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PubMed2004

Fiber types in rat laryngeal muscles and their transformations after denervation and reinnervation.

The intrinsic laryngeal muscles cricothyroid (CT) and thyroarythenoid (TA) differ in myosin expression. CT expresses limb myosin heavy chains (MyHCs) and TA expresses an MyHC found in extraocular (EO) muscles, in addition to limb isoforms. We used immunohistochemical (IHC) analyses with highly specific monoclonal antibodies (MAbs) against various MyHCs to study muscle fiber types in rat CT and TA and to investigate whether nerves to laryngeal muscles control MyHC expression. CT was found to have the full complement of limb fiber types. TA had three major fiber types: 2b/eo, co-expressing 2B and EO MyHCs, 2x/2b, co-expressing 2X and 2B MyHCs, and 2x, expressing 2X MyHC. Type 2a and slow fibers were absent. TA consisted of two divisions: the external division (TA-X), which is homogeneously 2b/eo, and the vocalis division (TA-V), composed principally of 2x and 2b/eo fibers with a minority of 2x/2b fibers. TA-V had two compartments that differ in fiber type composition. At 4 weeks after cutting and re-uniting the recurrent laryngeal nerve (RLN), many 2b/eo fibers in the TA-X began to express 2X MyHC, while EO and 2B MyHC expression in these fibers progressively declined. By 12 weeks, up to 16.5% of fibers in the TA-X were of type 2x. These findings suggest that nerve fibers originally innervating 2x fibers in TA-V and other muscles have randomly cross-innervated 2b/eo fibers in the TA-X and converted them into 2x fibers. We conclude that CT and TA are distinct muscle allotypes and that laryngeal muscle fibers are subject to neural regulation.

Animals↗
PubMed1993

An immunohistochemical study of sensory and autonomic innervation of the dog tongue with special reference to substance P- and calcitonin gene-related peptide-containing fibers in blood vessels and the intralingual ganglia.

The distribution, pathways and origins of peptide-containing nerve fibers in the anterior two thirds of the dog tongue were investigated using immunohistochemistry combined with retrograde axonal tracing and denervation experiments. Within the epithelium of the fungiform papillae, varicose nerve fibers immunoreactive to substance P (SP) and calcitonin gene-related peptide (CGRP) were present. These disappeared completely after severance of the lingual nerve (LN) alone. Dense CGRP-immunoreactive varicose fibers surrounded cell bodies in the intralingual ganglia (ILG), which consisted of neurons immunoreactive to vasoactive intestinal polypeptide (VIP), neuropeptide Y (NPY) and SP. These CGRP-immunoreactive fibers disappeared following severance of the chorda tympani (CT) alone. SP-, CGRP-, VIP-, NPY- and tyrosine hydroxylase (TH)-immunoreactive nerve fibers were distributed around the walls of blood vessels, especially arteriovenous anastomoses (AVAs). None of these immunoreactive fibers completely disappeared after severance of the LN or CT alone, but SP- and CGRP-immunoreactive fibers disappeared following severance of both the LN and CT. TH-immunoreactive fibers disappeared after ganglionectomy of the superior cervical ganglion (SCG) or severance of the hypoglossal nerve (HGN). VIP- and NPY-immunoreactive fibers invariably remained after various denervation experiments. In tracing experiments, CGRP-immunoreactive as well as SP and CGRP-immunoreactive cells in the trigeminal ganglion were labelled from the LN, and those in the geniculate ganglion and jugular ganglion were labelled from the CT. A large number of neurons in the SCG were labelled from the HGN, with some of these being SP and CGRP-immunoreactive. These results demonstrate that SP- and CGRP-immunoreactive fibers from the trigeminal ganglion are distributed to the lingual epithelium; vascular walls receive SP- and CGRP-immunoreactive sensory fibers from the LN as well as CT, some SP and CGRP-immunoreactive fibers from the SCG in addition to catecholaminergic sympathetic fibers, and VIP- and NPY-immunoreactive parasympathetic fibers from the ILG. The ILG is also considered to be innervated by CGRP-immunoreactive sensory fibers from the CT.

Animals↗
PubMed1988

Fiber and colon cancer.

