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PubMed2001

Changes in adhesion complexes define stages in the differentiation of lens fiber cells.

PURPOSE: During their differentiation, lens fiber cells elongate, detach from the lens capsule, associate at the sutures, and degrade all cytoplasmic membrane-bound organelles. Changes in the expression or organization of cell adhesion and cytoskeleton-associated proteins were correlated with these events during fiber cell differentiation in chicken embryos. METHODS: Fixed or living lenses were sliced with a tissue slicer, permeabilized or extracted with detergents, stained with antibodies or fluorescent-labeled phalloidin, and viewed with a confocal microscope. The distribution of N-cadherin in elongating and mature fiber cells was determined by Western blot analysis. Reverse transcription-polymerase chain reaction (RT-PCR) was used to determine the distribution of vinculin and paxillin transcripts. RESULTS: Staining for N-cadherin and band 4.1 protein decreased soon after fiber cells detached from the capsule. Detergent extraction of lens sections and Western blots of dissected lens regions showed that much of this decrease in staining was due to epitope masking. Vinculin immunoreactivity was barely detectable on the lateral membranes of elongating fiber cells but increased markedly once these cells reached their maximum length and formed the sutures. Staining for paxillin was also low in elongating fiber cells but increased late in fiber cell differentiation, just before the cells destroyed their membrane-bound organelles. Spectrin and ankyrin immunoreactivity did not change when fiber cells reached the sutures. Staining for F-actin increased transiently in cells that had just reached the sutures. Messenger RNAs for vinculin and paxillin were more abundant in maturing than in elongating fiber cells. CONCLUSIONS: The adhesion complexes of lens fiber cells change in organization and composition soon after these cells finish elongating and detach from the capsule. Increased staining for vinculin and paxillin defines distinct stages of fiber cell differentiation that are intermediate between the completion of cell elongation and the time when lens fiber cells degrade their membrane-bound organelles. Remodeling adhesion complexes during fiber cell maturation may assure the stability of fiber-fiber associations, once these cells are no longer transcriptionally active.

Actins↗

PubMed2005

[Local injection of alpha, beta-methylene ATP induces excitation of primary afferent fibers in rats].

OBJECTIVE: To observe the excitation and sensitization of dorsal cutaneous primary afferent fibers induced by P2X agonist alpha, beta-methylene ATP (alphabetame-ATP) in rats. METHODS: By means of single fiber electrophysiological recordings on the nerve filaments isolated from the dorsal cutaneous branches of the T(9)-T(13) spinal nerves, the effects of alphabetame-ATP (100 micromol/L, 10 microl) injection into the cutaneous receptive field on the mechanical threshold and spontaneous discharge of rat primary sensory afferent units were observed. RESULTS: The mean mechanical threshold of Adelta and C fibers prior to alphabetame-ATP injection were 0.384+/-0.018 and 0.943+/-0.102 mN, and lowered to 0.304+/-0.013 and 0.659+/-0.071 mN after the injection, respectively (P<0.05, P<0.01). The mechanical threshold of the Abeta fibers before alphabetame-ATP injection was 0.301+/-0.019 mN, and slightly lowered to 0.288+/-0.018 mN after the injection (P>0.05). Injection of alphabetame-ATP (10 microl) into the receptive fields evoked spontaneous discharge in 7.7% of the Abeta fibers, 66.7% of Adelta fibers and 75.0% of C fibres, respectively, and the proportions of Adelta and C fibers with spontaneous discharge evoked by alphabetame-ATP were significantly greater than that of Abeta fibers (P<0.05). In the control experiments, injection of saline did not significantly affect spontaneous discharge or excite the nerve fibers. The mean discharge frequency of Adelta and C fibers increased from 0.73+/-0.24 and 0.54+/-0.21 impulses/min before injection to 3.05+/-0.65 and 8.53+/-2.04 impulses/min during the injection, with subsequent reduction to 2.40+/-0.60 and 6.68+/-1.68 impulses/min in the following 5 min (P<0.05). In contrast to Adelta and C fibers, Abeta fibers exhibited no significant changes in the mean discharge frequency in response to alphabetame-ATP (0.23+/-0.09 impulses/min before injection, 0.28+/-0.09 impulses/min during injection and 0.22+/-0.14 impulses/min after injection, P>0.05). The excitatory effects of alphabetame-ATP on the discharge rate in Adelta and C primary afferent terminal could be observed in the entire course of experiment. CONCLUSION: Peripheral application of alphabetame-ATP, an ATP analogue, excites and sensitizes a subpopulation of Adelta and C fibers but not Abeta fibers of rat dorsal cutaneous primary afferent fibers.

