Is ammonia a better solvent than water for contact ion Pairs? Sciaini, Alberto German; Marceca, Ernesto José; Fernandez Prini, Roberto The existence of a charge-transfer-to-solvent process when a KI contact ion pair (GP) dissolved in supercritical water (SCW) is excited by UV light was confirmed by use of electronic structure calculations applied to molecular dynamics trajectories. We observed similar behavior with fluid density as that found for the KI-CIP in supercritical ammonia (SCA); nevertheless, there are some distinct features in the two supercritical solvents. First, the effect of the solvent field due to the molecules lying beyond the first solvation shell is very different in SCW compared with that observed in SCA; in SCW it actually has a destabilizing effect over the ground and excited states. Second, our results for the thermodynamic behavior of the CIP indicate that SCA is better solvent than SCW for this species. The differences found can be attributed to the solvent molecules surrounding the CIP and bridging the two ions; they shield more efficiently the ion pair from long-range solvent effects in SCA. The different behavior is partially attributed to a stronger solvent-solvent interaction in SCW than in SCA.

The effect of pre-corrosion and steel microstructure on inhibitor performance in CO2 corrosion Paolinelli, Luciano Daniel; Pérez, T.; Simison, Silvia Noemi The importance of chemical composition and microstructure on CO2 corrosion of carbon and low alloy steels has been widely recognized, still contradictory results can be found in the literature. The aim of this work is to assess the relationship between microstructure, surface condition and inhibitor efficiency in CO2 corrosion. A C-Mn steel with two different microstructures was tested in a deoxygenated 5% wt. NaCl solution saturated with CO2 at 40 °C, pH 6. A commercial imidazoline-based inhibitor was added after different pre-corrosion periods. The results obtained showed that pre-corrosion decreases the inhibitor efficiency, but that its impact is microstructure dependent.

Primera descripción de tripanosoma vivax en Argentina; Trypanosoma vivax in Argentina: first description Monzon, Carlos Manuel; Mancebo, Orlando Antonio; Giménez, Juana Noemí; Russo, Ana Maria El presente trabajo reporta por primera vez la presencia de Trypanosoma vivax en Argentina. Los hemo-parásitos fueron identificados en frotes finos de sangre de bovinos provenientes de un establecimiento ganadero en Formosa. En extendidos de gota fresca los parásitos mostraron característicos movimientos vibratorios que les permitía esquivar los glóbulos rojos y atravesar rápidamente el campo microscópico. Una cabra que fue infectada en forma experimental demostró la susceptibilidad de estos rumiantes a la cepa aislada, contrariamente de lo que ocurrió en ratones que mostraron resistencia. Información coincidente con la susceptibilidad de estos mamíferos al T. vivax. Los signos clínicos observados en los bovinos fueron: anemia, pérdida de peso, diarrea, emaciación e incoordinación de miembros. Se reporto la muerte de treinta y seis animales.; The present work reports the first occurrence of Trypanosoma vivax in Argentina. The hemoparasites were identified in thin blood smears of cows from a cattle-farm in Formosa. In weth blood films, the parasites showed characteristic vibratory movements, twisting its way between the red blood cells which allow crossing quickly the microscopic field. An experimentally infected goat showed the susceptibility of these ruminants to the isolated strain; contrarely mice were resistant to the infections, coincident with the susceptibility of these mammalians for T. vivax. The clinical signs observed in cattle were: anaemia, loss of weight, diarrhoea, emaciation, and difficulty in walking. The death of thirty six animals was reported

