bluuebunny/crossref_metadata_2025 huggingface dataset:
Heads or tails? Sexual dimorphism in helodermatid lizards
Authors: Gienger C.M. , Beck Daniel D.
Published: May 2007

We tested the hypothesis that helodermatid lizards (Gila monsters, Heloderma suspectum Cope, 1869, and beaded lizards, H. horridum (Wiegmann, 1829)) show sexual dimorphism in morphological traits related to male–male agonistic behaviors. Male–male combat in helodermatid lizards involves repeated sequences of ritualized grappling. Male Gila monsters use their heads in attempts to gain or maintain a superior position during repeated combat bouts that may last for hours. Pairs of fighting male beaded lizards form spectacular body arches, with abdomens adpressed and snouts, forelimbs, and tail tips contacting the ground. We measured body size, head size, and tail length in 208 preserved H. suspectum, and body size and tail length (but not head size) in 79 live H. horridum, then tested for sexual dimorphism using analysis of covariance. Male Gila monsters had proportionately larger heads than females but did not differ in tail length or body size. Male beaded lizards had proportionately longer tails than females and were larger in body size only when the largest individuals were included in the analysis. Differences in head dimensions (in H. suspectum) and tail length (in H. horridum) are likely the result of sexual selection acting through male–male agonistic behaviors in this unique lizard taxon.
Compensatory changes in escape and refuge use following autotomy in the lizard Sceloporus virgatus
Authors: Cooper, Jr. W.E.
Published: May 2007

Following autotomy of a body part to escape from a predator, prey may alter antipredatory strategies to compensate for the inability to use autotomy and impaired escape ability. Because prey that have been captured may increase their assessment of risk posed by a predator, effects of capture may have been attributed to autotomy. I conducted an experiment using three groups of striped plateau lizards ( Sceloporus virgatus Smith, 1938): control, captured, and autotomized. Captured and autotomized lizards were less active on the day after autotomy than controls. Flight initiation distance and distance fled were greater in both experimental groups than in the control group, but did not differ between experimental groups. Flight initiation distance was greater in autotomized than in captured lizards only in males. No sex difference occurred for distance fled. Autotomized lizards entered refuges more than other groups. Escape strategy changed after autotomy to increased reliance on refuge and, in males, to increased flight initiation distance; behaviours that are appropriate to compensate for impaired escape ability. Decreased activity and increased distance fled might erroneously have been considered effects of autotomy, had effects of capture not been assessed. Predictions of escape theory that flight initiation distance and distance fled increase with predation risk were supported.
Male reproductive success and female preference in bushy-tailed woodrats (Neotoma cinerea): do females prefer males in good physical condition?
Authors: Weber D.M. , Millar J.S. , Neff B.D.
Published: May 2007

In many mating systems, females may benefit by selecting a male with high genetic quality in the form of good genes or compatible genes. In bushy-tailed woodrats ( Neotoma cinerea Ord, 1815), previous research has shown that male reproductive success correlates with the mass change of males over the breeding season, indicating that physical body condition may directly influence female choice and hence male reproductive success. We examined male physical condition in relation to reproductive success in the field. Male physical condition was measured as body-mass change over the breeding season, body size, body condition (mass versus size), and anaemia (packed cell volume and mean corpuscular volume). We then conducted trials in the laboratory in which captive females were presented with visual and olfactory cues from two males simultaneously. In the field, males with a low mean corpuscular volume had the highest reproductive success. Captive females also showed a preference for males with low levels of anaemia based on mean corpuscular volume. These results suggest that females are employing a condition-dependent preference.
Physiology of the ciliate Orchitophrya stellarum and its experimental infection of Leptasterias spp.
Authors: Stickle William B. , Kozloff Eugene N. , Story Shana
Published: May 2007

Orchitophrya stellarum Cépède, 1907 is a facultative ciliate that parasitizes male asteriid sea stars in the North Atlantic and Pacific oceans. The ciliate also exists in seawater where it feeds on bacteria associated with tissue or yeast. This study is designed to determine the tolerance, growth rate, contractile vacuole activity, and infectivity to Leptasterias Verrill, 1866 spp. as a function of the sea star’s reproductive cycle stage. The tolerance range of O. stellarum in seawater containing bacteria is 2 practical salinity units (PSU) at 8 °C and 12.5 PSU at 25 °C; the ciliate tolerated a temperature range of 3–27 °C at 30 PSU. Ciliate population growth is most rapid at 24 °C and is minimal at 3 and 27 °C at 30 PSU. The ciliate’s contractile vacuole cycle frequency increases at low salinity, indicating increased water volume regulation as a function of decreased salinity. Unparasitized male Leptasterias spp. can be infected experimentally by injection of a culture of O. stellarum into the rays or from a culture in ambient seawater only when the testes are at full size, but the ciliates do not invade ovarian tissue. The normal path of entry of O. stellarum into the testes of reproductively mature male sea stars probably takes place through gonopores.
Regulation compliance by vessels and disturbance of harbour seals (Phoca vitulina)
Authors: Johnson Amber , Acevedo-Gutiérrez Alejandro
Published: May 2007