Adenosine Triphosphate↗

PubMed2006

Computer modeling of secondary fiber development and growth: I. Nonprimate lenses.

PURPOSE: The purpose of this study was to use qualitative and quantitative structural data from nonprimate lenses with branched (Y and line) sutures to generate computer models (animations) of secondary fiber development and suture formation. METHODS: A minimum of 12-18 adult lenses/species (mice, cows, frogs, and rabbits) were used in this study. Lenses were analyzed by light (LM), transmission (TEM), and scanning electron microscopy (SEM). Fiber width, thickness, and length were ascertained from micrographs and by using formulations to calculate distances between degrees of latitude and longitude on asymmetrical oblate spheroids. This information was then used to create scale computer assisted drawings (CADs) of fibers at different stages of their development. The CADs were then placed on a timeline and animated to produce dynamic representations of secondary fiber development and growth. RESULTS: Animating secondary fiber development and suture formation with the inclusion of quantifiable differences in fiber dimensions at progressive stages of their differentiation revealed the following: first, there is the presumption that fibers migrate, rotate, and elongate until they reach their sutural destinations is not likely to be correct. When developing fibers reach approximately 60-65% of their eventual total length, their migration and rotation is complete. The remaining fiber elongation (the production of end segments) occurs without either concomitant cellular migration or rotation. Second, it is presumed that suture branches originate peripherally and are then constructed sequentially until all of the branches come to confluence at the poles is also not likely to be correct. While suture branches do originate peripherally, if the rate of elongation is constant in the anterior and posterior directions (intrafiber elongation speed) and between developing fibers within a forming growth shell (interfiber elongation speed), then only a part of their construction proceeds sequentially toward the poles. A second suture branch origin will be established at the poles resulting in a short distal portion of suture branches being formed sequentially in the reverse direction. Suture formation will conclude when a long proximal and a short distal portion of branches come to confluence within unequal anterior and posterior polar cap regions. This segmented suture formation scheme will be more pronounced in line suture lenses than in Y suture lenses. Third, because lenses with branched sutures have growth shells consisting of fibers of unequal length, fiber maturation is likely to be initiated in these lenses before a growth shell as well as suture formation is completed and would proceed in distinct patterns over a period of time. This is in marked contrast to avian lens fiber maturation which does not begin until growth shell and suture (branchless umbilical) formation is completed and then occurs rapidly and essentially simultaneously across the entire growth shell. CONCLUSIONS: Animations of secondary fiber development and suture formation based on quantitative analysis of electron micrographs reveals important novel aspects of these processes that have not been apparent from the results of previous mechanistic studies. The more complex schemes of fiber differentiation and suture formation presented herein are consistent with the notion that lens function (dynamic focusing) is interdependent on lens structure and physiology. The animations confirm that while all vertebrate lenses have a similar structure, differences in the level of their structural complexity established early in development and maintained throughout life can account for the varying amount of optical quality known to exist between species.

Animals↗

PubMed1987

Muscle fiber type analysis in the mouse m. digastricus, m. stylohyoideus, m. zygomaticus and m. buccinator.

