Characterization of two novel gene cassettes, dfrA27 and aadA16, in a non-O1, non-O139 Vibrio cholerae isolate from China

Two novel integron-borne cassettes, dfrA27 (encoding trimethoprim resistance) and aadA16 (encoding streptomycin and spectinomycin resistance), located on a conjugative plasmid, have been found in a non-O1, non-O139 Vibrio cholera isolate. DfrA27 shares 75% amino acid identity with DfrA5, and AadA16 shares 88% identity with AdaA6. Cloning of the cassette region and expression analysis demonstrated that the aadA16 gene can be expressed from its own promoter sequence, which is present upstream of the aadA16 cassette.

Rat model of reperfused partial liver infarction: characterization with multiparametric magnetic resonance imaging, microangiography, and histomorphology

BACKGROUND

Rat model of reperfused partial liver infarction (RPLI) has been increasingly used in studying new diagnostics and therapeutics.

PURPOSE

To characterize the RPLI model using magnetic resonance imaging (MRI), microangiography, and histopathology.

MATERIAL AND METHODS

RPLI was induced in eight rats by occluding hepatic inflow to the right liver lobe for 3 hours. MRI was performed at a 1.5 T clinical scanner 6 hours after reperfusion to obtain T2-weighted (T2WI), T1-weighted (T1WI), contrast-enhanced (CE) T1WI, diffusion-weighted imaging (DWI) with apparent diffusion coefficient (ADC) maps, T1-weighted dynamic contrast-enhanced (T1-DC) perfusion-weighted imaging (PWI), and T2*-weighted dynamic susceptibility contrast-enhanced (T2*-DSC) PWI images. Rats were sacrificed for microangiography and histomorphology. In vivo morphological and functional MRI parameters, including maximum initial slope (MIS), K value, relative blood flow (rBF), relative blood volume (rBV), time to peak (TTP), and mean transit time (MTT), were matched with postmortem findings.

RESULTS

The infarcted lobe was conspicuous from normal liver with lower and higher signal intensity on T1WI (P=0.018) and T2WI (P=0.001), respectively. Contrast between infarcted and normal liver reversed on CE-T1WI after gadolinium injection. The infarction averaged 37.5% of total liver volume. DWI and ADC maps were able to detect subtle perfusion-related differences (P<0.05). With T1-DC-PWI, increased extravasation and vascular permeability were reflected by significantly greater MIS (P=0.034) and K value (P=0.014) in infarction. T2*-DSC-PWI showed lower rBF and rBV with shorter TTP and MTT in infarcted liver (P<0.05). In vivo MRI findings corresponded well with postmortem outcomes.

CONCLUSION

RPLI in rats could be characterized by multiparametric MRI and postmortem assessments, with insight into the no-reflow phenomenon, which implies its further application for preclinical assessments of new pharmaceutics.

A sperm GPI-anchored protein elicits sperm-cumulus cross-talk leading to the acrosome reaction

The acrosome reaction has long been thought to be induced by the zona pellucida. Here we report the identification and function of a novel human sperm glycosylphosphatidylinositol (GPI)-anchored membrane protein, NYD-SP8. The release of the protein during sperm-egg interaction and its binding to the cumulus, the first layer of egg investment, elicits cross-talk between the gametes and produces calcium dependant release of progesterone, which lead to the acrosome reaction. An in vivo mouse model of NYD-SP8 immunization is also established showing a reduced fertility rate. Thus, contrary to accepted dogma, our study demonstrates for the first time that, prior to reaching the zona pellucida, sperm may release a surface protein that acts on the cumulus cells leading to the acrosome reaction, which may be important for determining the outcome of fertilization.

Determination of Cr(VI) concentration in diluted samples based on the paper test strip method

At present, there are many methods for Cr(VI) concentration determination in diluted samples, however, these methods have their own inherent drawbacks, such as long response time, complicated pretreatment, expensive equipment etc. In this paper, a paper-based test strip method specific for determination of diluted Cr(VI) samples was developed. In this method, Aliquat 336, as an anion exchanger was loaded into filter paper to form a test strip. This test strip was used to pre-concentrate Cr(VI) when contacting with the diluted Cr(VI)-containing solution. The Cr(VI)-containing test strip was then immersed into a diphenylcarbazide (DPC) solution (a color forming solution), and the color intensity was correlated to the Cr(VI) concentration. The detection range of the present method was found to be 0.02-1.50 mg/L. The results also showed that the method gave a high selectivity for Cr(VI) in the diluted samples to be tested. The method was applied to synthesized samples and the results, which were compared to those from a reference method, showed that the developed method is an effective, reliable way for Cr(VI) determination in diluted samples.