Advanced Concepts for the Kinetic Modeling of Fatty Acid Methyl Esters Hydrogenation Cabrera, Maria Ines; Grau, Ricardo José Antonio Kinetic studies of the catalytic hydrogenation of vegetable oils and fatty acid methyl esters in liquid-phase are commonly performed in the framework of the Langmuir-Hinshelwood-Hougen-Watson (LHHW) formalism using the competitive and non-competitive adsorption models, which are certainly extreme. Based on the advanced concepts of multicentered adsorption and semi-competitive adsorption, mechanistic kinetic models including a distinction between occupiedsites and covered-sites by the large molecules of FAMEs were formulated without expressing an opinion a priori on whether the adsorption regime is competitive or non- competitive. The theoretical basis of the advanced kinetic modeling is described and successfully applied to three application examples of increasing complexity, including: (a) the hydrogenation of methyl oleate without cis-trans isomerization distinction, (b) the cis-trans isomerization and hydrogenation of the methyl oleate, and (c) the methyl linoleate hydrogenation including the cis-trans isomerization of the methyl oleate. The kinetic studies were carried out using a Ni/-Al2O3, at 398, 413, 428 and 443 K, under isobaric conditions at hydrogen pressures of 370, 510, and 650 kPa, in the absence of mass-transport limitation. After model discrimination based on statistical analysis and taking into account the physical meaning of the estimated parameters, semi-competitive adsorption models were found to be more realistic than the classical LHHW competitive and non-competitive ones, mainly because they give additional information indicating that the adsorbed molecules of methyl linoleate and methyl oleate could cover up to 12 and 7 surface sites, respectively. These values are in adequate agreement with those expected from a rough computational simulation and seem to be the most interesting result, since they are factual and unattainable from the classical LHHW approaches.-Al2O3, at 398, 413, 428 and 443 K, under isobaric conditions at hydrogen pressures of 370, 510, and 650 kPa, in the absence of mass-transport limitation. After model discrimination based on statistical analysis and taking into account the physical meaning of the estimated parameters, semi-competitive adsorption models were found to be more realistic than the classical LHHW competitive and non-competitive ones, mainly because they give additional information indicating that the adsorbed molecules of methyl linoleate and methyl oleate could cover up to 12 and 7 surface sites, respectively. These values are in adequate agreement with those expected from a rough computational simulation and seem to be the most interesting result, since they are factual and unattainable from the classical LHHW approaches.

Relaciones florísticas y características regenerativas en Apurimacia dolichocarpa (Griseb.) Burkart, especie endémica del centro de Argentina; Floristic relations and regenerative traits in Apurimacia dolichocarpa (Fabaceae), an endemic species of central Argentina Funes, Guillermo; Cabido, Marcelo Ruben Apurimacia dolichocarpa (Griseb.) Burkart is a narrow endemic species, restricted to rock outcrops in the western slope of Córdoba Mountains in central Argentina. The aim of this paper is to study the main characteristics of the sites where the species occurs, its phytosociology, the germination and the seedling morpho-functional traits in A. dolichocarpa. Floristic surveys were performed and some physical factors (altitude and size of the outcrops) measured in 18 stands dominated by this species. Imbibition and germination experiments were designed including four temperature regimes (15/5, 20/10, 30/15 and 35/20°C) in light (12/12 h daily photoperiod) and in continuous darkness. Additionally, morpho-functional traits were described in seedlings grown under laboratory conditions for that purpose. A. dolichocarpa was highly restricted to rock outcrops where it generally dominates saxicolous species arrangements. The seeds did not show physical dormancy, and germinated under different temperature regimes, both under light and darkness. Seedlings of A. dolichocarpa belong to the Cryptocotylar-hypogeal-reserve type. Taking into account that A. dolichocarpa is the dominant species in the outcrop communities where it occurs and that the germination of the seeds is not constrained by temperature nor by light/dark conditions, the species would be able to maintain viable populations and even expand its range; nevertheless, this range expansion is likely to be constrained by the low competitive ability exhibited at the seedling stage. Spanish Apurimacia dolichocarpa (Griseb.) Burkart es una especie de distribución altamente restringida al sector occidental de las Sierras Grandes de Córdoba, centro de Argentina. Con el fin de conocer la ecología de esta especie, en este trabajo estudiamos características de los sitios en los que prospera (altitud y tamaño de los afloramientos), su fitosociología y diferentes aspectos de la fase regenerativa que involucran la germinación y atributos de la plántula. Se realizaron inventarios fitosociológicos en los stands de las tres poblaciones conocidas de la especie. Se llevaron a cabo experimentos de imbibición y de germinación, teniendo en cuenta cuatro regímenes de temperatura (15/5 °C, 20/10 °C, 30/15 °C y 35/20 °C), bajo luz (12/12 hrs. luz/sombra) y oscuridad permanente. Además, se determinó la morfología funcional de su plántula. A. dolichocarpa mostró gran afinidad por los sitios rocosos en donde aparece como especie dominante acompañada por una flora de características saxícolas y rupícolas. Las semillas de A. dolichocarpa no presentaron dormición física. Además, mostraron gran capacidad de germinación a diferentes temperaturas, tanto en luz como en oscuridad. La morfología funcional de su plántula fue de tipo criptocotiledonar hipogea reservante. Teniendo en cuenta que A. dolichocarpa es la especie dominante en la comunidad que integra y que posee gran capacidad para germinar bajo diferentes temperaturas, esta especie no tendría inconvenientes en mantener sus poblaciones e incluso expandir su área de distribución. Sin embargo, la capacidad para ampliar su rango podría estar condicionada por la escasa habilidad competitiva de su plántula.