The US National Oceanic and Atmospheric Administration established a buffer zone around marine mammals to prevent harassment. The buffer zone varies by species listing status and by geographic area. However, it is unknown the extent to which vessels comply with these buffer zones. We selected harbor seals ( Phoca vitulina L., 1758) as a case study to describe compliance with the buffer zone. We conducted land-based observations from Yellow Island, Washington State, in a geographic area where the buffer zone is 91 m (100 yards), to estimate vessel distance from hauled-out seals and to evaluate seal response. We recorded 85.7% of kayaks, 57.1% of stopped powerboats, and 4.6% of passing powerboats violating the buffer zone. Seals were disturbed by kayaks and stopped powerboats at distances >91 m from the haul-out sites but not by moving powerboats ≤91 m from the sites. Hence, compliance of the buffer zone varied with vessel type and vessel activity. We suggest that a larger buffer zone for vessels lingering around the haul-out sites and enforcement of the buffer zone will minimize seal disturbance.
A field study of brook stickleback morphology: multiple predators and multiple traits
Authors: Zimmerman M.S.
Published: May 2007

This field-based study examined a suite of morphological traits expressed by brook sticklebacks ( Culaea inconstans (Kirtland, 1840)) coexisting with two types of predator communities. “Small-predator” communities included gape-limited predators only; “mixed-predator” communities included both gape-limited and non-gape-limited predators. Across 26 study sites in three drainages, sticklebacks in small-predator communities had longer bodies, longer spines, and deeper midbodies than those in mixed-predator communities. The observed differences were consistent with the hypothesis that stickleback morphology in small-predator communities would be better adapted for avoiding gape-limited predators and that in mixed-predator communities should be better adapted for avoiding large, non-gape-limited predators. Morphological differences were apparent in 1-year-old sticklebacks and likely resulted from predator–prey interactions early in the sticklebacks’ life history. Correlation among morphological traits involved in antipredator defense (i.e., morphological integration) was hypothesized to occur in small-predator communities, characterized by a single gape-limited predation pressure, but not mixed-predator communities where sticklebacks coexisted with multiple predator types in each site. Contrary to expectations, length-at-age, spine length, and body depth were not correlated in either predator community. Numerous variables, not present in controlled laboratory studies, may constrain morphological expression in the field environment.
Mountain beaver home ranges, habitat use, and population dynamics in Washington
Authors: Arjo W.M. , Huenefeld R.E. , Nolte D.L.
Published: May 2007

The mountain beaver ( Aplodontia rufa (Rafinesque, 1817)), endemic to western North America, is the only extant member of the family Aplodontidae. Limited information on movements and habitat use throughout the species’ range is available. We radio-collared 41 mountain beavers to determine home ranges, dispersal, habitat use, and population densities on two managed forest sites in coastal Washington. Both sites were recently harvested for timber. The Donovan site (16.6 ha) was treated with herbicide before seedling planting and the Sylvia site (8.9 ha) was not treated. Mountain beaver home ranges (Donovan: 4.18 ± 0.81 ha; Sylvia: 1.39 ± 0.4 ha) were greater than previously reported in the literature (0.02–0.2 ha). Home ranges (P = 0.009) and core use areas (P = 0.05) on the herbicide-treated Donovan site were larger than those observed on the untreated Sylvia site. Mountain beaver population density declined from 2002 (n = 16) to 2003 (n = 8) on the Donovan site, and reinvasion onto the site after removal trapping was low (n = 7). Population density more than doubled on the Sylvia site from 2002 (n = 21) to 2003 (n = 55), and reinvasion was greater (n = 27) than observed at Donovan. In addition, we documented habitat characteristics centered at 9 Donovan and 10 Sylvia nest locations. Sites were similar in most habitat characteristics, but the Sylvia site had more herbaceous forbs, stumps, and woody debris. Our findings suggest that mountain beaver populations and home ranges are affected by availability of forage, such as herbaceous forbs, after herbicide treatment, as well as by availability of woody cover.
Localization of metallothionein, heat shock protein (Hsp70), and superoxide dismutase expression inHemidiaptomus roubaui(Copepoda, Crustacea) exposed to cadmium and heat stress
Authors: Liberge Martine , Barthélémy Roxane-M.
Published: May 2007

Immunohistochemical methods were applied in the present study to investigate the expression of stress proteins such as metallothioneins (MT), which are metal-binding proteins, and heat shock proteins (Hsp70), as well as an antioxidant enzyme (superoxide dismutase, SOD), in the freshwater crustacean copepod Hemidiaptomus roubaui (Richard, 1888) exposed to cadmium or heat stress. The results show a tissue-specific distribution of MT-like protein after cadmium exposure in the brain and in the nerve cord. Cadmium stress did not provoke inducible Hsp70 or SOD expression. Unlike cadmium, heat stress induced the expression of Hsp70 and SOD in the shell glands, a structure involved in the reproductive function, and more particularly in the formation of the diapause egg envelope. MT expression is not induced in animals exposed to heat stress.
Patterns of differential migration in white-throated sparrows evaluated with isotopic measurements of feathers
Authors: Mazerolle Daniel F. , Hobson Keith A.
Published: May 2007

