Differences In Fiber Size Research Articles

Optimization of PVDF-TrFE Based Electro-Conductive Nanofibers: Morphology and In Vitro Response.

In this study, morphology and in vitro response of electroconductive composite nanofibers were explored for biomedical use. The composite nanofibers were prepared by blending the piezoelectric polymer poly(vinylidene fluoride-trifluorethylene) (PVDF-TrFE) and electroconductive materials with different physical and chemical properties such as copper oxide (CuO), poly(3-hexylthiophene) (P3HT), copper phthalocyanine (CuPc), and methylene blue (MB) resulting in unique combinations of electrical conductivity, biocompatibility, and other desirable properties. Morphological investigation via SEM analysis has remarked some differences in fiber size as a function of the electroconductive phase used, with a reduction of fiber diameters for the composite fibers of 12.43% for CuO, 32.87% for CuPc, 36.46% for P3HT, and 63% for MB. This effect is related to the peculiar electroconductive behavior of fibers: measurements of electrical properties showed the highest ability to transport charges of methylene blue, in accordance with the lowest fibers diameters, while P3HT poorly conducts in air but improves charge transfer during the fiber formation. In vitro assays showed a tunable response of fibers in terms of viability, underlining a preferential interaction of fibroblast cells to P3HT-loaded fibers that can be considered the most suitable for use in biomedical applications. These results provide valuable information for future studies to be addressed at optimizing the properties of composite nanofibers for potential applications in bioengineering and bioelectronics.

Sepiolite and Other Authigenic Mg-Clay Minerals Formation in Different Palustrine Environments (Madrid Basin, Spain)

Lithofacies belonging to mud-flat and palustrine deposits (lake margin) in the Miocene of the Madrid Basin (Spain) have been studied. Four lithofacies corresponding to mud flat (1 and 3) and palustrine (2 and 4) deposits have been differentiated. Units 1 and 3 consist mainly of mudstones and carbonates (calcretes and diolocretes). The clay fraction is dominated by trioctahedral smectite (up to 79%) with illite and kaolinite as minor components. The d(060) spacing value shows reflections at 1.52 and 1.50 Å indicating also the presence of dioctahedral phyllosilicates. Unit 2 consists predominantly of lutites (claystones), locally with carbonate and chert nodules. The clay fraction is dominated by sepiolite (up to 96%) with variable contents of smectite and subordinate illite. The d(060) spacing value shows reflections at 1.51 and 1.52 Å indicating trioctahedral clay minerals. Unit 4 consists mostly of carbonates (limestones) with mudstone and lutite inserts. The clay fraction shows different contents of sepiolite, palygorskite and dioctahedral smectite. The analysis of a selection of trace elements (Cr, Co, Th, La, Sc) has allowed us to determine the characteristics of the source area as dioritic, somewhat different from those of the nearby materials from the Batallones sector. Sepiolite shows FWHM values ranging between 0.68 and 1.10 (2θ), indicating “low crystallinity sepiolite”. Differences in the conditions of formation of magnesian smectite and palygorskite have been observed in the mud-flat and palustrine deposits. The formation of sepiolite mainly by neoformation in palustrine deposits with different hydrochemistry is remarkable, leading to differences in fibre size and crystallinity of the fibrous clay mineral. Authigenic transformation processes from previous Al-rich phases would be responsible for the formation of saponite and palygorskite in mud flat and palustrine environments, with different pH conditions.

Cumulative effects of H+ and Pi on peak power of skeletal muscle fibers from young and older adults

