bluuebunny/crossref_metadata_2025 huggingface dataset:
Molecular beam epitaxy of InP-based alloys for long-wavelength vertical cavity lasers
Authors: Buell David A. , Feezell Daniel , Finland Bjørn-Ove , Coldren Larry
Published: June 2006

In this article we describe the growth, design, and characterization of a 1310nm lattice-matched vertical cavity laser which take advantage of an AlGaAsSb distributed Bragg reflector and AlInGaAs active regions. The molecular beam epitaxial growth for this structure was particularly challenging due to the various III–V alloys used; in particular, the interfaces between them were observed to be a significant source of macroscopic defects and roughness. The AlGaAsSb–InP interface was seen to control the yield and overall quality of device structures, and so was the focus of the crystal growth optimization. InP heat- and current-spreading layers were utilized to offset the thermal and electrical limitations of the AlGaAsSb mirrors; we optimized the defect density and roughness of these epilayers by studying their dependence on growth temperature and P overpressure. Vertical cavity lasers grown using these optimized approaches and incorporating a thin, selectively etched tunnel-junction aperture were fabricated and tested, and demonstrated promising characteristics. Operating temperatures up to 90°C with single-mode power in excess of 1.6mW were observed. Differential quantum efficiency of 64% was seen for our best devices, a record for long-wavelength vertical cavity lasers.
Molecular beam epitaxial growth of ZnMgO∕ZnO∕ZnMgO single quantum well structure on Si(111) substrate
Authors: Fujita Miki , Suzuki Ryotaro , Sasajima Masanori , Kosaka Tomohiro , Deesirapipat Yuparwadee , Horikoshi Yoshiji
Published: June 2006

We grow Zn1−xMgxO∕ZnO∕Zn1−xMgxO single quantum well structures on Si(111) substrates by using ZnO∕MgO buffer layers. MgO buffer layer on Si substrate is essential to the crack-free ZnO epitaxial growth. On the other hand, ZnO buffer layer on MgO buffer layer guarantees the hexagonal ZnMgO layer on it. The two different Mg fractions, 0.12 and 0.32, are used for Zn1−xMgxO barrier layers. The photoluminescence measurement at 10K using He–Cd laser shows clear emission lines from the single quantum wells. Their peak energies increase with decreasing the quantum well width and coincide quite well with the simulation based on the previously reported parameters. These results show that good quality Zn1−xMgxO∕ZnO∕Zn1−xMgxO single quantum well structures have been grown on Si(111) substrates.
Atomic force microscopy study of sapphire surfaces annealed with a H2O flux from a baffled molecular-beam epitaxy effusion cell loaded with Al(OH)3
Authors: Oye Michael M. , Hurst Jeffrey B. , Shahrjerdi Davood , Kulkarni N. N. , Muller A. , Beck A. L. , Sidhu R. , Shih C. K. , Banerjee Sanjay K. , Campbell Joe C. , Holmes Archie L. , Mattord Terry J. , Reifsnider Jason M.
Published: June 2006

We present an atomic force microscopy (AFM) study of sapphire surfaces that contain scratches with various severities. The objective was to observe the effects of substrate annealing at 850°C for 200min with a H2O-based overpressure resulting from an Al(OH)3 powder that was thermally cracked at 1200°C. The Al(OH)3 was decomposed into Al2O3 and H2O according to a partial Bayer process in a modified molecular-beam epitaxy (MBE) effusion cell, which was equipped with homemade baffles placed at its outlet. These homemade, simple-to-construct tantalum baffles allow for the selective outfluxing of gaseous species, from those that are solid based. A UTI™ 100C-model mass spectrometer was used to monitor the species present at the sapphire surface during annealing. Any aluminum-based solid species from the Al(OH)3 were not observed in the mass spectrum, although the H2O-based species were. The sapphire substrates were annealed in a Varian Gen II™ MBE system, with H2O beam equivalent pressures (BEPs) of 5×10−6 and 2×10−5Torr, as well as with no H2O flux at all. The AFM images show that the samples annealed with a higher H2O BEP of 2×10−5Torr had noticeably less severe surface scratches than the samples that were annealed with lower H2O BEPs.
Large area all-dielectric planar chiral metamaterials by electron beam lithography
Authors: Zhang W. , Potts A. , Bagnall D. M. , Davidson B. R.
Published: June 2006

All-dielectric optically active planar chiral metamaterials have been fabricated by electron beam lithography. We have demonstrated the effectiveness of a polymeric charge dispersion layer in dramatically reducing charge buildup during the exposure of chemically amplified resists on dielectric substrates. This technique has allowed the fabrication of large-area high density planar chiral structures with sub-200nm resolutions and stitching accuracy. A significant change in the polarization state of visible light transmitted from patterned surfaces is observed, including a maximum 9° change in ellipticity and 22° change in polarization azimuth rotation. These effects are shown to be dependent on the sense of chirality of the surface and the input polarization state of the light. Furthermore, we have also demonstrated that these dielectric planar chiral surfaces, with enantiomeric chiral designs, show a strong modulation in the intensity of the diffracted beams. These optical activities could make these surfaces particularly promising candidates for the development of integrable solid-state polarization sensitive devices.
Effect of film thickness on the electrical properties of tantalum nitride thin films deposited on SiO2∕Si substrates for Π-type attenuator applications
Authors: Cuong Nguyen Duy , Kim Dong-Jin , Kang Byoung-Don , Kim Chang-Soo , Yoon Soon-Gil
Published: June 2006

