Biomedical subjects

S J Anderson

Publications and source records attributed to S J Anderson.

At least 19 recordsLinked to original sources

PubMed1992

Inhibition of T-cell receptor beta-chain gene rearrangement by overexpression of the non-receptor protein tyrosine kinase p56lck.

The variable region genes of the T cell receptor (TCR) alpha and beta chains are assembled by somatic recombination of separate germline elements. During thymocyte development, gene rearrangements display both an ordered progression, with beta chain formation preceding alpha chain, and allelic exclusion, with each cell containing a single functional beta chain rearrangement. Although considerable evidence supports the view that the individual loci are regulated independently, signaling molecules that may participate in controlling TCR gene recombination remain unidentified. Here we report that the lymphocyte-specific protein tyrosine kinase p56lck, when overexpressed in developing thymocytes, provokes a reduction in V beta--D beta rearrangement while permitting normal juxtaposition of other TCR gene segments. Our data support a model in which p56lck activity impinges upon a signaling process that ordinarily permits allelic exclusion at the beta-chain locus.

Animals↗

PubMed1992

Mouse macrophages contain a truncated CD4 transcript.

Mouse macrophages do not express CD4 on their surfaces. We used the polymerase chain reaction to investigate CD4 gene transcription in individual clones of primary mouse splenic macrophages and cell lines of spleen and bone marrow macrophages. The results show only the presence of CD4 mRNA transcripts that are truncated in the 3' coding sequence, thus explaining the lack of expression of a mature CD4 gene product by these cells.

Animals↗

PubMed1992

The use of cognitive style mapping as a predictor for academic success of first-semester diploma nursing students.

This study determined the relationship between the components of the cognitive map and the diploma nursing student's successful academic completion of the first semester. This ex post facto study applied the Modified Hill Cognitive Style Model (MHCSM) instrument; the final grade, the dependent variable, was intercorrelated with the instrument's 28 mapping elements. Data analysis indicated three positively correlated predictors: a preference for finding meaning from written words, for independent problem-solving, and for a logical deductive approach in decision-making. Four negatively correlated predictors included a preference for finding meaning from the spoken word, for finding meaning from sight, for problem-solving with peers, and for categorical reasoning. Implications applicable to nursing education are included.

Cognition↗

PubMed1991

Germline transcripts of the immunoglobulin heavy-chain and T cell receptor genes in a murine hematopoietic stem cell line LyD9 and its derivative cell lines.

We compared germline transcript levels of immunoglobulin heavy chain and T cell receptor (TcR) genes in a murine hematopoietic stem cell line, LyD9, and its derivative cell lines. LyD9 cells can be induced to differentiate into at least three lineages, namely, B lymphocyte, macrophage, and granulocyte lineages. Although C mu transcripts were found in stem cells to B lymphocytes, other myeloid-committed cells also expressed significant amounts of C mu transcripts. Germline TcR transcripts did not show good correlation with differentiation potential and stages of hematopoietic cells. During this search we identified a novel germline transcript containing the JH-C microliter sequence in LyD9 and some of its derivative cells. Expression of mRNAs for immunoglobulin- and TcR-associated molecules (lambda 5, MB1 and CD3 delta) was widespread except for lambda 5 mRNA. Among three mRNAs encoding putative recombinase proteins, RAG-1 and RAG-2 mRNAs were not expressed in any cell lines tested, while RBP-2 mRNA was expressed ubiquitously.

Animals↗

PubMed1991

Human peripheral spatial resolution for achromatic and chromatic stimuli: limits imposed by optical and retinal factors.

