Showing papers by "Laval University published in 1996"

A comprehensive genetic map of the human genome based on 5,264 microsatellites

Abstract: The great increase in successful linkage studies in a number of higher eukaryotes during recent years has essentially resulted from major improvements in reference genetic linkage maps, which at present consist of short tandem repeat polymorphisms of simple sequences or microsatellites. We report here the last version of the Genethon human linkage map. This map consists of 5,264 short tandem (AC/TG)n repeat polymorphisms with a mean heterozygosity of 70%. The map spans a sex-averaged genetic distance of 3,699 cM and comprises 2,335 positions, of which 2,032 could be ordered with an odds ratio of at least 1,000:1 against alternative orders. The average interval size is 1.6 cM; 59% of the map is covered by intervals of 2 cM at most and 1% remains in intervals above 10 cM.

The theory of planned behavior: a review of its applications to health-related behaviors.

Abstract: Purpose. To review applications of Ajzen's theory of planned behavior in the domain of health and to verify the efficiency of the theory to explain and predict health-related behaviors. Methods. Most material has been drawn from Current Contents (Social and Behavioral Sciences and Clinical Medicine) from 1985 to date, together with all peer-reviewed articles cited in the publications thus identified. Findings. The results indicated that the theory performs very well for the explanation of intention; an averaged R2 of .41 was observed. Attitude toward the action and perceived behavioral control were most often the significant variables responsible for this explained variation in intention. The prediction of behavior yielded an averaged R2 of .34. Intention remained the most important predictor, but in half of the studies reviewed perceived behavioral control significantly added to the prediction. Conclusions. The efficiency of the model seems to be quite good for explaining intention, perceived be...

Hyperinsulinemia as an Independent Risk Factor for Ischemic Heart Disease

Abstract: Background Prospective studies suggest that hyperinsulinemia may be an important risk factor for ischemic heart disease. However, it has not been determined whether plasma insulin levels are independently related to ischemic heart disease after adjustment for other risk factors, including plasma lipoprotein levels. Methods In 1985 we collected blood samples from 2103 men from suburbs of Quebec City, Canada, who were 45 to 76 years of age and who did not have ischemic heart disease. A first ischemic event (angina pectoris, acute myocardial infarction, or death from coronary heart disease) occurred in 114 men (case patients) between 1985 and 1990. Each case patient was matched for age, body-mass index, smoking habits, and alcohol consumption with a control selected from among the 1989 men who remained free of ischemic heart disease during follow-up. After excluding men with diabetes, we compared fasting plasma insulin and lipoprotein concentrations at base line in 91 case patients and 105 controls. Results ...

A gene map of the human genome

Abstract: The human genome is thought to harbor 50,000 to 100,000 genes, of which about half have been sampled to date in the form of expressed sequence tags. An international consortium was organized to develop and map gene-based sequence tagged site markers on a set of two radiation hybrid panels and a yeast artificial chromosome library. More than 16,000 human genes have been mapped relative to a framework map that contains about 1000 polymorphic genetic markers. The gene map unifies the existing genetic and physical maps with the nucleotide and protein sequence databases in a fashion that should speed the discovery of genes underlying inherited human disease. The integrated resource is available through a site on the World Wide Web at http://www.ncbi.nlm.nih.gov/SCIENCE96/.

The complete BRCA2 gene and mutations in chromosome 13q-linked kindreds.

Abstract: Breast carcinoma is the most common malignancy among women in developed countries. Because family history remains the strongest single predictor of breast cancer risk, attention has focused on the role of highly penetrant, dominantly inherited genes in cancer-prone kindreds. BRCA1 was localized to chromosome 17 through analysis of a set of high-risk kindreds, and then identified four years later by a positional cloning strategy. BRCA2 was mapped to chromosomal 13q at about the same time. Just fifteen months later, Wooster et al. reported a partial BRCA2 sequence and six mutations predicted to cause truncation of the BRCA2 protein. While these findings provide strong evidence that the identified gene corresponds to BRCA2, only two thirds of the coding sequence and 8 out of 27 exons were isolated and screened; consequently, several questions remained unanswered regarding the nature of BRCA2 and the frequency of mutations in 13q-linked families. We have now determined the complete coding sequence and exonic structure of BRCA2 (GenBank accession #U43746), and examined its pattern of expression. Here, we provide sequences for a set of PCR primers sufficient to screen the entire coding sequence of BRCA2 using genomic DMA. We also report a mutational analysis of BRCA2 in families selected on the basis of linkage analysis and/or the presence of one or more cases of male breast cancer. Together with the specific mutations described previously, our data provide preliminary insight into the BRCA2 mutation profile.