The human evidence that dietary fiber prevents the development of colon cancer has been reviewed. The correlational studies are consistent with a protective effect in 61.9 per cent of reports. However, these studies are all retrospective and largely uncontrolled. The case-control studies provide evidence of a protective effect in only 48 per cent of reports. It is of additional concern that some human studies have found an association between tumor enhancement and some fiber-containing foods. Whereas this is not sufficient evidence to implicate dietary fiber as a promoter of human colon cancer, it does perhaps argue for a more conservative approach to recommending high-fiber diets as a means of cancer prevention. The animal data show that different sources of dietary fiber produce markedly different effects on colon carcinogenesis. Although some fibers exhibit protective properties, others clearly promote tumor development. The mechanisms behind these opposing actions require further investigation. However, one thing is clear and that is that dietary fibers do modulate the carcinogenic process and as such provide a valuable tool for probing the mechanisms and stages of colon tumor development. Dietary fiber appears to play a major role in the regulation of normal intestinal function and in the maintenance of a healthy intestinal mucosa. Although there is some evidence that a fiber-deficient diet predisposes to colon carcinogenesis, it is still not known whether an increase in fiber consumption will prevent the development of colon cancer. This is further complicated by not knowing what constitutes a normal level of fiber intake. In the interim, physicians should perhaps advise their patients to consume a moderate diet that contains vegetables, fruits, and whole grains. This will provide a varied source of fiber-containing foods and if consumed in sufficient quantity will optimize intestinal transit and bulk according to individual needs. Isolated fiber supplements have not been shown to be effective in colon cancer prevention. Further attempts to be more specific about what type of fiber to recommend seem premature at this time. However, an intake in the range of 20 to 35 gm per day of dietary fiber from foods has recently been recommended by an Expert Panel.

Colonic Neoplasms↗
PubMed1987

Serotonergic afferents to the rat olfactory bulb: II. Changes in fiber distribution during development.

The present studies have defined the developmental time course and distribution patterns of serotonergic fibers in the main olfactory bulb (MOB) using immunocytochemistry, anterograde tracing and image analysis. The results indicate that the deployment of serotonergic fibers to the main olfactory bulb is essentially a postnatal event in the rat. During the first 4 d after birth, 5-HT fibers infiltrate and begin to arborize in the MOB. The density of fibers in each layer is sparse during this period, but increases rapidly. By postnatal day 8 all layers are much more heavily innervated by 5-HT fibers. The surge of fiber growth into all layers is rapid; the fibers arborize earlier at caudal than at rostral levels. This may be related to the increased metabolic activity that is reported to occur selectively in the caudal parts of the immature olfactory bulb. After the second postnatal week, 5-HT fiber density increases much more gradually in all layers except the glomerular layer; in the glomerular layer, 5-HT fiber density continues to increase rapidly. It is also during this time that the olfactory bulb begins to grow substantially in volume. Bulb volume increases from the second week into adulthood (greater than 60 d); during the same period, the density of 5-HT remains relatively constant in the infraglomerular layers. Thus, from the second week onward, the growth of 5-HT fibers appears to be closely linked to the increasing volumes of these layers. The density of 5-HT fibers in the glomerular layer, however, continues to increase from the second postnatal week. Thus, the density of fibers in the glomerular layer increases more than the increase in glomerular size, indicating that the glomerular 5-HT fibers are proliferating more than could be accounted for by simple glomerular expansion. In the adult, 5-HT fibers are 2-3 times denser in the glomerular than the infraglomerular layers (McLean and Shipley, 1987). This preferential innervation of glomeruli may be the result of a protracted period of arborization by glomerular versus infraglomerular fibers. This could be due to the prolonged focal release of a trophic factor by glomerular-associated neurons or to the earlier production of an inhibitory factor by infraglomerular neurons.

Aging↗
PubMed1996

Collateral sprouting of uninjured primary afferent A-fibers into the superficial dorsal horn of the adult rat spinal cord after topical capsaicin treatment to the sciatic nerve.