It is generally accepted in vertebrates that large motor nerve fibers innervate the white (fast) muscle fibers and small motor nerve fibers innervate the red (slow) muscle fibers. In the previous study (SHIMOZAWA, NAKAMURA 1985), we showed that nerve branches to the venter caudalis m. digastrici and m. stylohyoideus of the mouse consist of considerably larger myelinated nerve fibers compared with the truncus facialis distal to the foramen stylomastoideum innervating the other skeletal muscles in the face. To examine the relationship between the size of nerve fibers and the type of muscle fibers, we performed, in this investigation, quantitative analysis of muscle fiber types (white, intermediate and red) in the venter rostralis (RD) et venter caudalis (CD) m. digastrici, m. stylohyoideus (St), m. zygomaticus (Zy) and m. buccinator (Bu) of the mouse with the Sudan Black B stain preparations. Ratios of the number of muscle fibers of 3 types were RD (28.1%), CD (24.6%), St (27.5%), Bu (28.5%) less than Zy (40.8%) for the white muscle fibers, the RD (58.5%), CD (62.9%), St (53.9%), Bu (60.3%) greater than Zy (47.3%) for the red muscle fibers, while differences between the ratios for these muscles were not significant for the intermediate muscle fibers. Mean major and minor diameters and average transverse areas of the muscle fibers of 3 types were white greater than intermediate greater than red muscle fiber in all muscles examined in this study. When compared between these muscles, they were RD, CD, St greater than Zy, Bu for any type of muscle fibers.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1986

Age-related fiber order in the ferret's optic nerve and optic chiasm.

Although the mammalian optic tract shows a grouping of fibers by age, with newer fibers nearer the pial surface, the possible rules for fiber ordering in the mammalian optic nerve have not been well defined. In this study, preferential labeling of the older retinal fibers in the ferret, a close relative of the cat, shows that the age-related fiber order in the ferret's optic tract reflects a systematic sorting of fibers by age that occurs in the optic nerve, and that is maintained through the optic chiasm. The older retinofugal fibers, dispersed throughout the nerve near the retina, come to be limited to the perimeter of the nerve as it passes through the optic foramen, while newer fibers come to lie nearest the center of the nerve. These newest fibers approach the ventral surface of the brain nearer the optic chiasm. In the chiasm, as in the tract, the oldest fibers lie furthest from the pial surface of the brain, while newer fibers lie nearer the surface. The age-related fiber ordering in the ferret's optic nerve, with the newest fibers initially being furthest from the surface at the optic foramen, differs from age-related orderings seen in nonmammalian vertebrates, where the newest fibers are always nearest the surface. The changing patterns of fiber ordering along the ferret's optic nerve may relate to changes in the underlying glial structure of the developing nerve.

Age Factors↗

PubMed1984

A comparative study of the membrane structure in different types of muscle fibers in the frog.

The muscle membrane of slow and fast fibers in cruralis and iliofibularis muscles and of intermediate fibers in submaxillaris muscle of the frog is studied in freeze-fracture replicas. A comparison of membrane folds, number, size and distribution of caveolae and of intramembrane particles (IMP) is given. In slow muscle fibers, the membrane folds are systematically present at the level of the I zone with a transversal continuity, whereas in fast and intermediate types the membrane folds are small and are randomly distributed. In slow muscle the caveolae are more numerous at the I zone than in the part corresponding to the center of the sarcomere. In fast muscle, small groups of caveolae form linear patterns, and in intermediate fibers the distribution is random. The number of caveolae in slow muscle fibers is two times more than in fast and intermediate fibers. The mean area of caveolae opening is largest in fast and smallest in slow muscle fibers. The number of IMP is significantly different in the three types of fibers, being highest in slow and lowest in intermediate fibers. The different pattern of folds in slow fibers may correspond to the different contractile properties of this fiber type. The presence of double the number of caveolae in slow fibers correlated to the less elaborate T system in this fiber type shows the possibility that slow fibers may be the result of an arrest during development for the performance of a different function. The difference in IMP density in the three muscle fiber types may be interpreted as the difference in their electrical properties.

Animals↗

PubMed1984

Growth-related order of the retinal fiber layer in goldfish.

