Characteristics of the human masseter muscle during hypokinesia

Bioptates of the m. masseter from 20 male persons at the age of 21-30 years have been studied 3, 6, 12 and 24 days after immobilization of the mandible in connection with its fracture. Succinate dehydrogenase (SDG) activity and cross section area of muscle fibers have been determined. Relative volume (Vv) of submicroscopic structures of myons have been found stereologically. In the muscle tissue reactive-destructive changes are revealed; they depend on hypokinesia duration: decreasing SDG activity, cross section area of the fibers and contents of pinocytic vesicles in the endothelial cells of the capillaries. Vv of mitochondria and tubular formations in the sarcoplasmic reticulum change. Certain stageness of structural rearrangements in the muscles are noted, they are considered as a result of the influence of the restricted function and some disturbances occurring between the blood vessels and the muscle fibers.     

Characteristics of myohistogenesis during experimental mono- and bilocal distraction osteosynthesis

Regularities of the skeletal muscle tissue histogenesis have been studied in the canine shin at its elongation by 50% of its initial length by means of the mono- and bilocal distractive osteosynthesis after Ilizarov. Using light and electron microscopy, it has been stated that under conditions of monolocal distractive osteosynthesis, when the strain effort acts in the area of the muscle belly, together with elongation dystrophic and necrotic changes, proliferation of the intermuscular connective tissue and atrophy of myons increase. In a half of a year, after cessation of distraction there is no complete restoration of the skeletal muscle tissue structure. Under conditions of bilocal distractive osteosynthesis, when the conditions of the muscle distortion are comparable to those existing during the period of the extremity growth, cellular type of regeneration in the skeletal muscle tissue predominates. Therefore growth of the muscle fibers is longitudinal, like that of their growth in the process of ontogenesis and the structure of the muscle tissue of the extremity elongated is preserved. The results of the experiment performed demonstrate certain prospectiveness of application of the bilocal distractive osteosynthesis method in practical orthopedics.     

Fenestrated blood capillaries and lymphatic capillaries in rat skeletal muscle

Capillary fenestrae occur in one of about 60 cross-sectioned blood capillaries in normal adult rat skeletal muscles. The fenestrae occur singly or in groups. Fenestrated capillaries are found close to muscle fibers as well as in the perimysial and perineurial connective tissue. Small numbers of lymphatic capillaries are also present, mostly in the perimysial connective tissue.     

Lymphatic vessels in lungfishes (Dipnoi)

 Lymphatic capillaries are distributed throughout the body of lepidosirenid and protopterid Dipnoi, except in the central nervous system. They form small, interconnected units which are individually evacuated into nearby blood capillaries by lymphatic micropumps. The number of lymphatic micropumps varies considerably in different parts of the body. In fin areas, 30–50 per mm³ tissue may be considered normal in Protopterus annectens, but up to 105 per mm³ have been counted in an anterior fin of Lepidosiren paradoxa. Lymphatic capillaries are formed by thin endothelial cells with fine processes into the surrounding interstitial space. Occasionally there is a faint, discontinuous basal lamina. Pericytes, however, are completely absent. Microfibrils establish contact between endothelial cells and surrounding connective tissue fibers. The lymphatic micropumps are essentially spherical, contractile organs of 35–55 μm in diameter. Their central lumen is lined by extensions of a single endothelial cell. Additional endothelial cells form inflow and outflow valves. The endothelial layer is surrounded by a single large, highly specialized muscle cell. This spherical muscle cell has many perforations, allowing the passage of thin outward processes of the endothelial cell which form part of the suspension apparatus of the lymphatic micropump. The muscle cell establishes a specialized end-to-end contact between opposing parts of its own cell membrane. This contact is very similar to an intercalated disc in vertebrate heart muscle. Each lymphatic micropump is suspended within a cell-free tissue area by microfibrils which radiate from the lymphatic micropump into the surrounding connective tissue. The microfibrils are occasionally reinforced by single collagen fibers. The cell-free area around each lymphatic micropump appears as a bright halo in both light and electron micrographs. No type of lymphatic vessel other than lymphatic capillaries could be detected in the Dipnoi studied. Lepidosireniform Dipnoi are the only Vertebrata besides the Tetrapoda in which lymphatic vessels and characteristic lymphatic pumps have been documented. In addition, these Dipnoi and all Tetrapoda share the same overall design of blood circulation, which is not divided into a primary and a secondary system of vessels, as it is in Actinopterygii, Chondrichthyes, and Agnatha. Since there are primary and secondary blood vessels in the gills of Latimeria chalumnae, while the existence of lymphatic vessels has not been confirmed, general angioarchitecture should be taken into account as an important character when phylogenetic relationships among extant Sarcopterygii are discussed. Accepted: 7 October 1997     

