Search PubMed⌕ Search

Biomedical subjects

N F Johnson

Publications and source records attributed to N F Johnson.

At least 55 records · Page 3Linked to original sources

On the role of word frequency in the detection of component letters.

The experiments reported in this study were conducted to explore the issue of race models versus holistic models of word processing. In both types of model, it is assumed that an available word-level encoding for a display will conceal letter information, and thereby inhibit component-letter detection. However, whereas in holistic models it is assumed that encoding always should occur at the word or pattern level first, in the race models it is assumed that encoding occurs at all levels (e.g., feature, letter, and word) simultaneously, with the final level of encoding being at whatever level has been completed first. If the rate of word-level encoding is facilitated by increasing word frequency, the holistic models predict a generally declining latency for letter detection, because the initial step in letter detection (i.e., word-level encoding) will be occurring more rapidly. The race models, on the other hand, predict that with increasing word frequency there will be an increasing chance that the word-level encoding will win the encoding race, resulting in an increase in the latency for letter detection (i.e., the word code will conceal the letter codes). Two experiments are reported, and the obtained pattern of latency data appears to be most consistent with the race models.

Adult↗

The induction of chromosome damage in CHO cells by beryllium and radiation given alone and in combination.

Studies were conducted to determine the effects of BeSO4 or X rays, alone and in combination, on cell cycle kinetics, cell killing, and the production of chromosome aberrations in Chinese hamster ovary (CHO) cells. The concentration of BeSO4 required to kill 50% of CHO cells exposed to BeSO4 for 20 h was determined to be 1.1 mM with 95% confidence intervals of 0.72 to 1.8 mM. During the last 2 h of the 20-h beryllium treatment (0.2 and 1.0 mM), cells were exposed to 0.0, 1.0, or 2.0 Gy of X rays. Exposure to either BeSO4 or X rays produced a change in cell cycle kinetics which resulted in an accumulation of cells in the G2/M stage of the cell cycle. However, combined exposure to both agents resulted in a block similar to that observed following exposure to X rays only. The background level of chromosome damage was 0.05 +/- 0.015 aberrations/cell in the CHO cells. Seven hours after the end of exposure to 0.2 and 1.0 mM beryllium, 0.03 +/- 0.003 and 0.09 +/- 0.02 aberrations/cell, respectively, were observed. The data for chromosome aberrations following X-ray exposure were fitted to a linear model with a coefficient of 0.14 +/- 0.01 aberrations/cell/Gy. When beryllium was combined with the X-ray exposure the interactive response was predicted by a multiplicative model and was significantly higher (P less than 0.05) than predicted by an additive model. The influence of time after radiation exposure on the interaction between beryllium and X rays was also determined. No interaction between beryllium and X-ray exposure in the induction of chromosome-type aberrations (P greater than 0.05) was detected. The frequency of chromatid-type exchanges and total aberrations was significantly higher (P less than 0.05) in the radiation plus beryllium-exposed cells when compared to cells exposed to X rays only, at both 9 and 12 h after X-ray exposure. These data suggest that the multiplicative interaction may be limited to cells in the S and G2 stages of the cell cycle.

Animals↗

Transmission electron microscopy of small numbers of sorted cells.

A new method that allows the transmission electron microscopic examination of as few as 1 x 10(4) cells obtained by flow cytometric sorting is described. The approach involves "sandwiching" fixed cells in an agarose case by a microcentrifugation system consisting of small-diameter cell-centrifugation tubes and subsequent processing of the cells by conventional techniques. The advantages offered by this method are discussed.

Animals↗

Silica-induced alveolar cell tumors in rats.

Min-U-Sil5, a form of alpha quartz, has been shown to induce peripheral lung tumors in rats exposed to the dust by inhalation. The animals were exposed to a nominal particle concentration of 12.4 mg/m3 for 8 hr/day, 4 days/week, for 2 years. The induced tumors were large and peripheral, and, when examined by electron microscopy, were found to be composed predominantly of alveolar type II cells. These cells were found in papillary, acinar, and solid forms of the tumors and were characterized by lamellar inclusion bodies. This is in contrast to the mouse, in which the papillary form was associated with Clara cells and the acinar form was linked with the type II cell. In this study, the Clara cell was a minor component of the tumor mass. No clear risk is established in man linking silica exposure to increased lung tumor rates.

Animals↗

Asbestos-induced changes in rat lung parenchyma.

Fischer 344 rats have been exposed to UICC crocidolite by whole-body inhalation procedures for periods of 1 d to 12 mo. Material was obtained from the same location in the left lung, and the numbers of cells in the parenchyma were identified and determined by transmission electron microscopy. An immediate increase (1 d of exposure) was evident in the number of type II cells, suggesting a direct action of the dust on these cells. The number of interstitial and alveolar macrophages showed a significant increase after 3 mo of exposure. The number of alveolar macrophages containing dust particles after a 1-d exposure was 49%, and the corresponding value after 12 mo of exposure was 92%. The longer periods of exposure were associated with an increase in the number of particles per macrophage. Polymorphs appeared in the interstitium at airway bifurcations, prior to their appearance in the alveolar space. These bifurcations were also the initial sites where evidence of cell damage and collagen deposition was seen. In this experiment crocidolite appears to be weakly fibrogenic, and other factors may be needed to produce the marked lesions seen in human asbestosis.

Animals↗

Preparation of viable single cell suspensions of tracheal epithelial cells.

