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S Davidson

Publications and source records attributed to S Davidson.

At least 145 records · Page 8Linked to original sources
PubMed1986

Does stem cell self renewal and progenitor cell commitment operate through an effector-memory cell mechanism?

We propose a model for stem cell self renewal and transition into commitment towards a variety of cell lineages. In this model the production of both "effector cells" (as represented by the mature cells in the different cell lineages) and of progenitor "memory" lymphocytes, takes place concomitantly. The experimental evidence supporting this model is as follows: Pure lymphocytic suspensions (PLS) are established and persist in culture when nude mouse-spleen and lymph-node cells are maintained on X-irradiated fibroblast monolayers in the presence of the S-phase cytotoxic agent cytosine arabinoside (Ara-C). From these PLS the following colony types can be initiated by the corresponding inducing (stimulating) factors (CSF): histiocytes (tissue macrophages) - CSF-1; granulocytes-macrophages (GM) - CSF-GM; mast cells - MMSF; granular-NK mucus secreting cells - IL-2; and multilineage colonies - IL-3. Mitotically active blast cells (formed by transformation of lymphocytes), condense into motile small cells when the stimulatory factor is removed. These "memory" lymphocytes are committed as they carry the receptors for the specific CSF; they respond by retransformation into blast cells. A dramatic increase in mast-cell colony forming cells is found in bone marrow, spleen and lymph-nodes of mice infected with Schistosoma mansoni. By maintaining PLS with both Ara-C and each of the CSFs and then titrating the incidence of CFC in the residual PLS, we find that each one of the CSFs acts on an independent set of cells in the PLS to produce the corresponding colony type. Finally, the concept suggests that the various blast cells carrying the receptors, undergo condensation into memory lymphocytes when dissociated from the environment prevailed by the corresponding CSF. In this way pluripotential blast-cells condense into motile lymphocytes which are committed to pluripotentiality.

Animals↗
PubMed1986

Synergy between phorbol esters, 1-oleyl-2-acetylglycerol, urushiol, and calcium ionophore in eliciting aggregation of marine sponge cells.

Aggregation of marine sponge cells (Microciona prolifera) resembles stimulus-response coupling of higher organisms in which activation of protein kinase C and movements of intracellular Ca provide twin signals. We now report that activators of protein kinase C (phorbol esters) and ionomycin act synergistically to aggregate sponge cells. Surprisingly--since extracellular Ca is required for integrity of the species-specific aggregation factor--synergistic aggregation proceeded in the complete absence of added extracellular Ca (2.5-20 mM EDTA). The order of activity of phorbol esters and related compounds was that of their effect on protein kinase C (phorbol myristate acetate, phorbol dibutyrate greater than phorbol diacetate much greater than phorbol, 4 alpha-phorbol). 1-Oleyl, 2-acetylglycerol a synthetic activator of protein kinase C, also showed synergy with ionomycin. Phorbol esters and 1-oleyl, 2-acetylglycerol acted in synergy with ionomycin to liberate membrane Ca as detected by decreased fluorescence of chlortetracycline in prelabeled cells. Moreover, urushiol, the toxic principle of poison ivy, but not pentadecanylcatechol, its inert analogue, showed synergy with ionomycin. Synergistic aggregation was inhibited by calmidazolium (10 microM), piroxicam (20-100 microM), and pertussis toxin (20 micrograms/ml). The data not only confirm that marine sponge cell aggregation follows the general sequence of stimulus-response coupling in the cells of higher organisms but also support, in this most ancient of multicellular creatures, the hypothesis that mobilization of intracellular Ca and activation of protein kinase C provide the twin signals for cell activation in the absence of added extracellular Ca.

Animals↗
PubMed1986

Family therapy--where are we, and where are we going?

There has been considerable growth and development in the field of family assessment and therapy over the past thirty years. This management approach provides a useful tool in the assessment, management and treatment of children, adolescents and families with various psychiatric disorders and mental health problems. This paper provides a broad overview and a critical evaluation of the present state of the art, paying particular attention to the integration and present status of clinical practice, theoretical models, research, teaching and training programs. Based on the emerging trends, directions for the future are suggested including an exploration of the integration of different therapeutic modalities. Finally, the practical problems associated with the teaching of these approaches in General Psychiatry Training Programs are addressed.

