The association between work burnout and insomnia: how to prevent workers’ insomnia

Sleep and Biological Rhythms -     

Does a dose-response relationship reduce sensitivity to hidden bias?

It is often said that an important consideration in judging whether an association between treatment and response is causal is the presence or absence of a dose-response relationship, that is, larger ostensible treatment effects when doses of treatment are larger. This criterion is widely discussed in textbooks and is often mentioned in empirical papers. At the same time, it is well known through both important examples and elementary theory that a treatment may cause dramatic effects with no dose-response relationship, and hidden biases may produce a dose-response relationship when the treatment is without effect. What does a dose-response relationship say about causality? It is observed here that a dose-response relationship may or may not reduce sensitivity to hidden bias, and whether it has or has not can be determined by a suitable analysis using the data at hand. Moreover, a study without a dose-response relationship may or may not be less sensitive to hidden bias than another study with such a relationship, and this, too, can be determined from the data at hand. An example concerning cytogenetic damage among professional painters is used to illustrate.     

Does resource availability help determine the evolutionary route to multicellularity?

Genetic heterogeneity and homogeneity are associated with distinct sets of adaptive advantages and bottlenecks, both in developmental biology and population genetics. Whereas populations of individuals are usually genetically heterogeneous, most multicellular metazoans are genetically homogeneous. Observing that resource scarcity fuels genetic heterogeneity in populations, we propose that monoclonal development is compatible with the resource‐rich and stable internal environments that complex multicellular bodies offer. In turn, polyclonal development persists in tumors and in certain metazoans, both exhibiting a closer dependence on external resources. This eco‐evo‐devo approach also suggests that multicellularity may originally have emerged through polyclonal development in early metazoans, because of their reduced shielding from environmental fluctuations.     

Does developmental acclimatization reduce the susceptibility to predation in newt larvae?

Many organisms respond to the heterogeneity of abiotic environmental conditions by plastic modifications of their phenotypes (acclimation or acclimatization). Despite considerable research efforts in this area, the beneficial (adaptive) effect of acclimation or acclimatization is still debated. We examined whether the development of newt larvae (Ichthyosaura alpestris) under different natural light and thermal conditions subsequently altered their susceptibility to predation in sun‐exposed versus shaded tanks in nature. During predation trials in various light and temperature conditions, newt larvae that developed in sun‐exposed warmer tanks consistently suffered from higher predation by dragonfly nymphs (Aeshna cyanea) compared to larvae from shaded or colder tanks. We conclude that higher sun exposure during embryonic and larval development negatively affects antipredator performance even in sun‐exposed tanks: this result is inconsistent with the beneficial acclimation hypothesis. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, ●● , ●●–●●.     

Does chronological age reduce working ability?

Definitions of so-called older age often are based on a chronological age of 65 years and over, although by some authors aging is the process that starts after the 30th year of life. At the beginning occur changes in the organ functions, followed by anatomical changes as well. Some organs age faster, some slower. For example, kidneys decrease for one third, lungs do not change, liver shrinks a little, prostate increases twice. In some cross-sectional studies, muscle mass in men aged 65 is on average 12 kg less than in the so-called middle age, and in women it is approximately 5 kg less. In the heart the amount of connective tissue increases, lipofuscin is deposited in cardiac muscle, the strength of which is decreasing. In the respiratory tract the number of pathways cilia decreases, along with the alveolar surface, muscles involved in breathing change, lung elasticity is also diminished. But, in regard with the previous body capacity, "physiological aging" can be divided into three types of elderly: the "older" elderly have the highest functional capacity of 2-3 MET (MET--metabolic unit, i.e. the oxygen consumption of 3.5 ml/kg body mass in a minute), the "younger" elderly are the persons of older age having maximal functional capacity of 5-7 MET, while the "sport" elderly have the functional capacity of 9-10 MET, disregarding chronological age. The brain weight diminishes for approximately 7% compared to younger age. In temporal gyrus and area striata even 20-40% of cells are being lost, vacuolar and neuroaxonal degeneration occurs, lipofuscin is being accumulated. The brain blood flow, which is in normal conditions 50-60 ml/min/100 g of tissue, with the increase of biological age decreases to about 40 ml/min/100 g of tissue. However, this usually is not the consequence of biological age but of disease. A chronological age of 65 for the beginning of "elder hood" is a sociopolitical construct developed by social security systems and government organizations to decide an arbitrary age at which benefits should be paid. Thus, it neither a border nor do changes designating old age occurs exactly with that "age border". The changes in the organism during the so-called aging are individual. So, the functional capacity of an organism, both physical and intellectual, must be evaluated individually, having in mind biological age.     

