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At least 685 records · Page 38Linked to original sources
PubMed2006

Dynamics of D2 released from the dissociation of D2O on a zirconium surface.

Hydrogen is efficiently released during water dissociation on zirconium (Zr), while even very rapid temperature programmed heating of a hydrogen covered Zr surface predominantly leads to dissolution (approximately 99% dissolution). To help resolve these apparently contradictory observations, we have studied the dynamics of water (D2O) dissociation on a crystalline Zr surface by probing the rotational and vibrational energy distributions of the D2 produced using resonant enhanced multiphoton ionization spectroscopy. The internal-state energy distribution of the D2 product was found to be rotationally cold and vibrationally hot with respect to the temperature of the surface. The rotational distribution shows slight deviations from Boltzmann's law, with a mean rotational temperature of 426 K while the surface is at 800 K. The population of the nu"=1 vibration is at least four times higher than a 800 K temperature would allow, this corresponding to a vibrational temperature of 1100 K. Information on the translational energy of the D2 product have also been obtained by time-of-flight spectroscopy and it is found to be nearly thermally equilibrated with the surface temperature. Similar results were obtained from studies of D2 scattered from a clean Zr surface, and of D2 released by a slow thermal desorption process which involves dissolved hydrogen as the source. The reconciliation of the present results with those for thermal desorption of preadsorbed hydrogen implies a role for both surface and subsurface adsorption sites on the Zr surface and clearly demonstrates that at high temperatures, the release of D2 arises from the recombinative desorption of adsorbed hydrogen formed by the complete dissociation of D2O.

Journal Article↗
PubMed2003

Pregnancy outcome in spontaneous twins versus twins who were conceived through in vitro fertilization.

OBJECTIVE: The purpose of this study was to compare maternal and neonatal complications in spontaneous versus in vitro fertilization twins. STUDY DESIGN: Twin gestations that were delivered from 1995 to 2000 were reviewed. Cases consisted of 56 in vitro fertilization twins, each of which was matched to two control mothers by age and parity. They were compared regarding various maternal and neonatal complications. RESULTS: In vitro fertilization twins were more likely to have preterm labor compared with control twins, with no difference in the incidences of pregnancy-induced hypertension, gestational diabetes mellitus, placenta previa, or preterm premature rupture of membranes between the two groups. The cesarean delivery rate was significantly higher in cases of twins who were conceived by in vitro fertilization (76.8% vs 58.0%, P=.026), despite a similar rate of elective cesarean delivery and the incidence of nonvertex twin A in both groups. The preterm delivery rate was significantly higher (67.9% vs 41.1%, P=.002) and the gestational age was significantly lower (35+/-3 weeks vs 36+/-3 weeks, P=.043) in cases compared with control subjects. Both twins were, on the average, 230 g lighter in the in vitro fertilization group compared with the control group. However, intrauterine growth restriction was more frequent in the control group (36.6% vs 25%, P=.044). There was a significantly higher incidence of admission to the neonatal intensive care unit, respiratory distress syndrome, a need for mechanical ventilation, and pneumothorax in cases compared with control subjects. CONCLUSION: When compared with spontaneous twins, in vitro fertilization twins are more likely to be delivered by cesarean delivery and to have a higher incidence of preterm birth and prematurity-related respiratory complications with a longer nursery stay.

Adult↗
PubMed2004

Imidazoleacetic acid-ribotide: an endogenous ligand that stimulates imidazol(in)e receptors.

