Scanning electron microscopy of prenatal muscle development in the mouse

Summary Scanning electron microscopy was used to study prenatal muscle development in mouse fetuses ranging from 12 days to 18 days gestation. Some transmission electron micrographs were also used for comparison. At 12 days no myofibres were evident although at 13 days long fibres surrounded by many mononucleated cells could be seen. At 14 days bundles of primary myofibres were observed with new myofibres forming in crevices between adjacent fibres. At 16 days the primary myofibres had separated but smaller secondary myofibres could be seen forming along their surfaces. The myofibres were very compact at 18 days and often appeared fused but this was due to the basal lamina ensheathing clusters of primary myofibres with their secondaries. The scanning electron micrographs appeared to illustrate the theories of muscle development which have arisen out of the various studies employing sectioning techniques.     

Hyperplastic and hypertrophic growth of lateral muscle in Dicentrarchus labrax (L.). An ultrastructural and morphometric study

Summary In this EM study of lateral muscle in Dicentrarchus labrax, we observed that during the larval period, growth of the presumptive red and white muscle layers occurs both by hypertrophy (as fibres already present at hatching complete their maturation) and by production of new fibres in germinal zones specific to the two muscle layers.In the first half of larval life the presumptive white muscle increases in thickness by the addition, superficially, of new fibres derived from a germinal zone of presumptive myoblasts lying beneath the red muscle layer. In the second half of larval life new fibres produced in this same zone form the intermediate (or pink) muscle layer. Dorsoventrally the myotome grows throughout larval life, largely by addition of new fibres from germinal zones at the hypo- and epi-axial extremities. Towards the end of larval life all these germinal zones are becoming exhausted, but another source of fibres arises as satellite cells, associated with large-diameter presumptive white muscle fibres, are activated to produce new fibres. The addition of small, new fibres gives the white muscle its mosaic appearance.Morphometric analysis of fibre diameters in the white muscle confirms that whereas these hyperplastic processes are important during the larval and juvenile periods, when growth is very rapid, they have ceased by the time the adult stage is attained. By contrast, fibre hypertrophy continues through into adult life.The presumptive red muscle consists initially of a monolayer of fibres present only near the lateral line, and during larval life it grows hypo- and epi-axially by addition of fibres derived from myoblasts already present in these areas at hatching. Lying superficially to the presumptive red muscle monolayer there is a near-continuous layer of external cells with a flattened profile. During the second half of larval life, differentiation of these external cells into myoblasts provides the source of new fibres which are added to the red muscle layer. This process, which occurs initially in the region around the lateral line and later spreads outwards, is responsible for the increase in thickness of the red muscle.     

An electron microscope study of the differentiating capillaries of the mouse neurohypophysis

Summary The developing capillaries of the mouse neurohypophysis were studied in the electron microscope to elucidate the fine structural differentiation of the vascular component of the neuro-hemal contact zones in the external median eminence and the neural lobe.In the embryo the growth of the superficial net of the primary plexus of the hypophysial portal system is largely manifested by the presence of proliferation areas located within the capillary plexus covering the surface of the median eminence. Presumptive shallow capillary loops diverge from these areas in the first postnatal week. Differentiation of the capillary wall follows the pattern outlined for continuous capillaries. A few fenestrae appear in the endothelium of immature, superficial vessels at the 17th gestational day, increase in frequency during the following embryonic days, and occur regularly in the postnatal animal.In the neural lobe the internal capillaries proliferate by vascular sprouts emanating from the vessels on the surface of the gland. At the end of embryonic time an extensive net has developed, composed of capillaries with immature characteristics. Proliferation is largely finished by the end of the third postnatal week, when mature capillaries dominate the picture. Formation of attenuated, porous areas is a postnatal process, apart from single fenestrae appearing in the walls of a few immature capillaries in late fetal life.The structural possibilities for an onset of neurohypophysial function in the mouse is discussed.     

