bluuebunny/crossref_metadata_2025 huggingface dataset:
Coexistence and origin of trophic ecotypes of pygmy whitefish,Prosopium coulterii, in a south‐westernAlaskan lake
Authors: Gowell C. P. , Quinn T. P. , Taylor E. B.
Published: October 2012

Ecologically, morphologically and genetically distinct populations within single taxa often coexist in postglacial lakes and have provided important model systems with which to investigate ecological and evolutionary processes such as niche partitioning and ecological speciation. Within the Salmonidae, these species complexes have been well studied, particularly within theCoregonus clupeaformis–C. laveratus(lake andEuropean whitefish, respectively) group, but the phenomenon has been less well documented in the other whitefish genera,ProsopiumandStenodus. Here, we examined the morphology, feeding biology and genetic structure of three putative forms of the pygmy whitefish,Prosopium coulterii(Eigenmann & Eigenmann, 1892), first reported fromChignikLake, south‐westernAlaska, over 40 years ago. Field collections and morphological analyses resolved a shallow water (< 5 m depth) low gill raker count form (< 15 first arch gill rakers), a deepwater (> 30 m), low gill raker form and a deepwater, high gill raker count (> 15 gill rakers) form. The two low gill raker count forms fed almost exclusively on benthic invertebrates (mostly chironomids), while the deepwater, high gill raker count form fed almost exclusively on zooplankton; differences in diet were also reflected in differences both inδ13Candδ15Nstable isotopes. All three forms were characterized by the same major mitochondrialDNAclade that has been associated with persistence in, and postglacial dispersal from, aBeringian glacial refugium. Analysis of variation at nine microsatelliteDNAloci indicated low, but significant differentiation among forms, especially between the two low gill raker count forms and the high gill raker count form. The extent of differentiation along phenotypic (considerable) and genetic (subtle) axes among theChignikLake forms is similar to that found among distinct taxa ofProsopiumfound in pre‐glacialBearLake (Utah–Idaho,USA) which is probably at least ten times older than Chignik Lake. Our analyses illustrate the potential for the postglacial differentiation in traits subject to divergent natural selection across variable environments.
Occurrence, costs and heritability of delayed selfing in a free‐living flatworm
Authors: Ramm S. A. , Vizoso D. B. , Schärer L.
Published: October 2012

Evolutionary theory predicts that in the absence of outcrossing opportunities, simultaneously hermaphroditic organisms should eventually switch to self‐fertilization as a form of reproductive assurance. Here, we report the existence of facultative self‐fertilization in the free‐living flatworm Macrostomum hystrix, a species in which outcrossing occurs via hypodermic insemination of sperm into the parenchyma of the mating partner. First, we show that isolated individuals significantly delay the onset of reproduction compared with individuals with outcrossing opportunities (‘delayed selfing’) as predicted by theory. Second, consistent with the idea of M. hystrix being a preferential outcrosser under natural conditions, we report likely costs of selfing manifested via reduced hatchling production and offspring survival. Third, we demonstrate that selfing propensity has a genetic basis in this species, with a heritability estimated at 0.43 ± 0.11. Variation in selfing propensity could arise due to differing costs of inbreeding among families; despite marked inter‐family variation in apparent costs of inbreeding, we found no evidence for such a link. Alternatively, selfing propensity might differ across families because of heritable variation in reproductive traits that determine the likelihood of selfing. We speculate that adaptations to hypodermic insemination under outcrossing, most notably a highly modified copulatory stylet (male copulatory organ) and reduced sperm complexity, could also facilitate facultative selfing in this species.
Spatially explicit models of divergence and genome hitchhiking
Authors: Flaxman S. M. , Feder J. L. , Nosil P.
Published: October 2012

Strong barriers to genetic exchange can exist at divergently selected loci, whereas alleles at neutral loci flow more readily between populations, thus impeding divergence and speciation in the face of gene flow. However, ‘divergence hitchhiking’ theory posits that divergent selection can generate large regions of differentiation around selected loci. ‘Genome hitchhiking’ theory suggests that selection can also cause reductions in average genome‐wide rates of gene flow, resulting in widespread genomic divergence (rather than divergence only around specific selected loci). Spatial heterogeneity is ubiquitous in nature, yet previous models of genetic barriers to gene flow have explored limited combinations of spatial and selective scenarios. Using simulations of secondary contact of populations, we explore barriers to gene flow in various selective and spatial contexts in continuous, two‐dimensional, spatially explicit environments. In general, the effects of hitchhiking are strongest in environments with regular spatial patterning of starkly divergent habitat types. When divergent selection is very strong, the absence of intermediate habitat types increases the effects of hitchhiking. However, when selection is moderate or weak, regular (vs. random) spatial arrangement of habitat types becomes more important than the presence of intermediate habitats per se. We also document counterintuitive processes arising from the stochastic interplay between selection, gene flow and drift. Our results indicate that generalization of results from two‐deme models requires caution and increase understanding of the genomic and geographic basis of population divergence.
Synergistic effects of reserves and connectivity on ecological resilience
Authors: Olds Andrew D. , Pitt Kylie A. , Maxwell Paul S. , Connolly Rod M.
Published: October 2012

In light of the global extent and cascading effect of our impact on the environment, we design and manage reserves to restore biodiversity and the functioning of ecosystems. Mobile organisms link important processes across ecosystems, however, their roles in providing these services are often overlooked and we need to know how they influence ecosystem functions in reserves. Herbivorous fish play a key role in coral reef seascapes. By removing algae, they promote coral growth and recruitment, and help to increase resilience.

