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W Simon

Publications and source records attributed to W Simon.

At least 19 recordsLinked to original sources
PubMed2001

Isoflurane blocks synaptic plasticity in the mouse hippocampus.

BACKGROUND: The volatile anesthetic isoflurane depresses glutamatergic transmission. In this study, the authors investigated the effects of isoflurane on the induction of long-term potentiation (LTP) and long-term depression (LTD) in slices from the juvenile and adult mouse hippocampus. Both forms of synaptic plasticity involve the activation of glutamate receptors. METHODS: Field excitatory postsynaptic potentials and excitatory postsynaptic currents from neurons in the CA1 area were evoked by stimulation of the Schaffer collateral-commissural pathway. Two independent synaptic inputs were stimulated. Clinically relevant concentrations (0.2-0.3 mM) of isoflurane were added to the perfusion solution. RESULTS: Field excitatory postsynaptic potentials from slices of juvenile and adult mice were depressed to 37.3 +/- 6.1% and 58.3 +/- 7.4%, respectively, and excitatory postsynaptic currents were reduced to 36.7 +/- 5.4% by isoflurane. A brief tetanic stimulation (100 Hz, 1 s) induced stable LTP of field excitatory postsynaptic potentials. In the presence of isoflurane, tetanization failed to induce LTP. The effect of isoflurane on LTP induction was reversible and could be prevented by antagonizing gamma-aminobutyric acid type A receptors (GABAA). Low-frequency stimulation (1 Hz/900 pulses) induced LTD. In the presence of isoflurane, low-frequency stimulation failed to induce LTD. CONCLUSIONS: The prevention of the isoflurane-induced depression of LTP by the GABAA antagonist picrotoxin suggests an involvement of GABAA receptors. An enhancement of the efficacy of GABA-mediated inhibitory synaptic transmission prevents the depolarization of the postsynaptic membrane during tetanus, necessary for the induction of use-dependent alteration of synaptic strength. An impairment of these processes may be a cause for the transient loss of recall and cognitive impairment after anesthesia in juvenile and adult brains.

Aging↗
PubMed1999

Neurons may live for decades with neurofibrillary tangles.

Neurons containing neurofibrillary tangles (NFT) are one of the pathological hallmarks of Alzheimer disease (AD). It is known that this population of neurons express gene products and thus function to some degree, but it is unknown how long these neurons may survive with NFT. It is also thought that the formation of NFT results in the death of neurons. Using quantitative data on neuron loss and NFT formation as a function of disease duration, we have generated a computer program that models both the degeneration of CA1 hippocampal neurons and the formation of NFT in these neurons in AD. Modeling various neuron survival times with NFT and altering selected assumptions upon which the models are based, we arrive at the conclusions that 1) CA1 hippocampal neurons survive with NFT for about 20 years, and 2) NFT may not be obligatory for death of CA1 hippocampal neurons in AD.

Aged↗
PubMed1997

Recombinant antibody fragments that detect enoyl acyl carrier protein reductase in Brassica napus.

Purified Brassica napus enoyl acyl carrier protein reductase (ENR) was used to select specific antibodies from a library of antibody fragments, single-chain Fv (scFv), displayed on filamentous phage. Analysis of the selected clones by BstNI fingerprinting and nucleotide sequencing showed that the scFv were derived from three different human VH germline genes. The binding specificities were confirmed by Western blots and ELISA. The scFv preparations reacted with B. napus ENR, but not with beta-keto reductase, nor enoyl reductase from Escherichia coli. Analysis of fragments generated by CNBr treatment indicates that the scFv 3.13 recognized an epitope located within the N-terminal 80 amino acids of the enzyme molecule. The scFv were used to detect ENR directly in extracts of B. napus seeds.

Acyl Carrier Protein↗
PubMed1995

[Not Available].

Explore the source record for details and available documents.

History, 16th Century↗
PubMed1994

Deviance as history: the future of perversion.

An approach to the social construction of concepts of sexual deviance and sexual perversions is considered. Deviance is conceptualized as a problem of control, perversion a problem of desire. These are seen as related to the larger sexual and nonsexual discursive practices of society and given to change as these contextualizing practices change. Changing conceptions regarding masturbation, homosexuality, pedophilia, and sadomasochism are examined.

Female↗
PubMed1994

The influence of life table corrections for smokers and nonsmokers on the health effects of radon using the BEIR (biological effects of ioniziing radiation) IV method.

The BEIR IV report gives graphs and tables that are used to estimate the risks due to radon (222Rn) and its decay products. The BEIR IV hypothesis predicts that the lifetime risks will depend upon the "normal" incidence of fatal lung cancers for nonsmokers and smokers and the life expectancies of both groups. This paper examines the influence of recent information on these health risks. The factors considered are a) the life tables for both sexes and for those who never smoked, formerly smoked, are currently light smokers, or are currently heavy smokers, and b) the age-dependent fatal lung cancer rates for the same groups of people. In general, the calculations indicate that people who have never smoked would have the same risks as those listed in the BEIR IV report as nonsmokers. For males, those who smoke or formerly smoked would have calculated risks that are greater than people who never smoked; however, for males, the smokers and former smokers considered in this paper have lower calculated risks than the BEIR IV smokers. For females, the heavy smokers examined here would have greater calculated risks than the BEIR IV smokers. The reasons for these differences are presented.

