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Biomedical subjects

M Cheng

Publications and source records attributed to M Cheng.

At least 91 records · Page 5Linked to original sources
PubMed1982

Differentiation of fibre types in an extraocular muscle of the rat.

Mammalian extraocular muscles possess greater variation in structural and physiological properties than any other muscle. The superior rectus muscle of the adult rat contains five morphological fibre types. The differentiation of the muscle into these fibre types in embryonic and postnatal rats were studied by light and electron microscopy, and the distribution of each developing fibre type with its distinctive features was mapped. The muscle of the 18-day embryos did not display the specific structural fibre types that were observed in the adult muscle. Newborn rat muscle exhibited some differentiation that included scattered small-diameter fibres with large myofibrils (fibre type 'B'). As development proceeded, another small-diameter fibre type with small myofibrils (fibre type 'A') appeared in the 6-day postnatal rat muscle. By the end of the first week of development neuromuscular junctions were in evidence in these two fibre types. Postsynaptic folds were rare in the large-fibril fibre, and folds were extensive in the small-fibril fibre. The medium- (fibre type 'C') and large-diameter (fibre type 'D') fibres were fully differentiated with small myofibrils and abundant sarcoplasmic reticulum (SR) by the second week of the development. SR was most abundant in the large-diameter fibre, which constituted the predominant global fibre type in the adult muscle. The postsynaptic folds in the neuromuscular junctions of these two fibre types were highly developed, although the innervation did not extend widely in the global region of the muscle. The last fibre type (fibre type 'E') was fully differentiated with the largest myofibrils, a small amount of SR, and simple neuromuscular junction by the third week of the postnatal development. The superior rectus muscle of the four-week-old rat was differentiated with all fibre types present in the adult muscle. During the third to sixth, and final, week of development, the other types described above exhibited extensive differentiation of characteristic structural features.

Animals↗
PubMed1981

Adult mammalian cardiac muscle cells in culture.

Adult rat cardiac muscle cells were isolated from the ventricle by a retrograde perfusion technique through the aorta (Nag and Zak, 1979). These single, isolated cardiac muscle cells were cultured for 4 weeks. Throughout the culture period, a small number of muscle cells retained their cylindrical shape, while the rest exhibited alterations in shape and size assuming a flattened body of irregular shape with pseudopodia-like processes and thereby resembling embryonic/neonatal cardiac muscle cells in culture. Transmission electron microscopy revealed that the cylindrical muscle cells contained compactly arranged myofibrils and cellular organelles, similar to those of freshly isolated and in vivo cells. A few irregularly shaped cardiac muscle cells were similar to the cylindrical cells in their internal structural organization. Most of the irregular cells exhibited less myofibrillar content than that of the freshly dissociated and in vivo cells. Myofibrils in the irregular cells were widely spaced and myofilament of some of the myofibrils were loosely bunched. In addition, scattered patches of myofibrils and free myofilaments were observed in many of these cells. The internal structural organization of these irregularly shaped cardiac muscle cells closely resembled the embryonic and neonatal cardiac muscle cells in vitro and in vivo. Most of the muscle cells in culture continued to contract spontaneously, and electron microscope studies clearly indicated that they underwent dedifferentiation. Autoradiography studies demonstrated that the cylindrical and irregularly shaped cardiac muscle cells underwent DNA synthesis and cell division in culture.

Animals↗
PubMed1981

Multicellular in vivo sister-chromatid exchanges induced by urethane.

Following urethane inhalation exposure, clear dose--response relationships were apparent in all cell types examined in hepatectomized and intact mice. At concentrations of 0.1 mg/l and higher, induced SCE frequencies were linearly related to log urethane concentrations. No significant differences in SCE response between like cell types of hepatectomized and intact mice were apparent. In hepatectomized mice, there was no significant difference in the SCE response of regenerating liver and alveolar macrophage cells. However, bone-marrow response was significantly lower (p = 0.01). Likewise, in intact mice bone marrow response was significantly lower than in alveolar macrophages (p = 0.01). Inhalation and intravenous infusions of the same total dose of urethane (193 mg/kg) administered over a 4-h period produced comparable SCE responses in all cell types. However, a single intraperitoneal injection of 193 mg/kg just prior to BrdU infusion produced significantly higher SCE frequencies in bone marrow (alpha = 0.01), and alveolar macrophages (alpha = 0.05) of intact mice than did the equivalent inhalation dose. Intraperitoneal injections produced similar results in 2-month-old mice as in 4-month-old mice. However, regardless of the route of administration SCE frequencies in regenerating liver and/or alveolar macrophages were significantly higher than in bone marrow.

