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Biomedical subjects

M Stewart

Publications and source records attributed to M Stewart.

At least 289 records · Page 16Linked to original sources
PubMed1992

Structural comparison of urease and a GroEL analog from Helicobacter pylori.

Electron microscopy of purified protein preparations indicated that Helicobacter pylori urease consisted of circular particles that are 13 nm in diameter, some of which showed indications of threefold rotational symmetry. A GroEL analog of H. pylori (Hp60K) appeared as a disc-shaped molecule with a diameter similar to that of urease but possessed sevenfold rotational symmetry. In a side-view projection, Hp60K appeared as two or four discs stacked side by side.

Amino Acid Sequence↗
PubMed1992

Pathogenesis of feline leukemia virus T17: contrasting fates of helper, v-myc, and v-tcr proviruses in secondary tumors.

A naturally occurring feline thymic lymphosarcoma (T17) provided the unique observation of a T-cell antigen receptor beta-chain gene (v-tcr) transduced by a retrovirus. The primary tumor contained three classes of feline leukemia virus (FeLV) provirus, which have now been characterized in more detail as (i) v-tcr-containing recombinant proviruses, (ii) v-myc-containing recombinant proviruses, and (iii) apparently full-length helper FeLV proviruses. The two transductions appear to have been independent events, with distinct recombinational junctions and no sequence overlap in the host-derived inserts. The T17 tumor cell line releases large numbers of FeLV particles of low infectivity; all three genomes are encapsidated, but passage of FeLV-T17 on feline fibroblast and lymphoma cells led to selective loss of the recombinant viruses. The oncogenic potential of the T17 virus complex was, therefore, tested by infection of neonatal cats with virus harvested directly from the primary T17 tumor cell line. A single inoculation of FeLV-T17 caused persistent low-grade infection culminating in thymic lymphosarcoma and acute thymic atrophy, which was accelerated by coinfection with the weakly pathogenic FeLV subgroup A (FeLV-A)/Glasgow-1 helper. Molecularly cloned FeLV-tcr virus (T-31) rescued for replication by a weakly pathogenic FeLV-A/Glasgow-1 helper virus was similarly tested in vivo and induced thymic atrophy and thymic lymphosarcomas. Most FeLV-T17-induced tumors manifested either v-myc or an activated c-myc allele and had undergone rearrangement of endogenous T-cell antigen receptor beta-chain genes, supporting the proposition that the oncogenic effects of c-myc linked to the FeLV long terminal repeat are targeted to a specific window in T-cell differentiation. However, neither the FeLV-T17-induced tumors nor the T-31 + FeLV-A-induced tumors contained clonally represented v-tcr sequences. Only one of the FeLV-T17-induced tumors contained detectable v-tcr proviruses, at a low copy number. While v-tcr does not have a readily transmissible oncogenic function, a more restricted role is not excluded, perhaps involving antigenic peptide-major histocompatibility complex recognition by the T-cell receptor complex. Such a function could be obscured by the genetic diversity of the outbred domestic cat host.

Animals↗
PubMed1992

Use of an ammonia electrode for rapid quantification of Helicobacter pylori urease: its use in the endoscopy room and in the assessment of urease inhibition by bismuth subsalicylate.

The use of an ammonia electrode to quantify ammonia liberated by urease from Helicobacter pylori was assessed in an in vitro study. It was found to be highly sensitive (down to 0.7 ppm NH3) and highly reproducible (coefficient of variation 6.0%). Inhibition of urease by bismuth subsalicylate was evaluated as urease testing is often used to assess clearance of H. pylori in patients treated with bismuth. Concentrations of bismuth subsalicylate up to 5 mg/ml had no inhibitory effect but bismuth subsalicylate at 50 mg/ml resulted in 21% inhibition of the urease activity of an ultrasonicated H. pylori suspension. As a preliminary study, the ammonia electrode was assessed in the endoscopy room in comparison with conventional techniques for H. pylori diagnosis. Antral biopsies from 39 patients attending for routine diagnostic endoscopy were subjected to culture, histology, detection of urease activity with a commercially available slide test (CLO) and with the ammonia electrode to detect ammonia liberated from samples placed in urea solution. 21 patients were positive after 1 h with the ammonia electrode, compared to only 17 with the commercially available slide test. 20 were positive on histology and 19 by culture. All samples positive with the ammonia electrode were either positive by culture or by histology. The ammonia electrode offers a quick, sensitive, quantitative and cheap method for the detection and quantification of H. pylori.

Ammonia↗
PubMed1992

Cognitive planning deficit in patients with cerebellar atrophy.