Theoretical NMR Spectroscopic Analysis of the Intramolecular Proton Transfer Mechanism in o r t h o -Hydroxyaryl (Un-)Substitued Schiff Bases Zarycz, Maria Natalia Cristina; Aucar, Gustavo Adolfo Both NMR spectroscopic parameters are calculated as a function of the distance d(N−H) of the O···H···N subsystem of (un- or Z-) substituted ortho-hydroxyaryl Schiff bases, with Z = 4-OMe and 5-Cl. Typical patterns for NMR J couplings and magnetic shieldings, σ(N) (or the chemical shift δ(N)), are obtained showing that they are reliable sensors from which one can get a deeper insight on the intramolecular proton transfer mechanism. An inflection point is found by representing each NMR spectroscopic parameter as a function of d(N−H) or when the correlation between both parameters is depicted. The analysis of these (cubic) functions shows whether the proton is bound to the oxygen or to the nitrogen atom or is shared by both atoms. In line with these findings, it is possible to predict the position of the proton in the bridge. These theoretical findings are supported by previous experimental measurements. It is shown that nitrogen chemical shift is quite sensitive to substituent effects though 1J(15NH) is not. This last parameter depends on d(NH). When correlating both spectroscopic parameters, a previous δ(N) vs 1J(15NH) linear dependence is generalized to a cubic dependence which seems to be more reliable. Calculations are based on two state of the art methodologies: DFT-B3LYP and polarization propagators at second order of approach (SOPPA) with large enough basis sets.

Collisional activation of asteroids in cometary orbits Diaz, Carlos Gonzalo; Gil Hutton, Ricardo Alfredo Aims. We study the time an asteroid in a cometary orbit must wait to receive a collision producing a crater depth enough to expose subsurface volatiles, aiming to analyze the possibility of collisional reactivation of these objects if they are dormant comets.Methods. We perform a numerical integration of the asteroids in cometary orbits and a population of projectiles to find the mean intrinsic collision probabilities and mean impact velocities of the targets. The projectile population was obtained as a sample with the same distribution of orbital elements as observed for main belt asteroids, and we also take into account that its size distribution changes for different size ranges. Only 206 asteroids in cometary orbits, that are not members of other asteroid groups, with a Tisserand parameter 2 2.9 and perihelion distance > 1.3 AU were considered.Results. A large fraction of the objects in the sample receive at least 1 collision energetic enough to break the comet crust and allow a dormant comet to reach an active state in a period shorter than a Jupiter Family Comet dynamical lifetime. A large fraction of the objects in the sample with 8-9 km receive several collisions and could be active for more than 3 10 yr. We found an excess in the number of dormant comet candidates from the expected values which is indicative of the presence in the ACOs population of objects that are not comets in a dormant state. These objects could be asteroids with < 3 that reach their present orbits by some dynamical mechanism that perturbs the original asteroidal orbit changing its Tisserand invariant.

