Biomedical subjects

S Mathews

Publications and source records attributed to S Mathews.

At least 19 recordsLinked to original sources

PubMed1997

Ferroelectric Field Effect Transistor Based on Epitaxial Perovskite Heterostructures

Ferroelectric field effect devices offer the possibility of nonvolatile active memory elements. Doped rare-earth manganates, which are usually associated with colossal magnetoresistive properties, have been used as the semiconductor channel material of a prototypical epitaxial field effect device. The carrier concentration of the semiconductor channel can be "tuned" by varying the manganate stochiometry. A device with La0.7Ca0.3MnO3 as the semiconductor and PbZr0.2Ti0.8O3 as the ferroelectric gate exhibited a modulation in channel conductance of at least a factor of 3 and a retention loss of 3 percent after 45 minutes without power.

Journal Article↗

PubMed1996

Recombinant human renin produced in different expression systems: biochemical properties and 3D structure.

Human renin has been expressed in Sf9 and CHO cells using two different gene constructs. The first construct contained a foreign signal peptide fused directly to the sequence encoding mature renin, whereas the second construct harbors the sequence for preprorenin. Prorenin was produced in significantly higher amounts than the mature enzyme expressed without its propeptide in both expression systems. Both directly expressed mature renin and proteolytically derived active renin have been purified and cocrystallized with the renin inhibitor Ro 42-5892. The 3D structure has been solved for both versions and demonstrates identity despite different glycosylation and different N termini.

Amino Acid Sequence↗

PubMed1996

Tc-99m tetrofosmin myocardial distribution 4 hours post injection.

The recommended protocol for Tc99m tetrofosmin myocardial imaging suggests either a one- or two day imaging protocol so that stress and rest studies are sufficiently separated in time to allow optimum myocardium to background uptake ratios to differentiate between myocardial ischaemia and/or infarction. The biokinetic data for tetrofosmin suggest that no significant changes occur in myocardial distribution up to 180 minutes post injection. It is, therefore, necessary for two doses of the radiopharmaceutical and two separate studies to evaluate the myocardial status during stress and rest. This study assessed the differences between the 1 and 4 hour post injection SPET images obtained following peak exercise in 20 consecutively chosen patients. In addition, these images were compared to the rest images obtained on the following day after a second dose of the radiopharmaceutical was administered. In 4 patients, a one and four hour post injection study was also done during the rest phase. The results demonstrate significant changes in Tc-99m tetrofosmin distribution between the one hour and four hour post injection images. These differences are present during the stress as well as rest studies.

Aged↗

PubMed1996

Patient-controlled analgesia after spinal fusion for idiopathic scoliosis.

One hundred adolescents undergoing posterior spinal fusion for scoliosis were reviewed to assess the adequacy of postoperative patient-controlled analgesia. There were 94 females and 6 males. The mean settings for morphine dosage were a loading dose of 114.5 micrograms.kg-1, a bolus dose of 24.8 micrograms.kg-1, and a lockout interval of 9.9 minutes. This was used for an average of 75.8 h, with a 52.2% success rate. Adolescents using patient-controlled analgesia showed a great variability in morphine requirements with greater use as they became older. The requirement was not significantly different on the 1st, 2nd and 3rd postoperative days and the total consumption was 52.2 micrograms.kg-1.h-1. Nausea and vomiting occurred in 45% and pruritus in 15%. There were 7 cases of respiratory depression who all recovered promptly and completely. This method is associated with high morphine requirements in adolescents, but can be used safely.

Adolescent↗

PubMed1996

The phytochrome gene family in grasses (Poaceae): a phylogeny and evidence that grasses have a subset of the loci found in dicot angiosperms.

The phytochrome nuclear gene family encodes photoreceptor proteins that mediate developmental responses to red and far red light throughout the life of the plant. From studies of the dicot flowering plant Arabidopsis, the family has been modeled as comprising five loci, PHYA-PHYE. However, it has been shown recently that the Arabidopsis model may not completely represent some flowering plant groups because additional PHY loci related to PHYA and PHYB of Arabidopsis apparently have evolved independently several times in dicots, and monocot flowering plants may lack orthologs of PHYD and PHYE of Arabidopsis. Nonetheless, the phytochrome nucleotide data were informative in a study of organismal evolution because the loci occur as single copy sequences and appear to be evolving independently. We have continued our investigation of the phytochrome gene family in flowering plants by sampling extensively in the grass family. The phytochrome nuclear DNA data were cladistically analyzed to address the following questions: (1) Are the data consistent with a pattern of differential distribution of phytochrome genes among monocots and higher dicots, with homologs of PHYA, B, C, D, and E present in higher dicots, but of just PHYA, B, and C in monocots, and (2) what phylogenetic pattern within Poaceae do they reveal? Results of these analyses, and of Southern blot experiments, are consistent with the observation that the phytochrome gene family in grasses comprises the same subset of loci detected in other monocots. Furthermore, for studies of organismal phylogeny in the grass family, the data are shown to provide significant support for relationships that are just weakly resolved by other data sets.