Female↗
PubMed1993

Novel magnesium ion-selective microelectrodes based on a neutral carrier.

Two types of Mg(2+)-selective microelectrodes based on a synthetic neutral carrier and containing poly-(vinyl chloride) (PVC) are described. The first is applicable to intracellular Mg2+ assays and suffers no interference from alkali and all other alkaline-earth metal cations. The second can be used for determining intra- as well as extracellular Mg2+ activities, but Ca2+ and especially lipophilic cations (e.g. acetylcholine) may interfere. Cyclohexanone is used for dissolving the PVC-containing membrane phases thus avoiding problems encountered with the much more volatile tetrahydrofuran. The procedure gives a higher output of working microelectrodes and can also be applied with other membrane phases.

Calcium↗
PubMed1993

Effect of debt level on the residency preferences of graduating medical students.

BACKGROUND: The increased educational indebtedness of graduating medical students has led to speculation about the effects of students' debt levels on their choices of practice specialties as evidenced by their residency preferences. METHOD: Information was analyzed for 1,658 medical students who graduated from six private medical schools in 1988, 1989, and 1990; 1,431 of these students had educational debts. Chi-square analysis was used to compare the 1,431 students' average levels of indebtedness with their selections of residencies leading to specialties with higher or lower potential incomes. For this analysis, the students were grouped into four clusters based on the potential incomes of their specialty preferences. In addition, various subgroups, i.e., men, women, need-based scholarship recipients, and underrepresented-minority students, were also studied. RESULTS: For all the students, there was no relationship among their average levels of indebtedness and their specialty preferences. Similar results were obtained for all the subgroups--men, women, underrepresented-minority students, and scholarship recipients. However, the women students tended to have higher levels of indebtedness than the men. CONCLUSION: The results do not support the hypothesis that debt level is a determining factor among the variables that influence choices of residency by graduating medical students.

Career Choice↗
PubMed1993

Determining person-years of life lost using the BEIR V method.

A method is given that permits the calculation of the estimated person-years of life lost when groups of males or females are exposed to low linear energy transfer (LET) ionizing radiation. It is felt that this determination is informative in rating risks to populations from radiation exposures. For example, when 1,000,000 females have received an acute 10 mSv, the total number of radiation-induced fatal cancers is 835. The total number of person-years of life lost is 1.4 x 10(4) or an average of about 5 d. However, the 22 who die of leukemia suffer an average of about 34 y. Those who die of other forms of cancer lose an average of 16 y. Some examples have been reported by the U.S. National Academy of Sciences (1990) report. In those cases where the Committee presented results, the method given here is in good agreement.

Age Factors↗
PubMed1993

Characterization procedure for ion-selective electrode assays of magnesium activity in aqueous solutions of physiological composition.

A magnesium ion-selective liquid membrane electrode based on a synthetic neutral carrier is presented. The selectivity for Mg2+ over Na+, K+, and H+ is sufficient for assays in the physiological range, but a chemometric correction of approximately 10% is still necessary for the Ca2+ interference. We optimized the membrane composition especially with respect to selectivity and accuracy by performing a new characterization procedure in which we simulated the variety of blood serum samples with 10 aqueous solutions. After a three-point calibration, these solutions were measured alternately with the middlerange calibrator for 3 min. The magnesium activity was evaluated after correcting for the calcium interference according to the Nikolsky equation. The selectivity coefficient, KpotMgCa, was itself fitted to give the minimum deviations from the assigned magnesium activities. Electrodes with an optimized membrane composition show an average deviation from theoretical activity values of about 1.6% with logKpotMgCa = -0.8.

Calcium↗
PubMed1992

Age related rejoining of broken chromosomes in human leukocytes following X-irradiation.

One theory of aging is that the ability to repair DNA or chromosome damage decreases with age. This study made use of a method which allows the measurement of chromatid repair in interphase nuclei, the technique of premature chromosome condensation. The number of excess chromosome fragments per cell remaining after 24 h of incubation at 37 degrees C was determined and used as a measure of the ability of leukocytes to repair. The leukocytes from male donors of several ages were used and the cells from older donors showed greater residual damage and, therefore, less repair.

Adolescent↗
PubMed1992

Growth fraction in breast carcinoma determined by Ki-67 immunostaining: correlation with pathological and clinical variables.