Aerosols↗
PubMed1981

Competence of embryonic mammalian heart cells in culture: DNA synthesis, mitosis and differentiation.

The competence for DNA synthesis, mitosis and differentiation of cardiac muscle and non-muscle cells of 14- and 18-day rat embryos was studied in vivo. The heart cells of 14-day embryos were relatively more competent in DNA synthesis and mitosis than those of 18-day embryos. These in vitro findings conformed with those of the in vivo studies. Cardiac muscle and non-muscle cells of the younger age group showed higher labelling indices than those of the other age group during 7 days of culture. The general profile of DNA synthesis was similar in both age group during 7 days of culture. The general profile of DNA synthesis was similar in both age group cells. Maximum labelling indices in muscle and non-muscle cells were observed after 24 h of culture. The number of labelled cells was always higher in non-muscle cells than in muscle cells. As the culture continued, the labelling indices declined in both cell types of the two age groups. On day seven, 10% labelled cardiac muscle cells and 45% labelled non-muscle cells were observed in the 14-day embryonic group, in comparison with 5% cardiac muscle cells and 35% non-muscle cells of the 18-day embryonic group. When the rate of in vitro differentiation of myofibrils, intercellular junctions and some cellular organelles, were compared between cells of two different age group hearts, no significant difference was observed. During the first week of culture, a considerable number of muscle cells contained myofibrils throughout the length and girth of the cells. The intercalated discs differentiate over a period of 3 weeks of culture. As the culture proceeded, adjoining cardiac muscle cells differentiated desmosomes and gap junctions. Cardiac muscle cells retained these structural specializations and did not undergo dedifferentiation in long-term culture. Overgrowth of one cell type by another was the regular occurrence in all heart cell cultures studied.

Animals↗
PubMed1981

Potency of some carbamates as multiple tissue sister chromatid exchange inducers and comparison with known carcinogenic activities.

The ethyl, ethyl N-hydroxy, isopropyl, and methyl esters of carbamic acid were examined for their abilities to induce sister chromatid exchanges (SCEs) in alveolar macrophages, bone marrow, and regenerating liver cells of C57BL/6J X DBA/2J F1 mice. The relative potencies in inducing SCE, ethyl greater than ethyl N-hydroxy- greater than isopropyl, paralleled previously described activities for induction of lung adenomas in strain A mice. The noncarcinogenic methyl carbamate was inactive in the SCE assay. Relative to bone marrow, regenerating liver and alveolar macrophage cells demonstrated increased susceptibility to carbamate-induced SCE. Of all carbamates studied, only the directly active compound, ethyl N-hydroxycarbamate, produced distinctly different responses in extrahepatic tissues of hepatectomized and intact mice. In intact mice, SCE levels induced by ethyl carbamate in bone marrow and alveolar macrophage cells were not significantly different whether assay followed the last of 12 (three times weekly) serial injections of 2.2 mmol/kg each or after a single injection of 2.2 mmol/kg. Linear regression relationships of log ethyl carbamate versus log SCE or log adenoma response were found to be parallel with the two assays having similar sensitivities.

Animals↗
PubMed1980

Studies of adult amphibian heart cells in vitro: DNA synthesis and mitosis.

The ventricle of the adult newt heart was excised and cut into several pieces of approximately 0.5-1.0 mm. These heart pieces were then cultured for 60 days at 25 degrees C in a modified Leibovitz medium (L-15). Approximately 37% of the explants were attached to the substrate and more than 33% of the attached explants and approximately 15% of the unattached explants established pulsation rates which ranged 3-67 beats/min. The explants were labeled with 1 muCi/ml of 3H-thymidine for 24 hr at 7, 15, 21, 30, 45 and 60 days of culture initiation, and processed for electron microscopic autoradiography. The examination of the autoradiograms revealed that as the culture continued, the cardiac muscle cells altered their morphology, resembling embryonic cardiac muscle cells. These altered muscle cells were termed dedifferentiated cardiac muscle cells. The number of these dedifferentiated cells increased over the period of culture, showing 10.3-94% dedifferentiated cells after 7-60 days of culture respectively. DNA synthesis and mitosis were observed in the dedifferentiated cardiac muscle cells, apart from the non-muscle cells. The quantitation of the autoradiograms revealed that the number of labeled nuclei in the cardiac muscle cells gradually increased over the period of culture, and a maximum number of labeled cardiac muscle cells (30%) was observed in the third week. The peak was followed by a decline in the eighth week which exhibited 1.5% labeled cardiac muscle cells. The trend of mitosis was similar to that of DNA synthesis. The maximum number of mitotic figures (9%) was observed in the third week of culture, which was followed by a decline and finally absent in the eight week. The cardiac non-muscle cells, mostly fibroblasts and endothelial cells, also showed incorporation of 3H-thymidine in their nuclei. The number of labeled non-muscle cells nuclei and the mitotic index were highest (61 and 15% respectively) in the first week of culture, but then they decreased gradually over the eight-week period in culture. This study provides evidence for the first time that the adult amphibian cardiac myocytes can undergo DNA synthesis and mitosis when explanted and cultured. The significance of this cell replication is discussed.

