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Biomedical subjects

P Thompson

Publications and source records attributed to P Thompson.

At least 235 records · Page 13Linked to original sources
PubMed1984

The coding of velocity of movement in the human visual system.

A very simple model of velocity perception which requires only 17 channels is outlined. The important points of the model are that: (1) in each direction of movement just two temporal frequency channels are necessary at any spatial frequency, (2) at low temporal frequencies the spatial frequency domain is encoded by many channels, but only those at low spatial frequencies are direction-specific. Using a detection/discrimination technique the supposition that channels which detect high spatial, low temporal frequencies are not direction specific is investigated. Possible reasons for the apparent nondirectional behaviour of these channels are investigated: the notion that non-directionality reflects a failure of the stimulus to travel some threshold distance across the retina is rejected, but the proposal that a velocity threshold must be exceeded before the direction of a grating may be identified at detection threshold remains a possibility.

Humans↗
PubMed1984

The structure of mammalian rod opsins.

Ovine rhodopsin is organised in disc membranes as a monomer. The determination of its amino acid sequence has permitted the utilisation of structure prediction programmes which indicate the probable disposition of the polypeptide chain in the bilayer. This putative model is consistent with labelling data using the chemical probes, [14C]succinic anhydride, [125I]diazodiido sulphanilic acid and [125I]iodophenyl azide, and with the cleavage points for several proteases. More surprisingly the predicted structure points to the occurrence of breaks/distortions in the transmembrane helical segments. These distorted regions may be of primary functional importance to the protein and at least one is associated with the attachment point of the chromophore. This particular part of the structure is also identified as a "mutational hot spot", for bovine, equine, ovine and porcine opsins exhibit different sequences (but conserved molecular volumes) in the four residues following the retinyllysine. In an otherwise highly conserved protein with no obvious functional differences between the four species, the high substitution rate in this region is unexplained.

Amino Acid Sequence↗
PubMed1984

Gender and oral contraceptive effects on temporary auditory effects of noise.

The first experiment examined thresholds at 4 and 8 kHz and the threshold of octave masking at 4 kHz before and after noise for males, females, and females using oral contraceptives. Females using oral contraceptives evidenced greater threshold shifts at 4 kHz than either of the other two groups. The second experiment examined thresholds and the loudness discrimination index at 4 kHz for males and females before and after noise exposure. Females evidenced greater loudness discrimination index changes both with and without noise exposure than did males. In addition, females responded to the noise with cutaneous vasodilation while males evidenced vasoconstriction.

Adolescent↗
PubMed1983

Octamer reconstitution from acid-extracted chicken erythrocyte histones.

Histone octamers have been reconstituted from acid-extracted chicken erythrocyte histones. By the criteria of molecular size on exclusion chromatography as well as sedimentation velocity and conformational properties established by circular dichroism, fluorescence spectroscopy and imido-ester cross-linking, the reconstituted octamers have a structure identical to that of salt-extracted octamers.

Animals↗
PubMed1983

Discrimination of moving gratings at and above detection threshold.

Two experiments examined the discriminability of moving gratings. Experiment 1 measured the difference between detection and discrimination thresholds for gratings of equal spatial frequency drifting in the same direction at different rates. It was found that, as Watson and Robson [Vision Res. 21, 1115-1122 (1981)] had found with counterphase modulated gratings, only very coarse discriminations could be made. The results suggest that just two labelled channels can account for the velocity discrimination of gratings at detection threshold. The second experiment investigated the discriminability of suprathreshold moving gratings. These results also support the idea that rate of movement is mediated by two broadly tuned channels.

Discrimination, Psychological↗
PubMed1983

Hearing loss in pediatric renal patients.

Modern techniques of prolonging life and useful function for endstage renal patients have been accompanied by a variety of new clinical and pathological manifestations, among which are inner ear problems. Of 151 pediatric renal patients followed prospectively 47% had hearing loss, which closely approximates that found in renal patients of all ages. However, only 5.3% of pediatric-age patients, as compared with 15% of all age groups, have hearing loss of unknown etiology. Certain types of hearing loss, for example, those due to acoustic trauma and Ménière's, were not found in the pediatric-age group, while ototoxic, congenital and genetic hearing losses were more common in young persons than in the overall group. Management includes assessment of hearing and vestibular function prior to and at intervals during the administration of ototoxics, monitoring of blood levels, careful attention to otological symptoms and observing the principles of hearing conservation.

Adolescent↗
PubMed1983

Anatomico-radiological study of the borderline sella.

Multidirectional thin section tomography was performed on 62 excised sphenoidal bones. The pituitary gland was then sectioned and examined microscopically for evidence of microadenoma, cellular hyperplasia or cysts. There is absolutely no meaningful correlation between the radiological and the histological findings. Minor sellar changes in the form of slight irregularity of the lamina dura, asymmetry of the sellar floor or thinning of the dorsum sellae may be found in the absence of any histopathological abnormality.

Adolescent↗
PubMed1983

Thyroid autoantibody synthesis by cultures of thyroid and peripheral blood lymphocytes. II. Effect of thyroglobulin on thyroglobulin antibody synthesis.

The influence of antigen (thyroglobulin, Tg) on Tg antibody synthesis has been investigated using cultures of Hashimoto thyroid and peripheral blood lymphocytes. In cultures of thyroid lymphocytes, Tg antibody synthesis was stimulated by a 24h pulse of Tg (10-100 micrograms/ml) and similar results were obtained using spleen lymphocytes from BALB/c mice immunized with human Tg. In contrast, Tg antibody synthesis by Hashimoto peripheral blood lymphocytes was not affected by similar concentrations of Tg (1-240 micrograms/ml) in the presence or absence of pokeweed mitogen (PWM). However, peripheral blood lymphocytes from two out of nine patients produced increased levels of Tg antibody in the presence of very low concentrations of Tg (50 ng/ml). This increase in Tg antibody production was accompanied by a rise in total IgG synthesis indicating that the response to Tg was polyclonal. On the basis of other unusual features of the lymphocyte cultures from these two patients including a relatively small response to PWM and evidence of circulating plasma cells, it is suggested that sufficient numbers of lymphocytes responsive to Tg are only released into the circulation during active phases of the disease process.

