Skeletal muscle mass and composition during mammalian hibernation

Hibernation is characterized by prolonged periods of inactivity with concomitantly low nutrient intake, conditions that would typically result in muscle atrophy combined with a loss of oxidative fibers. Yet, hibernators consistently emerge from winter with very little atrophy, frequently accompanied by a slight shift in fiber ratios to more oxidative fiber types. Preservation of muscle morphology is combined with down-regulation of glycolytic pathways and increased reliance on lipid metabolism instead. Furthermore, while rates of protein synthesis are reduced during hibernation, balance is maintained by correspondingly low rates of protein degradation. Proposed mechanisms include a number of signaling pathways and transcription factors that lead to increased oxidative fiber expression, enhanced protein synthesis and reduced protein degradation, ultimately resulting in minimal loss of skeletal muscle protein and oxidative capacity. The functional significance of these outcomes is maintenance of skeletal muscle strength and fatigue resistance, which enables hibernating animals to resume active behaviors such as predator avoidance, foraging and mating immediately following terminal arousal in the spring

Microtubule Dynamics, Kinetochore Number, and Kinetochore Distribution in Cells Undergoing Mitosis with Unreplicated Genomes

In cells undergoing mitosis with unreplicated genomes (MUG), anaphase is successfully initiated despite the abundance of kinetochores that are attached to microtubules emanating from both spindle poles (merotely). In cultured cells, merotely is associated with lagging at the metaphase plate. Treatment with microtubule-perturbing drugs alters the frequency of lagging, but the effect of these drugs on MUG cells is unclear. In this study, low doses of a microtubule-stabilizing drug, taxol, or a microtubule-destabilizing drug, nocodazole, dramatically increased the frequency of lagging kinetochores in the midbody of MUG daughter cell pairs. Likewise, increasing the kinetochore number increased the frequency of lagging kinetochores. In this thesis, these data are used to propose a model of mitosis in which the bipolar attachments of MUG cells are reduced to monopolar attachments that are stabilized by their perpendicular orientation with respect to the kinetochore, allowing for spindle assembly checkpoint satisfaction without centromeric tension

Avoidance of skeletal muscle atrophy in spontaneous and facultative hibernators

Smooth and skeletal muscle changes were compared from overwintering white-tailed prairie dogs, spontaneous hibernators that undergo regular, low-temperature torpor bouts, and black-tailed prairie dogs, facultative hibernators that use sporadic, moderate-temperature torpor bouts. The objectives were to assess the abilities of these two species with dramatically different torpor patterns (1) to conserve skeletal muscle morphology, protein, and strength and (2) to use labile protein in the small intestine and liver during the winter season of reduced activity and food intake. Mass and protein concentration of the extensor digitorum longus (EDL), soleus, liver, and small intestine, as well as skeletal muscle strength and fiber morphology for the EDL and soleus, were compared before and after hibernation in both species. Both species appeared to be similar to overwintering black bears and underwent very little strength and protein loss, as compared with euthermic models of immobility and long-term fasting. Although the two species used vastly different hibernation strategies, none of the changes in parameters related to muscle atrophy and labile-protein use during the hibernation season differed significantly between them. Therefore, it appears that regardless of the phenotypic expressions of hibernation, the outcome is the conservation of skeletal muscle

Do hypothermic tissue tolerances limit torpor expression?

1. Arrest temperatures and Q10 values for extensor digitorum longus (EDL), soleus, trabecula, and jejunum muscle twitch strength, contraction time, and 0.5 relaxation time were calculated for a deep torpor hibernator, white-tailed prairie dog (WTPD) (Cynomys leucurus), a shallow torpor hibernator, black-tailed prairie dog (BTPD) (Cynomys ludovicianus), and a non-hibernator, lab rat (Rattus norvegicus) to test the hypothesis that tissue temperature tolerances limit the depth of expressed torpor. 2. There were no temperature tolerance differences between the tissues of the two species of hibernators. Both hibernating species had arrest temperatures and Q10 values more indicative of cold temperature tolerance than the lab rat in all tissues, with the exception of the soleus muscle. 3. These data imply that a limited cold tolerance of contractile tissue does not preclude a shallow torpor hibernator such as the black-tailed prairie dog from expressing deep torpor patterns. Other mechanisms, such as central neural control, are more likely to be important in determining the torpor strategy utilized by hibernating species

