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At least 325 records · Page 18Linked to original sources
PubMed2002

Radial glias and radial fibers: what is the function of radial fibers?

Radial glias have been thought to serve as a scaffold to support and direct neurons in their radial migration during the development of the cerebral cortex. However, a recent series of studies on neocortical development showed that these cells behave as multifunctional cells. These studies have provided strong support for the idea that radial glias function as multipotential progenitor cells that give rise to various cell types, including neurons. Proliferation of the radial glia was thought to result in inheritance of the radial fiber by a postmitotic neuron, and it was considered that one role of the radial fiber was to act as a cable to lift the postmitotic neuron. In this review, we propose another function of the radial fiber in the developing neocortex. This novel function is proposed based on the fact that the characteristics of the radial glias are identical to those of neuroepithelial cells. Before neuron production, the neuroepithelial cells proliferate and increase in number, retaining and reproducing radial fibers attached to the surface of the basement membrane (the pia mater). During neuron production, the radial glias also reproduce radial fibers at the time of each cell division. We believe that the radial fiber functions to receive signals for morphogenesis, proliferation and differentiation from the pia mater and acts as a cable to conduct information transduced from such signals to the cell soma.

Animals↗
PubMed1968

Cardiac muscle. A comparative study of Purkinje fibers and ventricular fibers.

With light and electron microscopy a comparison has been made of the morphology of ventricular (V) and Purkinje (P) fibers of the hearts of guinea pig, rabbit, cat, dog, goat, and sheep. The criteria, previously established for the rabbit heart, that V fibers are distinguished from P fibers by the respective presence and absence of transverse tubules is shown to be true for all animals studied. No evidence was found of a permanent connection between the sarcoplasmic reticulum and the extracellular space. The sarcoplasmic reticulum (SR) of V fibers formed couplings with the sarcolemma of a transverse tubule (interior coupling) and with the peripheral sarcolemma (peripheral coupling), whereas in P fibers the SR formed only peripheral couplings. The forms of the couplings were identical. The significance, with respect to excitation-contraction coupling, of the difference in the form of the couplings in cardiac versus skeletal muscle is discussed together with the electrophysiological implications of the differing geometries of bundles of P fibers from different animals.

Anatomy, Comparative↗
PubMed1980

Morphogenesis of human adenovirus type 2 studied with fiber- and fiber and penton base-defective temperature-sensitive mutants.

The nature, polypeptide composition, and antigenic composition of the particles formed by six human adenovirus type 2 temperature-sensitive (ts) mutants were studied. ts115, ts116, and ts125 were phenotypically fiber-defective mutants, and ts103, ts104, and ts136 failed to synthesize detectable amounts of fiber plus penton base at 39.5 degrees C. The mutants belonged to five complementation groups, one group including ts116 and ts125. Except for ts103 and ts136, the other mutants were capable of producing particles at 39.5 degrees C. ts116 and ts125 accumulated light assembly intermediate particles (or top components) at nonpermissive temperatures, with few virus particles. The sodium dodecyl sulfate polypeptide pattern of ts116- or ts125-infected cells, intermediate particles, and virus particles showed that polypeptide IV (fiber) was smaller by a molecular weight of 2,000 than that in the wild-type virion and was glycosylated. In fiber plus penton base-defective ts104-infected cells, equivalent quantities of top components and viruses with a buoyant density (rho) of 1.345 g/ml (rho = 1.345 particles) were produced at 39.5 degrees C. These rho = 1.345 particles corresponded to young virions, as evidenced by the presence of uncleaved precursors to proteins VI, VIII, and VII. These young virions matured upon a shift down. Virus capsid vertex antigenic components underwent a phase of eclipse during their incorporation into mature virus particles. No antigenic penton base or IIa was detected in intermediate particles of all the ts mutants tested. Only hexon and traces of fiber antigens were found in ts104 young virions. Penton base and IIIa appeared as fully antigenically expressed capsid subunits in mature wild-type virions or ts104 virions after a shift down. The ts104 lesion is postulated to affect a regulatory function related in some way to penton base and fiber overproduction and the maturation processing of precursors PVI, PVII, and PVII.

Adenoviruses, Human↗
PubMed1993

Effect of anabolic steroids on new fiber formation and fiber area during stretch-overload.

The efficacy of anabolic steroid treatment to increase the extent of overload-induced new fiber formation and fiber hypertrophy was examined in anterior latissimus dorsi (ALD) muscles of Japanese quails. Adult quails were assigned to a control group (n = 20), which received stretch but no steroid (NS), or a stretch+steroid group (S), which received either nandrolone decanoate (n = 20) or testosterone enanthate (n = 12). Steroids were administered at 4.0 mg.kg body wt-1 x day-1. A weight corresponding to 10% of each bird's body weight was added to the right wing to effect a stretch of the right ALD. Thirty days of stretch-overload resulted in a 145.3 and 143.1% increase in total muscle weight of NS and S groups, respectively. Stretch-induced increases in nonmuscle tissue, fiber length, and new fiber formation were not altered by steroid administration. These results indicate that anabolic steroids did not act synergistically to enhance the extent of fiber hypertrophy or new fiber formation after 30 days of stretch-overload.

