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PubMed1975

The radial fibers in the globus pallidus.

In our Golgi collection of adult monkey brains the striatal efferents, i.e., the radial fibers in the globus pallidus and the "comb" bundle fibers in the internal capsule and in the cerebral peduncle, are well impregnated in the horizontally sectioned brain and in a sagittal sectioned brain. Since collaterals emerging from radial fibers are seen only in the horizontal series and not in the saggittal series, the interpretation is that they proceed anteriorly and posteriorly only, following the curvature of the pallidal segments, and do not run superiorly or inferiorly as they emerge. Although radial fibers emitting collaterals in the lateral segment and in the medial segment of the globus pallidus have been observed, it has not been possible to observe the same radial fiber emitting collaterals in both pallidal segments and the prospects of ever doing so are not good. The radial fibers converging in the globus pallidus pursue many radii and there is little coincidence between the plane of section and the planes in which they travel. At most only severed radial fiber segments 100-150 microns in length can be found in the horizontal sections needed to observe the collaterals. Moreover, sagittal sections trodorsally, as they pass through the internal medullary lamina to enter the medial segment of the globus pallidus. The radial fibers in the medial segment of the globus pallidus are continuous with the "comb" bundle fibers and appear to be thinner than the radial fibers in the lateral segment of the globus pallidus. It is not proved; nonetheless, the view expressed here is that the radial fibers are thinner in the medial segment of the globus pallidus because they may be the same fibers that gave off collaterals in the lateral segment of the globus pallidus. This is discussed in the light of the electrophysiological disclosure of Yoshida et al. ('71, '72) that caudatopallidal fibers are collaterals off caudatonigral fibers. The afferent plexuses of fine, "bouton en passage" fibers, which completely ensheath the long radiating dendrites in the globus pallidus (Fox et al., '66) are well impregnated in the horizontal series. Obviously, they are formed by a number of ultimate branches converging from the collateral brances of a number of different radial fibers. The divergence, too, in this system must be considerable; however, its true extent can only be surmised from the several radial fibers and radial fiber collaterals seen in the incompletely impregnanted Golgi section. Continued.

Animals↗

PubMed1987

Carbon/graphite fiber reinforced poly(methyl methacrylate): properties under dry and wet conditions.

The flexural properties of poly(methyl methacrylate) (PMMA) reinforced with carbon/graphite (C/G) fibers with three different surface treatments were investigated by transverse bend testing after dry and wet storage. The fibers used were (1) commercially available fibers, (2) cleaned fibers, and (3) cleaned and sized fibers. The coating agents of commercial unidirectional and braided C/G fibers as well as impurities on C/G fibers for medical uses were characterized by means of high-performance liquid chromatography (HPLC). The agar overlay technique was used to assess the cytotoxicity of leachable elements from different fibers and processed composites. Composites with both unidirectional and braided tubular C/G fibers were investigated after storage in water. Fracture stress and flexural modulus decreased when "commercial" fibers were used as reinforcing material. Composites with cleaned and sized fibers gave only minor differences in flexural properties after dry and wet storage. By means of SEM micrographs the adhesion behavior of unsized C/G fibers, epoxy sized fibers, cleaned fibers, and cleaned and sized fibers were assessed. After water storage a substantial part of the cleaned fibers adhered to the matrix material. The adhesion capacity of the other fibers was reduced since the water absorption caused separation of fiber and matrix.

Biocompatible Materials↗

PubMed1990

Metabolic and morphologic properties of single muscle fibers in the rat after spaceflight, Cosmos 1887.

The adaptation of a slow (soleus, Sol) and a fast (medial gastrocnemius, MG) skeletal muscle to spaceflight was studied in five young male rats. The flight period was 12.5 days and the rats were killed approximately 48 h after returning to 1 g. Five other rats that were housed in cages similar to those used by the flight rats were maintained at 1 g for the same period of time to serve as ground-based controls. Fibers were classified as dark or light staining for myosin adenosine triphosphatase (ATPase). On the average, the fibers in the Sol of the flight rats atrophied twice as much as those in the MG. Further, the fibers located in the deep (close to the bone and having the highest percentage of light ATPase and high oxidative fibers in the muscle cross section) region of the MG atrophied more than the fibers located in the superficial (away from the bone and having the lowest percentage of light ATPase and high oxidative fibers in the muscle cross-section) region of the muscle. Based on quantitative histochemical assays of single muscle fibers, succinate dehydrogenase (SDH) activity per unit volume was unchanged in fibers of the Sol and MG. However, in the Sol, but not the MG, the total amount of SDH activity in a 10-microns-thick section of a fiber decreased significantly in response to spaceflight. Based on population distributions, it appears that the alpha-glycerophosphate dehydrogenase (GPD) activities were elevated in the dark ATPase fibers in the Sol, whereas the light fibers in the Sol and both fiber types in the MG did not appear to change. The ratio of GPD to SDH activities increased in the dark (but not light) fibers of the Sol and was unaffected in the MG. Immunohistochemical analyses indicate that approximately 40% of the fibers in the Sol of flight rats expressed a fast myosin heavy chain compared with 22% in control rats. Further, 31% of the fibers in the Sol of flight rats expressed both fast and slow myosin heavy chains compared with 8% in control rats. Immunohistochemical changes in the MG were minimal. These data suggest that the magnitude and direction of enzymatic activity and cell volume changes are dependent on the muscle, the region of the muscle, and the type of myosin expressed in the fibers. Further, the ability of fibers to maintain normal or even elevated activities per unit volume of some metabolic enzymes is remarkable considering the marked and rapid decrease in fiber volume.

