35 research outputs found

    Fine structural and functional development of the heart in the chick embryo with special reference to the onset of heartbeat

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    Fine structural changes of cardiocytes in the chick embryo before and after the onset of rhythmical contraction (Hamburger-Hamilton stages 8 to 17) were studied by light and electron microscopy. The earliest heartbeat was recognized at stage 10 by means of dissecting microscopy and the incidence of beating hearts increased as stage proceeded. In precontracting hearts, cardiocytes contained a small number of actin-like filaments, but thick filaments and primitive myofibrils were not discernible. At stage10, when some hearts are considered to commence rhythmical beating, myosin filaments and primitive myofibrils appeared in a few cardiocytes. The spatial orderly arrangement of actin and myosin filaments appears to play an important role for the onset of the first heartbeat. Desmosomes and intermediate junctions were well developed even in prebeating hearts. Elements of sarcoplasmic reticulum were rarely observed at postheartbeat stage 12 and remained infrequent in later stages of development. Thus these vesicles are unlikely to correlate closely with contraction in young embryonic hearts. It is clearly demonstrated that hearts are able to contract in an immature condition when not all but some cardiocytes contain only a few developing myofibrils

    Development of collagen fibers in the rat knee joint and intervertebral disc.

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    胎生18日から生後25週までの雌雄ラットを用い,膝関節の脛骨関節軟骨と胸部脊柱の椎間円板で,成長につれて膠原線維の量と分布がどのように変化するかを,光学顕微鏡(光顕)と電子顕微鏡(電顕)で調べた.胎生18日には,脛骨の近位骨端は軟骨で構成され,マッソン・ゴールドナー染色で膠原線維はほとんど認められなかった.生後0日には,膠原線維は関節軟骨の最も表層で弱く染まっただけだったが,成長とともに増加した.生後2,3週には,関節軟骨の表層の膠原線維が濃く染まり,骨端中心部の石灰化領域に近づくにつれて染色が薄くなった.生後9週には,関節軟骨全体が濃く染まった.このように,関節軟骨では,骨端の表面から中心部に向けて膠原線維が増加した.成長板は,生後2週で出現し,関節軟骨と対照的に膠原線維の増加はわずかだった.椎間円板では,胎生18日に最も周辺部の線維輪に膠原線維が認められた.膠原線維の増加は,成長とともに,周辺部の線維輪から椎間円板の中心部に,中心部では髄核に近い部位から椎体に向かって進行し,生後2週には椎間円板の膠原線維は均一に濃く染色された.生後9週以降は,椎間円板の所々に骨化が観察された.光顕で観察された線維は,電顕で膠原線維に特有な縞模様が観察されたので,膠原線維と同定した.また,光顕での染色の濃度と電顕での線維の増加とはよく相関した.このような膠原線維の増え方には,関節の運動,荷重や栄養の供給経路が関係しているものと推測される.本研究で,胎仔期の軟骨や成長板では膠原線維が乏しいことが示された.これらの軟骨は活発に増殖することが知られている.対照的に,関節軟骨や線維輪では膠原線維が豊富で,軟骨細胞はまれにしか分裂増殖しない.膠原線維の増加と軟骨細胞の増殖減少とは,関連があるのかもしれない.Changes in the amount and distribution of collagen fibers in the developing tibial articular cartilage of theknee joint and the thoracic intervertebral disc in the rat (ranging from 18 gestational days to postnatal 25weeks) were studied by light and electron microscopy. At 18 gestational days, the proximal epiphysis of thetibia, as revealed by Masson-Goldner staining, was composed of cartilage with few collagen fibers. On day 0,collagen fibers were weakly stained in the most marginal layer but increased in amount with time. At 2 and 3weeks, the staining of collagen fibers was pronounced in the superficial zone, but decreased in intensitytoward the deeper ossified region. At 9 weeks, uniform and intense staining was found throughout thearticular cartilage. In contrast, the collagen fibers in the growth plate, which appeared at 2weeks, increasedonly a little. In the intervertebral disc, collagen fibers were recognized at the most peripheral annulus fibrosusat 18 gestational days. The increase of collagen fibers proceeded from the peripheral annulus fibrosus towardthe center of disc, and at the center, from places near the nucleus pulposus toward the vertebral bodies in avertical direction. At 2 weeks, the intervertebral discs were intensely and homogeneously stained for collagenfibers. From 9 weeks onwards, ossified regions were occasionally found in the intervertebral discs.Electron microscopy demonstrated characteristic periodic striations for collagen in fibers observed bylight microscopy. In addition, the intensities of staining in light microscopic specimens correlated well withthe amount of collagen fiber at the electron microscopic level. The progression pattern of collagen fiberaccumulation is possibly correlated with the joint movement, weight loading and route of nutrient supply.The fetal cartilage and the growth plate were shown to contain only a small amount of collagen fiber in thepresent study. It is known that the chondrocytes in these cartilages actively proliferate. In contrast, thearticular cartilage and intervertebral disc contained a great deal of collagen fiber and chondrocytes withrare cell division. Some correlation may exist between an increase in collagen fibers and a reciprocaldecrease in the proliferative activity of chondrocytes