Radio Interferometers with wide bandwidths

The Australia Telescope Compact Array and the Very Large Array are currently being upgraded to operate with wide bandwidths; interferometers dedicated to the measurement of cosmic microwave background anisotropies are being designed with large instantaneous bandwidths for high sensitivity. Interferometers with wide instantaneous bandwidths that do not operate with correlators capable of decomposing the bands into narrow channels suffer from `bandwidth smearing' effects in wide-field imaging. The formalism of mosaic imaging is extended here to interferometers with finite bandwidths to examine the consequences for the imaging of wide fields if very wide instantaneous bandwidths are used. The formalism presented here provides an understanding of the signal processing associated with wide-band interferometers: mosaicing may be viewed as decomposing visibilities over wide observing bands and, thereby, avoiding `bandwidth smearing' effects in wide-field imaging. In particular, the formalism has implications for interferometer measurements of the angular power spectrum of cosmic microwave background anisotropies: mosaic-mode observing with wide-band radio interferometers decompose wide-band data and synthesize narrow filters in multipole space.Comment: 8 pages, includes 1 figure, accepted for publication in the MNRA

Niobium tetrahalide complexes with neutral diphosphine ligands

The reactions of NbCl4 with diphosphine ligands o-C6H4(PMe2)2, Me2PCH2CH2PMe2 or Et2PCH2CH2PEt2 in a 1:2 molar ratio in MeCN solution produced eight-coordinate [NbCl4(diphosphine)2]. [NbBr4(diphosphine)2] (diphosphine = o-C6H4(PMe2)2 or Me2PCH2CH2PMe2) were made similarly from NbBr4. X-ray crystal structures show that [NbCl4{o-C6H4(PMe2)2)2}] has a dodecahedral geometry but the complexes with dimethylene backboned diphosphines are distorted square antiprisms. The Nb-P and <P-Nb-P angles are very similar in the two types, but Nb-Cl distances are ~ 0.1Å longer in the square antiprismatic complexes. These paramagnetic (d1) complexes were also characterised by microanalysis, magnetic measurements, IR and UV-visible spectroscopy. Using a 1:1 molar ratio of NbCl4 : diphosphine (diphosphine = Me2PCH2CH2PMe2, Et2PCH2CH2PEt2, Cy2PCH2CH2PCy2 and Ph2PCH2CH2CH2PPh2) afforded [NbCl4(diphosphine)] and [NbBr4(Me2PCH2CH2PMe2)] was obtained similarly. These 1 : 1 complexes are unstable in solution, preventing X-ray crystallographic study, but based upon their diamagnetism, IR, UV-visible and 31P{1H} NMR spectra they are formulated as halide-bridged dimers [(diphosphine)X2Nb(μ-X)4NbX2(diphosphine)] with single Nb-Nb bonds and chelating diphosphines. The Nb(IV) complexes are prone to hydrolysis and oxidation in solution and the structures of the Nb(V) complexes [NbBr4(Me2PCH2CH2PMe2)2][NbOBr4(MeCN)] with a dodecahedral cation, and [{NbOCl3{Et2P(CH2)2PEt2}}2{μ-Et2P(CH2)2PEt2}] which contains seven-coordinate Nb(V) centres with a symmetrical diphosphine bridge are reported. The structure of niobium tetrabromide, conveniently made from NbCl4 and BBr3, is a chain polymer with edge-linked NbBr6 octahedra and alternating long and short Nb-Nb distances, the latter ascribed to Nb-Nb bonds

"One hand does not bring up a child:" Child fostering among single mothers in Nairobi slums