That terminals of uninjured primary sensory neurons terminating in the dorsal horn of the spinal cord can collaterally sprout was first suggested by Liu and Chambers (1958), but this has since been disputed. Recently, horseradish peroxidase conjugated to the B subunit of cholera toxin (B-HRP) and intracellular HRP injections have shown that sciatic nerve section or crush produces a long-lasting rearrangement in the organization of primary afferent central terminals, with A-fibers sprouting into lamina II, a region that normally receives only C-fiber input (Woolf et al., 1992). The mechanism of this A-fiber sprouting has been thought to involve injury-induced C-fiber transganglionic degeneration combined with myelinated A-fibers being conditioned into a regenerative growth state. In this study, we ask whether C-fiber degeneration and A-fiber conditioning are both necessary for the sprouting of A-fibers into lamina II. Local application of the C-fiber-specific neurotoxin capsaicin to the sciatic nerve has previously been shown to result in C-fiber damage and degenerative atrophy in lamina II. We have used B-HRP to transganglionically label A-fiber central terminals and have shown that 2 weeks after topical capsaicin treatment to the sciatic nerve, the pattern of B-HRP staining in the dorsal horn is indistinguishable from that seen after axotomy, with lamina II displaying novel staining in the identical region containing capsaicin-treated C-fiber central terminals. These results suggest that after C-fiber injury, uninjured A-fiber central terminals can collaterally sprout into lamina II of the dorsal horn. This phenomenon may help to explain the pain associated with C-fiber neuropathy.

Administration, Topical↗
PubMed1998

[Types and dimensions of mineral fibers in the atmosphere and from lungs of residents in the urban area].

OBJECTIVE: The objective of this study was to estimate the types and origin of the mineral fibers in the lungs of residents in the urban area. METHODS: Mineral fibers in the atmosphere from 21 urban areas were analyzed by direct transfer-analytical transmission electron microscopy (ATEM). Lung tissues of 36 urban residents without occupational asbestos exposure were also analyzed by ATEM after low temperature ashing. Measurement of dimensions of all types of mineral fibers, identification of asbestos, and classification of nonasbestos fibers according to the combination of main elements were carried out. RESULTS: 1. Chrysotile, amosite, actinolite, tremolite and 11 types of nonasbestos fibers were found in both the lung tissues and the atmospheric samples. The fibers, mainly composed of Al and Si, contributed 16.3% and 62.3% of the atmospheric samples and lung tissues respectively. On the other hand, the proportion of the fibers mainly composed of S and Ca were 43.7% and 0.0% in the atmosphere and lung tissues respectively. Those fibers mainly composed of P and Fe were 0.4% and 18.4% in the atmosphere and lung tissues respectively. 2. Fifteen types of nonasbestos fibers were found exclusively in the atmosphere. The average proportions for ten of these were less than 0.5% each. 3. Crocidolite was found exclusively in the lung tissues. 4. No significant difference in the geometric mean of length and diameter of asbestos was found between the atmospheric samples and lung tissues. Some types of nonasbestos fibers had significantly larger length and diameter in the atmospheres than in the lung tissues (p < 0.01). CONCLUSION: The results suggest that mineral fibers found in lung tissues could be classified into three groups on the basis of their behavior. 1) Some fibers, such as amphibole asbestos and fibers composed of Al and Si, are inhaled from the atmosphere and remain in the lung tissues for a long time. 2) Some fibers, such as those composed of S and Ca, are inhaled from the atmosphere and eliminated from the lung tissues within a relatively short time. 3) Some fibers found more in the lung tissues than in the atmospheres, such as those composed of P and Fe, are suspected to be generated in the lungs.

Air Pollutants↗
PubMed2005

Stretch-shortening cycle exercises: an effective training paradigm to enhance power output of human single muscle fibers.