This paper reports a procedure used for isolating the entire epithelial lining of the rat trachea. Isolated trachea was initially filled with 0.2% hyaluronidase and incubated at 37 degrees C for 30 min. Tracheas were flushed with medium and then reinflated with 0.5 microgram/ml cytochalasin B and re-incubated for 60 min. The tracheal lumens were again flushed and reinstilled with 24 iu/ml pronase and incubated for a further 30 min. The tracheas were flushed again and the cells removed enumerated and viability assessed by trypan blue dye exclusion. Cell yields (X 10(6)) from 30 consecutive Fischer 344 rats were 5.06 +/- 0.16 (s.e.m.) and the mean percentage of viable cells was 83.13 +/- 1.10 (s.e.m.). This cell yield was close to the estimated tracheal cell population (5.3 X 10(6)). The suspensions were predominantly single cells which apparently retained a normal ultrastructural appearance.

Animals↗

Radiobiology of ultrasoft X rays. I. Cultured hamster cells (V79).

Ultrasoft X rays (approximately less than keV) provide a useful probe for the study of the physical parameters associated with the induction of biological lesions because the spatial scale of their energy depositions is of nanometer dimensions, comparable to that of critical structures within the cell. We report on cell-killing experiments using cultured hamster cells (V79) exposed to carbon K (0.28 keV), aluminum K (1.5 keV), copper K (8.0 keV), and 250 kVp X rays, under oxic and hypoxic conditions, and as a function of cell-cycle phase. Our principal results are: RBE increases with decreasing X-ray energy; OER decreases with decreasing X-ray energy; and cell-cycle response is similar for all X-ray energies. Our RBE results confirm earlier observations using ultrasoft X rays on mammalian cells. The shapes of fitted curves through the data for each energy are statistically indistinguishable from one another, implying that the enhanced effectiveness is purely dose modifying. The results reported herein generally support the view that single-track effects of radiation are predominantly due to very local energy depositions on the nanometer scale, which are principally responsible for observed radiobiological effects.

Animals↗

Multipotential behaviour of cloned rat mesothelioma cells with epithelial phenotype.

Reference cultures derived from a transplantable rat mesothelioma were obtained by cloning cells three times in soft agar. Each line, designated "CARM-Lines", was selected on the basis of their epithelial or fibroblastic phenotype, and their uniform morphology. Three epithelial lines were used for more detailed in vitro studies comparing morphological and biological criteria at early and late passages. All three lines exhibited both epithelial and fibroblastic elements after 10-14 passages in vitro, demonstrating that the dimorphic histology of these tumours could be derived from a single aberrant cell. Morphology and growth characteristics of these cells were density-dependent. Anchorage dependent and independent clonogenic assays did not correlate. Anchorage dependent colony formation was the only parameter which differed markedly from the original parent line in the assays described. In vivo evidence of chondrogenesis and attempted ossification support the concept of a multipotential cell contributing to the diverse primary tumour morphology by cellular modulation or differentiation.

Animals↗

In vitro biological effects of volcanic ash from Mount Sakurajima.

Mount Sakurajima in the south of the Kyushu Island of Japan erupts hundreds of times a year and continuously emits large amounts of ash. More than a million people live under this ash plume, and there is considerable concern about the possible effects of this on their health. We have studied the physicochemical characteristics and in vitro effects of airborne ash collected at 8 km from the crater. More than 30% of the ash was found to be SiO2 (w/w) with most of the particles within the respirable size range. The ash did not inhibit the colony formation of V79-4 cells and failed to activate complement or generate chemotactic factor activity in samples of fresh human serum. It was minimally active in causing the release of lysosomal enzymes from human neutrophile, and did not cause arachidonic acid release from macrophage-like cells. These results were in accord with our epidemiological study, in which very low prevalences of nonspecific respiratory disease were demonstrated even at the area with highest ash exposure.

Air Pollutants↗

Pluripotential nature of mesotheliomata induced by inhalation of erionite in rats.

Mesotheliomata can be induced more rapidly and more frequently by inhalation of erionite than by asbestos inhalation. Erionite-induced tumours have in general a similar ultrastructural appearance to inoculum-induced pleural and peritoneal mesotheliomata. Unusual features of these tumours were the presence of dense-cored vesicles and cells staining positively for neuron-specific enolase which indicated the presence of endocrine cells. In addition, one tumour showed differentiation towards bone-forming cells. The expression of both epithelial and mesodermal characteristics demonstrates the pluripotential nature of mesothelial cells under certain circumstances.

Aluminum Silicates↗

The cytotoxicity of kaolin towards macrophages in vitro.

The inhalation of china clay dust by man can cause pneumoconiosis. In an attempt to identify the factors responsible the cytotoxicity in vitro of china clay dust towards mouse peritoneal macrophages was examined. Respirable dusts collected at china clay drying plants were cytotoxic towards the cells. This activity was caused by kaolinite (the major mineral in china clay) and was not due to the presence of ancillary minerals. The cytotoxicity of kaolinite was not due to particle morphology and the positively charged edges of the mineral contributed only slightly to cytotoxicity. An electron microscope study showed that macrophages phagocytosed PVPNO-coated kaolinite particles indicating that the low cytotoxicity of these particles was not due to poor phagocytosis. Residence of china clay in rat lungs appeared to reduce its cytotoxicity. It was concluded that the cytotoxicity of kaolinite was probably related to the proposed amorphous silica-rich gel coating on the particles. The relevance of the findings in vitro to the effects in vivo of china clay is discussed.

Animals↗