Comparing two methods for assessment of perfusion-diffusion mismatch in a rodent model of ischaemic stroke: a pilot study

This stroke experiment was designed to define the mismatch between perfusion-weighted imaging (PWI) and diffusion-weighted imaging (DWI) in MRI by applying early or instantly acquired PWI. Eight rats were induced with stroke through photothrombotic occlusion of the middle cerebral artery and scanned serially between 1 h and day 3 after induction using DWI and PWI with a 1.5 T MR scanner. The relative lesion volumes (rLV) on MRI and triphenyl tetrazolium chloride-stained specimens were defined as the proportion of lesion volume over brain volume. Discrepancies in the rLV between PWI- and DWI-derived apparent diffusion coefficient (ADC) maps were expressed by subtraction of the ADC from PWI, resulting in three possible patterns: (i) (PWI-ADC > 10% of PWI) denoting a mismatch; (ii) (-(10% of PWI) <or= PWI-ADC <or= 10% of PWI) denoting a match; and (iii) (PWI-ADC < -(10% of PWI)) denoting a reverse mismatch. The differences were compared with the minuend being either early PWI (ePWI) or instant PWI (iPWI) and the subtrahend being instant ADC (iADC). The occurrence and evolution of PWI-ADC patterns were analysed. Over time, PWI-ADC discrepancies evolved from mismatch, through to match, to reversed mismatch. The PWI-ADC mismatch still existed 3 days after MCA occlusion in one to three of the eight cases. The rLVs and mismatch incidences between the ePWI-iADC and iPWI-iADC models were linear correlated. A higher mismatch rate occurred in iPWI-iADC within day 1 and in ePWI-iADC at day 3. Both ePWI and iPWI proved useful to define PWI-ADC patterns within day 1. At day 3, iPWI appeared more adequate.

Can apparent diffusion coefficient discriminate ischemic from nonischemic livers? A pilot experimental study

PURPOSE

Using magnetic resonance imaging, the apparent diffusion coefficient (ADC) is an indicator to assess cerebral ischemia. The aim of this porcine study was to evaluate whether ADC assessed hepatic ischemia during ex vivo hypothermic machine perfusion (HMP) as well as in vivo.

METHODS

Ex vivo: ADC of normal versus warm ischemic (WI) livers was assessed during HMP and subsequent rewarming to mimic ischemia-reperfusion injury. As the preservation solution, we used either an acellular solution or diluted blood. WI was induced in the left lobe or in the whole liver and compared 2-hour WI and non-WI. In vivo: One liver was scanned with the left lobe vessels occluded for 2-hour WI and subsequently for 3 hour reperfusion to compare with the right lobe without WI. Aspartate aminotransferase (AST) in the perfusate and morphology were used as surrogates of WI.

RESULTS

In all WI livers, AST reached high levels and histology showed severe injury. Ex vivo ADC during acellular perfusion showed negligible differences between the livers with versus without WI, namely, 0.75 x 10(-3) or 0.88 x 10(-3) mm(2)/s during HMP. Ex vivo ADC using sanguineous perfusion showed 1.11 x 10(-3) or 0.83 x 10(-3) mm(2)/s during HMP in regions with versus without WI, respectively, a difference that remained stable during the whole experiment. ADC in vivo decreased from the physiological level of 1.07 x 10(-3) mm(2)/s to 0.75 x 10(-3) mm(2)/s in the first 30 minutes of WI, whereas ADC in the non-WI liver remained constant.

CONCLUSION

ADC in vivo decreased during hepatic ischemia, as previously seen in cerebral ischemia. However, the effect of WI on ADC was less clear during ex vivo HMP.

Dynamic block of disc valve - blocking of aortic disc prosthesis due to protrusion of mitral prosthesis into the left ventricular outflow tract

A case of blocking of an aortic disc prosthesis after mitral and aortic valve replacement is presented here. A hypothesis of "dynamic block of disc valve" is proposed to try to explain this phenomenon.