Muscle involvement in rheumatoid arthritis: an ultrastructural study

An electron microscopic investigation has been carried out on muscle bioptic samples from patients affected by rheumatoid arthritis (RA). This study was undertaken to seek further ultrastructural alterations affecting striated muscles in RA pathology. Bioptic samples were collected on a total of 30 surgical interventions of hip (10), knee(8), and foot (12). This yielded three muscle types: gluteus maximus, vastus lateralis, and extensor digitorum communis. Muscle samples from 12 patients with no RA stigmata, selected to match RA patients by age and gender, constituted the control group. Tissue samples were prepared both for conventional histochemical methods and according to conventional electron microscopic procedures, including morphometric analysis. Although to a different extent in each sample, in muscles from RA vs. controls the authors observed the simultaneous presence of discrete muscular alterations such as wider separation of myofibrils, myelin figures, dilated sarcotubular system, pleomorphic mitochondria, myofibril flaking, and lipofuscin deposition in the subsarcolemmal region. In addition to a progressive atrophy, the above findings are suggestive of rheumatoid myositis and lend further support to the still poorly documented presence of an idiopathic inflammatory myopathy and inclusion body myositis associated with RA.     

A monolayer preparation of innervated skeletal muscle fibres of the M. Cutaneus pectoris of the frog

Summary The preparation of a monolayer of innervated skeletal muscle fibres of theM. cutaneus pectoris of the frog is described. The advantage of this preparation is demonstrated by examples of living end-plates as viewed under Nomarskiinterference optics, and of nerve terminal regions investigated by scanning microscopy and freeze-cleavage techniques.This work was supported by the Deutsche Forschungsgemeinschaft Sonderforschungsbereich 38.     

Ultrastructural changes of mitochondria in the skeletal muscle of patients with amyotrophic lateral sclerosis

Functional defects and morphological changes of mitochondria have been reported to be in the skeletal muscle of patients with amyotrophic lateral sclerosis (ALS). Recent studies suggested that mitochondrial abnormalities are related to the pathogenesis of ALS. The purpose of this study is to evaluate the ultrastructural changes of muscle mitochondria in ALS patients. The authors examined 49 cases of diagnostic muscle biopsy samples with definite or probable ALS by electron microscopy. Of the 49 cases, 5 (10%) had ultrastructural abnormalities of muscle mitochondria, including giant mitochondria, paracrystalline inclusions, and abnormal cristae. These abnormal mitochondria were mainly observed among subsarcolemmal mitochondrial aggregates.     

Effect of prolonged,severe exercise on the ultrastructure of human skeletal muscle

Summary Three subjects exercised to exhaustion by pedaling a bicycle ergometer at a work load that required an oxygen uptake of 75–80% of their maximal aerobic capacity. Muscle samples were taken from the vastus lateralis with the needle biopsy technique before exercise and immediately after the onset of exhaustion. Muscle glycogen decreased from initial values of 2.57, 1.41, and 3.09 to 0.22, 0.85, and 0.37 g/100 g wet weight respectively for the three subjects during the exercise. The ultrastructure of the fatigued muscle was not dissimilar from that obtained from the muscle at rest. The electron micrographs of fatigued muscle did show an almost complete absence of glycogen particles.     

An ultrastructural study of the placenta in materno-fetal rhesus incompatibility

Summary An electronoptical study has been made of eleven placentae from cases of materno-fetal rhesus incompatibility. The characteristic findings are focal, but sometimes quite extensive, syncytial necrosis, retention of normal pinocytotic and secretory activity in the non-necrotic syncytiotrophoblast, cytotrophoblastic hyperplasia, thickening of the trophoblastic basement membrane, immature-type endothelial cells in the fetal villous vessels and thickening or lamination of the capillary basement membranes. The pathogenesis of many of these changes is not clear but there is no evidence that they are immunologically mediated. It is suggested that the syncytial necrosis may be due to narrowing of the intervillous space as a result of increased villous size, that the cytotrophoblastic hyperplasia is a response to the syncytial damage and is responsible for the changes in the trophoblastic basement membrane and that the fetal capillary changes are indicative of endothelial cell damage due, possibly, to fetal anaemia. Despite the damage suffered by the placenta in materno-fetal rhesus incompatibility there is little evidence of impaired functional efficiency.     