Functional performance of lower limb muscles and contractile properties of chemically skinned single muscle fibers were evaluated before and after 8 wk of maximal effort stretch-shortening cycle (SSC) exercise training. Muscle biopsies were obtained from the vastus lateralis of eight men before and after the training period. Fibers were evaluated regarding their mechanical properties and subsequently classified according to their myosin heavy chain content (SDS-PAGE). After training, maximal leg extensor muscle force and vertical jump performance were improved 12% (P<0.01) and 13% (P<0.001), respectively. Single-fiber cross-sectional area increased 23% in type I (P<0.01), 22% in type IIa (P<0.001), and 30% in type IIa/IIx fibers (P<0.001). Peak force increased 19% in type I (P<0.01), 15% in type IIa (P<0.001), and 16% in type IIa/IIx fibers (P<0.001). When peak force was normalized with cross-sectional area, no changes were found for any fiber type. Maximal shortening velocity was increased 18, 29, and 22% in type I, IIa, and hybrid IIa/IIx fibers, respectively (P<0.001). Peak power was enhanced in all fiber types, and normalized peak power improved 9% in type IIa fibers (P<0.05). Fiber tension on passive stretch increased in IIa/IIx fibers only (P<0.05). In conclusion, short-term SSC exercise training enhanced single-fiber contraction performance via force and contraction velocity in type I, IIa, and IIa/IIx fibers. These results suggest that SSC exercises are an effective training approach to improve fiber force, contraction velocity, and therefore power.

Adult↗
PubMed1990

Variation in histochemical enzyme profile and diameter along human masseter intrafusal muscle fibers.

The histochemical enzyme profile of human masseter intrafusal muscle fibers was analyzed in consecutive serial cross sections along the individual fibers. Two hundred intrafusal fibers in 21 muscle spindles were classified. On the basis of equatorial nucleation, myosin ATPase-staining reactions after alkaline and acid preincubations and diameter, four different populations or types of intrafusal fiber were identified: large-diameter alkaline-stable and acid-stable fibers, bag2; two types of fiber with intermediate-diameter, alkaline-labile and acid-labile fibers corresponding to bag1 and alkaline-labile and acid-stable fibers designated as AS-bag1; and small-diameter alkaline-stable and acid-stable (pH 4.6)-acid-labile (pH 4.3) fibers called chain fibers. Regional variability in staining and diameter along the individual fibers was noted. In general, intrafusal fibers showed stronger oxidative reactions than did extrafusal fibers. The enzyme profile of the human masseter intrafusal fibers differed from that of extrafusal fibers in jaw, limb, and trunk muscles and also from that reported for spindles in limb and trunk muscles in man. The result suggests unique properties of human jaw muscle spindles and the jaw motor system.

Adult↗
PubMed2005

Microzonal projection and climbing fiber remodeling in single olivocerebellar axons of newborn rats at postnatal days 4-7.

An adult olivocerebellar axon ramifies into about seven climbing fibers that innervate single Purkinje cells arranged in a longitudinal microzone. To clarify the developmental basis of this projection, individual olivocerebellar axons were labeled with biotinylated dextran amine injected into the inferior olive in rats at postnatal days 4-7. The entire trajectories of single olivocerebellar axons and single terminal arbors of climbing fibers were reconstructed from serial sections of the cerebellum and medulla. Single axons ramified into climbing fibers that terminated in a narrow band-shaped area comparable to the adult microzone. This indicated that olivocerebellar microzones are predetermined. Terminal arbors of climbing fibers were remodeled from loose creeper type, through intermediate transitional type, into dense nest type. Each olivocerebellar axon had some 100 nascent climbing fibers in the creeper stage, whereas each axon had about 10 climbing fibers and about as many atrophic climbing fibers in the nest stage. This decrease indicated that overabundant nascent climbing fibers degenerate concomitantly with the remodeling of remaining climbing fibers. Atrophic terminal arbors and non-climbing fiber thin collaterals were considered the intermediate forms of degenerating climbing fibers. This remodeling and degeneration of climbing fibers may be related to the electrophysiological regression of climbing fiber-Purkinje cell synapses. The remodeling of climbing fibers occurred earliest in lobules VIII (caudal part) and IXa-b, and then in lobules IXc and X. The more developed granular layer in these areas compared to other areas suggests that the cortical environment triggers climbing fiber remodeling.

Adaptation, Physiological↗
PubMed1986

The organization of hypothalamocerebellar cortical fibers in the squirrel monkey (Saimiri sciureus).