Synchronization of fast (30-40 Hz) spontaneous cortical rhythms during brain activation

Abstract: We investigated the synchronization of fast spontaneous oscillations (mainly 30–40 Hz) in anesthetized and behaving cats by means of simultaneous extra- and intracellular recordings from multiple neocortical areas. Fast Fourier transforms, auto- and cross- correlations, and spike- or wave-triggered averages were used to determine the frequency and temporal coherence of fast oscillations that outlasted the stimulation of ascending activating systems or that occurred naturally during behavioral states of waking and rapid eye movement (REM) sleep but also appeared during the depolarizing phases of slow sleep oscillations. In 90% of microelectrode tracks, the fast oscillations did not show field reversal at any depth of the cortex and were not observable in the underlying white matter. The negative field potentials of the fast oscillations were associated at all depths with neuronal firing. This field potential property of fast oscillations was in sharp contrast to the reversal of slow sleep oscillation or evoked potentials at depths of 0.25–0.5 mm. The coherence of fast spontaneous rhythms was spatially limited, being confined within a cortical column and among closely located neocortical sites, in contrast to the long- range synchronization of slow sleep rhythms. Depolarizing current pulses elicited spike-bursts (200–400 Hz) recurring at a frequency of 30–40 Hz. Our experiments demonstrate that the conventional notion of a totally desynchronized cortical activity upon arousal should be revised as fast rhythms are enhanced and synchronized within intracortical networks during brain activation. Spontaneously occurring, subthreshold membrane potential depolarizing oscillations may bias cortical and thalamic neurons to respond synchronously, at fast frequencies, to relevant stimuli in the wake state or to internally generated drives in REM sleep.

Sulfated Zirconia-Based Strong Solid-Acid Catalysts: Recent Progress

Abstract: This review article deals with recent progress in the preparation of sulfated zirconia (SZ)-bassed, strong solid-acid catalysts, the characterization of their physicochemical properties and the evaluation of their catalytic performance in various promising applications. Strong emphasis was put on discussion of controversial issues such as the strength of acid sites, the nature of active sites, the reaction mechanism, and the role and state of supported platinum. An important part of this work was devoted to recent catalytic applications.

Oxidative capacity of the skeletal muscle and lactic acid kinetics during exercise in normal subjects and in patients with COPD.

Abstract: Early lactic acidosis during exercise and abnormal skeletal muscle function have been reported in chronic obstructive pulmonary disease (COPD) but a possible relationship between these two abnormalities has not been evaluated. The purpose of this study was to compare and correlate the increase in arterial lactic acid (La) during exercise and the oxidative capacity of the skeletal muscle in nine COPD patients (age = 62 +/- 5 yr, mean +/- SD, FEV1 40 +/- 9% of predicted) and in nine normal subjects of similar age (54 +/- 3 yr). Following a transcutaneous biopsy of the vastus laterialis, each subject performed a stepwise exercise test on an ergocycle up to his or her maximal capacity during which 5-breath averages of oxygen consumption (Vo2), and serial La concentration measurements were obtained. From the muscle biopsy specimen, the activity of two oxidative enzymes, citrate synthase (CS) and 3-hydroxyacyl CoA dehydrogenase (HADH), and of three glycolytic enzymes, lactate dehydrogenase, hexokinase, and phosphofructokinase were determined. The La/Vo2 relationship during exercise was fitted by an exponential function in the form La = a + bvo2, where be represents the shape of the relationship. The activity of the oxidative enzymes was significantly lower in COPD than in control subjects (22.8 +/- 3.3 versus 36.8 +/- 8.6 mumol/min/g muscle for CS, and 3.1 +/- 1.1 versus 5.5 +/- 1.4 mumol/min/g for HADH, p < 0.0005) and the increase in lactic acid was steeper in COPD (b = 4.3 +/- 2.0 versus 2.1 +/- 0.2 for normal subjects, p = 0.0005). A significant inverse relationship was found between CS, HADH, and b. No difference was found between the two groups for the glycolytic enzymes. We conclude that in COPD the increase in arterial La during exercise is excessive, the oxidative capacity of the skeletal muscle is reduced, and that these two results are interrelated.