We examined how connectivity with mangroves affected herbivore populations and benthic succession on reefs in eastern Australia. We surveyed fish assemblages, examined reef composition and characterised benthic recruitment on reefs at multiple levels of connectivity with mangroves, in a no‐take reserve and areas open to fishing.

Our results show that connectivity enhanced herbivore biomass and richness in reserves, and that these connectivity and reserve effects interacted to promote herbivory on protected reefs near mangroves.

Connectivity and reserve protection combined to double the biomass of roving herbivorous fish on protected reefs near mangroves. The increase in grazing intensity drove a trophic cascade that reduced algal cover and enhanced coral recruitment and reef resilience.

Synthesis and applications. Our findings demonstrate that ecosystem resilience can be improved by managing both reefs and adjacent habitats together as functional seascape units. By understanding how landscapes influence resilience, and explicitly incorporating these effects into conservation decision‐making, we may have greater success with environmental restoration and preservation actions.
PD‐1 expression on CTL may be related to more severe liver damage in CHB patients with HBV genotype C than in those with genotype B infection
Authors: Xibing G. , Xiaojuan Y. , Juanhua W.
Published: October 2012

Compared with Chronic hepatitis B (CHB) patients infected with genotype B, those infected with genotype C have higher hepatic histopathological activity and higher level of alanine aminotransferase (ALT). Our previous studies suggest that this phenomenon is related to lower level of HBV specific cytotoxic T lymphocyte (CTL) of patients infected with genotype C than those infected with genotype B, but its mechanism was not clear. The aim of present study was to explain the possible mechanism of lower level of HBV specific CTL and more serious liver function damage of patients infected with genotype C than those infected with genotype B through study on relationship between expression of HBV specific CTL surface programmed death receptor‐1 (PD‐1) and viral genotypes of CHB patients. A total of 100 CHB patients were studied, human leukocyte antigen (HLA)‐A2 positive, hepatitis B virus (HBV) DNA>103 copies/ml, of which 48 cases were genotype C (48%) positive, and 52 cases were genotype B positive (52%). Expression of Peripheral blood HBV specific CTL surface PD‐1, levels of HBV specific CTL, HBV DNA, ALT and total bilirubin (TBil) of patients infected with genotype C and B were compared. Expression of HBV specific CTL surface PD‐1 of CHB patients infected with genotype C was significantly higher than that of patients infected with genotype B, t = 17.57, P < 0.001, level of HBV specific CTL was significantly lower than that of patients infected with genotype B, t = 23.64, P < 0.001, level of HBV DNA was significantly higher than that of patients infected with genotype B, t = 9.43, P < 0.001, level of ALT was significantly higher than that of patients infected with genotype B, t = 13.42, P < 0.001. Expression of peripheral blood HBV specific CTL surface PD‐1 of CHB patients infected with genotype C was significantly higher than that of patients infected with genotype B, resulting in lower level of HBV specific CTL and higher level of HBV DNA of patients infected with genotype C than those of patients infected with genotype B. So liver function damage of CHB patients infected with genotype C was more serious than those infected with genotype B.
A histone deacetylase inhibitor, largazole, decreases liver fibrosis and angiogenesis by inhibiting transforming growth factor‐β and vascular endothelial growth factor signalling
Authors: Liu Yuqing , Wang Zhuo , Wang Jianing , Lam Wingchi , Kwong Shuqin , Li Furong , Friedman Scott L. , Zhou Shuyan , Ren Qi , Xu Zhengshuang , Wang XinGen , Ji Ling , Tang Shoubin , Zhang Hui , Lui Eric L. , Ye Tao
Published: October 2012

Background & Aims

Largazole is a novel histone deacetylase (HDAC) inhibitor. This study investigated the effects of largazole against liver fibrosis.

Methods

The in vitro effects of largazole were examined using hepatic stellate cells (HSCs). In vivo effects of largazole were studied using a mouse liver fibrotic model induced by CCl4.