Ultrastructure of the capillaries of nerve tissue transplants growing in the anterior chamber of the eye

Blood capillaries have been studied electron microscopically in the areas of grafts (rat embryonal hippocamp and septal cerebral parts transplanted to mature rats) containing mainly nervous, glial or connective tissue cells. Certain differences in the capillary wall structure have been revealed. In areas with a great concentration of nervous cells, the blood capillaries are characterized by a dense arrangement of cellular elements in their walls, a continuous layer of the glial end-feet, this is specific for the CNS capillaries providing the blood--brain barrier. In peripheral area of the grafts, where glial elements predominate, the capillaries have loose arrangement of the mural cellular elements, great endotheliocyte activity, thick connective tissue tunic, lack of a dense glial surrounding. These characteristics make dubious the statement whether these capillaries possess the blood--brain barrier function. In places where connective tissue cells make aggregates, the capillaries do not possess the barrier properties because of perforations and fenestrae in endothelium and interruptions of the basal membrane, absence of pericapillary glial elements. All types of the capillaries demonstrate certain signs of a high functional activity. Formation of the capillary structure depends on the surrounding tissue.     

Localisation of lymphatic vessels and vascular endothelial growth factors-C and -D in human and mouse skeletal muscle with immunohistochemistry

The present study was aimed to localise lymphatic vessels and their growth factors in human and mouse skeletal muscle with immunohistochemistry and specific antibodies (VEGFR-3, LYVE-1, VEGF-C and VEGF-D). The largest lymphatic vessels were found in perimysial connective tissue next to the arteries and veins, as has been shown earlier with electron microscopy. As a new finding, we also found small LYVE-1 positive vessels in the capillary bed between muscle fibres. These vessels were located next to CD31 positive blood capillaries and were of the same size, but fewer in number. In addition, we described the localisation of the two main lymphangiogenic growth factor proteins, vascular endothelial growth factor-C and -D. Both proteins were expressed in skeletal muscle at mRNA and protein levels. VEGF-D was located under the sarcolemma in some of the muscle fibres, in the endothelia of larger blood vessels and in fibroblasts. VEGF-C protein was localised to the nerves and muscle spindles, to fibroblasts and surrounding connective tissue, but was not found in muscle fibres or endothelial cells. Our results are the first to suggest the presence of lymphatic capillaries throughout the skeletal muscle, and to present the localisation of VEGF-C and -D in the muscles. Electronic Supplementary Material Supplementary material is available to authorised users in the online version of this article at .     

Estimating diffusion distances in muscle

Models of fibers and capillaries in cross sections of muscle were used to quantify the relationships between diffusion distances and tissue capillarity. The fibers were constructed as square and hexagonal arrays, and the placement of capillaries around the perimeters of the fibers ordered them in similar arrays. Diffusion distances were measured as the percent cumulative frequency of fiber area within a given distance of a capillary when capillary-to-fiber ratio was increased from 0.5 to 4.0. Equations fitted to the data make it possible to estimate diffusion distances in muscle and to correlate changes in diffusion distances with fiber growth, capillary growth, and the geometrical arrangement of capillaries in the muscle bed.     

Effect of endurance training on muscle fiber type composition and capillary supply in rat diaphragm

Muscle fiber type composition and capillary supply in rat diaphragm were investigated after 14 weeks of endurance training: body weight and muscle fiber area were significantly decreased, the muscle fiber type composition, capillary to fiber ratio and number of capillaries around each fiber type were unchanged, and the capillary density and number of capillaries around each fiber relative to fiber type areas were significantly increased. These small fiber areas and increased capillary supplies in the trained rats would facilitate oxygen transport to all parts of the muscle fiber during exercise. It is concluded that the changes observed in the trained rat diaphragm appear to enhance the capacity for oxidative metabolism.     

Role of multipotent fibroblasts in the healing colonic mucosa of rabbits. Ultrastructural and immunocytochemical study.