The cellular mechanisms for the age‐related loss in muscle power output and increased fatigability during dynamic contractions remain unresolved. We recently observed that the depressive effects of fatiguing levels of acidosis (H+: pH 6.2) and inorganic phosphate (Pi: 30 mM) did not differ in muscle fibers from young compared with old men. However, the effects of these metabolites may have been saturated in the severe fatigue‐mimicking condition, potentially masking any age differences in the sensitivity of the cross‐bridge to these metabolites. Therefore, in this study we compared the contractile mechanics of myofibers (n = 327) from the vastus lateralis of 13 young (20‐32 years, 7 women) and 12 older adults (70‐90 years, 6 women) in conditions mimicking quiescent muscle and a range of fatiguing levels of acidosis (pH 6.8, 6.6, 6.2) and Pi(12, 20, 30 mM). The knee extensors of the older adults demonstrated hallmark signs of aging muscle including 19% lower thigh lean mass, 60% lower absolute power output, and ~1.8‐fold greater fatigability compared with young. Single fiber force, shortening velocity, and power decreased progressively with increasing concentrations of H+ and Pi; however, there were no age or sex differences in the depressive effects of these metabolites in any of the fatigue‐mimicking conditions. The cross‐sectional area of the fast fibers was 41% smaller in older compared with young adults, which corresponded with lower absolute fiber power. In contrast, there were no differences in fast fiber size‐specific power, indicating the age‐related decline in absolute fiber power was explained entirely by the differences in fiber size. Estimates of the amount of fast muscle in the thigh were associated with age‐related differences in whole‐muscle power output (r=0.78). These data suggest that the age‐related loss in whole‐muscle power output is primarily determined by the atrophy of fast fibers for both men and women, but that the age‐related increase in fatigability cannot be explained by an increased sensitivity of the cross‐bridge to H+ and Pi.

Ca2+ Sensitivity of Limb Muscle Fibers in Young and Older Adults

Age‐induced declines in skeletal muscle contractile function have been attributed to multiple cellular factors, including a loss of peak force (PO), decreased Ca2+ sensitivity, and reduced shortening velocity (VO). However, changes in these cellular properties with aging remain unresolved, especially in older women, and the effect of submaximal Ca2+ on contractile function is unknown. Thus, we compared contractile properties of muscle fibers from 19 young (24±3 years; 11 women) and 21 older adults (77±7 years; 7 women) under maximal and submaximal Ca2+ and assessed the abundance of three proteins thought to influence Ca2+ sensitivity. Fast fibers showed marked atrophy with aging in both men (young=8,599 μm2; old=5,404 μm2) and women (young=4,909 μm2; old=3,174 μm2) that corresponded with a decreased absolute PO in men (young=1.48 mN; old=0.92 mN) and women (young=0.85 mN; old=0.60 mN). There were no differences in fast fiber size‐specific PO, indicating the age‐related decline in force was explained by differences in fiber size. Except for fiber size and absolute PO, no age or sex differences were observed in Ca2+ sensitivity, rate of force development (ktr), or VO. Submaximal Ca2+ depressed ktr and VO, but the effects were not altered by age in either sex. Contrary to rodent studies, regulatory light chain (RLC) and myosin binding protein‐C abundance and RLC phosphorylation were unaltered by age or sex. These data suggest the age‐induced decline in whole‐muscle contractile function is primarily due to the atrophy of fast fibers and that caution is warranted when extending results from rodent studies to humans.Support or Funding InformationNational Institute on Aging grant (R01AG048262) to Robert Fitts and Sandra Hunter and an American Heart Association postdoctoral fellowship (19POST34380411) to Christopher Sundberg

