bluuebunny/crossref_metadata_2025 huggingface dataset:
Age and source of detrital zircons from the Missi Formation: a Proterozoic molasse deposit, Trans-Hudson Orogen, Canada
Authors: Ansdell Kevin M. , Kyser T. Kurtis , Stauffer Mel R. , Edwards Garth
Published: August 2009

The Missi Formation in the Flin Flon Basin forms part of a discontinuous series of molasse-type sediments found throughout the Early Proterozoic Trans-Hudson Orogen in northern Saskatchewan and Manitoba. The Flin Flon Basin contains a sequence of proximal-fan to braided-stream fluvial conglomerates and sandstones, which unconformably overlie subaerially weathered Amisk Group volcanic rocks. Stratigraphic way-up indicators have been preserved, even though these rocks have undergone greenschist-facies metamorphism and polyphase deformation. The sedimentary rocks are crosscut by intrusive rocks, which provide a minimum age of sedimentation of 1840 ± 7 Ma.Detrital zircons from each of the six stratigraphic subdivisions of the Flin Flon Basin were analyzed using the single-zircon Pb-evaporation technique. Euhedral to slightly rounded zircons dominate each sample, and these zircons give ages of between about 1854 and 1950 Ma. The Missi sediments were thus deposited between 1840 and 1854 Ma. Possible sources for the detrital zircons are Amisk Group felsic volcanic rocks and post-Amisk granitoid rocks and orthogneisses in adjacent domains within the Trans-Hudson Orogen. However, the immature character of the sedimentary rocks, the composition of clasts, the euhedral character of many of the zircons, and the range in ages suggest that most were likely derived from Amisk Group and granitoid rocks in the western Flin Flon Domain. Rounded zircons are uncommon but provide evidence for the reworking of older Proterozoic sedimentary rocks, or a distant Archean or Early Proterozoic granitoid terrane.
Geochemical alteration of felsic Archean rocks by Gunflint Formation-derived fluids, Quetico–Superior region, northwest Ontario
Authors: Kronberg B. I. , Fralick P. W.
Published: August 2009

Alteration of ferromagnesian minerals in felsic Archean rocks apparently was accomplished by diffusion of Gunflint Formation-derived fluids across the Proterozoic–Archean contact. The geochemical evidence documented here is consistent with slow mineral–fluid exchanges under diagenetic or low-grade metamorphic conditions. Chemical changes in mafic minerals include additions of iron, manganese, and water and losses of silica, calcium, and magnesium. The reaction layer extends ~3 m into felsic rocks immediately underlying the Proterozoic–Archean contact. From the evidence presented and the experimental information available it is concluded that these chemical changes occurred as Gunflint Formation-derived, iron-rich fluids diffused into underlying rock over a time frame of 105–107 years. The thermal energy for the reactions was most likely generated by the weight of the overlying sediments and water column.
A revised lithostratigraphy of the Lower–Middle Ordovician Beekmantown Group, St. Lawrence Lowlands, Quebec and Ontario
Authors: Bernstein Lawrence
Published: August 2009

The Lower – lower Middle Ordovician Beekmantown Group of the St. Lawrence Lowlands is a variably thick pertitidal succession of dolostone, limestone, quartzose carbonate, and subordinate siltstone and shale that is gradationally bound by the Potsdam Group below and unconformably to conformably by the Chazy Group above. It is here considered to include three regionally extensive formations, a basal Theresa, a middle Beauharnois, and an upper, redefined Carillon. A principal reference section is established in the subsurface. The Theresa Formation is a transgressive succession, above Potsdam Group siliciclastics and below Beauharnois Formation carbonates. It is dominated by quartz arenite and quartzose dolostone; skeletal fossils are rare (usually gastropods), whereas trace fossils are abundant. The Beauharnois Formation is divided into two members, a basal Ogdensburg and an upper Huntingdon. The Ogdensburg Member is sandy, especially in its lower part, and relatively more fossiliferous than the Huntingdon Member. Both members include fossiliferous and nonfossiliferous, stromatolitic and oolitic, coarse-grained dolostone and subordinate limestone and reflect the development of a relatively wide peritidal carbonate platform. The Carillon Formation is a widespread unit that marks the onset of Middle Ordovician Taconic orogeny at the continental margin. It consists mostly of cyclic packages of laminated and burrowed, fine-grained dolostone and limestone, and as well siltstone and shale. Thin fossiliferous beds are dispersed in its upper part.
Influence of zinc deficiency on Akt-Mdm2-p53 and Akt-p21 signaling axes in normal and malignant human prostate cells
Authors: Han Chung-Ting , Schoene Norberta W. , Lei Kai Y.
Published: August 2009

