Showing papers by "University of Buenos Aires published in 1984"

Ecological strategies in a Patagonian arid steppe

Abstract: The vegetation in the Coironal arid steppe consists of grasses and shrubs. The objective of this paper was to test Walter's hypothesis that woody vegetation and grasses compete for water in the upper layers of the soil, but woody vegetation has exclusive access to a source of water at deeper levels. Analysis of root profiles and patterns of leaf and soil water potential led us to accept the hypothesis for this arid steppe. Additional information on phenology and on the ability of the major grass species to respond to watering permitted to identify two ecological strategies corresponding to grasses and shrubs. Grasses behave as opportunists having always leaves ready to grow as soon as water becomes available. They have a shallow root system and are able to respond very rapidly to increases in soil water availability. In contrast, woody species have a clear-cut periodic pattern of growth and dormancy. They possess thick horizontal roots running below 35–40 cm and utilized water stored in lower layers of the soil. A diagrammatic model summarizes the role of periodic and opportunistic species upon water circulation in the ecosystem. The effect of changes in the proportion of the two groups upon water dynamics is also discussed.

Trigonometry in Lorentzian Geometry

Abstract: (1984). Trigonometry in Lorentzian Geometry. The American Mathematical Monthly: Vol. 91, No. 9, pp. 543-549.

Taurine Modulation of the Benzodiazepine-γ-Aminobutyric Acid Receptor Complex in Brain Membranes

Abstract: In unwashed brain membranes taurine produced an inhibition of [3H]flunitrazepam [( 3H]FNZ) binding with IC50 ranging between 31.5 and 11.9 microM; the IC20 varied between 18 and 26 nM. This inhibitory effect was of a mixed type, with a reduction in Bmax and an increase in KD. Various precursors and metabolites of taurine have a less inhibitory effect. Taurine also has little inhibitory effect (IC50 above 500 microM) on the binding of [3H]ethyl-beta-carboline-3-carboxylate. In extensively washed membranes, 10(-5) M taurine produces a 16-21% increase in the binding of [3H]FNZ while 10(-5) M gamma-aminobutyric acid (GABA) increases it between 31 and 42%. However, if 10(-5) M GABA plus 10(-5) M taurine is included in the assay there is a dramatic inhibitory effect. Taurine causes an inhibition of the GABAergic enhancement of [3H]FNZ binding with an IC50 between 7.3 and 7.8 microM. Binding experiments with [3H]taurine done under different conditions failed to detect a Na+-independent and specific [3H]taurine receptor. These results suggest that endogenous taurine, the second most abundant free amino acid in brain, may play an important modulatory role in the GABA-benzodiazepine receptor complex.

Effects of acute intoxication with uranyl nitrate on bone formation

Abstract: The alteration of bone formation by an acute intoxication with uranyl nitrate is demonstrated by histologic and histometric methods. When compared with the controls, intoxicated animals showed a markedly lower density in healing sockets, while bone formation was reduced in healing sockets as well as in metaphyseal bone.

3-D Space Location and Orientation Parameter Estimation of Lambertian Spheres and Cylinders From a Single 2-D Image By Fitting Lines and Ellipses to Thresholded Data

Abstract: An approach to object location and orientation estimation is discussed in which objects in 3-D space are approximated by chunks of spheres, cylinders, and planes. The surface-shape parameters of these chunks of primitive subobjects are estimated in real time from a single 2-D image assuming a Lambertian reflection model. This processing is realized by partitioning an image into small square windows and processing the windows in parallel. It is assumed that a small window views a portion of one of the spherical, cylindrical or planar chunks. The paper applies standard statistical estimators in new ways to the estimation of the 3-D shape parameters for spherical and cylindrical surfaces. Linear regression and scatter matrix eigenvalue analysis techniques are used here. The algorithms are computationally simple yet are robust and can handle noisy highly variable data.

Spontaneous Chemiluminescence of Soybean Embryonic Axes during Imbibition.