Locomotor muscle morphology of three species of pelagic delphinids

The locomotor muscle morphology of diving mammals yields insights into how they utilize their environment and partition resources. This study examined a primary locomotor muscle, the longissimus, in three closely related, similarly sized pelagic delphinids (n = 7-9 adults of each species) that exhibit different habitat and depth preferences. The Atlantic spotted dolphin (Stenella frontalis) is a relatively shallow diver, inhabiting continental shelf waters; the striped (Stenella coeruleoalba) and short-beaked common (Delphinus delphis) dolphins are sympatric, deep-water species that dive to different depths. Based upon comparative data from other divers, it was hypothesized that the locomotor muscle of the deepest-diving S. coeruleoalba would exhibit a higher percentage of slow oxidative fibers, larger fiber diameters, a higher myoglobin concentration [Mb], and a lower mitochondrial density than that of the shallow-diving S. frontalis, and that the muscle of D. delphis would display intermediate values for these features. As expected, the locomotor muscle of S. coeruleoalba exhibited a significantly higher proportion of slow (57.3 ± 3.9%), oxidative (51.7 ± 2.5%) fibers and higher [Mb] (8.2 ± 0.7 g/100 g muscle) than that of S. frontalis (41.3 ± 3.9%, 31.0 ± 3.2%, 4.7 ± 0.05 g/100 g muscle, respectively). There were no differences in fiber size or mitochondrial density among these species. Like other deep divers, S. coeruleoalba displayed locomotor muscle features that enhance oxygen storage capacity and metabolic efficiency but did not display features that limit aerobic capacity. These results suggest a previously undescribed muscle design for an active, small-bodied, deep-diving cetacean. HIGHLIGHTS: The locomotor muscle features displayed by the striped dolphin, which are unique among deep divers, enhance oxygen stores but do not limit aerobic capacity. This novel muscle design may facilitate the active lifestyle of this small-bodied deep diver.

Morphological Differences in the Upper Trapezius Muscle Between Female Office Workers With and Without Trapezius Myalgia: Facts or Fiction?: A Cross-Sectional Study.

Work-related trapezius myalgia is a common musculoskeletal disorder in office workers. Prolonged low-level muscle activity during office work may lead to morphological changes in the muscle tissue, causing pain and fatigue. The aim of the present study was to investigate differences in muscle morphology between office workers with and without trapezius myalgia. Muscle biopsy samples were obtained from the upper trapezius of female office workers with trapezius myalgia (n = 17) and healthy controls (n = 15). Myosin heavy chain immunohistochemistry and Gomori trichrome stainings were performed to identify differences in muscle fiber type proportion, Feret's diameter, and internal nuclear proportion. The myalgia group showed significantly more type IIA and IIA/IIX fibers and less type I and IIX fibers, compared with the control group (P < 0.001 to P = 0.005). No significant differences were found for Feret's diameter and internal nuclear proportion (P > 0.05). However, a significantly higher Feret's diameter was found for type I fibers, compared with type II fibers in both groups (P < 0.001 to P = 0.002). Several subjects of both groups displayed an internal nuclear proportion of more than 3%. Female office workers with trapezius myalgia show a different fiber type distribution compared with their healthy colleagues but display no differences in fiber size and internal nuclear proportion.

Effects of PLGA Nanofibre on Osteoarthritic Chondrocytes

Chondrocytes obtained from osteoarthritis (OA) joints has been recognized as an abnormal cell; however, it’s proven to have potential in supporting cartilage regeneration. We have isolated chondrocytes from OA joints (OAC) and expanded chondrocytes growth medium (CGM). The growth kinetic, immunophenotyping and cell multilineage differentiation were analyzed to confirm the OAC stemness. The optimal condition to developed PLGA nanofibre with ratio 50:50 were 20% concentration of PLGA, flow rate with 0.3 mL/h, 10 kv voltage and 10 cm distance from nozzle to the collector. The toxicity level, scanning electron microscopy (SEM) and q-PCR analysis was performed in the present study. OAC fulfills the minimal criteria to be known to have stem cell as the cell easily adheres to the culture plate, shows high expression (≥95%) for CD13, CD29, CD44, CD73 and CD90 and less expression (≤2%) for CD45 and HLA-DR and potentially induced to mesodermal multilineage, which is osteocytes, adipocytes and chondrocytes. Toxicity test showed no adverse effect of PLGA towards the cell. Based on the cell-PLGA nanofibre interaction, difference in fibre size will influence the proliferation of the cell. Nanofibres with 100 nm in size showed high proliferation of OAC and better gene and protein expression compared to monolayer culture. Thus, we concluded that OAC has the potential to be used in cartilage regeneration based on the presence of stem cell markers as similar to the human bone marrow. The cartilage regeneration will be more efficient if OAC cultured on 3D microenvironment as showed in the present study.