The retinal fiber layer and the juxtaretinal portion of the optic nerve of goldfish have been studied with light and electron microscopy in order to determine whether the age-related order of fibers in the nerve originates in the retina. In the retina, no patent spaces (channels) were noted. The fibers ran in fascicles and consisted of two classes: nonmyelinated fibers, which ran superficially (close to the vitreal surface), and "myelinated" fibers, which ran more deeply and were loosely wrapped by processes presumed to be glial. The myelinated fibers were larger and presumably older. The nonmyelinated fibers are believed to be the young ones, from the peripheral, more recently generated, ganglion cells, for the following reasons. (1) Their size and cytoskeletal elements were typical of young axons. (2) They were the only axons in peripheral retina. (3) They were continuous with the nonmyelinated fibers in the nerve, previously shown to be the young ones. (4) When retinal axons were cut peripherally, the degenerating axons were in the superficial part of the fiber layer. (5) Growth cones, presumably from the newest ganglion cells, were always observed at the most superficial position in the fiber layer, in direct contact with the basal lamina of the inner limiting membrane superficially and nonmyelinated fibers deeply. The nonmyelinated fibers always clustered together in the retinal fiber layer and occupied the most central portion in the cross-section of the optic nerve head. Thus, the age-related organization of fibers in the nerve is established in the retina. These results are discussed in the context of growth, with the aim of evaluating the relative importance of four factors that might influence the intraretinal course of the growth cone. Its interactions with other fibers and with the basal lamina of the inner limiting membrane seem to be more important than interactions with the glial end feet or guidance into open, preformed channels.

Aging↗

PubMed1993

Changes in cross-sectional area and capillary supply of the muscle fiber population in equine gluteus medius muscle as a function of sampling depth.

The right and left gluteus medius muscles of 4 mature Andalusian stallions were examined by repeated needle biopsy over a specific area and depth, as well as at different depths, to determine whether the cross-sectional area and capillary supply of the various fiber types are homogeneous throughout the muscle. The muscle biopsy specimens were histochemically analyzed for fiber types (myofibrillar adenosine triphosphatase) and capillaries (amylase-periodic acid-Schiff method). Differences between contralateral sites were not identifiable for any of the analyzed variables. Differences between sampling depths were larger than those between sample sites. The percentage of type-1 fibers increased, and that of type-2B fibers decreased as a function of increased sampling depth, but the relative frequency of type-2A fibers did not change with depth. The mean cross-sectional area of type-1 and type-2A fibers increased significantly, and that of type-2B fibers decreased between the most superficial and the deepest sampling sites. The capillary density and the mean number of capillaries per fiber increased as a function of sampling depth, but significant changes were not recorded between sampling depths for overall mean fiber area. The mean number of capillaries in contact with fibers of each histochemical type increased significantly with increasing sampling depth only for type-1 fibers. However, the number of capillaries in contact with fibers changed significantly, relative to the fiber area, as a function of sampling depth; for type-2B fibers this variable increased, whereas for type-2A and type-1 fibers, it decreased.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed2006

Plasticity of neuromuscular junction architectures in rat slow and fast muscle fibers following temporary denervation and reinnervation processes.

We evaluated the effects of brief, temporary denervation caused by ischiadic nerve-freezing on the processes of degeneration and regeneration of ultrastructural features in neuromuscular junction (NMJ) architecture in different types of rat skeletal muscle fibers. Nerve terminal (NT) area was decreased significantly 12 h after nerve freezing in both fast-twitch (FT) and slow-twitch (ST) fibers. One day after nerve freezing, some terminal axons were absent; decrease in NT area was remarkable in ST fibers, and there was retraction of Schwann cells and perineural epithelial cells. Fiber type-specific differences were observed in pattern of decrease in NT area between 24 h and 7 days after nerve freezing (there was significantly more decrease in FT fibers). The primary synaptic cleft became shallow, and the secondary junctional folds shorter and wider, but the basement lamina filling the subneural apparatus was unaltered. The number of secondary junctional folds decreased gradually between 6 h and 14 days after nerve freezing in both types of fiber. In control muscle fibers, synaptic vesicle density (SVD) per terminal area was significantly higher in FT fibers. The SVD densities decreased following nerve freezing-induced destruction of NMJs, and were minimal 3 days in FT fibers or 7 days ST fibers after nerve freezing. At 3 weeks, regeneration of both FT and ST fibers was well advanced, and all parameters had recovered to control values in FT fibers 28 days after nerve freezing. Severe degradation of the ultrastructural features in NMJs occurred due to temporary denervation during muscle fiber degeneration processes, and these structural changes were all reversible and fiber type-specific.

