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.

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.

A simple stereoscopic endoscope

A very simple method is described for producing and viewing stereoscopic endoscopic images. The addition of two simple prisms to the end of a conventional television-monitored endoscope with a simple viewing device produces a stereoscopic endoscope which appears to be suitable for surgical use.

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.

The scimitar syndrome: demonstration with magnetic resonance imaging

The authors describe a case of scimitar syndrome, which is a rare congenital lung abnormality characterized by partially anomalous pulmonary venous return. MRI findings as well as other methods of diagnosis are discussed.

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.

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.

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.

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.

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.

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.

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 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.

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.