Phosphorylated Akt (p-Akt), a phosphoinositide-3-OH-kinase-activated protein kinase, is highly expressed in prostate tumors. p-Akt can indirectly hinder p53-dependent growth suppression and apoptosis by phosphorylating Mdm2. Alternatively, p-Akt can directly phosphorylate p21 and restrict it to the cytoplasm for degradation. Because the prostate is the highest zinc-accumulating tissue before the onset of cancer, the effects of physiological levels of zinc on Akt-Mdm2-p53 and Akt-p21 signaling axes in human normal prostate epithelial cells (PrEC) and malignant prostate LNCaP cells were examined in the present study. Cells were cultured for 6 days in low-zinc growth medium supplemented with 0 [zinc-deficient (ZD)], 4 [zinc-normal (ZN)], 16 [zinc-adequate (ZA)], or 32 [zinc-supplemented (ZS)] μM zinc. Zinc status of both cell types was altered in a dose-dependent manner, with LNCaP cells reaching a plateau at >16 μM zinc. For both cell types, p-Akt was higher in the ZD than in the ZN cells and was normalized to that of the ZN cells by treatment with a PI3K inhibitor, LY-294002. PTEN, an endogenous phosphatase targeting Akt dephosphorylation, was hyperphosphorylated (p-PTEN, inactive form) in ZD PrEC. Nuclear p-Mdm2 was raised, whereas nuclear p53 was depressed, by zinc deficiency in PrEC. Nuclear p21 and p53 were lowered by zinc deficiency in LNCaP cells. Higher percentages of ZD, ZA, and ZS than ZN LNCaP cells were found at the G0/G1 phase of the cell cycle, with proportionally lower precentages at the S and G2/M phases. Hence, the increased p-PTEN in ZD PrEC would result in hyperphosphorylation of p-Akt and p-Mdm2, as well as reduction of nuclear p53 accumulation. For ZD LNCaP cells, Akt hyperphosphorylation was probably mediated through p21 phosphorylation and degradation, thus restricting p21 nuclear entry to induce cell cycle arrest. Thus zinc deficiency differentially modulated the Akt-Mdm2-p53 signaling axis in normal prostate cells vs. the Akt-p21 signaling axis in malignant prostate cells.
Activation of maxi-anion channel by protein tyrosine dephosphorylation
Authors: Toychiev Abduqodir H. , Sabirov Ravshan Z. , Takahashi Nobuyaki , Ando-Akatsuka Yuhko , Liu Hongtao , Shintani Takafumi , Noda Masaharu , Okada Yasunobu
Published: August 2009

The maxi-anion channel with a large single-channel conductance of >300 pS, and unknown molecular identity, is functionally expressed in a large variety of cell types. The channel is activated by a number of experimental maneuvers such as exposing cells to hypotonic or ischemic stress. The most effective and consistent method of activating it is patch membrane excision. However, the activation mechanism of the maxi-anion channel remains poorly understood at present. In the present study, involvement of phosphorylation/dephosphorylation in excision-induced activation was examined. In mouse mammary fibroblastic C127 cells, activity of the channel was suppressed by intracellular application of Mg-ATP, but not Mg-5′-adenylylimidodiphosphate (AMP-PNP), in a concentration-dependent manner. When a cocktail of broad-spectrum tyrosine phosphatase inhibitors was applied, channel activation was completely abolished, whereas inhibitors of serine/threonine protein phosphatases had no effect. On the other hand, protein tyrosine kinase inhibitors brought the channel out of an inactivated state. In mouse adult skin fibroblasts (MAFs) in primary culture, similar maxi-anion channels were found to be activated on membrane excision, in a manner sensitive to tyrosine phosphatase inhibitors. In MAFs isolated from animals deficient in receptor protein tyrosine phosphatase (RPTP)ζ, activation of the maxi-anion channel was significantly slower and less prominent compared with that observed in wild-type MAFs; however, channel activation was restored by transfection of the RPTPζ gene. Thus it is concluded that activation of the maxi-anion channel involves protein dephosphorylation mediated by protein tyrosine phosphatases that include RPTPζ in mouse fibroblasts, but not in C127 cells.
Identification of Sp1 and GC-boxes as transcriptional regulators of mouse Dag1 gene promoter
Authors: Rettino Alessandro , Rafanelli Francesca , Genovese Giannicola , Goracci Martina , Cifarelli Rosa Anna , Cittadini Achille , Sgambato Alessandro
Published: August 2009

Dystroglycan is a widely expressed adhesion complex that anchors cells to the basement membrane and is involved in embryonic development and differentiation. Dystroglycan expression is frequently reduced in human dystrophies and malignancies, and its molecular functions are not completely understood. Several posttranslational mechanisms have been identified that regulate dystroglycan expression and/or function, while little is known about how expression of the corresponding Dag1 gene is regulated. This study aimed to clone the Dag1 gene promoter and to characterize its regulatory elements. Analysis of the mouse Dag1 gene 5′-flanking region revealed a TATA and CAAT box-lacking promoter including a GC-rich region. Transfection studies with serially deleted promoter constructs allowed us to identify a minimal promoter region containing three Specificity protein 1 (Sp1) sites and an E-box. Sp1 binding was confirmed by chromatin immunoprecipitation assay, and Sp1 downregulation reduced dystroglycan expression in muscle cells. Treatment with 5-aza-2′-deoxycytidine and/or the histone deacetylase inhibitor trichostatin A increased Dag1 mRNA expression levels in myoblasts, and methylation decreased promoter activity in vitro. Furthermore, Dag1 gene promoter methylation was reduced while its expression increased during differentiation of C2C12 myoblast cells in myotubes. In conclusion, for the first time we have characterized the activity of the mouse Dag1 gene promoter, confirming a complex regulation by Sp1 transcription factor, DNA methylation, and histone acetylation, which might be relevant for a better understanding of the physiopathology of the dystroglycan complex.
Chloride transport in mitochondrion-rich cells of euryhaline tilapia (Oreochromis mossambicus) larvae
Authors: Horng Jiun-Lin , Hwang Pung-Pung , Shih Tin-Han , Wen Zhi-Hong , Lin Chan-Shing , Lin Li-Yih
Published: August 2009