We used stable isotope techniques to investigate differential migration in the white-throated sparrow ( Zonotrichia albicollis (J.F. Gmelin, 1789)), a short-distance migrant in North America, to clarify hypotheses about patterns and consequences of migration tactics. Sparrows staging in Manitoba, Canada, exhibited sex-biased differential timing of spring arrival and latitude of wintering origin. Specifically, females arrived later and originated from more southern latitudes. Furthermore, there was a negative relationship between wintering latitude and arrival dates of individuals, although this relationship was only present during the second spring of the study, since atypical cold temperatures were associated with a pulse of late-arriving sparrows during the first spring. The negative correlation between wintering latitude and arrival date was also present within males, suggesting that the distribution of males on wintering areas could have carry-over effects to reproduction. This study demonstrates potential links between events occurring on wintering and breeding grounds of migratory songbirds.
Free love in the far north: plural breeding and polyandry of arctic foxes (Alopex lagopus) on Bylot Island, Nunavut
Authors: Carmichael L.E. , Szor G. , Berteaux D. , Giroux M.A. , Cameron C. , Strobeck C.
Published: May 2007

Molecular studies show that canid breeding systems are more complex than field data have sometimes suggested. For example, microsatellite DNA fingerprints of offspring and adults within their social group indicate that many canid species thought to form monogamous pairs engage in polygyny, polyandry, and plural breeding. In many areas, arctic foxes ( Alopex lagopus (L., 1758)) are considered monogamous, with the complexity of their social systems increasing as population isolation increases. We combined a genetic approach with spatial data of arctic foxes on Bylot Island, Nunavut, Canada, to investigate breeding patterns in a population less isolated than many previously studied. As in previous field studies, single breeding pairs were most common, but one case of plural breeding and one case of polyandry with multiple paternity were also observed. Reproductive output in arctic foxes is closely tied to the productivity of their habitat in a given year; we support the hypothesis that abundant resources at our study site have also contributed to complex breeding patterns among resident foxes. We also suggest that increased genetic variation among offspring of multiply mated females may provide an additional adaptive advantage to species in uncertain environments.
Niche variation in burying beetles (Nicrophorusspp.) associated with marine and terrestrial carrion
Authors: Hocking M.D. , Darimont C.T. , Christie K.S. , Reimchen T.E.
Published: May 2007

Ecological opportunity can influence niche variation within and among species. Forensic reconstruction of diet has been made possible with the now widespread use of stable isotope analysis, although it has not to date been applied to communities based on carrion resources. Within a salmon-bearing watershed in coastal British Columbia, we reconstructed the dietary niches of two burying beetle species (Silphidae: Nicrophorus investigator Zetterstedt, 1824 and Nicrophorus defodiens Mannerheim, 1846) using stable isotopes (δ15N, δ13C). We separated available carrion sources for beetles of chum salmon ( Oncorhynchus keta (Walbaum, 1792)) and pink salmon ( Oncorhynchus gorbuscha (Walbaum, 1792)), the shrew Sorex monticolus Merriam, 1890, songbirds ( Troglodytes troglodytes (L., 1758), Catharus ustulatus (Nuttall, 1840), Catharus guttatus (Pallas, 1811)), and black-tailed deer ( Odocoileus hemionus hemionus (Rafinesque, 1817)) into three isotopically homogeneous subsets: (1) salmon, (2) shrews and songbirds, and (3) deer. The majority (86.5%) of N. investigator individuals were raised on a diet of salmon carrion, while 100% of N. defodiens individuals had a larval diet consistent with carrion from shrews and songbirds. Larger isotopic variance predicts wider dietary niches, which may be useful for testing functional ecological variation within and among species.
Do δ15N and δ13C values of feces reflect the isotopic composition of diets in small mammals?
Authors: Hwang Y.T. , Millar J.S. , Longstaffe F.J.
Published: May 2007

The stable isotope composition of carbon and nitrogen in feces can be a useful tool for reconstructing diet. To examine whether the isotopic composition of feces reflect those of diet, we determined the fractionation of 15N and 13C along the digestive tracts of several species of small mammals. There were significant differences in the δ15N values of digesta in different compartments of the gastrointestinal (GI) tract, with consistent enrichment of 15N in the stomach, intestine, and cecum, and the depletion of 15N in the colon (i.e., feces). Although feces had lower δ15N values than digesta in the cecum, feces of small mammals were significantly more enriched in 15N (by ~2.5‰) than diet. The mechanisms causing this enrichment in the GI tract may arise from the operation of different biochemical pathways within the different GI compartments. The stable carbon isotope composition of digesta in small mammals were similar along the GI tract, but the δ13C values of digesta and feces were significantly lower than reported previously for large ungulates (–3.5‰ vs. –0.5‰). The δ15N and δ13C values of feces did not directly reflect the isotopic compositions of these mammals’ diet. Our data offer evidence for variations in isotopic discrimination effects. This variation can probably be ascribed to metabolism of different body sizes of mammals and the complexities linked with digestive physiology of herbivores.
Involvement of vertebrate hemoglobin in antioxidant protection: chicken blood as a model
Authors: Dafre Alcir Luiz , Brandão Tiago A.S. , Reischl Evaldo
Published: May 2007

