1,720,957 research outputs found
Antisperm antibodies modify plasma membrane functional integrity and inhibit osmosensitive calcium influx in human sperm
No full textBACKGROUND:
The hypo-osmotic swelling (HOS) test evaluates the ability of the functional sperm plasma membrane to stretch following cell swelling when exposed to hypo-osmotic solutions. Sperm samples with low HOS scores show low fertilization and pregnancy rates during assisted reproductive techniques, though data are controversial. The aim of this study was to compare the results of the HOS test in a group of normozoospermic men with those in a group of subjects affected by autoimmune infertility due to the presence of antisperm antibodies (ASA) bound to the sperm surface.
METHODS:
Sperm from normozoospermic and from infertile subjects affected by autoimmune infertility were exposed to hypo-osmolar conditions to verify the effects on intracellular calcium concentrations and acrosome reaction.
RESULTS:
Sperm samples from infertile men with ASA showed HOS test scores that were significantly lower than those of normozoospermic subjects despite similar sperm viability percentages. Sperm with ASA bound to their plasma membrane showed a reduced rise in intracellular calcium concentrations and acrosome reaction after hypo-osmotic challenge with respect to sperm from normozoospermic subjects without ASA.
CONCLUSIONS:
Infertile subjects with ASA have a reduced sperm plasma membrane functional integrity that could explain, at least in part, the low fertilization and pregnancy rates observed in these subjects during assisted reproductive procedures. Evaluation for the presence of ASA in all sperm samples showing low HOS test scores in the presence of normal sperm viability percentages is suggested
Estradiol inhibits the effects of extracellular ATP in human sperm by a non genomic mechanism of action.
Full text linkAbstract
Steroid hormones, beside their classical genomic mechanism of action, exert rapid, non genomic effects in different cell types. These effects are mediated by still poorly characterized plasma membrane receptors that appear to be distinct from the classic intracellular receptors. In the present study we evaluated the non genomic effects of estradiol (17betaE(2)) in human sperm and its effects on sperm stimulation by extracellular ATP, a potent activator of sperm acrosome reaction. In human sperm 17betaE(2) induced a rapid increase of intracellular calcium (Ca(2+)) concentrations dependent on an influx of Ca(2+) from the extracellular medium. The monitoring of the plasma membrane potential variations induced by 17betaE(2) showed that this steroid induces a rapid plasma membrane hyperpolarization that was dependent on the presence of Ca(2+) in the extracellular medium since it was absent in Ca(2+) free-medium. When sperm were pre-incubated in the presence of the K(+) channel inhibitor tetra-ethylammonium, the 17betaE(2) induced plasma membrane hyperpolarization was blunted suggesting the involvement of K(+) channels in the hyperpolarizing effects of 17betaE(2). Extracellular ATP induced a rapid plasma membrane depolarization followed by acrosome reaction. Sperm pre-incubation with 17betaE(2) inhibited the effects of extracellular ATP on sperm plasma membrane potential variations and acrosome reaction. The effects of 17betaE(2) were specific since its inactive steroisomer 17alphaE(2) was inactive. Furthermore the effects of 17betaE(2) were not inhibited by tamoxifen, an antagonist of the classic 17betaE(2) intracellular receptor
Human sperm express cannabinoid receptor Cb1, the activation of which inhibits motility, acrosome reaction, and mitochondrial function.
No full textCannabinoids and endocannabinoids negatively influence sperm functions. These substances have been demonstrated in many mammalian tissues, including male and female reproductive tracts, and previous studies have shown the presence of functional receptors for cannabinoids in human sperm. The present study, by means of RT-PCR and Western blot techniques, demonstrates that human sperm express the CB(1), but not CB(2), cannabinoid receptor (CB-R) subtype located in the head and middle piece of the sperm. The activation of this receptor by anandamide reduces sperm motility and inhibits capacitation-induced acrosome reaction. Activation of the CB(1)-R did not induce any variation in sperm intracellular calcium concentrations, but produced a rapid plasma membrane hyperpolarization that was reduced by the K(+) channel blocker tetraethylammonium. The effects of anandamide on human sperm motility were dependent on the reduction of sperm mitochondrial activity as determined by rhodamine 123 fluorescence. The specificity of anandamide effects in human sperm were confirmed by the effects of the CB(1)-R antagonist SR141716. These findings provide additional evidence that human sperm express functional CB(1)-R, the activation of which negatively influences important sperm functions, and suggest a possible role for the cannabinoid system in the pathogenesis of some forms of male infertility
Testicular fine needle aspiration as a diagnostic tool in nonobstructive azoospermia
No full textAIM:
To report the fine needle aspiration cytology (FNAC) of the testes used as a diagnostic tool in non-obstructive azoospermic patients.
METHODS:
One hundred and twenty-five non-obstructive azoospermic male candidates to intracytoplasmic sperm injetion (ICSI) were analysed for follicle stimulating hormone (FSH), luteinizing hormone (LH), testosterone and inhibin B plasma levels. They were classified into three groups on the basis of FNAC: 1) Sertoli cell-only syndrome (SCOS) (70); 2) severe hypospermatogenesis (42); and 3) maturation arrest (13). Then, all men underwent testicular sperm extraction (TESE) for sperm recovery for ICSI.
RESULTS:
Mature spermatozoa were detected by FNAC in 24 of 42 men with severe hypospermatogenesis and nine of 13 men with maturation arrest; while they were retrieved by TESE in 29 of 70 men with SCOS, 35 of 42 men with severe hypospermatogenesis (including the 24 by FNAC) and 10 of 13 men with maturation arrest (including the nine by FNAC). The sensitivity and specificity of FNAC were 44.6 % and 100 %, respectively. There was no difference on testicular volume and hormonal parameters in men with and without sperm retrieved.
CONCLUSION:
These findings suggest that FNAC may be a simple and valid diagnostic parameter in non-obstructive azoospermic men and it may represent a valid positive prognostic parameter for sperm recovery at TESE
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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