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Biomedical subjects

S Demeter

Publications and source records attributed to S Demeter.

36 records · Page 2Linked to original sources
PubMed1988

Morphometric analysis of the human corpus callosum and anterior commissure.

The cross-sectional areas of the corpus callosum (CC) and anterior commissure (AC) were determined by computer-assisted morphometry in normal human brains obtained at autopsy. In addition, the shape of each CC was examined qualitatively by three "blind" observers. A two-fold variation was observed in the cross-sectional area of the CC. Surprisingly, callosal cross-sectional area was not significantly related to brain weight. Moreover, contrary to recent reports, neither simple inspection nor morphometry revealed structural variation related to sex. A striking, seven-fold, variation was observed in the cross-sectional area of the AC. However, AC cross-sectional area was not related either to brain weight or CC cross-sectional area. A trend toward sexual dimorphism in AC cross-sectional area was observed, with males having the larger AC's. Since the interhemispheric commissures are composed, to a large extent, of fibers that link the various cortical areas of the two hemispheres, these observations suggest that variation in the cross-sectional area of the interhemispheric commissures is not simply related to brain weight or sex but, rather, reflects a similar degree of variation in some aspect of cortical structure.

Brain↗
PubMed1985

Interhemispheric pathways of the hippocampal formation, presubiculum, and entorhinal and posterior parahippocampal cortices in the rhesus monkey: the structure and organization of the hippocampal commissures.

The interhemispheric pathways originating in the hippocampal formation, presubiculum, and entorhinal and posterior parahippocampal cortices and coursing through the fornix system were investigated by autoradiographic tracing in 29 rhesus monkeys (Macaca mulatta). The results revealed that crossing fibers are segregated into three contiguous systems. A ventral hippocampal commissure lies at the transition between the body and anterior columns of the fornix in the vicinity of the subfornical organ and the interventricular foramina of Monro; it is formed by axons arising in the most anterior (uncal and genual) subdivisions of the hippocampal formation. A dorsal hippocampal commissure lies inferior to the posterior end of the body of the corpus callosum; it is formed by axons arising in the presubiculum and entorhinal cortex of the anterior parahippocampal gyrus and the proisocortical and neocortical subdivisions of the posterior parahippocampal gyrus but not in the hippocampal formation. A hippocampal decussation lies between the ventral hippocampal commissure and dorsal hippocampal commissure; it is formed by axons arising in the body of the hippocampal formation. In contrast to the fibers of the ventral hippocampal commissure and dorsal hippocampal commissure, which terminate in contralateral cortical areas, these decussating fibers terminate in the contralateral septum. Thus, the ventral hippocampal commissure and dorsal hippocampal commissure of the rhesus monkey appear to be homologous to similarly designated structures in other mammals. To the extent that these observations also apply to the interhemispheric fibers of the human hippocampal formation and parahippocampal areas, their possible preservation must be considered when interpreting the effect of callosal transection on seizures and the results of "split-brain" studies, since callosal transection may fail to sever the hippocampal commissures in their entirety.

Animals↗
PubMed1985

Multiple organ failure resulting from intravenous abuse of methylphenidate hydrochloride.

A 32-year-old woman who abused methylphenidate hydrochloride developed complications including hepatic, renal, pancreatic, pulmonary, and CNS toxicities. These were manifested by abnormal liver function enzymes, poor urine output, hypotension, tachypnea, tachycardia, abnormal blood gases, rising serum BUN and creatinine, and hyperactive deep-tendon reflexes. All were reversible with medication withdrawal and supportive therapy. Toxicities of this medication and their implications are discussed.

Adult↗
PubMed1984

Pulmonary lymphangiomyomatosis.

Lymphangiomyomatosis is an interesting disease with distinctive clinical and histopathologic findings. We report herein two additional cases of lymphangiomyomatosis, including one with clinical improvement after therapy with progesterone. This case is of particular significance in view of the patient's negative sex steroid receptor analysis. These findings open new avenues for future considerations in the therapy of this unusual but interesting disease.

Adult↗
PubMed1983

Quantitative computed tomographic analysis in the diagnosis of dementia.

We compared the computed tomographic (CT) scans of 46 patients with dementia with those of 46 normal subjects matched for age and sex. We measured the areas subtended by the third ventricle, frontal horns, bodies of the lateral ventricles, and interhemispheric fissure as depicted in CT sections, then determined the ratio between each of those areas and the entire brain at each level. Patients with dementia had significantly larger ratios on all measures. A multivariate classification procedure showed that a composite formula of two measures, the bodies of the lateral ventricles and the interhemispheric fissure, predicted clinical status in 84% of the cases. Findings indicated that some CT measurements reflected cerebral changes associated with dementia. If appreciated in a suitable probabilistic framework, these data may be clinically useful in supporting or weakening the diagnostic hypothesis of dementia in the many cases in which diagnosis is unclear.

