of type 2A extrafusal muscle fibers and intrafusal fibers of the muscle spindle (m. quadriceps femoris) from the adult rat after long-term swimming].

We compared the ultrastructure of type 2A extrafusal muscle fibers, the nuclear chain, and other intrafusal fibers of muscle spindle (muscle stretch mechanoreceptor) in adult rats after a prolonged swimming (5-10 h/day, 10 days). The Golgi apparatus was expressed moderately in type 2A extrafusal fibers and hypertrophied in the motor B zone of nuclear chain intrafusal fibers. Intense development of the Golgi apparatus in the nuclear chain intrafusal fiber appears to be related to glycogenolysis in the autophagous vacuoles, involvement in the lysosome activity, and plasma membrane renewal. "Recapitulation" of the mechanism of glycogen autophagy, which is observed in newborn rats during mobilization of glycogen from the liver and muscle, was demonstrated in adult rats under the influence of physical load in the nuclear chain and nuclear bag 2 intrafusal fibers and in type 2A extrafusal fibers. This is accounted for by a weak differentiation of the intrafusal muscle fibers: structurally, they are similar to myotubes and have specific features of blood supply and innervation. Individual features of experimental adult rats may also play a certain role.

Animals↗

PubMed1981

Cercal sensory development following laser microlesions of embryonic apical cells in Acheta domesticus.

The hypothesis that pioneer fibers, which develop relatively early in the differentiation of insect appendages, serve to organize the peripheral sensory nerves was tested by ablating apical regions of the cercal rudiments in embryos of Acheta domesticus. Multiple nerve bundles rather than the normal middorsal and midventral pair of nerves were formed within the cercus following ablation of the cercal tip before pioneer fiber differentiation, but the cercal nerve was normal when lesions were made after formation of the pioneer fiber tracts and associated glia. These results indicate a necessary morphogenetic role for the pioneer fibers.

Animals↗

PubMed1984

Effects of magnesium chloride on smooth muscle actomyosin adenosine-5'-triphosphatase activity, myosin conformation, and tension development in glycerinated smooth muscle fibers.

The contractile system of smooth muscle exhibits distinctive responses to varying Mg2+ concentrations in that maximum adenosine-5'-triphosphatase (ATPase) activity of actomyosin requires relatively high concentrations of Mg2+ and also that tension in skinned smooth muscle fibers can be induced in the absence of Ca2+ by high Mg2+ concentrations. We have examined the effects of MgCl2 on actomyosin ATPase activity and on tension development in skinned gizzard fibers and suggest that the MgCl2-induced changes may be correlated to shifts in myosin conformation. At low concentrations of free Mg2+ (less than or equal to 1 mM) the actin-activated ATPase activity of phosphorylated turkey gizzard myosin is reduced and is increased as the Mg2+ concentration is raised. The increase in Mg2+ (over a range of 1-10 mM added MgCl2) induces the conversion of 10S phosphorylated myosin to the 6S form, and it was found that the proportion of myosin as 10S is inversely related to the level of actin-activated ATPase activity. Activation of the actin-activated ATPase activity also occurs with dephosphorylated myosin but at higher MgCl2 concentrations, between 10 and 40 mM added MgCl2. Viscosity and fluorescence measurements indicate that increasing Mg2+ levels over this concentration range favor the formation of the 6S conformation of dephosphorylated myosin, and it is proposed that the 10S to 6S transition is a prerequisite for the observed activation of ATPase activity. With glycerinated chicken gizzard fibers high MgCl2 concentrations (6-20 mM) promote tension in the absence of Ca2+.(ABSTRACT TRUNCATED AT 250 WORDS)

Actomyosin↗

PubMed1992

Late development of conduction block over the Mahaim fibers after electrical atrioventricular junction ablation for Mahaim fiber tachycardia.

A patient suffering from so called "Mahaim fiber" tachycardia is presented who developed complete heart block over Mahaim fibers after 18 months of AV junction ablation. Antegrade conduction along the Mahaim fiber was intact immediately after the procedure. This finding has not been previously described and suggests that permanent pacemaker implantation is mandatory in such patients.

Adult↗