The growth fractions (GF) of 151 mammary carcinomas were determined in situ by Ki-67 immunoperoxidase staining. A mean value of 14.6% Ki-67-positive tumor cells, with a standard deviation of 11.1, was found. Tumors of histological grades 1 and 2 had a mean GF of 13.1% which was significantly lower (p less than 0.05) than that of grade 3 tumors (mean GF 17.3%). The 14 patients in whom distant metastases appeared after primary staging had a significantly higher (p less than 0.05) GF (21.3%) than the other patients (13.9%). No significant correlation was found between GF and concentration of hormone receptors, lymph node status, tumor size, or patient's age. Our results suggest that immunostaining with Ki-67 could be used as an additional tool to detect breast carcinoma patients with a high risk of developing metastases.

Adenocarcinoma↗
PubMed1991

[Chemical sensors in medical use: ion-selective electrodes, limitations and potentials].

The electrolyte concentrations of potassium and sodium, for example, are routinely analyzed in diluted serum and plasma. In contrast, electrolyte activities are quantified by ISEs directly in undiluted whole blood and plasma and promise to be highly informative. Nevertheless, some drawbacks, such as the interaction between the biological matrix and the ISE surface, limit the accuracy of measurements. A symmetrical measuring arrangement allows one to localize and quantify the known sources of errors. These are minimized by adequate techniques. The membrane composition for sodium selective electrodes is optimized in particular. The interpretation of ISE values as compared to FAES (flame atomic emission spectroscopy) is closely related to the water concentration of the samples. Comparisons between ISE and FAES results obviously allow one to evaluate the water concentration of samples, as is shown by a linear regression plot.

Calibration↗
PubMed1991

Lifetime of neutral-carrier-based liquid membranes in aqueous samples and blood and the lipophilicity of membrane components.

On the basis of previously reported correlations between the lipophilicity of membrane components, their partition coefficient between the membrane and the sample, and the lifetime of corresponding neutral-carrier-based sensors, the lipophilicities of ionophores and plasticizers in analytically relevant ion-selective electrodes, ISFETs, and optodes are analyzed and reported. Equations for the estimation of the lifetimes of liquid membranes in continuous-flow systems are presented, and the experimental determination of the lipophilicity values by thin-layer chromatography (TLC) is described. The required lipophilicities for the lifetimes of liquid membranes over 30 24-h days for different applications in aqueous solutions as well as in blood are presented. A comparison of the experimental results of lifetime measurements with calculated theoretical values is given. The experimental results of the determination of the lipophilicity by TLC are compared with the lipophilicities estimated on the basis of Hansch parameters.

Animals↗
PubMed1991

Improvement of local control by regional hyperthermia combined with systemic chemotherapy (ifosfamide plus etoposide) in advanced sarcomas: updated report on 65 patients.

From July 1986 to 1990, 65 patients with deep-seated, advanced sarcomas (43 soft-tissue sarcomas, 12 Ewing's sarcomas, 7 chondrosarcomas and 3 osteosarcomas) were entered in a protocol involving regional hyperthermia (RHT) combined with systemic ifosfamide and etoposide. RHT was produced by an electromagnetic deep regional heating device (BSD Medical Corporation, Salt Lake City, Utah). Of these patients, 62% (40 patients) had received ifosfamide-containing drug regimens before entering the RHT study, 26% (17 patients) were pretreated by surgery and/or radiation and 12% (8 patients) were treated primarily. A total of 426 RHT treatments (mean 6.6 RHT/patient) were applied predominantly within the pelvic region (82%) bearing relative large tumours (mean volume 500 cm3). For systemic chemotherapy, all patients received ifosfamide (1.5 g/m2, days 1-5), etoposide (100 mg/m2, days 1, 3, 5) and 2-mercaptoethanesulphonic acid (mesna; 300 mg/m2 x 4, days 1-5) with RHT only given on days 1 and 5 in repeated cycles every 4 weeks. Detailed thermal mapping by invasive thermometry was performed in all patients. In 61 patients evaluable for tumour control the overall objective response rate including 9 complete responders (CR), 4 partial responders (PR) and 8 patients with favourable histological response (FHR) was 34% (95% confidence limits, 23%-46%). Following CR, the patients are alive and remain disease-free (mean disease-free survival 15.6 months). Of the patients with PR and FHR, 3 died from metastatic and/or local disease after 4, 17, and 39 months, and 1 patient died from other disease (acute myelocytic leukemia) after 27 months. The other 8 patients remain stable at 29, 25, 17, 11, 10, 8, 7, and 6 months. Twenty-two patients revealed no change and 18 patients showed local tumour progression (PD). Side-effects of RHT were tolerable and there was no indication of enhanced bone marrow toxicity due to the addition of RHT to the systemic chemotherapy. By analysis of temperature parameters, the time-averaged temperatures of all RHT treatments calculated for 20% (T20), 50% (T50) or 90% (T90) of measured tumour sites differed significantly between responders (CR + PR + FHR) and non-responders (PD), respectively (T20, P = 0.001; T50, P = 0.0005; T90, P = 0.0001). the data further support a strong potential for ifosfamide plus etoposide combined with RHT in pretreated patients with advanced sarcomas.

Adolescent↗