Abstract: Isolated soybean (Glycine max L. var Hood) embryonic axes have a spontaneous chemiluminescence (about 150 counts per minute per embryo) that increases showing two phases, upon water imbibition. The first photoemission burst was measured between 0 and 7 hours of imbibition with a maximum of about 350 counts per minute per embryo after 2 hours. The second photoemission phase, between 7 and 30 hours, increased from about 220 to 520 counts per minute per embryo. Both chemiluminescence phases were inhibited by infused butylated hydroxyanisole while only the second phase was inhibited by infused salicylhydroxamic acid. On the basis of the sensitivity of the lipoxygenase reaction to both inhibitors (about 90%), the first burst is tentatively assigned to oxy-radicals mobilized upon water uptake by the embryonic axes, and the second phase is tentatively identified as due to lipoxygenase activity. The in vivo lipoxygenase activity of the embryonic axes was estimated by both the fraction of total oxygen uptake that was inhibited by butylated hydroxyanisole and by the fraction of photoemission that was inhibited by butylated hydroxyanisole and by salicylhydroxamic acid. Both approaches indicated marked increases (5-fold and 12-fold, respectively) of lipoxygenase activity between 2 and 30 hours of imbibition. The measured chemiluminescence per O2 uptake ratio (the experimental quantum yield) for the lipoxygenase reaction (3.3 × 10−14 counts per O2 molecule) was used to estimate the O2 uptake due to lipoxygenase activity from the photoemission of the embryonic axes after 30 hours of imbibition. The value (0.54 microliters per minute per axis) was close to the butylated hydroxyanisole-sensitive O2 uptake (1.2 microliters O2 per minute per axis) of the same embryonic axes. Chemiluminescence may afford a noninvasive assay for lipoxygenase activity in intact plant tissues.

Serotoninergic Innervation of the Monkey Basal Ganglia: An Immunocytochemical, Light and Electron Microscopy Study

Abstract: Normal functioning of the basal ganglia system depends upon the proper balance among several substances controlling information transfer within the constituent neuronal circuits. Most of the components of this system are considerably richer than other regions of the central nervous system in these putative neurotransmitters and/or neuromodulators. This quality makes the basal ganglia an optimal group of structures in which to study the position of the neuropil elements with respect to each other, and the alterations induced by surgical, toxicological or pharmacological manipulations. The advent of immunocytochemical techniques which allow observations at the ultrastructural level (Moriarty and Halmi, 1972; Sternberger, 1979; Pickel, 1981) has superseded, to some extent, the autoradiographic method based on the uptake of radioactive exogenous substances. Thus, major strides have been made in the localization of dopamine, gamma amino butyric acid and acetylcholine through the use of antibodies to their corresponding synthesizing enzymes (tyrosine hudroxylase, glutamic acid decarboxylase and choline aeetyltransferase), and more directly with antibodies to certain peptides such as the enkephalins and substance P (Ribak et a., 1979; Pickel et al., 1980, 1981; Kimura et al., 1980; Cuello et al., 1981, 1982; DiFiglia et al., 1982a; Somogyi et al., 1982; Bolam et al., 1983).

Basis for the specificity of anti-5-HT-like antisera in immunocytochemistry applied to the central nervous system

Abstract: Recently (Pecci Saavedra et al. 1982; Brusco et al. 1982, 1983) we have showed that the actual specificity of the rabbit anti-5-HT antibodies, is for the β-carboline derivatives of 5-HT as a result of cyclization of the lateral chain. We explained this as resulting from the use of formaldehyde which acted both as a fixative in the preparation of the tissues, and as the couplng agent in the preparation of the immunogen. Following this line we have fixed several brain stem specimens with 0.5% p-benzoquinone; 3% glutaraldehyde; 4% paraformaldehyde plus 0.25% glutaraldehyde and compare the results with tissues fixed in 4% paraformaldehyde. Glutaraldehyde and p-benzoquinone do not produce cyclization of 5-HT but immobilize monoamines in situ. As expected, the antibodies applied according to the PAP technique did not stain the neuronal bodies of the raphe system, known to contain 5-HT when 3–4% glutaraldehyde or 0.5% p-benzoquinone were used. Good staining was obtained with 4% paraformaldehyde alone or with 4% paraformaldehyde plus 0.25% glutaraldehyde.