Time-varying cortical connectivity by high resolution EEG and directed transfer function: simulations and application to finger tapping data

The problem of the definition and evaluation of brain connectivity has become a central one in neuroscience during the latest years, as a way to understand the organization and interaction of cortical areas during the execution of cognitive or motor tasks. The method of the directed transfer function (DTF) is a frequency-domain approach to this problem, based on a multivariate autoregressive modeling of time series and on the concept of Granger causality. So far, all the connectivity estimations performed on cerebral electromagnetic signals were computed between signals gathered from the electric or magnetic sensors. However, the spreading of the potential from the cortex to the sensors makes it difficult to infer the relation between the spatial patterns on the sensor space and those on the cortical sites. In this paper we propose the use of the DTF method on cortical signals estimated from high resolution EEG recordings, which exhibit a higher spatial resolution than conventional cerebral electromagnetic measures. As main contributions of this work, we present the results of a wide simulation study, aiming to evaluate performances of DTF application on this kind of data, and a statistical analysis (via the ANOVA, analysis of variance) of the results obtained for different levels of signal to noise ratio and temporal length, as they have been systematically imposed on simulated signals. Finally, we provide an application to the estimation of cortical connectivity from high resolution EEG recordings related to finger tapping movements.

Control of Electron Localization in Molecular Dissociation

We demonstrated how the subcycle evolution of the electric field of light can be used to control the motion of bound electrons. Results are presented for the dissociative ionization of deuterium molecules (D2 --> D+ + D), where asymmetric ejection of the ionic fragment reveals that light-driven intramolecular electronic motion before dissociation localizes the electron on one of the two D+ ions in a controlled way. The results extend subfemtosecond electron control to molecules and provide evidence of its usefulness in controlling reaction dynamics.

Vesicular glutamate transporter expression in supraoptic neurones suggests a glutamatergic phenotype

Magnocellular neuroendocrine cells of the supraoptic nucleus (SON) release the peptides oxytocin (OT) and vasopressin (VP) from their dendrites and terminals. In addition to peptide-containing large dense-core vesicles, axon terminals from these cells contain clear microvesicles that have been shown to contain glutamate. Using multilabelling confocal microscopy, we investigated the presence of vesicular glutamate transporters (VGLUTs) in astrocytes as well as VP and OT neurones of the SON. Simultaneous probing of the SON with antibodies against VGLUT isoforms 1-3, OT, VP and glial fibrillary acidic protein (GFAP) revealed the presence of VGLUT-2 in somata and dendrites of SON neurones. Immunoreactivity (-ir) for VGLUT-3 was also detected in both OT and VP neurones as well as in GFAP-ir astrocytes and other cells of the ventral glial lamina. Colocalisation of VGLUT-2 and VGLUT-3 in individual SON neurones was also examined and VGLUT-ir with both antibodies could be detected in both types of SON neurones. Although VGLUT-1-ir was strong lateral to the SON, only sparse labelling was apparent within the nucleus, and no colocalisation with either SON neurones or astrocytes was observed. The SON or the SON plus its surrounding perinuclear zone was probed using the reverse transcriptase-polymerase chain reaction and the presence of mRNA for all three VGLUT isoforms was detected. These results suggest that similar arrangements of transmitters exist in SON neuronal dendrites and their neurohypophysial terminals and that magnocellular neuroendocrine somata and dendrites may be capable of glutamatergic transmission.

A review of the general aspects of radiofrequency ablation

As an alternative to standard surgical resection for the treatment of malignant tumors, radiofrequency ablation (RFA) has rapidly evolved into the most popular minimally invasive therapy. To help readers gain the relevant background knowledge and to better understand the other reviews in this Feature Section on the clinical applications of RFA in different abdominal organs, the present report covers the general aspects of RFA. After an introduction, we present a simple definition of the energy applied during RFA, a brief historical review of its technical evolution, and an explanation of the mechanism of action of RFA. These basic discussions are substantiated with descriptions of RFA equipment including those commercially available and those under preclinical development. The size and geometry of induced lesions in relation to RFA efficacy and side effects are discussed. The unique pathophysiologic process of thermal tissue damage and the corresponding histomorphologic manifestations after RFA are detailed and cross-referenced with the findings in the current literature. The crucial role of imaging technology during and after RFA is also addressed, including some promising new developments. This report finishes with a summary of the key messages and a perspective on further technologic refinements and identifies some specific priorities.

Response of polyatomic molecules to ultrastrong laser- and ion-induced fields

The exposure of molecules to short, ultrastrong electric fields leads to multiple ionization and a subsequent Coulomb explosion. We present a comparative study where uracil molecules are exposed to fields generated by high-power laser pulses (tau approximately 75 fs, I > 10(16) W/cm2) or swift highly charged ions (0.5 MeV Xe25+) representing a half-cycle pulse of less than 10 fs duration. Molecular dynamics and structural information contained in the fragmentation pathways can be assessed separately. Despite the similar field strengths large differences in fragment kinetic energies are found which are related to field shape and duration with the aid of molecular dynamics simulations.