Results

Largazole augmented acetylation of histone H3 (H3) and histone H4 (H4) in HSCs. It directly inhibited the activation of HSCs owing to HDAC inhibitory activity as the antifibrotic effect of largazole was significantly decreased in cells with HDAC1, HDAC2 and HDAC3 knockdown. Largazole also induced apoptosis of HSCs. Largazole not only inhibited the expression of TGFβR2, but also reduced phosphorylation of Smad2 and Akt induced by TGF‐β1. Largazole also inhibited the expression of vascular endothelial growth factor (VEGF) and its receptor. VEGF‐induced proliferation of HSCs and activation of Akt and p38MAPK were also suppressed by largazole. In vivo, largazole reduced the expression of collagen I, α‐smooth muscle actin and tissue inhibitor of metalloproteinase‐1 in CCl4–induced fibrosis, and these antifibrotic effects were associated with increased acetylation of H3 and H4. Largazole also induced HSCs to undergo apoptosis in vivo, which was correlated with downregulation of bcl‐2 and bcl‐xL. Furthermore, largazole inhibited angiogenesis in vivo as evidenced by reduced expression of CD34, VEGF and VEGFR. In addition to its antifibrotic activity, the drug reduced inflammatory activity in CCl4‐induced liver fibrosis.

Conclusions

Our findings revealed a novel role of largazole in the treatment of liver fibrosis. Through multiple mechanisms, largazole could be a potentially effective antifibrotic agent.
Restless leg syndrome is a treatable cause of sleep disturbance and fatigue in primary biliary cirrhosis
Authors: Anderson Kirstie , Jones David E. J. , Wilton Katharine , Newton Julia L.
Published: October 2012

Background

Primary biliary cirrhosis (PBC) patients frequently describe sleep problems. The cause remains unclear and treatment is challenging. Restless leg syndrome (RLS) is a common sleep disorder. In this study, we systematically screened PBC patients for the presence of RLS.

Methods

Participants were recruited from our specialist PBC clinical service. Subjects completed the International Restless Leg Syndrome Study Group rating scale (IRLSS) a validated measure of the presence of RLS and its severity. Those fulfilling diagnostic criteria for RLS underwent foot actigraphy (CamNtech Actiwatch) to objectively assess periodic limb movement index (PLMI) (normal <5/h).

Results

Restless leg syndrome was assessed in 42 consecutive early stage PBC patients. Twelve (29%) fulfilled the IRLSS criteria for RLS. Scores were significantly higher in PBC compared to controls (P = 0.005). Twenty‐four patients were further assessed with foot actigraphy for 3 nights (12 with subjective RLS symptoms and 12 with no RLS symptoms). Thirteen of twenty‐four subjects had PLMI >5/h and four had moderate or severe PLMI >15/h. All moderate or severe PLMI subjects had subjective symptoms of moderate or severe RLS. No patients had PLMI >10 in the absence of RLS symptoms. Eleven PBC patients with symptomatic RLS went on to have treatment. Sixty‐three per cent had clear benefit in restless leg symptoms and associated symptoms of fatigue.

Conclusion

Restless leg syndrome symptoms are common and underdiagnosed in PBC patients. RLS represents a potential therapy for PBC patients with daytime sleepiness, fatigue and unpleasant lower limb symptoms and this is worthy of further studies in larger cohorts.
Linking predator–prey interactions with exposure to a trophically transmitted parasite usingPCR‐based analyses
Authors: Luong Lien T. , Chapman Eric G. , Harwood James D , Hudson Peter J.
Published: October 2012

Parasite transmission is determined by the rate of contact between a susceptible host and an infective stage and susceptibility to infection given an exposure event. Attempts to measure levels of variation in exposure in natural populations can be especially challenging. The level of exposure to a major class of parasites, trophically transmitted parasites, can be estimated by investigating the host's feeding behaviour. Since the parasites rely on the ingestion of infective intermediate hosts for transmission, the potential for exposure to infection is inherently linked to the definitive host's feeding ecology. Here, we combined epidemiological data and molecular analyses (polymerase chain reaction) of the diet of the definitive host, the white‐footed mouse (Peromyscus leucopus), to investigate temporal and individual heterogeneities in exposure to infection. Our results show that the consumption of cricket intermediate hosts accounted for much of the variation in infection; mice that had consumed crickets were four times more likely to become infected than animals that tested negative for cricketDNA. In particular, pregnant female hosts were three times more likely to consume crickets, which corresponded to a threefold increase in infection compared with nonpregnant females. Interestingly, males in breeding condition had a higher rate of infection even though breeding males were just as likely to test positive for cricket consumption as nonbreeding males. These results suggest that while heterogeneity in host diet served as a strong predictor of exposure risk, differential susceptibility to infection may also play a key role, particularly among male hosts. By combiningPCRanalyses with epidemiological data, we revealed temporal variation in exposure through prey consumption and identified potentially important individual heterogeneities in parasite transmission.
Global lack of flyway structure in a cosmopolitan bird revealed by a genome wide survey of single nucleotide polymorphisms
Authors: Kraus Robert H. S. , van Hooft Pim , Megens Hendrik‐Jan , Tsvey Arseny , Fokin Sergei Y. , Ydenberg Ronald C. , Prins Herbert H. T.
Published: October 2012