Species-Specific and Ubiquitous-DNA-Based Assays for Rapid Identification of Staphylococcus aureus

Abstract: Staphylococcus epidermidis is an aerobic gram-positive coccus that is now recognized among the coagulase-negative staphylococci as an etiological agent with an important range of pathogenicity in humans. Several diagnostic kits based on biochemical or immunological reactions can efficiently identify Staphylococcus aureus. However, these tests are often unreliable for the identification of coagulase-negative staphylococcal species including S. epidermidis. Since DNA-based assays for the species-specific identification of S. epidermidis remain unavailable, we have developed such tests in order to improve the accuracy and the rapidity of tests for the diagnosis of S. epidermidis infections. On the basis of the results of hybridization assays with clones randomly selected from an S. epidermidis genomic library, we identified a chromosomal DNA fragment which is specific and 100% ubiquitous for the identification of S. epidermidis. This 705-bp fragment was sequenced and used to design PCR amplification primers. PCR assays with the selected primers were also highly specific and ubiquitous for the identification from bacterial cultures of clinical isolates of S. epidermidis from a variety of anatomic sites. While three strains of S. capitis were misidentified as S. epidermidis with the API Staph-Ident system and 2.5% of the S. epidermidis identifications were inconclusive with the MicroScan Autoscan-4 system, the PCR assay was highly specific and allowed for the correct identification of all 79 S. epidermidis strains tested. The PCR assays developed are simple and can be performed in about 1 h. The DNA-based tests provide novel diagnostic tools for improving the diagnosis of S. epidermidis infections.

Cleavage of lamin A by Mch2 alpha but not CPP32: multiple interleukin 1 beta-converting enzyme-related proteases with distinct substrate recognition properties are active in apoptosis.

Abstract: Although proteases related to the interleukin 1 beta-converting enzyme (ICE) are known to be essential for apoptotic execution, the number of enzymes involved, their substrate specificities, and their specific roles in the characteristic biochemical and morphological changes of apoptosis are currently unknown. These questions were addressed using cloned recombinant ICE-related proteases (IRPs) and a cell-free model system for apoptosis (S/M extracts). First, we compared the substrate specificities of two recombinant human IRPs, CPP32 and Mch2 alpha. Both enzymes cleaved poly-(ADP-ribose) polymerase, albeit with different efficiencies. Mch2 alpha also cleaved recombinant and nuclear lamin A at a conserved VEID decreases NG sequence located in the middle of the coiled-coil rod domain, producing a fragment that was indistinguishable from the lamin A fragment observed in S/M extracts and in apoptotic cells. In contrast, CPP32 did not cleave lamin A. The cleavage of lamin A by Mch2 alpha and by S/M extracts was inhibited by millimolar concentrations of Zn2+, which had a minimal effect on cleavage of poly (ADP-ribose) polymerase by CPP32 and by S/M extracts. We also found that N-(acetyltyrosinylvalinyl-N epsilon-biotinyllysyl)aspartic acid [(2,6-dimethylbenzoyl)oxy]methyl ketone, which derivatizes the larger subunit of active ICE, can affinity label up to five active IRPs in S/M extracts. Together, these observations indicate that the processing of nuclear proteins in apoptosis involves multiple IRPs having distinct preferences for their apoptosis-associated substrates.