The organization and distribution of hypothalamocerebellar cortical fibers in squirrel monkey were investigated by using horseradish peroxidase (HRP, WGA-HRP) and 3H-leucine as anterograde tracers. Following hypothalamic injections, anterogradely labeled fibers coursed bilaterally through the periventricular gray (ipsilateral preponderance) and into the cerebellar white matter. Sparse numbers of labeled fibers appeared to descend into the reticular formation and enter the cerebellum via the brachium pontis. The pattern of cerebellar cortical labeling does not conform to that of mossy or climbing fibers. Labeled axons enter and branch within the granular layer, proceed around Purkinje cell somata, and enter the molecular layer. Within the latter some labeled fibers branch outwardly in a fanlike manner whereas others ascend before branching. Many fibers within the molecular layer ultimately assume an orientation that is similar to that of parallel fibers. The distribution patterns of hypothalamocerebellar cortical axons resemble those reported for monoaminergic fibers in the cerebellar cortex. Afferent fibers to the cerebellar cortex (including hypothalamocerebellar) that do not terminate as mossy or climbing fibers may collectively constitute a third general category of cerebellar afferent axons. On the basis of their distribution within all cortical layers these fibers are designated as multilayered fibers. The morphology of multilayered fibers stands in contrast to the presumptive mossy fiber labeling seen in lobules IX and X following large injections. Such labeling may represent a subpopulation of hypothalamocerebellar fibers or result from enzyme deposition in areas bordering the hypothalamus that project to cerebellar structures.

Animals↗
PubMed1990

Preliminary characterization of bioresorbable and nonresorbable synthetic fibers for the repair of soft tissue injuries.

Preliminary characterizations of two new synthetic fibers were performed to determine their potentials for use in soft tissue scaffolding devices. A slowly bioresorbing random copolymer of dimethyltrimethylene carbonate (DMTMC) and trimethylene carbonate (TMC) was the first fiber evaluated. The second was a nonresorbable high-strength synthetic fiber of highly oriented polyethylene. Their in vitro mechanical behavior was evaluated by loading fibers in uniaxial tension to determine mechanical properties in dry and wet (saline) environments. The polyethylene fiber had a dry strength of approximately 2.0 GPa, an ultimate strain of 3 to 4%, a tangent modulus of 57 GPa, and was not affected by the saline environment. The bioresorbable fiber had a dry strength of approximately 500 MPa, an ultimate strain of 35%, and tangent modulus of 5.4 GPa. The in vitro resorption of the bioresorbable fibers produced a 15% loss in strength over a 10-week period. In vitro cell-fiber compatibility studies were conducted to assay material biocompatibility and fiber substrate efficacy. Fibroblasts proliferated and migrated on both the polyethylene and bioresorbable fibers at rates similar to those previously found for other compatible fibers, thus demonstrating the new materials to be similar in their in vitro biocompatibility profiles. Morphological assessment with SEM also confirmed that these materials were suitable substrates for cell attachment. A rabbit Achilles tendon repair model using oriented polyethylene or bioresorbable fiber tows was evaluated after 12 and 26 weeks of implantation. The mechanical performances of both types of tendon repairs were similar to those found in previous studies using carbon or PET fibers. The polyethylene fibers elicited a low-grade chronic inflammatory tissue response. The bioresorbable fibers were still intact at 26 weeks and remained relatively inert in the host tissue, eliciting a minimal foreign body response.

Animals↗
PubMed1992

The fracture toughness of titanium-fiber-reinforced bone cement.

Fracture of the poly(methyl methacrylate) bone cement mantle can lead to the loosening and ultimate failure of cemented total joint prostheses. The addition of fibers to the bone cement increases fracture resistance and may reduce, if not eliminate, in vivo fracturing. This study discusses the effect of incorporating titanium (Ti) fibers on fracture toughness. Essential characteristics of the composite bone cement included a homogeneous and uniform fiber distribution, and a minimal increase in apparent viscosity of the polymerizing cement. Ti fiber contents of 1%, 2%, and 5% by volume increased the fracture toughness over non-reinforced bone cement by up to 56%. Bone cements of two different viscosities were used as matrix material, but when reinforced with the same fiber type and content, they showed no difference in fracture toughness. Four different fiber aspect ratios (68, 125, 227, 417) were tested. At 5% fiber content, there was no statistically significant dependence of fracture toughness on fiber aspect ratio. Scanning electron microscopy revealed important toughening mechanisms such as fiber/matrix debonding, local fracture path alteration, and ductile fiber deformation and fracture. Fiber fracture was evidence that the critical fiber length was exceeded. The surfaces of the Ti fibers were rough and irregular, indicating that a high degree of mechanical interlock between matrix and fiber was likely. The energy absorption contribution of plastic deformation and ductile fracture is absent in brittle fibers, like carbon, but is a distinction of the Ti fibers used in this study.