1. The aim of this study was to determine whether optical, receptoral or higher-order neural properties limit spatial resolution (acuity) in human vision, especially in the peripheral regions of the visual field. 2. Both achromatic and chromatic stimuli were used, and measures were taken to ensure that the resolution estimates were not contaminated by the detection of spatial sampling artifacts. Spatial contrast sensitivity functions were measured at retinal locations from 0 to 55 deg along the naso-temporal meridian for: (i) discriminating the direction of drift of luminance-modulated (black-white) sinusoidal stimuli drifting at 8 Hz (achromatic task); and (ii) for detecting isoluminant red-green sinusoidal stimuli drifting at 0.4 Hz (chromatic task). Achromatic contrast sensitivity functions were also measured along the vertical meridian for eccentricities of 8 and 40 deg. Each achromatic function was extrapolated to a contrast sensitivity of one (100% contrast) to estimate achromatic acuity. Chromatic acuities were obtained by expressing chromatic contrast in terms of cone contrasts and using the same method of extrapolation. We compared the results with recent data on human optical properties and retinal anatomy. 3. Both achromatic and chromatic acuity decline with distance from the fovea, but at a faster rate than that dictated by the known optical and/or receptoral properties of the human eye. We conclude that, for stimuli of either achromatic or chromatic contrast, peripheral spatial resolution is limited by post-receptoral mechanisms. Also, chromatic acuity declines more steeply than luminance acuity with eccentricity suggesting that there are additional post-receptoral limitations on colour resolution in the periphery. 4. A clear naso-temporal asymmetry is seen in the resolution whose dependence is qualitatively, but not quantitatively, similar to the Nyquist limits imposed by the asymmetric density of human retinal ganglion cells. We discuss the possibility that in peripheral vision (beyond the optic nerve head) the spacing of ganglion cells may pose a fundamental limit on the resolution of achromatic stimuli, but not chromatic stimuli.

Color Perception↗

PubMed1991

Spatial summation properties of directionally selective mechanisms in human vision.

Our goal in this paper was to measure psychophysically the receptive-field size of motion units in human vision. To this aim, length and width spatial summation functions were measured for drifting (8-Hz) sinusoidal gratings of spatial frequencies 0.1, 1.0, and 10.0 cycles per degree (c/deg) with two threshold criteria: direction discrimination and simple detection. For each spatial frequency, contrast sensitivity for detection of the direction of drift increased with increasing stimulus size (length or width), at first rapidly (slope greater than or equal to 1.0) and then more gradually (slope 0.29). For most stimuli, the detection and direction-discrimination contrast thresholds were nearly the same. However, for stimuli severely curtailed in width, significantly more contrast was required for direction discrimination than for detection. These results were predicted with a summation model, which incorporated three-dimensional (space-space-time) linear input filters, and probability summation over space and among different filter types. The fit of the model gave an estimate of both the receptive-field length and width of motion-detector units in human vision. At each spatial frequency, the estimates of receptive-field width and length were similar, indicating that the receptive fields of motion-detector units are as long as they are wide at all spatial scales. Receptive-field size varied from approximately 0.12 cycle at 0.1 c/deg to 0.52 cycle at 10.0 c/deg.

Adult↗

PubMed1991

Two-dimensional spatial and spatial-frequency selectivity of motion-sensitive mechanisms in human vision.

Thresholds for detecting the direction of motion of drifting (8-Hz) vertical gratings [of spatial frequencies 0.1, 1.0, and 10.0 cycles per degree (c/deg)] were measured in the presence of masks that varied in both spatial frequency and orientation. Masks with different temporal properties were used. The specificity of masking was also measured for a stationary test grating of spatial frequency 3.0 c/deg. After suitable scaling and transformation, the masking data gave an estimate of the two-dimensional spatial-frequency tuning surface of cortical detector units in human vision. With the assumption of small-signal linearity and zero phase, the tuning surfaces were inverse Fourier transformed to give an indication of the size and structure of the psychophysical receptive fields of detector units. The results obtained with drifting test gratings and jittering (random phase) mask gratings indicate that motion-detector receptive fields increase in size (in cycles) with increasing spatial frequency but, at all spatial scales, have a length-width ratio of 1. These results are in close agreement with the summation results reported in J. Opt. Soc. Am. A 8, 1330 (1991). Using the same jittering mask stimuli and stationary test gratings, we confirm reports by Daugman [Vision Res. 24, 891 (1984)] and Harvey and Doan [J. Opt. Soc. Am. A 7, 116 (1990)] that motion-independent units have elongated receptive fields with a length-width ratio near 1.8. We conclude that the receptive fields of motion-dependent and -independent mechanisms in human vision are fundamentally different. The possibility that the orientation selectivity of a motion unit is sharpened by its selectivity for direction of motion is discussed.