Adenosine Triphosphatases↗

PubMed1989

Contractile function of single muscle fibers after hindlimb suspension.

The purpose of this investigation was to determine how muscle atrophy produced by the hindlimb suspension (HS) model alters the contractile function of slow- and fast-twitch single muscle fibers. After 2 wk of HS, small bundles of fibers were isolated from the soleus and the deep and superficial regions of the lateral and medial heads of the gastrocnemius, respectively. The bundles were placed in skinning solution and stored at -20 degrees C until studied. Single fibers were isolated and suspended between a motor arm and force transducer, the functional properties were studied, and subsequently the fiber type was established by myosin heavy chain (MHC) analysis on 1-D sodium dodecyl sulfate polyacrylamide gel electrophoresis. After HS, slow-twitch fibers of the soleus showed a significant reduction in fiber diameter (68 +/- 2 vs. 41 +/- 1 micron) and peak tension (1.37 +/- 0.01 vs. 0.99 +/- 0.06 kg/cm2), whereas the maximal shortening speed (Vmax) increased [1.49 +/- 0.11 vs. 1.92 +/- 0.14 fiber lengths (FL)/s]. A histogram showed two populations of fibers: one with Vmax values identical to control slow-twitch fibers and a second with significantly elevated Vmax values. This latter group frequently contained both slow and fast MHC protein isoforms. The pCa-force relation of the soleus slow-twitch fibers was shifted to the right; consequently, the free Ca2+ required for the onset of tension and for 50% of peak tension was significantly higher after HS. Slow-twitch fibers isolated from the gastrocnemius after HS showed a significant reduction in diameter (67 +/- 4 vs. 44 +/- 3 microns) and peak tension (1.2 +/- 0.06 vs. 0.96 +/- 0.07 kg/cm2), but Vmax was unaltered (1.70 +/- 0.13 vs. 1.65 +/- 0.18 FL/s). Fast-twitch fibers from the red gastrocnemius showed a significant reduction in diameter (59 +/- 2 vs. 49 +/- 3 microns) but no change in peak tension or Vmax. Fast-twitch fibers from the white superficial region of the medial head of the gastrocnemius were unaffected by HS. Collectively, these data suggest that the effects of HS on fiber function depend on the fiber type and location. Both slow-twitch type I and fast-twitch type IIa fibers atrophied; however, only slow-twitch fibers showed a decline in peak tension, and the increase in Vmax was restricted to a subpopulation of slow-twitch soleus fibers.

Animals↗

PubMed1999

In situ microscopic analysis of asbestos and synthetic vitreous fibers retained in hamster lungs following inhalation.

Hamsters breathed, nose-only, for 13 weeks, 5 days/week, 6 hr/day, either man-made vitreous fiber (MMVF)10a, MMVF33, or long amosite asbestos at approximately 300 World Health Organization (WHO) fibers/cc or long amosite at 25 WHO fibers/cc. [World Health Organization fibers are longer than 5 microm and thicker than 3 microm, with aspect ratio >3.] After sacrifice, fiber burden was estimated (left lungs) by ashing and scanning electron microscopy (ashing/SEM) or (right middle lobes) by confocal laser scanning microscopy (CLSM) in situ. In situ CLSM also provided three-dimensional views of fibers retained, undisturbed, in lung tissue. Fibers of each type were lodged in alveoli and small airways, especially at airway bifurcations, and were seen fully or partly engulfed by alveolar macrophages. Amosite fibers penetrated into and through alveolar septa. Length densities of fibers in parenchyma (total length of fiber per unit volume of lung) were estimated stereologically from fiber transsections counted on two-dimensional optical sections and were 30.5, 25.3, 20.0, and 81.6 mm/mm3 for MMVF10a, MMVF33, and low- and high-dose amosite, respectively. Lengths of individual fibers were measured in three dimensions by tracking individual fibers through series of optical sections. Length distributions of amosite fibers aerosolized, but before inhalation versus after retention in the lung were similar, whether determined by ashing/SEM or in situ CLSM. In contrast, the fraction of short MMVF10a and MMVF33 fibers increased and the geometric mean fiber lengths of both MMVFs decreased by approximately 60% during retention. Most likely due to fiber deposition pattern and differences in sampling, fiber burdens [MMVF10a, MMVF33, and amosite (high dose; 269 WHO fibers/cc)] determined by ashing/SEM were 1.4, 1. 5, and 3.5 times greater, respectively, than those calculated from in situ CLSM data. In situ CLSM is able to provide detailed information about the anatomic sites of fiber retention and also fiber lengths and burdens in good agreement with ashing/SEM results.