Superheated steam pretreatment of cellulose affects its electrospinnability for microfibrillated cellulose production

In this study, oil palm mesocarp fiber (OPMF) was pretreated with (1) superheated steam (SHS) and (2) potassium hydroxide (KOH) to remove hemicellulose. Both SHS–OPMF and KOH–OPMF underwent delignification step to isolate the cellulose and dissolved in selected ionic liquid and its co-solvent before being electrospun to obtain microfibrillated cellulose (MFC). FE-SEM images showed that SHS–OPMF cellulose produced discontinuous MFC fiber with diameter ranging from 100 to 500 nm, of which 15.5% were in the range of 100–200 nm; while KOH–OPMF cellulose produced continuous MFC with sizes larger than 200 nm. The differences in fiber size and continuity of fiber produced were due to incomplete removal of hemicellulose from SHS–OPMF sample that inhibited fiber re-coalescence and resulted in interruption in fiber formation.

Effects Of Concurrent Exercise During Simulated Microgravity On Soleus Muscle Fiber Myonuclear Content

INTRODUCTION: Exercise countermeasures administered on the International Space Station are time-consuming and use large/expensive equipment. Aerobic exercise has shown to maintain oxidative capacity of muscle fibers, while resistance exercise preserves muscle mass in Astronauts. Recently, Cotter et al. (2015) determined that concurrent exercise (combining aerobic and resistance exercises; CE) was effective at mitigating de-conditioning during ULLS (unilateral lower limb suspension, simulated microgravity) but resulted in differences in fiber-type responses (i.e., fast-twitch vs slow-twitch). This current study provides additional analyses of muscle samples used in Cotter et al. (2015), investigating soleus muscle (mostly slow-twitch) myonuclei. Modulations in fiber size and myonuclear domain (MND; the area each myonuclei controls) may provide mechanisms for preventing unloading decrements. PURPOSE: Our aim was to determine 1) if simulated microgravity affects soleus muscle fiber size and MND size and 2) if CE training mitigates these changes. Sixteen subjects were separated into two groups, 10-day ULLS and 10-day ULLS + CE. METHODS: Muscle biopsies were taken pre- and post- intervention, which were isolated into individual fibers (muscle cells), stained for myonuclei, three-dimensionally imaged, and analyzed for fiber size and MND size. 2x2 ANOVAs determined potential differences in fiber size and MND size between groups, before and after ULLS. RESULTS: No significant differences in fiber size or MND size after 10 days of ULLS were observed. These findings suggest that, while 10 days of ULLS may cause a decline in muscle function (as seen in Cotter et al., 2015), it may not significantly affect soleus muscle fiber size or MND size. However, individual variability occurred, suggesting that some people may be responders (or non-responders) to ULLS and ULLS+CE. CONCLUSION: The results of this study suggest a need for additional analyses to help develop “personalized” exercise countermeasures for those undergoing significant periods of unloading (e.g., people in bed rest or Astronauts).

A novel method to understand tumor cell invasion: integrating extracellular matrix mimicking layers in microfluidic chips by \u201cselective curing\u201d

A major challenge in studying tumor cell invasion into its surrounding tissue is to identify the contribution of individual factors in the tumor microenvironment (TME) to the process. One of the important elements of the TME is the fibrous extracellular matrix (ECM) which is known to influence cancer cell invasion, but exactly how remains unclear. Therefore, there is a need for new models to unravel mechanisms behind the tumor-ECM interaction. In this article, we present a new microfabrication method, called selective curing, to integrate ECM-mimicking layers between two microfluidic channels. This method enables us to study the effect of 3D matrices with controlled architecture, beyond the conventionally used hydrogels, on cancer invasion in a controlled environment. As a proof of principle, we have integrated two electrospun Polycaprolactone (PCL) matrices with different fiber diameters in one chip. We then studied the 3D migration of MDA-MB-231 breast cancer cells into the matrices under the influence of a chemotactic gradient. The results show that neither the invasion distance nor the general cell morphology is affected significantly by the difference in fiber size of these matrices. The cells however do produce longer and more protrusions in the matrix with smaller fiber size. This microfluidic system enables us to study the influence of other factors in the TME on cancer development as well as other biological applications as it provides a controlled compartmentalized environment compatible with cell culturing.