A noninvasive scanning ion-selective electrode technique (SIET) was applied to measure Cl− transport at individual mitochondrion-rich cells (MRCs) in the skin of euryhaline tilapia ( Oreochromis mossambicus) larvae. In seawater (SW)-acclimated larvae, outward Cl− gradients (20∼80 mM higher than the background) were measured at the surface, indicating a secretion of Cl− from the skin. By serial probing over the surface of MRCs and adjacent keratinocytes (KCs), a significant outward flux of Cl− was detected at the apical opening (membrane) of MRCs. Treatment with 100 μM ouabain or bumetanide inhibited the Cl− secretion by ∼75%. In freshwater (FW)-acclimated larvae, a lower level of outward Cl− gradients (0.2∼1 mM) was measured at the skin surface. Low-Cl− water (<0.005 mM) acclimation increased the apical Na+-Cl− cotransporter (NCC) immunoreactivity of MRCs in the larval skin. An inward flux of Cl− was detected when probing the exterior surface of a group of MRCs (convex-MRCs) that express the NCC. An NCC inhibitor (100 μM metolazone) reduced the flux by ∼90%. This study provides direct and convincing evidence for Cl− transport by MRCs of SW- and FW-acclimated euryhaline tilapia and the involvement of an apical NCC in Cl− uptake of MRCs of FW-acclimated fish.
Membrane trauma and Na+leak from Nav1.6 channels
Authors: Wang Jun A. , Lin Wei , Morris Terence , Banderali Umberto , Juranka Peter F. , Morris Catherine E.
Published: August 2009

During brain trauma, white matter experiences shear and stretch forces that, without severing axons, nevertheless trigger their secondary degeneration. In central nervous system (CNS) trauma models, voltage-gated sodium channel (Nav) blockers are neuroprotective. This, plus the rapid tetrodotoxin-sensitive Ca2+overload of stretch-traumatized axons, points to “leaky” Nav channels as a pivotal early lesion in brain trauma. Direct effects of mechanical trauma on neuronal Nav channels have not, however, been tested. Here, we monitor immediate responses of recombinant neuronal Nav channels to stretch, using patch-clamp and Na+-dye approaches. Trauma constituted either bleb-inducing aspiration of cell-attached oocyte patches or abrupt uniaxial stretch of cells on an extensible substrate. Nav1.6 channel transient current displayed irreversible hyperpolarizing shifts of steady-state inactivation [availability(V)] and of activation [ g(V)] and, thus, of window current. Left shift increased progressively with trauma intensity. For moderately intense patch trauma, a ∼20-mV hyperpolarizing shift was registered. Nav1.6 voltage sensors evidently see lower energy barriers posttrauma, probably because of the different bilayer mechanics of blebbed versus intact membrane. Na+dye-loaded human embryonic kidney (HEK) cells stably transfected with αNav1.6 were subjected to traumatic brain injury-like stretch. Cytoplasmic Na+levels abruptly increased and the trauma-induced influx had a significant tetrodotoxin-sensitive component. Nav1.6 channel responses to cell and membrane trauma are therefore consistent with the hypothesis that mechanically induced Nav channel leak is a primary lesion in traumatic brain injury. Nav1.6 is the CNS node of Ranvier Nav isoform. When, during head trauma, nodes experienced bleb-inducing membrane damage of varying intensities, nodal Nav1.6 channels should immediately “leak” over a broadly left-smeared window current range.
Endothelial barrier protection by FTY720 under hyperglycemic condition: involvement of focal adhesion kinase, small GTPases, and adherens junction proteins
Authors: Sarai Kei , Shikata Kenichi , Shikata Yasushi , Omori Kazuyoshi , Watanabe Naomi , Sasaki Motofumi , Nishishita Shingo , Wada Jun , Goda Noriko , Kataoka Noriyuki , Makino Hirofumi
Published: August 2009

Recently, sphingosine 1-phosphate (S1P) has been highlighted as an endothelial barrier-stabilizing mediator. FTY720 is a S1P analog originally developed as a novel immunosuppressant. The phosphorylated form of FTY720 binds to S1P receptors to exert S1P-like biological effects, suggesting endothelial barrier promotion by FTY720. To elucidate whether FTY720 induces signaling events related to endothelial barrier enhancement under hyperglycemic conditions, human microvascular endothelial cells (HMVECs) preincubated with hyperglycemic (30 mM) medium were treated with 100 nM FTY720 for 3 h. Immunofluorescent microscopy and coprecipitation study revealed FTY720-induced focal adhesion kinase (FAK)-associated adherens junction (AJ) assembly at cell-cell contacts coincident with formation of a prominent cortical actin ring. FTY720 also induced transmonolayer electrical resistance (TER) augmentation in HMVEC monolayers in both normoglycemic and hyperglycemic conditions, implying endothelial barrier enhancement. Similar to S1P, site-specific FAK tyrosine phosphorylation analysis revealed FTY720-induced FAK [Y576] phosphorylation without phosphorylation of FAK [Y397/Y925]. Furthermore, FTY720 conditioned the phosphorylation profile of FAK [Y397/Y576/Y925] in hyperglycemic medium to the same pattern observed in normoglycemic medium. FTY720 challenge resulted in small GTPase Rac activation under hyperglycemic conditions, whereas increased Rho activity in hyperglycemic medium was restored to the basal level. Rac protein depletion by small interfering RNA (siRNA) technique completely abolished FTY720-induced FAK [Y576] phosphorylation. These findings strongly suggest the barrier protective effect of FTY720 on HMVEC monolayers in hyperglycemic medium via S1P signaling, further implying the possibility of FTY720 as a therapeutic agent of diabetic vascular disorder.
Endotoxin depresses heart rate variability in mice: cytokine and steroid effects
Authors: Fairchild Karen D. , Saucerman Jeffrey J. , Raynor Laura L. , Sivak Joseph A. , Xiao Yuping , Lake Douglas E. , Moorman J. Randall
Published: August 2009

