Total Fiber Diameter Research Articles

Trilobatin contributes to the improvement of myopathy in a mouse model of Duchenne muscular dystrophy.

Duchenne muscular dystrophy (DMD) occurs due to genetic mutations that lead to a deficiency in dystrophin production and consequent progressive degeneration of skeletal muscle fibres, through oxidative stress and an exacerbated inflammatory process. The flavonoid trilobatin (TLB) demonstrates antioxidant and anti-inflammatory potential. Its high safety profile and effective action make it a potent therapy for the process of dystrophic muscle myonecrosis. Thus, we sought to investigate the action of TLB on damage in a DMD model, the mdx mouse. Eight-week-old male animals were treated with 160 mg/kg/day of trilobatin for 8 weeks. Control animals were treated with saline. Following treatment, muscle strength, serum creatine kinase (CK) levels, histopathology (necrotic myofibres, regenerated fibres/central nuclei, Feret's diameter and inflammatory area) and the levels of catalase and NF-κB (western blotting) of the quadriceps (QUA), diaphragm (DIA) and tibialis anterior (TA) muscles were measured. TLB was able to significantly increase muscle strength and reduce serum CK levels in dystrophic animals. The QUA of mdx mice showed a reduction in catalase and the number of fibres with a centralized nucleus after treatment with TLB. In the DIA of dystrophic animals, TLB reduced the necrotic myofibres, inflammatory area and NF-κB and increased the number of regenerated fibres and the total fibre diameter. In TA, TLB increased the number of regenerated fibres and reduced catalase levels in these animals. It is concluded that in the mdx experimental model, treatment with TLB was beneficial in the treatment of DMD.

Gray-White Matter Blurring of the Temporal Pole Associated With Hippocampal Sclerosis: A Microstructural Study Involving 3T MRI and Ultrastructural Histopathology.

Hippocampal sclerosis (HS) is often associated with gray-white matter blurring (GMB) of the anterior temporal lobe. In this study, twenty patients with unilateral temporal lobe epilepsy and HS were studied with 3T MRI including T1 MP2RAGE and DTI/DMI sequences. Anterior temporal lobe white matter T1 relaxation times and diffusion measures were analyzed on the HS side, on the contralateral side, and in 10 normal controls. Resected brain tissue of three patients without GMB and four patients with GMB was evaluated ultrastructurally regarding axon density and diameter, the relation of the axon diameter to the total fiber diameter (G-ratio), and the thickness of the myelin sheath. Hippocampal sclerosis GMB of the anterior temporal lobe was related to prolonged T1 relaxation and axonal loss. A less pronounced reduction in axonal fraction was also found on imaging in GMB-negative temporal poles compared with normal controls. Contralateral values did not differ significantly between patients and normal controls. Reduced axonal density and axonal diameter were histopathologically confirmed in the temporopolar white matter with GMB compared to temporal poles without. These results confirm that GMB can be considered an imaging correlate for disturbed axonal maturation that can be quantified with advanced diffusion imaging.

Disrupted CXCR2 Signaling in Oligodendroglia Lineage Cells Enhances Myelin Repair in a Viral Model of Multiple Sclerosis.