P.94 - Stimulated echo DTI of skeletal muscle in Becker muscular dystrophy: a pilot study

Diffusion tensor imaging (DTI) is an MRI technique that aims to probe muscle architecture. The technique could be relevant in neuromuscular disorders (NMDs) where differences in fiber size and increased membrane permeability occur. Two approaches are relevant, spin-echo (SE-)DTI and stimulated-echo (STE-)DTI. While STE-DTI has a lower signal to noise ratio (SNR), it allows probing of the long diffusion distances present in skeletal muscle, which SE-DTI cannot. STE-DTI may thus be more sensitive, but has not been applied in NMD, as fat reduces the amount of water signal per voxel, and thus water SNR. We evaluated the feasibility of STE-DTI with fat suppression and signal denoising in Becker muscular dystrophy (BMD) patients. BMD patients (n = 7, age 21–58) and controls (n = 6, age 33–60) were scanned at 3T. Fat suppressed STE-DTI images, (resolution = 2x2x6 mm3) water/fat images (3-point Dixon, resolution = 1x1x10mm3), and noise maps were acquired. DTI data was denoised before computation of fractional anisotropy (FA) and mean diffusivity (MD) maps. FA, MD, fat fraction (FF), and SNR were measured in 6 muscles of the lower leg. In controls, at low SNR < 7, FA values were overestimated. Therefore, data sets with an SNR < 7 (24/42 BMD muscles) were excluded, which corresponded to muscles with significantly higher FF (41 ± 26% vs 10 ± 8 %, p = 0.001). The tibialis anterior (TA) had the highest SNR, allowing the comparison of 7 BMD and 4 controls. FA was higher in BMD (0.30 ± 0.05) than in controls (0.24 ± 0.02, p = 0.016). Sample size was insufficient for group comparison in other muscles. While STE-DTI MRI can be promising, maintaining sufficient SNR is of high importance, especially when imaging muscles with high FF. We were able to use STE and long diffusion time in low fat BMD muscles, likely owing to the use of signal denoising. High FA in the TA could be due to smaller fiber size or fibrosis. Future studies should focus on increasing the SNR, and exploring multiple diffusion times.

Development and sexual dimorphism of the sonic system in deep sea neobythitine fishes: The upper continental slope

The anatomy of sound production in continental-slope fishes has been ignored since the work of NB Marshall in the 1960s. Due to food scarcity at great depths, we hypothesize that sonic muscles will be reduced in deep-water neobythitine cusk-eels (family Ophidiidae). Here we describe and quantify dimensions of the swimbladder and sonic muscles of three species from the upper slope. They have four pairs of well-developed sonic muscles (two medial and two lateral) with origins on the skull and insertions on the medial swimbladder (medial pair) or on modified epineural ribs that attach to the lateral swimbladder (lateral pair). Despite minor differences, relatively similar swimbladder dimensions, muscle length and external morphology suggest a conservative body plan. However, there are major differences in sonic muscle mass: medial muscles are heavier in males and made of relatively small fibers (ca 10µm in diameter). Lateral muscles are generally larger in females and consist of larger fibers, as in epaxial trunk muscle. Muscle weight varies between species, and we suggest males produce advertisement calls that vary in amplitude and duration in different species. Due to differences in fiber size, we hypothesize that lateral muscles with larger fibers remain contracted during sound production, and medial muscles with smaller fibers will oscillate to drive swimbladder sound production.

