Chronobiology of sleep in humans

Periodic circadian (24-h) cycles play an important role in daily hormonal and behavioural rhythms. Usually our sleep/wake cycle, temperature and melatonin rhythms are internally synchronized with a stable phase relationship. When there is a desynchrony between the sleep/wake cycle and circadian rhythm, sleep disorders such as advanced and delayed sleep phase syndrome can arise as well as transient chronobiologic disturbances, for example from jet lag and shift work. Appropriately timed bright light is effective in re-timing the circadian rhythm and sleep pattern to a more desired time, ameliorating these disturbances. Other less potent retiming effects may also be obtained from the judicious use of melatonin and exercise.     

A dynamic early East Antarctic Ice Sheet suggested by ice-covered fjord landscapes

The first Cenozoic ice sheets initiated in Antarctica from the Gamburtsev Subglacial Mountains and other highlands as a result of rapid global cooling ～34 million years ago. In the subsequent 20 million years, at a time of declining atmospheric carbon dioxide concentrations and an evolving Antarctic circumpolar current, sedimentary sequence interpretation and numerical modelling suggest that cyclical periods of ice-sheet expansion to the continental margin, followed by retreat to the subglacial highlands, occurred up to thirty times. These fluctuations were paced by orbital changes and were a major influence on global sea levels. Ice-sheet models show that the nature of such oscillations is critically dependent on the pattern and extent of Antarctic topographic lowlands. Here we show that the basal topography of the Aurora Subglacial Basin of East Antarctica, at present overlain by 2-4.5?km of ice, is characterized by a series of well-defined topographic channels within a mountain block landscape. The identification of this fjord landscape, based on new data from ice-penetrating radar, provides an improved understanding of the topography of the Aurora Subglacial Basin and its surroundings, and reveals a complex surface sculpted by a succession of ice-sheet configurations substantially different from today's. At different stages during its fluctuations, the edge of the East Antarctic Ice Sheet lay pinned along the margins of the Aurora Subglacial Basin, the upland boundaries of which are currently above sea level and the deepest parts of which are more than 1?km below sea level. Although the timing of the channel incision remains uncertain, our results suggest that the fjord landscape was carved by at least two iceflow regimes of different scales and directions, each of which would have over-deepened existing topographic depressions, reversing valley floor slopes.     

Two ten-billion-solar-mass black holes at the centres of giant elliptical galaxies

Observational work conducted over the past few decades indicates that all massive galaxies have supermassive black holes at their centres. Although the luminosities and brightness fluctuations of quasars in the early Universe suggest that some were powered by black holes with masses greater than 10 billion solar masses, the remnants of these objects have not been found in the nearby Universe. The giant elliptical galaxy Messier 87 hosts the hitherto most massive known black hole, which has a mass of 6.3 billion solar masses. Here we report that NGC 3842, the brightest galaxy in a cluster at a distance from Earth of 98 megaparsecs, has a central black hole with a mass of 9.7 billion solar masses, and that a black hole of comparable or greater mass is present in NGC 4889, the brightest galaxy in the Coma cluster (at a distance of 103 megaparsecs). These two black holes are significantly more massive than predicted by linearly extrapolating the widely used correlations between black-hole mass and the stellar velocity dispersion or bulge luminosity of the host galaxy. Although these correlations remain useful for predicting black-hole masses in less massive elliptical galaxies, our measurements suggest that different evolutionary processes influence the growth of the largest galaxies and their black holes.     