Light- and electron microscopy and immunocytochemistry were used to study the healing colonic mucosa of rabbits after experimental excision. Between 3 and 5 days, abundant young fibroblasts which retained many features of mesenchymal cells invaded the growing capillaries into the loose connective tissue of the healing colonic mucosa. Our electron microscopy revealed the transformation of these young fibroblasts into smooth muscle cells, into histiocyte-like cells involved in phagocytotic activity, and into vasoformative cells incorporated into the growing capillaries. The mitotic proliferation of pre-existing smooth muscle cells at the ulcer margin did not seem to be the major reason for re-establishment of the muscular tissue. The present immunocytochemistry revealed an active production of fibronectin in rough endoplasmic reticulum in the young fibroblasts. This may mean that this glycoprotein is involved in the re-establishment of both connective and muscular tissues by enhancement of adhesion and chemoattractant activities of such cells. In addition, the immunoreaction of endothelial cells of the growing capillaries suggests a role of this glycoprotein in the acceleration of the neocapillarization.     

Connective tissue changes in surgically overloaded muscle

Summary The effects of overload on the connective tissue component of the soleus muscle of the rat have been investigated. Three weeks after tenotomy of its synergistic muscles the soleus underwent considerable increase in weight. This was shown to have resulted from an increase in size of the predominant fibre type. Whilst occasional groups of fibres appeared to have resulted from the splitting of large single fibres, there was no significant increase in the number of fibres in cross-section of the muscle belly. The connective tissue content of the overloaded muscles was investigated using both histological and biochemical techniques. It was found that muscle fibre hypertrophy was accompanied by an increase in the connective tissue component. Furthermore, there was an increase in the proportion of collagen to muscle fibre tissue.The author wish to acknowledge the expert technical assistance given by Mr P. Prentis. This investigation was supported by a grant from the Medical Research Council.     

Localization of NTPDase1/CD39 in normal and transformed human pancreas.

Elevated levels of extracellular ATP have been observed in many tumors. We have localized NTPDase1/CD39, one of the principal extracellular nucleotide-hydrolyzing enzymes, in normal and cancerous human pancreas. NTPDase/E-ATPDase activity was demonstrated with an enzyme histochemical technique on cryosections of human pancreas. Acinar and duct epithelial cells were devoid of E-ATPDase activity in both normal and transformed tissue. Endothelial cells and smooth muscle around blood vessels and larger ducts showed strong activity. Nerves, connective tissue, and the beta-cells of the islets were also stained. In cancerous tissue this activity was diminished in the smooth muscle around the ducts and was absent from newly formed connective tissue. Immunostaining for CD39 supported these results but revealed the presence of inactive CD39 in the duct epithelial cells. We hypothesize that the significantly diminished activity of NTPDase1 in the tissues surrounding the ducts may be associated with the processes that lead to tumor formation in human pancreas.     

Spontaneous fibroblast‐derived pericyte recruitment in a human tissue‐engineered angiogenesis model in vitro

Cooperation between endothelial cells and pericytes is essential to the stabilization and maturation of blood microvessels. We developed a unique in vitro tissue‐engineered model to study angiogenesis. The human endothelialized reconstructed connective tissue model promotes the formation of a three‐dimensional branching network of capillary‐like tubes (CLT) with closed lumens. The purpose of this work was to investigate whether pericytes were spontaneously recruited around CLT in the model. We demonstrated that smooth muscle α‐actin (SMA)‐positive cells were found closely associated with PECAM‐1‐positive capillaries in the model. Twelve percent (±2.6) of SMA‐positive cells were detected along with 15% (±1.64) von Willebrand factor‐positive endothelial cells in the culture system after 31 days of in vitro maturation. Conversely, no SMA‐positive cells were detected in reconstructed connective tissues made solely of fibroblasts. Knowing that PDGF is a major factor in the recruitment of pericytes, we showed that blockade of the PDGFB receptor using the inhibitor AG1296 induced an overall 5, 2.6, and 2.4‐fold decrease in the SMA‐positive cells, von Willebrand factor‐positive cells, and number of capillaries, respectively. Using combinations of human GFP‐positive fibroblasts and endothelial cells, we demonstrated that pericytes were recruited from the fibroblast population in the model. In conclusion, our tissue‐engineered culture system promotes the spontaneous formation of a network of capillaries and the recruitment of pericytes derived from fibroblasts. Since pericytes are essential components of the blood microvasculature, this culture system is a powerful model to study angiogenesis and endothelial cell/pericyte interactions in vitro. J. Cell. Physiol. 227: 2130–2137, 2012. © 2011 Wiley Periodicals, Inc.     