Anabolic Agents↗
PubMed1993

Lung cancer in the lower lobe is associated with pulmonary asbestos fiber count and fiber size.

We studied exposure to asbestos, pulmonary fibrosis, fiber count, and fiber size in relation to the lobar origin of lung cancer in 90 consecutive patients. Among the 32 patients with a history of occupational exposure to asbestos, 22 were construction workers. The proportion of lower-lobe tumors increased with the duration of exposure from 45% in those working less than 15 years to 82% in those working 15 years or more in the construction trade, as compared with 25% in patients who were probably not exposed. The location of the tumor in the lower lobe was explained by the high number of total fibers [odds ratio (OR) = 9.0, CI = 2.3-34.6), of fibers 3 microns and longer (OR = 22.1, CI = 3.9-125), and fibers of anthophyllite (OR = 14.6, CI = 2.4-83.4) and crocidolite (OR = 7.0, CI = 1.2-41.2) when the effect of smoking and fibrosis was adjusted in the logistic regression analysis. The location of the tumor did not correlate with fibrosis, pack-years smoked, or the number of short (< 3 microns) fibers. Our findings suggest that asbestos causes an excess of lower-lobe tumors at a relatively low exposure level, independently of pulmonary fibrosis.

Asbestos↗
PubMed2002

Analysis of cladding-mode couplings for a lensed fiber integrated with a long-period fiber grating by use of the beam-propagation method.

The beam-propagation method (BPM) is employed to analyze the coupling behavior of our scheme proposed previously, which combines a lensed fiber and a long-period fiber grating (LPFG) [Chen and Wang, Appl. Opt. 39,4490-4500 (2000)]. The influences of a core within the fiber lens are investigated. As for the fiber dependence of our coupling scheme, two typical fibers are studied: dispersion-shifted and single-mode, step-index fibers. With the BPM, the optimal coupling efficiencies for various source waists with corresponding lens radii and working distances are determined. We also compare the results with those obtained by use of the ABCD method and found that the BPM gives better agreement with experimental results.

Journal Article↗
PubMed2002

Influence of scattering on transmission through long-period fiber gratings and tunable microstructure fibers.

Controlled optical scattering within or around an optical fiber provides a potentially useful mean for adjusting its transmission characteristic. This approach can complement conventional methods based on the establishment of well-defined variations in the index of refraction of the core or the cladding of the fiber. We describe the use of a highly scattering submonolayer of nanoparticles deposited onto the fiber surface for adjusting the resonance wavelength, depth, and width of an in-fiber long-period grating filter. We also introduce a polymer-dispersed liquid-crystal material that has a thermally tunable scattering cross section and can be incorporated into the channels of a microstructure optical fiber; this system may provide the means for a fiber-based scattering switch.

Journal Article↗
PubMed2003

Design optimization of a dual-core dispersion-compensating fiber with a high figure of merit and a large effective area for dense wavelength-division multiplexed transmission through standard G.655 fibers.

We report design optimization in terms of index-profile parameters of a dual-core dispersion-slope-compensating fiber suitable for broadband dispersion compensation in standard G.655 and G.655b single-mode fibers over the C and L bands of fiber amplifiers and additionally over the S band for the G.655b fibers. It takes into account profiles that can be achieved with state-of-the-art fabrication techniques such as modified chemical-vapor deposition. Relatively high mode effective areas ensure the reduced sensitivity of the fiber to detrimental nonlinear effects when the fiber is integrated into a dense wavelength-division-multiplexed network. The theoretical figures of merit of these DCFs were found to be > or = 700 (ps/dB)/nm; furthermore, the estimated bend losses were also quite low, even for bend radii as small as 16 mm.

Journal Article↗
PubMed2005

Optical-fiber-to-waveguide coupling using carbon-dioxide-laser-induced long-period fiber gratings.

Optical fibers are expected to play a role in chip-level and board-level optical interconnects because of limitations on the bandwidth and level of integration of electrical interconnects. Therefore, methods are needed to couple optical fibers directly to waveguides on chips and on boards. We demonstrate optical-fiber-to-waveguide coupling using carbon-dioxide laser-induced long-period fiber gratings (LPFGs). Such gratings can be written in standard fiber and offer wavelength multiplexing-demultiplexing performance. The coupler fabrication process and the characterization apparatus are presented. The operation and the wavelength response of a LPFG-based optical-fiber-to-waveguide directional coupler are demonstrated.