Heart rate variability (HRV) falls in humans with sepsis, but the mechanism is not well understood. We utilized a mouse model of endotoxemia to test the hypothesis that cytokines play a role in abnormal HRV during sepsis. Adult male C57BL/6 mice underwent surgical implantation of probes to continuously monitor electrocardiogram and temperature or blood pressure via radiotelemetry. Administration of high-dose LPS ( Escherichia coli LPS, 10 mg/kg, n = 10) caused a biphasic response characterized by an early decrease in temperature and heart rate at 1 h in some mice, followed by a prolonged period of depressed HRV in all mice. Further studies showed that LPS doses as low as 0.01 mg/kg evoked a significant decrease in HRV. With high-dose LPS, the initial drops in temperature and HR were temporally correlated with peak expression of TNFα 1 h post-LPS, whereas maximal depression in HRV coincided with peak levels of multiple other cytokines 3–9 h post-LPS. Neither hypotension nor hypothermia explained the HRV response. Pretreatment with dexamethasone prior to LPS significantly blunted expression of 7 of the 10 cytokines studied and shortened the duration of depressed HRV by about half. Interestingly, dexamethasone treatment alone caused a dramatic increase in both low- and high-frequency HRV. Administration of recombinant TNFα caused a biphasic response in HR and HRV similar to that caused by LPS. Understanding the role of cytokines in abnormal HRV during sepsis could lead to improved strategies for detecting life-threatening nosocomial infections in intensive care unit patients.
Control of respiration in flight muscle from the high-altitude bar-headed goose and low-altitude birds
Authors: Scott Graham R. , Richards Jeffrey G. , Milsom William K.
Published: August 2009

Bar-headed geese fly at altitudes of up to 9,000 m on their biannual migration over the Himalayas. To determine whether the flight muscle of this species has evolved to facilitate exercise at high altitude, we compared the respiratory properties of permeabilized muscle fibers from bar-headed geese and several low-altitude waterfowl species. Respiratory capacities were assessed for maximal ADP stimulation (with single or multiple inputs to the electron transport system) and cytochrome oxidase excess capacity (with an exogenous electron donor) and were generally 20–40% higher in bar-headed geese when creatine was present. When respiration rates were extrapolated to the entire pectoral muscle mass, bar-headed geese had a higher mass-specific aerobic capacity. This may represent a surplus capacity that counteracts the depressive effects of hypoxia on mitochondrial respiration. However, there were no differences in activity for mitochondrial or glycolytic enzymes measured in homogenized muscle. The [ADP] leading to half-maximal stimulation ( Km) was approximately twofold higher in bar-headed geese (10 vs. 4–6 μM), and, while creatine reduced Kmby 30% in this species, it had no effect on Kmin low-altitude birds. Mitochondrial creatine kinase may therefore contribute to the regulation of oxidative phosphorylation in flight muscle of bar-headed geese, which could promote efficient coupling of ATP supply and demand. However, this was not based on differences in creatine kinase activity in isolated mitochondria or homogenized muscle. The unique differences in bar-headed geese existed without prior exercise or hypoxia exposure and were not a result of phylogenetic history, and may, therefore, be important evolutionary specializations for high-altitude flight.
Identification of two glucocorticoid response elements in the promoter region of the ubiquitous isoform of glutamine synthetase in gulf toadfish,Opsanus beta
Authors: Esbaugh Andrew J. , Walsh Patrick J.
Published: August 2009

Unlike most teleosts, gulf toadfish have the capacity to switch from ammoniotely to ureotely as the predominate means of nitrogen excretion during periods of stress. The switch to ureotely is a result of increased glutamine synthetase (GS) mRNA expression/enzyme activity in the liver and muscle, which is initiated by cortisol. Cortisol typically affects gene expression through the action of cortisol-activated transcription factors, such as glucocorticoid receptors, which bind to glucocorticoid response elements (GRE) in the upstream regulatory region of genes. The purpose of the present study was to identify the GRE responsible for increased GS gene expression during crowding/confinement in gulf toadfish using an in vivo luciferase reporter assay. Upstream promoter regions for both the ubiquitous and gill GS isoforms were amplified by PCR. Additionally, an intron was amplified from the ubiquitous GS isoform that suggested the possibility of two discreet transcripts for the mitochondrial and cytoplasmic proteins. When tested via in vivo reporter assays, both the cytoplasmic and mitochondrial ubiquitous GS promoters showed increased luciferase activity during crowding vs. noncrowded controls; the gill GS promoter showed no effects in response to crowding. In silico analysis of the mitochondrial and cytoplasmic ubiquitous GS promoter constructs showed an overlapping section of 565 bp containing two potential GREs. Mutation of either site alone had no effect on luciferase activity vs. wild-type controls. However, when both sites were mutated a significant decrease in luciferase activity was observed. We conclude that two functional GREs combine to confer cortisol-inducible GS expression in the liver of gulf toadfish.
Induction of hepatic cyclooxygenase-2 by hyperhomocysteinemia via nuclear factor-κB activation
Authors: Wu Nan , Siow Yaw L. , O Karmin
Published: August 2009

