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Biomedical subjects

H Morgan

Publications and source records attributed to H Morgan.

At least 37 records · Page 2Linked to original sources
PubMed2000

Measurements of the dielectric properties of peripheral blood mononuclear cells and trophoblast cells using AC electrokinetic techniques.

The separation of trophoblast cells from the maternal circulation could provide a valuable diagnostic tool for prenatal diagnosis of genetic abnormalities. This has been attempted using antibody methods, but due to non-specificity of the antibodies, maternal cell contamination remains a problem. We have investigated the potential of dielectrophoretic separation methods as a means of isolating trophoblast cells from mixed peripheral blood mononuclear cells. To determine the potential of this method the dielectric properties of trophoblast cells and mixed peripheral blood mononuclear cells were measured using dielectrophoretic crossover and single cell electrorotation methods. Both dielectrophoretic crossover data and electrorotation data gave an average specific membrane capacitance of the peripheral blood mononuclear cells of 11.5 mF m(-2). Trophoblast cells prepared using three different methods had a higher average specific membrane capacitance in the range 13-18 mF m(-2). The differences in capacitance between the cell types could be exploited as the basis of an AC electrokinetic-based system for the separation of trophoblast cells from peripheral blood mononuclear cells.

Cell Membrane↗
PubMed2000

Preparation and characterisation of monoclinic hydroxyapatite and its precipitated carbonate apatite intermediate.

Five 100 g batches of a carbonate apatite (the intermediate) were produced by heating an aqueous slurry of CaCO3 and CaHPO4 with an overall Ca/P mole ratio of 5/3 with vigorous stirring. Each intermediate produced by boiling off water was heated in vacuum at 1100 degrees C to remove carbonate, then steamed at 900 degrees C to ensure complete hydroxylation. Comparison of calculated and observed X-ray diffraction patterns showed final products containing 50-100 wt% monoclinic hydroxyapatite (remainder hexagonal). Rietveld refinements in P6(3)/m gave structures similar to several hydroxyapatite standards, including NIST SRM 2910, although there was no evidence from X-ray diffraction that the latter was in the monoclinic form. Refinements from standards and final products were slightly different from published single crystal data for Holly Springs hydroxyapatite. This is attributed to known impurities in mineral hydroxyapatite and indicates that parameters from the Rietveld refinements are closer to the true values for pure hydroxyapatite. Rietveld refinements for intermediates showed small, but significant differences from the final product, the largest being in O1x, O2x and O(H)z. All P-O bond lengths were shorter than in the final product, resulting in a 3.2% lower PO4 tetrahedron volume. The occupancies of P and Ca(2) were reduced. These differences are attributed to partial replacement of PO4(3) by CO3(2-) ions.

Apatites↗
PubMed2000

Evaluation of BioStar FLU OIA assay for rapid detection of influenza A and B viruses in respiratory specimens.

BACKGROUND: Demand for the rapid diagnosis of influenza infections has increased with the advent of the availability of neuraminidase antiviral therapy for influenza A and B. Several rapid assays that detect both influenza A and B are now available. OBJECTIVES: In this study we compared the performance of the BioStar FLU OIA assay to Bartels Viral Respiratory Screening and Identification Kit (Bartels Inc., Issaquah, WA), and cell culture. STUDY DESIGN: A total of 145 patient specimens for influenza virus detection submitted in either viral transport medium or in sterile containers were evaluated by the three methods. Specimen types included nasal washings, nasal swabs, sputum, throat swabs, and bronchial alveolar lavage (BAL) fluids. RESULTS: Fifty six positive specimens were identified based on culture and/or DFA. Of these, 30 specimens were positive by the OIA assay for an overall sensitivity of 54%. The OIA assay detected 48% (n = 21) of the 44 culture positive specimens and 81% (n = 29) of the 36 DFA positive specimens. Eighty six of the 89 culture/DFA negative samples were negative by the OIA assay (97% specificity). Analysis of the OIA assay sensitivity from samples submitted in M4 transport medium or in sterile containers revealed that M4 transport medium does not reduce the sensitivity of the OIA assay. Fifteen of the 27 positive samples submitted in M4 transport medium were positive by the OIA assay (56% sensitivity) compared to 15 of 29 positive samples transported in sterile containers (52% sensitivity). Twelve specimens were either culture and/or DFA positive for viruses other than influenza, but negative by the OIA assay, suggesting that there was no cross reactivity of the OIA assay with the other virus types recovered in this study. CONCLUSIONS: The overall excellent specificity of the BioStar FLU OIA allows for treatment of positive patients for influenza, however, a negative result should be confirmed by DFA and culture.

Animals↗
PubMed2000

The transactivation-competent carboxyl-terminal domain of AF-9 is expressed within a sexually dimorphic transcript in rat pituitary.

