Showing papers by "University of Buenos Aires published in 1970"

The spatial relationship of the X and Y chromosomes during meiotic prophase in mouse spermatocytes.

Abstract: The ultrastructure of whole X-Y pairs has been reconstructed by serial sectioning and model building. Seven X-Y pairs were completely reconstructed and the lengths of the cores of the sex chromosomes were measured. These X-Y pairs corresponded to zygonema, early, middle and late pachynema. Special regions of the X-Y pair were reconstructed from thinner sections. — It has been shown that two cores exist in the sex pair during the cited stages, and that their lengths and morphology are rather constant in specific stages. The long core averages 8.9 μ in length and the short core is 3.5 μ long. Both cores have a common end region in which a synaptonemal complex is formed from zygonema up to midpachynema. This synaptonemal complex shortens progressively up to mid-pachynema and at late pachynema becomes obliterated. Each core has a free end touching the nuclear membrane. During mid-pachynema an anomalous synaptonemal complex is developed on most of the length of the long core. This complex is asymmetric and disappears at late pachynema. The meaning of the cores and the complexes are discussed, and the existence of a homologous region in the X-Y pair of the mouse is interpreted to be proved.

Effect of chlorambucil on spermatogenesis in the human with malignant lymphoma.

Abstract: This report is concerned with the action of chlorambucil in males. A group of 8 patients with malignant lymphoma were studied. Diagnoses of Hodgkins disease lymphosarcoma and reticulosarcoma had been established by biopsy. Ages were 18 to 38. As the sole medication chlorambucil was given in doses of .1 mg to .4 mg/Kg/day. Hormonal studies were done based on the determination of 17-ketosteroids in the urine and urinary excretion of gonadotropins. Testicular biopsies were performed by open surgery or at autopsy. After treatment 6 patients became azoospermic 1 developed sever oligospermia and 1 showed no change. With total doses up to 400 mg a progressive oligospermia developed from which the patient could recover slowly if the drug was stopped. 4 patients had elevated values of neutral 17-ketosteroids 3 had slightly low values. Gonadotropins were all within normal limits. Micropic studies showed that the germinal like disappears only Sertoli cells remain and peritubular fibrosis develops. The interstitial cells and blood vessels appeared normal. The condition of azoosperma is considered to be permanent.

The three-dimensional reconstruction of the xy chromosomal pair in human spermatocytes

Abstract: The spatial reconstruction of the XY pair of chromosomes from human spermatocytes has been made by the study of serial sections 1000 A in thickness. The sex pair during zygotene-pachytene forms a condensed mass of chromatin that has two filamentous, electron-opaque cores: the long and the short core. During early pachytene both cores have a common ending region, about 0.4–0.8 µ long. This common end is a synaptonemal complex, and each of the cores forms a lateral element of that complex. The cores become more convoluted during middle pachytene forming "ringlike bodies." Nucleoli from spermatocytes have three distinct regions: (a) granular; (b) dense fibrillar; and (c) clear intermediate. Occasional association of the XY pair and the heteropycnotic "basal knobs" results in apparent association of nucleoli and the sex pair in a minority of cells. The evidence presented is interpreted as a strong support of the hypothesis of homologous regions in the human XY pair.

The behaviour of chromosomal axes during diplotene in mouse spermatocytes.

Abstract: The fate of the synaptonemal complex and its elements after pachytene has been studied by serial sectioning of diplotene nuclei in mouse spermatocytes. The lateral elements of the synaptonemal complex separate from each other during diplotene, and they form single axes, 300 A wide, surrounded by chromatin fibrils. The single axes are continuous and end on the nuclear membrane by two different ends: the basal knob and the simple end. The single axes do not cross-over each other, but they remain approached at the convergence regions. In these regions a modified piece of synaptonemal complex is found. This piece changes into a chromatin bridge during diplotene. It has been inferred that the convergence regions represent chiasmata and that the single axes do not represent axial structures of chromatids.

Potassium-activated phosphatase from human red blood cells

Abstract: The cell membrane K+-activated phosphatase activity was measured in reconstituted ghosts of human red cells having different ionic contents and incubated in solutions of varying ionic composition. When K+-free ghosts are suspended in K+-rich media, full activation of the phosphatase is obtained. Conversely, very little ouabainsensitive activity is detected in K+-rich ghosts suspended in K+-free media. These results, together with the fact that Na+ competitively inhibits the effects of K+ only when present externally, show that the K+ site of the membrane phosphatase is located at the outer surface of the cell membrane. The Mg++ requirements for K+ activation of the membrane phosphatase are fulfilled by internal Mg++. Addition of intracellular Na+ to ATP-containing ghosts raises the apparent affinity of the enzyme for K+, suggesting that the sites where ATP and Na+ produce this effect are located at the inner surface of the cell membrane. The asymmetrical features of the membrane phosphatase are those expected from the proposed role of this enzyme in the Na+−K+-ATPase system.

