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Biomedical subjects

S Samson

Publications and source records attributed to S Samson.

At least 37 records · Page 2Linked to original sources
PubMed1994

X-ray diffraction study of the crystal structure of the pi-molecular compound pyrene ... pyromellitic dianhydride at 19 K.

The crystal structure of the pyrene ... pyromellitic dianhydride (PMDA) pi-molecular compound [(C16H10:C10H2O6); PYRPMA] has been refined from intensities measured at 19 K using the low-temperature accessory designed by Samson, Goldish & Dick [J. Appl. Cryst. (1980), 13, 425-432] for a four-circle diffractometer. Earlier results for the ordered structure [Herbstein & Snyman (1969). Philos. Trans. R. Soc. London Ser. A, 264, 635-666] are confirmed and extended; at 19 K, a = 13.664 (3), b = 9.281 (2), c = 14.420 (3) A, beta = 91.80 (2) degrees, space group P2(1)/n, Z = 4, with two sets of pyrenes at independent centres of symmetry and the four PMDAs at general positions. The geometrical structures of the two components are in good agreement with quantum mechanical calculations. Analyses of thermal motion and packing show that one set of pyrenes is more tightly packed than the other; the principal interactions in the crystal are pi-pi* plane-to-plane interactions between pyrene and PMDA and > CH ... O = C <, between pyrene and PMDA, and between PMDAs.

Benzoates↗
PubMed1994

X-ray diffraction study of the disorder-to-order transition at approximately 160 K in the pi-molecular compound pyrene ... pyromellitic dianhydride.

The crystal structure of pyrene ... pyromellitic dianhydride [(C16H10:C10H2O6); PYRPMA] has been studied over the range 300-19 K, using the low-temperature accessory designed by Samson, Goldish & Dick [J. Appl. Cryst. (1980), 13, 425-432] for a four-circle diffractometer. Earlier results for the disordered and ordered structures [Herbstein & Snyman (1969). Philos. Trans. R. Soc. London Ser. A, 264, 635-666] are confirmed and extended. At 295 K, a = 13.94 (1), b = 9.34 (1), c = 7.31 (1) A, beta = 93.65 (9) degrees, space group P2(1)/a, Z = 2, with pyrenes and pyromellitic dianhydrides (PMDAs) at crystallographic centres of symmetry. At 19 K, a = 13.664 (3), b = 9.281 (2), c = 14.420 (3) A, beta = 91.80 (2) degrees, space group P2(1)/n, Z = 4, with two sets of pyrenes at independent centres of symmetry and the four PMDAs at general positions. There are no discontinuities in cell dimensions with temperature (measurements at approximately 10 K intervals, down to 19 K) but db/dT and d beta/dT show discontinuities at approximately 167 K. Superlattice reflections appear below approximately 164 K (= Tc by X-ray diffraction), corresponding to the doubling of c and change of space group; the specific heat shows an anomalous increase over the range 120-155 K, giving a lambda-type peak. These results show that the transition is second order with regard to Ehrenfest's criteria. PYRPMA is a co-elastic crystal and quantitative analysis shows a linear dependence of the squares of spontaneous strain and of normalized superlattice intensity on temperature; hence, in terms of Landau theory, the transition is tricritical. However, the excess specific heat cannot be explained entirely on this basis. The physical nature of the transition is discussed. PYRPMA is so far unique among the pi-molecular compounds showing disorder-to-order transitions in the solid state in that there is a doubling of one of the axes; all indications are, however, that it resembles the other examples in the sense that subtle intermolecular packing interactions (here between pyrenes and PMDAs) are the driving force for the transition rather than electronic or charge-transfer interactions.

Benzoates↗
PubMed1994

Contribution of the right temporal lobe to musical timbre discrimination.

Patients with unilateral temporal lobe excisions and normal control subjects were tested in timbre discrimination tasks in which the stimuli differed by either the number of harmonics (a spectral cue) or by the duration of the rise and fall times (a time cue). Patients with right temporal lobe lesions exhibited a significant deficit in discriminating both spectral and time information, in comparison to patients with left temporal lobe lesions and normal control subjects. This finding suggests that musical timbre perception, examined in a psychoacoustic sense, depends on neural systems found within the right temporal lobe.

Acoustic Stimulation↗
PubMed1992

Learning and retention of melodic and verbal information after unilateral temporal lobectomy.

The role of the temporal lobes in auditory memory was tested in two analogous tasks assessing learning and 24-hr delayed recognition of unfamiliar melodies and nonsense words. The performance of patients with either anterior right (RT) or left (LT) temporal lobectomy was impaired in learning and delayed recognition of both melodies and words, as compared to normal control subjects, although some preserved learning over successive trials was observed. These results suggest a bilateral temporal-lobe contribution to the learning of these auditory patterns. However, melodies and nonsense words were not recognized in the same way by the two patient groups after 24 hr: subjects in the LT group tended to improve on melodies but drop on words, whereas subjects with RT lesions displayed the reverse pattern, suggesting a differential role for each temporal lobe in long-term memory, according to the nature of the cues inherent to a given type of stimulus.