An ultrastructural study of the lateral reticular nucleus in the rat

Summary A systematic study of the normal synaptic patterns within the lateral reticular nucleus (LRN) of the rat revealed various synaptic relationships. Two types of axon terminals were identified according to the morphology of the synaptic vesicles contained within them. Axon terminals with round vesicles established asymmetrical synaptic contacts with the somata and all areas of the dendritic trees including somatic and dendritic appendages. Pleomorphic-vesicle terminals established symmetrical synaptic contacts on somata and their appendages and on all sizes of dendrites and their appendages. Both round and pleomorphicvesicle terminals were infrequently seen to synapse upon the somata and proximal dendrites. The round-vesicle terminals outnumbered the pleomorphic-vesicle terminals on the dendritic trees. Terminals of the en passant type were also common throughout the LRN. Both round and pleomorphic-vesicle terminals were observed simultaneously contacting the soma and one or more dendritic profiles, or two different dendritic profiles. Synaptic configurations (glomeruli) were also observed in all three divisions of the nucleus. They consisted of a large, central, round-vesicle terminal contacting a number of small-calibre dendritic processes. This arrangement was surrounded by one or more sheets of glial lamellae. Puncta adherentia were observed on the apposed membranes of adjacent cells, adjacent dendrites and adjacent axon terminals.     

Capillary supply and mitochondrial content of different skeletal muscle fiber types in untrained and endurance-trained men. A histochemical and ultrastructural study

Summary The number of capillaries per fiber, per mm², around each fiber type and relative to fiber area was determined in six untrained subjects (UT) and six elite cross-country skiers (ET). Average values for maximal oxygen uptake were 49.8 ml·kg^–1·min^–1 (UT) and 77.9 ml·kg^–1·min^–1 (ET). Type I fibers constituted 39.2% (UT) and 68.6% (ET), type II A fibers 39.6% (UT) and 19.2% (ET), while 12.8% (UT) and 6.6% (ET) of the fibers were type II B. The mean fiber area for the type II A fibers was significantly greater (p<0.01) than the areas for type I and II B in the untrained group.The average numbers of capillaries around each fiber type (CA) were 4.76-4.84-2.94 (UT) and 7.79-6.63-4.5 (ET) for type I, II A, and II B, respectively. There was a significant difference (p<0.01) in the CA values relative to fiber area for all fiber types in both groups, being highest for type I and lowest for type II B. The CA increased linearly with increasing size of the fibers for all fiber types in both groups.The mitochondrial content was determined semiquantitatively for each fiber type. The differences in capillary supply between the fiber types are accompanied by similar differences in mitochondrial content.The results indicate that endurance training increases the capillary supply of all fiber types in the human quadriceps muscle. The fact that light microscopical studies have given lower capillarization values than those obtained with the electron microscope is discussed.     

Muscle spindles in immobilized muscle: electron microscopic study of recovery

This study is concerned with the morphological recovery process of muscle spindles following a long period of immobilization. The right hindlimbs of rats were fixed with a plaster cast for 4 weeks. Thereafter, four groups of rats were examined by electron microscopy. One group served as the control after the cast was removed. The other three groups were examined after free walking for 4, 8, and 12 weeks, respectively. The muscle spindles (tibialis anterior muscle) of the individual animals were then ultrastructurally analyzed. The morphological alterations (of the outer capsule, intrafusal muscle fibers, and intrafusal nerve components) gradually recovered during free walking and regained almost all normal features in 12 weeks after returning to walking.A part of this research was presented at the 25th Annual Meeting of the Clinical Electron Microscopy Society of Japan, Matsumoto, September 28–30, 1993.     

Mechanical and electrical correlates of isometric muscle fatigue in skeletal muscle in the cat

The amplitude and duration of motor unit action potentials, the rise time, peak tension, and half relaxation time of an isometric twitch, and forcevelocity relationship, and tetanic tension were measured at the beginning (fresh muscle) and at the end of a fatiguing isometric contraction at a tension of either 40 or 70% of the initial strength in the soleus (a slow twitch muscle) and the medial gastrocnemius (a fast twitch muscle) of the cat. These same parameters were also measured at set intervals following these contractions to assess their rate of recovery to pre-exercise values. At The end of a fatiguing contraction examined,V _mx, twitch tension and tetanic tension, were all reduced while there was a prolonged twitch duration and duration of the motor unit action potential for both types of muscle. The height of the motor unit action potential was only marginally effected by muscle fatigue. Following the fatiguing contraction, the endurance required several hours to recover in the medial gastrocnemius muscle but recovered fully within 15 min after either tension in the soleus muscle. Tetanic tension and twitch tension both required less than 10 min for full recovery in the medial gastrocnemius muscle but recovered fully to the pre-exercise values within 3 min following fatiguing isometric contractions in the soleus muscles.V _mx, and the height and duration of the motor unit action potential both recovered within 1 min following the end of the exercise.     