Redox balance can be described as the equilibrium between oxidative and reductive forces within the cell. These forces control several cellular events, including the modulation of redox-sensitive receptors and signaling pathways. In cells, glutathione is the major non-protein thiol and is considered the main redox buffer. The ratio between the oxidized (GSSG) and reduced (GSH) forms reflects the cellular redox balance. Reactive protein thiols, including vertebrate hemoglobin (Hb), have been proposed as effective antioxidants that can contribute to the redox balance. To further explore this possibility, chicken ( Gallus gallus (L., 1758)) blood was used as a model system. The use of known oxidants (hydroperoxides, diamide, and a system generating reactive oxygen species) originated a pattern of glutathiolation in chicken erythrocytes that was fully reversed after removal of the oxidant, this being consistent with a physiological response. The glutathiolation sequence correlates to kinetic data on chicken Hb cysteine reactivity. The major chicken hemoglobin (Hb A) is responsible for most of the glutathiolated protein where the presence of externally positioned and fast-reacting cysteines is a contributing factor. The antioxidant potential of fast-reacting Hb cysteines is in line with the conservation of cysteine residues in Hb stereochemical positions in more than 95% of the available avian Hb sequences. This may represent an evolutionary trend for the antioxidant function of externally positioned and reactive cysteines in abundant proteins.
ENERGY–MOMENTUM DISTRIBUTION: SOME EXAMPLES
Authors: SHARIF M. , AZAM M.
Published: May 2007

In this paper, we elaborate the problem of energy–momentum in General Relativity with the help of some well-known solutions. In this connection, we use the prescriptions of Einstein, Landau–Lifshitz, Papapetrou and Möller to compute the energy–momentum densities for four exact solutions of the Einstein field equations. We take the gravitational waves, special class of Ferrari–Ibanez degenerate solution, Senovilla–Vera dust solution and Wainwright–Marshman solution. It turns out that these prescriptions do provide consistent results for special class of Ferrari–Ibanez degenerate solution and Wainwright–Marshman solution but inconsistent results for gravitational waves and Senovilla–Vera dust solution.
THE EFFECTS OF DIFFERENT PERTURBATIONS ON THE DYNAMICS OF THE ACCRETION DISK AROUND THE BLACK HOLE
Authors: DÖNMEZ ORHAN
Published: May 2007

We investigate the special cases of the formation of shocks in the accretion disks around the nonrotating (Schwarzschild) black holes in cases where one or few stars perturb the disk. We model the structure of disk with a 2D fully general relativistic hydrodynamic code and investigate a variety of cases in which the stars interacting with the disk are captured at various locations. We have found the following results: (1) if the stars perturb the disk at nonsymmetric locations, a moving one-armed spiral shock wave is produced and it destroys the disk eventually; (2) if the disk is perturbed by a single star located close to the black hole, a standing shock wave is produced while the disk becomes an accretion tori; (3) if the disk is perturbed by stars at symmetric locations, moving two-armed spiral shock waves are produced while the disk reaches a steady state; (4) continuous injection of matter into the stable disk produces a standing shock wave behind the black hole. Our outcomes reinforce the view that different perturbations on the stable accretion disk carry out different types of shock waves which produce Quasi-Periodic Oscillation (QPO) phenomena in galactic black hole candidates and it is observed as a X-ray.
TOWARDS THE TWO-LOOP Lcc VERTEX IN LANDAU GAUGE
Authors: CVETIČ GORAZD , KONDRASHUK IGOR , KOTIKOV ANATOLY , SCHMIDT IVAN
Published: May 2007

We are interested in the structure of the Lcc vertex in the Yang–Mills theory, where c is the ghost field and L the corresponding BRST auxiliary field. This vertex can give us information on other vertices, and the possible conformal structure of the theory should be reflected in the structure of this vertex. There are five two-loop contributions to the Lcc vertex in the Yang–Mills theory. We present here calculation of the first of the five contributions. The calculation has been performed in the position space. One main feature of the result is that it does not depend on any scale, ultraviolet or infrared. The result is expressed in terms of logarithms and Davydychev integral J(1, 1, 1) that are functions of the ratios of the intervals between points of effective fields in the position space. To perform the calculation we apply Gegenbauer polynomial technique and uniqueness method.
EFFECT OF A FLEXIBLE SPINE EMOTIONAL BELLY DANCING ROBOT ON HUMAN PERCEPTIONS
Authors: OR JIMMY , TAKANISHI ATSUO
Published: May 2007

Recently, there has been a growing interest in human–robot interaction. Researchers in artificial intelligence and robotics have built various types of social robots which can express emotions through speech, facial expressions and hand gestures. Although some of these robots are able to interact with humans in interesting ways, they cannot move as naturally as we do because of the limited number of degrees of freedom in their body torsos (some of them do not even have a torso). Since we often express and perceive each other's emotions and motives at a distance using body language alone, it would be good for the next generation of humanoid robots to possess similar capabilities. As a first step towards this goal, we developed a 28-DOF full-body humanoid robot as an experimental platform. Unlike the current generation of humanoid robots, our robot has a flexible spine. This feature is very important because counterbalancing movements of the spine are required to maintain dynamic stability in humans and humanoid robots. Our robot can belly dance and communicate affective motions via full-body movements. Using a Central Pattern Generator (CPG) based controller, we generated rhythmic motions for the arms, upper and lower bodies. We then conducted psychological experiments using both the robot and a human actors. Statistical analyses were carried out to test our hypotheses on human perception of affective movements. Experimental results show that human subjects were able to perceive emotions from the robot based only on its body motions, sometimes as well as recognizing the movements being performed by the human actor. Our robot can be used to examine the relationship between the movement of the spine, shoulders, arms, neck and head when attempting to reproduce affective movements. Psychologists, actors, dancers and animators can benefit from this line of research by learning how emotions can be conveyed through body motions and knowing how body part movements combine to communicate emotional expressions.
TOWARDS ARTICULATORY CONTROL OF TALKING HEADS IN HUMANOID ROBOTICS USING A GENETIC-FUZZY IMITATION LEARNING ALGORITHM
Authors: MUMOLO ENZO , NOLICH MASSIMILIANO
Published: May 2007