Hepatocytes corrected by gene therapy are selected in vivo in a murine model of hereditary tyrosinaemia type I

Abstract: Current strategies for hepatic gene therapy are either quantitatively inefficient or suffer from lack of permanent gene expression. We have utilized an animal model of hereditary tyrosinaemia type I (HT1), a recessive liver disease caused by deficiency of fumarylacetoacetate hydrolase (FAH), to determine whether in vivo selection of corrected hepatocytes could improve the efficiency of liver gene transfer. As few as 1,000 transplanted wild-type hepatocytes were able to repopulate mutant liver, demonstrating their strong competitive growth advantage. Mutant hepatocytes corrected in situ by retroviral gene transfer were also positively selected. In mutant animals treated by multiple retrovirus injections >90% of hepatocytes became FAH positive and liver function was restored to normal. Our results demonstrate that in vivo selection is a useful strategy for hepatic gene therapy and may lead to effective treatment of human HT1 by retroviral gene transfer.

Apolipoprotein A-I and B levels and the risk of ischemic heart disease during a five-year follow-up of men in the Québec cardiovascular study

Abstract: Background Results obtained largely from case-control studies have suggested that an elevated plasma concentration of apolipoprotein (apo) B may be considered an important risk factor for ischemic heart disease (IHD). Prospective data on the relevance of measuring apo A-I and apo B levels in the assessment of IHD risk, however, remain sparse as well as controversial. Methods and Results Plasma lipid, apo B, and apo A-I levels as well as other risk factors were evaluated at baseline in 1985 in a sample of 2155 men (45 to 76 years old) who were followed for a period of 5 years for clinical signs of IHD. Proportional-hazards analyses indicated that plasma apo B concentrations measured at entry were strongly associated with onset of IHD (relative rate, 1.4; 95% confidence interval [CI], 1.2 to 1.7), independent of covariables such as age, smoking, diabetes mellitus, and systolic blood pressure. Controlling for triglycerides, HDL cholesterol, and total/HDL cholesterol ratio did not eliminate the relationship b...

Skeletal muscle adaptation to endurance training in patients with chronic obstructive pulmonary disease.

Abstract: The purpose of this study was to evaluate the physiologic responses to endurance training in patients with moderate to severe airflow obstruction by specifically looking at changes in skeletal muscle enzymatic activities. Eleven patients (age = 65 +/- 7 yr, mean +/- SD, FEV1 = 36 +/- 11% of predicted value, range = 24 to 54%) were evaluated before and after an endurance training program. Each evaluation included a percutaneous biopsy of the vastus lateralis and a stepwise exercise test on an ergocycle up to his/her maximal capacity. VE, VO2, VcO2, and serial arterial lactic acid concentration were measured during the exercise test. The activity of two oxidative enzymes, citrate synthase (CS) and 3-hydroxyacyl-CoA dehydrogenase (HADH), and of three glycolytic enzymes, lactate dehydrogenase, hexokinase, and phosphofructokinase was determined. The training consisted of 30-min exercise sessions on a calibrated ergocycle, 3 times a week for 12 wk. The aerobic capacity was severely reduced at baseline (VO2max = 54 +/- 12% of predicted) and increased by 14% after training (p < 0.05). For an identical exercise workload, there was a significant reduction in VE (34.5 +/- 10.0 versus 31.9 +/- 9.0 L/min, p < 0.05) and in arterial lactic acid concentration (3.4 +/- 1.3 versus 2.8 +/- 0.9 mmol/L, p < 0.01) after training. The lactate threshold also increased after training (p < 0.01) while the activity of the three glycolytic enzymes was similar at the two evaluations. In contrast, the activity of CS and HADH increased significantly after training (22.3 +/- 3.5 versus 25.8 +/- 3.8 mumol/min/g muscle for CS, p < 0.05, and 5.5 +/- 2.9 versus 7.7 +/- 2.5 mumol/min/g for HADH, p < 0.01). A significant inverse relationship was found between the percent changes in the activity of CS and HADH, and the percent changes in arterial lactic acid during exercise (p = 0.01). We conclude that endurance training can reduce exercise-induced lactic acidosis and improve skeletal muscle oxidative capacity in patients with moderate to severe chronic obstructive pulmonary disease (COPD).