Capillary growth in overloaded,hypertrophic adult rat skeletal muscle: An ultrastructural study

We examined the early stages of angiogenesis in overloaded m. extensor digitorum longus following extirpation of the agonist m. tibialis anterior. Capillary-to-fibre ratio increased after 1 week (1.54 ± 0.02) vs. control (1.38 ± 0.06; P < 0.01) and resulted in a greater tortuosity of the capillary bed at 2 weeks, indicating the presence of lateral sprouts or anastomoses. Capillary endothelial cells (ECs) showed ultrastructural signs of activation, were thickened, and had irregular luminal and abluminal surfaces. The proportion of ECs with abluminal processes increased after overload (13.5 ± 0.6% vs. 2.0 ± 1.5%, 1 week vs. contralateral, P < 0.01; 12.5 ± 2.6% vs. 3.5 ± 0.6%, 2 weeks vs. contralateral, P < 0.01), whereas there was no significant change in proportion of luminal processes. Abluminal processes occurred in approximately 13% of capillaries in overloaded muscles (P < 0.01 v. control and contralateral), and most were associated with focal breakage of the basement membrane (BM). Small sprouts (<3 μm in diameter) comprised of one or two ECs sometimes lacked a lumen, and others had a slitlike or vacuolelike lumen between adjacent ECs or vacuolelike lumen formed by fusion of vesicles within a single EC. Endothelial mitosis was occasionally seen in nonsprouting capillaries with intact BM, increasing the average number of ECs per capillary from approximately 1.7 in control muscles to 2.1 after 1 week of overload (P < 0.05) when bromodeoxyuridine incorporation was also higher (P < 0.001). We conclude that muscle overload induces capillary growth by sprouting of existing capillaries, probably due to mechanical stretch acting from the abluminal side of the vessels. Anat. Rec. 252:49–63, 1998. © 1998 Wiley-Liss, Inc.     

Mechanical activation of the contractile system in skeletal muscle

Summary Fibre bundles of frogs m. semitendinosus and rabbit psoas were extracted with glycerol and then suspended in ATP-salt solution at varying levels of free calcium. Abrupt stretch by 0.2–0.5% of the fibre length caused a (transient) delayed rise in tension and a quick release often produced a delayed tension fall. Consequently the extracted fibre system was able to oscillate since during sinusoidal length changes (0.5% at 5–10 c/sec) the sinusoidal tension changes lagged behind, as in myogenic oscillation of insect flight muscle.Supported by the Deutsche Forschungsgemeinschaft (Grant RU 154/3).     

Regeneration pattern of cardiac and skeletal muscle after transplantation into a skeletal muscle bed in rats

Background: The ability of skeletal muscle to regenerate after injury is well established. In contrast, cardiac muscle is incapable of regeneration and recovery after injury. The aim of the present study was to evaluate and compare the regeneration pattern of cardiac and skeletal muscle after transplantation into a skeletal muscle bed in rats. Methods: The following group of transplants were performed at the site prepared by removing the host extensor digitorum longus (EDL) muscle. The first group consisted of cardiac muscle transplanted as one piece or after mincing into 1-mm pieces. The second group included cotransplants of cardiac and skeletal muscle minces that were intermixed. Entire EDL muscle or minced EDL muscle were also transplanted for comparison. Rats were sacrificed 3–30 days after transplantation for morphological analysis. Results: The results demonstrated that skeletal muscle transplants underwent rapid regeneration, and by 30 days the entire muscle was filled with regenerated myofibers. In transplants of cardiac muscle significant inflammation, myocardial degeneration and necrosis were observed. In spite of the necrosis and fibrosis, the presence of a few regenerated myotubes in the outer region was observed. In cardiac and skeletal muscle cotransplants, the inflammation was restricted to cardiac tissue; however, by 30 days the entire contransplant was filled with regenerated myotubes and myofibers. Conclusions: These results show that skeletal muscle is capable of growth, regeneration, and integration with the cardiac muscle after cotransplantation. Combination of skeletal and cardiac muscle may prove useful in defining the cellular processes necessary for enhancing cardiac repair after injury. © 1995 Wiley-Liss, Inc.     