Contrast Sensitivity↗

PubMed1991

Peripheral spatial vision: limits imposed by optics, photoreceptors, and receptor pooling.

We examined the contribution of optical and photoreceptor properties as well as receptor pooling to eccentricity-dependent variations in spatial vision by comparing the performance of ideal observers with that of human observers. We measured contrast sensitivity functions in human observers and calculated such functions in ideal observers for retinal eccentricities of 0-40 deg. Comparisons of human and ideal performance in a variety of tasks reveal that many aspects of the variation in spatial vision with eccentricity can be understood from an analysis of the discrimination information available at the retinal ganglion cells.

Contrast Sensitivity↗

PubMed1991

Mixtures of wheat and high-moisture corn in finishing diets: feedlot performance and in situ rate of starch digestion in steers.

Wheat and high-moisture corn (HMC) were fed singly and in three combinations using dry-rolled wheat (DRW) (ratios of 75:25, 50:50, and 25:75, respectively, Trial 1), or singly and in two combinations using steam-rolled wheat (SRW) (ratios of 67:33 and 33:67, respectively, Trial 2) to finishing beef cattle fed a high-concentrate diet. In situ rate of starch digestion (Trial 3) was measured on grains used in Trial 1 (excluding the 25 HMC: 75 DRW mixture) and ground dry corn. In Trial 1 (132 d), gain/feed did not differ (P greater than .10); however, final weight, hot carcass weight, and ADG decreased linearly (P less than .05) and DMI exhibited a cubic response (P less than .05) as the percentage of wheat in the diet increased. Carcass characteristics were not different. In Trial 2 (113 d), there were no differences attributable to treatment for ADG, DMI, gain/feed, or carcass characteristics. Positive associative responses for gain efficiency (gain/feed) were greatest for the first increment of wheat addition (25% DRW and 33% SRW in Trials 1 and 2, respectively) and for the early portion of the feeding period (57 and 28 d for Trials 1 and 2, respectively), indicating a more rapid diet adaptation and(or) less propensity for subacute acidosis. In Trial 3, the treatment grains or mixtures did not differ in rate of starch digestion. Although the differences were not statistically significant, starch in the 100% wheat diet was digested twice as fast as the 100 or 75% HMC mixtures.(ABSTRACT TRUNCATED AT 250 WORDS)

Animal Feed↗

PubMed1991

Evidence for tau expression in cells of monocyte lineage and its in vitro phosphorylation by v-fms kinase.

The v-fms encoded kinase, which is known to associate with cytoskeletal elements, was shown to phosphorylate histiocytic proteins that had physical and immunological attributes in common with tau. Tau is a microtubule associated protein that is aberrantly phosphorylated in Alzheimer's disease of the brain. Since c-fms expression is normally exclusive to cells of monocyte lineage, these cells were examined for expression of tau. Heat stable tau was identified in cultured peripheral blood monocytes. This represents the first molecular characterization of tau in cells of non-neural origin.

Cell Line↗

PubMed1990

Polyacrylamide gel analysis of polypeptides in gene transfer cell lines.

Differential polypeptide expression in gene transfer cell lines of limited genetic complexity was analyzed as a gene mapping strategy. Subcellular fractionation preceding two-dimensional gel electrophoretic analysis simplified protein patterns and revealed subcellular location of differentially expressed polypeptides. As a model system, human MET oncogene polypeptide was identified in gene transfer lines by this approach. Genes encoding five putative human proteins were identified and provisionally assigned to chromosomal region 7q21-31 or to chromosome 1.

Amino Acids↗

PubMed1990

Post-receptoral undersampling in normal human peripheral vision.