Difference between the thyroid gland of normal and hypomyelinated jimpy mice--a light microscopic study

A light microscopic quantitative analysis was performed on normal and jimpy male mice for studying the difference between the structures of the thyroid glands of the two animals. The results of this analysis showed that the thyroid gland of the normal mice consisted of numerous homogenous round follicles with cuboidal follicular cells, separated by thin interlobular and interfollicular connective tissue and a few adipose tissue. The thyroid gland of jimpy mice consisted of a few, small follicles surrounded by columnar follicular cells and intraepithelial capillaries, separated by thick connective tissue and abundant adipose tissue. The number of thyroid follicles are significantly less in the jimpy mice than in the normal mice. Another striking difference is that almost every follicular cell surrounding the follicular lumen of jimpy mice is accompanied by an intraepithelial capillary. In addition, the ratio of the number of intraepithelial capillaries to the number of the thyroid follicular cells are significantly higher in the jimpy mice than in the normal mice. The S-follicles or ultimobranchial cysts of the thyroid gland are well developed in the jimpy mice. The parafollicular cells are normal in appearance. Morphological evidence suggested that the thyroid follicular cells of the jimpy mice are very active in the transport, synthesis and release of thyroglobulin, and secretion of thyroid hormones. But owing to the significantly decreased number of thyroid follicles, the inadequate secretion of the thyroid hormones result in the hypothyroidism and the hypomyelination of the jimpy mice.     

Connective tissue in the perivascular spaces of subependymal capillaries of the spinal cord in the rabbit]

The normal structure of the subependymal capillaries and venules of the spinal cord was studied in rabbit. The endothelial cells of the capillaries and venules are surrounded by an irregularly formed perivascular space, about 0.5 to 3.3 micrometer wide, which is delimited by an endothelial and glial basal lamina. The space contains a framework of collagen fibers. A period-acid-bisulfit-aldehydthionine-method (Specht) permits to find the perivascular connective tissue lightmicroscopically, while they can be identified by electron microscopy. The significance of the perivascular connective tissue is open to discussion. Structural and functional problems have been reviewed in this context.     

The structure and functional significance of variations in the connective tissue within muscle

The amount of intramuscular connective tissue (IMCT) and its morphological distribution is highly variable between muscles of differing function. The functional roles of this component of muscle have been poorly understood, but a picture is gradually emerging of the central role this component has in growth, transmission of mechanical signals to muscle cells and co-ordination of forces between fibres within a muscle. The aim of this review is to highlight recent advances that begin to show the functional significance of some of the variability in IMCT. IMCT has a number of clearly defined roles. It patterns muscle development and innervation, and mechanically integrates the tissue. In developing muscles, proliferation and growth of muscle cells is stimulated and guided by cell-matrix interactions. Recent work has shown that the topography of collagen fibres is an important signal. The timing and rates of expression of connective tissue proteins also show differences between muscles. Discussion of mechanical roles for IMCT has traditionally been limited to the passive elastic response of muscle. However, it is now clear that IMCT provides a matrix to integrate the contractile function of the whole tissue. Mechanical forces are co-ordinated and passed between adjacent muscle cells via cell-matrix interactions and the endomysial connective tissue that links the cells together. An emerging concept is that division of a muscle into fascicles by the perimysial connective tissue is related to the need to accommodate shear strains as muscles change shape during contraction and extension.     

Scanning electron microscope study of the liver microcirculation

During the experimental investigation performed in dogs and rats, by means of scanning electron microscopy of corrosive anatomical preparations, the spatial organization of all parts of the hepatic vascular bed (arterial, venous and lymphatic) has been studied, specific features of their components construction have been described. Within the limits of one hepatic lobule the number of vessels included in the portal vein system exceeds that of the arterial ones, originating from the proper hepatic artery system. In every part of the vascular bed the gradient of the form, orientation and pronouncement of the nuclei-containing zones in endotheliocytes and myocytes has been established. Various appliances participating in the blood and lymph stream regulation in different parts of the vascular bed have been revealed. As initial elements of the lymph bed, closed digital or loop-like capillaries should be regarded, they localize in the organ's connective tissue framework. Around the portal and hepatic veins and their branches, as well as around the biliary ducts, well developed plexuses of the lymphatic and blood capillaries and vessels localize, they are the main draining pathways of the organ. The degree of development and pronouncement of these plexuses depends on the lumen size in the formation they accompany.     