    Formaldehyde Concentration in the Air and in Cadavers at the Gross Anatomy Laboratory in Hiroshima University

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    The formaldehyde concentration in the air and in various tissues of 35 human cadavers were measured during a gross anatomy course held at the Faculty of Medicine of Hiroshima University in the 2003 educational year. Atmospheric formaldehyde levels were 0.25-0.55 ppm and thus less than the upper limit of the guideline for formaldehyde exposure (0.5 ppm) set by the Japan Society for Occupational Health (1988) except for one out of 10 measurements. The formaldehyde concentrations in tissues were as follows: the lung, 0.12 ± 0.09% (n=29); the liver, 0.12 ± 0.09% (n=29); and the brachioradialis muscle, 0.11 ± 0.09% (n=30). Considerable variation was found among the cadavers and these values were lower than those of Tsurumi University which provided the only other data (average formaldehyde concentrations ranged from 0.27 to 0.32%). At Hiroshima University, blood is allowed to drain during embalming, whereas it is not at Tsurumi University. Differences in the embalming procedure are thus responsible for low and fluctuating formaldehyde concentrations in cadavers at Hiroshima University, and it is conceivable that relatively low formaldehyde levels in the air result from low formaldehyde concentrations in cadavers and good room ventilation (10 room-air changes per hour). However, the Japanese Ministry of Health and Welfare recommended lower formaldehyde exposure levels (0.08 or 0.25 ppm) in 2002. Thus, it may be necessary to further reduce formaldehyde levels in the gross anatomy laboratory by means of such measures as neutralizing formaldehyde with ammonium carbonate; using a locally ventilated dissection worktable, etc

    Reduction of formaldehyde concentrations in the air and cadaveric tissues by ammonium carbonate

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    The reduction of formaldehyde by ammonium carbonate was examined in cadavers and in vitro. Formaldehyde concentrations in the air (10 cm above human cadavers) and in various cadaveric tissues were measured with or without perfusion of ammonium carbonate solution into formaldehyde-fixed cadavers. Air samples were monitored using Kitagawa gas detector tubes. For measurement of formaldehyde in tissues, muscles and organs were cut into small pieces and tissue fluids were separated out by centrifugation. These specimen fluids were diluted, supplemented with 3-methyl-2-benzothiazolinone hydrazone hydrochloride and quantified by spectrophotometry. In five cadavers without ammonium carbonate treatment, the formaldehyde concentrations in the air above the thorax and in various tissue fluids were 1.2?3.0 p.p.m. and 0.15?0.53%, respectively. Arterial reperfusion of saturated ammonium carbonate solution (1.0, 1.5 or 2.0 L) into five formaldehyde-fixed cadavers successfully reduced the formaldehyde levels, both in the air (0.5?1.0 p.p.m.) and in various tissue fluids (0.012?0.36%). In vitro experiments demonstrated that formaldehyde concentrations decreased, first rapidly and then gradually, with the addition of ammonium carbonate solution into fluids containing formaldehyde. It was confirmed that formaldehyde reacted with the ammonium carbonate and was thereby changed into harmless hexamethylenetetramine. The application of ammonium carbonate solution via intravascular perfusion and, if necessary, by infusion into the thoracic and peritoneal cavities, injection into muscles and spraying on denuded tissues can be anticipated to reduce formaldehyde to satisfactorily low levels in cadaveric tissues and, consequently, in the air, which may provide safe and odorless dissecting rooms

    Effects of short-term denervation and subsequent reinnervation on motor endplates and the soleus muscle in the rat

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    The rat sciatic nerve was locally frozen, and changes in the nerve, motor endplates, and the soleus muscle were examined for up to 6 weeks by light and electron microscopy. The wet weights of denervated soleus muscles compared with contralateral values progressively declined to a minimum at 2 weeks after injury (60.7±2.5%) and began to reverse following 3 weeks. The sciatic nerve thoroughly degenerated after freezing. However, numerous regenerated myelinated and thin nerve fibers were observed at 3 weeks. They were considerably enlarged but still smaller than normal counterparts at 6 weeks postoperatively. Nerve terminals containing synaptic vesicles of endplates disappeared at day 1 and mostly reappeared at 3 weeks (about 700f the endplates). All endplates examined were reinnervated at 4, 5, and 6 weeks. On the other hand, postsynaptic folds of muscle fibers seemed to be only slightly influenced by denervation or reinnervation. Ultrastructural alterations of myofibrils, in particular the loss of register, immediately appeared after denervation, spread progressively, peaked at 2 weeks, ameliorated following reinnervation, and became significantly normalized at 6 weeks after freezing. The proportion of type II fibers in the soleus muscle similary showed an increase and a decrease with a short delay in response to denervation and reinnervation, respectively. This study clearly demonstrated that the nerve supply affects the ultrastructural integrity of skeletal muscles. In addition, changes in the endplates and the soleus muscle evaluated in this study after short-term denervation are largely reversible following reinnervation