Journal Article↗
PubMed2005

Fabrication of long-period fiber gratings by twisting a standard single-mode fiber.

A new method of fabrication of long-period fiber gratings by twisting of a standard single-mode fiber at high temperature is presented. The method relies on the fact that there always exists some core-cladding eccentricity in the optical fiber. Therefore, when the fiber is twisted, its core follows a helicoidal path inside the cladding. The transmission spectrum of the helicoidal long-period fiber grating that is produced contains several dips that correspond to resonances with the fiber cladding modes.

Journal Article↗
PubMed1981

Accumulation of fibers in the eyes of workers handling man-made mineral fiber products.

The external eye can be considered a passive dust sampler. Foreign material deposited in the conjunctival cul-de-sac becomes enclosed by mucous fibrils. The fibrils adhere to the conjunctival mucous thread. Hence, by removing the mucus, one can study, eg, man-made mineral fibers deposited in the eye. In this study a simple method for this purpose has been developed, and the sampling characteristics of the eye for nonrespirable fibers is described. The numbers of nonrespirable fibers accumulated in the eyes correlated with the total dust exposure dose (correlation coefficient r = 0.92) and with the nonrespirable fiber exposure dose (r = 0.82). There was no correlation between the airborne fiber concentration and the number of fibers in the mucous thread alone.

Air Pollution↗
PubMed1992

[Quantitative skeletal muscle pathology of aging regarding ragged-red fibers and cytochrome c oxidase-negative fibers].

A statistical analysis of mitochondrial abnormality of aging in human skeletal muscle fibers was performed. Sixty one muscle samples were obtained from patients with acute medical illness autopsied strictly within 2 hours after death, or with orthopedic or surgical diseases biopsied with informed consents. The patients aged from 16 to 89, averaging 58 +/- 21 years in males and 21 to 92, averaging 55 +/- 20 years in females. Sections were stained by modified Gomori's trichrome, succinate dehydrogenase and cytochrome c oxidase-negative [CCO(-)] fibers approximately in 10,000 fibers in each muscle were evaluated. Both RRF and CCO (-) fibers were not observed below the fourth decade, but sequentially increased with age, especially after the seventh decade. The incidence of CCO (-) fibers was higher than that of RRF. RRF did not necessarily correspond to CCO (-) fibers. The present quantitative pathological result is a useful tool to evaluate the mitochondrial function in fresh human skeletal muscles by the age.

Adolescent↗
PubMed1990

Fiber density in congenital muscle fiber type disproportion. I. Congenital myopathies.

In 15 cases with congenital muscle fiber type disproportion, concentric needle EMG (CNEMG) and single fiber EMG (SFEMG) with fiber density (FD) estimation was performed. The aim of the work was to establish the nature of congenital muscle fiber type disproportion. In 11 cases CNEMG revealed interference pattern on maximal effort and low, polyphasic motor unit action potentials (MUAPs) of short duration indicating a myopathic lesion. In four other cases electromyographic changes were less evident. The FD values were slightly increased in 9 cases. This finding could be explained by pronounced muscle fiber splitting with subsequent ephaptic transmission or even secondary denervation and reinnervation. The most important conclusion from our pilot study is the confirmation of the fact that reinnervation with excessive sprouting is not the only mechanism responsible for muscle fiber type disproportion.

Adult↗
PubMed1995

Parabrachial area and nucleus raphe magnus-induced modulation of electrically evoked trigeminal subnucleus caudalis neuronal responses to cutaneous or deep A-fiber and C-fiber inputs in rats.

The aim of this study was to determine whether trigeminal subnucleus caudalis (Vc) neurons show differential inhibitory effects produced by parabrachial area (PBA) or nucleus raphe magnus (NRM) conditioning stimulation (CS) on their A-fiber versus C-fiber inputs electrically evoked from cutaneous and deep tissues. A total of 55 Vc neurons in urethane/chloralose-anesthetized rats were functionally classified as low-threshold mechanoreceptive (LTM; n = 12), nociceptive (wide-dynamic-range, WDR, and nociceptive-specific, NS; n = 11), deep (D; n = 6), or nociceptive convergent neurons receiving skin and deep inputs (S+D; n = 26). Most neuronal responses were tested for both PBA and NRM CS (20-40 microA) delivered 50 msec prior to test stimulation (1.1-1.5 x threshold) of their mechanoreceptive field (RF) or the hypoglossal nerve (XII). Inhibition of responses to both cutaneous and deep A-fiber and C-fiber inputs occurred in over two-thirds of the Vc neurons tested in each neuronal class, and facilitation of responses was only occasionally found. In general, both PBA (ipsi- and contralateral) and NRM CS produced profound inhibition of electrically evoked responses in all neuron types, e.g., responses reduced to mean values of 50-53% of control in LTM neurons, 35-46% in WDR, NS, and S+D neurons, and 61-63% in D neurons. No significant difference in the magnitude of their inhibitory effects was found between PBA and NRM, and between Vc neuronal responses to A- and C-fiber inputs irrespective of their origin from skin or deep tissues.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Free nerve ending terminal morphology is fiber type specific for A delta and C fibers innervating rabbit corneal epithelium.