Animals↗

PubMed2003

Functional adaptability of muscle fibers to long-term resistance exercise.

PURPOSE: We compared the functional properties of muscle fibers from two groups of subjects that differed widely in their training history to investigate whether long-term resistance exercise alters the intrinsic contractile properties of skeletal muscle fibers. METHODS: Vastus lateralis muscle biopsies were obtained from six sedentary males (NT group, age = 23 +/- 1 yr) and six males who had participated in regular resistance exercise training over the preceding 7.6 +/- 1.6 yr (RT group, 22 +/- 1 yr). Chemically skinned muscle fiber segments were activated with a saturating free [Ca2+] to quantify fiber peak Ca2+-activated force (P(o)), unloaded shortening velocity (V(o)), and peak power. Fiber segment myosin heavy chain (MHC) isoform content was identified by gel electrophoresis. RESULTS: Slow and fast fibers from the RT group were larger in CSA and produced greater absolute P(o) and absolute peak power in comparison with fibers from the NT group. However, these differences were no longer evident after P(o) and peak power were normalized to fiber CSA and fiber volume, respectively. V(o)/fiber length was dependent on fiber MHC content but independent of training status. CONCLUSION: Fiber hypertrophy was sufficient to account for intergroup differences in P(o) and peak power of slow and fast fibers. There was no evidence that the intrinsic contractility of slow or fast fibers, as evaluated by force, shortening velocity, and power normalized to the appropriate fiber dimensions, differed between RT and NT groups.

Adaptation, Physiological↗

PubMedDate not supplied

Motor and sensory fibers of the superior laryngeal nerve in the rat. A light and electron microscopic study.

A quantitative and qualitative study of the superior laryngeal nerve (SLN) and its branches was performed on the intact nerve and after experimental denervation procedures. The distribution patterns of the myelinated fibers of the intact internal (SLNI) and external (SLNE) branches in the rat were unimodal with a fiber diameter range of 0.5-12 microns and with peaks at 2-4 microns. Numerous unmyelinated fibers, ranging in diameter from 0.1-2.3 microns, were evenly distributed all over the nerve. The SLNI contained no degenerated myelinated fibers after intracranial vagotomy, but about 25% of the unmyelinated fibers showed degenerative features. In the SLNE 2-10% of the myelinated fibers and about 25% of the unmyelinated fibers were degenerated after the same procedure. Extracranial vagotomy caused degeneration of nearly all fibers in the SLNI and SLNE. Single unmyelinated fibers appeared normal after this procedure. Occasional myelinated and a few unmyelinated fibers were degenerated after excision of the superior cervical ganglion. It is inferred from the results that a majority of the myelinated fibers in the SLN (96-99%) are sensory, with the cell bodies in the extracranial vagal ganglia. The SLNE was also found to be predominantly sensory, as only 2-10% of the myelinated fibers and about 25% of the unmyelinated fibers had their cell bodies in the brainstem. Single myelinated and a few unmyelinated fibers in both the SLNI and SLNE had their origin in the superior cervical ganglion.

Animals↗

PubMed1997

Fiber-matrix interface studies on bioabsorbable composite materials for internal fixation of bone fractures. II. A new method using laser scanning confocal microscopy.