Administration, Inhalation↗

PubMed1997

Calcium homeostasis of isolated single cortical fibers of rat lens.

PURPOSE: To investigate the calcium homeostasis in single fiber cells isolated from rat ocular lens cortex and to quantify the changes in the concentration of free intracellular calcium [Ca2+]i during the process of disintegrative globulization. METHODS: Individual fiber cells from the cortex of the adult rat lens were isolated by treatment with trypsin in ion-free buffered sucrose. The isolated fiber cells were loaded with the acetoxymethyl esters of Fluo-3 or Calcium Green-2, or with Fluo-3 and Fura Red, and changes in [Ca2+]i of single cortical fibers were measured using a microfluorometer. The time course of increase of [Ca2+]i in fiber cells exposed to Ringer's solution was measured, and the effects on the increase of [Ca2+]i of calcium channel blocker, verapamil, Na-Ca exchange inhibitors Ni2+ and Zn2+, and protease inhibitor, leupeptin, Na+-free and K+-free media and Ca2+-containing isotonic sucrose solution, were investigated. RESULTS: In Hepes sucrose solution (containing approximately 1.5 microM Ca2+), the isolated fiber cells maintained stable values of [Ca2+]i at 99.6+/-10 nM (n = 32). Exposure of the isolated fibers to Ringer's solution (containing 2 mM Ca2+) led to a monoexponential increase of [Ca2+]i at a rate of 0.12 min(-1). This increase in [Ca2+]i was accompanied by disintegration of the isolated fibers into discrete but resealed globules. Changes in [Ca2+]i, monitored by using a two-dye ratiometric method using Fura Red and fluo-3, showed a progressive increase in [Ca2+]i in fibers exposed to Ringer's solution, preceding globulization. The [Ca2+]i in the globules in Ringer's solution, determined using Calcium Green-2, was 3.6+/-0.7 microM (n = 23). Compared with that in fibers in Ringer's solution, the rate of increase of [Ca2+]i in fibers was much slower in the presence of 50 microM verapamil (0.047 min[-1]), in Na+-free (0.086 min[-1]) and in K+-free (0.062 min[-1]) Ringer's solution, or when the fibers were suspended in Hepes-sucrose solution, containing 2 mM Ca2+ (0.046 min[-1]). After 30 minutes, the [Ca2+]i of fiber cells exposed to Ringer's solution, containing 2 mM Ni2+ (574.7+/-29 nM; n = 7) or Zn2+ (402.6+/-77 nM; n = 7) was significantly lower (P < 0.001) compared with that in fiber cells exposed to Ringer's solution alone (1995+/-461 nM, n = 10). In Ringer's solution, leupeptin delayed globulization without significantly affecting the increase in [Ca2+]i. The [Ca2+]i of fiber cells isolated from outer and inner cortex and suspended in Hepes-sucrose was comparable; however, after 15 minutes of exposure to Ringer's solution, [Ca2+]i in fibers from the outer cortex was approximately three times higher than [Ca2+]i in those from the inner cortex. CONCLUSIONS: Exposure to high (millimolar) concentrations of calcium in the external medium leads to an increase in [Ca2+]i of isolated individual fiber cells, which precedes disintegrative globulization. The protective effects of Na+-free and K+-free solutions on globulization appear to be due to a lower rate of increase of [Ca2+]i. Part of the calcium influx may be mediated by L-type calcium channels and by Na-Ca exchange, operating in reverse. Proteolytic inhibitors do not affect the increase in [Ca2+]i but delay globulization by inhibiting calcium-mediated proteolysis. The isolated fiber cells and the disintegrated globules maintain a 100- to 300-fold gradient of calcium across their plasma membranes.

Aniline Compounds↗

PubMed2001

Interrelations of myogenic response, progressive atrophy of muscle fibers, and cell death in denervated skeletal muscle.