Animals↗
PubMed1980

Irradiation of the surgeon during pinning of femoral fractures.

The intensity of scattered radiation in both a forward and a backward direction from a portable fluoroscope during pinning of the neck of the femur was measured by experiments on a cadaver. The intensity decreased rapidly with increasing distance from the flare of the greater trochanter. Hazard to the surgeon's hands from scattered radiation can be greatly reduced by positioning the C-arm of the fluoroscope so that the x-ray beam is directed laterally.

Background Radiation↗
PubMed1980

Coaggregation and formation of a joint myocardial tissue by embryonic mammalian and avian heart cells.

Intercellular adhesion and tissue reconstruction from homologous dissociated embryonic cells from two species were studied. Dissociated 12-day-old embryonic rat heart cells and 50-h-old embryonic chick heart cells were labeled with tritiated thymidine and allowed to aggregate in Erlenmeyer flasks during rotation culture on a gyratory water-bath shaker. The cultures were continued for 72 h. Cell aggregates were examined microscopically for evidence of contractility and subsequently processed at intervals between 1 and 72 h for transmission electron microscopic autoradiography. Rat and chick hearts used in this study appeared comparable in their stage of development and cellular composition. With the exception of mature blood cells and some fibroblastic non-muscle cells, all chick cardiac muscle cells were labeled with tritiated thymidine. As the cultures continued, aggregates increased in size by continuous accretion of cells and joining of small clusters. The cells within these mixed aggregates exhibited synchronous contractility from 1 h until the cultures were terminated. Most of the aggregation in both control and mixed aggregates was completed within 24 h. Control aggregates consisted of cells from a single species, either chick or rat. Approximately 18% of labeled chick cardiac muscle cells established intercellular contacts and junctions with unlabeled rat cardiac muscle cells after 6 h of culture. This increased to 72% after 72 h in culture. The junctions observed between chick and rat cardiac muscle cells were desmosomes and hemidesmosomes. Approximately 13% of the cardiac muscle cells of one species either chick or rat were found scattered within clusters which contained 15% of the cells from the other species after 72 h of culture. These scattered cells did not form junctions with monospecific cell groups. The implications of these intercellular adhesions between the same and different species are discussed, bearing two hypothesis in mind: (1) Moscona and collaborators, (2) Burdick and Steinberg. This study suggests that cellular as well as species identity plays an important role in the determination of intercellular adhesion among the embryonic cells from different species.

Animals↗
PubMed1979

DNA synthesis and mitosis in adult amphibian cardiac muscle cells in vitro.

High-resolution autoradiography and fine structural analysis of adult newt heart tissue in long-term culture revealed that tritiated thymidine was concentrated in the nuclei of dedifferentiated myocardial cells. Mitotic chromosomes were observed in some of these cells. This demonstrates that adult amphibian myocardial cells in vitro are capable of DNA synthesis and mitosis.

Animals↗
PubMed1979

Organ culture of adult amphibian heart: a fine structural analysis.