Metapopulation dynamics: Does it help to have more of the same?

With the interest in conservation biology shifting towards processes from patterns, and to populations from communities, the theory of metapopulation dynamics is replacing the equilibrium theory of island biogeography as the population ecology paradigm in conservation biology. The simplest models of metapopulation dynamics make predictions about the effects of habitat fragmentation - size and isolation of habitat patches - on metapopulation persistence. The simple models may be enriched by considerations of the effects of demographic and environmental stochasticity on the size and extinction probability of local populations. Environmental stochasticity affects populations at two levels: it makes local extinctions more probable, and it also decreases metapopulation persistence time by increasing the correlation of extinction events across populations. Some controversy has arisen over the significance of correlated extinctions, and how they may affect the optimal subdivision of metapopulations to maximize their persistence time.     

Calculating egg volume when shape differs: when are equations appropriate?

ABSTRACT Egg volume is often calculated from length and breadth, assuming little variation in egg shape within species. However, egg shape may vary among females, over time, or within clutches. If this variation is not predictable, volume should be estimated using another method. For example, in some species, egg shape changes consistently with laying order and volume can be estimated using laying‐order specific equations. We measured the length, breadth, volume, and mass of 249 Magellanic Penguin (Spheniscus magellanicus) eggs and regressed volume on length and breadth for first and second eggs separately. Differences between measured and calculated volume averaged <1% for both eggs. Using linear measurements, we calculated egg volume for 7085 clutches from 1983 to 2006. First and second eggs had similar calculated volumes (P > 0.05) in 19 of 24 yr; when they differed, the second egg was larger. In contrast, using single equations typically employed to compute egg volume, we erroneously concluded that first eggs were usually (20 of 24 yr) significantly larger than second eggs. Our regression equations should be applicable to other Spheniscus penguins because ratios of elongation coefficients (length divided by breadth) of first and second eggs are similar among these species. In other species of birds where egg shape changes with laying order, the volume of a sample of eggs should be measured to develop regression equations specific to the species and laying order. Slight variation in egg volume can have important evolutionary and ecological implications that would be erroneously interpreted without field tests to measure volume.     

Does increased endogenous CCK interact with serotonin to reduce food intake in rats?

The present study was aimed to test the hypothesis that increased endogenous CCK may interact with the anorectic serotonergic agent dl-fenfluramine to reduce food intake in rats. Previous studies, using selective CCK receptor antagonists, could demonstrate CCK-dependent 5-HT-induced anorexia. In the present approach, we used protease inhibitors to increase levels of endogenous CCK instead of blocking CCK receptors by antagonists. The protease inhibitors we used were soybean trypsin inhibitor (STI) and camostate. We hypothesized that combining the anorectic serotonergic drug dl-fenfluramine with either STI or camostate should result in an enhanced hypophagic effect when compared to single drug treatment. All feeding experiments were performed in non-deprived rats during night time feeding. Given alone, STI (500 mg/kg, po), camostate (200 mg/kg po) and also fenfluramine (1–9 mg/kg ip) reduced significantly food intake, with a more pronounced effect following fenfluramine. However, the experiments do not provide evidence for any additive or synergistic action between camostate or STI and the anorectic serotonergic drug dl-fenfluramine on food intake.     

Does schooling reduce fast-start response latencies in teleosts?

• 1.1. Response latencies, denned as the time between a d.c. electric shock and initiation of a fast-start (startle response) were measured for eight species of teleosts.
• 2.2. Fast-start response latencies varied from 10 to 36 cm. Highest values were found for individuals of two solitary species, Etheostoma caeruleum and Cottus cognatus. Lowest values were found for Esox and Salwo gairdneri.
• 3.3. Schooling in Perca flavescens, Lepomis macrochirus and Pimephales promelas significantly reduced fast-start response latencies by 7–16 msec. A 4 msec. reduction for Notropis cornutus was not significant.
• 4.4. No reduction in fast-start response latency was found for Pimephales promelas given the illusion of a school or for individuals greater than 15 cm from a school.
• 5.5. The observed variation in fast-start response latency would favour attack success of predators and escape success for schooled, but not solitary, presumptive prey.

     

Does pollen competition reduce the cost of inbreeding?