We compared the performance of 12 patients with cerebellar atrophy (CA) and 12 normal controls matched for age and education on the Tower of Hanoi, a nine-problem task that requires cognitive planning. CA patients performed significantly worse than controls on this task despite no difference in planning and between-move pause times. A reanalysis of the data using just the subgroup of patients with pure cerebellar cortical atrophy (CCA) (N = 9) replicated the above results and also showed that CCA patients had significantly increased planning times compared with controls. Neither age, sex, education level, severity of dementia, word fluency, response time, memory, nor visuomotor procedural learning predicted CA or CCA performance. This deficit in cognitive planning suggests a functional link between the cerebellum, basal ganglia, and the frontal lobe concerning specific cognitive processes. However, the exact role of the cerebellum in cognitive planning remains undetermined.

Adult↗
PubMed1992

Structure and macromolecular assembly of two isoforms of the major sperm protein (MSP) from the amoeboid sperm of the nematode, Ascaris suum.

Ascaris sperm are amoeboid cells that crawl by extending pseudopods. Although amoeboid motility is generally mediated through an actin-based cytoskeleton, Ascaris sperm lack this system. Instead, their major sperm protein (MSP) forms an extensive filament system that appears to fulfil this function. Because their motility appears to be essentially the same as that of their actin-rich counterparts, Ascaris sperm offer a simple alternative system for investigation of the molecular mechanism of amoeboid movement. To examine the structure and composition of the cytoskeleton, we stabilized the extremely labile native MSP filaments by detergent lysis of sperm in the presence of either glutaraldehyde or polyethylene glycol (PEG). Biochemical analysis showed that the cytoskeleton contained two isoforms of MSP, designated alpha- and beta-, that we purified and sequenced. Both contain 126 amino acids and have an acetylated N-terminal alanine, but differ at four residues so that alpha-MSP is 142 Da larger and 0.6 pH unit more basic than beta-MSP. Neither isoform shares sequence homology with other cytoskeletal proteins. In ethanol, 2-methyl-2,4-pentanediol (MPD), and other water-miscible alcohols each isoform assembled into filaments 10 nm wide with a characteristic substructure repeating axially at 9 nm. These filaments were indistinguishable from native fibers isolated from detergent-lysed sperm. Pelleting assays indicated a critical concentration for assembly of 0.2 mM for both isoforms in 30% ethanol, but alpha-MSP formed filaments at lower solvent concentration than beta-MSP. When incubated in polyethylene glycol, both isoforms formed thin, needle-shaped crystals that appeared to be constructed from helical fibers, with a 9 nm axial repeat that matched that seen in isolated filaments. These crystals probably contained a parallel array of helical filaments, and may enable both the structure of MSP molecules and their mode of assembly into higher aggregates to be investigated to high resolution.

Actins↗
PubMed1992

Intracerebral penetration of infrared light. Technical note.

Near infrared transmission spectroscopy of the human cerebrum may allow noninvasive evaluation of cerebral hemoglobin saturation in humans. The emerging spectroscopy configuration for this application is a side-by-side source-receiver construct. The ability of this spectroscopy paradigm to detect changes in intracerebral attenuation by selective injection of the infrared tracer indocyanine green into the internal and external carotid arteries during endarterectomy is evaluated in five adult patients. In all five, simultaneous two-channel infrared transmission spectroscopy over the ipsilateral hemisphere documented tracer bolus transit with a signal-to-noise ratio greater than 100:1. In addition, the two channels could be configured to achieve depth resolution of the collected spectra.

Brain↗
PubMed1992

A case of Woringer-Kolopp disease with Ki-1 (CD30) + cytotoxic/suppressor cells.

BACKGROUND: Woringer-Kolopp (W-K) disease is a rare, localized, histologically malignant, but clinically indolent lymphoproliferative disorder. Most authors have regarded W-K disease as a variant of mycosis fungoides. However, a recent case suggests that W-K disease may represent a spectrum of lymphoproliferative disorders that may not be related to mycosis fungoides. OBSERVATIONS: A patient with a 40-year history of localized cutaneous eruption characterized by markedly atypical epidermotropic lymphocytes was seen at Stanford (Calif) University Hospital. The lymphocytes were predominantly CD30+ cytotoxic/suppressor T cells, an immunophenotype not previously described in W-K disease. Genotype analysis revealed a clonal rearrangement. CONCLUSIONS: The findings in our patient, along with a review of all cases previously reported in the literature, suggest that W-K disease may be an entity with a uniform clinical and histologic presentation, but one with marked immunophenotypic heterogeneity of the malignant-appearing atypical cells. Some cases showed immunophenotypic similarities to mycosis fungoides. However, in almost half of the reviewed cases, including the one presented here, the immunophenotypic differences exceeded the similarities.

Aged↗
PubMed1992

Efficacy of CAPD as the primary treatment for end-stage renal failure in children.