Aged↗
PubMed1982

Chiroptical properties of chlorophyll-protein complexes separated on Deriphat/polyacrylamide gel.

Circular dichroism (c.d.) was measured for four chlorophyll-protein complexes, resolved from sodium dodecyl sulphate extracts of chloroplasts by electrophoresis in polyacrylamide gel containing Deriphat 160 (disodium N-dodecyl beta-imidopropionate), a zwitterionic detergent. The slowest-band (1) complex was found to be identical with the complex CP1 as found on electrophoresis in the presence of anion detergent, but it was in a much higher yield (30% of the chlorophyll a). In band-2 and -3 protein complexes a c.d. pattern described for the complex CP2 could be recognized. Another c.d. component of a split-exciton type with extrema at 680 (-) and 669 (+)nm, together with evidence of disorganized chlorophyll, was found in band-2, -3 and -4 complexes. When a barley (Hordeum vulgare) mutant lacking chlorophyll b was examined, only bands 1 and 4 were obtained, and the c.d. of the band-4 complex was much less affected by disorganized chlorophyll. C.D. spectra resembling that of this band-4 complex could be generated by subtracting the c.d. of complex CP1 from the c.d. of photochemically active mutant chloroplast fragments, or by subtracting the c.d. of complexes CP1 and CP2 from pea (Pisum sativum) chloroplast fragments. The Deriphat appears to have preserved at least to some extent a new type of chlorophyll a-protein complex.

Chlorophyll↗
PubMed1981

Photosynthetic energy conservation investigated by thermoluminescence. Activation energies and half-lives of thermoluminescence bands of chloroplasts determined by mathematical resolution of glow curves.

Thermoluminescence of isolated chloroplasts was analysed by a computer-assisted multicomponent curve fitting procedure to determine the activation energies, the free energies of activation, frequency factors and half-lives of the component bands of the glow curve. Optimal fit was obtained in the temperature region from -80 degrees C to +80 degrees C by the resolution of the glow curve into seven bands with peak positions at -24, -12, +12, +17, +28, +44, and +69 degrees C. All of the activation free energies of the thermoluminescence bands were much higher than 0.59 eV, the minimum free energy of activation required for the back reaction of the primary charge separation as calculated on the basis of the theory of Ross and Calvin (Ross, R.T. and Calvin, M. (1967) Biophys. J. 7, 595-614). The high free energies of activation and long half-lives (longer than 50 ms) of the thermoluminescence bands suggest that thermoluminescence in the temperature region from -80 degrees C to 80+ C does not reflect the change recombination of primary products but represent the reversal of subsequent stabilization steps of the charge separation process which proceed along the acceptor and donor sides of Photosystem II.

Chloroplasts↗
PubMed1980

Macromolecular organization of chlorophyll a in aggregated chlorophyll a/b protein complex as shown by circular dichroism at room and cryogenic temperatures.

This report concerns the circular dichroic (CD) signal of intact chloroplasts of higher plants. The CD spectra of chloroplasts are compared with the aggregated form of the light-harvesting chlorophyll a/b complex at 25 degrees C and -250 degrees C. The light-harvesting chlorophyll aggregate has a CD of magnitude equal to or greater than chloroplasts, but of opposite sign, and it is not related to the CD of the unaggregated form, and hence its arrangement is an artefact compared to the arrangement in the chloroplast. We suggest that this preparation, which has pseudo-lamellar structure, is a clear example of a large CD signal being generated by macromolecular association. The asymmetry of organization in the chloroplast has an opposite sense to that of the aggregate, but affects only chlorophyll a, not chlorophyll b.

Cell Membrane↗
PubMed1977

Electrochemical and spectro-kinetic evidence for an intermediate electron acceptor in photosystem I.

Absorption changes accompanying light-induced P-700 formation and its decay in the dark at 15 K in Photosystem-I particles poised at various redox potentials have been examined. In unpoised samples, the light-induced absorption change is practically irreversible. At increasingly negative potentials, an increasing fraction of the absorption change, proportional to the fraction of bound iron-sulfur protein chemically reduced, becomes reversible, and the titration curve has a midpoint potential of --530 mV (vs. normal hydrogen electrode). At --66 mV, the P-700 absorption change is 97% reversible. The total P-700-signal amplitude decreases over the same potential span and levels off at about 43% (to slightly over 50% at a substantially higher excitation intensity). These results provide additional support to previous suggestions of an existence of an intermediate electron acceptor located between the primary donor, P-700, and the more stable primary electron acceptor (P-430 or bound iron-sulfur protein).