Knowledge about population structure and connectivity of waterfowl species, especially mallards (Anas platyrhynchos), is a priority because of recent outbreaks of avian influenza. Ringing studies that trace large‐scale movement patterns have to date been unable to detect clearly delineated mallard populations. We employed 363 single nucleotide polymorphism markers in combination with population genetics and phylogeographical approaches to conduct a population genomic test of panmixia in 801 mallards from 45 locations worldwide. Basic population genetic and phylogenetic methods suggest no or very little population structure on continental scales. Nor could individual‐based structuring algorithms discern geographical structuring. Model‐based coalescent analyses for testing models of population structure pointed to strong genetic connectivity among the world's mallard population. These diverse approaches all support the conclusion that there is a lack of clear population structure, suggesting that the world's mallards, perhaps with minor exceptions, form a single large, mainly interbreeding population.
Resprouting as a key functional trait: how buds, protection and resources drive persistence after fire
Authors: Clarke P. J. , Lawes M. J. , Midgley J. J. , Lamont B. B. , Ojeda F. , Burrows G. E. , Enright N. J. , Knox K. J. E.
Published: October 2012

Resprouting as a response to disturbance is now widely recognized as a key functional trait among woody plants and as the basis for the persistence niche. However, the underlying mechanisms that define resprouting responses to disturbance are poorly conceptualized. Resprouting ability is constrained by the interaction of the disturbance regime that depletes the buds and resources needed to fund resprouting, and the environment that drives growth and resource allocation. We develop a buds‐protection‐resources (BPR) framework for understanding resprouting in fire‐prone ecosystems, based on bud bank location, bud protection, and how buds are resourced. Using this framework we go beyond earlier emphases on basal resprouting and highlight the importance of apical, epicormic and below‐ground resprouting to the persistence niche. The BPR framework provides insights into: resprouting typologies that include both fire resisters (i.e. survive fire but do not resprout) and fire resprouters; the methods by which buds escape fire effects, such as thick bark; and the predictability of community assembly of resprouting types in relation to site productivity, disturbance regime and competition. Furthermore, predicting the consequences of global change is enhanced by the BPR framework because it potentially forecasts the retention or loss of above‐ground biomass.

Contents

Summary
19

I.
Introduction
20

II.
Resprouters rather than ‘sprouters’
21

III.
How do plants resprout?
21

IV.
Life‐history consequences of resprouting
27

V.
Environmental constraints on resprouting
28

VI.
Resprouting, community patterns and assembly
29

VII.
Global change, carbon storage and resprouting
30

VIII.
Conclusions
31

Acknowledgements
31

References
32
Catch crop biomass production, nitrogen uptake and root development under different tillage systems
Authors: Munkholm L. J. , Hansen E. M.
Published: October 2012

Catch crops are generally regarded as an efficient tool to reduce nitrate leaching. However, the benefits need to be balanced against potential adverse effects on the main crop yields. The objectives of the study were to study three contrasting catch crops, that is, dyer's woad (DW) (Isatis tinctoria L.), perennial ryegrass (RG) (Lolium perenne L.) and fodder radish (FR) (Raphanus sativus L.) under three tillage systems. For that, we used a tillage experiment established in 2002 on a Danish sandy loam. The tillage treatments were direct drilling (D), harrowing to 8–10 cm (H) and ploughing (P). Above‐ground biomass production and N uptake were measured in the catch crops and the main crop. Catch crop root growth was studied using both minirhizotron and core methods. Soil penetration resistance was recorded to 60 cm depth. Fodder radish and RG produced up to 1800 kg/ha dry matter and DW 900 kg/ha. The nitrogen uptake in November was 55, 37 and 31 kg N/ha for FR, RG and DW, respectively, when averaged across the 2 yr of study. The yield of the spring barley main crop was in general highest where FR was grown as a catch crop. Ploughing tended to result in highest yields although differences were only significant in 2008. The minirhizotron root measurements showed that the crucifers FR and DW achieved better subsoil rooting than RG. In contrast, the soil core data showed no significant difference between FR and RG in subsoil root growth. Our study highlights the need for further studies on subsoil root growth of different catch crops.
Endogenous silencing of Puccinia triticina pathogenicity genes through in planta‐expressed sequences leads to the suppression of rust diseases on wheat
Authors: Panwar Vinay , McCallum Brent , Bakkeren Guus
Published: October 2012

Rust fungi are destructive plant pathogens. The draft genomes of several wheat‐infecting species have been released and potential pathogenicity genes identified through comparative analyses to fungal pathogens that are amenable to genetic manipulation. Functional gene analysis tools are needed to understand the infection process of these obligate parasites and to confirm whether predicted pathogenicity genes could become targets for disease control. We have modified an Agrobacterium tumefaciens‐mediated in planta‐induced transient gene silencing (PITGS) assay for use in Triticum spp. (wheat), and used this assay to target predicted wheat leaf rust fungus, Puccinia triticina (Pt) pathogenicity genes, a MAP kinase (PtMAPK1), a cyclophilin (PtCYC1) and calcineurin B (PtCNB), to analyze their roles in disease. Agroinfiltration effectively delivered hairpin silencing constructs in wheat, leading to the generation of fungal gene‐specific siRNA molecules in infiltrated leaves, and resulting in up to 70% reduction in transcription of the endogenous target genes in superinfected Pt. In vivo silencing caused severe disease suppression, compromising fungal growth and sporulation, as viewed by confocal microscopy and measured by reductions in fungal biomass and emergence of uredinia. Interestingly, using the same gene constructs, suppression of infection by Puccinia graminis and Puccinia striiformis was also achieved. Our results show that A. tumefaciens‐mediated PITGS can be used as a reverse‐genetics tool to discover gene function in rust fungi. This proof‐of‐concept study indicates that the targeted fungal transcripts might be important in pathogenesis, and could potentially be used as promising targets for developing RNA interference‐based resistance against rust fungi.
Glaucoma associated with uveal cysts and goniodysgenesis in American Bulldogs: a case series
Authors: Pumphrey Stephanie A. , Pizzirani Stefano , Pirie Christopher G. , Needle David B.
Published: October 2012