We identified the previously unknown structures of ribosylated imidazoleacetic acids in rat, bovine, and human tissues to be imidazole-4-acetic acid-ribotide (IAA-RP) and its metabolite, imidazole-4-acetic acid-riboside. We also found that IAA-RP has physicochemical properties similar to those of an unidentified substance(s) extracted from mammalian tissues that interacts with imidazol(in)e receptors (I-Rs). ["Imidazoline," by consensus (International Union of Pharmacology), includes imidazole, imidazoline, and related compounds. We demonstrate that the imidazole IAA-RP acts at I-Rs, and because few (if any) imidazolines exist in vivo, we have adopted the term "imidazol(in)e-Rs."] The latter regulate multiple functions in the CNS and periphery. We now show that IAA-RP (i) is present in brain and tissue extracts that exhibit I-R activity; (ii) is present in neurons of brainstem areas, including the rostroventrolateral medulla, a region where drugs active at I-Rs are known to modulate blood pressure; (iii) is present within synaptosome-enriched fractions of brain where its release is Ca(2+)-dependent, consistent with transmitter function; (iv) produces I-R-linked effects in vitro (e.g., arachidonic acid and insulin release) that are blocked by relevant antagonists; and (v) produces hypertension when microinjected into the rostroventrolateral medulla. Our data also suggest that IAA-RP may interact with a novel imidazol(in)e-like receptor at this site. We propose that IAA-RP is a neuroregulator acting via I-Rs.

Adrenal Medulla↗
PubMed2003

Visualizing the distribution and transport of mRNAs in living cells.

We have visualized the movements of native mRNAs in living cells. Using nuclease-resistant molecular beacons, we imaged the transport and localization of oskar mRNA in Drosophila melanogaster oocytes. When the localization pattern was altered by genetic manipulation of the mRNA's 3' untranslated region, or by chemical perturbation of the intracellular tubulin network, the distribution of the fluorescence signals changed accordingly. We tracked the migration of oskar mRNA in real time, from the nurse cells where it is produced to the posterior cortex of the oocyte where it is localized. Our observations reveal the presence of a transient, and heretofore elusive, stage in the transport of oskar mRNA. Direct visualization of specific mRNAs in living cells with molecular beacons will accelerate studies of intracellular RNA trafficking and localization, just as the use of green fluorescent protein has stimulated the study of specific proteins in vivo.

3' Untranslated Regions↗
PubMed2000

A role for the homeobox protein Distal-less 3 in the activation of the glycoprotein hormone alpha subunit gene in choriocarcinoma cells.

Synthesis and secretion of chorionic gonadotropin in trophoblast cells of the placenta is required for establishment of early pregnancy in primates. Chorionic gonadotropin is a heterodimeric glycoprotein hormone consisting of alpha and beta subunits. Regulation of the alpha subunit gene within the placenta requires an array of cis elements within the 5'-flanking region of the promoter. Within this array of elements, the junctional regulatory element (JRE) putatively binds a placental-specific transcription factor. The aim of our studies was to determine the identity and role of the transcriptional regulator that binds to the JRE in choriocarcinoma cells (JEG3 cells). Mutations within the JRE resulted in reduction in basal expression of an alpha subunit reporter gene, suggesting that the JRE binding factor was necessary for full basal activity. Using electrophoretic mobility shift assays, we determined that the JRE was capable of serving as a homeobox factor-binding site. The homeobox factor, Distal-less 3 (Dlx 3) was found to be expressed in JEG3 cells and in the trophoblast layer of human chorionic villus but not in a gonadotrope cell line that also expresses the alpha subunit gene. Electrophoretic mobility shift assays revealed that recombinant Dlx 3 could bind specifically to the JRE and endogenous Dlx 3 was present in JRE/JEG3 nuclear protein complexes. Overexpression of Dlx 3 resulted in activation of an alpha subunit reporter gene. A JRE mutation resulted in attenuated activation of the alpha subunit reporter via an adjacent cis element, suggesting that JRE/Dlx 3 interactions may facilitate regulation of the alpha subunit gene at sites immediately upstream of the JRE. Our studies support the conclusion that Dlx 3 is a placental-specific transcriptional regulator that binds to the JRE and contributes to expression of the alpha subunit gene in cells of trophoblast origin.

Base Sequence↗
PubMed2002

Protein kinase A-mediated phosphorylation of the beta 2-adrenergic receptor regulates its coupling to Gs and Gi. Demonstration in a reconstituted system.