In human heads there is a strong structural linkage between the vocal tract and facial behavior during speech. For a robotic talking head to have human-like behavior, this linkage should be emulated. One way to do that is to estimate the articulatory features from a given utterance and to use them to control a talking head. In this paper, we describe an algorithm to estimate the articulatory features from a spoken sentence using a novel computational model of human vocalization. Our model uses a set of fuzzy rules and genetic optimization. That is, the places of articulation are considered as fuzzy sets whose degrees of membership are the values of the articulatory features. The fuzzy rules represent the relationships between places of articulation and speech acoustic parameters, and the genetic algorithm estimates the degrees of membership of the places of articulation according to an optimization criteria and it performs imitation learning. We verify our model by performing audio-visual subjective tests of animated talking heads showing that the algorithm is able to produce correct results. In particular, subjective listening tests of artificially generated sentences from the articulatory description resulted in an average phonetic accuracy slightly under 80%. Through the analysis of large amounts of natural speech, the algorithm can be used to learn the places of articulation of all phonemes of a given speaker. The estimated places of articulation are then used to control talking heads in humanoid robotics.
HUMANOID MOTION REPLICATION BY A SPHERICAL MOTION BASE
Authors: MAZA MARIO , ORTIZ JESUS
Published: May 2007

A humanoid is a robot that looks like a human (it has human shape, with a trunk, two arms, two legs and a head) and has been specially designed to act like a human being. This paper presents the procedures and results of a series of tests consisting of the reproduction of some target humanoid movements (walking, sitting, standing up, etc.) by a 4-DOF spherical motion base. In this way, an operator seated on the motion base will be able to feel the movements of the humanoid, creating a feeling of teleexistence. This paper contributes to the improvement and development of the teleexistence/telepresence technology applied to humanoid research.
Prevention of concentric hypertrophy and diastolic impairment in aortic-banded rats treated with resveratrol
Authors: Juric Danijel , Wojciechowski Peter , Das Dipak K. , Netticadan Thomas
Published: May 2007

This study was designed to examine the effects of the antioxidant resveratrol on cardiac structure and function in pressure overload (PO)-induced cardiac hypertrophy. Male Sprague-Dawley rats were subjected to sham operation and the aortic banding procedure. A subgroup of sham control and aortic-banded rats were treated with resveratrol for 2 wk after surgery. Echocardiographic analysis of cardiac structure and function along with Western blot analysis of endothelial nitric oxide synthase (eNOS), inducible nitric oxide synthase (iNOS), and redox factor-1 (ref-1) were performed in all groups after 4 wk of surgery. Banded rats showed significantly increased left ventricle-to-body weight ratio. Echocardiographic analysis showed that the interventricular septal wall thickness and left ventricular posterior wall thickness at systole and diastole were significantly increased in banded rats. Also, a significant increase in isovolumic relaxation time was observed in banded rats. Measured eNOS, iNOS, and ref-1 protein levels were significantly reduced in banded rats. Resveratrol treatment prevented the above changes in cardiac structure, function, and protein expression in banded rats. Aortic banding after 4 wk resulted in concentric remodeling and impaired contractile function due to PO on the heart. The 2-wk treatment with resveratrol was found to abolish PO-induced cardiac hypertrophy. Resveratrol may therefore be beneficial against PO-induced cardiac hypertrophy found in clinical settings of hypertension and aortic valve stenosis.
Ih Without Kir in Adult Rat Retinal Ganglion Cells
Authors: Lee Sherwin C. , Ishida Andrew T.
Published: May 2007

Antisera directed against hyperpolarization-activated mixed-cation (“ Ih”) and K+ (“Kir”) channels bind to some somata in the ganglion cell layer of rat and rabbit retina. Additionally, the termination of hyperpolarizing current injections can trigger spikes in some cat retinal ganglion cells, suggesting a rebound depolarization arising from activation of Ih. However, patch-clamp studies showed that rat ganglion cells lack inward rectification or present an inwardly rectifying K+ current. We therefore tested whether hyperpolarization activates Ih in dissociated, adult rat retinal ganglion cell somata. We report here that, although we found no inward rectification in some cells, and a Kir-like current in a few cells, hyperpolarization activated Ih in roughly 75% of the cells we recorded from in voltage clamp. We show that this current is blocked by Cs+ or ZD7288 and only slightly reduced by Ba2+, that the current amplitude and reversal potential are sensitive to extracellular Na+ and K+, and that we found no evidence of Kir in cells presenting Ih. In current clamp, injecting hyperpolarizing current induced a slowly relaxing membrane hyperpolarization that rebounded to a few action potentials when the hyperpolarizing current was stopped; both the membrane potential relaxation and rebound spikes were blocked by ZD7288. These results provide the first measurement of Ih in mammalian retinal ganglion cells and indicate that the ion channels of rat retinal ganglion cells may vary in ways not expected from previous voltage and current recordings.
Cardiac Improvement During Mechanical Circulatory Support
Authors: Maybaum Simon , Mancini Donna , Xydas Steve , Starling Randall C. , Aaronson Keith , Pagani Francis D. , Miller Leslie W. , Margulies Kenneth , McRee Susan , Frazier O.H. , Torre-Amione Guillermo
Published: May 2007

Background—

Myocardial recovery after left ventricular assist device (LVAD) support has been reported. The LVAD Working Group Recovery Study was a prospective multicenter trial to assess the incidence of myocardial recovery in patients bridged to cardiac transplantation.