CXCR2 is a chemokine receptor expressed on oligodendroglia that has been implicated in the pathogenesis of neuroinflammatory demyelinating diseases as well as enhancement of the migration, proliferation, and myelin production by oligodendroglia. Using an inducible proteolipid protein (Plp) promoter-driven Cre-loxP recombination system, we were able to assess how timed ablation of Cxcr2 in oligodendroglia affected disease following intracranial infection with the neurotropic JHM strain of mouse hepatitis virus (JHMV). Generation of Plp-Cre-ER(T)::Cxcr2flox/flox transgenic mice (termed Cxcr2-CKO mice) allows for Cxcr2 to be silenced in oligodendrocytes in adult mice following treatment with tamoxifen. Ablation of oligodendroglia Cxcr2 did not influence clinical severity in response to intracranial infection with JHMV. Infiltration of activated T cells or myeloid cells into the central nervous system (CNS) was not affected, nor was the ability to control viral infection. In addition, the severity of demyelination was similar between tamoxifen-treated mice and vehicle-treated controls. Notably, deletion of Cxcr2 resulted in increased remyelination, as assessed by g-ratio (the ratio of the inner axonal diameter to the total outer fiber diameter) calculation, compared to that in vehicle-treated control mice. Collectively, our findings argue that CXCR2 signaling in oligodendroglia is dispensable with regard to contributing to neuroinflammation, but its deletion enhances remyelination in a preclinical model of the human demyelinating disease multiple sclerosis (MS).IMPORTANCE Signaling through the chemokine receptor CXCR2 in oligodendroglia is important for developmental myelination in rodents, while chemical inhibition or nonspecific genetic deletion of CXCR2 appears to augment myelin repair in animal models of the human demyelinating disease multiple sclerosis (MS). To better understand the biology of CXCR2 signaling on oligodendroglia, we generated transgenic mice in which Cxcr2 is selectively ablated in oligodendroglia upon treatment with tamoxifen. Using a viral model of neuroinflammation and demyelination, we demonstrate that genetic silencing of CXCR2 on oligodendroglia did not affect clinical disease, neuroinflammation, or demyelination, yet there was increased remyelination. These findings support and extend previous findings suggesting that targeting CXCR2 may offer a therapeutic avenue for enhancing remyelination in patients with demyelinating diseases.

Conceptual description of the llama fleece structure and the potential of classing and dehairing

For an overall description of llama fiber, its fleece structure and differences between fleece types are illustrated schematically, defined through a resumed evaluation, and determined as a compound of different fiber types. A dissection method is described and 252 samples of llama fleeces were dissected forming three fiber groups, within which fine, medium, and coarse fibers are gathered separately and, therefore, a dehairing process is simulated. Taking the group of fine fibers as a reference for the product to be obtained by dehairing, an average dehairing yield of 69% was calculated, which varies depending on the fineness of the fleece. The following fiber attributes were analyzed: fiber diameter, fiber length, crimp frequency, and crimp type. These were evaluated within fiber groups and among fleece types. The process of fleece classing regarding fineness is simulated through successively excluding coarse fleeces when evaluating the results. As a step previous to dehairing, and in order to assemble the most homogenous raw material, the necessity of fleece classing regarding fineness and type was confirmed. Fleece classing regarding fineness including only fleeces with a total mean fiber diameter lower than 28 µm and a subsequent dehairing process resulted in a mean of 21.6 µm for the group of fine fibers, with 96% of the fleeces with a mean fiber diameter of the group of fine fibers lower than 25 µm and 61% lower than 22 µm. We conclude that this segment of fine fibers reflects the potential of llama fiber as a textile raw material.

Effect of long term-administration of aspartame on the ultrastructure of sciatic nerve

Aspartame is the most widely used artificial sweetener worldwide. There is much controversy about the effect of aspartame on different cells in the body. The aim of this study was to evaluate the effect of aspartame on the structure of the sciatic nerve. Thirty adult male albino rats were divided into three groups. Group I served as control; Group II received aspartame orally in a dose of 250mg/kg/d for 3 months; Group III received aspartame at the same dose and for the same period, and was allowed to recover for 1 month. Specimens of sciatic nerve were processed, and semithin and ultrathin sections were examined by light and electron microscopy. A morphometric study was done to evaluate the g-ratio, which is the ratio between the axon diameter and total fiber diameter. Long-term aspartame administration resulted in many degenerative changes affecting mainly the myelin sheath, in the form of focal and extensive demyelination; disruption and splitting of myelin lamellae with loss of compact lamellar structure; and excessive enfolding with irregular thickening of myelin sheaths. Less frequent than those observed in the myelin sheath, some axonal changes were detected, such as compression and distortion. Dilated rough endoplasmic reticulum and vacuolation of the cytoplasm of Schwann cells were also detected. Partial improvement was observed in the recovery group. It was concluded that long-term administration of aspartame had a harmful effect on the structure of sciatic nerve and 1 month stoppage of aspartame was not enough to achieve complete recovery.