HSP27 Phosphorylation-mediated Resistance against Actin Fragmentation and Cell Death Induced by Oxidative Stress

Abstract: Phosphorylation of heat shock protein 27 (HSP27) has been suggested to play an important role in the regulation of F-actin dynamics in response to growth factors and stress. Because the microfilament network is one of the earliest targets of oxidative stress and because phosphorylation of HSP27 is strongly induced by reactive oxygen metabolites, we have investigated the role of HSP27 phosphorylation in regulating actin dynamics in response to oxidative stress. Experiments were done in Chinese hamster CCL39 cells overexpressing various levels of the wild-type or a nonphosphorylatable form of human HSP27 (pm3 HSP27). In control cells, both H2O2 and menadione induced fragmentation of F-actin, which forms aggregates and patches concentrated around the nucleus. Stable overexpression of wild-type HSP27, but not of pm3 HSP27, conferred resistance against actin fragmentation, suggesting that HSP27 has a phosphorylation-activated protective function against actin disruption by oxidative stress. Cell lines that overexpressed the highest levels of the wild-type form of human HSP27 also showed an increased cell survival following exposure to H2O2. In contrast, cells expressing pm3 HSP27 were as sensitive as the controls to the lethal effect of H2O2. These results suggest that phosphorylation of HSP27 is causally related to the regulation of microfilament dynamics following oxidative stress and may be involved in mediating an adaptive response to oxyradical-generating agents such as carcinogens, anticancer drugs, and other xenobiotics.

Control of Spatiotemporal Coherence of a Thalamic Oscillation by Corticothalamic Feedback

Abstract: The mammalian thalamus is the gateway to the cortex for most sensory modalities. Nearly all thalamic nuclei also receive massive feedback projections from the cortical region to which they project. In this study, the spatiotemporal properties of synchronized thalamic spindle oscillations (7 to 14 hertz) were investigated in barbiturate-anesthetized cats, before and after removal of the cortex. After complete ipsilateral decortication, the long-range synchronization of thalamic spindles in the intact cortex hemisphere changed into disorganized patterns with low spatiotemporal coherence. Local thalamic synchrony was still present, as demonstrated by dual intracellular recordings from nearby neurons. In the cortex, synchrony was insensitive to the disruption of horizontal intracortical connections. These results indicate that the global coherence of thalamic oscillations is determined by corticothalamic projections.

Planning and spatial working memory: a positron emission tomography study in humans.

Abstract: Previous work with both neurosurgical and neurodegenerative patient groups has suggested that high level planning is mediated by neural circuitry which includes both the prefrontal cortex and the striatum. In this study, the functional anatomy of cognitive planning was investigated further, using positron emission tomography (PET). Regional cerebral blood flow (rCBF) was measured in 12 normal volunteers while performing easy and difficult versions of (i) a modified Tower of London planning task; (ii) a mnemonic variant of this task that required short-term retention and reproduction of problem solutions; and (iii) a control condition that involved identical visual stimuli and motor responses. Significant increases in rCBF were observed in the left hemisphere, in both the mid-dorsolateral frontal cortex and in the head of the caudate nucleus, when the difficult planning task was compared with the control condition. Moreover, subtraction of a simple planning condition from the more difficult one revealed focal increases in rCBF in the caudate nucleus and the thalamus only. During both mnemonic variants of the planning task, changes were also observed in the mid-dorsolateral frontal cortex and in more ventral frontopolar regions, bilaterally. When compared directly, the planning and memory conditions differed in terms of these ventral activation foci, but not in the pattern of activation observed in the mid-dorsolateral frontal cortex. These findings further implicate frontostriatal circuitry in high-level planning and provide evidence for functionally distinct contributions from ventral and dorsolateral frontal regions to spatial working memory.