Neurochemical and structural studies on the mechanism of action of hemicholinium-3 in central cholinergic synapses.

Abstract: —The action of hemicholinium-3 (HC-3) on the cerebral cortex of the rat was studied after subarachnoidal administration. There was a marked decrease of content of ACh in nerve endings and especially in the fraction containing synaptic vesicles, despite the fact that the number of synaptic vesicles was not reduced, as judged by electron microscopy, by the rate of incorporation of ortho [32P]phosphate, and by the phosphorus content of the phospholipids of the isolated synaptic vesicles. There was a close association of [l4C]HC-3 and of monoaminoxidase, which indicated that the drug was preferentially bound to mitochondria. Experiments indicating that HC-3 could be acetylated suggested that this drug may compete with choline not only for entry but also for acetylation.

Potassium-activated phosphatase from human red blood cells : The Effects of Adenosine Triphosphate.

Abstract: The behavior of the red cell membrane K(+)-activated phosphatase is significantly altered by ATP. When ATP is added, the apparent affinity of the enzyme for its substrate and for K(+) is lowered, whereas its sensitivity to ouabain is increased. Under these conditions, addition of Na(+) raises the apparent affinity of the enzyme for K(+) to values well above those found in the absence of Na(+) and ATP. The effect of Na(+) is blocked by hydroxylamine and oligomycin. Low concentrations of Ca(++), Sr(++) or Ba(++), which have little effect in the absence of ATP, induce large increases in the K(+)-dependent phosphatase activity in the presence of ATP. This effect is associated with the loss of ouabain sensitivity of the phosphatase. The velocity vs. divalent cation concentration curves of the K(+)-dependent phosphatase and the (Na(+)+K(+))-independent ATPase activities are very similar. The effects of ATP seem to be specific for this nucleotide and are exerted at concentrations similar to those normally found in red cells. They may therefore be relevant to the proposed physiological role of the cell membrane phosphatase.

Palaeomagnetism of some Middle Jurassic Lavas from South-east Argentina

Abstract: IN the classic papers on palaeomagnetism1,2 the relative positions of South America and Africa in Gondwanaland are obtained from Palaeozoic data.

Through‐circulation drying of tapioca root

Abstract: SUMMARY— The drying characteristics of fresh/y harvested tapioca root (Manihot utilissima Pohl) from Posadas, Argentina, have been investigated in a laboratory through-circulation dryer. Variables studied were bed depth (2-12 cm), air velocity (2,300-5,200 kg/(hr)(sq meter), and air temperature (55—100°Cl. Static pressure drops of air passing through beds of dried and wet slices also were investigated. Straight lines are obtained plotting on semilogarithmic paper the nondimensional moisture content (W-We) (Wo-We) against time. This allows deduction that a diffusional mechanism is controlling the drying rate. Factors to be considered in the design of a continuous through-circulation dryer are given.

The neuromuscular junctions of a pulmonate mollusc. I. Ultrastructural study.

Abstract: The innervation of muscle cells in the posterior (optical) tentacle of the Argentine slug Vaginula soleiformis D'Orbigny was studied with the electron microscope. The neuromuscular junctions showed some degree of complexity regarding the apposed membranes of the pre- and postsynaptic elements in comparison to other molluscan species so far studied. Two populations of granulated vesicles with mean diameters of 855 and 1,190 A respectively, in addition to clear synaptic vesicles, were observed. Since these two populations occur in separate nerve endings, which also show other distinctive morphological features, the existence of two different types of neuromuscular junctions is postulated.

Thiamine pyrophosphatase activity in a fraction rich in golgi-like structures from crushed sciatic nerve of the cat.

Abstract: —The activity of thiamine pyrophosphatase was determined in segments and segment subfractions from normal and crushed sciatic nerves of the cat. Activity of the enzyme was increased in segments near the site of compression. The highest activity of the enzyme was in a fraction rich in tubular and vesicular elements resembling those observed in intact compressed nerves. On morphological grounds these structures have been interpreted as originating from Golgi-like structures.