We present a series of three American Bulldogs with clinical signs of glaucoma and intraocular inflammation accompanied by bilateral uveal cysts and abnormal gonioscopic findings. All dogs proved refractory to medical management and were enucleated. Histopathologic findings were similar in all three and included significant preiridal fibrovascular membranes and mononuclear inflammatory infiltrates in the anterior uvea. On microscopic evaluation, cysts appeared to arise primarily from the ciliary body and iridociliary sulcus, with smaller cysts also budding from the posterior iris. Pigment dispersion was variable but consistent, involving deposition of a small number of pigment‐laden cells in the dependent trabecular meshwork. Cataract formation was not noted. Glaucoma associated with uveal cysts has been described previously in Golden Retrievers and Great Danes, although clinical and histopathologic findings in those breeds are not identical to those described here. American Bulldogs with uveal cysts should have gonioscopy performed and should be monitored carefully for signs of increased intraocular pressure and intraocular inflammation. Furthermore, documentation of cyst‐associated glaucoma in a third breed suggests clinicians should exercise caution in dismissing uveal cysts in dogs as incidental findings.
Transsynaptic inhibition of spinal transmission by A2 botulinum toxin
Authors: Akaike Norio , Shin Min‐Chul , Wakita Masahito , Torii Yasushi , Harakawa Tetsuhiro , Ginnaga Akihiro , Kato Keiko , Kaji Ryuji , Kozaki Shunji
Published: October 2012

Key points

Botulinum toxin A (BoNT/A) blocks synaptic transmission via the cleavage of SNAP‐25. Axonal transport of BoNT/A (A1 type botulinum toxin (A1LL) and A2 type botulinum toxin (A2NTX)) from periphery to the CNS has been described in trigeminal nerve and foreleg muscles.

A1LL and A2NTX were injected into the ipsilateral soleus, and their effects on ipsilateral and contralateral contractions were compared as a measure of local and systemic/transport‐mediated effects. Spinal transmission was also measured to determine axonal and transsynaptic transport of neurotoxin.

A2NTX induced faster and stronger muscle relaxation than A1LL. A1LL arrived at the contralateral muscle by almost equal transport via neural pathways and by the circulation.

A2NTX was mainly transported to contralateral muscles via the blood.

A1LL and A2NTX were carried from peripheral to CNS and vice versa by dual antero‐ and retrograde axonal transport through either motor or sensory neurons.

Our results may point to greater potential safety in A2NTX form.

Abstract  Type A botulinum toxin blocks not only ACh release from motor nerve terminals but also central synaptic transmission, including glutamate, noradrenaline, dopamine, ATP, GABA and glycine. Neurotoxins (NTXs) are transported by both antero‐ and retrogradely along either motor or sensory axons for bidirectional delivery between peripheral tissues or the CNS. A newly developed type A2 NTX (A2NTX) injected into one rat foreleg muscle was transported to the contralateral muscle. This finding was consistent with the NTX traveling retrogradely via spinal neurons and then transsynaptically through motor neurons to the contralateral motor neurons within the spinal cord and on to the soleus muscle. In the present study we found that toxin injection into the rat left soleus muscle clearly induced bilateral muscle relaxation in a dose‐dependent fashion, although the contralateral muscle relaxation followed the complete inhibition of toxin‐injected ipsilateral muscles. The toxin‐injected ipsilateral muscle relaxation was faster and stronger in A2NTX‐treated rats than A1LL (BOTOX). A1LL was transported almost equally to the contralateral muscle via neural pathways and the bloodstream. In contrast, A2NTX was mainly transported to contralateral muscles via the blood. A1LL was more successfully transported to contralateral spinal neurons than A2NTX. We also demonstrated that A1LL and A2NTX were carried from peripheral to CNS and vice versa by dual antero‐ and retrograde axonal transport through either motor or sensory neurons.
α2‐containing GABAA receptors expressed in hippocampal region CA3 control fast network oscillations
Authors: Heistek Tim S. , Ruiperez‐Alonso Marta , Timmerman A. Jaap , Brussaard Arjen B. , Mansvelder Huibert D.
Published: October 2012

Key points

Hippocampal oscillations are thought to be important for memory encoding and retrieval and depend on inhibition via GABA synapses.