Little is known concerning the time-course and structural dynamics of reactivation of compensatory myogenesis in denervated muscle, its initiating cellular mechanisms, and the relationship between this process and the progression of postdenervation atrophy. The purpose of this study was to investigate the interrelations between temporal and spatial patterns of the myogenic response in denervated muscle and progressive atrophy of muscle fibers. Another objective was to study whether reactivation of myogenesis correlates with destabilization of the differentiated state and death of denervated muscle cells. It has remained unclear whether muscle fiber atrophy was the primary factor activating the myogenic response, what levels of cellular atrophy were associated with its activation, and whether the initiation and intensity of myogenesis depended on the local and individual heterogeneity of atrophic changes among fibers. For this reason, our objective was also to identify the levels of atrophic and degenerative changes in denervated muscle fibers that are correlated with activation of the myogenic response. We found that the reactivation of myogenesis in the tibialis anterior and extensor digitorum longus muscles of the rat starts between days 10-21 following nerve transection, before atrophy has attained advanced level, long before dead cells are found in the tissue. Formation of new muscle fibers reaches its maximum between 2 and 4 months following denervation and gradually decreases with progressive postdenervation atrophy. The myogenic response is biphasic and includes two distinct processes. The first process resembles the formation of secondary and tertiary generations of myotubes during normal muscle development and dominates during the first 2 months of denervation. During this period, activated satellite cells form new myotubes on live differentiated muscle fibers. Most of the daughter myotubes in 1- and 2-month denervated muscle develop on the surface of fast type parent muscle fibers, and some of the newly formed muscle fibers express slow myosin. Some fast type parent fibers are weakly or, more rarely, moderately immunopositive for embryonic isomyosin. This indicates that reactivation of myogenesis may also depend on the fiber type. The level of atrophy, destabilization of the differentiated myofiber phenotype, and degenerative changes of individual fibers in denervated muscle are very heterogeneous. The myogenic response of the first type is associated predominantly with fibers of average and higher than average levels of atrophy. Muscle cells that undergo a lesser degree of atrophy also form daughter fibers, although with a lower incidence. We did not find any correlation between the size of newly formed fibers and the level of atrophy of parent fibers. The topographical distribution of new myotubes both in the peripheral and central areas of the mid-belly equatorial sections at the early stages following nerve transection indicates that myogenesis of the first type represents a systemic reaction of muscle to the loss of neural control. These data indicate that activation of the myogenic response does not depend on cell death and degenerative processes per se. The second type of myogenesis is a typical regenerative reaction that occurs mainly within the spaces surrounded by the basal laminae of dead muscle fibers. Myocytes of different sizes are susceptible to degeneration and death, which indicates that cell death in denervated muscle does not correlate with levels of muscle cell atrophy. The regenerative process frequently results in development of abnormal muscle cells that branch or form small clusters. Replacement of lost fibers becomes activated between 2 and 4 months following nerve transection, i.e., mainly at advanced stages of postdenervation atrophy, when cell death becomes a contributing factor of the atrophic process. In long-term denervated muscle, the first and second types of myogenesisoccur concurrently, and the topographical distribution of the myogenic response becomes more heterogeneous than during the first weeks following denervation. Thus, our data demonstrate differential temporal and spatial expression of two patterns of myogenesis in denervated muscle that appear to be controlled by different regulatory mechanisms during the postdenervation period. (c) 2001 Wiley-Liss, Inc.

Animals↗

PubMed2003

[Unmyelinated nerve fibers].

The paper presents a critical review of various current concepts of the structure and kinetics of unmyelinated nerve fiber. A classification of nerve fibers, different from the earlier ones, is proposed, that demonstrates not only the morphological fiber types, but also the kinetics of their reversible transition stages from non-glial to myelinated fiber. Evidence is presented to show the erroneousness of conceptions, still appearing in many publications, that consider the unmyelinated nerve fiber as "the Remak's cable type fiber". According to the current data, "Remak's fiber" is a glial-neurite complex, i.e. a bundle of unmyelinated nerve fibers covered with a single glial cell. Using the electron microscope, it was demonstrated that comparable glial-neurite complexes of myelinated nerve fibers, formed in CNS in a similar way by a single oligodendrocyte, cannot be named a single fiber. Cutting the nerves makes visible that the single fibers forming "the Remak's fiber" stem from different cells, therefore they cannot be a single "fiber". It has been shown for the first time experimentally, that in extreme situations, as a result of contraction of gliocyte processes, unmyelinated fibers may "leave" the glial-neurite complexes and become the nonglial fibers. Some data are presented that may serve as criteria for differentiation of unmyelinated fiber with a stratified sheath from developing myelinated fiber.

Animals↗

PubMed2005

Myosin light chain isoform expression among single mammalian skeletal muscle fibers: species variations.

