Subglacial drainage processes at a High Arctic polythermal valley glacier

Peer reviewedPublisher PD

Identification of a non-mammalian leptin-like gene:characterization and expression in the tiger salamander (Ambystoma tigrinum)

Leptin is well established as a multifunctional cytokine in mammals. However, little is known about the evolution of the leptin gene in other vertebrates. A recently published set of ESTs from the tiger salamander (Ambystoma tigrinum) contains a sequence sharing 56% nucleotide sequence identity with the human leptin cDNA. To confirm that the EST is naturally expressed in the salamander, a 409 bp cDNA was amplified by RT-PCR of salamander testis and stomach mRNAs. The coding sequence of the cDNA is predicted to encode 169 amino acids, and the mature peptide to consist of 146 residues, as in mammals. Although the overall amino acid identity with mammalian leptins is only 29%, the salamander and mammalian peptides share common structural features. An intron was identified between coding exons providing evidence that the sequence is present in the salamander genome. Phylogenetic analysis showed a rate of molecular divergence consistent with the accepted view of vertebrate evolution. The pattern of tissue expression of the leptin-like cDNA differed between metamorphosed adult individuals of different sizes suggesting possible developmental regulation. Expression was most prominent in the skin and testis, but was also detected in tissues in which leptin mRNA is present in mammals, including the fat body, stomach, and muscle. The characterization of a salamander leptin-like gene provides a basis for understanding how the structure and functions of leptin have altered during the evolution of tetrapod vertebrates

The evidence for automated grading in diabetic retinopathy screening

Peer reviewedPostprin

Investigating the impact of occupant response time on computer simulations of the WTC North Tower evacuation

This work explores the impact of response time distributions on high-rise building evacuation. The analysis utilises response times extracted from printed accounts and interviews of evacuees from the WTC North Tower evacuation of 11 September 2001. Evacuation simulations produced using these “real” response time distributions are compared with simulations produced using instant and engineering response time distributions. Results suggest that while typical engineering approximations to the response time distribution may produce reasonable evacuation times for up to 90% of the building population, using this approach may underestimate total evacuation times by as much as 61%. These observations are applicable to situations involving large high-rise buildings in which travel times are generally expected to be greater than response time

Uncoupling clutch size, prolactin, and luteinizing hormone using experimental egg removal

Clutch size is a key avian fitness and life history trait. A physiological model for clutch size determination CSD), involving an anti-gonadal effect of prolactin (PRL) via suppression of luteinizing hormone (LH),was proposed over 20 years ago, but has received scant experimental attention since. The few studies looking at a PRL-based mechanistic hypothesis for CSD have been equivocal, but recent experiments utilizing a pharmacological agent to manipulate PRL in the zebra finch (Taeniopygia guttata) found no support for a role of this hormone in clutch size determination. Here, we take a complementary approach by manipulating clutch size through egg removal, examining co-variation in PRL and LH between two breeding attempts, as well as through experimentally-extended laying. Clutch size increased for egg removal females, but not controls, but this was not correlated with changes in PRL or LH. There were also no differences in PRL between egg removal females and controls, nor did PRL levels during early, mid- or late-laying of supra-normal clutches predict clutch size. By uncoupling PRL, LH and clutch size in our study, several key predictions of the PRL-based mechanistic model for CSD were not supported. However,a positive correlation between PRL levels late in laying and days relative to the last egg (clutch completion) provides an alternative explanation for the equivocal results surrounding the conventional PRL-based physiological model for CSD. We suggest that females coordinate PRL-mediated incubation onset with clutch completion to minimize hatching asynchrony and sibling hierarchy, a behavior that is amplified in females laying larger clutches

Effect of creatine supplementation on the airways of youth elite soccer players

Introduction Owing to its well-established ergogenic potential, creatine is a highly popular food supplement in sports. As an oral supplement, creatine is considered safe and ethical. However, no data exist on the safety of creatine on lung function in athletes. The aim of this project was to evaluate the effects of a standard course of creatine on the airways of youth elite athletes. Methods Nineteen elite soccer players, 16-21 yr old, completed a stratified, randomized, double-blind, placebo-controlled, parallel-group trial. The creatine group (n = 9) ingested 0.3 g·kg-1⋅d-1 of creatine monohydrate (CM) for 1 wk (loading phase) and 5 g·d-1 for 7 wk (maintenance phase), and the placebo group (n = 10) received the same dosages of maltodextrin. Airway inflammation (assessed by exhaled nitric oxide, FENO) and airway responsiveness (to dry air hyperpnoea) were measured pre- and postsupplementation. Results Mild, unfavorable changes in FENO were noticed by trend over the supplementation period in the CM group only (P = 0.056 for interaction, η2 = 0.199), with a mean group change of 9 ± 13 ppb in the CM group versus -5 ± 16 ppb in the placebo group (P = 0.056, d = 0.695). Further, the maximum fall in forced expiratory volume in 1 s after dry air hyperpnoea was larger by trend postsupplementation in the CM group compared with the placebo group: 9.7% ± 7.5% vs 4.4% ± 1.4%, respectively (P = 0.070, d = 0.975). These adverse effects were more pronounced when atopic players only (n = 15) were considered. Conclusion On the basis of the observed trends and medium to large effect sizes, we cannot exclude that creatine supplementation has an adverse effect on the airways of elite athletes, particularly in those with allergic sensitization. Further safety profiling of the ergogenic food supplement is warranted