Methods and Results—

After LVAD implantation, patients were evaluated with the use of rest echocardiograms with partial LVAD support and cardiopulmonary exercise testing. Dobutamine echocardiography with hemodynamic measurements was performed in those patients with left ventricular ejection fraction >40% during resting studies. Histological analysis was performed on myocardial samples taken at LVAD implantation and explantation. Sixty-seven LVAD patients with heart failure participated in the study. After 30 days, significant improvement occurred in left ventricular ejection fraction (17±7% versus 34±12%;
P
<0.001) and reductions in left ventricular end-diastolic diameter (7.1±1.2 versus 5.1±1.1 cm;
P
<0.001) and left ventricular mass (320±113 versus 194±79 g;
P
<0.001) compared with before LVAD. Thirty-four percent of patients had left ventricular ejection fraction >40% with partial device support. Left ventricular ejection fraction decreased over time to pre-LVAD measurement by 120 days. Peak V̇
o
2
improved with mechanical support (13.7±4.2 versus 18.9±5.5 mL/kg per minute, 30 versus 120 days;
P
<0.001). Tissue analysis revealed significant reductions in myocyte size, collagen content, and cardiac tumor necrosis factor-α. Six subjects (9%) underwent LVAD explantation for recovery.

Conclusions—

Cardiac function improves significantly after device implantation. Although cellular recovery and improvement in ventricular function are observed, the degree of clinical recovery is insufficient for device explantation in most patients with chronic heart failure.
Risk of Thromboembolism in Heart Failure
Authors: Freudenberger Ronald S. , Hellkamp Anne S. , Halperin Jonathan L. , Poole Jeanne , Anderson Jill , Johnson George , Mark Daniel B. , Lee Kerry L. , Bardy Gust H.
Published: May 2007

Background—

In patients with heart failure, rates of clinically apparent stroke range from 1.3% to 3.5% per year. Little is known about the incidence and risk factors in the absence of atrial fibrillation. In the Sudden Cardiac Death in Heart Failure Trial (SCD-HeFT), 2521 patients with moderate heart failure were randomized to receive amiodarone, implanted cardioverter-defibrillators (ICDs), or placebo.

Methods and Results—

We determined the incidence of stroke or peripheral or pulmonary embolism in patients with no history of atrial fibrillation (n=2114), predictors of thromboembolism and the relationship to left ventricular ejection fraction. Median follow-up was 45.5 months. Kaplan-Meier estimates (95% CIs) for the incidence of thromboembolism by 4 years were 4.0% (3.0% to 4.9%), with 2.6% (1.1% to 4.1%) in patients randomized to amiodarone, 3.2% (1.8% to 4.7%) in patients randomized to ICD, and 6.0% (4.0% to 8.0%) in patients randomized to placebo (approximate rates of 0.7%, 0.8%, and 1.5% per year, respectively). By multivariable analysis, hypertension (
P
=0.021) and decreasing left ventricular ejection fraction (
P
=0.023) were significant predictors of thromboembolism; treatment with amiodarone or ICD treatment was a significant predictor of thromboembolism-free survival (
P
=0.014 for treatment effect; hazard ratio [95% CI] versus placebo, 0.57 [0.33 to 0.99] for ICD; 0.44 [0.24 to 0.80] for amiodarone). Inclusion of atrial fibrillation during follow-up in the multivariable model did not affect the significance of treatment assignment as a predictor of thromboembolism.

Conclusions—

In the SCD-HeFT patient cohort, which reflects contemporary treatment of patients with moderately symptomatic systolic heart failure, patients experienced thromboembolism events at a rate of 1.7% per year without antiarrhythmic therapy. Those treated with amiodarone or ICDs had lower risk of thromboembolism than those given placebo. Hypertension at baseline and lower ejection fraction were independent predictors of risk.
Case Volume and Mortality in Pediatric Cardiac Surgery Patients in California, 1998–2003
Authors: Bazzani Lianna G. , Marcin James P.
Published: May 2007

Background—

Previous reports have found an inverse relationship between pediatric cardiac surgery case volume and in-hospital mortality. This association has been noted recently to be decreasing for coronary artery bypass grafting, possibly because of improved training programs, quality improvement activities, or other innovations to improve outcomes. It is unknown whether the volume-mortality association among pediatric cardiac surgery patients is decreasing similarly.

Methods and Results—

We used data from the state of California’s patient discharge data set from the years 1998–2003 to replicate 4 previous research studies of pediatric cardiac surgery volume and mortality. The total number of pediatric surgeries varied from 12 801 to 13 971 depending on the selection criteria applied. Using this larger and more contemporary data set, we found a weaker and less consistent volume-mortality relationship than had been reported previously. We also developed a new model, which incorporated elements of the old models, and found a statistically significant relationship with higher volume and lower mortality (odds ratio=0.86 per 100-patient increase in annual volume; 95% CI, 0.81 to 0.92). Post hoc analyses show that this relationship was related to the performance of the single largest-volume hospital.