Capillary Supply in Relation to Myosin Heavy Chain Fibre Composition of Human Intrinsic Tongue Muscles

The capillary supply and myosin heavy chain (MyHC) composition of three different intrinsic tongue muscles was analysed in the anterior and posterior regions of the human tongue with biochemical and immunohistochemical techniques. Mean capillary density for the whole tongue was 796 ± 82 cap/mm², without regional differences. The overall number of capillaries around each fibre (CAF) was higher in the posterior than in the anterior region (2.5 vs. 2.1, p = 0.009). However, correcting for regional differences in fibre size, CAF per fibre area was higher in the anterior region (4.3 vs. 3.0, p < 0.001). Muscle fibres containing fast MyHCs predominated in the anterior region (78.7%), consisting of MyHCIIa (58.5%), MyHCIIx (1.0%), MyHCIIa+MyHCIIx (11.3%) and MyHCI+MyHCIIa (7.9%). Fibres containing slow MyHC predominated in the posterior region (65.2%), consisting of MyHCI (45.5%) and MyHCI+MyHCIIa (19.7%). A minor fibre population (<2%) contained unusual MyHC isoforms, namely MyHC foetal, MyHC slow-tonic, MyHC α-cardiac or MyHC embryonic. The microvascularization of the human tongue was twice as high as in human limb muscles. Regional similarities in capillary supply, but differences in fibre phenotype composition, suggest that human tongue muscle fibres are fatigue resistant independently of MyHC content. High frequency of hybrid fibres, that is fibres co-expressing two or more MyHC isoforms, indicates a wider spectrum of fibre contractile properties than in limb muscles. In conclusion, human intrinsic tongue muscles showed internal specialization in distribution of MyHC isoforms and capillary supply, but not in the expression of unusual MyHCs.

Effects of chronic heart disease on skeletal muscle fiber size

Size changes in muscle fibers of subjects with chronic heart disease (CHD) have been reported, although a consensus has not been achieved. The aims of the present study were to investigate a possible association between CHD and fiber size changes in the brachial biceps compared to subjects without heart disease. Forty-six muscle samples were obtained in autopsies of individuals (13 to 84 years) without neuromuscular disorders, 19 (10 males and 9 females) with, and 27 (14 males and 13 females) without CHD. In all cases muscle sections were stained with hematoxylin and eosin and processed for the visualization of myofibrillar ATPase activity. The lesser diameter of type 1 and type 2 fibers was obtained tracing their outlines (at least 150 fibers of each type per sample) onto an image analyzer connected to a computer. The results were analyzed statistically comparing males and females with and without CHD. Type 1 fiber mean lesser diameters were 51.51 and 54.52 microm in males (normal range 34-71 microm) and 45.65 and 55.42 microm in females (normal range 34-65 microm) without and with CHD, respectively; type 2 fibers measured 54.31, 58.23, 41.15, and 49.57 microm, respectively (normal range 36-79 microm for males and 32-59 microm for females). No significant difference in fiber size was detected in 24 males with and without CHD, while in 22 females there was a significant increase in size in those with cardiomyopathy. We concluded that CHD does not determine significant changes in fiber size. However, in females, there is some hypertrophy which, despite within normal range, may reflect morphologic heterogeneity of the sample, or the daily life activities in the upper limbs as a compensatory mechanism to fatigability that affect predominantly the lower limbs in subjects with CHD.

A comparison of the effects of unloading in young adult and aged skeletal muscle.

The objective of this investigation was to determine whether morphological adaptations to unloading are different in young adult and aged skeletal muscle. Sixteen young adult (8-month) Fischer 344 rats were randomly assigned to either a control or hindlimb suspension (HS) group. Sixteen aged (22-month) rats were similarly assigned to either control or HS conditions. After 4 wk, animals were euthanized and soleus and EDL muscles were histochemically analyzed. In controls, neither the soleus nor EDL displayed age-related differences in fiber size or composition. Unloading elicited fiber atrophy of the soleus in both age groups but to a greater extent (P < 0.05) in aged rats. Only in aged solei were HS-induced fiber type conversions (Type I --> II) detected. In the EDL, unloading caused atrophy only among the aged. These data suggest that aged muscle experiences greater detriment as a result of unloading. This may have important consequences in the aged because they are more likely to be restricted to bed rest or limb immobilization due to falls and other afflictions.