Adult↗
PubMed1982

The effect of Ca2+ on the stability of chicken erythrocyte histone octamers.

Histones can be extracted from chicken erythrocyte chromatin with 2 M CaCl2 10 mM Tris (pH 7.4). The core histones so extracted exist as H3-H4 tetramers and H2A-H2B dimers since calcium at greater than 0.5 M result in dissociation of the histone octamer. Reconstitution of octamers occurs on removal of the Ca2+ by dialysis. Although less than 0.5 M calcium do not result in octamer dissociation, perturbations in the structure can be detected by CD and tyrosine fluorescence spectroscopy.

Animals↗
PubMed1982

Fungating Bowen's disease with presumed arsenic intoxication. A case report.

A patient with a bizarre fungating tumour of the anterior abdominal wall is described. The lesion had the histological features of Bowen's disease and also had the appearance of a basal cell carcinoma with sebaceous differentiation. In addition, the patient had 'raindrop' pigmentation typical of chronic arsenic intoxication. As far as we know, Bowen's disease has once previously been reported in a Black patient in South Africa. We have not encountered any other description in the literature of Bowen's disease presenting as a fungating tumour.

Adult↗
PubMed1982

The reconstitution of histone H3-H4 tetramer from acid extracted histones in the absence of urea.

Simple mixing of acid purified histones H3 and H4 in equimolar quantities at low ionic strength near pH 7 does not yield the tetramer but rather a high Mr aggregate. Dialysis of acid extracted total or core histones into 2 M NaCl 150 mM phosphate (pH 7.4) followed by fractionation of the histone complexes at lower ionic strength (150 mM NaCl) results in an H3-H4 tetramer of a structure identical to that derived from salt-extracted histones. Dialysis of acid extracted total or core histones directly into the lower ionic strength buffer with subsequent fractionation, results in H3-H4 tetramer of closely similar structure.

Animals↗
PubMed1982

Changes in plasma angiotensin II with noise exposure and their relationship to TTS.

Plasma concentrations of the vasoconstrictor Angiotensin II (AII) were measured in male human subjects before and after either rest or exposure to 100-dB white noise. Plasma AII concentrations decreased for subjects in the control (no noise) condition but remained high in the noise condition. In the noise exposure condition both the pre- and post-exposure AII concentrations were negatively but nonsignificantly correlated with TTS. The cardiovascular effects of noise appear to be mediated in part by AII.

Angiotensin II↗
PubMed1982

Iodothyronine levels in human cerebrospinal fluid.

Iodothyronines were measured by RIA in concentrated human cerebrospinal fluid (CSF). In measurements performed in one laboratory at a 4-fold concentration of CSF, rT3 was detected in all 30 patients in whom the measurement was attempted and averaged 15.1 +/- 2.8 ng/dl (mean +/- SE). IN an independent laboratory, rT3 measurements at this 4-fold concentration were performed on 11 different samples and averaged 9.3 +/- 0.9 ng/dl, while at a 40-fold CSF concentration, rT3 averaged 13.1 +/- 0.72 ng/dl. CSF T3 values were detected in only 4 of 30 patients as a 4-fold concentration and averaged 8.2 +/- 3.1 ng/dl, while in pooled CSF at a 40-fold concentration, 4 of 4 samples were detectable and averaged 2.6 +/- 0.4 ng/dl. Levels of T4 could only be detected in CSF concentrated 40-fold and averaged 0.22 +/- 0.04 microgram/dl. Values for the percent dialyzable thyronines were 0.44 +/- 0.03% for T4, 4.39 +/- 0.29% for T3, and 0.91 +/- 0.04% for rT3. TSH was detected in CSF concentrated 4-fold, averaging 0.43 +/- 0.05 microunits/ml; in an independent assay with CSF concentrated 40-fold, TSH averaged 0.06 +/- 0.02 microunits/ml. Thyroid binding globulin was undetectable (less than 0.1 mg/dl). We have confirmed the presence of thyroid hormones (T4 and T3) in human CSF and have shown that rT3 is present as well. The role these hormones play in the development, function, and nourishment of the central nervous system and the role the CSF plays in the transport of these hormones into the central nervous system remains to be determined.

Humans↗
PubMed1982

[Effects of anterior chamber perfusion on the rabbit corneal endothelium: a scanning electron microscopy study (author's transl)].

The effects of intraocular irrigating solutions (TC Earle and NaCl 9%) on the rabbit corneal endothelium were evaluated utilizing scanning electron microscopy. Introcular pressure was maintained at 15 or 50 mm Hg. Rate of perfusion was between 50 microliter/min and 2 ml/min. With NaCl 9%, in eyes exposed to high pressure (50 mm Hg) for 2 hours with a rate of 50 microliter/min changes could be detected: rupture of apical junctions and minimal structural changes. Similar lesions appeared with a pressure of 15 mm Hg at a rate of ml/min. With Earle solution, no lesions were seen after 3 hours and minimal changes after 4 hours. Intraocular irrigating solution seems to be more toxic than increased intraocular pressure on the structure of endothelial cells, as seen on scanning electron microscopy. Greater sensitivity of endothelium to perfusion fluid than intraocular pressure probably explains the paradoxical appearance of corneal edema in diseased states, and suggests that endo-ocular surgical procedures require modification.

Animals↗