Hyperhomocysteinemia, an elevation of blood homocysteine (Hcy), is a metabolic disorder associated with dysfunction of multiple organs. Apart from endothelial dysfunction, Hcy can cause hepatic lipid accumulation and liver injury. However, the mechanism responsible for Hcy-induced liver injury is poorly understood. The aim of this study was to investigate the regulation of cyclooxygenase-2 (COX-2), a proinflammatory factor, expression in the liver during the initial phase of hyperhomocysteinemia. Sprague-Dawley rats were fed a high-methionine diet for 1 or 4 wk. Serum and liver concentrations of Hcy were significantly elevated after 1 or 4 wk of dietary treatment. COX-2 mRNA and protein levels were significantly elevated in the liver of hyperhomocysteinemic rats. The induction of COX-2 expression was more prominent in 1-wk hyperhomocysteinemic rats than that in the 4-wk group. EMSA revealed an activation of NF-κB in the same liver tissue in which COX-2 was induced. Administration of a NF-κB inhibitor to hyperhomocysteinemic rats effectively abolished hepatic COX-2 expression, inhibited the formation of inflammatory foci, and improved liver function. Further investigation revealed that oxidative stress due to increased superoxide generation was responsible for increased phosphorylation and degradation of IκBα leading to NF-κB activation in the liver. Administration of 4-hydroxy-tetramethyl-piperidine-1-oxyl, an SOD mimetic, to hyperhomocysteinemic rats not only inhibited NF-κB activation but also prevented hepatic COX-2 induction and improved liver function. These results suggest that hyperhomocysteinemia-induced COX-2 expression is mediated via NF-κB activation. Increased oxidative stress and inflammatory response may contribute to liver injury associated with hyperhomocysteinemia.
Jugular venous pooling during lowering of the head affects blood pressure of the anesthetized giraffe
Authors: Brøndum E. , Hasenkam J. M. , Secher N. H. , Bertelsen M. F. , Grøndahl C. , Petersen K. K. , Buhl R. , Aalkjær C. , Baandrup U. , Nygaard H. , Smerup M. , Stegmann F. , Sloth E. , Østergaard K. H. , Nissen P. , Runge M. , Pitsillides K. , Wang T.
Published: August 2009

How blood flow and pressure to the giraffe's brain are regulated when drinking remains debated. We measured simultaneous blood flow, pressure, and cross-sectional area in the carotid artery and jugular vein of five anesthetized and spontaneously breathing giraffes. The giraffes were suspended in the upright position so that we could lower the head. In the upright position, mean arterial pressure (MAP) was 193 ± 11 mmHg (mean ± SE), carotid flow was 0.7 ± 0.2 l/min, and carotid cross-sectional area was 0.85 ± 0.04 cm2. Central venous pressure (CVP) was 4 ± 2 mmHg, jugular flow was 0.7 ± 0.2 l/min, and jugular cross-sectional area was 0.14 ± 0.04 cm2 ( n = 4). Carotid arterial and jugular venous pressures at head level were 118 ± 9 and −7 ± 4 mmHg, respectively. When the head was lowered, MAP decreased to 131 ± 13 mmHg, while carotid cross-sectional area and flow remained unchanged. Cardiac output was reduced by 30%, CVP decreased to −1 ± 2 mmHg ( P < 0.01), and jugular flow ceased as the jugular cross-sectional area increased to 3.2 ± 0.6 cm2 ( P < 0.01), corresponding to accumulation of ∼1.2 l of blood in the veins. When the head was raised, the jugular veins collapsed and blood was returned to the central circulation, and CVP and cardiac output were restored. The results demonstrate that in the upright-positioned, anesthetized giraffe cerebral blood flow is governed by arterial pressure without support of a siphon mechanism and that when the head is lowered, blood accumulates in the vein, affecting MAP.
Peritubular capillary preservation with COMP-angiopoietin-1 decreases ischemia-reperfusion-induced acute kidney injury
Authors: Jung Yu Jin , Kim Duk Hoon , Lee Ae Sin , Lee Sik , Kang Kyung Pyo , Lee Sang Yong , Jang Kyu Yun , Sung Mi Jeong , Park Sung Kwang , Kim Won
Published: August 2009

Ischemia followed by reperfusion induces microvascular endothelial cell injury, leading to the loss of functions such as regulation of vascular tone, tissue perfusion, permeability, and inflammation in kidney. Improvement of this endothelial dysfunction could be a good approach to treating ischemia-reperfusion-induced renal injury. Cartilage oligomeric matrix protein-angiopoietin-1 (COMP-Ang1) is a variant of native angiogenic factor angiopoietin-1 engineered to have higher activity. We evaluated the protective effect of COMP-Ang1 in an ischemia-reperfusion renal injury model. COMP-Ang1 preserved renal peritubular capillaries after ischemia-reperfusion injury without recruiting pericytes. Pretreatment with COMP-Ang1 attenuated the increase of blood urea nitrogen and serum creatinine levels after ischemia-reperfusion. In addition, the morphological examination indicated less tubular injury in mice pretreated with COMP-Ang1 than in those treated with the vehicle. COMP-Ang1 treatment reduced the increase in the number of Gr-1-positive neutrophils or ER-HR3-positive macrophages infiltrating kidneys, increased phosphorylation of Akt, and preserved renal tissue perfusion flow and microvascular permeability. Furthermore, COMP-Ang1 decreased renal interstitial fibrosis 30 days after the ischemia-reperfusion injury. In conclusion, COMP-Ang1 can be a possible endothelial cell-targeted therapy for preventing ischemia-reperfusion-induced acute kidney injury.
Adrenalectomy prevents renal ischemia-reperfusion injury
Authors: Ramírez Victoria , Trujillo Joyce , Valdes Rafael , Uribe Norma , Cruz Cristino , Gamba Gerardo , Bobadilla Norma A.
Published: August 2009