Isolation and characterization of structural components of Aloe vera L. leaf pulp

The clear pulp, also known as inner gel, of Aloe vera L. leaf is widely used in various medical, cosmetic and nutraceutical applications. Many beneficial effects of this plant have been attributed to the polysaccharides present in the pulp. However, discrepancies exist regarding the composition of pulp polysaccharide species and an understanding of pulp structure in relation to its chemical composition has been lacking. Thus, we examined pulp structure, isolated structural components and determined their carbohydrate compositions along with analyzing a partially purified pulp-based product (Acemannan hydrogel) used to make Carrisyn hydrogel wound dressing. Light and electron microscopy showed that the pulp consisted of large clear mesophyll cells with a diameter as large as 1000 microm. These cells were composed of cell walls and cell membranes along with a very limited number of degenerated cellular organelles. No intact cellular organelles were found in mesophyll cells. Following disruption of pulp by homogenization, three components were isolated by sequential centrifugation. They were thin clear sheets, microparticles and a viscous liquid gel, which corresponded to cell wall, degenerated cellular organelles and liquid content of mesophyll cells based on morphological and chemical analysis. These three components accounted for 16.2% (+/-3.8), 0.70% (+/-0) and 83.1% of the pulp on a dry weight basis. The carbohydrate composition of each component was distinct; liquid gel contained mannan, microparticles contained galactose-rich polysaccharide(s) and cell walls contained an unusually high level of galacturonic acid (34%, w/w; Gal A). The same three components were also found in Acemannan Hydrogel with mannan as the predominant component. Thus, different pulp structural components are associated with different polysaccharides and thus may potentially be different functionally. These findings may help lay a basis for further studies and development of better controlled processing methods and applications for this well-accepted medicinal plant.

Progesterone primes zona pellucida-induced activation of phospholipase A2 during acrosomal exocytosis in guinea pig spermatozoa

We investigated, using guinea-pig spermatozoa as a model, whether phospholipase A2 (PLA2) is involved in progesterone or zona pellucida (ZP)-stimulated acrosomal exocytosis, if progesterone enhances ZP-induced activation of PLA2, and mechanisms underlying PLA2 regulation. Spermatozoa were capacitated and labeled in low Ca2+ medium with [14C]choline chloride or [14C]arachidonic acid, washed, and then exposed to millimolar Ca2+ and progesterone and/or ZP. Each agonist stimulated decrease of phosphatidylcholine (PC) and release of arachidonic acid and lysoPC, indicative of PLA2 activation. Aristolochic acid (a PLA2 inhibitor) abrogated lipid changes and exocytosis, indicating that these lipid changes are essential for exocytosis. Exposure of spermatozoa to submaximal concentrations of both progesterone and ZP resulted in a synergistic increase of arachidonic acid and lysoPC releases, and exocytosis, suggesting that, under natural conditions, both agonists interact to bring about acrosomal exocytosis. Progesterone-induced PLA2 activation appears to be mediated by a GABA(A)-like receptor, because bicuculline (a GABA(A) receptor antagonist) blocked arachidonic acid release and exocytosis. In agreement with this, GABA mimicked progesterone actions. ZP-induced activation of PLA2 seemed to be transduced via G(i) proteins because pertussis toxin blocked arachidonic acid release and acrosomal exocytosis. PLA2 may be regulated by PKC because progesterone- or ZP-induced release of arachidonic acid was blocked by the PKC inhibitors staurosporine or chelerythrine chloride. PLA2 could also be regulated by the cAMP-PKA pathway; inclusion of the PKA inhibitor 14-22 amide or H-89 led to a reduction in arachidonic acid release or exocytosis after progesterone or ZP. Taken together, these results suggest that PLA2 plays an essential role in progesterone or ZP-stimulated exocytosis with progesterone priming ZP action.