Coaxial additive manufacture of biomaterial composite scaffolds for tissue engineering

An inherent difficulty associated with the application of suitable bioscaffolds for tissue engineering is the incorporation of adequate mechanical characteristics into the materials which recapitulate that of the native tissue, whilst maintaining cell proliferation and nutrient transfer qualities. Biomaterial composites fabricated using rapid prototyping techniques can potentially improve the functionality and patient-specific processing of tissue engineering scaffolds. In this work, a technique for the coaxial melt extrusion printing of core-shell scaffold structures was designed, implemented and assessed with respect to the repeatability, cell efficacy and scaffold porosity obtainable. Encapsulated alginate hydrogel/thermoplastic polycaprolactone (Alg-PCL) cofibre scaffolds were fabricated. Selective laser melting was used to produce a high resolution stainless steel 316 L coaxial extrusion nozzle, exhibiting diameters of 300 μm/900 μm for the inner and outer nozzles respectively. We present coaxial melt extrusion printed scaffolds of Alg-PCL cofibres with ∼0.4 volume fraction alginate, with total fibre diameter as low as 600 μm and core material offset as low as 10% of the total diameter. Furthermore the tuneability of scaffold porosity, pore size and interconnectivity, as well as the preliminary inclusion, compatibility and survival of an L-929 mouse fibroblast cell-line within the scaffolds were explored. This preliminary cell work highlighted the need for optimal material selection and further design reiteration in future research.

Improvement of Peripheral Nerve Regeneration following Immunological Demyelination In Vivo

To improve regeneration of the peripheral nervous system, a therapy was utilized in the adult rat sciatic nerve in which nerve regeneration is enhanced following acute crush injury. The authors hypothesized that (1) axon regeneration within a region of injury increases following experimental, immunological demyelination; and (2) regenerated axons partially derive from the proximal motor axons. The sciatic nerves of 10 Sprague-Dawley rats were injected with a demyelinating agent following crush injury, while the nerves of 10 control rats received a crush injury without therapy. The sciatic nerves were harvested at 14 and 28 days. The lesion containing length of the nerve was cut into 1-mm blocks, and specimens were fixed and evaluated using structural and immunohistochemical analyses. A Flouro-Ruby tracer was injected into the sciatic nerves of a separate group of rats to determine the source of axonal regrowth. An epineural injection of complement proteins plus antibodies to galactocerebroside resulted in demyelination followed by Schwann cell remyelination. At 14 days, remyelination was demonstrated spanning the injured sciatic nerve segment. At 28 days, peripheral nerve regeneration was quantified by total axon count, axon density, and nerve fiber diameter. Tracers demonstrated that regeneration arose partially from proximal motor axons. This study demonstrates enhanced regeneration in the peripheral nervous system using experimental, immunological demyelination. Findings indicate that axon count, axon density, and nerve fiber diameter within a region of acute crush injury in the rat sciatic nerve can be improved using a demyelinating treatment.

Regulation of electrospun scaffold stiffness via coaxial core diameter

Scaffold mechanics influence cellular behavior, including migration, phenotype and viability. Scaffold stiffness is commonly modulated through cross-linking, polymer density, or bioactive coatings on stiff substrates. These approaches provide useful information about cellular response to substrate stiffness; however, they are not ideal as the processing can change substrate morphology, density or chemistry. Coaxial electrospinning was investigated as a fabrication method to produce scaffolds with tunable stiffness and strength without changing architecture or surface chemistry. Core solution concentration, solvent and feed rate were utilized to control core diameter with higher solution concentration and feed rate positively correlating with increased fiber diameter and stiffness. Coaxial scaffolds electrospun with an 8wt./vol.% polycaprolactone (PCL)-HFP solution at 1mlh–1 formed scaffolds with an average core diameter of 1.1±0.2μm and stiffness of 0.027±3.3×10–3Nmm–1. In contrast, fibers which were 2.6±0.1μm in core diameter yielded scaffolds with a stiffness of 0.065±4.7×10–3Nmm–1. Strength and stiffness positively correlated with core diameter with no significant difference in total fiber diameter and interfiber distance observed in as-spun scaffolds. These data indicate that coaxial core diameter can be utilized to tailor mechanical properties of three-dimensional scaffolds and would provide an ideal scaffold for assessing the effect of scaffold mechanics on cell behavior.