We have investigated the biological role of the cellular counterpart of the leukemogenic AF-9 gene by cloning the rat AF-9 (rAF-9) cDNA and defining the regulation of an anterior pituitary-specific rAF-9 transcript that is expressed in a sexually dimorphic manner. Expression of this transcript is down-regulated after puberty in females and can be subsequently up-regulated in adults by ovariectomy. Hormone replacement studies have provided direct evidence that rAF-9 mRNA expression is suppressed by estrogen. Mapping the 1.9 kb anterior pituitary transcript has shown that it corresponds in size to the rAF-9 cDNA clone, which contains an open reading frame (ORF) that is truncated compared with the human AF-9 ORF, but encodes a previously defined transcriptional activation domain. Thus, the cellular AF-9 gene is alternatively expressed in a manner that reflects the presence of translocated, functionally active (oncogenic) AF-9 sequences in leukemias. Using a novel antisera raised against a rAF-9 peptide, we have also demonstrated tissue- and sex-specific expression of a nuclear 41 kDa anterior pituitary protein and have localized this protein to a major population of growth hormone synthesizing cells. By localizing the expression and defining the physiological regulation of rAF-9, our studies have provided novel insights into the AF-9 gene that will facilitate an understanding of both oncogenic and endocrine roles.

Alternative Splicing↗
PubMed2000

Fluid flow induced by nonuniform ac electric fields in electrolytes on microelectrodes. I. Experimental measurements

Under the influence of an ac electric field, electrolytes on planar microelectrodes exhibit fluid flow. The nonuniform electric field generated by the electrodes interacts with the suspending fluid through a number of mechanisms, giving rise to body forces and fluid flow. This paper presents the detailed experimental measurements of the velocity of fluid flow on microelectrodes at frequencies below the charge relaxation frequency of the electrolyte. The velocity of latex tracer particles was measured as a function of applied signal frequency and potential, electrolyte conductivity, and position on the electrode surface. The data are discussed in terms of a linear model of ac electroosmosis: the interaction of the nonuniform ac field and the induced electrical double layer.

Journal Article↗
PubMed2000

Fluid flow induced by nonuniform ac electric fields in electrolytes on microelectrodes. II. A linear double-layer analysis

Frequency-dependent fluid flow in electrolytes on microelectrodes subjected to ac voltages has recently been reported. The fluid flow is predominant at frequencies of the order of the relaxation frequency of the electrode-electrolyte system. The mechanism responsible for this motion has been termed ac electro-osmosis: a continuous flow driven by the interaction of the oscillating electric field and the charge at the diffuse double layer on the electrodes. This paper develops the basis of a theoretical approach to this problem using a linear double layer analysis. The theoretical results are compared with the experiments, and a good correlation is found.

Journal Article↗
PubMed1999

The Dielectrophoretic Behavior of Submicron Latex Spheres: Influence of Surface Conductance.

An analysis of the dielectrophoretic crossover frequency as a function of medium conductivity has been made for submicron spheres with different surface functionalities. It is shown that the AC electrokinetic behavior of the particles can be explained by modeling the surface conductivity of the particle as the sum of two surface conductance components: one due to charge motion behind the slip plane (the Stern layer) and the other due to charge motion in front of the slip plane. Copyright 1999 Academic Press.

Journal Article↗
PubMed1999

AC Electric-Field-Induced Fluid Flow in Microelectrodes.

During the AC electrokinetic manipulation of particles in suspension on microelectrode structures, strong frequency-dependent fluid flow is observed. The fluid movement is predominant at frequencies below the reciprocal charge relaxation time, with a reproducible pattern occurring close to and across the electrode surface. This paper reports measurements of the fluid velocity as a function of frequency and position across the electrode. Evidence is presented indicating that the flow occurs due to electroosmotic stress arising from the interaction of the electric field and the electrical double layer on the electrodes. The electrode polarization plays a significant role in controlling the frequency dependence of the flow. Copyright 1999 Academic Press.

Journal Article↗
PubMed1999

Cell reactions to dielectrophoretic manipulation.