Extensive heterogeneity in myosin heavy chain and light chain (MLC) isoform expression in skeletal muscle has been well documented in several mammalian species. The initial objective of this study was to determine the extent of heterogeneity in myosin isoform expression among single fibers in limb muscles of dogs, a species for which relatively little has been reported. Fibers were isolated from muscles that have different functions with respect to limb extension and limb flexion and were analyzed on SDS gels, with respect to myosin isoform composition. The results of this part of the study indicate that there are at least four distinct fiber types in dog limb and diaphragm muscles, on the basis of MLC isoform expression: conventional fast (expressing fast-type isoforms of MLC1 (MLC1F) and MLC2 (MLC2F), plus MLC3), conventional slow (expressing slow-type MLC1 (MLC1S) and MLC2 (MLC2S)), hybrid (expressing MLC1S, MLC1F, MLC2S, MLC2F and MLC3) and a second slow fiber type, designated as S1F. S1F fibers express MLC1F, along with MLC1S and MLC2S and relatively low levels of MLC3. The fraction of slow fibers that are S1F fibers varies among dog limb muscles, being greater in limb extensors than flexors. Furthermore, the mean level of MLC1F in S1F fibers is greater in extensors than flexors (mean levels range from approximately 3% to 50% of total MLC1). The study was, therefore, extended to include six additional species, spanning a broad range in adult body size to more thoroughly characterize heterogeneity in MLC isoform expression among mammals. The results indicate that there are distinct patterns in MLC isoform expression among fast and slow fibers among different species. Specifically, large-size mammals have two distinct types of slow fibers, based upon MLC isoform composition (conventional and S1F fibers), whereas small mammals exhibit variations in MLC isoforms between different types of fast fibers, including a fast fiber type that expresses MLC1S (designated as F1S fibers). S1F fibers were absent in rodent muscles and F1S fibers were not found in large mammals. We conclude that extensive variation exists in MLC isoform expression in mammalian skeletal muscle fibers, yet there are distinct patterns among different species and among muscles within an individual species.

Animals↗

PubMed2002

Position of the American Dietetic Association: health implications of dietary fiber.

Dietary fiber consists of the structural and storage polysaccharides and lignin in plants that are not digested in the human stomach and small intestine. A wealth of information supports the American Dietetic Association position that the public should consume adequate amounts of dietary fiber from a variety of plant foods. Recommended intakes, 20-35 g/day for healthy adults and age plus 5 g/day for children, are not being met, because intakes of good sources of dietary fiber, fruits, vegetables, whole and high-fiber grain products, and legumes are low. Consumption of dietary fibers that are viscous lowers blood cholesterol levels and helps to normalize blood glucose and insulin levels, making these kinds of fibers part of the dietary plans to treat cardiovascular disease and type 2 diabetes. Fibers that are incompletely or slowly fermented by microflora in the large intestine promote normal laxation and are integral components of diet plans to treat constipation and prevent the development of diverticulosis and diverticulitis. A diet adequate in fiber-containing foods is also usually rich in micronutrients and nonnutritive ingredients that have additional health benefits. It is unclear why several recently published clinical trials with dietary fiber intervention failed to show a reduction in colon polyps. Nonetheless, a fiber-rich diet is associated with a lower risk of colon cancer. A fiber-rich meal is processed more slowly, which promotes earlier satiety, and is frequently less calorically dense and lower in fat and added sugars. All of these characteristics are features of a dietary pattern to treat and prevent obesity. Appropriate kinds and amounts of dietary fiber for the critically ill and the very old have not been clearly delineated; both may need nonfood sources of fiber. Many factors confound observations of gastrointestinal function in the critically ill, and the kinds of fiber that would promote normal small and large intestinal function are usually not in a form suitable for the critically ill. Maintenance of body weight in the inactive older adult is accomplished in part by decreasing food intake. Even with a fiber-rich diet, a supplement may be needed to bring fiber intakes into a range adequate to prevent constipation. By increasing variety in the daily food pattern, the dietetics professional can help most healthy children and adults achieve adequate dietary fiber intakes.

Cardiovascular Diseases↗

PubMed2001

Postnatal differentiation of unipolar brush cells and mossy fiber-unipolar brush cell synapses in rat cerebellum.