Blotting, Southern↗

PubMed1995

Accommodation responds to changing contrast of long, middle and short spectral-waveband components of the retinal image.

We simulated the effects of longitudinal (axial) chromatic aberration and defocus on contrast of the long-, middle- and short-wavelength components of the retinal image to determine whether the effects of chromatic aberration are sufficient to drive accommodation. Accommodation was monitored continuously while subjects (12) viewed a 3 c/deg white sine-wave grating (0.92 contrast) in a Badal stimulus system. The contrasts (amplitudes) of the red, green and blue components of the white grating changed independently to simulate a grating oscillating from 1 D behind the retina to 1 D in front of the retina at 0.2 Hz. Subjects responded strongly to the chromatic simulation but poorly to a luminance control. The results support the hypothesis that focus is specified by the contrast of spectral-wavebands of the retinal image, and that conventional color mechanisms, monitoring chromatic contrast at luminance borders (1-8 c/deg), mediate the signals that specify dioptric vergence.

Accommodation, Ocular↗

PubMed1995

Small amounts of chromatic aberration influence dynamic accommodation.

The prevailing view of accommodation is that the eye changes focus to maximize luminance contrast by trial and error. Negative feedback is considered essential in this view because luminance contrast provides no directional information. Fincham proposed an alternate view in which longitudinal (axial) chromatic aberration (LCA) provides a directional stimulus for accommodation. For spatial frequencies above approximately 0.5 cpd contrast of the retinal image is different for long, middle, and short spectral waveband components of the image. We varied the amount of LCA in small steps (0.25 D) to determine how much LCA is needed to enhance or impair the response. An infrared optometer monitored accommodation continuously while subjects viewed a yellow/black square-wave grating (3.5 cpd) in a Badal stimulus system. The yellow/black grating was produced by superimposing red (600 nm) and green (520 nm) gratings, and LCA was increased, decreased, neutralized, and reversed by repositioning the red grating component along the axis of the optical system. Target vergence was modulated sinusoidally (0.2 Hz) over a 1 D range (1.5 to 2.5 D) and gain and phase-lag of the accommodation response were determined by Fourier analysis. Subjects accommodated well as long as a normal amount of LCA was present--0.5 D in the correct direction enhanced accommodative gain, and 0.25 D in the reverse direction markedly inhibited the response. We conclude that the contrast of the retinal image in different spectral wavebands specifies focus of the eye, and provides a powerful directional stimulus for reflex accommodation.

Accommodation, Ocular↗

PubMed1995

Spectral bandwidth and ocular accommodation.

Previous studies have suggested that targets illuminated by monochromatic (narrow-band) light are less effective in stimulating the eye to change its focus than are black-white (broadband) targets. The present study investigates the influence of target spectral bandwidth on the dynamic accommodation response in eight subjects. The fixation target was a 3.5-cycle/deg square-wave grating illuminated by midspectral light of various bandwidths [10, 40, and 80 nm and white (CIE Illuminant B)]. The target was moved sinusoidally toward and away from the eye, and accommodation responses were recorded and Fourier analyzed. Accommodative gain increases, and phase lag decreases, with increasing spectral bandwidth. Thus the eye focuses more accurately on targets of wider spectral bandwidth. The visual system appears to have the ability to analyze polychromatic blur to determine the state of focus of the eye for the purpose of guiding the accommodation response.

Accommodation, Ocular↗

PubMed1994

Canine galanin: sequence, expression and pancreatic effects.

To determine if dog galanin is a potent inhibitor of dog insulin secretion we determined its primary structure from its cloned cDNA, evaluated its expression in celiac ganglia and determined its effect on islet hormone secretion. The predicted amino acid sequence differs from the other known species of galanin by three to six amino acids in the C-terminal half of the molecule. In situ hybridization revealed the presence of dog progalanin mRNA in every neuronal cell body in the dog celiac ganglion. The predicted dog galanin peptide was synthesized and infused i.v. at 0.25, 2.5, 25 or 250 pmol/kg/min. It potently inhibited insulin secretion, less potently inhibited pancreatic somatostatin release and stimulated glucagon secretion, similar to the effects of porcine galanin in the dog. In summary, dog galanin is expressed in the neuronal cell bodies that innervate the pancreas and the sequence of the dog galanin preserves the potent insulin inhibitory part of the galanin molecule. These data support the hypothesis that galanin is a sympathetic neurotransmitter in dog pancreas.