Biocompatible Materials↗
PubMed1988

Histochemical and biochemical characterization of two slow fiber types in decapod crustacean muscles.

Myofibrillar proteins in muscles of the claws and abdomen of lobster, Homarus americanus, and the claws of fiddler crab, Uca pugnax, and land crab, Gecarcinus lateralis, have been analyzed with sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Fibers contained numerous isoforms of structural and regulatory proteins in assemblages correlated with fiber type. One fast (F) and two slow (S1 and S2) fibers were identified. All F fibers possessed two isoforms of paramyosin (P1 and P2), while all slow fibers, with the exception of Uca major claw, contained only the P2 variant. S1 and S2 fibers were distinguished by the distribution of a large isoform of troponin-T (T1; Mr = 55,000); S2 fibers in all three species contained T1 in addition to one or two smaller-molecular-weight variants usually associated with S1 fibers. In order to determine whether the slow fibers differed in histochemical properties, land crab claw closer muscle was cryosectioned and stained for myofibrillar ATPase and NADH diaphorase activities. Most S2 fibers had lower ATPase and higher NADH diaphorase activities than S1 fibers, which indicated that S2 fibers had a lower rate of contraction and were more fatigue-resistant than S1 fibers. It is proposed that the S1 and S2 fibers defined by biochemical and histochemical criteria are identical to the slow-twitch and tonic fibers, respectively characterized physiologically.

Adenosine Triphosphatases↗
PubMed2000

Spatiotemporal distribution of zonulae adherens and associated actin bundles in both epithelium and fiber cells during chicken lens development.

Zonulae adherens and associated actin bundles (ZA/AB) are believed to play a major role in epithelial folding and invagination during morphogenesis of neural tube and other vesicular structures. The lens morphogenesis is associated with the formation of the lens vesicle in which ZA/AB would be needed during the formation process. However, the existence of ZA/AB in the lens has never been established. In this study we report for the first time the existence of ZA/AB in both lens epithelium and fiber cells during embryonic development of chicken lens from E4 to E20. Light microscopy revealed contacts between the lens epithelium and primary fiber cells, and between the lens epithelium and secondary fiber cells at E4 and E11, respectively. Thin-section electron microscopy consistently revealed ZA/AB near both the apical ends of lens epithelial cells and primary fiber cells at E4. This arrangement manifests as a parallel pair of belt-like ZA/AB along the epithelium-fiber interface. In semi-tangential sections, a continuous belt-like ZA/AB was also evidenced in individual epithelial cells and fiber cells. Furthermore, the same ZA/AB arrangement was observed near both the apical ends of epithelial cells and secondary fiber cells at E11. Besides ZA/AB, macular-type fasciae adherens were distributed regularly between epithelial cells, between primary fibers, between secondary fibers, and between epithelium and both primary and secondary fibers. Immunofluorescence strongly and preferentially labeled N-cadherin at both the apical ends of lens epithelium and primary or secondary fibers at the corresponding ages, suggesting a direct association with the zonulae adherens. Also punctate N-cadherin labeling was commonly seen along various regions of primary and secondary fiber cells at different ages, and to a larger extent in the mature fibers of older lenses. This study suggests that: (1) ZA/AB located at the apices of lens epithelial cells may play a crucial role in the early stages of lens morphogenesis (e.g. lens vesicle formation); (2) ZA/AB of primary and secondary fiber cells originate from the epithelial cells during their elongation and differentiation; (3) owing to the restricted distribution of ZA/AB, abundant fasciae adherens are needed to maintain the structural stability of the epithelium and fiber cells during development and maturation; and (4) N-cadherin is the principle adhesion protein for both the zonulae adherens and fasciae adherens in the lens.