Fabrication of Nonwoven Coaxial Fiber Meshes by Electrospinning

There is a great need for biodegradable polymer scaffolds that can regulate the delivery of bioactive factors such as drugs, plasmids, and proteins. Coaxial electrospinning is a novel technique that is currently being explored to create such polymer scaffolds by embedding within them aqueous-based biological molecules. In this study, we evaluated the influence of various processing parameters such as sheath polymer concentration, core polymer concentration and molecular weight, and salt ions within the core polymer on coaxial fiber morphology. The sheath polymer used in this study was poly(e-caprolactone) (PCL), and the core polymer was poly(ethylene glycol) (PEG). We examined the effects of the various processing parameters on core diameters, total fiber diameters, and sheath thicknesses of coaxial microfibers using a 2(4) full factorial statistical model. The maximum increase in total fiber diameter was observed with increase in sheath polymer (PCL) concentration from 9 to 11 wt% (0.49+/-0.03 microm) and salt concentration within the core from 0 to 500 mM (0.38+/-0.03 microm). The core fiber diameter was most influenced by the sheath and core polymer (PCL and PEG, respectively) concentrations, the latter of which increased from 200 to 400 mg/mL (0.40+/-0.01 microm and 0.36+/-0.01 microm, respectively). The core polymer (PEG) concentration had a maximal negative effect on sheath thickness (0.40+/-0.03 microm), while salt concentration had the maximal positive effect (0.28+/-0.03 microm). Molecular weight increases in core polymer (PEG) from 1.0 to 4.6 kDa caused moderate increases in total and sheath fiber diameters and sheath thicknesses. These experiments provide important information that lays the foundation required for the synthesis of coaxial fibers with tunable dimensions.

Measurements and mapping of 282,420 nerve fibers in the S1–5 nerve roots

The study aims to analyze nerve fiber types in the sacral nerve roots as a prerequisite for stimulation. One-micrometer cross-sections of human ventral and dorsal S1-5 roots were stained with osmium and toluidine blue. The total fiber diameter and myelin sheath were measured in 282,420 nerve fibers. The analysis revealed the following 3 main nerve fiber types: Aalpha fibers (diameter 6-14 microm), Agamma fibers (diameter 2-4 microm), and B fibers (diameter < 2 microm). The B fibers were absent in S-1, present in some S-2 fascicles, and abundant from S-3 to S-5. The Aalpha fibers dominated the S-1 roots and most fascicles of S-2 roots. In the S3-5 roots, only a few Aalpha fibers were present. The relative occurrence of Agamma fibers increased from S-1 to S-5. In dorsal roots, Agamma fibers represented approximately 70% of all nerve fibers in every root and fascicle. The B fibers represented efferent parasympathetic fibers. These fibers were concentrated in certain areas of the nerve roots, not randomly distributed. The Aalpha fibers innervate lower-extremity muscles and sphincters. The inverse correlation of Aalpha and Agamma fibers in the ventral roots from S-1 to S-5 is surprising. In dorsal roots, Agamma fibers may conduct pain, touch, and temperature signals. Highly selective fiber stimulation specific for type, location, and direction may improve sacral nerve stimulation for a spastic bladder in paraplegic individuals.

Aortic Depressor Nerve Myelinated Fibers in Acute and Chronic Experimental Diabetes

Preliminary data from our laboratory have demonstrated baroreflex dysfunction as early as 5 days after the onset of experimental diabetes in rats. The aim of the present study was to determine the morphologic alterations of the aortic depressor nerve of rats submitted to acute (15 days) or chronic (12 weeks) experimental diabetes. Wistar rats received a single intravenous injection of streptozotocin (50 mg/kg) 15 days or 12 weeks before the experiments. Time control animals received vehicle. Under pentobarbital anesthesia the aortic depressor nerves were identified by means of electroneurographic recording simultaneously with the recording of arterial pressure. After identification, the aortic depressor nerves were prepared for light microscopy and our analysis only included the myelinated fibers. Five of 10 aortic depressor nerves from animals with acute diabetes showed clear signs of axonal atrophy with significantly smaller average diameter of myelinated fibers (1.9 +/- 0.1 microm) and their axons (1.0 +/- 0.1 microm) than the time control (2.1 +/- 0.1 microm and 1.2 +/- 0.1 microm, respectively). Histograms of the G-ratio (ratio between axon diameter and total fiber diameter--an index of axonal atrophy) distribution of acute diabetic animal nerves were shifted to the left. All aortic depressor nerves from animals with chronic diabetes showed signs of axonal atrophy with the average diameter of myelinated fibers (2.3 +/- 0.1 microm) and their axons (1.2 +/- 0.1 microm) also being significantly smaller than the time control (2.6 +/- 0.2 microm and 1.5 +/- 0.1 microm, respectively). These findings provide morphologic support for an impaired baroreflex during acute and chronic experimental diabetes.