Spironolactone treatment prevents renal damage induced by ischemia-reperfusion (I/R), suggesting that renoprotection conferred by spironolactone is mediated by mineralocorticoid receptor (MR) blockade. It is possible, however, that this effect is due to other mechanisms. Therefore, this study evaluated whether adrenalectomy prevented renal damage induced by I/R. Three groups of Wistar rats were studied: 1) a group subjected to a sham surgery, 2) a group subjected to bilateral I/R, and 3) a group of rats in which adrenal glands were removed 3 days before induction of I/R. As expected, I/R resulted in renal dysfunction and severe tubular injury that was associated with a significant increase in tubular damage markers. In contrast, there was no renal dysfunction or tubular injury in rats that were adrenalectomized before I/R. These effects were demonstrated by normalization of glomerular filtration rate, markers of oxidative stress, and tubular injury markers in adrenalectomized rats. The renoprotection observed was associated with the reestablishment of nitric oxide metabolites, increased endothelial nitric oxide synthase expression and its activating phosphorylation, as well as normalization of Rho-kinase expression and ETAmRNA levels. Our results show that aldosterone plays a central role in the pathogenesis of renal damage induced by I/R and that MR blockade may be a promising strategy that opens a new therapeutic option for preventing acute renal injury.
Mammalian stanniocalcin-1 activates mitochondrial antioxidant pathways: new paradigms for regulation of macrophages and endothelium
Authors: Sheikh-Hamad David
Published: August 2009

The mammalian homolog of the fish calcium regulatory hormone stanniocalcin-1 (STC1) is ubiquitously expressed and likely functions in an autocrine/paracrine fashion. Mammalian STC1 does not appear to exert significant effects on serum calcium, and its physiological role remains to be determined. In macrophages, STC1 decreases intracellular calcium and cell mobility; attenuates the response to chemoattractants; and diminishes superoxide generation through induction of uncoupling protein-2 (UCP2). In cytokine-treated endothelial cells, STC1 attenuates superoxide generation and the activation of inflammatory pathways [c-Jun NH2-terminal kinase (JNK) and NF-κB]; maintains the expression of tight junction proteins, preserving the endothelial monolayer seal; and decreases transendothelial migration of leukocytes. Combined, the effects of STC1 on endothelial cells and macrophages predict potent anti-inflammatory action. Indeed, application of the anti-glomerular basement membrane (GBM) glomerulonephritis model to STC1 transgenic mice that display increased expression of STC1 transgene in endothelial cells and macrophages yields renal protection. Our data suggest that STC1 activates antioxidant pathways in endothelial cells and macrophages and displays cytoprotective and anti-inflammatory actions.
Human heat shock protein 27-overexpressing mice are protected against acute kidney injury after hepatic ischemia and reperfusion
Authors: Park Sang Won , Chen Sean W. C. , Kim Mihwa , D'Agati Vivette D. , Lee H. Thomas
Published: August 2009

Liver ischemia-reperfusion injury (IRI) causes acute kidney injury (AKI) in mice characterized by renal endothelial cell apoptosis, renal tubular necrosis, inflammation, and filamentous (F)-actin disruption. Since heat shock protein 27 (HSP27) protects against apoptosis, necrosis, and stabilizes F-actin, we questioned whether overexpression of human HSP27 (huHSP27 OE) in mice would attenuate AKI after liver IRI. Twenty-four hours after hepatic IRI, HSP27 wild-type (WT) mice developed acute liver and kidney injury with elevated plasma alanine aminotransferase and creatinine, a reduced glomerular filtration rate, and histological evidence of renal endothelial cell apoptosis and tubular injury (necrosis, vacuolization, and F-actin disruption). The huHSP27 OE mice, however, were significantly protected against both liver and kidney injury after hepatic IRI. The huHSP27 OE mice also showed less induction of several proinflammatory mRNAs (TNF-α, MIP-2, and keratinocyte-derived cytokine), neutrophil infiltration, and reduction in apoptosis (terminal deoxynucleotidyl transferase biotin-dUTP nick end-labeling assay and DNA laddering) in the kidney compared with the HSP27 WT mice. Moreover, the huHSP27 OE mice showed significantly less disruption of F-actin in renal proximal tubules and better preserved vascular endothelial cell integrity compared with the huHSP27 OE mice. Finally, the kidney plays a major role in the hepatoprotective effects of huHSP27 overexpression as the hepatoprotection was reduced or abolished in mice subjected to unilateral or bilateral nephrectomy, respectively. Our results show that overexpression of huHSP27 protects against hepatic injury and AKI associated with liver IRI in vivo. Harnessing the mechanisms of cytoprotection with renal HSP27 may lead to new therapies for the perioperative AKI and liver injury associated with liver IRI.
Mechanoregulation of BK channel activity in the mammalian cortical collecting duct: role of protein kinases A and C
Authors: Liu Wen , Wei Yuan , Sun Peng , Wang Wen-Hui , Kleyman Thomas R. , Satlin Lisa M.
Published: August 2009

Flow-stimulated net K secretion ( JK) in the cortical collecting duct (CCD) is mediated by an iberiotoxin (IBX)-sensitive BK channel, and requires an increase in intracellular Ca2+concentration ([Ca2+]i). The α-subunit of the reconstituted BK channel is phosphorylated by PKA and PKC. To test whether the BK channel in the native CCD is regulated by these kinases, JKand net Na absorption ( JNa) were measured at slow (∼1) and fast (∼5 nl·min−1·mm−1) flow rates in rabbit CCDs microperfused in the presence of mPKI, an inhibitor of PKA; calphostin C, which inhibits diacylglycerol binding proteins, including PKC; or bisindolylmaleimide (BIM) and Gö6976, inhibitors of classic and novel PKC isoforms, added to luminal (L) and/or basolateral (B) solutions. L but not B mPKI increased JKin CCDs perfused at a slow flow rate; a subsequent increase in flow rate augmented JKmodestly. B mPKI alone or with L inhibitor abolished flow stimulation of JK. Similarly, L calphostin C increased JKin CCDs perfused at slow flow rates, as did calphostin C in both L and B solutions. The observation that IBX inhibited the L mPKI- and calphostin C-mediated increases in JKat slow flow rates implicated the BK channel in this K flux, a notion suggested by patch-clamp analysis of principal cells. The kinase inhibited by calphostin C was not PKC as L and/or B BIM and Gö6976 failed to enhance JKat the slow flow rate. However, addition of these PKC inhibitors to the B solution alone or with L inhibitor blocked flow stimulation of JK. Interpretation of these results in light of the effects of these inhibitors on the flow-induced elevation of [Ca2+]isuggests that the principal cell apical BK channel is tonically inhibited by PKA and that flow stimulation of JKin the CCD is PKA and PKC dependent. The specific targets of the kinases remain to be identified.
Clock genes and metabolic disease
Authors: Marcheva Biliana , Ramsey Kathryn Moynihan , Affinati Alison , Bass Joseph
Published: August 2009