Schistosoma mansoni: peritoneal plasmacytogenesis and polypoid transformation of mesenteric milky spots in infected mice.

We have studied inflammatory reactions in the mesenteric tissue of mice infected with Schistosoma mansoni. Perivascular tissue contained diffuse infiltrates of macrophages, eosinophilic granulocytes and lymphocytes. Angiogenesis in the perivascular adipose tissue was associated with superficial plasmacytogenic foci. Polypoid structures were occasionally formed adjacent to inflammatory foci in the adipose tissue, organized around loops of capillaries, with terminal formation of a glomerular capillary network embedded in connective tissue, covered by plasmacytes. We conclude that these structures are specialized milky spots dedicated to active plasmacytogenesis and antibody secretion into the peritoneal cavity of schistosome-infected mice.     

Localization of hyaluronan in various muscular tissues

Summary The histochemical distribution of hyaluronan (hyaluronic acid, HYA) was analysed in various types of muscles in the rat by use of a hyaluronan-binding protein (HABP) and the avidin-biotin/peroxidase complex staining procedure. Microwave-aided fixation was used to retain the extracellular location of the glycosaminoglycan. In skeletal muscles, HYA was detected in the connective tissue sheath surrounding the muscles (epimysium), in the septa subdividing the muscle fibre bundles (perimysium) and in the connective tissue surrounding each muscle fibre (endomysium). HYA was heterogeneously distributed in all striated muscles. In skeletal muscles with small fibre dimensions (e.g., the lateral rectus muscle of the eye and the middle ear muscles), HYA was predominantly accumulated around the individual muscle fibres. Perivascular and perineural connective tissue formations were distinctly HYA-positive. In cardiac muscles, HYA was randomly distributed around the branching and interconnecting muscle fibres. In comparison, smooth muscle tissue was devoid of HYA.     

The distribution of capillaries in the somatic musculature of two vertebrate types with particular reference to teleost fish

The distribution of capillaries in teleost and rat striated muscles was investigated using a number of different methods. A new method for directly viewing capillaries was developed. Teleost white muscle has a capillary: fibre (C:F) ratio of between 0.2 and 0.3; and 0.6 to 1.0 peripheral capillaries per muscle fibre. 26-49% of fibres had no peripheral capillaries. Values for the rat gastrocnemius were 1.2, 2.6 and 4.8% respectively which compares well with literature values. Flathead red muscle had a C:F ratio of between 1.9 and 2.5; and between 5.3 and 6.6 peripheral capillaries per muscle fibre depending on the method used. Values for rat soleus were 1.8 and 4.1 respectively. Teleost pink fibres had an intermediate number of capillaries. Rat striated muscle, particularly the gastrocnemius, was found to be heterogeneous with respect to the distribution of capillaries. Flathead red muscle was homogeneous whilst teleost white muscle was only slightly variable. Flathead red muscle fibres are well suppled with subsarcolemmal mitochondria. These show a clumped distribution corresponding to the position of capillaries. In contrast teleost white fibres are almost totally devoid of these and all other mitochondria. No differences were observed in the vascularisation of either muscle type along the length of the fish. The results are discussed in relation to the division of labour between fibre types during swimming.     

Capillarization of the myocardium of the yak

Organometric and histometric characteristics of various parts of the heart have been performed in the yak, a permanent inhabitant at altitudes of 3,000-5,000 m above the sea level. Forty hearts of mature animals have been studied. Morphometric investigations of capillaries in the muscle fibers have been carried out in the atrial walls, in the right and left auriculae. in the ventricles and in the papillary muscles. The data are presented for each cardiac part: they describe diameters, density and volume of the capillary network and muscle fibers. In order to estimate the degree of capillarization of the cardiac muscle tissue, a new parameter is suggested to be used, when analyzing the morphometric data. It characterizes ratio of capillaries volume. According to the criterion given, a significant difference is stated between the degree of capillarization in the myocardium of the right and left ventricles. We suppose that this adequately reflects an increased loading experienced by the right cardiac parts under a long-lasting effect of altitude factors.