Morphological correlates of the differential responses of muscles to vecuronium

We have noted previously that duration of vecuronium block correlated with fibre size in six muscle groups in the goat. Electrophysiological considerations suggest that the important factor should be the number of acetylcholine receptors (AChR) relative to fibre size. However, this hypothesis could not be verified in the goat because the number of AChR was relatively constant in the different muscles despite differences in fibre size. Therefore, in this study, we have investigated the relationship between sensitivity to vecuronium, as reflected by the ED50 and duration of block, of six muscles in the cat and the number of AChR per unit fibre cross-sectional area (CSA). The ED50 and duration of action (time to 50% recovery of the first twitch after a dose of 15 micrograms kg-1) of vecuronium in the tibialis cranialis, soleus, rectus abdominis, masseter, diaphragm and thyroarytenoideus muscles were determined during train-of-four stimulation and EMG recording in seven cats anaesthetized with pentobarbital. CSA of the muscle fibres and number of junctional AChR in these muscles were measured by histological methods and 125I-alpha-bungarotoxin binding assay, respectively, and the number of AChR per unit fibre CSA calculated. The association between muscle response (ED50 and duration of block) and fibre CSA or number of AChR per unit fibre CSA was then tested by regression analyses. Duration of block varied between the six muscles (mean 8.9 (SEM 2.6) to 20.3 (3.1) min; P = 0.0001) but ED50 did not (7.5 (1.5) to 15.6 (2.5) micrograms kg-1; P = 0.185). Fibre CSA and number of AChR per unit fibre CSA also varied between these muscles (P = 0.0001). Duration to 50% TI recovery was prolonged in muscles with a low number of AChR relative to fibre CSA (r2 = 0.30; P = 0.0002) and the ED50 increased as the number of AChR per fibre CSA increased (r2 = 0.240; P = 0.0016). These results in the cat suggest that the number of junctional AChR relative to fibre CSA is a morphological predictor of the differential sensitivities of muscles to neuromuscular blocking agents.

Maintenance of myonuclear domain size in rat soleus after overload and growth hormone/IGF-I treatment.

The purpose of this study was to determine the effects of functional overload (FO) combined with growth hormone/insulin-like growth factor I (GH/IGF-I) administration on myonuclear number and domain size in rat soleus muscle fibers. Adult female rats underwent bilateral ablation of the plantaris and gastrocnemius muscles and, after 7 days of recovery, were injected three times daily for 14 days with GH/IGF-I (1 mg/kg each; FO + GH/IGF-I group) or saline vehicle (FO group). Intact rats receiving saline vehicle served as controls (Con group). Muscle wet weight was 32% greater in the FO than in the Con group: 162 +/- 8 vs. 123 +/- 16 mg. Muscle weight in the FO + GH/IGF-I group (196 +/- 14 mg) was 59 and 21% larger than in the Con and FO groups, respectively. Mean soleus fiber cross-sectional area of the FO + GH/IGF-I group (2,826 +/- 445 microm2) was increased compared with the Con (2,044 +/- 108 microm2) and FO (2,267 +/- 301 microm2) groups. The difference in fiber size between the FO and Con groups was not significant. Mean myonuclear number increased in FO (187 +/- 15 myonuclei/mm) and FO + GH/IGF-I (217 +/- 23 myonuclei/mm) rats compared with Con (155 +/- 12 myonuclei/mm) rats, although the difference between FO and FO + GH/IGF-I animals was not significant. The mean cytoplasmic volume per myonucleus (myonuclear domain) was similar across groups. These results demonstrate that the larger mean muscle weight and fiber cross-sectional area occurred when FO was combined with GH/IGF-I administration and that myonuclear number increased concomitantly with fiber volume. Thus there appears to be some mechanism(s) that maintains the myonuclear domain when a fiber hypertrophies.