Ta 2 N films were deposited on SiO2∕Si substrates using reactive dc magnetron sputtering, and were then annealed in a vacuum ambient. The structural and electrical properties of Ta2N films and their dependence on the film thickness (50–200nm) were characterized with respect to their application as Π-type attenuators. The root mean square roughness and temperature coefficient of resistance (TCR) increased with increasing film thickness. The near zero TCR value of the films is possible by controlling the annealing temperature or film thickness. The sheet resistance and TCR of 50nm thick Ta2N films are approximately 80Ω∕◻ and −24ppm∕K, respectively, and are suitable for 10dB applications in Π-type attenuators.
Formation of nickel nanoparticles on amorphous silicon thin film and its effect on crystallization
Authors: Lee Sung Bo , Choi Duck-Kyun , Phillipp Fritz , Kim Young-Min , Kim Youn-Joong
Published: June 2006

Using in situ high-resolution transmission electron microscopy, we observe that, while annealed at 550°C in the TEM, a Ni-deposited amorphous silicon thin film is crystallized, which is preceded by the formation of NiSi2 precipitates. In addition to the NiSi2 precipitates, nanometer-sized Ni particles, single crystalline or multiply twinned, form. Their unusual formation is attributed to beam heating effect by beam irradiation during the observations. Unlike the NiSi2 precipitates, no crystallization occurs around the Ni nanoparticles.
Emission characteristics of printed carbon nanotube cathodes after laser treatment
Authors: Hosono Akihiko , Shiroishi Tetsuya , Nishimura Kunihiko , Abe Fumio , Shen Zhiying , Nakata Shuhei , Okuda Soichiro
Published: June 2006

Recently, field emission displays using printed carbon nanotubes (CNTs) as an emitter have been researched eagerly. By laser irradiation, some CNTs in the printed CNT layer stand out, and they work as the emission sites. We found that the higher CNTs that are easier to be the emission sites tend to exist at the boundary of the laser irradiation pattern. We used the irradiation patterns that consist of the arrays of microirradiation pattern to increase the total length of boundary. Both emission characteristics and emission uniformity were improved by the increase of the boundary length. We examined several lasers, and the irradiation by the second harmonic generation yttrium aluminum garnet laser of which wavelength was greatest in our experiment provided the best emission characteristics (turn-on electric field <2V∕μm) and emission uniformity (turn-on electric field deviation <5%).
Thermal stability of chemical vapor deposition grown W and WNx thin films in low-k integration structure
Authors: Jeon Sungho , Yong Kijung , Park Sung-Gyu , Rhee Shi-Woo
Published: June 2006

The Cu/barrier/low-k SiCOH∕Si structures were fabricated and their thermal stability was investigated. SiCOH films were deposited by plasma-enhanced chemical vapor deposition using divinyldimethylsilane (DVDMS) and O2. As barrier materials, tungsten and tungsten nitride films were deposited by chemical vapor deposition using W(CO)6 and NH3 sources at 450°C. Variations of scanning electron microscopy and x-ray diffraction results of Cu/barrier/low-k SiCOH∕Si were examined depending on the annealing temperature. Both results showed that W and W2N film were stable up to 500 and above 600°C, WO3 nanorods were grown from the sample surface. It is thought that the thermal stability of the Cu/barrier/SiCOH∕Si structure is closely related with the thermal destruction of the W and WNx films.
Formation of nanostructured cobalt wires with Chinese caterpillar type structure
Authors: Huang F.-T. , Liu R. S. , Hu S. F. , Lee C.-L. , Li A. K.
Published: June 2006

A synthetic method of cobalt wires with platelike structure similar to Chinese caterpillar fungus (cordyceps sinensis) has been developed in aqueous media. Cobalt nanoparticles as seeds were prepared by reducing cobalt chloride with NaBH4 under inert atmosphere which act as nucleation sites. We added an even weaker reducing agent, hydrazine, to the growth solution, and the solution was kept undisturbed at 80°C for 90min to obtain our product. A mechanism that involved in the formation of cobalt wires has also been proposed. The discovered cobalt wires may be applied to the fabrication of nanocircuitry or ultrahigh-density storage media.
ErAs island-stacking growth technique for engineering textured Schottky interfaces
Authors: Zimmerman Jeramy D. , Gossard Arthur C. , Young Adam C. , Miller Merritt P. , Brown Elliott R.
Published: June 2006

We demonstrate a molecular beam epitaxy growth technique to create intentionally textured interfaces between semimetallic ErAs and GaAs that result in interface orientations that are different from the substrate. To grow the textured interfaces, ErAs is deposited on (100) GaAs and islands form in an island growth mode. Enough GaAs is then deposited to fill the space between islands with semiconductor. More ErAs is deposited on the ErAs∕GaAs surface and the new ErAs islands are thought to nucleate on the exposed top surface of the partially covered islands. The process is repeated to “stack” the islands. By quadratically increasing the amount of ErAs deposited in each repetition, the islands form into cones/pyramids that coalesce into a complete film with an intentionally roughened interface. Compared to a smooth interface between ErAs and GaAs, the Schottky barrier height between textured ErAs and n-GaAs can be reduced from ∼0.81to∼0.52eV, and the Schottky barrier height between ErAs and p-GaAs can be increased from ∼0.38to∼0.63eV.
STATEFINDER PARAMETERS FOR PHANTOM DARK ENERGY
Authors: WU PUXUN , YU HONGWEI
Published: June 2006