While classically viewed as a prototypic G(s) and adenylyl cyclase-coupled G protein-coupled receptor, recent studies have indicated that some aspects of beta(2)-adrenergic receptor (beta(2)-AR) signaling are inhibited by pertussis toxin, indicating that they are mediated by G(i)/G(o) proteins. These signals include activation of ERK MAPKs and Akt activation, as well as hypertrophic and anti-apoptotic pathways in cardiac myocytes. Studies in cultured cells have suggested the hypothesis that protein kinase A (PKA)-mediated phosphorylation of the beta(2)-AR regulates its coupling specificity with respect to G(s) and G(i). Using a Chinese hamster ovary cell system, we show that mutant beta(2)-ARs with Ala substituted for Ser at consensus PKA sites stimulate robust cyclic AMP accumulation (G(s)) but are unable to activate ERK (G(i)). In contrast, Ser --> Asp mutants are dramatically impaired in their ability to activate adenylyl cyclase but are significantly more active than wild type receptor in activating ERK. Activation of adenylyl cyclase by wild type and Ser --> Ala mutant receptors is not altered by pertussis toxin, whereas adenylyl cyclase stimulated through the Ser --> Asp mutant is enhanced. Activation of ERK by wild type and Ser --> Asp receptors is inhibited by pertussis toxin. To further rigorously test the hypothesis, we utilized a completely reconstituted system of purified recombinant wild type and PKA phosphorylation site mutant beta(2)-ARs and heterotrimeric G(s) and G(i). G protein coupling was measured by receptor-mediated stimulation of GTPgammaS binding to the G protein. PKA-mediated phosphorylation of the beta(2)-AR significantly decreased its ability to couple to G(s), while simultaneously dramatically increasing its ability to couple to G(i). These results are reproduced when a purified recombinant Ser --> Asp mutant beta(2)-AR is tested, whereas the Ser --> Ala receptor resembles the unphosphorylated wild type. These results provide strong experimental support for the idea that PKA-mediated phosphorylation of the beta(2)-adrenergic receptor switches its predominant coupling from G(s) to G(i).

Adenylate Cyclase Toxin↗
PubMed2002

Selective inhibition of heterotrimeric Gs signaling. Targeting the receptor-G protein interface using a peptide minigene encoding the Galpha(s) carboxyl terminus.

The blockade of heptahelical receptor coupling to heterotrimeric G proteins by the expression of peptides derived from G protein Galpha subunits represents a novel means of simultaneously inhibiting signals arising from multiple receptors that share a common G protein pool. Here we examined the mechanism of action and functional consequences of expression of an 83-amino acid polypeptide derived from the carboxyl terminus of Galpha(s) (GsCT). In membranes prepared from GsCT-expressing cells, the peptide blocked high affinity agonist binding to beta(2) adrenergic receptors (AR) and inhibited beta(2)AR-induced [35S]GTPgammaS loading of Galpha(s). GsCT expression inhibited beta(2)AR- and dopamine D(1A) receptor-mediated cAMP production, without affecting the cellular response to cholera toxin or forskolin, indicating that the peptide inhibited receptor-G(s) coupling without impairing G protein or adenylyl cyclase function. [35S]GTPgammaS loading of Galpha(q/11) by alpha(1B)ARs and Galpha(i) by alpha(2A)ARs and G(q/11)- or G(i)-mediated phosphatidylinositol hydrolysis was unaffected, indicating that the inhibitory effects of GsCT were selective for G(s). We next employed the GsCT construct to examine the complex role of G(s) in regulation of the ERK mitogen-activated protein kinase cascade, where activation of the cAMP-dependent protein kinase (PKA) pathway reportedly produces both stimulatory and inhibitory effects on heptahelical receptor-mediated ERK activation. For the beta(2)AR in HEK-293 cells, where PKA activity is required for ERK activation, expression of GsCT caused a net inhibition of ERK activation. In contrast, alpha(2A)AR-mediated ERK activation in COS-7 cells was enhanced by GsCT expression, consistent with the relief of a downstream inhibitory effect of PKA. ERK activation by the G(q/11)-coupled alpha(1B)AR was unaffected by GsCT. These findings suggest that peptide G protein inhibitors can provide insights into the complex interplay between G protein pools in cellular regulation.

Animals↗
PubMed2005

Reduced stability of mitogen-activated protein kinase kinase-2 mRNA and phosphorylation of poly(A)-binding protein (PABP) in cells overexpressing PABP.

