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Biomedical subjects

P Berg

Publications and source records attributed to P Berg.

At least 19 recordsLinked to original sources
PubMed1992

Physical aspects of the EEG in schizophrenics.

Physical and dynamic aspects of the electroencephalogram (EEG) were evaluated in 12 schizophrenic patients and 12 matched healthy control subjects by means of two descriptive measures proposed by Hjorth (complexity and mobility) and by a nonlinear measure, dimensional complexity. These measures were compared to power spectra analyses. EEG was recorded from frontal, central, and parietal leads under resting conditions (eyes open and eyes closed) for 12 epochs each of 25 sec. Patients showed the expected increased activity in the 1-7 Hz band and, furthermore, a scalp distribution of dimensional complexity and Hjorth complexity opposite to the distribution in controls: in patients dimensional complexity yielded higher values at frontal (Fz) than central (Cz) leads, whereas the resemblance to sinusoidal waveshape (Hjorth complexity) was larger at Fz than Cz. Results indicate more dynamic complexity or variables determining the dynamics of brain processes in frontal areas in patients.

Adult↗
PubMed1992

Eyeblinks evoke potentials in the occipital brain region.

The subjects performed voluntary eyeblinks under illuminated and dark laboratory conditions. 32-channel EEG recordings were averaged in relation to the eyeblinks and a brain electric source analysis (BESA) was performed. Two dipoles located near the eyeballs and a third dipole in the occipital region of the brain were found to explain the scalp potentials. The frontally located potentials described electromechanical potentials associated with lid movements and simultaneous eye movements. The occipitally located dipole explained a visually evoked potential with a first peak at about 180 ms after the maximum of the frontal blink potential. The visually evoked potential was observed only under illumination and was probably caused by changes in luminance during the eyeblinks.

Adult↗
PubMed1992

Rapid assembly and disassembly of complementary DNA strands through an equilibrium intermediate state mediated by A1 hnRNP protein.

A1 hnRNP protein, which rapidly renatures complementary strands of nucleic acids in vitro, affects both the equilibrium and kinetic properties of the reaction (single-stranded DNA in equilibrium with double-stranded DNA). A1 lowers the melting transition of duplex DNA. However, at temperatures above this new Tm, both single- and double-stranded DNAs are present at equilibrium and are rapidly interconverting. Although the ratio of single and double strands under these conditions is a function of both the A1 protein and complementary DNA strand concentrations, it is not strongly affected by further increases in temperature. These surprising results demonstrate that A1 does not act as a simple catalyst in promoting renaturation and indicate how A1 and other proteins could act to speed the turnover of intermediate complexes in important biological processes.

DNA↗
PubMed1992

Methylene dianiline: assessment of exposure and cancer morbidity in power generator workers.

The biaromatic amine 4,4'-methylene dianiline (MDA) is an animal carcinogen, possibly also carcinogenic to humans. In a cohort of 595 power generator workers potentially exposed to MDA in a curing agent of an epoxy system, the overall standardised cancer incidence ratio (SIR) among males (n = 550), however, was only 0.52 [95% confidence interval (CI) 0.16-1.21] based on five observed cases. One male urinary bladder cancer case was found in comparison to 0.6 expected (SIR 1.67; 95% CI 0.04-9.31). This case was identified in an unexposed subcohort. High levels of MDA metabolites were ascertained in the urine of currently exposed workers, probably following percutaneous absorption. Although no evidence of an increased overall or bladder cancer risk was detected, the limitations of the study in regard to the size of the cohort, age and cancer latency preclude a definite risk assessment. The dermal absorption of MDA has been highlighted.

Aniline Compounds↗
PubMed1992

Homologous recombination of copackaged retrovirus RNAs during reverse transcription.

According to prevailing models, the high frequency of recombination in retroviruses occurs during reverse transcription of two genetically different genomes copackaged into virion particles. This view has been tested in our studies of the mechanism of recombination within homologous sequences of two retroviral genomes during a single round of virus replication and in the absence of helper virus. The recombination substrates were Moloney murine leukemia virus-based vectors, each of which contains an altered defective neomycin gene (neo) under the transcriptional control of the 5' long terminal repeat; the 3' sequences of each construct contain either the Moloney murine leukemia virus or simian virus 40 large-T polyadenylation sequence. One neo gene contained a linker insertion mutation at the 5' end (neo minus), and the other contained a deletion and linker insertion at the 3' end (neo delta 3). Each of the mutant neo constructs was introduced into the packaging helper cell line psi 2 by sequential cotransfection, and individual psi 2 double transformants were selected. Supernatant fluids from the cloned psi 2 double transformants were used to infect NIH 3T3 cells, and recombinant neo+ proviruses were detected by their ability to confer G418 resistance during infection of NIH 3T3 cells. Our results show that (i) recombination between a homologous sequence of about 560 bp occurred with a frequency of about 10(-4) per virus replication cycle; (ii) recombination occurred only after the viral RNAs had been packaged into particles, i.e., recombination between the two vector DNAs or between viral RNAs prior to packaging was not detected; and (iii) copackaging of two different genomic RNAs as a heterodimer is a prerequisite for recombination. Furthermore, our results indicate that recombination can occur during the DNA negative-strand synthesis of reverse transcription.