In this study, a new visual characterization method was developed using laser scanning confocal microscopy (LSCM) to study morphologic properties, particularly at the fiber-matrix interface, by optical sectioning of bioabsorbable single-fiber composites. The interface gap width (IGW) between the fiber and matrix, and the changes in IGW after in vitro hydrolysis, named the gap rate (Rg), were measured from images obtained using the LSCM. Higher values for IGW and Rg showed faster degradation of the fiber-matrix interface. These parameters were used to investigate the effects of strain, wicking, different reinforcing fibers, and gamma-irradiation on the fiber-matrix interface morphology. The component materials used were nonbioabsorbable AS4 carbon (C) fibers, bioabsorbable calcium phosphate (CaP), poly(glycolic acid) (PGA), and chitin fibers, and bioabsorbable poly(L-lactic acid) (PLLA) matrix. The application of strain on CaP/PLLA composites increased the IGW up to about 15%, after which there was no change up to 25%. The Rg for CaP/PLLA composites with the fiber ends exposed in vitro (permitting wicking) was greater than for CaP/PLLA with the fiber ends embedded completely within the matrix (preventing wicking). Open-end C/PLLA composites had the slowest rate of interface degradation in vitro, followed by chitin/PLLA, PGA/PLLA, and CaP/PLLA. The exposure of closed-end CaP/PLLA composites to 4 Mrad of gamma-irradiation, in air at room temperature or in vaccuum at 77K, accelerated the rate of interface degradation in vitro. In conclusion, an effective new visual characterization method was developed using LSCM, and it was used to show that (a) moderate strain could accelerate the degradation of the interface, (b) fiber-matrix interface wicking could accelerate the rate of degradation of the interface, (c) the rate of interface degradation depends on the type of fiber used, and (d) gamma-irradiation could accelerate the rate of interface degradation. Furthermore, the results of LSCM analysis of different reinforcing fibers with a PLLA matrix agree with measurements of interfacial shear strength (IFSS) and single-fiber tensile strength reported in Part I of this study.

Chitin↗

PubMed2000

Visualization of nerve fiber orientation in gross histological sections of the human brain.

Diffusion weighted magnetic resonance imaging (DWMRI) allows visualization of the orientation of the nervous fibers in the living brain. For comparison, a method was developed to examine the orientation of fibers in histological sections of the human brain. Serial sections through the entire human brain were analyzed regarding fiber orientation using polarized light. Direction of fibers in the cutting plane was obtained by measuring the azimuth with the lowest intensity value at each point, and inclination of fibers in the section was evaluated using fuzzy logic approximations. Direction and inclination of fibers revealing their three-dimensional orientation were visualized by colored arrows mapped into the images. Using this procedure, various fiber tracts were identified (pyramidal tract, radiatio optica, radiatio acustica, arcuate fascicle, and 11 more). Intermingled fibers could be separated from each other. The orientation of the fiber tracts derived from polarized light microscopy was validated by confocal laser scanning microscopy in a defined volume of the internal capsule, where the fiber orientation was studied in four human brains. The polarization method visualizes the high degree of intermingled fiber bundles in the brain, so that distinct fiber pathways cannot be understood as solid, compact tracts: Neighbouring bundles of fibers can belong to different systems of fibers distinguishable by their orientation.

Aged↗

PubMed1986

Ventral root nonmedullated fibers: proportion, calibers, and microtubular content.

Proportion, caliber, and microtubular content of the L7 ventral root nonmedullated fibers were studied in the cat. Nonmedullated fibers constituted 28% of the axonal population at the far end of the root. The number of myelinated profiles at the far end of the root and in the vicinity of the ventral surface of the cord (1-2 mm distance) was the same whereas the number of nonmedullated fibers decreased toward the proximal site of the root by 42%. Caliber and microtubular content of nonmedullated fibers were assessed only at the far end of the ventral root. Nearly 90% of the axons were smaller than 0.3 micron2. The average cross-sectional area was 0.15 micron2, a value 35% below that of the L7 dorsal root fibers. The microtubular density was highest in the finest fibers (116 microtubules/micron2 in fibers smaller than 0.1 micron2) and decreased with the increase in cross-sectional area (25 microtubules/micron2 for 0.7-0.8 micron2 axons). The number of microtubules per axon in axons of both roots was similar in fibers smaller than 0.3 micron2; in larger axons, composing about 10% of the population, ventral root fibers had more microtubules than dorsal root fibers. The ventral and dorsal nonmedullated fibers differ slightly but significantly in caliber and microtubule content. However, they are similar in contrast to peripheral nonmedullated fibers, which are three to four times as big and contain two to three times as many microtubules as radicular fibers. Our results confirm the presence of a large admixture of nonmedullated profiles in the L7 ventral root of the cat, support the notion that a number of these fibers make a U turn in the ventral root, and suggest that these arise from the central process of the primary sensory axon.

