Environmental Light Exposure Is Associated with Increased Body Mass in Children

The timing, intensity, and duration of exposure to both artificial and natural light have acute metabolic and physiological effects in mammals. Recent research in human adults suggests exposure to moderate intensity light later in the day is concurrently associated with increased body mass; however, no studies have investigated the effect of light exposure on body mass in young children. We examined objectively measured light exposure and body mass of 48 preschool-aged children at baseline, and measured their body mass again 12 months later. At baseline, moderate intensity light exposure earlier in the day was associated with increased body mass index (BMI). Increased duration of light exposure at baseline predicted increased BMI 12-months later, even after controlling for baseline sleep duration, sleep timing, BMI, and activity. The findings identify that light exposure may be a contributor to the obesogenic environment during early childhood.     

31° South: The physiology of adaptation to arid conditions in a passerine bird

Arid environments provide ideal ground for investigating the mechanisms of adaptive evolution. High temperatures and low water availability are relentless stressors for many endotherms, including birds; yet birds persist in deserts. While physiological adaptation probably involves metabolic phenotypes, the underlying mechanisms (plasticity, genetics) are largely uncharacterized. To explore this, we took an intraspecific approach that focused on a species that is resident over a mesic to arid gradient, the Karoo scrub‐robin (Cercotrichas coryphaeus). Specifically, we integrated environmental (climatic and primary productivity), physiological (metabolic rates: a measure of energy expenditure), genotypic (genetic variation underlying the machinery of energy production) and microbiome (involved in processing food from where energy is retrieved) data, to infer the mechanism of physiological adaptation. We that found the variation in energetic physiology phenotypes and gut microbiome composition are associated with environmental features as well as with variation in genes underlying energy metabolic pathways. Specifically, we identified a small list of candidate adaptive genes, some of them with known ties to relevant physiology phenotypes. Together our results suggest that selective pressures on energetic physiology mediated by genes related to energy homeostasis and possibly microbiota composition may facilitate adaptation to local conditions and provide an explanation to the high avian intraspecific divergence observed in harsh environments.     

Kinetic Parameters of Denitrification in a River Continuum

Kinetic parameters for nitrate reduction in intact sediment cores were investigated by using the acetylene blockage method at five sites along the Swale-Ouse river system in northeastern England, including a highly polluted tributary, R. Wiske. The denitrification rate in sediment containing added nitrate exhibited a Michaelis-Menten-type curve. The concentration of nitrate for half-maximal activity (K_map) by denitrifying bacteria increased on passing downstream from 13.1 to 90.4 μM in the main river, but it was highest (640 μM) in the Wiske. The apparent maximal rate (V_maxap) ranged between 35.8 and 324 μmol of N m⁻² h⁻¹ in the Swale-Ouse (increasing upstream to downstream), but it was highest in the Wiske (1,194 μmol N m⁻² h⁻¹). A study of nitrous oxide (N₂O) production at the same time showed that rates ranged from below the detection limit (0.05 μmol of N₂O-N m⁻² h⁻¹) at the headwater site to 27 μmol of N₂O-N m⁻² h⁻¹ at the downstream site. In the Wiske the rate was up to 570 μmol of N₂O-N m⁻² h⁻¹, accounting for up to 80% of total N gas production.     

Denitrification in river sediments: relationship between process rate and properties of water and sediment

1. A survey was made of denitrification and nitrous oxide (N₂O) production in river sediments at fifty sites in north‐east England during one season in order to investigate the relationship between rates and environmental factors likely to influence these processes. The sites were chosen to represent a wide range of physical and chemical conditions. Denitrification rate and N₂O production were measured within 5 h of sampling using the slurry acetylene blockage technique.
2. Denitrification rate ranged from less than 0.005–260 nmol N g^–1 DW h^–1, tending to increase in a downstream direction. N₂O production ranged from negative values (net consumption) to 13 nmol N₂O‐N g^–1 DW h^–1 and accounted for 0–115% of the N gases produced.
3. Denitrification rate and N₂O concentration in the sediment were correlated positively with nitrate concentration in the water column, water content of the sediment and percentage of fine (< 100 μm) particles in the sediment.
4. The variation in denitrification rate was satisfactorily explained (64% total variance) by a model employing measurements of water nitrate and water content of sediments. No simple or multiple relationship was found for N₂O production.     

