87,610 research outputs found
Evidence for a GABAergic system in rodent and human testis: Local GABA production and GABA receptors
No full textThe major neurotransmitter of the central nervous system, gamma-aminobutyric acid (GABA), exerts its actions through GABA(A), GABA(B) and GABA(C) receptors. GABA and GABA receptors are, however, also present in several non-neural tissues, including the endocrine organs pituitary, pancreas and testis. In the case of the rat testis, GABA appears to be linked to the regulation of steroid synthesis by Leydig cells via GABA(A) receptors, but neither testicular sources of GABA, nor the precise nature of testicular GABA receptors are fully known. We examined these points in rat, mouse, hamster and human testicular samples. RT-PCR followed by sequencing showed that the GABA-synthesizing enzymes glutamate decarboxylase (GAD) 65 and/or GAD67, as well as the vesicular GABA transporter vesicular inhibitory amino acid transporter (VIAAT/VGAT) are expressed. Testicular GAD in the rat was shown to be functionally active by using a GAD assay, and Western blot analysis confirmed the presence of GAD65 and GAD67. Interstitial cells, most of which are Leydig cells according to their location and morphological characteristics, showed positive immunoreaction for GAD and VIAAT/VGAT proteins. In addition, several GABA(A) receptor subunits (alpha1-3, beta1-3, gamma1-3), as well as GABAB receptor subunits R1 and R2, were detected by RT-PCR. Western blot analysis confirmed the results for GABA(A) receptor subunits beta2/3 in the rat, and immunohistochemistry identified interstitial Leydig cells to possess immunoreactive GABA(A) receptor subunits beta2/3 and alpha1. The presence of GABA(A) receptor subunit alpha1 mRNA in interstitial cells of the rat testis was further shown after laser microdissection followed by RT-PCR analysis. In summary, these results describe molecular details of the components of an intratesticular GABAergic system expressed in the endocrine compartment of rodent and human testes. While the physiological significance of this peripheral neuroendocrine system conserved throughout species remains to be elucidated, its mere presence in humans suggests the possibility that clinically used drugs might be able to interfere with testicular function. Copyright (C) 2003 S. Karger AG, Basel
Superconductivity in metal-coated graphene
No full textIn this work we explore, by first-principles density functional theory (DFT) calculations, the possibility of inducing electronphonon mediated superconductivity in a graphene sheet by doping its surface with alkaline metal adatoms. We demonstrate that, contrary to what could be naively believed, simple exfoliation to one layer of superconducting graphite intercalated compounds (GICs) does not necessarily lead to superconducting graphene, as it is the case in CaC6. On the contrary, it is meaningful to look for superconductivity in monolayers obtained by exfoliating non-superconducting GICs. In particular, we demonstrate that Li coating and double-coating of graphene leads to superconductivity in graphene with T-c that could be as large as 18 K. (C) 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinhei
Phonon-mediated superconductivity in graphene by lithium deposition
No full textGraphene(1) is the physical realization of many fundamental concepts and
phenomena in solid-state physics(2). However, in the list of graphene's
many remarkable properties(3-6), superconductivity is notably absent. If
it were possible to find a way to induce superconductivity, it could
improve the performance and enable more efficient integration of a
variety of promising device concepts including nanoscale superconducting
quantum interference devices, single-electron superconductor-quantum dot
devices(7,8), nanometre-scale superconducting transistors(9) and
cryogenic solid-state coolers(10). To this end, we explore the
possibility of inducing superconductivity in a graphene sheet by doping
its surface with alkaline metal adatoms, in a manner analogous to which
superconductivity is induced in graphite intercalated compounds(11,12)
(GICs). As for GICs, we find that the electrical characteristics of
graphene are sensitive to the species of adatom used. However, contrary
to what happens in GICs, Li-covered graphene is superconducting at a
much higher temperature with respect to Ca-covered graphene
Stability analysis of injection-locked oscillators in their fundamental mode of operation
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Perturbation technique for the investigation of oscillating frequency-converters in the dynamical phasor-domain
No full textNecessary and sufficient conditions for frequency entrainment of quasi-sinusoidal injection-synchonised oscillators
No full textOn the degenerate phase-interaction-free operation of multi-frequency negative-conductance oscillators
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