Analysis of a topside ionospheric model using GPS and ionosonde observables Meza, Amalia Margarita; Brunini, Claudio Antonio; Gularte Scarone, Angela Erika; Mosert, Marta Estela Ground-based vertical incidence soundings are well suited to model the bottom-side ionosphere but are not so good for dependably modelling the topside ionosphere. This study aims to combine vertical incidence sounding and dual-frequency GPS measurements to reconstruct the topside profile. The reconstruction technique relays on the use of the so-called vary-Chap approach that use an α-Chapman function with a continuously varying scale height. We tested our technique with ionograms and GPS observations recorded at Ebro observatory, Spain (geomagnetic coordinates 43.6°N and 80.9°E). The contribution of the topside ionosphere to the vertical TEC was calculated as the difference between the vertical TEC estimated from GPS measurements and the contribution of the bottom-side ionosphere estimated by integration of the electron density obtained from ionograms. The obtained topside vertical TEC were used to estimate the parameters of the vary-Chap function that represents the topside profile, namely the transition height where the dominant ion species change from O + to H + , the scale height at the transition height, and the shape factor that controls the steepness of the O + to H + transition. The results are analyzed for solstices and equinoxes for a high solar activity year. The values obtained for the transition height are in agreement with those derived by other author. The topside profile seems to merge swiftly with an empirical plasmasphere model based on Radio Plasma Image measurements.

Involvement of septal Cdk5 in the emergence of excessive anxiety induced by stress Bignante, Elena Anahi; Rodriguez Manzanares, Pablo Andrés; Mlewski, Estela Cecilia; Bertotto, Maria Eugenia; Bussolino, Daniela Fernanda; Paglini, Maria Gabriela; Molina, Víctor Alejandro The aim of the present study was to evaluate whether the activation of Cdk5, a protein that has been suggested to participate in higher cognitive functions, is required for the onset of a sensitized anxiety-related behavior induced by stress. The exposure to restraint enhanced both Cdk5 expression in certain subareas of the septohippocampal system, principally in the lateral septum (LS) and septal Cdk5 kinase activity in rats. Behaviorally, restrained wild type mice showed a behavior indicative of enhanced anxiety in the elevated plus maze (EPM). In contrast, unstressed mice and stressed knockout mice, which lacked the p35 protein, the natural activator of Cdk5, displayed similar anxiety-like behavior in the EPM. Finally, the intra-LS infusion of olomoucine - a Cdk5 inhibitor - blocked the enhanced anxiety in the EPM induced by prior stress in rats. All these data provide evidence that septal Cdk5 is required in the emergence of a sensitized emotional process induced by stress. © 2008 Elsevier B.V. and ECNP.

Multiple spawning and length of embryonic development of Munida gregaria in northern Patagonia (Argentina) Dellatorre, Fernando Gaspar; Baron, Pedro Jose Munida gregaria is a small galatheid widely distributed around the southern hemisphere, considered a key species in food webs of coastal and shelf marine ecosystems. Previous studies conducted at 55°S and 46°S on the Atlantic coast of South America, have shown that the species can adapt its reproductive patterns to different environmental conditions. The objectives of this work are to complete this analysis by determining: (1) the reproductive season span; (2) the potential of the species to produce multiple clutches of eggs; (3) the length of its embryonic development; and (4) based on previous objectives, the potential number of clutches produced by M. gregaria by reproductive season in the northern range of its coastal distribution (42-43°S, northern Patagonia). In this region, brooding females were present from June to December, representing more than 80% of total females between July and October. Females presented previtellogenic oocytes beginning maturation just after egg extrusion, and fully developed vitellogenic oocytes just before hatching. From November to February increasing proportions of females showed signs of athresia and resorption of mature oocytes. The complete embryonic development of M. gregaria lasted 26-29 days at 11°C constant temperature. Considering the pattern of synchronous ovary re-maturation and embryonic development, the length of embryogenesis at water temperatures typical from costal waters off northern Patagonia during the breeding season, it is concluded that female M. gregaria have the potential to consecutively lay more than three egg clutches per reproductive season. Copyright © Marine Biological Association of the United Kingdom 2008.

Discriminación hacia diferentes grupos en la Argentina: Gitanos Schencman, Pablo Informe sobre las vejaciones, y hechos discriminatorios, padecidas por la comunidad gitana de Argentina durante el año 2007. El capítulo se confeccionó a partir de fuentes secundarias y trabajo con los datos de la primera encuesta de opinión realizada solo entre alumnos de diversas escuelas de nivel medio.