The circadian system is a key integrator of behavior and metabolism that synchronizes physiological processes with the rotation of the Earth on its axis. In mammals, the clock is present not only within the central pacemaker neurons of the hypothalamus, but also within extra-suprachiasmatic nucleus (SCN) regions of brain and nearly all peripheral tissues. Recent evidence suggests that the complex feedback networks that encompass both the circadian and metabolic systems are intimately intertwined and that disruption of either system leads to reciprocal disturbances in the other. We anticipate that improved understanding of the interconnections between the circadian and metabolic networks will open new windows on the treatment of sleep and metabolic disorders, including diabetes mellitus and obesity.
Breakdown of Effective Connectivity During Slow Wave Sleep: Investigating the Mechanism Underlying a Cortical Gate Using Large-Scale Modeling
Authors: Esser Steve K. , Hill Sean , Tononi Giulio
Published: August 2009

Effective connectivity between cortical areas decreases during slow wave sleep. This decline can be observed in the reduced interareal propagation of activity evoked either directly in cortex by transcranial magnetic stimulation (TMS) or by sensory stimulation. We present here a large-scale model of the thalamocortical system that is capable of reproducing these experimental observations. This model was constructed according to a large number of physiological and anatomical constraints and includes over 30,000 spiking neurons interconnected by more than 5 million synaptic connections and organized into three cortical areas. By simulating the different effects of arousal promoting neuromodulators, the model can produce a waking or a slow wave sleep-like mode. In this work, we also seek to explain why intercortical signal transmission decreases in slow wave sleep. The traditional explanation for reduced brain responses during this state, a thalamic gate, cannot account for the reduced propagation between cortical areas. Therefore we propose that a cortical gate is responsible for this diminished intercortical propagation. We used our model to test three candidate mechanisms that might produce a cortical gate during slow wave sleep: a propensity to enter a local down state following perturbation, which blocks the propagation of activity to other areas, increases in potassium channel conductance that reduce neuronal responsiveness, and a shift in the balance of synaptic excitation and inhibition toward inhibition, which decreases network responses to perturbation. Of these mechanisms, we find that only a shift in the balance of synaptic excitation and inhibition can account for the observed in vivo response to direct cortical perturbation as well as many features of spontaneous sleep.
Motor Unit Rotation in a Variety of Human Muscles
Authors: Bawa Parveen , Murnaghan Chantelle
Published: August 2009

The phenomena of substitution and rotation among motor units of a muscle were examined in seven different muscles. Intramuscular motor unit activity and surface electromyographic (EMG) activity were recorded from one of the following muscles: abductor digiti minimi, first dorsal interosseous, extensor digitorum communis, flexor and extensor carpi radialis, tibialis anterior, and soleus. The subject was asked to discharge a discernible unit at a comfortable constant or rhythmically (pseudosinusoidally) modulated rate with audio and visual feedback. Results are reported from a total of 42 sets of motor units from all seven muscles. We observed that when a subject fired a motor unit for a long period, an additional motor unit frequently started to discharge after a few minutes. When the subject was asked to keep activity down to one unit, very often it was Unit 1 that dropped and Unit 2 continued to fire. Whereas Unit 2 had fired for a few minutes, Unit 1 resumed firing without any conscious effort by the subject. If the subject was then asked to retain just one unit, it was Unit 2 that dropped. Rhythmic modulation of firing rate of a tonically firing unit showed that whereas the threshold of this unit increased, the threshold of a phasically discharging unit decreased substantially. The increase in threshold of a tonically discharging unit is suggested to arise from inactivation of Na+and Ca2+channels and the decrease in threshold of higher-threshold units is suggested to arise from an increase in persistent inward currents that may occur during prolonged contractions. Whether a unit stops or starts to fire is suggested to depend on a balance between the strength of the central motor command, persistent inward currents, and inactivation of voltage-gated channels. Such rotations among low-threshold motoneurons would ensure low-level sustained contractions to be viable not only in small hand muscles but also in larger limb muscles.
Synaptic Noise and Physiological Coupling Generate High-Frequency Oscillations in a Hippocampal Computational Model
Authors: Stacey William C. , Lazarewicz Maciej T. , Litt Brian
Published: August 2009