Background: Childrearing in sub-Saharan Africa is often viewed as collaborative, where children benefit from support from kin. For single mothers living in informal settlements, kin networks may be highly dispersed and offer little day-to-day childrearing support, but may provide opportunities for child fostering. Objective: Our study uses a linked lives approach, where single mothers' connections with kin and romantic partners may influence whether - and what type of - kin are relied on to support child fostering. Methods: We leverage an innovative survey on the kin networks of 404 single mothers and 741 children, collected in 2016, and 41 in-depth interviews conducted in 2011 and 2013, to explore fostering among single mothers in Korogocho and Viwandani, two slums in Nairobi, Kenya. Results: Quantitative findings show 6.2Š of single mothers' children are fostered, with provision of emotional support associated with lower likelihood of fostering. Both quantitative and qualitative results reflect strong reliance on maternal kin. Maternal kin play a key role in fostering to protect children, to fulfill traditional lineage obligations, and due to their willingness to foster when others will not. Contribution: This study contributes to a growing body of research on the role of kin in contemporary fostering arrangements in sub-Saharan Africa. In particular, we highlight fostering among a potentially highly vulnerable group: the children of single mothers in slum settlements. Sending children to live with kin may be an important coping strategy for single mothers, both to reduce the burden of raising children alone and to provide children with opportunities to grow up outside the slums

The Contribution of Set Switching and Working Memory to Sentence Processing in Older Adults

This study evaluates the involvement of switching skills and working memory capacity in auditory sentence processing in older adults. The authors examined 241 healthy participants, aged 55 to 88 years, who completed four neuropsychological tasks and two sentence-processing tasks. In addition to age and the expected contribution of working memory, switching ability, as measured by the number of perseverative errors on the Wisconsin Card Sorting Test, emerged as a strong predictor of performance on both sentence-processing tasks. Individuals with both low working-memory spans and more perseverative errors achieved the lowest accuracy scores. These findings are consistent with compensatory accounts of successful performance in older age

Are Drivers of Root-Associated Fungal Community Structure Context Specific?

The composition and structure of plant-root-associated fungal communities are determined by local abiotic and biotic conditions. However, the relative influence and identity of relationships to abiotic and biotic factors may differ across environmental and ecological contexts, and fungal functional groups. Thus, understanding which aspects of root-associated fungal community ecology generalise across contexts is the first step towards a more predictive framework. We investigated how the relative importance of biotic and abiotic factors scale across environmental and ecological contexts using high-throughput sequencing (ca. 55 M Illumina metabarcoding sequences) of >260 plant-root-associated fungal communities from six UK salt marshes across two geographic regions (South-East and North-West England) in winter and summer. Levels of root-associated fungal diversity were comparable with forests and temperate grasslands, quadrupling previous estimates of salt-marsh fungal diversity. Whilst abiotic variables were generally most important, a range of site- and spatial scale-specific abiotic and biotic drivers of diversity and community composition were observed. Consequently, predictive models of diversity trained on one site, extrapolated poorly to others. Fungal taxa from the same functional groups responded similarly to the specific drivers of diversity and composition. Thus site, spatial scale and functional group are key factors that, if accounted for, may lead to a more predictive understanding of fungal community ecology

High altitude diving in river otters: coping with combined hypoxic stresses

River otters (Lontra canadensis) are highly active, semi-aquatic mammals indigenous to a range of elevations and represent an appropriate model for assessing the physiological responses to diving at altitude. In this study, we performed blood gas analyses and compared blood chemistry of river otters from a high-elevation (2357 m) population at Yellowstone Lake with a sea-level population along the Pacific coast. Comparisons of oxygen dissociation curves (ODC) revealed no significant difference in hemoglobin-oxygen (Hb-O2) binding affinity between the two populations - potentially because of demands for tissue oxygenation. Instead, high-elevation otters had greater Hb concentrations (18.7 g dl-1) than sea-level otters (15.6 g dl-1). Yellowstone otters displayed higher levels of the vasodilator nitric oxide (NO), and half the concentration of the serum protein albumin, possibly to compensate for increased blood viscosity. Despite compensation in several hematological and serological parameters, theoretical aerobic dive limits (ADL) were similar between high-elevation and sea-level otters because of the lower availability of O2 at altitude. Our results suggest that recent disruptions to the Yellowstone Lake food web could be detrimental to otters because at this high elevation, constraints on diving may limit their ability to switch to prey in a deep-water environment