Towards a general multi-view registration technique

Abstract: We present an algorithm that reduces significantly the level of the registration errors between all pairs in a set of range views. This algorithm refines initial estimates of the transformation matrices obtained from either the calibrated acquisition setup or a crude manual alignment. It is an instance of a category of registration algorithms known as iterated closest-point (ICP) algorithms. The algorithm considers the network of views as a whole and minimizes the registration errors of all views simultaneously. This leads to a well-balanced network of views in which the registration errors are equally distributed, an objective not met by previously published ICP algorithms which all process the views sequentially. Experimental results show that this refinement technique improves the calibrated registrations and the quality of the integrated model for complex multi-part objects. In the case of scenes comprising man-made objects of very simple shapes, the basic algorithm faces problems common to all ICP algorithms and so must be extended.

Synchronization of fast (30-40 Hz) spontaneous oscillations in intrathalamic and thalamocortical networks

Abstract: The synchronization of fast (mainly 30 to 40 Hz) oscillations in intrathalamic and thalamocortical (TC) networks of cat was studied under ketamine-xylazine anesthesia and in behaving animals by means of field potential, extra- and intracellular recordings from multiple sites in the thalamic reticular (RE) nucleus, dorsal (sensory, motor, and intralaminar) thalamic nuclei, and related neocortical areas. Far from being restricted to tonically activated behavioral states, the fast oscillations also appeared during resting sleep and deep anesthesia, when they occurred over the depolarizing component of the slow (<1 Hz) oscillation and were suppressed during the prolonged hyper-polarizations of RE, TC, and cortical neurons. The synchronization of fast rhythms among different thalamic foci was robust. Fast rhythmic cortical waves and subthreshold depolarizing potentials in TC neurons were highly coherent; however, the synchronization of the fast oscillation required recordings from reciprocally related neocortical and thalamic foci, as identified by monosynaptic responses in both directions. The short-range spatial confinement of coherent fast rhythms contrasted with the large-scale synchronization of low-frequency sleep rhythms. Transient fast rhythms, appearing over the depolarizing envelope of the slow sleep oscillation, became sustained when brain activation was elicited by stimulation of mesopontine cholinergic nuclei or during brain-active behavioral states in chronic experiments. These data demonstrate that fast rhythms are part of the background electrical activity of the brain and that desynchronization, used to designate brain-active states, is an erroneous term inasmuch as the fast oscillations are synchronized not only in intracortical but also in intrathalamic and TC networks.

Growth promotion of maize and lettuce by phosphate-solubilizing Rhizobium leguminosarum biovar. phaseoli

Abstract: Rhizobium leguminosarum bv. phaseoli strains P31 and R1, Serratia sp. strain 22b, Pseudomonas sp. strain 24 and Rhizopus sp. strain 68 were examined for their plant growth-promoting potential on lettuce and forage maize. All these phosphate solubilizing microorganisms (PSM) were isolated from Quebec soils. The plants were grown in field conditions in three sites having high to low amounts of available P. In site 1 (very fertile soil), strains R1 and 22b tended to increase the dry matter yield of lettuce shoots (p≤0.10). Lettuce inoculated with rhizobia R1 had a 6% higher P concentration (p≤0.10) than the uninoculated control. In site 2 (poorly fertile soil), the dry matter of lettuce shoots was significantly increased (p≤0.05) by inoculation with strain P31 and 24 plus 35 kg ha-1 P-superphosphate, or with strain 68 plus 70 kg ha-1 P-superphosphate. In site 3 (moderately fertile soil), the dry matter of maize shoots was significantly increased (p≤0.05) by inoculation with strain 24 plus 17.5 kg ha-1 P-superphosphate, or with strain P31 plus 35 kg ha-1 P-superphosphate. Inoculation with PSM did not affect lettuce P uptake in the less fertile soil in site 2. In site 3 with the moderately fertile soil, maize plants inoculated with strain R1 had 8% higher P concentration than the uninoculated control (p≤0.01), and 6% with strains P31 and 68 (p≤0.05). The results clearly demonstrate that rhizobia specifically selected for P solubilization function as plant growth promoting rhizobacteria with the nonlegumes lettuce and maize. The P solubilization effect seems to be the most important mechanism of plant growth promotion in moderately fertile and very fertile soils when P uptake was increased with rhizobia and other PSM.