Estimation of the cortical functional connectivity with the multimodal integration of high-resolution EEG and fMRI data by directed transfer function

Nowadays, several types of brain imaging device are available to provide images of the functional activity of the cerebral cortex based on hemodynamic, metabolic, or electromagnetic measurements. However, static images of brain regions activated during particular tasks do not convey the information of how these regions communicate with each other. In this study, advanced methods for the estimation of cortical connectivity from combined high-resolution electroencephalography (EEG) and functional magnetic resonance imaging (fMRI) data are presented. These methods include a subject's multicompartment head model (scalp, skull, dura mater, cortex) constructed from individual magnetic resonance images, multidipole source model, and regularized linear inverse source estimates of cortical current density. Determination of the priors in the resolution of the linear inverse problem was performed with the use of information from the hemodynamic responses of the cortical areas as revealed by block-designed (strength of activated voxels) fMRI. We estimate functional cortical connectivity by computing the directed transfer function (DTF) on the estimated cortical current density waveforms in regions of interest (ROIs) on the modeled cortical mantle. The proposed method was able to unveil the direction of the information flow between the cortical regions of interest, as it is directional in nature. Furthermore, this method allows to detect changes in the time course of information flow between cortical regions in different frequency bands. The reliability of these techniques was further demonstrated by elaboration of high-resolution EEG and fMRI signals collected during visually triggered finger movements in four healthy subjects. Connectivity patterns estimated for this task reveal an involvement of right parietal and bilateral premotor and prefrontal cortical areas. This cortical region involvement resembles that revealed in previous studies where visually triggered finger movements were analyzed with the use of separate EEG or fMRI measurements.

Assessing cortical functional connectivity by linear inverse estimation and directed transfer function: simulations and application to real data

OBJECTIVE

To test a technique called Directed Transfer Function (DTF) for the estimation of human cortical connectivity, by means of simulation study and human study, using high resolution EEG recordings related to finger movements.

METHODS

The method of the Directed Transfer Function (DTF) is a frequency-domain approach, based on a multivariate autoregressive modeling of time series and on the concept of Granger causality. Since the spreading of the potential from the cortex to the sensors makes it difficult to infer the relation between the spatial patterns on the sensor space and those on the cortical sites, we propose the use of the DTF method on cortical signals estimated from high resolution EEG recordings, which exhibit a higher spatial resolution than conventional cerebral electromagnetic measures. The simulation study was followed by an analysis of variance (ANOVA) of the results obtained for different levels of Signal to Noise Ratio (SNR) and temporal length, as they have been systematically imposed on simulated signals. The whole methodology was then applied to high resolution EEG data recorded during a visually paced finger movement.

RESULTS

The statistical analysis performed returns that during simulations, DTF is able to estimate correctly the imposed connectivity patterns under reasonable operative conditions, i.e. when data exhibit a SNR of at least 3 and a length of at least 75 s of non-consecutive recordings at 64 Hz of sampling rate, equivalent, more generally, to 4800 data samples.

CONCLUSIONS

Functional connectivity patterns of cortical activity can be effectively estimated under general conditions met in any practical EEG recordings, by combining high resolution EEG techniques, linear inverse estimation and the DTF method.

SIGNIFICANCE

The estimation of cortical connectivity can be performed not only with hemodynamic measurements, by using functional MRI recordings, but also with modern EEG recordings treated with advanced computational techniques.

Control of atomic ionization by two-color few-cycle pulses

We have studied the ionization of Rydberg atoms by few-cycle radio-frequency pulses and used two-color fields to control the ionization dynamics. We show that the number of times that electrons are emitted during a pulse can be limited and that the duration of the electron emission can be shortened. These results, once they are transposed to the optical domain, may inspire new strategies for the production of single attosecond pulses.

Size and geometry of hepatic radiofrequency lesions

AIM

To report and compare the size and geometry of hepatic radiofrequency (RF) lesions using the currently available commercial devices.

METHODS

A literature search was carried out for the period from January 1st 1990 to June 15th 2003. The commercial suppliers were asked to provide all available data. For each electrode and protocol, size and geometry of single-cycle thermal lesions were registered.

RESULTS

No information at all on size and geometry of the inducible lesions was available for 17 of the 28 current commercial electrodes. Many descriptions of RF lesions are limited to the mean transverse diameter. With normal blood flow, diameter of lesions is often smaller than suggested by the length of the electrode tip or the diameter of the deployed prongs. Lesions are rarely perfect spheres but either ellipses or flattened spheres. Distortion of the RF lesion by nearby blood vessels is very common. Fusion of thermal zones between prongs of expandable electrodes can be incomplete. Blood flow interruption using a Pringle maneuver yields larger lesions that are less distorted and more complete.

CONCLUSIONS

There is insufficient experimental data for many electrodes that are currently used in patients. RF companies should provide these data before releasing electrodes for use. For those electrodes for which data exist, coagulation lesions are often smaller, less spherical, less complete and less regular than generally presumed. Accurate knowledge of size and geometry of RF lesions is crucial to prevent local recurrence.