Evidence for fractal correlation properties in variations of peripheral arterial tone during REM sleep

Previous studies utilizing detrended fluctuation analysis (DFA) of heart rate variability during sleep revealed a higher fractal exponent during rapid eye movement (REM) sleep than non-REM sleep. The aim of this study was to determine whether the same difference exists in the variations of peripheral arterial tone (PAT). Finger pulse wave measured by a novel plethysmographic technique was monitored during sleep in 12 chronic heart failure patients, 8 heavy snorers, and 12 healthy volunteers. For each subject, at least two 15-min time series were constructed from the interpulse intervals and from pulse wave amplitudes during REM and non-REM sleep. Fractal scaling exponents of both types of time series were significantly higher for REM than non-REM sleep in all groups. In each of the groups and in both sleep stages, the fractal scaling exponents based on pulse wave amplitude were significantly higher than those based on pulse rate variability. A repeat of the analysis for short-, intermediate-, and long-term intervals revealed that the fractal-like exponents were evident only in the short- and intermediate-term intervals. Because PAT is a surrogate of sympathetic activation, our results indicate that variations in sympathetic activation during REM sleep have a fractal-like behavior.     

Handling long targets and errors in sequencing by hybridization.

Sequencing by hybridization (SBH) is a DNA sequencing technique, in which the sequence is reconstructed using its k-mer content. This content, which is called the spectrum of the sequence, is obtained by hybridization to a universal DNA array. Standard universal arrays contain all k-mers for some fixed k, typically 8 to 10. Currently, in spite of its promise and elegance, SBH is not competitive with standard gel-based sequencing methods. This is due to two main reasons: lack of tools to handle realistic levels of hybridization errors and an inherent limitation on the length of uniquely reconstructible sequence by standard universal arrays. In this paper, we deal with both problems. We introduce a simple polynomial reconstruction algorithm which can be applied to spectra from standard arrays and has provable performance in the presence of both false negative and false positive errors. We also propose a novel design of chips containing universal bases that differs from the one proposed by Preparata et al. (1999). We give a simple algorithm that uses spectra from such chips to reconstruct with high probability random sequences of length lower only by a squared log factor compared to the information theoretic bound. Our algorithm is very robust to errors and has a provable performance even if there are both false negative and false positive errors. Simulations indicate that its sensitivity to errors is also very small in practice.     

The relationship between short-term antibiotic treatments and fatigue in healthy individuals

Antibiotic treatment tends sometimes to result in sensations of fatigue and decreased physical performance. The effects of antibiotics were therefore studied in 50 healthy, male trainees, aged 18–25 years, assigned in a random, double-blind fashion to one of the following treatments: tetracycline, ampicillin, trimethoprim/sulphamethoxazole, placebo I and placebo II. Duration of treatment was five times the half-life of each agent and the placebo was matched accordingly. Muscle enzyme activity (serum glutamine oxaloacetate transaminase, lactate dehydrogenase, creatine phosphokinase), maximal aerobic capacity ( O_2max), muscle strength (MS), and rating of subjective sensation of fatigue were assessed prior to and upon conclusion of treatment. Compared to pretreatment values, plasma enzymes activity was elevated in all five groups (P<0.005). No differences in O_2max or in MS were found among the subjects treated with either one of the antibiotics or those given a placebo. A significant difference in O_2max was found between the groups treated for 1 day (antibiotic and placebo) and the groups treated for 3 days (antibiotic and placebo) (P<0.0001). The rating of subjective sensation was not affected by any of the agents. We concluded that in healthy individuals, a short-term antibiotic treatment had no deleterious effect on aerobic capacity or on muscle strength and was not associated with subjective side effects. The time interval between the two maximal tests could, however, have affected the aerobic capacity. Physiological disturbances associated with a sensation of fatigue following a longer period of antibiotics cannot be excluded.     

Modification of subtelomeric DNA

There is a discrepancy in telomere length as measured by signal intensity of telomere restriction fragments on gels and fluorescence in situ hybridization analysis. This difference has been ascribed to the X-region, a segment of subtelomeric DNA that is resistant to being cut by restriction enzymes. To explore the nature of this region, we analyzed the digestibility of an artificial seeded telomere in HeLa cells as well as the Xp/Yp autosomal telomere in human BJ fibroblasts. We found that there is a substantial fraction of subtelomeric DNA containing restriction sites that is not digested with enzymes such as EcoRI, NlaIII, and SphI. Comparison of methylation-sensitive and -resistant enzymes excluded the possibility of the X-region being maintained by DNA methylation. We show that the X-region represents a variable domain whose size changes with telomere length, and neither non-TTAGGG sequences nor cytidine methylation can adequately explain the size of the X-region.     

The La antigen associates with the human telomerase ribonucleoprotein and influences telomere length in vivo

La is an important component of ribonucleoprotein complexes and telomerase is a ribonucleoprotein that compensates for the shortening of the ends of linear DNA by adding telomeric repeats onto the ends of chromosomes by using an integral RNA as the template. We have identified a direct and specific interaction between La and the RNA component of human telomerase. Antibodies specific to La precipitate the human telomerase ribonucleoprotein complex derived from tumor cells, telomerase immortalized normal cells, and in vitro transformed cells. Overexpression of La in both experimentally immortalized human cells and prostate cancer cells results in gradual telomere shortening. Our results demonstrate that La can associate with telomerase and its expression level can influence telomere homeostasis in vivo.     

Zinc deficiency reduces leptin gene expression and leptin secretion in rat adipocytes

The present study was conducted to measure ob mRNA abundance in the zinc-deficient (ZD) rats and the secretion of leptin from adipose tissue obtained from ZD, zinc-adequate (ZA), and pair-fed (PF) rats. It was found that ob mRNA abundance was greatest (P < 0.05) in adipose tissue obtained from ZA and PF rats. Ob mRNA abundance was similar in PF and ZD rats. To study leptin secretion from adipose tissue in a cell culture model, a method was developed to use excised epididymal adipose tissue from ZD, ZA, and PF rats. Tissue was incubated in Opti-modified Eagle's medium (MEM) cell culture medium in which concentrations of zinc and insulin were manipulated. It was observed that leptin secretion was higher (P < 0.05) in adipose tissue obtained from ZA than ZD and PF rats. Secretion of leptin was higher in adipose tissue of PF than ZD rats (P < 0.05). Surprisingly, media zinc content in this ex vivo model tended to suppress secretion of leptin. This suppression seems to be zinc specific and might be caused by the sequestration of insulin in the culture medium. Our results indicate that the reduction in serum leptin observed in ZD rats is likely caused by not only a reduction in body fat, but also by a decrease in leptin synthesis and secretion per gram of adipose tissue. Taking these results into account along with a prior study (1), it is possible that even a marginal zinc deficiency could affect leptin secretion and serum leptin concentrations. Impaired leptin secretion caused by zinc deficiency might be one factor contributing to hypogonadism observed in zinc deficiency.