The poly(A)-binding protein (PABP) is an important regulator of mRNA translation and stability. The cellular level of PABP is controlled by regulating its mRNA translation by a feedback mechanism. The important aspect of this mechanism is that PABP binds to an adenosine-rich cis-element at the 5'-untranslated region of its own mRNA and inhibits its translation. To assess the importance of controlling the PABP level, we studied the effect of PABP overexpression on the transcription profile using the microarray technique. In PABP-overexpressing cells, 19 mRNAs showed a reduction in cellular levels due to reduced mRNA stability, and one showed an increase due to increased mRNA stability. Among these mRNAs, the MKK-2 mRNA encodes the protein kinase activator of ERK1/2 kinase, which is involved in the phosphorylation of eukaryotic initiation factor (eIF) 4E. As a result, mRNA translation may be regulated by the cellular level of MKK-2. In this study, we show that the abundance of the MKK-2 polypeptide is reduced in PABP-overexpressing cells. In these cells, the levels of phosphorylated PABP, eIF4E, and ERK2 are also reduced. Treatment of HeLa cells with the MKK-2 inhibitor U0126 reduced PABP phosphorylation, suggesting that the phosphorylation of PABP is mediated by the MKK-2/ERK signaling pathway. Thus, a novel signaling pathway involving MKK-2 and ERK1/2 may down-regulate the activity of PABP and eIF4E by controlling their phosphorylation and compensates for the effect of excess cellular PABP.

5' Untranslated Regions↗
PubMed2004

Klebsiella variicola, a novel species with clinical and plant-associated isolates.

A new Klebsiella species, K. variicola, is proposed on the basis of total DNA-DNA hybridization, on the monophyly observed in the phylogenetic analysis derived from the sequences of rpoB, gyrA, mdh, infB, phoE and nifH genes and on distinct phenotypic traits. The bacteria from this new species seem to be genetically isolated from K. pneumoniae strains, do not ferment adonitol and were obtained from plants (such as banana, rice, sugar cane and maize) and hospitals. The type strain is F2R9T (= ATCC BAA-830T = CFNE 2004T).

Base Sequence↗
PubMed2002

Evaluation of pseudostem trapping as a control measure against banana weevil, Cosmopolites sordidus (Coleoptera: Curculionidae) in Uganda.

Controlled studies to determine the efficacy of pseudostem trapping in reducing adult populations of the banana weevil, Cosmopolites sordidus (Germar), were conducted under farmer conditions in Ntungamo district, Uganda. Twenty-seven farms were stratified on the basis of C. sordidus population density (estimated by mark and recapture methods) and divided among three treatments: (i) researcher-managed trapping (one trap per mat per month): (ii) farmer-managed trapping (trap intensity at discretion of farmer); and (iii) controls (no trapping). Intensive trapping (managed by researchers) resulted in significantly lower C. sordidus damage after one year. Over the same period, C. sordidus numbers declined by 61% on farms where trapping was managed by researchers, 53% where farmers managed trapping and 38% on farms without trapping; however, results varied greatly among farms and, overall, there was no significant effect of trapping on C. sordidus numbers. Moreover, there was only a weak relationship between the number of C. sordidus removed and the change in population density. Trapping success appeared to be affected by management levels and immigration from neighbouring farms. Although farmers were convinced that trapping was beneficial, adoption has been low due to resource requirements.

Animals↗
PubMed2002

The influence of crop management on banana weevil, Cosmopolites sordidus (Coleoptera: Curculionidae) populations and yield of highland cooking banana (cv. Atwalira) in Uganda.