Palaeomagnetic and Rock Magnetic Studies on the Cenozoic Basalts from Western Argentina

Abstract: Summary Results are presented of a study of 234 samples of Cenozoic basalts from the extra-Andean region of the Provinces of Mendoza and Neuquh in the Argentine Republic, between latitudes 34" S and 40" S. These basalts have been divided into seven groups of flows on the basis of their stratigraphy, ranging in age from the Miocene (Basalts I) to historic (Basalts VII). The TRM of Basalts V, VI and VII is normally polarized and it is concluded that they belong to the Brunhes geomagnetic epoch. The TRM directions of Basalt IV flows are neither parallel nor antiparallel to the axial dipole field. These differences in direction are significant and persistent after cleaning. It is therefore suggested that Basalt IV was extruded during a magnetic transition after the Brunhes geomagnetic epoch. Some Basalt I11 flows are normally polarized, some are reversely poled and some are magnetized obliquely to the axial dipole field. Hence the time of extrusion of these flows may span the Jaramillo and/or Olduvai events within the Matuyama epoch. Basalt I1 flows, which are stratigraphically placed in the Upper Pliocene, are all reversely magnetized while Basalt I flows, some of which are said to be Miocene, exhibit both normal and reversed polarities. It is deduced from the palaeomagnetism of these Basalts that some modifications should be made to their stratigraphy and these deductions have been substantiated by radiometric studies described in the following paper. Estimates of the palaeosecular variation have been made for the Brunhes and Matuyama epochs and compared with other similar data from other parts of the world. Ore microscope observations do not reveal any obvious correlation between polarity and state of oxidation, but a relationship between stability and the degree of exsolution is observed. Electron microprobe studies reveal a high titanium content: the unexsolved titanomagnetites have between 50 and 75 per cent ulviSspine1. It is provisionally suggested that these characteristics of these basalts vary more in time than in geographical area at a given time. 1. Geology These effusive rocks are exposed in the western part of Mendoza and Neuquh Provinces, Argentina, and samples were collected from the area contained between 69"W and 71"W meridians and 35"s and 40"s parallels. The numerous lava flows exposed in this area, principally basalts and andesites, have been classified in chronological order from I (Miocene) to VII (Holocene) by Groeber (1929,1933,1937,

Effects of melatonin on changes induced by castration and testosterone in sexual structures of male rats.

Abstract: The effect of parenteral administration of melatonin on the levels of pituitary LH activity of castrated and castrated, testosterone- treated male rats was studied. The possible direct effect of melatonin on the accessory sex glands, structures well recognized to be under the control of androgenic hormones, was also investigated. Melatonin caused a significant decrease in the weight of the adenohypophyses in castrated rats and also in 1 of the 2 groups of castrated, testosterone-treated male rats. Melatonin also induced significant decreases in ventral prostate weights in both groups of castrated, testosterone-treated rats. Pituitary LH concentration was not significantly affected in any group. Pituitary LH content appeared lower in all groups treated with melatonin. These results suggest a possible direct effect of melatonin on the ventral prostates, which in some way modifies the stimulatory effect of testosterone on these structures.

Structural studies on ovine growth hormone. Cyanogen bromide fragments: N- and C-terminal sequences.

Abstract: 1 The cyanogen bromide fragments obtained from ovine growth hormone have been isolated and chemically characterized Two N-terminal peptides 4 and 5 amino acids long and a C-terminal dodecapeptide have been identified among them The sequence of these fragments has been established and found identical to the corresponding peptides in bovine growth hormone 2 All the information obtained gives further support to the already known analogy between ovine and bovine growth hormones

Isolation, characterization and C-terminal sequence of ovine growth hormone.

Abstract: 1 A procedure is described for the isolation of ovine growth hormone which involves: extraction of frozen pituitaries with borate buffer at pH 8.4, fractionation by ammonium sulphate precipitation and chromatography on DEAE cellulose. This is followed by removal of various impurities by isoelectric precipitation and by the addition of ethanol. The last step consists in a gel-filtration through a column of Sephadex G-100. 2 The protein obtained is homogeneous judged by free electrophoresis, ultracentrifugation, analytical dialysis and C-terminal amino acid analysis; only polyacrylamide gel electrophoresis reveals two minor components accompanying a major anionic band. It has an isoelectric pH of 6.3 and a weight average molecular weight of 20300. 3 The comparison of the amino acid compositions and of the tryptic peptide maps of ovine and bovine growth hormones indicates great homology between these two proteins. The C-terminal amino acid sequence in ovine growth hormone is as follows: (Phe,Glu,Gly)-Ala-Ser-Cys-Ala-Phe-OH.