Screening of Argentine marine algae for antimicrobial activity

Abstract: Recent publications have extensively reviewed the existence of antimicrobial agents in seaweeds (McConnell et al. 1979; Aubert et al. 1979). In these investigations numerous substances were identified as antimicrobial agents: chlorellin derivatives, acrylic acid, halogenated aliphatic compounds, terpenes, sulfur containing heterocyclic compounds, phenolic inhibitors, etc. to mention only those clearly isolated and purified (Glombitza 1979). Recently a study was reported for marine algae in southern Chile, where numerous species were found to have activity against three distinct bacteria (Henriquez et al. 1979). No similar study has been performed with seaweeds growing along the Atlantic coastline of Argentina to our knowledge.

Short communication. Role of agar beads in the pathogenicity of Pseudomonas aeruginosa in the rat respiratory tract.

Abstract: Sterile agar beads plus Pseudomonas aeruginosa injected intratracheally produced local infection in rats, similar to that described for the injection of agar beads containing the same pathogen. It is suggested that it is not necessary for P. aeruginosa to be inside the beads to induce lung infection.

Asymptotic Behaviour of the Estimates Based on Residual Autocovariances for ARMA Models

Abstract: In a recent paper Bustos and Yohai introduce the class of estimates based on residual auto-covariances (RA-estimates) for the parameters of an ARMA model. They show using a Monte Carlo study that this class contains estimates which are highly efficient when the observations correspond, to a perfectly observed Gaussian ARMA model and robust under the presence of outliers. In this paper we show the consistency and asymptotic normality of a class of estimates containing the RA-estimates.

Arquitectura foliar de las especies del género Prosopis

Abstract: Los caracteres morfologicos de la hoja, principalmente aquellos referidos a la venacion, han sido revalorizados en los ultimos anos como auxiliares importantes en el tratamiento sistematico de las angiospermas a distintos niveles taxonomicos. En este sentido los trabajos de Mouton (1970), Hickey (1973), Dilcher (1974) y Mel ville (1976) tienden a sistematizar y ampliar la terminologia existente sobre arqui tectura foliar, lo cual permite normalizar las observaciones, realizar descripciones mas completas y por lo tanto hacer un uso mas eficiente de los caracteres foliares en la definicion y delimitacion de grupos taxonomicos. Recientemente se han llevado a cabo trabajos sobre arquitectura foliar en varias familias de dicotiledoneas, entre otros los de Sehgal y Paliwal (1974), Hickey y Wolfe (1975), Rury y Dickison (1977), Schadel y Dickison (1979) y Romero (1980). Particularmente en Leguminosas, Weyland (1968) estudio la arquitectura de la venacion foliar en la subfamilia Papilionoideas y Freire de Carvalho (1967, 1970) la venacion foliar de varias especies de Cesalpinoideas y Mimosoideas de Brasil.

Pulmonary rhabdomyosarcoma with isolated small bowel metastasis: A report of a case with immunohistochemical and ultrastructural studies

Abstract: A unique case of pulmonary rhabdomyosarcoma with an isolated, symptomatic small bowel metastasis is presented. The tumor affected the middle lobe, and was treated with a right pneumonectomy. Eleven months after the operation, an isolated small bowel metastasis, which produced intestinal obstruction, was resected. The patient is currently alive, 11 months after operation. The myogenous nature of the tumor was confirmed by the immunohistochemical demonstration of myoglobin in the pulmonary and enteric lesion by the ultrastructural findings of poorly developed sarcomeres.

Photochemical‐like destruction of tryptophan in serum albumins induced by enzyme‐generated triplet species

Abstract: —Human and bovine serum albumin quench enzyme-generated acetone phosphorescence (Ksv=ca. 104M1). Concomitantly, these proteins are altered as shown by diminished tryptophan absorption at 280 nm, appearance of products of the formylkynurenine type (max=ca. 320 nm) and disappearance of tryptophan fluorescence. These alterations—which are similar to those induced photochemically—were also observed with serum albumins exposed to enzyme-generated triplet acetaldehyde. On the other hand, triplet acetone generated by the thermolysis of tetramethyldioxetane failed to induce alterations. Presumably energy transfer occurs from the enzyme-generated triplet species to tryptophan group(s) in the serum albumin associated with the acting enzyme. The detailed mechanism is, however, not yet understood.