Pieces of hearts from adult newts were cultured up to 2 months. Within 7 days of culture, approximately 37% of the cardiac explants were attached to the substrate and more than 33% of the attached explants and approximately 15% of the unattached explants established pulsation rates ranging from 3 to 67 beats/min. The control and cultured explants were processed at weekly intervals for electron microscopy. The diameter of the control cardiac muscle cells ranged approximately 3-5 micron. The cell surface was provided with microvilli. The intercellular spaces ranged approximately 150-500 A. The intercalated discs lacked the step-like courses observed in the mammalian cardiac muscle. Sarcoplasmic reticulum was scanty. Desmosomal-dense materials were frequently continuous with the Z-bands of both control and cultured cardiac muscle cells. The transverse tubular system and gap junction were absent in newt ventricles. The functional implications of these characterisitics are discussed. At the end of 1 week of culture, the surfaces of the explants were covered by one or more layers of non-muscle cells, and the core of the explants consisted mostly of cardiac muscle cells. In a few cardiac muscle cells the myofibrillar organization was disrupted, resulting in the distribution of scattered patches of myofibrils and free myofilaments in the sarcoplasm. A small number of intact muscle cells contained a considerable number of dense granules in the sarcoplasm. At 15 days in culture, a large number of muscle cells showed structural features reminiscent of embryonic cardiac muscle cells. These cells possessed patches of myofibrils, scattered myofilaments and scanty sarcoplasmic reticulum along with other cellular organelles and inclusions. Several of these altered cardiac muscle cells contained mitotic figures. The cardiac explants maintained the initial beating rate until the end of 2 months of culture, except for the 11% of the explants which stopped beating. By 3-4 weeks in culture, most of the cardiac muscle cells possessed the altered cell morphology mentioned above. The explants after 60 days in culture became more flattened than the earlier explants. The intact cardiac muscle cells were rare, and the cores of the explants were mostly occupied by the altered cardiac muscle cells. It is evident from our studies that the cardiac muscle cells have undergone dedifferentiation in long-term culture, and that this dedifferentiation process has yet had no effect in the maintenance of contractility of the explants. Furthermore, these dedifferentiated cardiac muscle cells are capable of DNA synthesis and mitosis.

Animals↗
PubMed1977

Distribution of antibodies to the troponin complex, troponin-C and troponin-I in chicken skeletal muscle as determined by a simplified method for immuno-electron microscopy.

Antisera against the troponin complex, troponin-C and troponin-I have been utilized to locate these proteins in normal, adult chicken skeletal muscle and in filaments prepared from chicken acetone dried powder. The antisera had been previously characterized by immunochemical methods and were employed to ascertain the distribution of the proteins by a simple method for immuno-electron microscopy. Glycerinated chicken breast muscle was treated with the antisera, unreacted antibody was washed from the muscle, and a goat anti-rabbit gamma-globulin was added to enhance the electron density of the antigen-antibody complexes. A periodic distribution of anti-troponin-C at a mean interval of 389 A was observed along the thin filaments in the sectioned tissue. Anti-troponin-I was deposited every 399 A (P less than 0-01). Thin filaments were prepared from acetone dried powder and reacted with the antisera. The anti-troponin-C was located every 389 A; anti-troponin-I, every 399 A (P less than 0-01). Our technique for immuno-electron microscopy is compared with that used by others, and the significance of the findings is discussed.

Analysis of Variance↗
PubMed1977

The safety of local anesthesia and outpatient treatment: a controlled study of induced abortion by vacuum aspiration.

The safety of early vacuum aspiration performed as an outpatient procedure using local anesthesia was examined in a controlled study sponsored by the World Health Organization and undertaken in two centers in Yugoslavia and Singapore. The sample consisted of healthy women whose pregnancies were between 7 and 12 weeks in duration. Follow-up four weeks after abortion was nearly 100 percent in both centers. No important differences in complication rates were found between the different types of services and anesthesia, even though overall complication rates differed markedly between centers. Overnight postabortion observation was not associated with any decrease in complications.

Abortion, Induced↗
PubMed1977

Complications following induced abortion by vacuum aspiration: patient characteristics and procedures.

Complications following early induced abortion by vacuum aspiration were examined in a controlled study. Data were collected on healthy women 7--12 weeks pregnant at the time of abortion. No association was found between complication rates and age, marital status, or parity. However, women in their first pregnancies and those who had experienced an induced or spontaneous abortion in their previous pregnancy had a higher rate of complications following the current induced abortion.

Abortion, Induced↗
PubMed1975

Optokinetic nystagmus during selective retinal stimulation.

Nystagmic eye movements in response to selective optokinetic stimulation of different parts of the retina were studied in normal human subjects by two methods: 1. a digital computer controlled by the eye movement signal was used to generate an optokinetic display which stimulated only the peripheral retina, simulating a central scotoma, and 2. a single dot of 0.6 degrees in diameter was used as the stimulus during maintained forward gaze. The results show that stimulation of the central or peripheral retina alone can produce optokinetic nystagmus in man, and that essentially the same type of nystagmus is produced in both cases. The slow phase velocity of nystagmus evoked from the peripheral retina falls off rapidly with distance from the fovea but can be facilitated by attention. Results are compared with other findings and a possible explanation is offered for the observed variation in slow phase speed which occurs during constant velocity optokinetic stimulation.

Adolescent↗