Actins↗
PubMed2002

Micromechanics of isolated sickle cell hemoglobin fibers: bending moduli and persistence lengths.

Pathogenesis in sickle cell disease depends on polymerization of deoxyhemoglobin S into rod-like fibers, forming gels that rigidify red cells and obstruct the systemic microvasculature. Fiber structure, polymerization kinetics and equilibria are well characterized and intimately related to pathogenesis. However, data on gel rheology, the immediate cause of obstruction, are limited, and models for structure and rheology are lacking. The basis of gel rheology, micromechanics of individual fibers, has never been examined. Here, we isolate fibers by selective depolymerization of gels produced under photolytic deliganding of CO hemoglobin S. Using differential interference contrast (DIC) microscopy, we measure spontaneous, thermal fluctuations in fiber shape to obtain bending moduli (kappa) and persistence lengths (lambda(p)). Some fibers being too stiff to decompose shape accurately into Fourier modes, we measure deviations of fiber midpoints from mean positions. Serial deviations, sufficiently separated to be independent, exhibit Gaussian distributions and provide mean-squared fluctuation amplitudes from which kappa and lambda(p) can be calculated. Lambda(p) ranges from 0.24 to 13 mm for the most flexible and stiffest fibers, respectively. This large range reflects formation of fiber bundles. If the most flexible are single fibers, then lambda(p) =13 mm represents a bundle of seven single fibers. Preliminary data on the bending variations of frozen, hydrated single fibers of HbS obtained by electron microscopy indicate that the value 0.24 mm is consistent with the persistence length of single fibers. Young's modulus is 0.10 GPa, less than for structural proteins but much larger than for extensible proteins. We consider how these results, used with models for cross-linking, may apply to macroscopic rheology of hemoglobin S gels. This new technique, combining isolation of hemoglobin S fibers and measurement of micromechanical properties based on thermal fluctuations and midpoint deviations, can be used to study fibers of mutants, hemoglobin A/S, and mixtures and hybrids of hemoglobin S.

Anemia, Sickle Cell↗
PubMed1977

Mossy and climbing fiber inputs from cutaneous mechanoreceptors to cerebellar Purkynĕ cells in unanesthetized cats.

1. Mossy and climbing fiber inputs from cutaneous mechanoreceptors to Purkynĕ cells of vermis and pars intermedia of the cerebellar anterior lobe were studied in locally anesthetized, paralyzed cats prepared for painless recording sessions. In this preparation the mossy fiber and climbing fiber pathways remain fully functional. Simple spikes and climbing fiber discharges were recorded simultaneously through extracellular glass micro-electrodes and thereafter filtered off from each other for separate, computer-assisted analysis. Controlled mechanical stimulation (air jets, taps, pressure) was performed on the foot pads of all four limbs and on the hairy skin of the limbs and the body. 2. Long term recording of the spontaneous activity of 110 Purkynĕ cells revealed a simple spike activity of 85 imp./s +/- 49 imp./s (mean +/- S.D.) and 1.00+/-0.78 climbing fiber responses per second. 3. Taps to foot pads and air jets to hairy skin revealed that most of the short latency responses via mossy fibers resulted from activation of the receptors of the ipsilateral forefoot. With the same stimuli climbing fiber discharges from the ipsilateral feet were more frequently evoked than from the contralateral feet. Both via mossy and climbing fibers the contralateral hindlimb gave the smallest contribution. 4. Simple spike responses were evoked more commonly by pad stimulation (tap stimuli) than by hair stimulation (air jets). For both types of stimuli excitatory responses were more frequent (3:1) than inhibitory ones. Similarly, pad stimulation was more effective than hair stimulation in inducing climbing fiber responses. Ipsilateral stimuli were much more effective than contralateral ones in evoking both simple spike and climbing fiber responses. 5. Steady pressure stimuli modify the Purkynĕ cell discharges via mossy and climbing fiber pathways. Excitatory and inhibitory effects often of very long duration have been observed via both pathways. Again the ipsilateral forelimb was more effective than the other limbs. Mossy fiber responses were at least three times as common as climbing fiber responses and excitatory responses were more frequent than inhibitory ones. 6. There is no apparent relation between the spontaneous discharge rates of the Purkynĕ cells and the response magnitudes of the mossy fiber and climbing fiber induced excitatory and inhibitory changes inthe impulse pattern of Purkynĕ cells during steady pressure stimuli.