Animals↗

PubMed1991

Trajectory of spinocerebellar fibers passing through the inferior and superior cerebellar peduncles in the rat spinal cord: a study using horseradish peroxidase with pedunculotomy.

The course of spinocerebellar fibers in the rat spinal cord was investigated by injecting horseradish peroxidase into the cerebellar anterior vermis after complete transection of the left inferior and right superior cerebellar peduncles. By this procedure, fibers passing via the inferior cerebellar peduncles (icp-fibers) were labeled retrogradely on the right side of the spinal cord, whereas fibers passing via the superior cerebellar peduncles (scp-fibers) were labeled on the left side. Crossed icp-fibers were located diffusely in the anterior and lateral funiculi in the sacral to lower lumbar segments. They gradually migrated laterally and dorsally in these funiculi and received many uncrossed icp-fibers moving laterally in the lateral funiculus from the gray substance in the upper lumbar to lower thoracic segments. These mixed fibers shifted more dorsally and laterally in the anterior and lateral funiculi to aggregate in the narrow peripheral zone of the lateral funiculus in the upper thoracic and lower cervical segments, and received many crossed fibers in the upper cervical segments. There were more icp-fibers than scp-fibers through the spinal cord. However, the extent of scp-fibers in the anterior and lateral funiculi was essentially the same as that for icp-fibers, except that a few scp-fibers were found in the dorsolateral marginal zone of the lateral funiculus. It has been generally accepted that the dorsal spinocerebellar tract ascends in the dorsal half of the lateral funiculus and enters the cerebellum via the inferior cerebellar peduncle, whereas the ventral spinocerebellar tract ascends in the ventral half of it and takes the superior cerebellar peduncle route. The results of this study suggest that it is necessary to revise this concept.

Animals↗

PubMed1991

Prenatal descent of rubrospinal fibers through the spinal cord of the rat.

This study is the first description of the descent of rubrospinal fibers through the spinal cord of the rat fetus. Either horseradish peroxidase or wheat germ agglutinin-horseradish peroxidase conjugate was injected into the spinal cord, at different levels and at different gestational ages. At embryonic day 17 (E17) fibers from all subdivisions of the nucleus ruber (NR) started their descent towards the spinal cord. At E18 fibers from the ventrolateral NR reached the lower cervical spinal cord, and those from the caudal NR reached the lower thoracic spinal cord. At E19 fibers from the dorsomedial NR and from the parvicellular NR had just reached the cervical spinal cord, while fibers from the ventrolateral and caudal NR descended to lower thoracic levels. At E21 fibers from the dorsomedial NR reached the lower cervical spinal cord. Fibers from the ventrolateral and caudal NR completed their descent through the lumbosacral spinal cord during the first three postnatal days. During their descent the rubrospinal fibers were confined to the white matter of the spinal cord. The earliest descending fibers originated in the caudal NR. Fibers from the caudal part of each magnocellular subdivision of the NR descended before their rostral counterparts. Fibers from the dorsomedial NR only reached the cervical enlargement as the fibers from the ventrolateral NR descended through the cervical enlargement. The somatotopy of the adult rubrospinal projection reflects this sequence; the dorsomedial NR (dmNR) projects to the cervical spinal cord, and the ventrolateral NR (vlNR) projects to the lumbosacral spinal cord. In general, early descending fibers originated from neurons located caudally and ventrolaterally, while later descending fibers originated from neurons located progressively more rostrally and dorsomedially in the magnocellular NR.