The unipolar brush cells are excitatory, cerebellar granular layer interneurons that receive mossy fiber input on their dendritic brushes in the form of a giant glutamatergic synapse. We investigated the postnatal development of the brush of the unipolar brush cell in lobules IX and X by light microscopy and defined the maturation of mossy fiber-unipolar brush cell synapses and mossy fiber-granule cell synapses by electron microscopy using calretinin immunocytochemistry to identify unipolar brush cells. During the first postnatal week, unipolar brush cells possessed one or two short, branched dendrites. The brush differentiated primarily during the successive 21 postnatal (P) days, during which it underwent progressive maturation. This developmental process was subdivided into stages 1-4, which were descriptively termed protodendritic unipolar brush cell (P2-12), filopodial brush (P12-16), intermediate brush (P16-21), and dendriolar brush (P21-28) stages. Electron microscopic measurements of individual mossy fiber-unipolar brush cell and mossy fiber-granule cell synaptic junctions were made at P12, 16, 21, and 28. While the average length of mossy fiber-unipolar brush cell synapses increased during development, that of mossy fiber-granule cell synapses decreased. Comparisons of the lengths of mossy fiber-unipolar brush cell and mossy fiber-granule cell synapses demonstrated that mossy fiber-unipolar brush cell synapses were longer on average than mossy fiber-granule cell synapses for all ages. Frequency distribution histograms also showed that the percentage of mossy fiber-unipolar brush cell synapses longer than 0.5 microm was lower in the pooled P12-P16 groups than in the pooled P21-P28 groups (8 versus 20%). In contrast, mossy fiber-granule cell synapses longer than 0.5 microm were a small minority at P12, 16, and 21, and occurred rarely at P28. The present study indicates that mossy fiber-unipolar brush cell synapses increase in length with the differentiation of the brush dendrioles, while that of mossy fiber-granule cell synapses decrease with differentiation of the granule cell dendritic claws. The finding that mossy fiber-unipolar brush cell synapses were generally longer than mossy fiber-granule cell synapses may indicate that the properties of the postsynaptic targets play a major role in shaping synaptic appositions within cerebellar glomeruli.

Aging↗

PubMed2005

The effect of rate of distraction osteogenesis on structure and function of anterior digastric muscle fibers.

The authors hypothesized that distraction at a rate of 3 mm/day, compared with mandibular distraction at a rate of 1 mm/day, would produce a maladaptive response in adjacent muscles of mastication. The authors further hypothesized that the maladaptive response would manifest at the single fiber level by means of increased sarcomeric heterogeneity, decreased maximum force output, and increased susceptibility to stretch-induced injury. In an ovine model, distraction osteogenesis of the right hemimandible was performed at either 1 mm/day for 21 days (n = 2) or 3 mm/day for 7 days (n = 2) to achieve a total distraction distance of 21 mm. The left hemimandibles served as controls. After a consolidation period of 2 days, the anterior digastric muscles were harvested; in six randomly selected single fibers from each muscle, maximum calcium-activated force (Po) was measured at optimal sarcomere length. The amount of damage to the sarcomeres in each fiber was assessed microscopically. To test susceptibility to contraction-induced injury, each fiber was given an activated stretch of 20 percent. Compared with control fibers and fibers distracted at 1 mm/day, maximum tetanic force (Po) was significantly lower in fibers distracted at 3 mm/day. Compared with control fibers, specific Po (Po/cross-sectional area) was lower in fibers distracted at 3 mm/day. The number of sarcomeres appearing damaged in fibers distracted at 3 mm/day was significantly higher than in control fibers or in fibers distracted at 1 mm/day. A greater deficit in Po was observed after a single activated stretch in fibers distracted at 3 mm/day than in control fibers or in fibers distracted at 1 mm/day. The authors conclude that distraction of the anterior digastric muscle in sheep at 3 mm/day produces a maladaptive response in the muscle fibers but a rate of 1 mm/day is tolerated by the muscle fibers. These data are consistent with the hypothesis that distraction of skeletal muscle at high rates results in increased heterogeneity of sarcomere lengths and that this increase in heterogeneity is the most likely potential mechanism resulting in whole muscle force deficits and in increased susceptibility to stretch-induced injury in distracted muscles.

Animals↗

PubMed2002

Statistical analysis of fiber area in human skeletal muscle.

Previous research has indicated that 50 fiber measurements per individual for type I and II fibers would be sufficient to characterize the fiber areas. This study replicated the work of McCall et al. (1998) using the three major fiber types (I, IIA, and IIB) and sampling larger populations of fibers. Random blocks of fibers were also examined to investigate how well they correlated with the overall mean average fiber area. Using random blocks of 50 fibers provided an accurate reflection of the type IIB fibers (r = 0.96-0.98) but not for the type I (r = 0.85-0.94) or IIA fibers (r = 0.80-0.91). Type I fibers were consistently reflected by a random block of 150 fibers (r = 0.95-0.98) while type IIA fibers required random blocks of 200 fibers (r = 0.94-0.98), which appeared to provide an accurate reflection of the cross-sectional area. These results indicate that for a needle biopsy different numbers of fibers are needed depending on the fiber type to accurately characterize the mean fiber population.

Histocytochemistry↗

PubMed1996

Force-velocity and force-power properties of single muscle fibers from elite master runners and sedentary men.