Education, Medical, Graduate↗
PubMed1985

Breast feeding as prophylaxis for atopic eczema: a controlled study of 368 cases.

The present study was undertaken in an attempt to draw data whether breast-feeding is beneficial in prevention of atopic eczema. Three-hundred and sixty-eight babies given different feeding modalities were examined for the presence of atopic eczema at the age of three and six months. Seven percent of breast-fed infants developed eczema compared to 10% of formulae-fed and 6% of mixed breast and formulae-fed infants. No difference in the severity of atopic eczema was recorded in the three study groups. Our experience demonstrates the absence of a protective effect of breast-feeding against the development and severity of atopic eczema.

Breast Feeding↗
PubMed1984

Adherence of Candida albicans to buccal epithelial cells of neonates.

Adherence of Candida albicans to buccal epithelial cells of newborn infants was studied by the visual adherence method. Forty-five samples of buccal epithelial cells were obtained from 21 normal newborns at different times following delivery. In group 1 (mean age 7.5 hr) 367 +/- 51 yeast cells adhered to 100 epithelial cells. In group 2 (mean age 2.3 days) 384 +/- 36 yeast cells adhered to 100 cells. In group 3 (mean age 6.2 days) 488 +/- 57 yeast cells adhered to 100 cells. Differences among the groups were not significant (p greater than 0.1). A significant difference was found in the percentage of epithelial cells binding 10 yeast cells between group 1 (7.25 +/- 0.9) and group 3 (14.9 +/- 2.5), and group 2 (8.0 +/- 2.0) and group 3 (p less than or equal to 0.025). In 12 infants studied twice at mean age of 2.1 and 6.3 days (included in groups 2 and 3) a significant increase was found in the number of adherent yeasts binding to 100 epithelial cells (330 +/- 87 and 485 +/- 52 respectively) (p less than or equal to 0.03), and in the percentage of epithelial cells binding greater than or equal to 10 yeast cells (5.0 +/- 3.0 and 14.7 +/- 3.5 respectively, p less than or equal to 0.004) for each infant. The age-related increased affinity of buccal epithelial cells to Candida albicans may have relevance in the development of oral thrush.

Animals↗
PubMed1984

Infusion cholecystography in the early diagnosis of acute gallbladder disease.

The value of infusion cholecystography 99mTc HIDA cholescintigraphy and ultrasonography was compared in 51 patients presenting with a clinical diagnosis of acute cholecystitis. Of the 35 patients with proven gallbladder disease, the presence of gallstones was correctly predicted in 31 (88 per cent) by infusion cholecystography, 32 (90 per cent) by 99mTc HIDA cholescintigraphy and 27 (77 per cent) by ultrasonography. There were no false positive investigations. Infusion cholecystography may be of particular interest to surgeons with no ready access to isotope scanning techniques.

Acute Disease↗
PubMed1984

Effects of dichloroacetate and glyoxylate on low density lipoprotein uptake and on growth of cultured fibroblasts.

The effects of dichloroacetate, a known hypocholesterolemic agent, were studied in cultured growing and confluent human fibroblast cells. Microscopic examination showed no visible adverse effects of dichloroacetate on confluent cells during exposure to concentrations as high as 5 mM for 96 hr. Higher concentrations resulted in cell death after varying periods of incubation. There were no viable cells after 24 hr of exposure to 100 mM dichloroacetate. In contrast, much lower concentrations proved lethal to growing cells; cell growth, as determined by cell numbers at specified times after splitting, was suppressed by 1 mM dichloroacetate and 5 mM concentrations resulted in cell death. Similar effects were noted with glyoxylate. The hypocholesterolemic effect of dichloroacetate is probably not due to any effect on the low density lipoprotein pathway, since concentrations of up to 1 mM dichloroacetate did not affect the cellular binding and uptake of 125I-labeled low density lipoprotein. It is concluded that growing and rapidly metabolizing cells are much more sensitive to the toxic effects of dichloroacetate and glyoxylate than confluent cells.

Acetates↗