GABAA receptor subunits are differentially expressed throughout the hippocampal circuitry. Here we address which subunit controls cholinergically induced fast network oscillations and where it is expressed.

By selectively increasing and decreasing the function of α1 and α2 subunits, we find that hippocampal oscillations are controlled by α2 subunits expressed in CA3.

Synapses from fast spiking interneurons to pyramidal cells in CA3 that provide the perisomatic inhibition necessary for fast network oscillations contain GABAA receptors with the α2 subunit.

Our data suggest that α2‐containing GABA receptors in CA3 have an important role in rhythmic hippocampal activity and thereby possibly in cognitive processing.

Abstract  GABAA receptors are critically involved in hippocampal oscillations. GABAA receptor α1 and α2 subunits are differentially expressed throughout the hippocampal circuitry and thereby may have distinct contributions to oscillations. It is unknown which GABAA receptor α subunit controls hippocampal oscillations and where these receptors are expressed. To address these questions we used transgenic mice expressing GABAA receptor α1 and/or α2 subunits with point mutations (H101R) that render these receptors insensitive to allosteric modulation at the benzodiazepine binding site, and tested how increased or decreased function of α subunits affects hippocampal oscillations. Positive allosteric modulation by zolpidem prolonged decay kinetics of hippocampal GABAergic synaptic transmission and reduced the frequency of cholinergically induced oscillations. Allosteric modulation of GABAergic receptors in CA3 altered oscillation frequency in CA1, while modulation of GABA receptors in CA1 did not affect oscillations. In mice having a point mutation (H101R) at the GABAA receptor α2 subunit, zolpidem effects on cholinergically induced oscillations were strongly reduced compared to wild‐type animals, while zolpidem modulation was still present in mice with the H101R mutation at the α1 subunit. Furthermore, genetic knockout of α2 subunits strongly reduced oscillations, whereas knockout of α1 subunits had no effect. Allosteric modulation of GABAergic receptors was strongly reduced in unitary connections between fast spiking interneurons and pyramidal neurons in CA3 of α2H101R mice, but not of α1H101R mice, suggesting that fast spiking interneuron to pyramidal neuron synapses in CA3 contain α2 subunits. These findings suggest that α2‐containing GABAA receptors expressed in the CA3 region provide the inhibition that controls hippocampal rhythm during cholinergically induced oscillations.
Heterogeneous properties of central lateral and parafascicular thalamic synapses in the striatum
Authors: Ellender T. J. , Harwood J. , Kosillo P. , Capogna M. , Bolam J. P.
Published: October 2012

Key points

The excitatory afferents to the striatum from the cortex and thalamus are critical in the expression of basal ganglia function.

Thalamostriatal afferents are markedly heterogeneous and arise in different subnuclei of the intralaminar thalamus.

We used an optogenetic approach, to isolate and selectively activate thalamostriatal afferents arising in the central lateral or parafascicular thalamic nuclei, and to study the properties of their synapses with principal striatal neurons, the medium‐spiny neurons.

Thalamostriatal synapses differ in many aspects and our data suggest that inputs from the central lateral nucleus are efficient drivers of medium‐spiny neuron action potential firing, whereas inputs from the parafascicular nucleus are likely to be modulatory.

These results suggest distinct roles for thalamostriatal inputs from different subnuclei of the thalamus and will help us understand how the striatal circuit operates in health and disease.

Abstract  To understand the principles of operation of the striatum it is critical to elucidate the properties of the main excitatory inputs from cortex and thalamus, as well as their ability to activate the main neurons of the striatum, the medium spiny neurons (MSNs). As the thalamostriatal projection is heterogeneous, we set out to isolate and study the thalamic afferent inputs to MSNs using small localized injections of adeno‐associated virus carrying fusion genes for channelrhodopsin‐2 and YFP, in either the rostral or caudal regions of the intralaminar thalamic nuclei (i.e. the central lateral or parafascicular nucleus). This enabled optical activation of specific thalamic afferents combined with whole‐cell, patch‐clamp recordings of MSNs and electrical stimulation of cortical afferents, in adult mice. We found that thalamostriatal synapses differ significantly in their peak amplitude responses, short‐term dynamics and expression of ionotropic glutamate receptor subtypes. Our results suggest that central lateral synapses are most efficient in driving MSNs to depolarization, particularly those of the direct pathway, as they exhibit large amplitude responses, short‐term facilitation and predominantly express postsynaptic AMPA receptors. In contrast, parafascicular synapses exhibit small amplitude responses, short‐term depression and predominantly express postsynaptic NMDA receptors, suggesting a modulatory role, e.g. facilitating Ca2+‐dependent processes. Indeed, pairing parafascicular, but not central lateral, presynaptic stimulation with action potentials in MSNs, leads to NMDA receptor‐ and Ca2+‐dependent long‐term depression at these synapses. We conclude that the main excitatory thalamostriatal afferents differ in many of their characteristics and suggest that they each contribute differentially to striatal information processing.
Aerodynamics of a Low-Pressure Turbine Airfoil at Low Reynolds Numbers—Part I: Steady Flow Measurements
Authors: Mahallati Ali , McAuliffe Brian R. , Sjolander Steen A. , Praisner Thomas J.
Published: October 2012