Conclusions—

With the use of data from California, the volume-mortality relationship among pediatric cardiac surgery patients has changed since previous research, such that the old models no longer describe a clear or consistent association. With the use of a continuous definition of volume and an updated model, an association is observed but is dependent on highly leveraged covariate patterns found in the largest-volume hospital.
Association of Fetuin-A With Mitral Annular Calcification and Aortic Stenosis Among Persons With Coronary Heart Disease
Authors: Ix Joachim H. , Chertow Glenn M. , Shlipak Michael G. , Brandenburg Vincent M. , Ketteler Markus , Whooley Mary A.
Published: May 2007

Background—

Fetuin-A is a multifunctional hepatic secretory protein that inhibits dystrophic vascular and valvular calcification. Lower serum fetuin-A concentrations are associated with valvular calcification in persons with end-stage renal disease. Whether fetuin-A is associated with valvular calcification in other patient populations is unknown.

Methods and Results—

We evaluated the associations among serum fetuin-A concentrations, mitral annular calcification, and aortic stenosis in 970 ambulatory persons with coronary heart disease and without severe kidney disease. The presence or absence of mitral annular calcification and aortic stenosis was determined by transthoracic echocardiography. The subjects’ mean age was 66 years; 81% were men; 189 (20%) had mitral annular calcification; and 79 (8%) had aortic stenosis. Participants were categorized by tertiles of fetuin-A concentrations. Those within the highest fetuin-A tertile had significantly lower odds of mitral annular calcification compared with the lowest tertile (adjusted odds ratio, 0.47; 95% confidence interval, 0.29 to 0.77;
P
=0.002); this association was similar regardless of diabetes status (
P
for interaction=0.34). In contrast, the association of fetuin-A with aortic stenosis was modified by the presence or absence of diabetes mellitus (
P
for interaction=0.03). Among participants without diabetes, the highest fetuin-A tertile had a significantly lower odds of aortic stenosis compared with the lowest tertile (adjusted odds ratio, 0.37; 95% confidence interval, 0.15 to 0.92;
P
=0.03), whereas among participants with diabetes, no statistically significant association was observed between fetuin-A and aortic stenosis (adjusted odds ratio, 1.49; 95% confidence interval, 0.48 to 4.63;
P
=0.49).

Conclusions—

Among persons with coronary heart disease, we observed an inverse association of fetuin-A and mitral annular calcification. An inverse association also was observed between fetuin-A and aortic stenosis among participants without diabetes mellitus. Fetuin-A may represent an important inhibitor of dystrophic calcification in persons with coronary heart disease.
Heritability of Blood Pressure Responses to Dietary Sodium and Potassium Intake in a Chinese Population
Authors: Gu Dongfeng , Rice Treva , Wang Shiping , Yang Wenjie , Gu Chi , Chen Chung-Shiuan , Hixson James E. , Jaquish Cashell E. , Yao Zhi-Jian , Liu De-Pei , Rao Dabeeru C. , He Jiang
Published: May 2007

The heritability of blood pressure responses to dietary intervention has not been well studied. We examined the heritability of blood pressure responses to dietary sodium and potassium intake in a family feeding study among 1906 study participants living in rural North China. The dietary intervention included a 7-day low-sodium feeding (51.3 mmol per day), a 7-day high-sodium feeding (307.8 mmol per day), and a 7-day high-sodium plus potassium supplementation (60 mmol per day). Blood pressure was measured 9 times during the 3-day baseline period preceding the intervention and also during the last 3 days of each intervention phase using a random-zero sphygmomanometer. Heritability was computed using maximum likelihood methods under a variance components model as implemented in the computer program SOLAR. The heritabilities of baseline blood pressure were 0.31 for systolic, 0.32 for diastolic, and 0.34 for mean arterial pressure. The heritabilities increased significantly under dietary intervention and were 0.49, 0.49, and 0.51 during low sodium; 0.47, 0.49, and 0.51 during high sodium; and 0.51, 0.52, and 0.53 during potassium supplementation for systolic, diastolic, and mean arterial pressure, respectively. The heritabilities for percentage of blood pressure responses to low sodium were 0.20, 0.21, and 0.23; to high-sodium were 0.22, 0.33, and 0.33; and to potassium supplementation were 0.24, 0.21, and 0.25 for systolic, diastolic, and mean arterial pressure, respectively. Our study indicated that the heritabilities of blood pressure under controlled dietary sodium and potassium intake were significantly higher than those under a usual diet. In addition, the heritabilities of blood pressure responses to dietary sodium and potassium intake were moderate in this study population.
Central Pressure More Strongly Relates to Vascular Disease and Outcome Than Does Brachial Pressure
Authors: Roman Mary J. , Devereux Richard B. , Kizer Jorge R. , Lee Elisa T. , Galloway James M. , Ali Tauqeer , Umans Jason G. , Howard Barbara V.
Published: May 2007