Fresnel's laws,ceteris paribus

This article is about structural realism, historical continuity, laws of nature, and ceteris paribus clauses. Fresnel's Laws of optics support Structural Realism because they are a scientific structure that has survived theory change. However, the history of Fresnel's Laws which has been depicted in debates over realism since the 1980s is badly distorted. Specifically, claims that J. C. Maxwell or his followers believed in an ontologically-subsistent electromagnetic field, and gave up the aether, before Einstein's annus mirabilis in 1905 are indefensible. Related claims that Maxwell himself did not believe in a luminiferous aether are also indefensible. This paper corrects the record. In order to trace Fresnel's Laws across significant ontological changes, they must be followed past Einstein into modern physics and nonlinear optics. I develop the philosophical implications of a more accurate history, and analyze Fresnel's Laws' historical trajectory in terms of dynamic ceteris paribus clauses. Structuralists have not embraced ceteris paribus laws, but they continue to point to Fresnel's Laws to resist anti-realist arguments from theory change. Fresnel's Laws fit the standard definition of a ceteris paribus law as a law applicable only in particular circumstances. Realists who appeal to the historical continuity of Fresnel's Laws to combat anti-realists must incorporate ceteris paribus laws into their metaphysics.     

Glioma cell activation by Alzheimer's peptide Abeta1-42, alpha1-antichymotrypsin,and their mixture

We compared the effects ofAlzheimer's peptide (Abeta1-42), a,-antichymotrypsin (ACT) and an ACT/Abeta1-42 mixture on human glioma DK-MG cells. The solution of Abeta (5 microM) formed by 2-h incubation at room temperature induced tumour necrosis factor-alpha (TNF-alpha) and interleukin (IL)-6 levels by 55 and 45%, respectively, and increased gelatinase B activity by 67%, while exposure of cells to the ACT/Abeta1-42 mixture (1:10 molar ratio ACT: Abeta1-42) under the same experimental conditions showed no effect on IL-6 levels or gelatinase B activity, but strongly induced TNF-alpha (by 190%), compared to the controls. Stimulation of the cells with Abeta1-42 alone, but not with ACT, increased by about 20% low-density lipoprotein (LDL) uptake and mRNA levels for LDL receptor and HMG-CoA reductase, while the ACT/Abeta1-42 mixture significantly increased LDL uptake (by 50%), up-regulated mRNA levels for LDL receptor and HMG-CoA reductase by 48 and 63%, respectively, and increased lipid accumulation by about 20-fold. These data suggest a possible new role for Abeta in Alzheimer's disease through its interaction with the inflammatory reactant, ACT.     

Glucose/galactose malabsorption caused by a defect in the Na+/glucose cotransporter

Glucose/galactose malabsorption (GGM) is an autosomal recessive disease manifesting within the first weeks of life and characterized by a selective failure to absorb dietary glucose and galactose from the intestine. The consequent severe diarrhoea and dehydration are usually fatal unless these sugars are eliminated from the diet. Intestinal biopsies of GGM patients have revealed a specific defect in Na(+)-dependent absorption of glucose in the brush border. Normal glucose absorption is mediated by the Na+/glucose cotransporter in the brush border membrane of the intestinal epithelium. Cellular influx is driven by the transmembrane Na+ electrochemical potential gradient; thereafter the sugar moves to the blood across the basolateral membrane via the facilitated glucose carrier. We have previously cloned and sequenced a Na+/glucose cotransporter from normal human ileum and shown that this gene, SGLT1, resides on the distal q arm of chromosome 22. We have now amplified SGLT1 complementary DNA and genomic DNA from members of a family affected with GGM by the polymerase chain reaction. Sequence analysis of the amplified products has revealed a single missense mutation in SGLT1 which cosegregates with the GGM phenotype and results in a complete loss of Na(+)-dependent glucose transport in Xenopus oocytes injected with this complementary RNA.     

Respiratory function of blood and relative weight of certain organs in two species of shrew: Crocidura russula and Suncus etruscus (Soricidae mammals)]

A high oxygen capacity combined with a low oxygen affinity and a large Bohr effect achieve a high oxygen transport capacity in small shrews. The high metabolic rate (Suncus estruscus: 100 to 350 ml O2/kg. min) can be explained by the combination of the favorable blood parameters with a high relative heart weight (1,2% of body weight) and heart frequencies of 1,000 to 1,350 per minute.