This two-part paper presents a detailed experimental investigation of the laminar separation and transition phenomena on the suction surface of a high-lift low-pressure turbine airfoil, PakB. The first part describes the influence of Reynolds number, freestream turbulence intensity and turbulence length scale on the PakB airfoil under steady inflow conditions. The present measurements are distinctive in that a closely-spaced array of hot-film sensors has allowed a very detailed examination of the suction surface boundary layer behavior. In addition, this paper presents a technique for interpreting the transition process in steady, and periodically unsteady, separated flows based on dynamic and statistical properties of the hot-film measurements. Measurements were made in a low-speed linear cascade facility at Reynolds numbers between 25,000 and 150,000 at three freestream turbulence intensity levels of 0.4%, 2%, and 4%. Two separate grids were used to generate turbulence intensity of 4% with integral length scales of about 10% and 40% of the airfoil axial chord length. While the higher levels of turbulence intensity promoted earlier transition and a shorter separation bubble, turbulence length scale did not have a noticeable effect on the transition process. The size of the suction side separation bubble increased with decreasing Reynolds number, and under low freestream turbulence levels the bubble failed to reattach at low Reynolds numbers. As expected, the losses increased with the length of the separation bubble, and increased significantly when the bubble failed to reattach.
Wall Shear Stress Measurements on a Highly Loaded Compressor Cascade
Authors: Zander Vincent , Dobriloff Christoph , Lumpe Mathias , Nitsche Wolfgang
Published: October 2012

This paper presents wall shear stress measurements obtained with a new type of wall-mounted probe based on the thermal electrical principle. The sensor consists of three single surface hot wires arranged in a δ configuration. This allows for measuring wall shear stress magnitude and direction simultaneously. Each probe has to be calibrated in a flat plate experiment for a number of wall shear values and flow directions before applying it to the relevant flow situation. To assess the full potential of the newly designed sensors, they were applied to a low-speed, large-scale cascade test section equipped with highly loaded compressor blades. The high blade loading in conjunction with a small blade aspect ratio results in a strongly three-dimensional flow field with large secondary flow structures and flow separation. Furthermore, laminar separation bubbles can be observed on the blade surface. The wall shear stress distribution allows for resolving these existing flow structures and provides detailed insight into the flow on the blade’s surface. The additionally measured flow direction reveals further details of the flow field. Parallel to the experiments, RANS simulations were conducted using the commercial flow solver CFX to compare the simulated results with the measured values.
Evaluation of CFD Predictions Using Thermal Field Measurements on a Simulated Film Cooled Turbine Blade Leading Edge
Authors: Mathew Sibi , Ravelli Silvia , Bogard David G.
Published: October 2012

Computational fluid dynamics (CFD) predictions of film cooling performance for gas turbine airfoils are an important part of the design process for turbine cooling. Typically, industry relies on the approach based on Reynolds Averaged Navier Stokes equations, together with a two-equation turbulence model. The realizable k-ɛ (RKE) model and the shear stress transport k-ω (SST) model are recognized as the most reliable. Their accuracy is generally assessed by comparing to experimentally measured adiabatic effectiveness. In this study, the performances of the RKE and SST models were evaluated by comparing predicted and measured thermal fields in a turbine blade leading edge with three rows of cooling holes, positioned along the stagnation line and at ±25 deg. Predictions and measurements were done with high thermal conductivity models which simulated the conjugate heat transfer effects between the coolant flow and the solid. Particular attention was placed on the thermal fields along the stagnation line, and immediately downstream of the off-stagnation line row of holes. Conventional evaluations in terms of adiabatic effectiveness were also carried out. Predictions of coolant flows at the stagnation line were significantly different when using the two different turbulence models. For a blowing ratio of M = 2.0, the predictions with the SST model showed coolant jet separation at the stagnation line, while the RKE predictions showed no separation. Experimental measurements showed that there was coolant jet separation at the stagnation line, but the actual thermal fields obtained from experimental measurements were significantly different from that predicted by either turbulence model. Similar results were seen for predicted and measured thermal fields downstream of the off-stagnation row of holes.
Tip-Leakage Losses in Subsonic and Transonic Blade Rows
Authors: Wheeler Andrew P. S. , Korakianitis Theodosios , Banneheke Shashimal
Published: October 2012

In this paper the effect of blade-exit Mach number on unshrouded turbine tip-leakage flows is investigated. Previously published experimental data of a high-pressure turbine blade are used to validate a computational fluid dynamics (CFD) code, which is then used to study the tip-leakage flow at blade-exit Mach numbers from 0.6 to 1.4. Three-dimensional (3D) calculations are performed of a flat-tip and a cavity-tip blade. Two-dimensional calculations are also performed to show the effect of various squealer-tip geometries on an idealized tip flow. The results show that as the blade-exit Mach number is increased the tip-leakage flow becomes choked. Therefore the tip-leakage flow becomes independent of the pressure difference across the tip and hence the blade loading. Thus the effect of the tip-leakage flow on overall blade loss reduces at blade-exit Mach numbers greater than 1.0. The results suggest that for transonic blade rows it should be possible to raise blade loading within the tip region without increasing tip-leakage loss.
Stall Warning by Blade Pressure Signature Analysis
Authors: Young Anna , Day Ivor , Pullan Graham
Published: October 2012

