Estradiol rapidly activates a microcircuit in the arcuate nucleus of the hypothalamus (ARH) that is needed for maximal female sexual receptivity. Membrane estrogen receptor-α complexes with and signals through the metabotropic glutamate receptor-1a stimulating NPY release within the ARH activating proopiomelanocortin (POMC) neurons. These POMC neurons project to the medial preoptic nucleus (MPN) and release β-endorphin. Estradiol treatment induces activation/ internalization of MPN μ-opioid receptors (MOR) to inhibit lordosis. Estradiol membrane action modulates ARH gamma-aminobutyric acid receptor-B (GABA B ) activity. We tested the hypothesis that ARH GABA B receptors mediate estradiol-induced MOR activation and facilitation of sexual receptivity. Double label immunohistochemistry revealed expression of GABA B receptors in NPY, ERα and POMC expressing ARH neurons. Approximately 70% of POMC neurons expressed GABA B receptors. Because estradiol initially activates an inhibitory circuit and maintains activation of this circuit, the effects of blocking GABA B receptors were evaluated before estradiol benzoate (EB) treatment and after at the time of lordosis testing. Bilateral infusions of the GABA B receptor antagonist, CGP52432, into the ARH prior to EB treatment of ovariectomized rats prevented estradiol-induced activation/internalization of MPN MOR, and the rats remained unreceptive. However, in EB treated rats, bilateral CGP52432 infusions 30 minutes before behavior testing attenuated MOR internalization and facilitated lordosis. These results indicated that GABA B receptors were located within the lordosis-regulating ARH microcircuit and are necessary for activation and maintenance of the estradiol inhibition of lordosis behavior. Although GABA B receptors positively influence estradiol signaling, they negatively regulate lordosis behavior since GABA B activity maintains the estradiol-induced inhibition.

Resumen En aplicaciones a elevadas temperaturas como por ejemplo en cámaras de combustión y toberas de vehículos aeroespaciales se requiere el uso de aleaciones que permitan una elevada extracción de calor y buenas propiedades mecánicas. En este trabajo se realiza un análisis comparativo de las aleaciones Cu-Cr-Zr y Cu-Ag-Zr. Las mismas fueron sometidas a ensayos de resistividad eléctrica entre 25ºC y 700ºC y de tracción a 150ºC, 450ºC y 700ºC. Los resultados de los ensayos de resistividad eléctrica fueron convertidos a conductividad térmica mediante la relación de Wiedemann-Franz. A través de este análisis se observa que la aleación con mejor conductividad térmica es la de Cu-Ag-Zr presentando además un cambio de fase que no es observado en la aleación Cu-Cr-Zr. Respecto al ensayo de tracción la aleación Cu-Cr-Zr presenta mayores valores de resistencia a la tracción y tensión de fluencia a las temperaturas estudiadas. Palabras-clave: Conductividad térmica; Resistividad eléctrica; Tracción. Abstract In High-heat-flux applications as in the main combustion chamber and liners of rocket engines, the use of certain alloys that have high thermal conductivity with high strength is required. The present work makes a comparison between Cu-Cr-Zr and Cu-Ag-Zr alloys. They have been subjected to electrical resistivity tests between 25ºC and 700ºC and tensile tests at 150ºC, 450ºC and 700ºC. The electrical resistivity test results have been converted to thermal conductivity by the use of the Wiedemann-Franz equation. The thermal conductivity results show that the Cu-Ag-Zr alloys have better thermal conductivity than the Cu-Cr-Zr alloy. However, the Cu-Ag-Zr alloy has a phase change that is not present in the Cu-Cr-Zr alloy. According to the tensile test, the Cu-Cr-Zr has higher ultimate tensile and yield strength than the Cu-Ag-Zr alloys, at the temperatures that have been studied.

Corrosion of YBa2Cu3O7−x pellets has been studied using magnetic levitation. Pellets compressed at green compaction pressures of 120–200 MPa were exposed to water and air and the levitation heights were measured over a period of more than a month. A model based on diffusion as a rate-controlling step has been proposed. Levitation height normalized with respect to the initial levitation height was used as the modeling parameter. The experiments indicate that the normalized levitation height decreased with time up to a certain level called the saturation leviation, beyond which there is no change in the levitation height. Samples in air degraded faster than samples in water. The initial period of degradation before saturation fits the proposed model well and therefore appears to be diffusion controlled. The saturation levitation shows a dependence on the green compaction pressure. It has been proposed that corrosion (degrading reactions) is due to open porosities which are closed by the reaction products, thus causing a saturation in the levitation height dependent on the porosities.

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