Search PubMed⌕ Search

Biomedical subjects

D W Williams

Publications and source records attributed to D W Williams.

At least 91 records · Page 5Linked to original sources
PubMed1989

Direction perception in complex dynamic displays: the integration of direction information.

We created random-dot cinematograms in which each dot's successive movements were independently drawn from a Gaussian distribution of directions of some characteristic bandwidth. Such a display, comprising many different, spatially intermingled local motion vectors, can produce a percept of global coherent motion in a single direction. Using pairs of cinematograms, direction discrimination of global motion was measured under various conditions of direction distribution bandwidth, exposure duration, and constancy of each dot's path. A line-element model gave an excellent account of the results: (i) over a considerable range, discrimination was unaffected by the cinematogram's direction distribution bandwidth; (ii) only for the briefest presentations did changes in duration have an effect; (iii) so long as the overall directional content of the cinematogram remained unchanged, the constancy or randomness of individual dots' paths did not affect discrimination. Finally, the line-element model continued to give a good account of the results when we made additional measurements with uniform rather than Gaussian distributions of directions.

Discrimination, Psychological↗
PubMed1989

Evidence for autocrine production of IGF-1 in human thyroid adenomas.

We have recently shown that epithelial cells from a high proportion of benign human thyroid tumours (follicular adenomas) have escaped from the requirement of the normal cell for an exogenous source of insulin-like growth factor 1 (IGF-1), suggesting either autocrine production or intracellular generation of an IGF-1-induced growth signal. We show here that conditioned medium from these adenoma cells can confer IGF-1 independence on normal thyroid epithelial cells and that this activity is abolished by immunoadsorption with an anti-IGF-1 antibody. In addition, tumour but not normal cells contain immunoreactive IGF-1. Our data provide the first evidence for autocrine production of IGF-1 (or a related factor) in a benign epithelial tumour and suggest that this may be a key early step in thyroid tumorigenesis.

Adenoma↗
PubMed1988

Orthodontics.

Explore the source record for details and available documents.

Education, Dental, Graduate↗
PubMed1988

Loss of dependence on IGF-1 for proliferation of human thyroid adenoma cells.

The proliferative responses to IGF-1 (Somatomedin C) and TSH, as assessed by 3H-thymidine (3H-TdR) incorporation and autoradiographic labelling index (LI), of suspension and monolayer cultures of human thyroid follicular epithelium derived from both normal and adenoma tissue have been compared. In cultures of normal follicles, whilst neither TSH nor IGF-1 alone produced any effect, a combination of TSH (0.1 mU ml-1) together with IGF-1 (10 ng ml-1) induced a highly significant proliferative response as shown by a peak of 3HTdR incorporation and LI, 4-5 days after growth factor addition. The TSH concentration-effect curve was bell-shaped, a higher concentration of TSH (10 mU ml-1) resulting in a reduced response. In cultures derived from adenoma tissue, however, TSH alone at 0.1 mU ml-1 was sufficient to permit a highly significant proliferative response (equivalent to, or greater than the normal) in 4 out of 5 adenomas examined; again a higher concentration of TSH (10 mU ml-1) resulted in a diminished response. Addition of IGF-1 (10 ng ml-1) produced no significant change in the response to TSH (0.1 mU ml-1) in 3 of these 4 adenomas, and significantly inhibited the response in the fourth adenoma. It is concluded that escape from the requirement for an exogenous source of IGF-1 may be a key step in the development of human thyroid epithelial (follicular cell) neoplasia.

Adenoma↗
PubMed1988

Ventilator-induced pulmonary pseudocysts in preterm neonates.

Twenty-three pulmonary pseudocysts were identified in 20 preterm neonates undergoing mechanically assisted ventilation. Most of the pseudocysts occurred in a right parahilar location; cysts were either single (13) or multiple/multilocular (10). The pseudocysts persisted from less than 2 days to longer than 3 months (modal duration, 7 days), and they were commonly associated with generalized pulmonary interstitial emphysema (18 of 20), pneumothorax (18 of 20), bronchopulmonary dysplasia (16 of 20), and pneumomediastinum (six of 20). The reason for the predominantly right parahilar location of these pseudocysts remains uncertain. Pulmonary pseudocysts are almost always right-sided and are associated with pulmonary interstitial emphysema and pneumothoraces; complete resolution usually occurs.

Cysts↗
PubMed1987

Control of human thyroid follicular cell proliferation in suspension and monolayer culture.

We have used both suspension and monolayer cultures to investigate the in vitro control of normal human thyroid follicular cell proliferation as assessed by both [3H]TdR incorporation and autoradiography. In suspension cultures, whilst TSH alone produced no effect, inclusion of two permissive factors, namely a supraphysiological concentration of insulin (80 micrograms/ml) and a low concentration of FCS (1%) (which, in the absence of TSH, gave only a weak proliferative response) permitted a highly significant response to TSH at 0.1 mU/ml. A higher concentration of TSH (10 mU/ml) resulted in a reduced response. In monolayer cultures in contrast, insulin and FCS were themselves highly growth stimulatory, with no super-added effect on addition of TSH. Our data indicate that suspension culture provides a more valid in vitro model for the investigation of growth factor control of normal and neoplastic human thyroid epithelium.

Cell Division↗
PubMed1987

Incidence of familial hypercholesterolaemia in premature deaths due to coronary heart disease.