Reversal of antiprogestin resistance and progesterone receptor isoform ratio in acquired resistant mammary carcinomas Wargon, Victoria; Helguero, Luisa; Bolado, Julieta; Rojas, Paola Andrea; Novaro, Virginia; Molinolo, Alfredo; Lanari, Claudia Lee Malvina To explore mechanisms related to hormone resistance, three resistant variants of the MPA mouse breast cancer tumor model with low levels of progesterone receptor (PR) isoform A (PR-A)/high PR-B expression were developed by prolonged selective pressure with antiprogestins. The resistant phenotype of one tumor line was reversed spontaneously after several consecutive passages in syngeneic BALB/c mice or by 17-beta-estradiol or tamoxifen treatment, and this reversion was significantly associated with an increase in PR-A expression. The responsive parental tumors disclosed low activation of ERK and high activation of AKT; resistant tumors on the other hand, showed the opposite, and this was associated with a higher metastatic potential, that did not revert. This study shows for the first time in vivo a relationship between PR isoform expression and antiprogestin responsiveness, demonstrating that, whereas acquired resistance may be reversed, changes in kinase activation and metastatic potential are unidirectional associated with tumor progression.

An approach for identification of uncertain Wiener systems Figueroa, Jose Luis; Biagiola, Silvina Ines; Agamennoni, Osvaldo Enrique As reported in the literature, Wiener models have arisen as an appealing proposal for nonlinear process representation due to their simplicity and their property of being valid over a larger operating region than a LTI model. These models consist of a cascade connection of a linear time invariant system and a static nonlinearity. In the description of these models, there are several ways to represent the linear and the nonlinear blocks, and several approaches can be found in the literature to perform the identification process. In this article, we provide a parametric description for the Wiener system. This approach allows us to describe the uncertainty as a set of parameters. The proposed algorithm is illustrated through a pH neutralization process.

Testing of photomultiplier tubes for use in the surface detector of the Pierre Auger observatory Barnhill, D.; Suarez, Federico; Arisaka, K.; Garcia, Beatriz Elena; Gongora, J. P.; Lucero, Luis Agustin; Navarro, I.; Ohnuki, T.; Risi, A.; Tripathi, A. In the array of water Cherenkov detectors of the Pierre Auger Observatory, 4800 large photomultiplier tubes (PMTs) will be used. Before being deployed, each PMT is evaluated to check that various parameters, such as the linearity, dark noise, and gain, fall within a specified range. The large scale test system, designed and constructed for this purpose, is capable of testing multiple large PMTs simultaneously. The test system and the results of the tests for the first 3964 PMTs are presented in this paper.

Upper Oligocene-Miocene clinoforms of the foreland Austral Basin of Tierra del Fuego, Argentina: Stratigraphy, depositional sequences and architecture of the foredeep deposits Ponce, Juan Jose; Olivero, Eduardo Bernardo; Martinioni, Daniel Roberto The Upper Oligocene-Miocene deposits of the foreland Austral Basin of Tierra del Fuego represent the youngest foredeep fill, developed in front of the adjacent fold and thrust belt. They consist of superbly exposed, sub-horizontal clastic successions of more than 600 m of sedimentary thickness. The study of 11 sections by means of facies analysis and sequence stratigraphic criteria enabled the identification of five depositional sequences (SI-SV), bounded by unconformities (dI-dV) involving hiatuses of different magnitudes. The basal sequence (SI) includes two members: A, mudstone dominated, deposited by cohesive flows; and B, glauconite-rich, sandstone dominated, deposited by episodic turbidity currents. The remaining sequences (SII-SV) are composed of complex arrangements of fine conglomerates, coarse- to fine-grained sandstones, and mudstones that were deposited mainly by hyperpycnal flows. The basal unconformities of the SI to SIV involve minor hiatuses, while that of the SV is a major order unconformity. Two types of clinofom geometries are recognized in the foredeep sequences. Type a clinoforms present a wedge shaped geometry and characterize the foredeep infill during the compressional tectonic regime. Regarding this clinoform type, SI is situated closer to the orogen and shows variations in the bedding dip with development of internal unconformities. SII to SIV are situated towards the foreland and are characterized by subhorizontal conformable beds of large lateral extension. Type b clinoforms, with sigmoidal geometry, show a clear northeast progradation related to a progressive foredeep fill under tectonic quiescence. This clinoform type characterizes the deposits in SV. The recognition of hyperpycnites and different types of clinoform geometries in these sequences incorporates new concepts in reservoir prospects, which are critical for the evaluation of the petroleum system in the Austral Basin.