In human far peripheral vision, drifting stimuli of particular periodicities appear to move in the opposite direction from their true direction of motion. This "reverse motion illusion" is a consequence of spatial undersampling of the retinal image. The illusion occurs for spatial frequencies an order of magnitude lower than that expected on the basis of anatomical measurements of human photoreceptor density. We conclude that for naturally imaged stimuli the site of undersampling in far peripheral vision must be post-receptoral.

Contrast Sensitivity↗

PubMed1990

A comparison of levels of intrinsic single strand breaks/alkali labile sites associated with human melanoma cell invasion.

Intrinsic levels of protein-free single strand breaks/alkali-labile sites in human melanoma cell populations of varying in vitro invasive capacity have been assayed with DNA filter elution methodology. DNA from two human melanoma cell lines, A375P and C8161, and from a subpopulation selected from A375P, A375P-5, were assayed to test the hypothesis that increased levels of DNA damage may be associated with the phenotype of increased invasive and metastatic capacities. The elution profiles obtained reveal statistically significant increases in the level of single strand breaks and/or alkali-labile sites (SSB/ALS) which correlate with increasing invasive and metastatic capacities. The increased levels of SSB/ALS in A375P-5 observed in freshly selected cells decline as these cells are maintained in culture. The stability of this A375P-5 phenotype correlates with previously reported levels of double minute chromosomes, an indicator of genomic instability. Alterations in average intrinsic levels of cellular lesions are therefore an additional factor to be considered in the phenotypic characterization of invasive and metastatic tumor cells and may reflect or contribute to the genomic instability characteristic of tumor cell populations.

Alkalies↗

PubMed1990

Genetic and environmental influences on echocardiographically determined left ventricular mass in black twins.

Genetic and environmental influences on left ventricular mass were examined in normotensive black twins. Left ventricular mass was measured echocardiographically in 7 sets of monozygotic (MZ) and 15 sets of dizygotic (DZ) twins and adjusted for body surface area (LVMI). Regression analyses showed significant effects of gender (R2 = 0.48; P less than .01), systolic blood pressure (R2 = 0.21; P less than .01) and age (R2 = 0.10; P less than .05) on LVMI but did not show an effect for either diastolic blood pressure or caloric expenditure. Monozygotic twins showed smaller within-pair differences (7 +/- 5) than DZ twins (17 +/- 11) for LVMI following adjustment for gender, systolic blood pressure and age (P less than .03). The intraclass correlation for MZ twins was 0.90 (P less than .01) and 0.33 (P = NS) for DZ twins. These results indicate that both genetic and environmental factors are important determinants of left ventricular mass in blacks, independent of gender, blood pressure and age.

Adult↗

PubMed1990

Using smoothing splines for detecting ventilatory thresholds.

A recently developed nonparametric regression technique, called a polynomial smoothing spline, is presented for detecting the ventilatory threshold (VT) and respiratory compensation (RC) points from gas exchange response data taken during an incremental exercise test. This type of curve fitting has the advantage of not requiring investigators to specify, a priori, the form of the underlying model, as is required with all linear regression techniques. This procedure yields a mathematically optimal fitted curve through the O2 uptake (VO2) vs CO2 output (VCO2) data and estimates of the process' first and second derivatives. A breakpoint or threshold is indicated by an increase in the value of the derivative and a peak in the second derivative. To evaluate this approach we analyzed gas exchange data collected on nine healthy subjects during a ramp exercise test (15 W.min-1) to the limits of tolerance. Utilizing this procedure we detected VT and RC breakpoints in four subjects and only VT breakpoints in the remaining five subjects. Our results and those obtained using the more conventional linear regression method were similar for those subjects whose RC points were detected using the smoothing spline procedure. However, using regression techniques for subjects with low or otherwise undetectable RC breakpoints, the linear regression method yielded less reliable results in our hands.

Anaerobic Threshold↗

PubMed1990

Supplemental fat source affects feedlot performance and carcass traits of finishing yearling steers and estimated diet net energy value.