Ionic mechanisms underlying synchronized oscillations and propagating waves in a model of ferret thalamic slices

Abstract: 1. A network model of thalamocortical (TC) and thalamic reticular (RE) neurons was developed based on electrophysiological measurements in ferret thalamic slices. Single-compartment TC and RE cells included voltage- and calcium-sensitive currents described by Hodgkin-Huxley type of kinetics. Synaptic currents were modeled by kinetic models of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA), gamma-aminobutyric acid-A (GABAA) and GABAB receptors. 2. The model reproduced successfully the characteristics of spindle and slow bicuculline-induced oscillations observed in vitro. The characteristics of these two types of oscillations depended on both the intrinsic properties of TC and RE cells and their pattern of interconnectivity. 3. The oscillations were organized by the reciprocal recruitment between TC and RE cells, due to their manual connectivity and bursting properties. TC cells elicited AMPA-mediated excitatory postsynaptic potentials (EPSPs) in RE cells, whereas RE cells elicited a mixture of GABAA and GABAB inhibitory postsynaptic potentials (IPSPs) in TC cells. Because of the presence of a T current, sufficiently strong EPSPs could elicit a burst in RE cells, and TC cells could generate a rebound burst following GABAergic IPSPs. Under these conditions, interaction between the TC and RE cells produced sustained oscillations. 4. In the absence of spontaneous oscillation in any cell, the TC-RE network remained quiescent. Spindle oscillations with a frequency of 9-11 Hz could be initiated by stimulation of either TC or RE neurons. A few spontaneously oscillating TC neurons recruited the entire network model into a "waxing-and waning" oscillation. These "initiator" cells could be an extremely small proportion of TC cells. 5. In intracellular recordings, TC cells display a reduced ability for burst firing after a sequence of bursts. The "waning" phase of spindles was reproduced in the network model by assuming an activity-dependent upregulation of Ih operating via a calcium-binding protein in TC cells, as shown previously in a two-cell model. 6. Following the global suppression of GABAA inhibition, the disinhibited RE cells produced prolonged burst discharges that elicited strong GABAB-mediated currents in TC cells. The enhancement of slow IPSPs in TC cells was also due to cooperativity in the activation of GABAB-mediated current. These slow IPSPs recruited TC and RE cells into slower waxing-and-waning oscillations (3-4 HZ) that were even more highly synchronized. 7. Local axonal arborization of the TC to RE and RE to TC projections allowed oscillations to propagate through the network. An oscillation starting at a single focus induced a propagating wavefront as more cells were recruited progressively. The waning of the oscillation also propagated due to upregulation of Ih in TC cells, leading to waves of spindle activity as observed in experiments. 8. The spatiotemporal properties of propagating waves in the model were highly dependent on the intrinsic properties of TC cells. The spatial pattern of spiking activity was markedly different for spindles compared with bicuculline-induced oscillations and depended on the rebound burst behavior of TC cells. The upregulation of Ih produced a refractory period so that colliding spindle waves merged into a single oscillation and extinguished. Finally, reducing the Ih conductance led to sustained oscillations. 9. Two key properties of cells in the thalamic network may account for the initiation, propagation, and termination of spindle oscillations, the activity-dependent upregulation of Ih in TC cells, and the localized axonal projections between TC and RE cells. In addition, the model predicts that a nonlinear stimulus dependency of GABAB responses accounts for the genesis of prolonged synchronized discharges following block of GABAA receptors.

Induction of Defense-Related Ultrastructural Modifications in Pea Root Tissues Inoculated with Endophytic Bacteria