There is great interest in the role of coherent oscillations in the brain. In some cases, high-frequency oscillations (HFOs) are integral to normal brain function, whereas at other times they are implicated as markers of epileptic tissue. Mechanisms underlying HFO generation, especially in abnormal tissue, are not well understood. Using a physiological computer model of hippocampus, we investigate random synaptic activity (noise) as a potential initiator of HFOs. We explore parameters necessary to produce these oscillations and quantify the response using the tools of stochastic resonance (SR) and coherence resonance (CR). As predicted by SR, when noise was added to the network the model was able to detect a subthreshold periodic signal. Addition of basket cell interneurons produced two novel SR effects: 1) improved signal detection at low noise levels and 2) formation of coherent oscillations at high noise that were entrained to harmonics of the signal frequency. The periodic signal was then removed to study oscillations generated only by noise. The combined effects of network coupling and synaptic noise produced coherent, periodic oscillations within the network, an example of CR. Our results show that, under normal coupling conditions, synaptic noise was able to produce gamma (30–100 Hz) frequency oscillations. Synaptic noise generated HFOs in the ripple range (100–200 Hz) when the network had parameters similar to pathological findings in epilepsy: increased gap junctions or recurrent synaptic connections, loss of inhibitory interneurons such as basket cells, and increased synaptic noise. The model parameters that generated these effects are comparable with published experimental data. We propose that increased synaptic noise and physiological coupling mechanisms are sufficient to generate gamma oscillations and that pathologic changes in noise and coupling similar to those in epilepsy can produce abnormal ripples.
Simultaneous Preparation of Multiple Potential Movements: Opposing Effects of Spatial Proximity Mediated by Premotor and Parietal Cortex
Authors: Praamstra Peter , Kourtis Dimitrios , Nazarpour Kianoush
Published: August 2009

Neurophysiological studies in monkey have suggested that premotor and motor cortex may prepare for multiple movements simultaneously, sustained by cooperative and competitive interactions within and between the neural populations encoding different actions. Here, we investigate whether competition between alternative movement directions, manipulated in terms of number and spatial angle, is reflected in electroencephalographic (EEG) measures of (pre)motor cortical activity in humans. EEG was recorded during performance of a center-out pointing task in which response signals were preceded by cues providing prior information in the form of arrows pointing to one or more possible movement targets. Delay-period activity in (pre)motor cortex was modulated in the predicted manner by the number of possible movement directions and by the angle separating them. Response latencies, however, were determined not only by the amplitude of movement-preparatory activity, but also by differences in the duration of stimulus evaluation against the visuospatial memory of the cue, reflected in EEG potentials originating from posterior parietal cortex (PPC). Specifically, the spatial proximity of possible movement targets was processed differently by (pre)motor and posterior parietal cortex. Spatial proximity enhanced the amplitude of (pre)motor cortex preparatory activity during the delay period but delayed evaluation of the response signal in the PPC, thus producing opposite effects on response latency. The latter finding supports distributed control of movement decisions in the frontoparietal network, revealing a feature of distributed control that is of potential significance for the understanding of distracter effects in reaching and pointing.
Spatial and Temporal Integration of Visual Motion Signals for Smooth Pursuit Eye Movements in Monkeys
Authors: Osborne Leslie C. , Lisberger Stephen G.
Published: August 2009

To probe how the brain integrates visual motion signals to guide behavior, we analyzed the smooth pursuit eye movements evoked by target motion with a stochastic component. When each dot of a texture executed an independent random walk such that speed or direction varied across the spatial extent of the target, pursuit variance increased as a function of the variance of visual pattern motion. Noise in either target direction or speed increased the variance of both eye speed and direction, implying a common neural noise source for estimating target speed and direction. Spatial averaging was inefficient for targets with >20 dots. Together these data suggest that pursuit performance is limited by the properties of spatial averaging across a noisy population of sensory neurons rather than across the physical stimulus. When targets executed a spatially uniform random walk in time around a central direction of motion, an optimized linear filter that describes the transformation of target motion into eye motion accounted for ∼50% of the variance in pursuit. Filters had widths of ∼25 ms, much longer than the impulse response of the eye, and filter shape depended on both the range and correlation time of motion signals, suggesting that filters were products of sensory processing. By quantifying the effects of different levels of stimulus noise on pursuit, we have provided rigorous constraints for understanding sensory population decoding. We have shown how temporal and spatial integration of sensory signals converts noisy population responses into precise motor responses.
A Simple Experimentally Based Model Using Proprioceptive Regulation of Motor Primitives Captures Adjusted Trajectory Formation in Spinal Frogs
Authors: Kargo William J. , Ramakrishnan Arun , Hart Corey B. , Rome Lawrence C. , Giszter Simon F.
Published: August 2009

Spinal circuits may organize trajectories using pattern generators and synergies. In frogs, prior work supports fixed-duration pulses of fixed composition synergies, forming primitives. In wiping behaviors, spinal frogs adjust their motor activity according to the starting limb position and generate fairly straight and accurate isochronous trajectories across the workspace. To test whether a compact description using primitives modulated by proprioceptive feedback could reproduce such trajectory formation, we built a biomechanical model based on physiological data. We recorded from hindlimb muscle spindles to evaluate possible proprioceptive input. As movement was initiated, early skeletofusimotor activity enhanced many muscle spindles firing rates. Before movement began, a rapid estimate of the limb position from simple combinations of spindle rates was possible. Three primitives were used in the model with muscle compositions based on those observed in frogs. Our simulations showed that simple gain and phase shifts of primitives based on published feedback mechanisms could generate accurate isochronous trajectories and motor patterns that matched those observed. Although on-line feedback effects were omitted from the model after movement onset, our primitive-based model reproduced the wiping behavior across a range of starting positions. Without modifications from proprioceptive feedback, the model behaviors missed the target in a manner similar to that in deafferented frogs. These data show how early proprioception might be used to make a simple estimate initial limb state and to implicitly plan a movement using observed spinal motor primitives. Simulations showed that choice of synergy composition played a role in this simplicity. To generate froglike trajectories, a hip flexor synergy without sartorius required motor patterns with more proprioceptive knee flexor control than did patterns built with a more natural synergy including sartorius. Such synergy choices and control strategies may simplify the circuitry required for reflex trajectory construction and adaptation.