Brachial blood pressure is predictive of cardiovascular outcome; however central pressure may better represent the load imposed on the coronary and cerebral arteries and thereby bear a stronger relationship to vascular damage and prognosis. Relations of brachial and central pressures to carotid artery hypertrophy (intimal-medial thickness and vascular mass), extent of atherosclerosis (plaque score), and incident cardiovascular events were examined in the Strong Heart Study. Central pressures were calculated using radial applanation tonometry. Among 3520 participants, central and brachial pulse pressures were more strongly related to vascular hypertrophy and extent of atherosclerosis than were systolic pressures. Central pulse pressure was more strongly related to all 3 arterial measures than was brachial pulse pressure (
r
=0.364 versus 0.309 for plaque score;
P
<0.001 for comparison of Spearman correlation coefficient;
r
=0.293 versus 0.249 for intimal-medial thickness;
P
<0.002;
r
=0.320 versus 0.289 for vascular mass;
P
<0.05). Among the 2403 participants free of clinical cardiovascular disease at baseline, 319 suffered fatal or nonfatal cardiovascular events during mean follow-up of 4.8±1.3 years. After adjustment for age, gender, current smoking, body mass index, cholesterol:HDL ratio, creatinine, fibrinogen, diabetes, and heart rate, central pulse pressure predicted cardiovascular events more strongly than brachial pulse pressure (hazards ratio=1.15 per 10 mm Hg, χ
2
=13.4,
P
<0.001 versus hazards ratio=1.10, χ
2
=6.9,
P
=0.008). In conclusion, noninvasively-determined central pulse pressure is more strongly related to vascular hypertrophy, extent of atherosclerosis, and cardiovascular events than is brachial blood pressure. These findings support prospective examination of use of central blood pressure as a treatment target in future trials.
Transcranial Magnetic Stimulation in a Finger-tapping Task Separates Motor from Timing Mechanisms and Induces Frequency Doubling
Authors: Levit-Binnun Nava , Handzy Nestor Z. , Peled Avi , Modai Ilan , Moses Elisha
Published: May 2007

We study the interplay between motor programs and their timing in the brain by using precise pulses of transcranial magnetic stimulation (TMS) applied to the primary motor cortex. The movement of the finger performing a tapping task is periodically perturbed in synchronization with a metronome. TMS perturbation can profoundly affect both the finger trajectory and its kinematics, but the tapping accuracy itself is surprisingly not affected. The motion of the finger during the TMS perturbation can be categorized into two abnormal behaviors that subjects were unaware of: a doubling of the frequency of the tap and a stalling of the finger for half the period. More stalls occurred as the tapping frequency increased. In addition, an enhancement of the velocity of the finger on its way up was observed. We conclude that the timing process involved in controlling the tapping movement is separate from the motor processes in charge of execution of the motor commands. We speculate that the TMS is causing a release of the motor plan ahead of time into activation mode. The observed doubles and stalls are then the result of an indirect interaction in the brain, making use of an existing motor plan to correct the preactivation and obtain the temporal goal of keeping the beat.
Stronger Synaptic Connectivity as a Mechanism behind Development of Working Memory-related Brain Activity during Childhood
Authors: Edin Fredrik , Macoveanu Julian , Olesen Pernille , Tegnér Jesper , Klingberg Torkel
Published: May 2007

The cellular maturational processes behind cognitive development during childhood, including the development of working memory capacity, are still unknown. By using the most standard computational model of visuospatial working memory, we investigated the consequences of cellular maturational processes, including myelination, synaptic strengthening, and synaptic pruning, on working memory-related brain activity and performance. We implemented five structural developmental changes occurring as a result of the cellular maturational processes in the biophysically based computational network model. The developmental changes in memory activity predicted from the simulations of the model were then compared to brain activity measured with functional magnetic resonance imaging in children and adults. We found that networks with stronger fronto-parietal synaptic connectivity between cells coding for similar stimuli, but not those with faster conduction, stronger connectivity within a region, or increased coding specificity, predict measured developmental increases in both working memory-related brain activity and in correlations of activity between regions. Stronger fronto-parietal synaptic connectivity between cells coding for similar stimuli was thus the only developmental process that accounted for the observed changes in brain activity associated with development of working memory during childhood.
Neural Correlates of Positive and Negative Emotion Regulation
Authors: Kim Sang Hee , Hamann Stephan
Published: May 2007

The ability to cope adaptively with emotional events by volitionally altering one's emotional reactions is important for psychological and physical health as well as social interaction. Cognitive regulation of emotional responses to aversive events engages prefrontal regions that modulate activity in emotion-processing regions such as the amygdala. However, the neural correlates of the regulation of positive emotions remain largely unexplored. We used event-related functional magnetic resonance imaging to examine the neural correlates of cognitively increasing and decreasing emotional reactions to positive and negative stimuli. Participants viewed negative, positive, and neutral pictures while attempting to increase, decrease, or not alter their emotional reactions. Subjective reactions were assessed via on-line ratings. Consistent with previous studies, increasing negative and positive emotion engaged primarily left-lateralized prefrontal regions, whereas decreasing emotion activated bilateral prefrontal regions. Different activations unique to increasing versus decreasing emotion were observed for positive and negative stimuli: Unique increase-related activations were observed only for positive stimuli, whereas unique decrease-related activations were observed only for negative stimuli. Regulation also modulated activity in the amygdala, a key emotion-processing region. Regulation effects on amygdala activity were larger for positive than for negative stimuli, potentially reflecting a greater malleability of positive emotional reactions. Increasing and decreasing positive and negative emotion can thus increase and decrease subjective reactions and associated amygdala activity in line with regulatory goals, and is associated with different patterns of prefrontal activation as a function of emotional valence and regulatory goal.