The statefinder parameters were introduced recently to differentiate different dark energy models. In this paper we perform a statefinder diagnostic to the phantom dark energy model with two different phantom field potentials. Our results show that the statefinder diagnostic is rather robust in differentiating not only different dark energy models but also the same kind of models with different potentials which lead to different fate of the universe.
REMARKS ON THE SPHERICAL WAVES OF THE DIRAC FIELD ON de SITTER SPACETIME
Authors: COTĂESCU ION I. , RACOCEANU RADU , CRUCEAN COSMIN
Published: June 2006

The Shishkin's solutions of the Dirac equation in spherical moving frames of the de Sitter spacetime are investigated pointing out the set of commuting operators whose eigenvalues determine the integration constants. It is shown that these depend on the usual angular quantum numbers and, in addition, on the value of the scalar momentum. With these elements a new result is obtained finding the system of solutions normalized (in generalized sense) in the scale of scalar momentum.
QUANTIZATION OF FIELDS BASED ON GENERALIZED UNCERTAINTY PRINCIPLE
Authors: MATSUO TOSHIHIRO , SHIBUSA YUUICHIROU
Published: June 2006

We construct a quantum theory of free scalar field in (1+1) dimensions based on the deformed Heisenberg algebra [Formula: see text] where β is a deformation parameter. Both canonical and path integral formalisms are employed. A higher dimensional extension is easily performed in the path integral formalism.
TWIST TO CLOSE
Authors: VASSILEVICH D. V.
Published: June 2006

It has been proposed that the Poincaré and some other symmetries of noncommutative field theories should be twisted. Here we extend this idea to gauge transformations and find that twisted gauge symmetries close for arbitrary gauge group. We also analyse twisted-invariant actions in noncommutative theories.
Tight Junctions and Cell Polarity
Authors: Shin Kunyoo , Fogg Vanessa C. , Margolis Ben
Published: June 2006

The tight junction is an intracellular junctional structure that mediates adhesion between epithelial cells and is required for epithelial cell function. Tight junctions control paracellular permeability across epithelial cell sheets and also serve as a barrier to intramembrane diffusion of components between a cell's apical and basolateral membrane domains. Recent genetic and biochemical studies in invertebrates and vertebrates indicate that tight junction proteins play an important role in the establishment and maintenance of apico-basal polarity. Proteins involved in epithelial cell polarization form evolutionarily conserved multiprotein complexes at the tight junction, and these protein complexes regulate the architecture of epithelia throughout the polarization process. Accumulating information regarding the regulation of these polarity proteins will lead to a better understanding of the molecular mechanisms whereby cell polarity is established.
Intersection of Signal Transduction Pathways and Development
Authors: Vivekanand Pavithra , Rebay Ilaria
Published: June 2006

One of the challenges of modern biology is to understand how cells within a developing organism generate, integrate, and respond to dynamic informational cues. Based on over two decades of intensive research, many parts and subroutines of the responsible signal transduction networks have been identified and functionally characterized. From this work, it has become evident that a complicated interplay between signaling pathways, involving extensive feedback regulation and multiple levels of cross-talk, underlies even the “simplest” developmental decision. Thus a signaling pathway can no longer be thought of as a rigid linear process, but rather must be considered a dynamic, self-interacting, and self-adjusting network. The Epidermal Growth Factor Receptor tyrosine kinase signaling pathway provides a prime vantage point from which to explore emerging principles in developmental signal transduction.
The Social and Legal Construction of Suspects
Authors: Cole Simon A. , Lynch Michael
Published: June 2006

▪ Abstract  DNA profiling and searchable databases enhance the ability of policing organizations to search for criminal suspects. In many respects, these technologies are incorporated within traditions of police work, supplementing familiar “subjective” methods of constructing suspects. In other ways, however, the construction of DNA databases in Britain, the United States, and elsewhere shifts criminal investigation toward suspect populations and statistical suspects. Not only is DNA evidence used to confirm that a criminal suspect is the source of crime scene evidence, it can be used to search freely through a suspect population for a possible source of such evidence. This method, commonly known as database trawling, comprises a new way of constructing suspects, one that bears close connections with new data mining technologies for prospectively identifying terrorist suspects.
Understanding Microbial Metabolism
Authors: Downs Diana M.
Published: June 2006

Metabolism encompasses the biochemical basis of life and as such spans all biological disciplines. Many decades of basic research, primarily in microbes, have resulted in extensive characterization of metabolic components and regulatory paradigms. With this basic knowledge in hand and the technologies currently available, it has become feasible to move toward an understanding of microbial metabolism as a system rather than as a collection of component parts. Insight into the system will be generated by continued efforts to rigorously define metabolic components combined with renewed efforts to discover components and connections using in vivo–driven approaches. On the tail of a detailed understanding of components and connections that comprise metabolism will come the ability to generate a comprehensive mathematical model that describes the system. While microbes provide the logical organism for this work, the value of such a model would span biological disciplines. Described herein are approaches that can provide insight into metabolism and caveats of their use. The goal of this review is to emphasize that in silico, in vitro, and in vivo approaches must be used in combination to achieve a full understanding of microbial metabolism.
Cascade model of ventricular-arterial coupling and arterial-cardiac baroreflex function for cardiovascular variability in humans
Authors: Shibata Shigeki , Zhang Rong , Hastings Jeff , Fu Qi , Okazaki Kazunobu , Iwasaki Ken-ichi , Levine Benjamin D.
Published: June 2006