Gastrocnemius muscle fiber bundles were obtained by needle biopsy from five middle-aged sedentary men (SED group) and six age-matched endurance-trained master runners (RUN group). A single chemically permeabilized fiber segment was mounted between a force transducer and a position motor, subjected to a series of isotonic contractions at maximal Ca2+ activation (15 degrees C), and subsequently run on a 5% polyacrylamide gel to determine myosin heavy chain composition. The Hill equation was fit to the data obtained for each individual fiber (r2 > or = 0.98). For the SED group, fiber force-velocity parameters varied (P < 0.05) with fiber myosin heavy chain expression as follows: peak force, no differences: peak tension (force/fiber cross-sectional area), type IIx > type IIa > type I; maximal shortening velocity (Vmax, defined as y-intercept of force-velocity relationship), type IIx = type IIa > type I; a/Pzero (where a is a constant with dimensions of force and Pzero is peak isometric force), type IIx > type IIa > type I. Consequently, type IIx fibers produced twice as much peak power as type IIa fibers, whereas type IIa fibers produced about five times more peak power than type I fibers. RUN type I and IIa fibers were smaller in diameter and produced less peak force than SED type I and IIa fibers. The absolute peak power output of RUN type I and IIa fibers was 13 and 27% less, respectively, than peak power of similarly typed SED fibers. However, type I and IIa Vmax and a/Pzero were not different between the SED and RUN groups, and RUN type I and IIa power deficits disappeared after power was normalized for differences in fiber diameter. Thus the reduced absolute peak power output of the type I and IIa fibers from the master runners was a result of the smaller diameter of these fibers and a corresponding reduction in their peak isometric force production. This impairment in absolute peak power production at the single fiber level may be in part responsible for the reduced in vivo power output previously observed for endurance-trained athletes.

Adult↗

PubMed1996

Parapodial swim muscle in Aplysia brasiliana. I. Voltage-gated membrane currents in isolated muscle fibers.

1. We describe voltage-gated membrane currents present in single muscle fibers dissociated from the parapodia (swim appendages) of the marine gastropod mollusk Aplysia brasiliana. These muscles are utilized in swimming behavior and their activity is modulated by serotonin. It is necessary to characterize the innate membrane properties of these fibers before defining the mechanism of action of serotonin in facilitating muscle fiber responses to motoneuron input. 2. Freshly dissociated parapodial muscle fibers appear by morphological criteria to be a uniform population with an average length of 240 microns and width of 15 microns. The average resting potential of all fibers is -56 mV and the fibers contract in response to elevated extracellular K+ concentration or intracellular depolarization. 3. Muscle membrane currents were studied by single-electrode voltage clamp with the use of intracellular microelectrodes. The muscle fibers were found to fall into one of two groups, which we have classified as type I and type II, the former having two voltage-gated outward K+ currents and a small, less frequently seen Ca2+ current. Type II fibers display the same two K+ currents, a prominent Ca2+ current and, in addition, two Ca(2+)-dependent K+ currents, the latter described in a companion paper. 4. Membrane currents were characterized using 1-s voltage ramps and several voltage step protocols, including ones for analyzing K+ tail currents. Both fiber types had similar current-voltage relationships and input resistance of > or = 60 - 300 M omega. The current-voltage curves were quite flat at potentials more negative than resting potential, with no evidence of a voltage-gated, inwardly rectified (anomalous) potassium current. Outward K+ currents and a Ca2+ current were seen to appear at a threshold of near -40 mV. 5. Because type I fibers had no apparent Ca(2+)-activated K+ currents, the two voltage-gated outward K+ currents were most conveniently studied in these fibers. Compared with type II fibers, type I fibers display a relatively slowly rising total outward current with depolarization comprised of a delayed rectifier current and a transient A current (IA). These two currents were distinguished by slightly different thresholds for activation, by inactivation properties of IA, and by their partially selective sensitivity to tetraethylammonium and 4-aminopyridine. 6. Although contraction of all parapodial muscle fibers is dependent on extracellular Ca2+, an inward Ca2+ current was detected in only about one third of type I fibers, and the current was small. A similar and more prominent Ca2+ current was observed in all type II fibers and was analyzed more fully in these cells. This current had an activation threshold near -40 mV and peaked between -10 and 0 mV. It displayed little inactivation with depolarization steps of 80-200 ms, was blocked in the absence of Ca2+ or in the presence of Co2+, and was present, although not enhanced, when Ba2+ was substituted for Ca2+. This current was completely blocked by the dihydropyridine nifedipine (10 microM), and is therefore similar to an L-type Ca2+ current. 7. The voltage-gated membrane currents described in parapodial muscle fibers provide a framework for analyzing possible mechanisms by which serotonin facilitates neuromuscular output. This facilitatory mechanism will provide a better understanding of the role of serotonin in controlling locomotion.

4-Aminopyridine↗

PubMed1996

Quantitative morphology and histochemistry of intrinsic lingual muscle fibers in Macaca fascicularis.