Adult↗
PubMed1991

Recognition memory for text and melody of songs after unilateral temporal lobe lesion: evidence for dual encoding.

The role of left and right temporal lobes in memory for songs (words sung to a tune) was investigated. Patients who had undergone focal cerebral excision for the relief of intractable epilepsy along with normal control subjects were tested in 2 recognition memory tasks. The goal of Experiment 1 was to examine recognition of words and of tunes when they were presented together in an unfamiliar song. In Experiment 2, memory for spoken words and tunes sung without words was independently tested in 2 separate recognition tasks. The results clearly showed (a) a deficit after left temporal lobectomy in recognition of text whether sung to a tune or spoken without musical accompaniment, (b) impaired melody recognition when the tune was sung with new words following left or right temporal lobectomy and (c) impaired melody recognition in the absence of lyrics following right but not left temporal lobectomy. The different role of each temporal lobe in memorizing songs provides evidence for the use of dual memory codes. The verbal code is consistently related to left temporal lobe structures, whereas the melodie code my depend on either or both temporal lobe mechanisms, according to the type of encoding involved.

Attention↗
PubMed1991

Role of the right temporal neocortex in retention of pitch in auditory short-term memory.

In order to investigate the neural mechanisms underlying short-term memory for auditory information, 71 patients who had undergone focal excision from the left or right temporal or right frontal or fronto-temporal area for the relief of intractable epilepsy were tested, together with 18 normal control subjects, on a task requiring short-term retention of tonal pitch. In the control condition, a target tone was presented, followed 1650 ms later by a comparison tone, and subjects determined whether the two had the same pitch or not. In the interference condition a series of interpolated tones was presented between target and comparison tone. Results indicated that there was no significant impairment in any patient group on the control task. In the interference task there was a significant deficit in retention of tonal information in the patients with right temporal-lobe damage, as well as in those with lesions in the right frontal lobe, and in the right frontal and temporal area. Patients with left temporal-lobe excisions did not demonstrate a significant deficit. These findings are in agreement with research on non-human primates suggesting that structures in the superior temporal gyrus are important in retaining auditory information over short time spans, and further indicate that the human right temporal area is specialized for this function.

Adolescent↗
PubMed1988

Melodic and harmonic discrimination following unilateral cerebral excision.

Seventy-seven subjects who had undergone unilateral temporal, frontal, or frontotemporal lobectomy for the relief of focal epilepsy as well as a group of 20 normal control subjects were tested in two discrimination tasks, requiring the detection of a single-note change in a pattern of three notes played either successively or simultaneously. Patients with right temporal and right frontotemporal excisions demonstrated a significant deficit in melodic discrimination in comparison to the normal control subjects. Further analysis showed that left-temporal lobectomy including excision of Heschl's gyri (the primary auditory receiving area) led to a significant impairment as well, whereas anterior left temporal-lobe damage did not result in a significant deficit. The results suggest that melodic discrimination depends largely but not exclusively on the right temporal lobe, and that the left Heschl's gyri also seem to be necessary to succeed in this task. In the harmonic task, the differences between the groups did not reach significance, although the two tasks were highly correlated.

Adult↗
PubMed1987

Risk of AIDS for recipients of blood components from donors who subsequently developed AIDS.

Reported cases of acquired immunodeficiency syndrome (AIDS) in San Francisco as of March 31, 1986, include 92 individuals who had donated blood subsequent to 1978. Their donated blood components had been transfused into 406 different recipients. The current status of 336 of these recipients was ascertained as of April 1, 1986. Of these, 223 had died at the time of our first contact, almost all as a result of the condition for which they were transfused. Seven had developed AIDS; five of these died, two before entry into the study and three subsequently. Forty-six additional living recipients were interviewed and evaluated. Seven had the AIDS-related complex, 18 had antibody to the human immunodeficiency virus (HIV) but were otherwise healthy, and 19 had no detectable anti-HIV. Two had risk factors other than transfusion. The frequency of infection of the recipient decreased as the time interval between transfusion and the diagnosis of AIDS in the donor increased. This information should be useful when counseling patients who have been transfused with blood components from donors later found to be infected with HIV.

Acquired Immunodeficiency Syndrome↗
PubMed1986

Effect of oral penicillin on pneumococcal carriage in elderly men with chronic bronchitis.

A double-blind, randomized, placebo-controlled trial was undertaken to evaluate the effect of penicillin on the pneumococcal carrier state of 32 men with chronic bronchitis. Treatment consisted of 250-mg phenoxymethyl penicillin or placebo tablets taken by mouth twice daily for periods of one to three years. Penicillin eradicated Streptococcus pneumoniae from the respiratory tracts of all carriers and prevented colonization with pneumococci for the duration of treatment, whereas placebo had no discernible effect on the carrier state (P = 0.0015). The conclusion is that daily penicillin orally in low doses eliminates pneumococci from the oropharynx of elderly patients with clinically stable chronic bronchitis.

Administration, Oral↗
PubMed1986

Hyperthermia-induced cell death, thermotolerance, and heat shock proteins in normal, respiration-deficient, and glycolysis-deficient Chinese hamster cells.