Cardiovascular variability reflects autonomic regulation of blood pressure (BP) and heart rate (HR). However, systolic BP (SBP) variability also may be induced by fluctuations in stroke volume through left ventricular end-diastolic pressure (LVEDP) variability via dynamic ventricular-arterial coupling during respiration. We hypothesized that dynamic ventricular-arterial coupling is modulated by changes in left ventricular compliance associated with altered preload and that a cascade control mechanism of ventricular-arterial coupling with arterial-cardiac baroreflex function contributes to the genesis of cardiovascular variability at the respiratory frequency. Seven healthy young subjects underwent 6-min recordings of beat-by-beat LVEDP, SBP, and HR in the supine position with controlled respiration at 0.2 Hz during hyper- and hypovolemia. Spectral and transfer function analysis of these variables was conducted between 0.18 and 0.22 Hz. Dynamic ventricular-arterial coupling gain (Gain LVEDP-SBP) was smaller by 25% ( P = 0.009) during hypervolemia than during hypovolemia, whereas arterial-cardiac baroreflex function gain (Gain SBP-HR) was similar. As predicted from a cascade model, a linear relationship between Gain LVEDP-HR and LVEDP-SBP times Gain SBP-HR was identified ( R2 = 0.93, P < 0.001). Gain LVEDP-HR was smaller by 40% ( P = 0.04) during hypervolemia than during hypovolemia, leading to a reduction in spectral power of HR variability by 45% ( P = 0.08). We conclude that dynamic ventricular-arterial coupling gain is reduced during hypervolemia because of a decrease in left ventricular compliance. A cascade model of ventricular-arterial coupling with the arterial-cardiac baroreflex contributes to the genesis of cardiovascular variability at the respiratory frequency.
Baroreceptor Reflex Sensitivity Estimated by the Sequence Technique is Reliable in Rats
Authors: Stauss Harald M. , Moffitt Julia A. , Chapleau Mark W. , Abboud Francois M. , Johnson Alan Kim
Published: June 2006

The following is the abstract of the article discussed in the subsequent letter:

The function of the arterial baroreflex has traditionally been assessed by measurement of reflex changes in heart rate (HR) or sympathetic nerve activity resulting from experimenter-induced manipulation of arterial blood pressure (the Oxford method, also termed the pharmacological method). However, logistical and flexibility limitations of this technique have promoted the development of new methods for assessing baroreflex function such as the evaluation of changes in spontaneous arterial pressure and HR. Although this new spontaneous method has been validated in dogs and humans, it has not been rigorously tested in rats. In the present study, the method of correlating spontaneous changes in systolic blood pressure and HR was evaluated in resting, normotensive Sprague-Dawley rats. This technique was found to be neither reliable nor valid under the conditions employed in the present protocol. We also tested a variation of the spontaneous method that evaluates particular sequences of data during which arterial pressure and pulse interval are changing in the same direction for at least three consecutive heart beats (the sequence method). The sequence method did not provide extra reliability or validity over the spontaneous method. We conclude that due to the restricted range of variability obtained by measuring spontaneous blood pressure fluctuations, the spontaneous and sequence techniques do not provide data that are comparable to the traditional method of assessing HR changes triggered by arterial blood pressure increases and decreases induced by vasoactive drugs. However, it is possible that surgical stress obscured the relationship between blood pressure and HR, and therefore additional studies are needed to determine whether the spontaneous and sequence methods can be applied to rats during different behavioral states.
TNF-α activation of arterioles and venules alters distribution and levels of ICAM-1 and affects leukocyte-endothelial cell interactions
Authors: Sumagin Ronen , Sarelius Ingrid H.
Published: June 2006

The observation that leukocyte-endothelial cell (EC) interactions are localized to specific regions on the microvessel wall suggests that adhesion molecule distribution is not uniform. We investigated ICAM-1 distribution and leukocyte-EC interactions in blood-perfused microvessels (<80 μm) in cremaster muscle of anesthetized mice, using intravital confocal microscopy and immunofluorescent labeling. Variability of ICAM-1 expression directly determines leukocyte adhesion distribution within the venular microcirculation and contributes to leukocyte rolling in arterioles during inflammation. The number of rolling interactions increased with ICAM-1 intensity ( r2= 0.69, P < 0.05), and rolling velocity was lower in regions of higher ICAM-1 intensity. In controls, venular ICAM-1 expression was approximately twofold higher than in arterioles. After TNF-α treatment, ICAM-1 expression was significantly increased, 2.8 ± 0.2-fold in arterioles and 1.7 ± 0.2-fold in venules ( P < 0.05). ICAM-1 expression on activated arteriolar ECs only reached the level of control venular ICAM-1. Arteriolar but not venular ECs underwent redistribution of ICAM-1 among cells; some cells increased and some decreased ICAM-1 expression, magnifying the variability of ICAM-1. TNF-α treatment increased the length of bright fluorescent regions per unit vessel length (42%, control; 70%, TNF-α) along the arteriolar wall, whereas no significant change was observed in venules (60%, control; 63%, TNF-α). The spatial distribution and expression levels of adhesion molecules in the microcirculation determine the timing and placement of leukocyte interactions and hence significantly impact the inflammatory response. That arteriolar ECs respond to TNF-α by upregulation of ICAM-1, although in a different way compared with venules, suggests an explicit role for arterioles in inflammatory responses.
Percutaneous intracoronary delivery of SERCA gene increases myocardial function: a tissue Doppler imaging echocardiographic study
Authors: Logeart Damien , Vinet Laurent , Ragot Thierry , Heimburger Michèle , Louedec Liliane , Michel Jean-Baptiste , Escoubet Brigitte , Mercadier Jean-Jacques
Published: June 2006