Cholesterol estimations were performed on blood collected postmortem from a group of subjects coming to autopsy and showing that they had had a high risk for hypercholesterolaemia, and from an unselected group of subjects dying in hospital. Subjects from the first group had apparently been healthy, aged less than 45 years, had had no known risk factors for hyperlipidaemia, and showed extensive coronary artery atheroma (stenosis greater than 50% by diameter). Eleven cases from 485 consecutive autopsies fulfilled these criteria; three showed considerable hypercholesterolaemia (11.2, 11.8, and 21.6 mmol/L). Family studies confirmed the diagnosis of familial hypercholesterolaemia in one case; the other two remain unproven. Cholesterol measurement by cholesterol oxidase and quinoneimine dye production is subject to interference by haemolysis; provided that serum haemoglobin is less than 200 mg/dl, the cholesterol underestimate is less than 5%. The decline in serum cholesterol in the group of unselected subjects was 1.7 (0.3-4.9) mmol/L, 50.4 (28-84) h postmortem. Results are means and ranges for seven subjects. Measurement of cholesterol in serum obtained postmortem (provided that the sample is not grossly haemolysed) is a valid approximation of antemortem levels: this measurement should be made when autopsy reveals evidence of premature coronary heart disease. If hypercholesterolaemia is discovered, the diagnosis of familial hypercholesterolaemia, a common genetic disorder inherited in an autosomal dominant fashion, should be considered and appropriate family studies instituted.

Adult↗
PubMed1984

Coherent global motion percepts from stochastic local motions.

A percept of global, coherent motion results when many different localized motion vectors are combined. We studied the percept with dynamic random dot kinematograms whose elements took independent, random walks of constant step size; their directions of displacement were drawn from a uniform distribution. The tendency to see global, coherent flow along the mean of the uniform distribution varied with the range of the distribution. Psychometric functions were obtained with kinematograms having various step sizes and element densities. The changes in the psychometric function with step size and density are consistent with Ullman's "minimal map theory" of motion correspondence.

Form Perception↗
PubMed1983

Spatial-frequency adaptation affects spatial-probability summation.

The effects of spatial-frequency adaptation on spatial-probability summation were investigated by two techniques: the measurement of the dependence of cosine grating sensitivity on the number of cycles presented and the determination of the frequency-of-seeing curve for a cosine grating. Both measurements indicate that the contribution of spatial-probability summation to adapted grating thresholds is reduced in comparison with unadapted conditions. This reduction in the effects of spatial-probability summation, together with the decrease in local sensitivity, which depends on the spatial inhomogeneity of the visual system, is sufficient to account for the threshold elevation aftereffect measured when adapting and testing with cosine gratings.

Adaptation, Ocular↗
PubMed1982

Localized effects of spatial frequency adaptation.

The spatially localized threshold-elevation aftereffect of spatial-frequency adaptation was measured by using localized, aperiodic test patterns that have bandpass Fourier transforms. At a given retinal location, the threshold-elevation curves are consistent with the fatigue of size-turned mechanisms with center-surround sensitivity profile. Only a few different sizes of such mechanisms were required to fit the local results. The local aftereffect was also measured as a function of eccentricity near the fovea. The results indicate that the threshold-elevation aftereffect of spatial-frequency adaptation is not spatially homogeneous.

Adaptation, Ocular↗
PubMed1982

The ultrastructure of the centroacinar cells within the pancreas of the starling (Sturnus vulgaris).

Tissues from the dorsal lobe of the pancreas of 8 starlings (Sturnus vulgaris) were examined electron microscopically using conventionally prepared samples. Centroacinar cells were distinguished from exocrine pancreas cells by differences in size, shape, distribution, position and zymogen granule content. The centroacinar cells closely resembled ductal cells and were separated from them only by position. Both electron-lucent and electron-dense forms of centroacinar cells were observed. Centroacinar cells show a prominent single nucleus, often displaying at least one nucleolus, surrounded by cytoplasm in which lies a spectrum of both primary and secondary lysosomes, mitochondria which appear to have some tubulovesicular cristae amongst the predominating transverse cristae, a sparse para- or supranuclear Golgi apparatus, and variable populations of ribosomes and profiles of both rough and smooth endoplasmic reticulum. Cell surface features include microvilli, 'blebs' and the occasional single cilium. Centroacinar cells are believed to be involved in electrolyte secretion although, from a study of their ultrastructure, the absence of beta cytomembranes with numerous mitochondria in their neighbourhood, would appear to contra-indicate the maintenance of an osmotic gradient between the extracellular fluid and any secretory product.

Animals↗
PubMed1975

Intra-epidermal carcinoma of the eyelid margin.

Twenty-two cases of intra-epidermal carcinoma of the ciliary margin have been diagnosed in a 15-year survey. The clinical appearance is variable, resembling in some instances a benign warty lesion, and in others a fully developed squamous cell carcinoma. As the lesion grows it produces keratotic plugging of the lash follicles and nodules on the lid margin; in due course this results in loss of the related cilia. When dermal invasion occurs the resultant squamous cell carcinoma is potentially dangerous because of the involvement of the adnexal structures, which on the ciliary margins are particularly large and penetrate deeply into the lid substance. Adequate biopsy which includes at least one lash follicle is essential for accurate diagnosis, and treatment requires complete excision with a reasonable margin for safety. Of the twenty-two patients, nineteen were male and three female; fourteen of the men involved had handled oils and greases for prolonged periods.

Adult↗