1. A delta and C fibers are the smallest diameter and most numerous axons in peripheral nerve bundles. They have been thought to terminate as "free" nerve endings lacking organized structure. The present study used a vital fluorescent dye to selectively visualize living free nerve endings innervating rabbit corneal epithelium, allowing structure to be correlated with electrophysiological and functional characteristics. 2. Conduction velocity measurement of visually identified nerve endings were used to discriminate between C and A delta fibers. C fiber sensory endings terminated as short (< 50 microns) vertically directed processes clustered within the epithelium. A delta fibers terminated as long (0.1-1.2 mm) horizontal processes running parallel to the epithelial surface. 3. Only A delta fiber endings were mechanoreceptive, and the unique elongated structure imparted directional selectivity. Comparison of physiological and electrical activation indicated that mechanical stimuli were transduced in < 600 microseconds. This study confirms previous suggestions of structural and functional specialization for "free" nerve endings.

Animals↗
PubMed1999

Morphometric comparison of the human optic nerve fiber with various other human nerve fibers.

The morphometric characteristics of nerve fibers of the human optic nerve in the chiasmatic region were measured with the combination of an image analyzer and a computer, using the Luxol fast blue-periodic acid-Schiff-hematoxylin discriminative staining method. The mean axonal transverse area of the human optic nerve fibers was 0.644 +/- 0.361 micron 2. Comparison of the size of the axon of the human optic nerve fiber with that of various other human nerves showed optic nerve fibers were definitely thinner than the other nerve fibers, and were surrounded by a thinner myelin sheath. Optic nerves may be more liable to mechanical damage at surgery that previously believed.

Aged↗
PubMed1998

Single muscle fiber analysis of myoclonus epilepsy with ragged-red fibers.

We examined two muscle biopsy specimens from a proband and her mother with myoclonus epilepsy with ragged-red fibers (MERRF), both obtained at an interval of about 10 years, using histochemistry, in situ hybridization, and single-fiber polymerase chain reaction. Total (wild-type and mutant) mitochondrial DNAs (mtDNAs) were greatly increased in ragged-red fibers (RRF) over non-RRF in all muscle specimens analyzed. The proportion of mutant mtDNA was also significantly higher in RRF than in non-RRF. By comparing the first and second muscle biopsied specimens in each patient, we found that while the proportion of RRF, cytochrome coxidase deficient fibers, and mutant DNA in muscle changed over a 10-year period, the proportion of wild-type and mutant mtDNAs in RRF and in non-RRF was similar between the two specimens. These results suggest that the ratio of wild-type to mutant mtDNAs in RRF and non-RRF in MERRF is at a steady state level in each muscle fiber, without replicative advantage of mutant mtDNA.

Adult↗
PubMed1995

Fiber composition and fiber transformations in neck muscles of patients with dysfunction of the cervical spine.

Biopsies of ventral neck muscles (sternocleidomastoid, omohyoid, and longus colli) and dorsal neck muscles (rectus capitis posterior major, obliquus capitis inferior, splenius capitis, and trapezius) were taken from 64 patients who underwent spondylodesis for cervical dysfunction of different etiologies. The muscle fibers were classified histochemically as type I, IIA, IIB, or IIC (transitional or intermediate fibers) according to the pH lability of their myofibrillar ATPase. Signs of muscle fiber transformations were observed in all muscles investigated, as evidenced by an increased relative amount of type-IIC fibers. The transformations occurred independently of (a) the type of muscle (i.e., more "postural" or more "phasic"), (b) the sex and age of the patient, (c) the type of condition, and (d) the presence of additional neurological deficits. Thus, the same pattern of muscular reaction was found in patients with rheumatoid arthritis as in patients with soft-tissue injuries of the neck (e.g., "whiplash injury"). In the ventral muscles and the obliquus capitis inferior, the occurrence of transformations correlated strongly with the duration of symptoms; in the ventral muscles the vast majority of transformations were encountered in patients with a shorter history of symptoms, whereas in the obliquus capitis inferior the reverse occurred. In the other dorsal muscles, no correlation with the duration of symptoms was found. Muscles in which transformations had ceased displayed, on average, a significantly higher percentage of fast type-IIB fibers than were found in muscles with ongoing transformations. This strongly indicates that the transformations proceeded in the direction from "slow oxidative" to "fast glycolytic."

Adolescent↗