The aim of this study was to examine the efficiency of adenovirus-mediated overexpression of sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA1a) gene in a realistic model based on percutaneous intracoronary delivery and on noninvasive functional monitoring. Catheter-based selective coronary delivery of saline or adenoviruses (Ad.CMV.SERCA1a or Ad.CMV.lacZ, 1010plaque-forming units) was performed in the circumflex artery of rabbits. Effects were assessed and compared by using serial Doppler echocardiography, hemodynamics, and measurements of SERCA protein and Ca2+uptake activity. On day 3, a 21% increase in SERCA proteins and a 37% increase in the maximal rate of Ca2+uptake were observed in the transfected left ventricular (LV) walls of Ad.CMV.SERCA1a rabbits. Baseline hemodynamics and conventional echographic measurements of global LV function were poorly affected. In contrast, tissue Doppler imaging (TDI) was able to assess a strong increase in the baseline function of transfected LV walls, as assessed with maximal wall velocities (+32% and +43%, respectively) and strain rates (+18% and +30%, respectively). TDI parameters were closely related to the maximal rate of Ca2+uptake ( r2= 0.68 for the systolic strain rate). Serial TDI analysis during follow-up showed that the effects lasted for 7 days and were no longer detectable 15 days after adenoviruses injection. In conclusion, LV function can be increased by adenovirus-mediated overexpression of SERCA in a clinically relevant model, and TDI provides an accurate and noninvasive tool for monitoring effects on global as well as regional myocardial function.
β1-Adrenoceptor blockade mitigates excessive norepinephrine release into cardiac interstitium in mitral regurgitation in dog
Authors: Hankes Gerald H. , Ardell Jeffrey L. , Tallaj José , Wei Chih-Chang , Aban Inmaculada , Holland Merrilee , Rynders Patricia , Dillon Ray , Cardinal Rene , Hoover Donald B. , Armour J. Andrew , Husain Ahsan , Dell'Italia Louis J.
Published: June 2006

Mitral regurgitation (MR) is associated with increased neuronal release of norepinephrine (NE) and epinephrine (EP) into myocardial interstitial fluid (ISF) that may be necessary in sustaining left ventricular (LV) function via activation of cardiomyocyte β-adrenergic receptors (ARs). However, activation of neuronal β-ARs on cardiac neurons may lead to further catecholamine release, with an attendant risk of functional deterioration. We hypothesize that a beneficial effect of β-AR blockade may therefore mitigate excessive catecholamine release from cardiac adrenergic neurons in dogs with MR. We measured the effects of chronic β-receptor blockade (β-RB) on ISF NE and EP release using in vivo microdialysis in open-chest anesthetized dogs after 4 wk of MR with or without extended release of metoprolol succinate (100 mg/day) as well as in control dogs. Fractional shortening increased by 30% in both MR and MR + β-RB dogs after 4 wk of MR. In MR + β-RB dogs, stellate-stimulated heart rate change was attenuated compared with control and MR dogs, whereas peak change of LV pressure over time (+dP/d t) increased equally in all groups. Stellate-stimulated ISF NE increased fivefold over baseline in MR versus twofold in control dogs (<0.05), but the NE release was significantly attenuated in MR + β-RB dogs. In contrast, stellate-stimulated increases in ISF EP did not differ in control, MR, and MR + β-RB dogs. This study demonstrates that β-RB attenuates ISF NE release from cardiac neurons and that the LV functional response to MR is not dependent on an excess increase in ISF NE. Thus β1-RB may exert a beneficial effect by attenuating untoward effects of excessive sympathetic efferent neural NE release while sustaining early LV functional adaptation to MR.
Monoamine uptake inhibitors block α7-nAChR-mediated cerebral nitrergic neurogenic vasodilation
Authors: Long Cheng , Chen Mei-Fang , Sarwinski Susan J. , Chen Po-Yi , Si Minliang , Hoffer Barry J. , Evans M. Steven , Lee Tony J. F.
Published: June 2006

We have proposed that activation of cerebral perivascular sympathetic α7-nicotinic acetylcholine receptors (α7-nAChRs) by nicotinic agonists releases norepinephrine, which then acts on parasympathetic nitrergic nerves, resulting in release of nitric oxide and vasodilation. Using patch-clamp electrophysiology, immunohistochemistry, and in vitro tissue bath myography, we tested this axo-axonal interaction hypothesis further by examining whether blocking norepinephrine reuptake enhanced α7-nAChR-mediated cerebral nitrergic neurogenic vasodilation. The results indicated that choline- and nicotine-induced α7-nAChR-mediated nitrergic neurogenic relaxation in endothelium-denuded isolated porcine basilar artery rings was enhanced by desipramine and imipramine at lower concentrations (0.03–0.1 μM) but inhibited at higher concentrations (0.3–10 μM). In cultured superior cervical ganglion (SCG) neurons of the pig and rat, choline (0.1–30 mM)-evoked inward currents were reversibly blocked by 1–30 μM mecamylamine, 1–30 μM methyllycaconitine, 10–300 nM α-bungarotoxin, and 0.1–10 μM desipramine and imipramine, providing electrophysiological evidence for the presence of similar functional α7-nAChRs in cerebral perivascular sympathetic neurons of pigs and rats. In α7-nAChR-expressing Xenopus oocytes, choline-elicited inward currents were attenuated by α-bungarotoxin, imipramine, and desipramine. These monoamine uptake inhibitors appeared to directly block the α7-nAChR, resulting in diminished nicotinic agonist-induced cerebral nitrergic vasodilation. The enhanced nitrergic vasodilation by lower concentrations of monoamine uptake inhibitors is likely due to a greater effect on monoamine uptake than on α7-nAChR blockade. These results further support the hypothesis of axo-axonal interaction in nitrergic regulation of cerebral vascular tone.
Atorvastatin protects against cerebral infarction via inhibition of NADPH oxidase-derived superoxide in ischemic stroke
Authors: Hong Hua , Zeng Jin-Sheng , Kreulen David L. , Kaufman David I. , Chen Alex F.
Published: June 2006