¿Reforzador o atenuador? "Evidentemente" como adverbio evidencial en el discurso académico escrito Estrada, Andrea Maria En este artículo, a partir de un corpus de aplicación constituido por ponencias y artículos científicos pertenecientes a ciencias exactas, ciencias sociales y ciencias humanas, me propongo identificar y describir en el marco de la semántica argumentativa las propiedades del adverbio evidencial evidentemente en discurso académico escrito. En primer lugar, a partir del análisis cuantitativo y cualitativo del corpus, compruebo que este marcador ocurre mayormente en las ciencias fácticas lo que me permite esbozar una hipótesis explicativa: efectivamente, la ocurrencia de evidentemente está relacionada con la configuración discursiva propia de cada disciplina, es decir, con los efectos de cientificidad emanados de la construcción del objeto de estudio y de la presencia del locutor como intermediario de los fenómenos descriptos. En segundo lugar, y con la intención de superar ciertas contradicciones que surgen del análisis de la bibliografía de hecho algunos estudiosos analizan evidentemente como un reforzador, mientras que otros lo consideran un evidencial de inferencia, que atenúa el grado de certeza del locutor propongo un nuevo análisis a partir de ejemplos extraídos del corpus de ciencias fácticas.

Improving the schedulability of soft real-time open dynamic systems: The inheritor is actually a debtor Santos, Rodrigo Martin; Lipari, Giuseppe; Santos, Jorge This paper presents the Clearing Fund Protocol, a three layered protocol designed to schedule soft real-time sets of precedence related tasks with shared resources. These sets are processed in an open dynamic environment. Open because new applications may enter the system at any time and dynamic because the schedulability is tested on-line as tasks request admission. Top-down, the three layers are the Clearing Fund, the Bandwidth Inheritance and two versions of the Constant Bandwidth Server algorithms. Bandwidth Inheritance applies a priority inheritance mechanism to the Constant Bandwidth Server. However, a serious drawback is its unfairness. In fact, a task executing in a server can potentially steal the bandwidth of another server without paying any penalty. The main idea of the Clearing Fund Algorithm is to keep track of processor-time debts contracted by lower priority tasks that block higher priority ones and are executed in the higher priority servers by having inherited the higher priority. The proposed algorithm reduces the undesirable effects of those priority inversions because the blocked task can finish its execution in its own server or in the server of the blocking task, whichever has the nearest deadline. If demanded, debts are paid back in that way. Inheritors are therefore debtors. Moreover, at certain instants in time, all existing debts may be waived and the servers are reset making a clear restart of the system. The Clearing Fund Protocol showed definite better performances when evaluated by simulations against Bandwidth Inheritance, the protocol it tries to improve.