We hypothesize that floral features promoting pollen competition in angiosperms may have evolved, in some cases, in response to selection generated by the negative effects of inbreeding, at least in plants with mixed-mating systems. Screening of haploid genotypes through pollen competition may purge recessive (or additive) deleterious alleles that are expressed in haploid pollen and hence may reduce the fitness cost of self-pollination, geitonogamy, or biparental inbreeding. We tested one prediction of this hypothesis, that offspring produced by more intense competition among self-pollen have higher fitness than offspring produced by less intense competition. Dalechampia scandens (Euphorbiaceae) flowers were pollinated with pollen from other flowers on the same plant (geitonogamous self-fertilization). Those flowers experiencing more intense pollen competition as a result of low pollen dispersion (positional variance) on the stigma produced heavier seeds and seedlings with faster-growing radicles than flowers experiencing less intense pollen competition (high pollen dispersion), as predicted by our hypothesis.     

Mitral regurgitation: when to intervene?

Although mitral regurgitation (MR) is the most common valvular heart disease, it should be regarded as a complex multifactorial disease that involves     

Does the effect of pelleting depend on the wheat sample when fed to chickens?

Experimental comparisons of the nutritional value of different wheat cultivars commonly use feeds in meal form even though the large-scale broiler producers use steam pelleted feeds. The aim of this experiment was to examine the effect of steam pelleting on the performance, dietary N-corrected apparent metabolisable energy (AMEn), total tract dry matter retention (DMR), nitrogen retention (NR) and fat digestibility (FD) coefficients, and digestive tract development of broilers fed four different wheat samples in complete diets. Four European wheat samples, with different chemical composition and endosperm characteristics, were used in a broiler experiment. The wheat samples were milled through a 5 mm screen and four basal feeds containing 670 g/kg of each selected wheat sample were mixed. The basal feeds were then split into two batches and one of them was steam pelleted resulting in eight experimental diets. Each diet was fed ad libitum to eight pens of two male Ross 308 broilers from 10 to 24 days of age. Feeding pelleted diets improved (P<0.001) feed intake and weight gain, and daily water intake of the birds. Pelleting also improved dietary AMEn and FD (P<0.001) and DMR (P<0.05). An interaction (P<0.05) was observed between wheat samples and steam pelleting for NR. Steam pelleting improved (P<0.05) NR in the wheat sample with high starch and protein and hard endosperm but not in the rest of the wheat samples. Similar interactions (P<0.05) were also observed between wheat sample and steam pelleting for gain to feed (G : F) and water to feed (W : F) ratios. Pelleting improved G : F ratio the greatest in the wheat sample with high starch and protein and hard endosperm. Feeding the same wheat sample also decreased (P<0.05) W : F but only in the mash diets. Regardless of the wheat sample the values of dietary AMEn did not differ (P>0.05). Feeding different wheat types and pelleting did not (P>0.05) change the development of the gastrointestinal tract of the birds. The study showed that there were differences between four wheat samples when they were fed in pelleted complete feed, but no differences were observed when fed in mash form complete diets. Research on the interaction between pelleting and wheat chemical and quality characteristics is warranted.     

Does sleep really shorten when we get older?

Sleep and Biological Rhythms -     

Can biosensors help to protect drinking water?

A large proportion of drinking water is abstracted for treatment from lowland rivers—about 30% in the UK—and this water is at particular risk from sudden and poisonous industrial or agricultural pollution. To cover the range of potential pollutants it may be possible to use biosensors as broadband monitors for toxins. The underlying assumption is that some biological processes, when challenged with a toxin, will be affected in a way analogous to that of man, and that therefore on-line scrutiny of such processes will provide early warning of substances liable to be detrimental to human health. Suitable processes for study might involve multi-cellular organisms, whole cells or enzymes. To date, most practical work has concentrated on fish, but enzymes and single cells hold out the promise of quicker response and, possibly, easier maintenance.     

Can imperfections help to improve bioreactor performance?

Pilot-scale and larger bioreactors differ from small laboratory-scale reactors in terms of a greater occurrence of noise and incomplete mixing of the broth. Conventional control tries to induce good mixing and to filter out the noise as completely as possible. As such an 'ideal' operation is difficult to achieve, recent work has tried to exploit the non-ideal features to improve the performance. Using artificial neural networks, the degree of mixing, the extent of filtering of noise and the distribution of plasmid copy number (in a recombinant fermentation) can be controlled effectively on-line. This strategy generates better productivities than well-mixed noise-free operations, which suggests that deviations from ideal behaviour should be gainfully harnessed and not suppressed.