Two trials that utilized 356 yearling steers were conducted to evaluate the effects of fat sources (3.5% of diet dry matter) in steam-flaked milo finishing diets. Fats differed in fatty acid composition and level of free fatty acids. In Trial 1, soybean oil, tallow and yellow grease were compared to a nonfat control. Feeding fat increased (P less than .05) daily gain, feed efficiency, estimated diet NE concentration, carcass weight and dressing percentage of steers. In Trial 2, fat treatments were control, acidulated soybean soapstock (SBSS), tallow, a blend of 70% SBSS:30% tallow, and yellow grease. Feeding tallow or the SBSS:tallow blend improved (P less than .05) feed efficiency and estimated dietary NE compared to control. Proportions of palmitic, stearic, oleic, linoleic and linolenic acid in longissimus muscle of steers were altered (P less than .05) by source of supplemental fat. Potential variability in animal response to fat blends was demonstrated by differences in animal response to yellow grease in the two trials. It was concluded that fats vary in feeding value and may alter carcass composition, contrary to putative thought. Further, potential associative effects of fat blends and interactions of fat with other dietary components in high-grain finishing diets require further investigation.

Animal Feed↗

PubMed1989

The use of permeabilized cells to study the ion requirements of receptor-ligand dissociation in endosomes.

The mannose receptor mediates the transport of high-mannose glycoproteins from the cell surface to lysosomes in macrophages. The binding of ligand to the receptor is dependent on both pH and Ca2+. Upon internalization, ligands enter an acidic pre-lysosomal compartment where receptor-ligand dissociation takes place. Acidification is driven by an endosomal proton pump and anion transport is coupled to this acidification step. A permeabilized-cell assay has been designed to characterize the ionic requirements for receptor-ligand dissociation in endosomes. The plasma membrane of macrophages has been permeabilized selectively with digitonin without affecting endosomal membranes. Receptor-ligand dissociation in permeabilized cells required ATP and was blocked by proton ionophores. Di-isothiocyanostilbene-disulphonic acid and N-ethylmaleimide also blocked dissociation, but mitochondrial ATPase inhibitors and vanadate were ineffective. To explore the nature of the anion requirement for acidification, the ability of different anions to compensate for Cl- was tested. For the halide series, Br- was as equally effective as Cl- in supporting receptor-ligand dissociation, but I- was inhibitory. Citrate and gluconate were only partially effective, while SO4(2-), NO3- and PO4(2-) blocked dissociation. Addition of Ca2+ to permeabilized-cell preparations impaired ATP-dependent dissociation without affecting endosome acidification. These results suggest that the endosomal membrane has a Ca2+ conductance that would permit the rapid efflux of Ca2+ from endosomes during acidification, and this would appear to be a necessary step for efficient sorting of Ca2+-dependent receptors from their ligands.

Adenosine Triphosphate↗

PubMed1989

Receptive field properties of human motion detector units inferred from spatial frequency masking.

This study was designed to investigate the spatial frequency selectivity and spatial structure of receptive fields of motion sensitive mechanisms in human vision. Spatial frequency selectivity was inferred from masking measurements, using dynamic test and mask stimuli. For test frequencies between 0.025 and 15.0 c/deg, maximal masking occurred when the mask frequency matched that of the test, suggesting that the test was detected by mechanisms tuned to (or near to) that frequency. For tests below 0.025 c/deg or above 15.0 c/deg, maximal masking occurred at 0.025 and 15.0 c/deg, respectively, suggesting that there exist no mechanisms selective to frequencies outside these limits. A masking model, suitable for interpreting results obtained with drifting test stimuli, was developed and used to calculate spatial frequency selectivity functions from masking data. Assuming small signal linearity, and a constant phase spectrum, the selectivity functions were inverse-Fourier transformed to yield estimates of the extent and structure of receptive fields. Field width was found to vary with test spatial frequency from 5.8 deg at 0.03 c/deg to 0.05 deg at 10.0 c/deg. These estimates were compared with width estimates previously obtained by a summation technique (Anderson & Burr, 1987), and found to be similar over a wide range of spatial frequencies (2.5 log units). Gabor functions provided a reasonable fit to the calculated field profiles at high spatial frequencies (above 1.0 c/deg), but not at low frequencies.

Fourier Analysis↗