Stiffness measurements of diamond fibre reinforced plastic composites

Diamond fibre reinforced poly(methylmethacrylate) matrix composite test pieces have been fabricated and their Young's modulus values measured as a function of number of fibres incorporated. The fibres were 50 μm tungsten cores coated with 50 μm of CVD diamond, giving a total fibre diameter of 150 μm with 89% diamond by volume. The composites were made with fibres situated (i) close to one edge, or (ii) close to two opposite edges of the test pieces, in order to maximise the reinforcing effect of the fibres. Plastic matrix composites (PMC) containing two layers of 100 fibres (equivalent to a diamond fibre volume fraction of only 3.5%), exhibit a three-fold increase in the Young's modulus value over that for a corresponding sample of the pure polymer. This is a significantly greater increase than is achieved by inclusion of comparable fibres made from materials such as C fibre, SiC or for the uncoated W wire cores.

MODIFICATION OF POLYMER FOR TISSUE ENGINEERING HEART VALVES

A) Purpose of Study: Cell attachment on a polymer is a critical step when tissue engineering cardiovascular structures. It has been reported that hydrolysis of polyglycolic acid (PGA) mesh by exposure to sodium hydroxide increases cell attachment. This study examines the effect of this treatment on smooth muscle cell (SMC) attachment to a PGA, poly-4-hydroxybuterate (P4HB) composite scaffold. B) Methods: One-cm2 disks of PGA dip-coated in 1% P4HB were prepared. In a first set of experiments, smooth muscle cells (SMC) were delivered onto untreate disks (n=3) and disks treated for 1 minute in 1 M NaOH and then for 2 hours in fetal bovine serum (FBS) (n=3). After six hours the constructs were vacuum died an weighed, and total DNA content per disk was assayed. In a second set of experiments, SMC were delivered onto untreated disks (n=3), disks treated for 1 minute in NaOH (n=3), disks treated for 2 hours in FBS (n=3) and disks treated for minute in NaOH and then 2 hours in FBS (n=3). An alamarBlue® proliferatio assay was used to assess the cell viability and proliferation of SMC on each disk After six days, each disks was vacuum dried and weighed, and total DNA conten was measured. In a third set of experiments, SMC were delivered onto disks treate in 1M NaOH for 1, 3, 5 and 10 minutes. An alamarBlue® proliferation assay was performed. After six days DNA content was measured. Mass analysis and scannin electron microscopy (SEM) was used to assess the effects of NaOH on each dis after 1, 5 and 10 minutes. C) Results: A difference in total DNA content could no be detected between untreated and treated groups after 6 hours (p=0.43) or between the untreated group and any of the treatment combinations after 6 days (NaOH group, p=0.93; FBS group, p=0.30; NAOH and FBS group, p=0.97). A difference in total DNA content after 6 days could not be detected between disks treated with NaOH for different lengths of time (1 min., p=0.12; 3 min., p=0.70; 5min., p=0.18 10min., p=0.19). Treatment with NaOH for 1,5 and 10 minutes reduced the fiber diameter PGA on the disks by 4%, 40% and 62% respectively. Mass analysis showed a comparable decrease in total mass. In conclusion, NaOH treatment of PGA, 1%P4HB composite disks does not affect cell attachment or proliferation Furthermore, surface degradation of PGA fibers by NaOH increases with treatment over time resulting in a decrease in total mass and PGA fiber diameter.

A descriptive and quantitative light and electron microscopy study of the aortic depressor nerve in normotensive rats.