Amino Acid Sequence↗

PubMed1994

The phytochrome apoprotein family in Arabidopsis is encoded by five genes: the sequences and expression of PHYD and PHYE.

Two novel Arabidopsis phytochrome genes, PHYD and PHYE, are described and evidence is presented that, together with the previously described PHYA, PHYB and PHYC genes, the primary structures of the complete phytochrome family of this plant are now known. The PHYD- and PHYE-encoded proteins are of similar size to the other phytochrome apoproteins and show sequence similarity along their entire lengths. Hence, red/far-red light sensing in higher plants is mediated by a diverse but structurally conserved group of soluble photoreceptors. The proteins encoded by the PHYD and PHYE genes are more closely related to phytochrome B than to phytochromes A or C, indicating that the evolution of the PHY gene family in Arabidopsis includes an expansion of a PHYB-related subgroup. The PHYB and PHYD phytochromes show greater than 80% amino acid sequence identity but the phenotypes of phyB null mutants demonstrate that these receptor forms are not functionally redundant. The five PHY mRNAs are, in general, expressed constitutively under varying light conditions, in different plant organs, and over the life cycle of the plant. These observations provide the first description of the structure and expression of a complete phytochrome family in a higher plant.

Amino Acid Sequence↗

PubMed1994

Spatiotemporal transfer function of human accommodation.

We have investigated the spatiotemporal transfer function of human "reflex" accommodation. An accommodative mechanism that is sensitive to an intermediate temporal rate of retinal image contrast change is proposed as the basis of the fine focus control hypothesis. To test the proposed mechanism accommodative responses were monitored by a dynamic infrared optometer while the subject focused on sinusoidal gratings (0.98-10.5 c/deg) which were moving sinusoidally at temporal frequencies in the range of 0.05-0.80 Hz over a 0.50 or 2.00 D peak-to-peak amplitude. The accommodative responses were best at 3 and 5 c/deg at both amplitudes of target motion. This result does not support the proposed mechanism or the fine focus control hypothesis for "reflex" accommodation. Fitting the data with first-order response functions showed little evidence of prediction. In addition, a second experiment found that the profile of the accommodative gain function is not altered by instruction at spatial frequencies above 5 c/deg in this type of dynamic accommodation experiment. The use of sinusoidally moving accommodative blur targets, particularly with careful instruction, seems to discourage voluntary accommodation in investigations of "reflex" control mechanisms of accommodation.

Accommodation, Ocular↗

PubMed1994

Ciprokiren (Ro 44-9375). A renin inhibitor with increasing effects on chronic treatment.

The present study characterizes the new transition-state renin inhibitor ciprokiren (Ro 44-9375) in squirrel monkeys. Arterial blood pressure was monitored by telemetry in freely moving, chronically instrumented conscious animals. In vitro at pH 7.4, ciprokiren inhibited human renin in buffer and human plasma with an IC50 of 0.07 and 0.65 nmol/L, respectively. It was equipotent against primate plasma renin and also inhibited plasma renin from dog and guinea pig in the nanomolar range (IC50, 29 and 65 nmol/L, respectively). After acute oral administration it reduced arterial blood pressure dose dependently in normotensive sodium-depleted and cyclosporin-induced hypertensive squirrel monkeys, starting with the minimal oral dose of 3 micrograms/kg. Daily oral doses of 1 microgram/kg showed a progressive blood pressure decrease, with a maximal response reached after 1 week. The drug could also be applied transdermally with similar hemodynamic effects without any decrease of plasma renin activity or plasma immunoreactive angiotensin II. Thus, ciprokiren is characterized in squirrel monkeys as a renin inhibitor with high in vivo potency that might act mainly in the tissular compartment.

Animals↗

PubMed1993

Chromatic aberration and ocular focus: Fincham revisited.

Longitudinal chromatic aberration of the eye (LCA) produces "color fringes" at edges that specify focus. Fincham [(1951) British Journal of Ophthalmology, 35, 381-393] concluded that these chromatic effects were important for accommodation, but most investigators disagree. We monitored accommodation in 25 subjects while they viewed a sinusoidally moving target (1.5-2.5 D at 0.2 Hz) in a Badal optometer. The target was monochromatic (590 nm with 10 nm bandwidth), or white (3000 K) with LCA normal, neutralized or reversed. Sensitivity to the effects of LCA is profound and widespread. Gain decreases substantially and phase-lag increases when LCA is eliminated, and reversing the aberration severely disrupts accommodation. The ordered arrangement of spectral foci produced by LCA seems to be a fundamental aspect of the stimulus for "reflex" accommodation.