The phenomenon of dielectrophoretic particle manipulation holds promise for many biotechnology applications, including cell sorting. In our system cell manipulation normally involves transient exposure (15 minutes) to radio-frequency AC electric fields generated using planar microelectrodes. The present study was designed to investigate the range of acute effects of dielectrophoretic manipulation on the normal physiology of isolated cells. Cells were suspended in isoosmotic Mannitol and exposed to a 5 MHz, 21 V (peak to peak) electric field with 100 micrometer gap electrodes. Cells were assigned to three experimental groups; non-exposed controls, exposed cells processed immediately after cessation of the field, and exposed cells processed after a time delay. SEM observations of spread cells cultured on the devices showed no apparent acute effects of field exposure on cell morphology. Cell-doubling rates in exposed cells subsequent to field-exposure or transient incubation in mannitol were no different from control cells. An MTT 'mitochondrial stress' assay indicated no alteration in the rate of oxidative respiration in exposed cells 0.5 hour after exposure to the field. Western blot analysis indicated upregulation of fos protein in cells 0.5 hour after field-exposure, which was confirmed using densitometry. Reverse transcription of cellular mRNA followed by PCR amplification, polyacrylamide gel electrophoresis and autoradiography of cDNA banding revealed differential gene expression between controls and exposed cells processed immediately after cessation of the field. Differential gene expression persisted in exposed cells at least 0.5 hours after removal from the field. Observations indicated that temperature fluctuation in the mannitol solution was minimal, suggesting that upregulated mRNA may not have been related to thermally-induced heat shock protein. The present study has indicated that exposure to AC fields during dielectrophoretic cell manipulation is associated with upregulation of the intermediate-early gene cfos and also transcription of other as yet unidentified genes. These transcriptional events were not manifest as gross changes in cell morphology or cell-cycle dynamics.

Animals↗
PubMed1999

Separation of submicron bioparticles by dielectrophoresis.

Submicron particles such as latex spheres and viruses can be manipulated and characterized using dielectrophoresis. By the use of appropriate microelectrode arrays, particles can be trapped or moved between regions of high or low electric fields. The magnitude and direction of the dielectrophoretic force on the particle depends on its dielectric properties, so that a heterogeneous mixture of particles can be separated to produce a more homogeneous population. In this paper the controlled separation of submicron bioparticles is demonstrated. With electrode arrays fabricated using direct write electron beam lithography, it is shown that different types of submicron latex spheres can be spatially separated. The separation occurs as a result of differences in magnitude and/or direction of the dielectrophoretic force on different populations of particles. These differences arise mainly because the surface properties of submicron particles dominate their dielectrophoretic behavior. It is also demonstrated that tobacco mosaic virus and herpes simplex virus can be manipulated and spatially separated in a microelectrode array.

Electric Conductivity↗
PubMed1999

Electrorotation studies of baby hamster kidney fibroblasts infected with herpes simplex virus type 1.

The dielectric properties of baby hamster kidney fibroblast (BHK(C-13)) cells have been measured using electrorotation before and after infection with herpes simplex virus type 1 (HSV-1). The dielectric properties and morphology of the cells were investigated as a function of time after infection. The mean specific capacitance of the uninfected cells was 2.0 microF/cm2, reducing to a value of 1. 5 microF/cm2 at 12 h after infection. This change was interpreted as arising from changes in the cell membrane morphology coupled with alterations in the composition of the cell membrane as infection progressed. The measured changes in the cell capacitance were correlated with alterations in cellular morphology determined from scanning electron microscope (SEM) images. Between 9 and 12 h after infection the internal permittivity of the cell exhibited a rapid change, reducing in value from 75epsilono to 58epsilono, which can be correlated with the generation of large numbers of Golgi-derived membrane vesicles and enveloped viral capsids. The data are discussed in relation to the known life cycle of HSV-1 and indicate that electrorotation can be used to observe dynamic changes in both the dielectric and morphological properties of virus-infected cells. Calculations of the dielectrophoretic spectrum of uninfected and infected cells have been performed, and the results show that cells in the two states could be separated using appropriate frequencies and electrode arrays.

Animals↗
PubMed1999

Does reducing safety behaviours improve treatment response in patients with social phobia?

OBJECTIVE: This study assessed the efficacy of instructions to drop 'safety behaviours' during exposure tasks in a cognitive-behaviour therapy (CBT) group treatment program for social phobia. METHOD: Fourteen subjects with social phobia received a standardised CBT treatment program and were compared to 16 subjects with social phobia who were given additional instructions to drop safety behaviours. RESULTS: Repeated measures of ANOVA between groups on a specific social phobia measure (SPAI) demonstrated significant benefit when instructions to drop safety behaviours were added to the treatment program. CONCLUSIONS: The addition of instruction to drop safety behaviours in exposure tasks in the course of CBT treatment for social phobia may be useful. This result supports the cognitive model of social phobia developed by Clark and Wells (1995), which postulates that anxiety and negative beliefs about social situations are in part maintained by engaging in safety behaviours. Further replication with larger samples is required and warranted on the basis of the present study.

Adult↗
PubMed1999

Effect of environmental tobacco smoke on peak flow variability.