    Injury and repair of the soleus muscle after electrical stimulation of the sciatic nerve in the rat

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    To study injury and subsequent changes in skeletal muscles, the rat sciatic nerve was electrically stimulated at 50 Hz and muscle contraction was induced for 30 min. Muscle damage was classified into five types (hypercontraction, hyperstretching, Z band disorders, misalignment of myofilament and regions of scarce myofilaments) by electron microscopy and quantified by ultrastructural assessment. After electrical nerve stimulation, the percentages of the injured areas of the soleus muscle were 18.8 ± 15.8% (mean ± SD) at O h, 9.7 ± 1.0 0x1.3f1c4p-890t 6 h, 22.0 ± 23.6 0x0p+0t 12 h, 13.1 ± 3.2 0x0p+0t 24 h, 4.9 ± 6.0 0x0p+0t 3 days and 0.5 ± 0.4 0x0p+0t 7 days. At 0 h, the vast majority of ultrastructural alterations were sarcomere hypercontraction. At 6 h, hypercontraction was not recognizable and sarcomere hyperstretching and Z band disarrangement constituted the major findings. At 12 h, when the injury reaehed its maximum, myofilament disorganization and hyperstretching were predominant. At 24 h or afterwards, the injury began to decrease and recovered to almost normal conditions by 7 days. There were very few necrotic muscle fibers in all specimens. It is considered that the muscle lesions in the present study were reversible, and recovered through changes in various types of sarcomere alterations. Z band streaming and free ribosomes were frequently found at 12 and 24 h, which may indicate repair processes rather than newly formed lesions

    Structure of the rat subcutaneous connective tissue in relation to its sliding mechanism

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    Mammalian skin can extensively slide over most parts of the body. To study the mechanism of this mobility of the skin, the structure of the subcutaneous connective tissue was examined by light microscopy. The subcutaneous connective tissue was observed to be composed of multiple layers of thin collagen sheets containing elastic fibers. These piled-up collagen sheets were loosely interconnected with each other, while the outer and inner sheets were respectively anchored to the dermis and epimysium by elastic fibers. Collagen fibers in each sheet were variable in diameter and oriented in different directions to form a thin, loose meshwork under conditions without mechanical stretching. When a weak shear force was loaded between the skin and the underlying abdominal muscles, each collagen sheet slid considerably, resulting in a stretching of the elastic fibers which anchor these sheets. When a further shear force was loaded, collagen fibers in each sheet seemed to align in a more parallel manner to the direction of the tension. With the reduction or removal of the force, the arrangement of collagen fibers in each sheet was reversed and the collagen sheets returned to their original shapes and positions, probably with the stabilizing effect of elastic fibers. Blood vessels and nerves in the subcutaneous connective tissue ran in tortuous routes in planes parallel to the unloaded skin, which seemed very adaptable for the movement of collagen sheets. These findings indicate that the subcutaneous connective tissue is extensively mobile due to the presence of multilayered collagen sheets which are maintained by elastic fibers

    Distribution and Change of Collagen Types I and III and Elastin in Developing Leg Muscle in Rat

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    The distribution of collagen types I and III and elastin in the developing leg muscles were studied by immunohistochemistry in rat. From 0-day to 8-weeks old, the size of the gastrocnemius and plantaris muscles increased. The muscle connective tissue developed in the order of epimysium, perimysium and finally endomysium. The epimysium contained a considerable amount of collagen types I and III and some elastin in the neonates. These components in the epimysium remained almost unchanged in their distribution during development. The perimysium had little collagen type I and III or elastin at 0 day. Collagen type I and elastin slightly increased around 2 and 1 week, respectively, and returned to the previous levels. Collagen type III, however, increased and became abundant after 1 week. In the endomysium, the amounts of collagen type I and elastin were slight during postnatal growth, while collagen type III gradually increased after 2 weeks. The intramuscular tendons consistently showed intense reactivity for collagen type I and weak staining for elastin, whereas the staining for collagen type III decreased after 1 week and was finally restricted to the surface of intramuscular tendons. This study clearly demonstrated that the distribution of collagens, but not of elastin, significantly changed during development. The increase in collagen type III in the perimysium and endomysium, and its decrease in the intramuscular tendons probably reflect functional demands imposed on these connective tissues, i.e., shear forces in the former two and tensile loading in the latter
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