Leachate from a Waste Disposal Centre reduces the initiation of arbuscular mycorrhiza,and spread of hyphae in soil

Irrigating arbuscular mycorrhizal plants with leachate from a waste disposal centre was examined in a set of experiments. Application of leachate at half the average concentration found in the field or higher reduced the growth of the host plant, the initiation of mycorrhizal colonisation, and hyphal growth of the mycorrhizal fungus Glomus pellucidum through the soil. Causes of these reductions are complex and interrelated, and associated with the electrical conductivity of the solution, toxicity of specific ions, in particular NH₄ ⁺, NH₃ and HCO₃ ⁻, and changes in the pH causing shifts in the equilibria of the soil solution. This revised version was published online in June 2006 with corrections to the Cover Date.     

Effect of exercise on cerebral perfusion in humans at high altitude.

The effects of submaximal and maximal exercise on cerebral perfusion were assessed using a portable, recumbent cycle ergometer in nine unacclimatized subjects ascending to 5,260 m. At 150 m, mean (SD) cerebral oxygenation (rSO2%) increased during submaximal exercise from 68.4 (SD 2.1) to 70.9 (SD 3.8) (P < 0.0001) and at maximal oxygen uptake (.VO2(max)) to 69.8 (SD 3.1) (P < 0.02). In contrast, at each of the high altitudes studied, rSO2 was reduced during submaximal exercise from 66.2 (SD 2.5) to 62.6 (SD 2.1) at 3,610 m (P < 0.0001), 63.0 (SD 2.1) to 58.9 (SD 2.1) at 4,750 m (P < 0.0001), and 62.4 (SD 3.6) to 61.2 (SD 3.9) at 5,260 m (P < 0.01), and at .VO2(max) to 61.2 (SD 3.3) at 3,610 m (P < 0.0001), to 59.4 (SD 2.6) at 4,750 m (P < 0.0001), and to 58.0 (SD 3.0) at 5,260 m (P < 0.0001). Cerebrovascular resistance tended to fall during submaximal exercise (P = not significant) and rise at .VO2(max), following the changes in arterial oxygen saturation and end-tidal CO(2). Cerebral oxygen delivery was maintained during submaximal exercise at 150 m with a nonsignificant fall at .VO2(max), but at high altitude peaked at 30% of .VO2(max) and then fell progressively at higher levels of exercise. The fall in rSO2 and oxygen delivery during exercise may limit exercise at altitude and is likely to contribute to the problems of acute mountain sickness and high-altitude cerebral edema.     

Isolation of two cholic acid-binding proteins from rat liver cytosol using affinity chromatography

Using an affinity matrix coupled with cholic acid, two proteins that recognise bile acids were isolated from rat liver cytosol. One protein of molecular weight 68 000 was immunologically identical to rat albumin. The other protein was of molecular weight 46 000. On discontinuous sodium dodecyl sulphate-polyacrylamide gel electrophoresis the 46 000 molecular weight protein dissociated to a single band with an RF value identical to the Yb subunit of the bromosulphophthalein-binding fraction (Y-fraction) of whole liver cytosol. The monomers of purified ligandin under these conditions resolved into two bands which corresponded to the Ya and Yc subunits of liver cytosol Y-fraction. Anti-serum to the purified ligandin reacted monospecifically with purified ligandin and whole liver cytosol, but did not cross-react with the Yb dimer eluted from the affinity column. The Yb dimer was shown to possess glutathione-S-transferase activity with a substrate specificity distinct from ligandin but similar to glutathione-S-transferase C. Cholic acid inhibited the catalytic activity of the transferase.     

Formation of cyclic AMP from exogenous ATP by isolated hepatocytes and adipocytes

Suspensions of isolated rat hepatocytes and adipocytes converted exogenous ATP to cyclic AMP at a rate which was about 30--50% of that observed with homogenates of isolated cells. Formation of cyclic AMP was stimulated by hormones (isoprenaline in the case of adipose tissue and glucagon in the case of liver) and sodium fluoride. Experiments with [alpha-32P]ATP indicated that the conversion of exogenous ATP to cyclic AMP did not occur within the cells. It is proposed that in isolated hepatocytes ad adipocytes some catalytic units of adenylate cyclase are exposed on the outer surface of the cell membrane.     

Purification by affinity chromatography of glutathione S-transferases A and C from rat liver cytosol

Purification of glutathione S-transferases A and C from rat liver cytosol using an affinity matrix coupled with cholic acid is described. The method provides a convenient means for the rapid and homogeneous preparation of both transferases.