Animals↗

PubMed1995

Fiber-type composition of hindlimb muscles in the turtle, Pseudemys (Trachemys) scripta elegans.

A description is provided of the fiber-type composition of several hindlimb muscles of the adult turtle, Pseudemys (Trachemys) scripta elegans. In addition, cross-section areas of each fiber type and an estimation of the relative (weighted) cross-section area (wCSA) occupied by the different fiber types are also provided. Seven muscles were selected for study, based on their suitability for future neurophysiological analysis as components of the segmental motor system, and on their homologies with muscles in other vertebrates. The test muscles were iliofibularis (ILF), ambiens (AMB), external gastrocnemius (EG), extensor digitorum communis (EDC), flexor digitorum longus (FDL), tibialis anterior (TA), and peroneus anterior (PA). Serial sections of these muscles were stained for myosin adenosine triphosphatase (ATPase), NADH-diaphorase, and alpha-glycerophosphate dehydrogenase (alpha-GPDH), thereby enabling fiber-type classification on the basis of indirect markers for contraction speed and oxidative (aerobic) vs. glycolytic (anaerobic) metabolism. All muscles contained three fiber types: slow oxidative (SO; possibly including some non-twitch tonic fibers); fast oxidative glycolytic (FOG); and fast glycolytic (Fg). There were at least 30% FOG and 50% FOG + Fg fibers in the seven muscles, the extreme distributions being the predominantly glycolytic ILF vs. the predominantly oxidative FDL muscle (ILF--15.5% SO, 35.2% FOG, 49.3% Fg vs. FDL--49.1% SO, 41.1% FOG, 9.8% Fg). As in other species, the test muscles exhibited varying degrees of regional concentration (compartmentalization) of the different fiber types. This feature was most striking in ILF. Pronounced compartmentalization was also observed in AMB, EG, PA, TA, and EDC, whereas the distribution of fiber types in the highly oxidative FDL was homogeneous. In five of the seven muscles, fiber size was ranked with Fg > FOG > SO. In terms of wCSA, which provides a coarse-grain measure of the different fiber types' potential contribution to whole muscle peak force, all muscles exhibited a higher Fg and lower SO contribution to cross-section area than suggested by their corresponding fiber-type composition. The largest relative increase in wCSA vs. fiber-type composition were in the ILF and AMB muscles. We conclude that the turtle hindlimb provides some interesting possibilities for testing for a division of labor among different muscles during different movements (e.g., sustained vs. ballistic), and for study of the behavior of the different fiber (and motor unit) types under normal and perturbed conditions. The relationships between the present results and previous findings on homologous muscles of the mammalian (cat, rat) and reptilian (lizard) hindlimb are discussed.

Animals↗

PubMed1994

Identification, distribution, and myosin subunit composition of type IIX fibers in mouse muscles.

The purpose of the present investigation was to study the distribution and subunit composition of type IIX fibers in mouse muscles. The existence of a population of type IIX fibers in fast-twitch muscles of the mouse was shown by mean of immunohistochemistry and gel electrophoresis. In the hindlimb muscles, tibialis anterior (TA) and extensor digitorum longus (EDL), type IIX fibers account for approximately one third of the total fiber number, with the superficial portion of the TA (TAS) being composed exclusively of type IIB and IIX fibers. A similar proportion of IIX fibers was found in diaphragm (DIA) while in tongue muscles approximately 40% of the fibers were IIX. Single fiber gel electrophoresis revealed a significant number of fibers in TAS that contain both IIB and IIX myosin heavy chain (MyHC). This was confirmed with immunohistochemistry, which revealed the presence of fibers with various degrees of staining intensity. This suggests that there may exist a degree of plasticity which results in the conversion of IIX fibers to IIB fibers and vice versa. Analysis of myosin light chain (MyLC) composition of type IIX fibers revealed that the ratio of MyLC3f to MyLC1f was significantly lower than in type IIB fibers.

Animals↗