Absence of daytime 50 Hz, 100 microT(rms) magnetic field or bright light exposure effect on human performance and psychophysiological parameters

The purpose of this study was to reproduce and extend two earlier studies of the effects of human exposure to 50 Hz magnetic fields (MF). In a recent paper, we described results of two double-blind investigations performed to examine effects of 100 microT(rms) 50 Hz MF exposure on psychological parameters in the same group of healthy human volunteers. In each exposure session, at 1 week intervals, with sham, continuous, and intermittent (15 s ON/OFF cycles) MF conditions, mood ratings, performance measures, and electrophysiological measures were taken. In the first study, significant amplitude changes were observed in the event-related brain potentials (ERP) recorded during a dichotic listening task. In the second study, latency and reaction time (RT) slowing were seen on a visual discrimination task (P(300) paradigm). Although these results were little related to the number of parameters analysed, they indicate that low level 50 Hz MF might have a slight influence on ERP and RT under specific circumstances of sustained attention. Before concluding that moderately strong MF exposure can influence cognitive function, previous results should be replicated, using the same paradigms with another group of healthy volunteers. In the present study, 18 healthy subjects were exposed to three experimental sessions of 30 min each, given at 1 week intervals. The sessions consisted of continuous 100 microT(rms) 50 Hz MF exposure, sham condition, and bright light (5000 lux) exposure. The study was performed double-blind, with the exposure order counter-balanced. The data on mood, ERP, RT, and other performance measures did not show any differences among the sham exposure, light exposure, and MF exposure conditions. The results of this study do not support the hypothesis that extremely low frequency (ELF) MF exposure affects the brain's electrical activity or cognitive function at field strength (100 microT(rms)) similar to that found in very close proximity of some household and industrial electrical appliances and well in excess of the average MF strength (c. 0.1 microT) found in homes. The sensitivity of the experiment was possibly not sufficient to detect an effect at this relatively low MF, and larger sample sizes would be required in further studies.     

Effect of hypobaric air, oxygen, heliox (50:50), or heliox (80:20) breathing on air bubbles in adipose tissue.

The fate of bubbles formed in tissues during decompression to altitude after diving or due to accidental loss of cabin pressure during flight has only been indirectly inferred from theoretical modeling and clinical observations with noninvasive bubble-measuring techniques of intravascular bubbles. In this report we visually followed the in vivo resolution of micro-air bubbles injected into adipose tissue of anesthetized rats decompressed from 101.3 kPa to and held at 71 kPa corresponding to approximately 2.750 m above sea level, while the rats breathed air, oxygen, heliox (50:50), or heliox (80:20). During air breathing, bubbles initially grew for 30-80 min, after which they remained stable or began to shrink slowly. Oxygen breathing caused an initial growth of all bubbles for 15-85 min, after which they shrank until they disappeared from view. Bubble growth was significantly greater during breathing of oxygen compared with air and heliox breathing mixtures. During heliox (50:50) breathing, bubbles initially grew for 5-30 min, from which point they shrank until they disappeared from view. After a shift to heliox (80:20) breathing, some bubbles grew slightly for 20-30 min, then shrank until they disappeared from view. Bubble disappearance was significantly faster during breathing of oxygen and heliox mixtures compared with air. In conclusion, the present results show that oxygen breathing at 71 kPa promotes bubble growth in lipid tissue, and it is possible that breathing of heliox may be beneficial in treating decompression sickness during flight.     

Studies on poly(L-lysine50, L-tyrosine50)-DNA interaction

Interaction between poly(Lys⁵⁰, Tyr⁵⁰) and DNA has been studied by absorption, circular dichroism (CD), and fluorescence spectroscopy and thermal denaturation in 0.001M Tris, pH 6.8. The binding of this copolypeptide to DNA results in an absorbance enhancement and fluorescence quenching on tyrosine. There is also an increase in the tyrosine CD at 230 nm. The CD of DNA above 250 nm is slightly shifted to the longer wavelength which is qualitatively similar to, but quantitatively much smaller than, that induced by polylysine binding. At physiological pH the poly(Lys⁵⁰, Tyr⁵⁰)–DNA complex is soluble until there is one lysine and one tyrosine per nucleotide in the complex. The same ratio of amino acid residues to nucleotide has also been observed in copolypeptide-bound regions of the complex. The addition of more poly(Lys⁵⁰, Tyr⁵⁰) to DNA yields a constant melting temperature, T_m′, for bound base pairs at 90°C which is close to that of polylysine-bound DNA under the same condition. The melting temperature, T_m, of free base pairs at about 60°C on the other hand, is increased by 10°C as more copolypeptide is bound to DNA. As the temperature is raised, both absorption and CD spectra of the complexes with high coverage are changed, suggesting structural alteration, perhaps deprotonation, on bound tyrosine. The results in this report also suggest that intercalation of tyrosine in DNA is unlikely to be the mode of binding.