Statins have recently been shown to exert neuronal protection in ischemic stroke. Reactive oxygen species, specifically superoxide formed during the early phase of reperfusion, augment neuronal injury. NADPH oxidase is a key enzyme for superoxide production. The present study tested the hypothesis that atorvastatin protects against cerebral infarction via inhibition of NADPH oxidase-derived superoxide in transient focal ischemia. Transient focal ischemia was created in halothane-anesthetized adult male Sprague-Dawley rats (250–300 g) by middle cerebral artery occlusion (MCAO). Atorvastatin (Lipitor, 10 mg/kg sc) was administered three times before MCAO. Infarct volume was measured by triphenyltetrazolium chloride staining. NADPH oxidase enzymatic activity and superoxide levels were quantified in the ischemic core and penumbral regions by lucigenin (5 μM)-enhanced chemiluminescence. Expression of NADPH oxidase membrane subunit gp91phox and membrane-translocated subunit p47phox and small GTPase Rac-1 was analyzed by Western blot. NADPH oxidase activity and superoxide levels increased after reperfusion and peaked within 2 h of reperfusion in the penumbra, but not in the ischemic core, in MCAO rats. Atorvastatin pretreatment prevented these increases, blunted expression of membrane subunit gp91phox, and prevented translocation of cytoplasmic subunit p47phox to the membrane in the penumbra 2 h after reperfusion. Consequently, cerebral infarct volume was significantly reduced in atorvastatin-treated compared with nontreated MCAO rats 24 h after reperfusion. These results indicate that atorvastatin protects against cerebral infarction via inhibition of NADPH oxidase-derived superoxide in transient focal ischemia.
Phosphorylation of phospholamban at threonine-17 reduces cardiac adrenergic contractile responsiveness in chronic pressure overload-induced hypertrophy
Authors: Mills Geoffrey D. , Kubo Hajime , Harris David M. , Berretta Remus M. , Piacentino Valentino , Houser Steven R.
Published: June 2006

Physiological hemodynamic stress, such as aerobic exercise, is intermittent and requires an increase in Ca2+-dependent contractility through sympathetic nervous system activation. Pathological hemodynamic stress, such as hypertension, is persistent and requires sustained increases in cardiac function. Over time, this causes left ventricular hypertrophy (LVH)-reduced responsiveness to sympathetic stimulation. In this study, we examined the hypothesis that blunted in vivo adrenergic contractile responsiveness in pressure overload (PO)-induced cardiac hypertrophy is caused by abnormalities in the abundance and/or basal phosphorylation state of Ca2+regulatory proteins. PO, induced by aortic constriction, caused concentric LVH or dilated LVH. Only animals with dilation exhibited a decrease in baseline left ventricle function [fractional area change (FAC); measured with echocardiography]. All PO animals had a reduced contractile response to adrenergic agonists (increase in FAC with 40 μg·kg−1·min−1dobutamine, control 0.30 ± 0.04, n = 5 vs. banded 0.10 ± 0.03, n = 10; P < 0.01). PO animals had reduced phospholamban (PLB) protein abundance ( P = 0.07, not significant) and increased PLB phosphorylation at the calmodulin-dependent kinase II (CaMKII)-specific site (PLB-Thr17, P < 0.05) but not at the protein kinase A-specific site (PLB-Ser16). PLB-Thr17phosphorylation was inversely correlated with dobutamine-induced increases in contractility in PO animals ( r2= 0.81, P < 0.05). Continuous induction of Ca2+transients in isolated ventricular myocytes for 24 h increased phosphorylation at PLB-Thr17and diminished inotropic responsiveness and PLB-Ser16phosphorylation after exposure to isoproterenol ( P < 0.05). These data show that reduced adrenergic responsiveness in feline PO hypertrophy and failure involves increases in basal PLB-Thr17phosphorylation, suggesting that activation of CaMKII in PO hypertrophy contributes to defective adrenergic reserve in compensated LVH and early heart failure.
Expression of intermediate-conductance, Ca2+-activated K+channel (KCNN4) in H441 human distal airway epithelial cells
Authors: Wilson S. M. , Brown S. G. , McTavish N. , McNeill R. P. , Husband E. M. , Inglis S. K. , Olver R. E. , Clunes M. T.
Published: June 2006

Electrophysiological studies of H441 human distal airway epithelial cells showed that thapsigargin caused a Ca2+-dependent increase in membrane conductance ( GTot) and hyperpolarization of membrane potential ( Vm). These effects reflected a rapid rise in cellular K+conductance ( GK) and a slow fall in amiloride-sensitive Na+conductance ( GNa). The increase in GTotwas antagonized by Ba2+, a nonselective K+channel blocker, and abolished by clotrimazole, a KCNN4 inhibitor, but unaffected by other selective K+channel blockers. Moreover, 1-ethyl-2-benzimidazolinone (1-EBIO), which is known to activate KCNN4, increased GKwith no effect on GNa. RT-PCR-based analyses confirmed expression of mRNA encoding KCNN4 and suggested that two related K+channels (KCNN1 and KCNMA1) were absent. Subsequent studies showed that 1-EBIO stimulates Na+transport in polarized monolayers without affecting intracellular Ca2+concentration ([Ca2+]i), suggesting that the activity of KCNN4 might influence the rate of Na+absorption by contributing to GK. Transient expression of KCNN4 cloned from H441 cells conferred a Ca2+- and 1-EBIO-sensitive K+conductance on Chinese hamster ovary cells, but this channel was inactive when [Ca2+]iwas <0.2 μM. Subsequent studies of amiloride-treated H441 cells showed that clotrimazole had no effect on Vmdespite clear depolarizations in response to increased extracellular K+concentration ([K+]o). These findings thus indicate that KCNN4 does not contribute to Vmin unstimulated cells. The present data thus establish that H441 cells express KCNN4 and highlight the importance of GKto the control of Na+absorption, but, because KCNN4 is quiescent in resting cells, this channel cannot contribute to resting GKor influence basal Na+absorption.
Patterns of Laryngeal Electromyography and the Activity of the Respiratory System During Spontaneous Laughter
Authors: Luschei Erich S. , Ramig Lorraine O. , Finnegan Eileen M. , Baker Kristen K. , Smith Marshall E.
Published: June 2006