At low mass flow rates, axial compressors suffer from flow instabilities leading to stall and surge. The inception process of these instabilities has been widely researched in the past---primarily with the aim of predicting or averting stall onset. In recent times, attention has shifted to conditions well before stall and has focused on the level of irregularity in the blade passing signature in the rotor tip region. In general, the irregularity increases in intensity as the flow rate through the compressor is reduced. Attempts have been made to develop stall warning/avoidance procedures based on the level of flow irregularity, but little effort has been made to characterize the irregularity itself, or to understand its underlying cause. Work on this project has revealed for the first time that the increase in irregularity in the blade passing signature is highly dependent on both tip-clearance size and eccentricity. In a compressor with small, uniform, tip-clearance, the increase in blade passing irregularity that accompanies a reduction in flow rate will be modest. If the tip-clearance is enlarged, however, there will be a sharp rise in irregularity at all circumferential locations. In a compressor with eccentric tip-clearance, the increase in irregularity will only occur in the part of the annulus where the tip-clearance is largest, regardless of the average clearance level. In this paper, some attention is also given to the question of whether the irregularity observed in the prestall flow field is due to random turbulence or to some form of coherent flow structure. Detailed flow measurements reveal that the latter is the case. From these findings, it is clear that a stall warning system based on blade passing signature irregularity would be difficult to implement in an aero-engine where tip-clearance size and eccentricity change during each flight cycle and over the life of the compressor.
Application of Endwall Contouring to Transonic Turbine Cascades: Experimental Measurements at Design Conditions
Authors: Taremi Farzad , Sjolander Steen A. , Praisner Thomas J.
Published: October 2012

An experimental investigation of the endwall flows in two high-turning turbine cascades was presented by Taremi et al. (2010, “Measurements of Endwall Flows in Transonic Linear Turbine Cascades: Part II—High Flow Turning,” ASME Conf. Proc., GT2010-22760, pp. 1343–1356). Endwall contouring was subsequently implemented in these cascades to control the secondary flows and reduce the total pressure losses. The current paper presents experimental results from these cascades to assess the effectiveness of endwall contouring in the transonic flow regime. The results include blade loadings, total pressure losses, streamwise vorticity and secondary kinetic energy distributions. In addition, surface flow visualization results are presented in order to interpret the endwall limiting streamlines within the blade passages. The flat-endwall and contoured-endwall cascades produce very similar midspan loading distributions and profile losses, but exhibit different secondary flows. The endwall surface flow visualization results indicate weaker interaction between the secondary flows and the blade suction surface boundary layers in the contoured cascades. Overall, the implementation of endwall contouring results in smaller and less intense vortical structures, and the reduction of the associated secondary kinetic energy (SKE) and exit flow angle variations. However, the mass-averaged losses at the main measurement plane, located 40% axial chord lengths downstream of the cascade (1.4CX), do not corroborate the numerically predicted improvements for the contoured cascades. This is in part attributed to slower mixing rates of the secondary flows in the compressible flow regime. The mass-averaged results at 2.0CX, on the other hand, show smaller losses for the contoured configurations associated with smaller SKE dissipation downstream of the cascades. Accordingly, the mixed-out row losses also show improvements for the contoured cascades.
From Chip to Cooling Tower Data Center Modeling: Influence of Air-Stream Containment on Operating Efficiency1
Authors: Breen Thomas J. , Walsh Ed J. , Punch Jeff , Shah Amip J. , Bash Cullen E. , Rubenstein Brandon , Heath Scot , Kumari Niru
Published: October 2012

In the drive to enhance data center energy efficiency, much attention has been placed on the prospect of airflow containment in hot-aisle cold-aisle raised floor arrangements. Such containment prevents airflow recirculation, eliminating the mixing effects of the hot and cold air streams that can cause an undesirable temperature rise at the inlet of the equipment racks. The intuitive assessment of the industry has been that the elimination of such mixing effects increases the energy efficiency of the data center cooling system by enabling delivery of air at higher inlet temperatures, thus reducing the amount of infrastructure cooling required. This paper employs an end-to-end modeling approach to analyze the effect of air stream containment in the computer room and its impact on the holistic system efficiency. Dimensionless heat index parameters are employed to characterize the effects of containment, recirculation, and mixing within the computer room environment. The extent of recirculation is shown to primarily influence the operation of the rack and computer room air conditioning (CRAC) level cooling systems, with the chiller systems also impacted. The overall effect on the complete cooling system performance and data center efficiency requires balancing of these effects. Through this model analysis, it is shown that containment may negatively impact overall energy efficiency in some circumstances, and that recirculation may actually be beneficial to overall energy efficiency under certain system dependent operating thresholds.