3T3 Cells↗
PubMed1991

Rapid renaturation of complementary DNA strands mediated by cationic detergents: a role for high-probability binding domains in enhancing the kinetics of molecular assembly processes.

The rate of renaturation for complementary DNA strands can be enhanced greater than 10(4)-fold by the addition of simple cationic detergents, and the reaction is qualitatively and quantitatively very similar to that found with purified heterogeneous nuclear ribonucleoprotein A1 protein. Under optimal conditions, renaturation rates are greater than 2000-fold faster than reactions run in 1 M NaCl at 68 degrees C. The reaction is second-order with respect to DNA concentration, and reaction rates approach or equal the rate with which complementary strands are expected to encounter each other in solution. Renaturation can even be observed well above the expected melting temperature of the duplex DNA, demonstrating that some cationic detergents have DNA double-helix-stabilizing properties. The reaction is also extremely rapid in the presence of up to a 10(6)-fold excess of noncomplementary sequences, establishing that renaturation is specific and relatively independent of heterologous DNA. This finding also implies that up to several thousand potential target sequences can be sampled per strand per second. Such reagents may be useful for procedures that require rapid nucleic acid renaturation, and these results suggest ways to identify and design other compounds that increase the kinetics of association reactions. Moreover, this work provides further support for a model relating the existence of flexible, weakly interacting, repeating domains to their function in rapid molecular assembly processes in vitro and in vivo.

Cations↗
PubMed1991

Expression of the type 1 human immunodeficiency virus Nef protein in T cells prevents antigen receptor-mediated induction of interleukin 2 mRNA.

Stable transformants of the Jurkat T-cell line have been obtained that express either of two distinct forms of the type 1 human immunodeficiency virus nef gene: the nef-1-encoded protein (Nef-1) contains alanine, glycine, and valine at positions 15, 29, and 33, respectively; the protein specified by nef-2 (Nef-2) has threonine, arginine, and alanine at the corresponding positions. When Jurkat cells or their Nef-2-expressing transformants are treated with phorbol 12-myristate 13-acetate (PMA) plus either phytohemagglutinin (PHA) or antibodies against CD3 epsilon, T-cell receptor beta chain, or CD2, there is a prompt increase in interleukin 2 (IL-2) mRNA and intracellular calcium and in the IL-2 receptor alpha chain on the cell surface. Although cells expressing Nef-1 also induce calcium mobilization and the production of IL-2 receptor alpha chain, the formation of IL-2 mRNA is blocked in response to these stimuli. Moreover, Nef-1-expressing cells transfected with a plasmid in which the IL-2 promoter is fused to the chloramphenicol acetyltransferase (CAT) gene fail to induce CAT following treatment with PMA and PHA. By contrast, the parental and Nef-2-containing cells induce CAT normally. Nef-1-expressing cells can produce IL-2 mRNA in response to a combination of PMA and ionomycin, although much less efficiently than the parental Jurkat cells or Nef-2-expressing cells. These findings, and others described herein, suggest that the virally encoded Nef protein interferes with a signal emanating from the T-cell receptor complex that induces IL-2 gene transcription.

Chloramphenicol O-Acetyltransferase↗
PubMed1991

Use of prior knowledge in brain electromagnetic source analysis.

Using multichannel measurements of EEG and/or MEG, macroscopic source activities can be estimated in the human brain using brain electric source analysis (BESA, Scherg 1990). If a discrete number of brain areas is active, functional brain images which depict the locations and orientations of equivalent dipole sources as well as the dynamics of the local macroscopic currents can be obtained from such data--in principle--without external knowledge. However, given a certain number of sources or 'neural masses' (Freeman 1975) which contribute to an event related response (ERP), it can be difficult to find the correct solution due to background noise in the data and distortions from the head model. Prior knowledge based on anatomy and physiology can be useful to constrain spatial or temporal parameters of the model and to define better cost functions for fitting locations and orientations. An analysis of the auditory evoked N100 complex and of the auditory mismatch negativity (MMN) is presented which illustrates the use of spatial constraints. Also, the use of a modified cost function is demonstrated which limits source currents in certain time intervals.