Laryngeal muscle electromyography (EMG) and measures of the behavior of the respiratory system have been made during spontaneous laughter in two groups of subjects. The smaller group also had a direct measure of tracheal pressure during this behavior. Laryngeal adductors such as the thyroarytenoid (TA) and lateral cricoarytenoid (LCA) exhibited brief high-amplitude bursts of activity, at a rate of approximately 5 Hz, which were usually associated on a 1 : 1 basis with the sound bursts (ha ha ha) of laughter. The laryngeal abductor, posterior cricoarytenoid (PCA), also showed bursts of activity that were out of phase with TA and LCA. The cricothyroid (CT) was only weakly, if at all, modulated during the bursting activity of the other laryngeal muscles. Tracheal pressure usually exhibited positive pressure pulses during laughter that were often, but not always, temporally correlated to the bursts of laryngeal adductor EMG activity. Such pressure modulations appeared to precisely determine when—and if—phonation was produced during the laugh. During laughter, laryngeal EMG is highly stereotyped both within and between subjects. In most instances, this activity appears to be supported by coordinated pulses of tracheal pressure. The periaqueductal gray (PAG) has been shown in animal studies to produce emotionally indicative vocalizations, in which the laryngeal and respiratory system are coordinated. Therefore, it is suggested that the PAG is involved with the production of laughter.
Lesions of the Vestibular System Disrupt Hippocampal Theta Rhythm in the Rat
Authors: Russell Noah A. , Horii Arata , Smith Paul F. , Darlington Cynthia L. , Bilkey David K.
Published: June 2006

The hippocampus has a major role in memory for spatial location. Theta is a rhythmic hippocampal EEG oscillation that occurs at ∼8 Hz during voluntary movement and that may have some role in encoding spatial information. We investigated whether, as part of this process, theta might be influenced by self-movement signals provided by the vestibular system. The effects of bilateral peripheral vestibular lesions, made ≥60 days prior to recording, were assessed in freely moving rats. Power spectral analysis revealed that theta in the lesioned animals had a lower power and frequency compared with that recorded in the control animals. When the electroencephalography (EEG) was compared in epochs matched for speed of movement and acceleration, theta was less rhythmic in the lesioned group, indicating that the effect was not a result of between-group differences in this behavior. Blood measurements of corticosterone were also similar in the two groups indicating that the results could not be attributed to changes in stress levels. Despite the changes in theta EEG, individual neurons in the CA1 region of lesioned animals continued to fire with a periodicity of ∼8 Hz. The positive correlation between cell firing rate and movement velocity that is observed in CA1 neurons of normal animals was also maintained in cells recorded from lesion group animals. These findings indicate that although vestibular signals may contribute to theta rhythm generation, velocity-related firing in hippocampal neurons is dependent on nonvestibular signals such as sensory flow, proprioception, or motor efference copy.
Pattern of Motor Coordination Underlying Backward Swimming in the Lamprey
Authors: Islam Salma S. , Zelenin Pavel V. , Orlovsky Grigori N. , Grillner Sten , Deliagina Tatiana G.
Published: June 2006

The main form of locomotion in the lamprey (a lower vertebrate, cyclostome) is forward swimming (FS) based on periodical waves of lateral body flexion propagating from head to tail. The lamprey is also capable of backward swimming (BS). Here we describe the kinematical and electromyographic (EMG) pattern of BS, as well as the effects on this pattern exerted by different lesions of the spinal cord. The BS was evoked by tactile stimulation of a large area in the anterior part of the body. Swimming was attributed to the waves of lateral body undulations propagating from tail to head. The EMG bursts on the two sides alternated, and the EMG in more caudal segments led in phase the EMG in more rostral segments. Main kinematical characteristics of BS strongly differed from those of FS: the amplitude of undulations was much larger and their frequency lower. Also, the maintenance of the dorsal-side-up body orientation ascribed to vestibular postural reflexes (typical for FS) was not observed during BS. A complete transection of the spinal cord did not abolish the generation of forward-propagating waves rostral to the lesion. After a lateral hemisection of the spinal cord, the BS pattern persisted on both sides rostral to the lesion; caudal to the lesion, it was present on the intact side and reduced or abolished on the lesioned side. The role of the spinal cord in generation of different forms of undulatory locomotion (FS and BS) is discussed.
Causes and Consequences of Heart Failure After Prophylactic Implantation of a Defibrillator in the Multicenter Automatic Defibrillator Implantation Trial II
Authors: Goldenberg Ilan , Moss Arthur J. , Hall W. Jackson , McNitt Scott , Zareba Wojciech , Andrews Mark L. , Cannom David S.
Published: June 2006

Background—

Implantable cardioverter-defibrillator (ICD) therapy may be associated with an increased risk for heart failure (HF). The present study evaluated the frequency, causes, and consequences of HF after ICD implantation.