Hyperthermia-induced cell inactivation, thermotolerance development, and heat shock protein synthesis were characterized in a Chinese hamster cell line and its two derivatives, respectively, deficient in glycolysis and respiration. No difference was found in the intrinsic thermosensitivity of the cells or in their ability to respond to heat by developing thermotolerance and synthesizing the heat shock proteins. The results indicate that the direct thermal inactivation of either respiration or glycolysis is not an obligatory rate-limiting event in hyperthermic cell killing and that thermotolerance and heat shock proteins are not triggered exclusively as a consequence of damages induced directly by heat in energy metabolism nor do they result specifically in an increased thermostability of respiration or glycolysis. It is concluded that if energy metabolism is involved somehow in the induction by heat of cell death, thermotolerance, and heat shock protein synthesis, it is due to a heat-induced alteration that indirectly causes changes in the cellular energy status rather than to a direct interaction of heat with energy production.

Animals↗
PubMed1985

Solubilization of a high affinity CA-ATPase from dog antrum smooth muscle.

A Mg-independent high affinity Ca-ATPase has recently been reported to be present in the plasma membranes of smooth muscle. This enzyme has now been solubilized using deoxycholate. The membrane-bound and the solubilized enzymes resemble each other in Km for Ca2+, and inhibition by fluphenazine. The solubilized enzyme is, however, more sensitive to inhibition by Mg2+ than the membrane bound enzyme. Radiation inactivation analysis shows that whereas the membrane-bound enzyme had a target size of 98,000 +/- 4,000 Daltons, the solubilized enzyme was only 70,000, +/- 7,000 Daltons.

Activation Analysis↗
PubMed1985

Tubulin genes of the African trypanosome Trypanosoma brucei rhodesiense:nucleotide sequence of a 3.7-kb fragment containing genes for alpha and beta tubulins.

Most tubulin genes of the African trypanosome Trypanosoma rhodesiense are contained in 3.7-kb tandemly repeating units. One member of the 3.7-kb repeat family has been isolated from a T. rhodesiense genomic library, cloned, and sequenced. The 3646-bp fragment contains a complete alpha-tubulin gene and portions of two beta-tubulin genes. No introns are present. The genes are separated by 634- and 333-bp intergenic regions, which lack typical eukaryotic promoter and poly(A) signal sequences. However, both intergenic regions exhibit some structural similarity with sequences proposed to be involved in transcription termination and poly(A) addition in yeast. The 634-bp intergenic region shows homology to the "mini-exon" sequence associated with variable surface glycoprotein (VSG) and other trypanosome mRNAs. A comparable sequence is not found in the 333-bp intergenic region. T. rhodesiense alpha and beta-tubulins exhibit about 84-85% amino acid (aa) sequence homology with tubulins of mammals; the genes show about 74-75% nucleotide sequence homology. The alpha-tubulin contains 451 aa and the beta tubulin 442 aa; both have tyrosine as the C-terminal aa.

Amino Acid Sequence↗
PubMed1983

Hemophilus influenzae biotypes and chronic bronchitis.

Hemophilus influenzae can be differentiated into 6 biotypes on the basis of 3 biochemical reactions. This study was undertaken to determine the biotypes of respiratory isolates from an adult population with chronic bronchitis and to compare the biotypes of upper and lower respiratory tract isolates of individual patients. For rapid biotyping of serologically nontypable H. influenzae, we used 2 commercially prepared kits (Minitek and IDS RapID Systems). Twenty-three of 29 isolates (79%) had biochemical characteristics of biotype II with the Minitek system. Eighteen of the same 29 isolates were retested with the IDS RapID System and reacted as biotype II organisms. Seven of 9 and 4 of 4 paired transtracheal/oropharyngeal samples had identical biotypes when tested with the Minitek and IDS RapID System, respectively. These findings suggest that H. influenzae organisms are exchanged between the oropharynx and tracheobronchial tree of elderly male patients with chronic bronchitis.

Bronchitis↗
PubMed1982

Structure of a B-DNA dodecamer at 16 K.

The crystal structure of the B-DNA dodecamer C-G-C-G-A-A-T-T-C-G-C-G, previously solved and refined at room temperature (290 K), has been analyzed at 16 K (-257 degrees C). The end-to-end winding of the helix does not vary with temperature but remains constant at 10.1 base pairs per turn. Negatively charged phosphate groups throughout the structure do move closer together on cooling, however, probably because of increase in the dielectric constant of water as the temperature is lowered. This has the two-fold effect of reducing the spacing between neighboring double helices from 24.0 to 22.9 A and of narrowing the helix grooves within any isolated molecule. Overall lattice displacements as deduced from crystallographic temperature factors are very much decreased in the 16 K structure, yet displacements at phosphates continue to exceed those of deoxyribose sugars by B = 9 A2 and those of base pairs by B = 22 A2, even at this very low temperature at which practically all thermal motion has been eliminated. These differences, formerly interpreted as evidence for thermal vibration, must now be attributed to static disorder.

DNA↗