Accommodation, Ocular↗

PubMed1993

Symptomatic spondylolysis: correlation of CT and SPECT with clinical outcome.

Twenty-seven patients with spondylolysis and back pain were considered for spinal fusion. All patients underwent clinical evaluation, multiplanar computed tomography (CT) and single photon emission computed tomography (SPECT). After clinical evaluation 12 patients were not considered suitable for fusion on clinical grounds. SPECT was normal in these patients. Fifteen underwent a trial of lumbar immobilization and nine of those rendered pain free subsequently underwent spinal fusion. The results of clinical examination, lumbar immobilization, imaging and final outcome were compared in these patients. Those patients rendered pain free by surgery all had positive SPECT scans. Those with persistent pain after surgery had negative scans. This small series suggests a positive relationship between SPECT scanning and patient outcome following fusion. These findings need to be confirmed by larger studies with longer periods of follow-up.

Adolescent↗

PubMed1993

Accommodation and chromatic aberration: effect of spatial frequency.

When subjects view an edge in white light, a colour fringe, produced by longitudinal chromatic aberration (LCA) of the eye, is formed at the edge. The colour fringe changes with changes in focus, and serves as a complex colour-coded cue for reflex accommodation. Fincham found that 60% of his subjects failed to accommodate appropriately when the colour fringe was removed with an achromatizing lens or by the use of monochromatic light. Our experiment sought to determine the spatial frequencies at which LCA is most effective. We monitored accommodation in 10 subjects while they viewed sinusoidally moving sine-wave gratings (1-3 D at 0.2 Hz; 1-10.5 c/deg) in a Badal optometer. The targets were 'white' gratings with LCA normal, doubled, neutralized or reversed. Doubling the aberration has minimal effect, removing the aberration reduces gain and increases phase-lag, and reversing the aberration severely disrupts accommodation. Sensitivity to these chromatic cues exists at all spatial frequencies tested, but is most prominent between 3 and 5 c/deg. These results support the view that the system monitors focus by comparing contrast in red-green and perhaps blue-yellow colour-opponent mechanisms.

Accommodation, Ocular↗

PubMed1992

A trial of desmopressin to reduce blood loss in patients undergoing spinal fusion for idiopathic scoliosis.

Desmopressin (DDAVP) has been reported to reduce bleeding in patients undergoing spinal fusion. To evaluate its efficacy in normal patients, 30 healthy young patients (ASA physical status I or II) undergoing spinal fusion for idiopathic scoliosis were randomly allocated to receive either 100 mL of physiologic saline solution (placebo group) or DDAVP (10 micrograms/m2 of body surface area) (DDAVP group) in a prospective, double-blind trial. Intraoperative blood loss was measured by weighing sponges and suction drainage and postoperative bleeding by wound drainage. The amount of blood loss expressed as a percent of the estimated blood volume was similar in both groups during the intraoperative period (67.0% +/- 28.8% [mean +/- SD] placebo group vs 57.4% +/- 26.5% DDAVP group), the postoperative period up to 24 h (32.5% +/- 6.4% placebo group vs 31.1% +/- 10.6% DDAVP group), and both periods (94.3% +/- 29.4% placebo group vs 88.2% +/- 30.7% DDAVP group). With the dose used in our study, we conclude that DDAVP does not reduce surgical bleeding in patients undergoing spinal fusion for idiopathic scoliosis.

Adolescent↗

PubMed1992

The differentiation pathway of HL60 cells is a model system for studying the specific regulation of some myeloid genes.

During granulopoiesis, certain myeloid genes encoding products of azurophilic granules are specifically down-regulated. The myeloid specific enzyme myeloperoxidase belongs to this group of genes. It is responsible for the production of hypochlorous acid, a potent microbicidal agent which is involved in host defense. During induced differentiation of promyelocytic leukemic HL60 cells to granulocyte- or monocyte-like cells, myeloperoxidase RNA is depressed. We studied this depression process in more detail by limiting the exposure to the inducer phorbol 12-myristate 13-acetate to 24 h. During this time period, no significant decrease in cell number and cell viability could be observed. Analysis of these in vitro differentiated HL60 cells on the protein and RNA levels showed that they can be used under defined conditions as a cell system to study the specific depression of myeloid genes. Under the described conditions, both the transcriptional rate of the myeloperoxidase gene as well as the stability of its transcript was reduced.

Actins↗

PubMed1992

What is the utility of the psychophysical 'light scattering factor'?

It has been suggested by Sjöstrand and his colleagues that an index of scatter by the ocular media may be derived from contrast sensitivity measured with and without a glare source. This index was tested under different conditions of stimulus luminance and found not to be constant and thus to not reflect a property of the media.

Adult↗