Electrochemistry↗
PubMed1976

The development of the intense circular-dichroic signal during granum formation in greening etiolated maize.

In greening maize mesophyll, circular dichroism (c.d.) revealed the early formation of protein-chlorophyll complexes, followed by unorganized chlorophyll. The intense c.d. [Gregory & Raps (1974) Biochem. J. 142, 193-201] appeared later still, whereas membrane-membrane contact (stacking), measured from electron micrographs, appeared much earlier. Isolated grana, which still showed stacking, lost 92% of their original intense c.d.; intense c.d. is not therefore simply dependent on stacking.

Chloroplasts↗
PubMed1973

Circular dichroism spectra of granal and agranal chloroplasts of maize.

Granum-containing chloroplasts from mesophyll cells of maize (Zea mays L. var. MV 861) leaves exhibited circular dichroism spectra with a large double signal; peaks at 696 nm (+) and 680 nm (-). In the circular dichroism spectra obtained with agranal chloroplasts of bundle sheath cells, this large double signal is absent. Separation of grana lamellae, in a medium of low salt concentration and in KSCN solution, resulted only in a slight decrease of the amplitude, while upon treatment with digitonin the large double signal disappeared. A negative signal of the chlorophyll b peak at 654 nm was observed in the case of both granal and agranal chloroplasts, and it was not affected either by low salt or by digitonin treatment. A positive peak at about 515 nm was higher in granal than in agranal chloroplasts.

Journal Article↗
PubMedDate not supplied

Time is of the essence: a conjecture that hemispheric specialization arises from interhemispheric conduction delay.

Tomasch (1954) and Aboitiz et al. (1992) found the majority of the fibers of the human corpus callosum are under 1 micron in diameter. Electron microscopic studies of Swadlow et al. (1980) and the detailed study of LaMantia and Rakic (1990a) on macaques show the average size of the myelinated callosal axons also to be less than 1 micron. In man, the average-sized myelinated fiber interconnecting the temporal lobes would have a one-way, interhemispheric delay of over 25 msec. Thus, finely detailed, time-critical neuronal computations (i.e., tasks that strain the capacity of the callosum and hence could not be handled by just the larger fibers) would be performed more quickly via shorter and faster intrahemispheric circuits. While one transit across the commissural system might yield tolerable delays, multiple passes as in a system involving "setting" would seem prohibitively slow. We suggest that these temporal limits will be avoided if the neural apparatus necessary to perform each high-resolution, time-critical task is gathered in one hemisphere. If the, presumably overlapping, neural assemblies needed to handle overlapping tasks are clustered together, this would lead to hemispheric specialization. The prediction follows that the large brains of mammals such as elephants and cetaceans will also manifest a high degree of hemispheric specialization.

Animals↗
PubMedDate not supplied

Chemical probes for water-oxidation: synthetic manganese complexes in photoactivation of water splitting complex and as exogenous electron donors to photosystem II.

Photoactivation of the water splitting enzyme was performed with 13 different synthetic manganese complexes and characterized by oxygen evolution yield, thermoluminescence and chlorophyll fluorescence induction kinetics. The efficiency of different compounds in photoactivation correlated with the rate of linear electron transport in the presence of these compounds. The organic ligands, associated with the manganese ions, do not prevent the photoactivation of the water splitting complex (WOC). Photoactivation with different manganese complexes depended on the number of the Mn-ions in the complex, their valence state and the nature of their donor atoms. The most efficient restorations were achieved by using tetrameric complexes having a dimer+dimer structure, complexes containing Mn(II) ions, and having 4-6 oxygen and 0-2 nitrogen atoms as donor atoms. Further, the effectiveness of photoactivation depended largely on the structure of the complexes. Our data support the notion that WOC in intact thylakoids requires the cooperation and well determined arrangement of all four manganese ions, and argue against the hypothesis that two manganese ions are sufficient for water splitting. Photoactivation by some complexes led to anomalous flash-oxygen patterns, which are explained by a modified/perturbed water splitting complex.

Chlorides↗
PubMedDate not supplied

Prevalence of HBeAg and anti-HBe in blood donors with HBs antigenemia.

250 HBsAg-positive sera from apparently healthy blood donors were tested for HBeAg and anti-HBe by immunodiffusion(ID) and counterelectrophoresis(CEP). HBeAg was identified in 2.4% and anti-HBe in 34% of the sera. After serum concentration a larger rate of both HBeAg and anti-HBe could be detected by ID. There was no difference in sensitivity between ID and CEP techniques in the detection of the e-system. There was no correlation between HBeAg or anti-HBe and HBsAg subtypes. Generally sera containing HBeAg showed higher titers of HBsAg in complement fixation.

Antibodies, Viral↗