This study was undertaken to determine whether exposure to various indoor pollutants is associated with a higher prevalence of respiratory symptoms, a diagnosis of asthma, or more variable peak flow rates. Four hundred and twenty-six children aged 8-11 years in four junior schools at three locations recorded respiratory symptoms and diagnosis of asthma using the ISAAC questionnaire. Daily peak flow measurements were taken during two six-week periods (winter and summer). Symptoms in children with and without asthma were not related to gas fires, cookers, smokers, or pets in the home. However, the variability of lung function, expressed as the coefficient of variation, in all children was increased with a household smoker. Environmental tobacco smoke increases airways variability in children with and without asthma. Its effects were not apparent from a questionnaire completed by parents, and the coefficient of variation of serially measured peak flows was a more sensitive indicator of lung function.

Air Pollution, Indoor↗
PubMed1999

Prospective study of outcome in antenatally diagnosed renal pelvis dilatation.

AIMS: To ascertain the outcome associated with antenatal renal pelvis dilatation; to recommend guidelines for postnatal investigation and determine an upper limit of normal for the anterioposterior dimensions of the fetal renal pelvis. METHODS: Infants whose antenatal ultrasound scan showed a fetal renal pelvis of 5 mm or greater were investigated using postnatal renal tract ultrasound and a micturating cystogram. Isotope studies were also performed, where appropriate. RESULTS: Vesicoureteric reflux (VUR), the most common diagnosis, was evident in 23/104 (22%). In 14 infants with VUR the postnatal ultrasound scan was normal. There was no evidence of renal scarring or dysplasia in any of the refluxing kidneys. Other diagnoses were pelviureteric junction obstruction, renal dysplasia, and idiopathic dilatation. Antenatal counselling and parental information facilitated postnatal assessment. CONCLUSIONS: Infants with antenatal renal pelvis measurements of 5 mm or greater should be investigated postnatally, as a significant percentage will have VUR. A normal postnatal ultrasound scan does not preclude the presence of VUR.

Female↗
PubMed1998

Manipulation of herpes simplex virus type 1 by dielectrophoresis.

The frequency-dependent dielectrophoretic behaviour of an enveloped mammalian virus, herpes simplex virus type 1 is described. It is demonstrated that over the range 10 kHz-20 MHz, these viral particles, when suspended in an aqueous medium of conductivity 5 mS m(-1), can be manipulated by both positive and negative dielectrophoresis using microfabricated electrode arrays. The observed transition from positive to negative dielectrophoresis at frequencies around 4.5 MHz is in qualitative agreement with a simple model of the virus as a conducting particle surrounded by an insulating membrane.

Biophysics↗
PubMed1998

Cells for the study of acidic dissolution in packed apatite powders as model systems for dental caries.

A number of different designs of cells have been developed for the study of dissolution processes in packed apatite powders. Basic design requirements were that no deleterious processes, such as high temperature sintering or binding agents, were involved, and that there was maximum opportunity for experimental study. One design used alternating filter paper discs and apatite layers (typically 42 mg). At the end of an experiment, the cell could be disassembled and infrared spectra and X-ray powder diffraction patterns made of individual layers. Cells without filter paper discs were also made, but terminal sampling at well-defined depths was more difficult or impossible. The cells were constructed from poly(methylmethacrylate) so the course of dissolution could be monitored by radiography. Subsurface loss of apatite was almost always seen after from 2 weeks to 8 months exposure to buffer solutions at pH 3.0-5.5. The greatest loss of apatite was typically 0.4-2 mm below the surface, which is at a larger distance than usually seen for dental enamel. This may be attributable to the low packing density (typically 35-60 vol%) found in the present systems compared with enamel.

Acids↗
PubMed1998

Disc herniation at T1-2. Report of four cases and literature review.

In preparing this paper, the authors reviewed their experiences with four cases of T1-2 disc herniation as well as the medical literature on the subject. Intervertebral thoracic disc herniations are uncommon and high thoracic disc herniations are rare. In the upper third of the thoracic spine, T1-2 is the most common level for disc ruptures. Four cases of disc herniation at T1-2 that caused T-1 radiculopathy are reported in this paper. In reviewing the literature on thoracic disc herniation, the authors found 27 cases at the T1-2 level, 23 of which were lateral disc herniations that produced radiculopathy and four of which were central disc herniations that caused myelopathy. The clinical signs and symptoms of T-1 radiculopathy are similar to those of C-8 radiculopathy; however, distinguishing features can frequently be found on neurological examination. The T-1 radiculopathy usually involves weakness of the intrinsic muscles of the hand. The motor deficit of C-8 radiculopathy involves the intrinsic muscles of the hand and most of the flexors and extensors of the fingers and wrist. The T-1 radiculopathy may produce Horner's syndrome (oculosympathetic paralysis) and diminished sensation in the axilla, which are not found with C-8 radiculopathy. In clinical presentation as well as in treatment, the lateral T1-2 disc herniation resembles a cervical disc herniation, whereas the central T1-2 disc herniation displays the usual appearance of a thoracic disc herniation.

Aged↗