There is no literature report of a detailed morphologic study of the aortic depressor nerve. The aim of this study was to describe the general morphological aspects and to obtain morphometric parameters for the aortic depressor nerve of normotensive Wistar rats (n=12). Before the morphologic studies, nerves were isolated and pressure-nerve activity curves were obtained. Basal mean arterial pressure was 117+/-5 mm Hg, the systolic pressure threshold was 100+/-7 mm Hg, and mean arterial pressure at 50% of maximal activity was 115+/-5 mm Hg and the baroreceptor gain 1.99+/-0.09%/mm Hg. Semithin and thin sections of proximal and distal nerve segments were then examined by light and electron microscopy, respectively. The main nerve components were (1) unmyelinated and myelinated axons; (2) Schwann cells; (3) capillary wall endothelial cells and pericytes; (4) collagen fibers in the epineurium and endoneurium and between perineurial cell layers; and (5) fibroblasts and mast cells. The depressor nerves were found to contain 204-996 axons per nerve, 80% of which, on average, were unmyelinated, with a 4:1 unmyelinated/myelinated axon ratio. The unmyelinated axon histogram was unimodal, with a mean diameter of 0.5+/-0.02 microm. Myelinated fibers had axons averaging 1.3+/-0.06 microm in diameter and representing 53% of the total fiber diameter. The ratio between axonal and total fiber diameter of myelinated fiber ranged from 0.4 to 0.8 and tended to increase with axon size. Proximal and distal segments were morphologically similar. In conclusion, the morphologic description of the depressor nerve provides important data for further investigations of the structural basis of altered baroreflex responses in conditions such as arterial hypertension, aging, atherosclerosis, and peripheral neuropathies.

SURAL NERVE MORPHOMETRY IN DIABETIC AUTONOMIC AND PAINFUL SENSORY NEUROPATHY

Observations have been made on a selected series of insulin-dependent patients with neuropathy, subdivided into three groups: (1) severe autonomic neuropathy with an accompanying painless sensory neuropathy; (2) severe autonomic neuropathy with a chronic painful sensory neuropathy; and (3) chronic or acute painful sensory neuropathy with no autonomic neuropathy. All three groups showed a loss of large and small myelinated nerve fibres in sural nerve biopsy specimens which was greater in Groups 1 and 2. Regenerative activity was prominent in all three groups, but least in Group 3. Teased fibre studies showed evidence both of axonal regeneration and remyelination. Active fibre degeneration was rare. Measurements of g ratio (axon diameter:total fibre diameter) gave no indication of axonal atrophy. The density of unmyelinated axons was reduced in all three groups, as was their median diameter. Vibration sense threshold was positively correlated with the total number of myelinated fibres and thermal sensory threshold with median unmyelinated axon diameter but not with total unmyelinated axon numbers. No correlation between the occurrence of pain and active degeneration of myelinated fibres or with regenerative activity either in myelinated or unmyelinated axons was detectable. Assessment of differential loss of large or small myelinated nerve fibres was difficult because of the presence of large numbers of small regenerating myelinated axons. The results are discussed in relation to the concept of 'diabetic small fibre neuropathy' and the causation of pain in diabetic neuropathy.

Relative growth and maturation of axon size and myelin thickness in the tibial nerve of the rat

Morphometric observations have been made on the medial plantar division of the tibial nerve (MPD) and on the motor branches of the tibial nerve to the calf muscles (MBC) in rats ranging in age from weaning (3 weeks) to 12 months. Axon size, assessed by measurements of circumference and cross-sectional area, increased rapidly until 3 months with further slight increases between 3 and 9 months and a slight fall between 9 and 12 months. Axon size distributions were unimodal throughout in the MPD but bimodal for the MBC except at 3 weeks. Distributions of myelin thickness were bimodal throughout for both nerves. Scatter plots of g ratios (axon diameter:total fibre diameter) confirmed the presence of two fibre populations: a group of small fibres with relatively thin myelin sheaths, and a group of larger fibres within which sheath thickness was relatively less on the larger than on the smaller axons. These two fibres populations were less easily separable in the MBC than in the MPD nerves. These results document morphometrically the normal growth changes in the rat tibial nerve and also provide control data for the analysis of the effects of experimental procedures on the growth and maturation of peripheral nerve fibres.

X-linked recessive bulbospinal neuronopathy. A clinicopathological study.