Brain↗
PubMed1991

Long-term results of thrombectomy for late occlusions of aortofemoral bypass.

Sixty-two first episodes of aortofemoral (eight patients) or aortobifemoral (42 patients) bypass thrombosis were operated upon in 50 patients between 1980 and 1985. There were 47 men and three women whose mean age was 58 years. Retrograde thrombectomy through the distal anastomosis was achieved in all cases by using either a balloon catheter or Vollmar rings. If thrombectomy was impossible, revascularization was ensured by an extraanatomic bypass or complete replacement of the graft. Angioplasty, repeat distal anastomosis or femoropopliteal bypass of the native runoff artery were done in 55 (89%) operations. The cause of thrombosis was elucidated in 45 cases. Suture line stenosis and atheromatous stenosis of the native runoff artery were the two most common causes. Three patients died and two required above-knee amputation in the immediate postoperative period. Contralateral embolism occurred in two patients undergoing retrograde thrombectomy. Mean follow-up was 47 months. Thrombectomy was possible in 51 or 62 prosthetic thromboses (Group I). Thirty-nine of these grafts have remained patent. Twelve instances of repeat thrombosis occurred, requiring either repeat thrombectomy or a new bypass. Primary patency in group I was 97.8%, 81.2%, and 71.3% at one, three, and five years, respectively. Thrombectomy was impossible in 11 graft thromboses (Group II). A new bypass was performed in all 11 cases. Primary patency in Group II was 100%, 75% and 50% at one, three, and five years, respectively. Retrograde thrombectomy combined with treatment of native runoff artery anomalies can restore long-term patency when thrombosis occurs late after aortofemoral bypass and is associated with low mortality and morbidity.

Adult↗
PubMed1991

Dipole models of eye movements and blinks.

Average EOGs were recorded from 4 subjects for vertical and horizontal eye movements of 15 degrees away from and back to a central fixation point, and for eyeblinks while looking at the fixation point. Using spatio-temporal dipole modelling, several alternative dipole models of the electrical activity of the eyes were compared. A reasonable fit was only obtained if the equivalent dipoles were allowed to take up different locations and orientations depending on the type of eye activity. It appears that (a) the equivalent ocular dipole is located away from the axis of rotation of the eyeball, (b) eyelid movements contribute to a change in location of the dipole in vertical eye movements and blinks, and (c) some of the apparent dipole movement is due to inadequacy of the 3-shell spherical head model near to the eyes. Consequences of the results for eye-artifact correction are discussed.

Adult↗
PubMed1991

Slow cortical potentials (SCPS) in schizophrenic patients during performance of the Wisconsin card-sorting test (WCST).

Fifteen schizophrenic patients (diagnosed according to DSM-III-R) and 15 age- and education-matched controls were tested on a computerized version of the Wisconsin card-sorting test (WCST). Slow Cortical Potentials (SCPs) were recorded throughout the performance from frontal, central and parietal electrode sites. As expected, the patients were impaired on the WCST, achieving fewer categories overall and incurring significantly more "unique" errors, although they were not significantly more perseverative than the controls. The patients did not display a generalized impairment in SCPs, differences between the groups emerging only before presentation of the key-cards and after presentation of the feedback regarding the correctness of the response. Neither the choice-card at the beginning of the trial, nor the presentation of the key-cards resulted in attenuated Evoked Potentials (EPs) in the patients. The lack of any abnormality in EPs suggests that the reason for the poor performances of schizophrenic patients on the WCST lies elsewhere than in perceptual stimulus processing. Contrary to expectations no specific impairment in frontal SCPs was detected.

Adult↗
PubMed1991

[Significance of autoimmunity in various forms of uveitis].

Autoimmune diseases are the result of a false recognition by the immune system of the own tissue as foreign. Suppressor cells serve to inhibit these mechanisms, however, their influence can be bypassed by other cells. Many antigen structures have been isolated in the uvea. With them it is possible to induce a model of autoimmune uveitis. The diagnostic value of eye specific and non-specific autoantibodies in uveitis patients was studied. In this report are show indications of autoimmune phenomena in the following diseases: sympathetic uveitis, Behçet's disease, Vogt-Koyanagi-Harada syndrome and birdshot retinopathy.

Animals↗