Methods and Results—

We performed a retrospective analysis of the clinical factors and outcomes associated with postenrollment HF events in 1218 patients enrolled in the Multicenter Automatic Defibrillator Implantation Trial II. The adjusted hazard ratios (HRs) of ICD:conventional therapy for first and recurrent HF events were 1.39 (
P
=0.02) and 1.58 (
P
<0.001), respectively. The risk was increased among patients who received single-chamber or dual-chamber ICDs. Development of HF was associated with an increased mortality risk (HR, 3.80;
P
<0.001). Among patients who received a single-chamber ICD, there was a similar survival benefit before and after the development of HF (HR, 0.59 and 0.61, respectively;
P
=0.92 for difference), whereas among patients with dual-chamber devices, there was a significant reduction in survival benefit after HF (HR, 0.26 and 0.83, respectively;
P
=0.01 for difference). Within the defibrillator arm of the trial, patients who received life-prolonging therapy from the ICD had an increased risk for first and recurrent HF events (HR, 1.90;
P
=0.01 and 1.74;
P
<0.001, respectively).

Conclusions—

Patients with chronic ischemic heart disease who are treated with either single-chamber or dual-chamber ICDs have improved survival but an increased risk of HF. The present data suggest that ICD therapy transforms sudden death risk to a subsequent HF risk. These findings should direct more attention to the prevention of HF in patients who receive an ICD.
Determinants of Arterial Wall Remodeling During Lipid-Lowering Therapy
Authors: Schoenhagen Paul , Tuzcu E. Murat , Apperson-Hansen Carolyn , Wang Chaohui , Wolski Kathy , Lin Songhua , Sipahi Ilke , Nicholls Stephen J. , Magyar William A. , Loyd Aaron , Churchill Tammy , Crowe Tim , Nissen Steven E.
Published: June 2006

Background—

Coronary plaque progression and instability are associated with expansive remodeling of the arterial wall. However, the remodeling response during plaque-stabilizing therapy and its relationship to markers of lipid metabolism and inflammation are incompletely understood.

Methods and Results—

Serial intravascular ultrasound (IVUS) data from the Reversal of Atherosclerosis with Aggressive Lipid Lowering Therapy (REVERSAL) trial were obtained during 18 months of intensive versus moderate lipid-lowering therapy. In a subgroup of 210 patients, focal coronary lesions with mild luminal narrowing were identified. Lumen area, external elastic membrane (EEM) area, and plaque area were determined at the lesion and proximal reference sites at baseline and during follow-up. The remodeling ratio (RR) was calculated by dividing the lesion EEM area by the reference EEM area. The relationship between the change in remodeling, change in plaque area, lipid profile, and inflammatory markers was examined. At the lesion site, a progression in plaque area (8.9±25.7%) and a decrease in the RR (−3.0±11.2%) occurred during follow-up. In multivariable analyses, the percentage change in plaque area (
P
<0.0001), baseline RR (
P
<0.0001), baseline lesion lumen area (0.019), logarithmic value of the change in high-sensitivity C-reactive protein (
P
=0.027), and hypertension at baseline (
P
=0.014) showed a significant, direct relation with the RR at follow-up. Lesion location in the right coronary artery (
P
=0.006), percentage change in triglyceride levels (
P
=0.049), and age (
P
=0.037) demonstrated a significant, inverse relation with the RR at follow-up. Changes in LDL cholesterol, HDL cholesterol, and treatment group demonstrated no significant associations.

Conclusions—

Constrictive remodeling of the arterial wall was observed during plaque-stabilizing therapy with statin medications and appears related to their antiinflammatory effects.
Cognitive Outcomes in Elderly High-Risk Patients After Off-Pump Versus Conventional Coronary Artery Bypass Grafting
Authors: Jensen Birte Ostergaard , Hughes Pia , Rasmussen Lars S. , Pedersen Preben U. , Steinbrüchel Daniel A.
Published: June 2006

Background—

It has been suggested that the risk of cerebral dysfunction is less with off-pump coronary artery bypass grafting (OPCAB) than with conventional coronary artery bypass grafting (CCAB). However, evidence for this statement is preliminary, and additional insight is needed.

Methods and Results—

The study was a substudy of the randomized Best Bypass Surgery trial that compared OPCAB with CCAB treatment with respect to intraoperative and postoperative mortality and morbidity in patients with a moderate to high level of predicted preoperative risk. The outcome was cognitive function. A total of 120 elderly patients (mean age 76 years, SD 4.5 years) underwent psychometric testing before surgery and at a mean of 103 (SD 15) days postoperatively with a neuropsychological test battery that included 7 parameters from 4 tests. Cognitive dysfunction was defined as the occurrence of at least 2 of the 7 possible deficits. Secondary analysis was performed on the basis of the definition of a 20% decline in cognitive scores compared with baseline, and with
z
score analysis. Cognitive dysfunction was identified in 4 of the 54 patients (7.4%, 95% confidence interval [CI] 2.1% to 17.9%) in the OPCAB group and 5 of the 51 patients (9.8%, 95% CI 3.3% to 21.4%) in the CCAB group. We found no difference in incidence of cognitive dysfunction between the groups regardless of the definition applied.

Conclusions—

In elderly high-risk patients, no significant difference was found in the incidence of cognitive dysfunction 3 months after either OPCAB or CCAB.