A clinicopathological study on X-linked recessive bulbospinal neuronopathy was undertaken on 9 cases, with morphological observations on 3 autopsied cases and sural nerve biopsies from 6 patients. Both lower motor and primary sensory neurons were involved. Lower motor neurons were markedly depleted through all spinal segments and in brainstem motor nuclei except for the third, fourth and sixth cranial nerves. Primary sensory neurons were less severely affected. A quantitative study of primary sensory axons at several levels in the peripheral nervous system suggested that a distally accentuated axonopathy was the salient pathological process. Segmental demyelination and remyelination clustered on individual fibres, and g ratios (axon diameter: total fibre diameter) in the sural nerve showed an increased scatter in some cases. Evidence of regeneration was inconspicuous. Unmyelinated fibres were well preserved throughout all the nerves examined. Neurons in the Onufrowicz nuclei, in the intermediolateral columns and in Clarke's columns of the spinal cord were generally well preserved. These observations indicate that a lower motor and primary sensory neuronopathy is a major neurological manifestation in this disease.

Effect of exercise and pre-slaughter stress on pork muscle characteristics

The effects of exercise, stress and chill temperature on pork muscle characteristics were studied in a 3 × 2 × 2 factorial experiment in which treatments were assigned to blocks made up of six pigs of the same sex from the same litter. Pigs were fed a corn-soybean meal diet with the two littermate pigs on each treatment fed together. Treatments were (1) a control group receiving no exercise and fed in an 8 m 2 pen; (2) a treatment group fed in an 8 m 2 pen and driven 1·6 km/day for 100 days prior to slaughter; and (3) a treatment group fed in pens with 40 m 2 floor space with feeders placed 5 m from their waterers. When the animals averaged approximately 105 kg in weight, one animal from each pair treated alike was subjected to standardized stress. After slaughter, one side was chilled at 2–3°C and the other at 13–15°C for 24 h. Both sides were then chilled at 2–3°C for an additional 24 h. Exercise did not affect average daily gain (ADG), feed efficiency, yield of total wholesale cuts, muscle pH, protein solubility, fiber diameter and sarcomere length of the Longissimus dorsi (LD) and Quadriceps femoris (QF) muscles or the tenderness of the QF muscle. Exercise decreased backfat thickness and the subjective tenderness of the LD muscle. The effects of stress on the characteristics evaluated were consistent with those that have been previously reported. Chilling temperature and interactions involving chilling temperature did not affect any of the characteristics studied. No exercise × stress interactions were observed. Protein solubility values indicated that pale, soft exudative (PSE) muscle was not a factor in any of the treatments. It was concluded that exercise will produce leaner carcasses but less tender muscle and that exercise will not counteract the effects of pre-slaughter stress.

Internodal Schwann cell fingers in the ventral spinal roots in mice: Incidence and relationship to the diameter of myelinated fibers

Internodal Schwann cell fingers were present in the lumbar, cervical, and thoracic spinal roots of adult mice at the age of 3 months, but they were not recognized in five mice examined at the age of 3 weeks. In the L4 ventral roots of ICR mice aged 3 months, the incidence of internodal Schwann cell fingers was 0.79% at the centralperipheral transitional zone and 2.43% at the distal regions, respectively. The ratio of axon diameter to total fiber diameter of myelinated fibers with internodal Schwann cell fingers was lower than that of fibers without them. Therefore, we conclude that internodal Schwann cell fingers are probably related to the developmental increase in the thickness of the myelin sheaths in the ventral spinal roots at all levels of the spinal cord.

A morphometric study of human fetal sural nerve

A morphometric study was performed on sural nerves from human fetuses at 15 to 36 weeks postovulation. There were no myelinated fibres at 15 and 16 weeks, but by 21 weeks there were 5,000/mm2, rising to 25,000/mm2 at 36 weeks. During the fetal period, the mean myelin lamellar count trebled and the g ratio (axon diameter: total fibre diameter) decreased from 0.90 to 0.75, although the axon diameter of myelinated fibres did not increase. The smallest myelinated axon diameter was 0.63 micron, whereas the largest unmyelinated axon in a 1:1 relationship with a Schwann cell was 2.83 micron, suggesting that axon size is unlikely to be the only stimulus for myelination. The density of unmyelinated axons that were the sole occupants of a Schwann cell fell considerably between 23 and 33 weeks, while the ratio of total unmyelinated axons to myelinated fibres decreased from 82:1 at 21 weeks to 6:1 at 36 weeks. Data for Schwann cell nuclear density and percentages of fibres cut through the nucleus are also presented.