Histological, histochemical, and quantitative morphometric techniques were used to determine muscle fiber-type distributions and sizes in four intrinsic tongue muscles of Macaca fascicularis. Histologically, fiber interdigitation among muscles was striking with pronounced infiltration of endomysium into muscle fascicles. Endomysium and perimysium were most prominent anteriorly. Histochemically, with a sample of 20,106 fibers, type II fibers predominated (73.9%) over type I fibers (26.1%) and 99% of type II fibers were categorized as IIA. The relative density of type I and type IIA fibers varied consistently within all muscles from anterior to posterior and to a lesser degree from superficial to deep. Although the tongue apex was composed almost exclusively of type IIA fibers, the proportion of type I to type IIA fibers increased posteriorly. Most posteriorly, type I and IIA fibers were in about equal proportions. These nonuniform fiber-type concentrations may suggest that different segments of individual primate intrinsic tongue muscles may be functionally independent, supporting recent models of tongue motor system biomechanics. For example, predominantly type IIA fibers in the anterior segments of a given muscle may underlie characteristic rapid tongue tip movements while slower movements of the posterior tongue are executed via separately activated type I fibers. Mean fiber diameters were quantified in one animal (n = 7,758). The distribution was unimodal (5.61-63.03 microns) and overall type IIA fibers were larger than type I fibers. However, within all muscles studied, sizes of both fiber types were greater at posterior sites, further suggesting functional intramuscular segregation.

Animals↗

PubMed1998

Evidence for three adult fast myosin heavy chain isoforms in type II skeletal muscle fibers in pigs.

Three main fiber types (one slow [type I] and two fast [type IIA and IIB] can be distinguished using conventional actomyosin ATPase (AM-ATPase) histochemistry after acidic pretreatment in mature pig skeletal muscle. We report the isolation, characterization, and identification of four adult 3'-untranslated regions corresponding to types I, IIA, IIB, and IIX myosin heavy chains (MyHC) from a cDNA library. Identification of different type II clones was based on sequence homology, in situ hybridizations (ISH), AM-ATPase histochemistry, and immunocytochemistry. Enzyme histochemistry, immunocytochemistry, and ISH were performed on serial transverse sections of longissimus and red portion of semitendinosus muscle. Results showed that all three fast MyHC transcripts were expressed in the longissimus, whereas only type IIA and IIX transcripts were present in deep red semitendinosus muscle. Type I and IIA fibers contained mostly type I and IIA transcripts, respectively, whereas type IIB fibers contained a heterogeneous population of transcripts. In longissimus muscle, 18, 31, and 51% of conventional IIB fibers were pure IIX, hybrid IIX/IIB, and pure IIB fibers, respectively. Conversely, conventional IIB fibers were actually IIX in deep red semitendinosus muscle. Expression of the three fast adult MyHC isoforms in longissimus was spatially regulated around the typical islets of type I fibers encountered in pig skeletal muscle. Thus, IIA fibers were contiguous to type I fibers, pure IIX fibers were in the direct vicinity of type I and IIA fibers, and hybrid IIX/IIB fibers were located mostly within primary fascicles between the islets of type I fibers; however, pure IIB fibers were located mainly at the periphery of the rosettes near the edges of primary fascicles. In light of the present study, conventional IIB fibers, as defined with AM-ATPase staining, are a heterogeneous population that should be split into pure IIX, hybrid IIX/ IIB, and pure IIB fibers for a more accurate fiber typing.

Amino Acid Sequence↗

PubMed1992

Studies on the presence and functional properties of afferent C-fibers in the cat's dental pulp.

The present investigation describes how intradental afferent C-fibers can be identified and characterized in the anaesthetized cat. Functional single fibers innervating the lower canine tooth were recorded from filaments split from the inferior alveolar nerve. Fibers responding to monopolar electrical stimulation of the tooth were classified as slowly and fast conducting according to their conduction velocity (c.v.). The axonal c.v. was determined for 31 slowly conducting fibers by electrical stimulation of the nerve. Sixty-eight percent of these proved to be C-fibers. The slowly conducting fibers had higher activation thresholds, smaller amplitudes and longer durations of the action potentials than the fast conducting fibers. Many of the fast but none of the slowly conducting fibers were repetitively activated by a single stimulus pulse. The highest frequency at which the fibers responded to every stimulus pulse was much lower for the slowly than for the fast conducting fibers. Most of the slowly conducting intradental fibers tested were activated by both hot and cold stimulation of the tooth, by pressure applied to the pulp chamber and by the application of KCl or bradykinin to the pulp. Eight C-fibers responded to mechanical stimulation of the pulp. For some fibers the response magnitude correlated with the stimulus intensity. Many slowly conducting intradental fibers developed an ongoing discharge after heat and pressure stimulation. The results indicate that there exists in the dental pulp of the cat afferent C-fibers that resemble polymodal C-nociceptors. They might be involved in the generation of the dull aching pain present in inflammatory conditions of the pulp. The activation of intradental C-fibers in pulpitis might result either from the elevated pressure and/or by sensitization of the C-fiber endings by inflammatory substances released.

Action Potentials↗