A field study was undertaken in Uganda using highland cooking banana (cv. Atwalira) to test the hypothesis that bananas grown under stressed conditions are more susceptible to attack by Cosmopolites sordidus (Germar). Four banana treatments were employed to create different levels of host-plant vitality: (1) high stress: intercrop with finger millet; (2) moderate stress: monoculture without soil amendments; (3) low stress: monoculture with manure; (4) high vigour: monoculture with continuous mulch and manure. Adult C. sordidus were released at the base of banana mats 11 months after planting and populations were monitored for three years using mark and recapture methods. Cosmopolites sordidus density was greatest in the mulched plots which may have reflected increased longevity and/or longer tenure time in moist soils. Lowest C. sordidus numbers were found in intercropped banana. Damage, estimated as percentage corm tissue consumed by larvae, was similar among treatments. However, the total amount of tissue consumed was greater in mulched banana than in other systems. Plants supporting the heaviest levels of C. sordidus damage displayed bunch size reductions of 40-55%. Banana yield losses ranged from 14-20% per plot with similar levels in the intercropped and mulched systems. Yield reductions, reported as t ha-1, were twice as high in the mulched system as in the intercrop. The results from this study indicate that C. sordidus problems are not confined to stressed banana systems or those with low levels of management, but that the weevil can also attain pest status in well-managed and productive banana stands.

Animals↗
PubMed2006

Analysis of the vestibulo-ocular reflex time constant in patients with benign recurrent vertigo associated with head-shaking nystagmus.

CONCLUSIONS: When considering benign recurrent vertigo and a similar peripheral vestibular deficiency, the asymmetry of the vestibulo-ocular reflex (VOR) time constant (Tc) is lower in those patients with paretic head-shaking nystagmus (HSN) than in those with reversed HSN or without HSN. OBJECTIVE: To determine whether the existence of HSN is related to the time constant of the VOR in patients with benign recurrent vertigo (BRV). PATIENTS AND METHODS: This was a prospective study conducted at a tertiary care center in which patients were subjected to the head-shaking test, the caloric test and rotatory chair impulsive test on the same day. The clinical features of the disease analyzed were the disease duration, frequency of vertigo spells, time since the last vertigo spell and the existence of migraine. The results of the head-shaking test were considered positive when nystagmus appeared after head-shaking had ended. Two groups of patients were established on the basis of these results and the group that displayed HSN was divided according to the direction of nystagmus. In the impulsive test, the time constant of the VOR after ipsilesional and contralesional acceleration was analyzed, as was the symmetry of the response. The differences in the means were calculated. RESULTS: BRV was diagnosed in 25% of patients suffering recurrent spells of vertigo, of which 33 patients were HSN- and 29 were HSN+. In the latter group, vestibular migraine was frequently observed (83% of the patients), the spells of vertigo were more frequent and the patients were seen closer to the previous spell of vertigo. No differences were observed in the Tc of the VOR between HSN+ and HSN- patients, although the asymmetry of this Tc was higher in HSN- patients than in HSN+ patients. Nevertheless, the differences observed were only significant between paretic and reversed HSN patients and paretic HSN patients and HSN- patients.

Caloric Tests↗
PubMed1978

The nephrotic syndrome in the Sudan with special reference to schistosomal nephropathy. A preliminary morphological study.

The morphology of 68 renal biopsies from the Sudan is analysed. Schistosomal infection was more common among the nephrotic patients than in the average population (32% against less than 1%). In the schistosomal group the high incidence of focal sclerosing glomerulonephritis (28%) and of secondary amyloidosis (38%) was remarkable. The history is described of a boy in whom repeated biopsies showed the decrease of glomerular amyloid depositions accompanied by mesangial cell proliferation following treatment for schistosomiasis.

Adolescent↗
PubMed1986

Malumfashi Endemic Diseases Research Project XXI. Some aspects of the collection of demographic data.

This paper considers some of the procedures used and problems encountered in the collection of demographic data for a large-scale medical project: the Endemic Diseases Research Project at Malumfashi in northern Nigeria, 1974-1979. 43,216 people were enumerated and a subset of 26,100 were visited monthly for one year for the purpose of registration of vital events. The majority of problems encountered are relevant to similar studies in developing countries. Some difficulties cannot be avoided, but it is considered helpful to identify them. Other situations, however, deserve particular attention, such as the development of adequate on-site data-checking mechanisms, as these are areas in which future programmes could benefit from the experience of the demographic studies in Malumfashi. More effort still needs to be put into the improvement of data collection methods themselves.

Attitude to Health↗