In the 6 years before this paper, all children presenting with end-stage renal failure (ESRF) in Northern Ireland were electively commenced on continuous ambulatory peritoneal dialysis (CAPD). In that period, 22 patients were treated, 16 received renal transplants and 6 remained on CAPD. Active treatment was withdrawn in 1 child due to obliterative peritonitis. There were no deaths. One incident of peritonitis was documented per 11.6 patient treatment months. Recurring peritonitis lead to catheter replacement in 3 patients. Other problems encountered were catheter exit site infections, hernia formation and in one instance, hydrothorax. Peritonitis was more common in children under 2 years of age as was undernutrition, growth retardation and developmental delay. Home CAPD can be recommended as a viable first option treatment for childhood ESRF where suitable haemodialysis facilities are not easily accessible.

Adolescent↗
PubMed1992

[Consequences of AIDS in the lives of hemophiliacs and their caregiving families in Quebec: stress, response to stress and social support].

The following article focuses on the Québec portion of a national survey on the care needed by hemophiliacs with AIDS or having contracted the HIV virus. The survey was based on an approach that considers social support as a means to face stress. It also examined the needs of dispensers of care and relatives (whether mourning or not) of these persons. Participants revealed having experienced more stress because of an absence of support or simply negative support, than because of the physical deterioration caused by the disease. In addition, the question of confidentiality was often raised. In general, participants said they were satisfied with the support they had received, especially on the part of members of their family.

Acquired Immunodeficiency Syndrome↗
PubMed1991

Hippocampal theta activity in monkeys.

The hippocampal theta rhythm has been extensively studied in many subprimate mammals. Considering the technical difficulties involved in recording from freely moving animals during voluntary motion and REM sleep, it was thought that urethane anesthesia might be appropriate for initial studies of the primate hippocampal EEG. Three of three macaques and one of two squirrel monkeys showed clear rhythmic hippocampal EEG activity. One very old squirrel monkey (a 16-year-old female) showed no theta activity in the hippocampal EEG. Similarities of the monkey theta activity with theta rhythm of urethane-anesthetized rats included: (1) a high coherence between recordings from electrodes separated by several millimeters within the hippocampal formation; (2) sensitivity of the theta activity to muscarinic drugs; and (3) its correlation with spontaneous movements during light anesthesia. Important differences were: (1) the frequency of the monkey theta activity was 7-9 Hz compared to the 4-5 Hz found in rats; (2) theta activity was not detected in the distal apical dendritic regions of CA1 or dentate in the monkey; (3) considerable amounts of low-frequency EEG co-existed with the monkey theta activity; and (4) the durations of bouts of theta activity in monkeys were much shorter than in rats. We conclude that primates generate hippocampal theta activity homologous, but not identical, to that of rats.

Animals↗
PubMed1991

A new inexpensive pump for vitreoretinal surgery.

An inexpensive and reliable fluid-gas exchange system has been developed for vitreous surgery. The system relies on a fish-tank air pump and was compared with the Grieshaber Air System in several laboratory and operating room situations. No significant differences were found between the two systems. Details of the Davis Ocular Air Pump are provided along with a cost analysis.

Drainage↗
PubMed1991

Nasalance measurements in hearing-impaired children.

Nasalance measurements were recorded utilizing a Nasometer 6200 instrument and speech samples were obtained from 18 hearing-impaired children with ages ranging from 3.8 to 11.7 years. Three conditions were used: speech without amplification (unaided), speech with amplification (aided), and speech with FM amplification. Percent nasalance in each speech condition was compared according to the degree of hearing loss and the age of the subject. No significant difference was found when (1) comparisons were made between younger and older groups in all three conditions and when (2) comparisons were made according to the severity of hearing loss across the three conditions.

Animals↗
PubMed1991

Measurement of regional cerebrovascular haemoglobin oxygen saturation in cats using optical spectroscopy.

We describe the use of optical spectroscopy in the near infra-red light range to non-invasively measure regional cerebral haemoglobin oxygen saturation (rSHbO2) in cats during progressive cerebral hypoxia. This technique differs from spectroscopic techniques previously described in that the concentration ratio--percentage haemoglobin: oxygen saturation--is quantified. This saturation is the weighted summation of saturation in the cerebrovascular system: arterial, venous, and capillary beds. In a cat model of progressive cerebral hypoxia, a positive linear correlation between this regional measurement of cerebral saturation and actual saturation, calculated from cerebral arterial and mixed venous blood, was noted (n = 20, r = 0.88, p less than 0.01). The spectroscopic measurement rSHbO2 is also used to index cerebral oxygen extraction. During hypoxia spectroscopic indexed oxygen extraction (iOE) and cerebral arterial-venous difference in oxygen content were simultaneously measured. A least-squares positive linear correlation between these two parameters was noted [AVDO2 = iOE (0.05) + 4.4] (n = 40, r = 0.6, s = 1.2). Objective measurement of 'regional cerebrovascular haemoglobin saturation' and an index of cerebral oxygen extraction are possible using optical spectroscopy.

Algorithms↗