Inactivation of baroafferents leads to loss of barosensitivity without changes in nerve morphology

Baroreceptors are stretch-sensitive mechanoreceptors, which are silenced by preventing distension of the receptor zone. Does chronic inactivation of these peripheral afferents alter their function or morphology? Compound action potentials and morphometry of carotid sinus nerves of 10 rabbits were investigated. The baroafferents were inactivated by embedding the pressure-released carotid sinus into silicon gel. The success of this procedure was validated by the absence of spike activity of the sinus nerve during normal and elevated systemic blood pressure. The contralateral vessels of the same animals were sham-operated and also embedded into silicon, but without prevention of wall movements. After 5, 7, 14 or 28 days the nerves were functionally reinvestigated before and after release of the sinus wall. Afterwards, the morphology of the nerve cross-sections was analysed by morphometry of electron micrographs. Baroafferents did not regain spike activity during immobilisation of the sinus wall. After release of the carotid sinus wall only nerves inactivated for five days regained their pulse synchronous baroreceptor discharge. Following seven days of inactivation, baroreceptor discharge could be elicited by maximal pressure elevation in only one of three nerves. At any time later, the baroreceptor response to arterial pressure changes was lost completely. The activity of the control nerves was preserved after 28 days. No obvious differences in fibre size and myelin thickness were observed between inactivated and control nerves. Inactivation of baroafferents for more than one week leads to a loss of pressure-dependent spike activity. Since morphology did not differ between inactivated and control nerves, it is suggested that changes of baroreceptor endings are responsible for this loss of function.

Effect of flying activity on capillary-fiber geometry in pigeon flight muscle

The effect of flying activity on capillary density and geometry was investigated in pectoralis muscle of 4 wild-caught (W) pigeons (BW 233–348 g) perfusion-fixed in situ and processed for electron microscopy. Morphometric analysis revealed both differences and similarities with similar sampling sites (superficial and deep in central area of right or left pectoralis major muscle, approximately midway along cranio-caudal and lateral axis) in sedentary (S) pigeons. Differences were the greater fractional cross-sectional area of aerobic fibers (W, 82 ± 2%; S, 63 ± 6%; p = 0.006) and the greater volume density of mitochondria per volume of fiber (W, 22.0 ± 1.3%; S, 15.7 ± 1.7%; p = 0.011) in wild-caught pigeons. While glycolytic fibers were significantly narrower in W, the size of the majority of fibers comprising the muscles, i.e. aerobic fibers, was similar in the two groups. Other similarities were found in capillary-to-fiber ratio (W, 2.0 ± 0.2; S, 2.1 ± 0.2) and in the degree of orientation of capillaries in the two groups. In addition, both capillary density at a given fractional cross-sectional area of aerobic fibers and capillary length per fiber volume at a given mitochondrial volume density were similar in the two groups, indicating a proportional increase in capillarity and muscle aerobic capacity in W compared with S. Comparison of capillary numbers around aerobic fibers at a given mitochondrial volume per μm length of fiber showed no difference between W and S groups nor with previous data in muscles with wide differences in fiber size and mitochondrial density such as rat soleus, bat muscles and hummingbird flight muscles. This supported the notion of a tight correlation between capillary numbers around individual fibers and mitochondrial volume per unit length of fiber in aerobic muscles. It also supported the idea that it is the number of capillaries around the fibers rather than diffusion distance which determines O 2 flux rates in highly aerobic muscles.

Residual stress distribution in carbon fibre/thermoplastic matrix pre-impregnated composite tapes

The distribution of residual strain in carbon fibre (P75) reinforced thermo-plastic (polyetheretherketone, PEEK) composites has been studied by monitoring the Raman frequencies of the embedded carbon fibres at the microscopic level. The average longitudinal strain in the fibre measured in a 100 mm 2 section of a P75/PEEK prepreg was found to be compressive and comparable in magnitude to residual strain values computed analytically. The combined effects of differential thermal expansion of the two materials, differences in fibre size and in the thickness of resin layer, are offered as likely explanations for the incurred variations in the Raman frequency values and the considerable spread of the fibre Raman frequency distribution in the prepreg tape. Finally, it is demonstrated that the previously reported high values of apparent compressive strain in similar composite tapes by means of Raman spectroscopy were artefacts of the experimental procedure.