Orexin in the chicken hypothalamus: immunocytochemical localisation and comparison of mRNA concentrations during the day and night, and after chronic food restriction

In mammals Orexin-A and -B are neuropeptides involved in the hypothalamic regulation of diverse physiological functions including food intake and the sleep-wake cycle. This generalisation was investigated in meat-(broiler) and layer-type juvenile domestic chickens by immunocytochemical localisation of orexin A/B in the hypothalamus, and by measurements of hypothalamic hypocretin mRNA which encodes for orexin A/B after chronic food restriction, and during the sleep-wake cycle. Orexin immunoreactive fibres were observed throughout the hypothalamus with cell bodies in and around the paraventricular nucleus. No differences were observed in the pattern of immunoreactivity using anti- human orexin-A, or -B antisera. The amount of hypothalamic hypocretin mRNA in food -restricted broilers was higher than in broilers fed ad libitum, but the same as in layer- type hens fed ad libitum. Hypothalamic hypocretin mRNA was increased (Po0.01) in 12-week-old broilers fed 25% of their ad libitum intake between 6–12 weeks of age. No difference in hypothalamic hypocretin mRNA was seen in 12-week-old layer- type hens when they were awake (1–2 h after lights on) or sleeping (1–2 h after lights off). It is concluded that in the chicken, we could not find evidence that hypothalamic orexin plays a role in the sleep-wake cycle and it may be involved in aspects of energy balance

An investigation into the mechanisms controlling seasonal speedup events at a High Arctic glacier

Seasonal variations in ice motion have been observed at several polythermal ice masses across the High Arctic, including the Greenland Ice Sheet. However, such variations in ice motion and their possible driving mechanisms are rarely incorporated in models of the response of High Arctic ice masses to predicted climate warming. Here we use a three-dimensional finite difference flow model, constrained by field data, to investigate seasonal variations in the distribution of basal sliding at polythermal John Evans Glacier, Ellesmere Island, Canada. Our results suggest that speedups observed at the surface during the melt season result directly from changes in rates of basal motion. They also suggest that stress gradient coupling is ineffective at transmitting basal motion anomalies to the upper part of the glacier, in contrast to findings from an earlier flow line study at the same glacier. We suggest that stress gradient coupling is limited through the effect of high drag imposed by a partially frozen bed and friction induced by valley walls and significant topographic pinning points. Our findings imply that stress gradient coupling may play a limited role in transmitting supraglacially forced basal motion anomalies through Arctic valley and outlet glaciers with complex topographic settings and highlight the importance of dynamically incorporating basal motion into models predicting the response of the Arctic's land ice to climate change

Up to the challenge?: hormonal and behavioral responses of free-ranging male Cassin's sparrows, Peucaea cassinii, to conspecific song playback

The Challenge Hypothesis postulates that male vertebrates can respond to social challenges, such as simulated territorial intrusions (STI), by rapidly increasing their concentrations of plasma androgens, such as testosterone (T). This increase may facilitate the expression of aggressive behavior and lead to persistence of this behavior even after withdrawal of the challenge, thus potentially promoting territoriality and the probability of winning future challenges. The validity of the Challenge Hypothesis was investigated in socially monogamous free-ranging male Cassin’s Sparrows, Peucaea cassinii. Exposure to STI at the beginning of the vernal nesting season stimulated aggressive behavior but did not increase plasma T. Furthermore, plasma T did not correlate with the duration of exposure to STI and the behavioral response to STI did not differ in males that were challenged a second time shortly after the first challenge. As birds were investigated at a stage of their reproductive cycle when plasma T is presumably seasonally high due to photostimulation, the lack of hormonal response to STI may have been due to the hypothalamo-pituitary-gonadal axis secreting hormones at maximum rates. This was not the case, however, because administration of gonadotropin-releasing hormone I (GnRH-I) rapidly stimulated the secretion of luteinizing hormone (LH) and T, and treatment with ovine LH rapidly stimulated T secretion