Plasma cells in acute hepatitis: An ultrastructural study

Summary Plasma cells and their precursors were studied by electron microscopy in liver biopsies from 41 patients with acute viral or drug-induced hepatitis. Mature plasma cells showed the ultrastructural features of the reticular or lymphatic type. Blast cells of different types were also observed. Type 1 predominated in classical acute hepatitis, and appears to transform directly into mature plasma cells. Type 2 corresponds to the centroblast of lymphoid tissue. It was found in fully developed hepatitis, especially when necrosis was severe. Type 3 resembled the centrocyte of lymphoid organs; it was seen particularly in viral hepatitis, and only in severe cases with extensive necrosis. The type 4 plasmablast had the ultrastructural characteristics of a plasmacytoid T cell.     

A comparative ultrastructural study of in vivo versus in vitro fertilization of bovine oocytes

Summary Heifers were superovulated by PMSG or FSH, and oestrus was induced by prostaglandin. One group of animals was ovariectomized 19–26 h after the LH peak, the content of preovulatory follicles aspirated, and the oocytes processed for in vitro fertilization. Another group was inseminated and ova were collected from the oviducts for study of in vivo fertilization. All ova were examined ultrastructurally. The developmental rate following in vitro fertilization was delayed compared to fertilization in vivo. A high proportion of the in vitro fertilized ova showed polyspermic penetration of the zona pellucida, and supernumerary spermatozoa were found in the ooplasm of some ova. In vivo fertilization was associated with release and subsequent dispersal of the cortical granule content in the perivitelline space. In contrast to this the released granule content of the in vitro fertilized ova remained undispersed close to the oolemma. This feature may account for the high incidence of polyspermic penetration of the zona pellucida. In addition, the study provided an ultrastructural visualization of the initial contact between the equatorial segment of the spermatozoon and the microvilli of the oocyte, and the subsequent internalization of the sperm head.     

Lithopedion: case report and ultrastructural study of the skeletal muscle

A case of lithopedion (lythokelyphopedion) is reported in a 69 year old woman who had carried a nearly full term dead fetus for at least 20 years. The fine structure of the skeletal muscle was in an astonishingly good state of preservation with contractile elements and myosin molecules identifiable. The conditions and modifying factors that may play a role in the development of a lithopedion are discussed, and x-ray, histologic, and electron microscopic studies are described.     

Biochemical and ultrastructural changes of skeletal muscle mitochondria after chronic electrical stimulation in rabbits

The purpose of the present investigation was to follow and correlate changes of structural and biochemical markers of energy metabolism during chronic electrical stimulation of tibialis anterior muscle in rabbits.In the superficial portion of the muscle, 5 to 6-fold increases occurred in enzyme activities of the citric acid cycle and of fatty acid oxidation after 28 days of stimulation. Enzyme activity changes in the deep, more oxidative part of the muscle were relatively smaller. Consequently, levels of the citric acid cycle enzymes became similar in superficial and deep parts of the muscle after the longest stimulation periods. With the exception of hexokinase, which increased in parallel with the citric acid cycle enzymes, glycolytic enzymes decreased 2 to 3-fold. Muscle mass and fibre size remained unchanged, while capillary density and capillary to fiber ratio increased 2-fold. The volume density of total mitochondria increased in a fashion similar to the changes of the enzymes of the citric acid cycle (7-fold in superficial and 3.5-fold in deep parts of the muscle) and, thus, approached values found in heart muscle. Disproportionate changes in enzyme activities of ketone body utilisation and of mitochondrial glycerolphosphate oxidase indicated qualitative changes within the mitochondrial population. However, the proportion of subsarcolemmal to interfibrillar mitochondria, as well as the area of inner mitochondrial membrane per unit volume of mitochondrion remained unchanged. Similarly, intracellular lipid deposits remained unchanged with stimulation.It is concluded that there is an excellent agreement between morphometric and biochemical measurements of tissue oxidative capacity.