Showing papers by "National University of Cuyo published in 1983"

The blood–testis barrier in the toad (Bufo arenarum hensel): A freeze‐fracture and lanthanum tracer study

Abstract: Intercellular junctions between Sertoli cells in the toad testis were studied by freeze-fracture and electron-opaque intercellular markers. These junctional specializations are characterized in thin sections by a series of focal fusions on the outer leaflets of both adjacent cell plasmalemmas, associated with bundles of fine filaments in the subjacent Sertoli cell cytoplasms. However, the wide subsurface cisterna of the endoplasmic reticulum, a component constantly associated with Sertoli cell junctions in mammals, is absent in the toad. The intravascularly injected lanthanum hydroxide, used as a tracer compound, gains access to the seminiferous tubules and surrounds spermatogonia and leptotene spermatocytes, but is persistently excluded from germ cells in later stages of development. This indicates that, as is the case in the mammalian testis, a permeability barrier to lanthanum is established which isolates all germ cells beyond leptotene spermatocytes. Freeze-fracture reveals the characteristic occluding junctions between Sertoli cells, but a variation in their geometric patterns was clearly observed in different regions of the toad seminiferous epithelium. The membrane-fractured faces of Sertoli cells embracing differentiating spermatids exhibit a deep junctional complex: up to 50 rows of particles between adjacent Sertoli cells separate these late germ cells from the periphery of the seminiferous tubules. Sertoli cells surrounding early germ cells generally exhibit, instead, a discontinuous, poorly developed network of interconnected rows of particles with few widely spaced strands. This seems to permit the percolation of the intercellular marker in areas of the seminiferous epithelium containing spermatogonia and leptotene spermatocytes.

Lattice distortions and local compressibility around trivalent rare-earth impurities in fluorites

Abstract: We have calculated the lattice distortions around trivalent rare-earth dilute impurities, occupying substitutionally metal sites in fluorites. Explicit results are given for the equilibrium positions of the nearest fluorine ligands, $R$, the induced electric dipole moments, and the local hydrostatic strains for $M{\mathrm{F}}_{2}$ ($M=\mathrm{C}\mathrm{d},\phantom{\rule{0ex}{0ex}}\mathrm{C}\mathrm{a},\phantom{\rule{0ex}{0ex}}\mathrm{S}\mathrm{r},\phantom{\rule{0ex}{0ex}}\mathrm{P}\mathrm{b},\phantom{\rule{0ex}{0ex}}\mathrm{a}\mathrm{n}\mathrm{d}\phantom{\rule{0ex}{0ex}}\mathrm{B}\mathrm{a}$). These results are used to study the impurity-ligand distance dependence of the fourth-order cubic-crystal-field parameter, ${b}_{4}$, for ${\mathrm{Gd}}^{3+}$ and the isoelectronic ion ${\mathrm{Eu}}^{2+}$. Comparison is made with the change of ${b}_{4}$ with hydrostatic stress using the calculated local compressibility of the lattice. A consistent description of the experimental data is obtained assuming ${b}_{4}\ensuremath{\propto}{R}^{\ensuremath{-}m}$ with $m\ensuremath{\sim}10$.

Effect of prenatal and postnatal exposure to therapeutic doses of chlorimipramine on emotionality in the rat.

Abstract: Prenatal administration of high doses of tricyclic antidepressants have been reported to produce teratogenic and behavioral effects in rat offspring. In the present work, behavioral abnormalities are described in offspring of rats treated with therapeutic doses of chlorimipramine (CIM) during pregnancy (CIM-P), lactation (CIM-L) and during the whole pregnancy-lactation period (CIM-PL). CIM-P treatment did not produce teratogenic effects, did not affect number or body weight of pups at birth and did not induce neonatal mortality. At 2 months of age, the CIM-P males showed a significant increase in digging and grooming (familiar environment test), a decrease in “exploration” (novel environment test) and a decrease in active social interactions (social behavior test). Females were more resistant than males to the prenatal CIM treatment. The results suggest increased emotionality in CIM-P pups. Some behavioral abnormalities were also observed in the tests performed at 4 months of age. CIM-L treatment had minor effects on litter behavior. CIM-PL treatment potentiated the effects of the CIM-P treatment. In the CIM-PL males, impairment of exploration of a novel environment still remained in the tests performed at 4 months of age. It is speculated that when prenatal brain development is altered by CIM, further postnatal treatment may impair compensatory processes occurring in early postnatal life.

Ultrastructural effects of cadmium on the rat epididymis

Abstract: The short-term effect of a subcutaneous injection of 3 mumol of cadmium chloride/100 g body weight were examined 90 min later in male rats. The main target of cadmium, as shown by electron microscopy, was the endothelial lining of capillaries of the caput epididymidis. Intercellular junctions between endothelial cells were disorganized, ranging from slight separation between cytoplasmic leaflets to wide gaps which communicated freely with the pericapillary tissue. Disruption of platelets and intravascular clotting followed these early endothelial lesions, and clotting was found in venules as an extension of clotting from the capillaries. Pre-treatment with zinc (300 mumol zinc chloride/100 g body weight) prevented all of the lesions described above.

Upper critical fields of regular superconductive networks. Surfaces and impurities

Abstract: The upper critical field of several defect structures is studied using the de Gennes--Alexander theory of superconductive networks. The systems considered include a terminated ladder, an impurity site within the ladder, and a square lattice with a surface. Localized modes of condensation appear in all the structures considered. Four different methods have been used alternatively or concurrently: direct diagonalization, continuous-fraction expansion, transfer matrix, and a renormalization-group decimation procedure. This last method has proved very useful to study irrational values of the ratio flux to flux quantum in the square lattice. The case of the square lattice with a surface shows several characteristics in common with surface superconductivity (H/sub c/3) in bulk materials.

Low-energy scattering of charged particles

Abstract: The off-energy-shellT-matrix for two charged particles is studied in the low momentum limit (k → 0). TheT-matrix for a Coulomb interaction (TC) is usually considered as the limit of the amplitude for a screened potential (Ts) when the screening is removed. We show that this statement is not true for small enough energies. For an attractive interactionTC andTS differ significantly when k→0.TC behaves as k-1/2, whileTS keeps itsk-1 behaviour even when the screening is turned off. We note that this is an effect which would be observed in ion-atom collisions when one electron is ejected from the atom and captured into a continuum state of the ion.

Effects of the chronic ingestion of therapeutic doses of chlorimipramine on the behavioral action of agonists and antagonists of serotonin in male rats

Abstract: Locomotor activity and hole-board exploration (frequency and time spent head-dipping) were impaired in male rats by injecting IP the 5-HT agonists, fluoxetine and 5-HTP. This treatment produced also myoclonus and increased the time spent resting during trials. The chronic ingestion of chlorimipramine (CIM) or the injection of the 5-HT receptor blocker, methysergide (15 mg/kg) prevented the action of the 5-HT agonists on locomotion and resting and blocked the appearance of myoclonus. Both, CIM and methysergide prevented to a minor degree the fluoxetine-5-HTP-induced decrease of exploration. The chronic ingestion of CIM clearly potentiated the effects of methysergide on hole-board exploration. Results suggest that the chronic treatment with therapeutic doses of CIM reduces the functional activity of some 5-HT systems in the brain of the rat, probably by blockade of post-synaptic 5-HT receptors. This does not preclude, however, that CIM may also alter some NA systems.

About Singer theorem

Abstract: The purpose of this work is to provide the nonmathematician with a clear specification, of some conditions at ∞ which, because of singer theorem, make it impossible to choose a gauge without ambiguity.