Effect of translocator protein (18 kDa)-ligand binding on neurotransmitter-induced salivary secretion in rat submandibular glands Ostuni, Mariano; Tumilasci, Omar Rene; Péranzi, Gabriel; Cardoso, Estela M. del Luján; Contreras, Liliana Noemí; Arregger, Alejandro Luis; Papadopoulos, Vassilios; Lacapere, Jean Jacques Background information. TSPO (translocator protein), previously known as PBR (peripheral-type benzodiazepine receptor), is a ubiquitous 18 kDa transmembrane protein that participates in diverse cell functions. High-affinity TSPO ligands are best known for their ability to stimulate cholesterol transport in organs synthesizing steroids and bile salts, although they modulate other physiological functions, including cell proliferation, apoptosis and calcium-dependent transepithelial ion secretion. In present study, we investigated the localization and function of TSPO in salivary glands. Results. Immunohistochemical analysis of TSPO in rat salivary glands revealed that TSPO and its endogenous ligand, DBI (diazepam-binding inhibitor), were present in duct and mucous acinar cells. TSPO was localized to the mitochondria of these cells, whereas DBI was cytosolic. As expected, mitochondrial membrane preparations, which were enriched in TSPO, exhibited a high affinity for the TSPO drug ligand, 3H-labelled PK 11195, as shown by Bmax and Kd values of 10.0+− 0.5 pmol/mg and 4.0+− 1.0 nM respectively. Intravenous perfusion of PK 11195 increased the salivary flow rate that was induced by muscarinic and α-adrenergic agonists, whereas it had no effect when administered alone. Addition of PK 11195 also increased the K+, Na+, Cl− and protein content of saliva, indicating that this ligand modulated secretion by acini and duct cells. Conclusions. High-affinity ligand binding to mitochondrial TSPO modulates neurotransmitter-induced salivary secretion by duct and mucous acinar cells of rat submandibular glands.

Effect of aging on 24-hour pattern of stress hormones and leptin in rats Cano, Pilar; Cardinali, Daniel Pedro; Spinedi, Eduardo Julio; Esquifino, Ana I. This work analyzes the 24-hour changes of hypothalamic–pituitary–adrenal (HPA) axis activity and leptin release in aged rats. Three- and 22-month-old male Wistar rats were killed at 6 time intervals during a 24- hour cycle (n= 8–10 rats/group). Aging augmented plasma ACTH while it decreased plasma and adrenal gland corticosterone levels. Plasma and adrenal corticosterone levels attained high levels during all the scotophase, concomitantly with the maxima in ACTH levels, whereas in aged rats only a brief plasma corticosterone peak at the early scotophase and no time of day variations of adrenal corticosterone were observed. Aging augmented circulating leptin, with a significant interaction “age × time” in the factorial ANOVA, i.e. only in young rats time of day changes were significant, with the lowest values of leptin at the middle of the light period and higher values at night. When plasma leptin was expressed on body weight basis, the age-related differences became not significant but the daily pattern of plasma leptin found in young rats persisted. Plasma and adrenal corticosterone levels correlated significantly with plasma ACTH only in young rats. Likewise, plasma leptin correlated with plasma corticosterone only in young rats. These changes can be attributed to a disrupting effect of aging on the homeostatic mechanisms modulating HPA activity and leptin release.

Tillage effects on soil carbon balance in a semiarid agroecosystem Bono, Alfredo; Alvarez, Roberto; Buschiazzo, Daniel Eduardo; Cantet, Rodolfo Juan Carlos Tillage systems may affect soil C sequestration, with a potential impact on crop productivity or organic matter mineralization. We evaluated crop yield, C inputs to the soil, and in situ CO2-C fluxes under no-till and conventional tillage (disk tillage) during the 3- to 6-yr period from the installation of an experiment in an Entic Haplustoll of the Semiarid Pampean Region of Argentina to elucidate the mechanisms responsible for possible management-induced soil organic matter changes. Yield and biomass production were greater under no-till than disk tillage for all the crops included in the rotation (oat [Avena sativa L.] + hairy vetch [Vicia villosa Roth ssp. villosa], corn [Zea mays L.], wheat [Triticum aestivum L.], and oat). This result was attributed to the higher soil water content under no-till. Carbon inputs to the soil averaged 4 Mg C ha-1 yr-1 under no-till and 3 Mg C ha-1 yr-1 under disk tillage. Soil temperature was similar between tillage systems and CO2-C emission was about 4 Mg C ha yr-1 yr-1, with significant but small differences between treatments (-0.2 Mg C ha-1 yr-1). Carbon balance of the soil was nearly equilibrated under no-till; meanwhile, greater C losses as CO2 than inputs in crop residues were measured under conventional tillage. Organic C in the soil was 5.4 Mg ha-1 higher under no-till than the disk tillage treatment 6 yr after initiation of the experiment. Results showed that in our semi-arid environment, C sequestration occurred under no-till but not conventional tillage. The sequestration process was attributed to the effect of the tillage system on crop productivity rather than on the mineralization intensity of soil organic pools.