Afferent Pathways↗
PubMed1994

Morphological changes during fiber type transitions in low-frequency-stimulated rat fast-twitch muscle.

This study investigates morphological adaptations of rat extensor digitorum longus muscle to chronic low-frequency stimulation (10 Hz, 10 h/d, up to 61 +/- 7d). During the early stimulation period (2-4 d), increased basophilia and accumulation of RNA were seen predominantly in type-IIB fibers. Putative satellite cell activation, as indicated by 3H-thymidine incorporation, was also evident during this phase. By 12 d, fiber composition remained unaltered, but there was a decrease in the cross-sectional area of the type-IIB fibers. Following 28 d of low-frequency stimulation, the percentage of type-IIB fibers decreased from 43 +/- 3% to 0%, while type-IID fibers increased from 30 +/- 3% to 60 +/- 6%. The fraction of type-IIA fibers tended to increase (controls 19 +/- 3%; stimulated 29 +/- 4%), whereas that of the type-I fibers was unaltered (4 +/- 1%). At this time, the cross-sectional area of type-IID fibers was unaltered, but that of type-IIA and type-I fibers increased. Further stimulation resulted in a return of type-IID fibers to control levels (23 +/- 5%), and a marked increase in type-IIA fibers (45 +/- 8%). The percentage of type-I fibers increased from 4 +/- 1% to 8 +/- 1%. Throughout each stage of chronic stimulation, there was no histological evidence of fiber degeneration and regeneration. These results indicate that, in contrast to the rabbit, chronic low-frequency stimulation-induced fiber conversion in the rat extensor digitorum longus muscle is entirely due to fiber transformation.

Adaptation, Physiological↗
PubMed1976

Analysis of chromatin-associated fiber arrays.

Electron microscopic examination of chromatin from embryonic nuclei of Oncopeltus fasciatus and Drosophila melanogaster reveals arrays of chromatin associated fibers. The lengths and spacings of these fibers were analyzed to provide a basis for defining and interpreting regions of transcriptionally active chromatin. The results of the analysis are consistent with the interpretation of some fibers as nascent RNA with associated protein (RNP). The chromatin segments underlying these fiber arrays were classified as ribosomal or non-ribosomal transcription units according to definitions and criteria described by Foe et al. (1976). Nascent fibers on active ribosomal transcription units were analyzed and compared for Drosophila melanogaster, Triturus viridescens, and Oncopeltus fasciatus. A common feature of the fiber patterns on ribosomal TUs is that origin-distal fibers exhibit greater length variability and a lower slope relative to proximal fibers. The region of increased variability in fiber lengths is correlated with the expected location of 28S ribosomal RNA sequences in the distal half of each ribosomal transcription unit. Because 28S ribosomal RNA appears to contain more extensive regions of base sequence complementarity, we suggest that the length of ribosomal RNP fibers is influenced under our spreading conditions by the secondary structure of the nascent RNA. In order to calculate the RNA content of RNP fibers, chromatin morphology was used to estimate lengths of transcribed DNA. The packing ratio of DNA in chromatin, which we express as the length of B-structure DNA divided by length of chromatin, is 1.1-1.2 and 1.6 for the DNA in active ribosomal and non-ribosomal chromatins, respectively. These DNA packing ratios are used to determine the extent to which nascent RNP fibers are shorter than the transcribed DNA (expressed as DNA/RNP length ratio). For non-ribosomal transcription units and for proximal fibers of ribosomal transcription units. DNA/RNP length ratios are relatively constant within each array. However, considerable variability in this ratio (4-23) is observed for different arrays of fibers. Possible sources of this variability are considered by comparing ratios derived from the presumably identical ribosomal transcription units. Further analysis of the morphology of nascent fibers may elucidate the contributions of proteins and successive RNA sequences to RNP structure.

Animals↗