Abstract: The stimulation exerted by the endophytic bacterium Bacillus pumilus strain SE34 in plant defense reactions was investigated at the ultrastructural level using an in vitro system in which root-inducing T-DNA pea (Pisum sativum L.) roots were infected with the pea root-rotting fungus Fusarium oxysporum f. sp. pisi. In nonbacterized roots, the pathogen multiplied abundantly through much of the tissue including the vascular stele, whereas in prebacterized roots, pathogen growth was restricted to the epidermis and the outer cortex In these prebacterized roots, typical host reactions included strengthening the epidermal and cortical cell walls and deposition of newly formed barriers beyond the infection sites. Wall appositions were found to contain large amounts of callose in addition to being infiltrated with phenolic compounds. The labeling pattern obtained with the gold-complexed laccase showed that phenolics were widely distributed in Fusarium-challenged, bacterized roots. Such compounds accumulated in the host cell walls and the intercellular spaces as well as at the surface or even inside of the invading hyphae of the pathogen. The wall-bound chitin component in Fusarium hyphae colonizing bacterized roots was preserved even when hyphae had undergone substantial degradation. These observations confirm that endophytic bacteria may function as potential inducers of plant disease resistance.

BRCA2 germline mutations in male breast cancer cases and breast cancer families.

Abstract: The breast cancer susceptibility gene, BRCA2 on chromosome 13q12–13, was recently isolated1–3. Mutations in BRCA2 are thought to account for as much as 35% of all inherited breast cancer as well as a proportion of inherited ovarian cancer1. Many BRC2-linked families also contain cases of male breast cancer. We have analysed germline DMA from 50 males with breast cancer (unselected for family history) and 26 individuals from site-specific female breast and breast–ovarian cancer families for mutations in BRCA2. All 17 breast–ovarian cancer families have been screened for BRCA1 coding region mutations and none were detected. Conformation-sensitive gel electrophoresis (CSGE) analysis of PCR-amplifed DMA followed by direct sequencing was used to detect sequence variants. Three of eleven individuals carry the same mutation, all are of Ashkenazi Jewish descent, supporting the observation by Neuhausen et al, in this issue4 that there is a common mutation in this population. Eleven truncating mutations and nine polymorphisms were identified — all were coding region variants. No loss-of-transcript mutations were identified in the sixteen samples for which this analysis was possible. Seven of the nine disease-associated mutations were detected in the 50 men with breast cancers; thus in our series, BRCA2 mutations account for 14% of male breast cancer, all but one of which had a family history of male and/or female breast cancer.

The Dense LDL Phenotype: Association with plasma lipoprotein levels, visceral obesity, and hyperinsulinemia in men

Abstract: OBJECTIVE To investigate the potential relationship between the cluster of metabolic abnormalities found in visceral obesity and the small dense LDL phenotype RESEARCH DESIGN AND METHODS We have estimated LDL peak particle size by nondenaturing 2–16% gradient gel electrophoresis in a sample of 79 men Glucose tolerance and fasting plasma insulin and lipoprotein levels were also measured RESULTS The LDL particle score, calculated from migration, distances and relative band intensities and reflecting the proportion of small dense LDL particles, was positively correlated with plasma triglyceride (TG) ( r = 060, P r = −056, P r = 060, P r = 023 and 029, respectively, P CONCLUSIONS It thus appears that the high TG–low HDL cholesterol dyslipidemia frequently found in visceral obesity and in a hyperinsulinemic state is a strong correlate of the small dense LDL phenotype Although associated with the dense LDL phenotype, visceral obesity and hyperinsulinemia were not independent predictors of an increased proportion of small dense LDL particles after controlling for TG and HDL cholesterol levels

Mechanisms of long-lasting hyperpolarizations underlying slow sleep oscillations in cat corticothalamic networks.

Abstract: 1. To explore the nature of the long-lasting hyperpolarizations that characterize slow oscillations in corticothalamic circuits in vivo, intracellular recordings were obtained under ketamine-xylazine anaesthesia from cortical (Cx) cells of the cat precruciate motor cortex, thalamic reticular (RE) cells from the rostrolateral sector, and thalamocortical (TC) cells from the ventrolateral (VL) nucleus. 2. Measurements in the three cell types showed input resistance (Rin) to be highest during the long-lasting hyperpolarizations that correspond to depth-positive waves of the cortical EEG. Rin was lowest during the early phase of high-amplitude depth-negative EEG waves and increased thereafter until the next cycle of the slow oscillation. 3. Spontaneous long-lasting hyperpolarizations were compared with those evoked by dorsal thalamic stimulation. Voltage versus current (V-I) plots showed similar membrane potential (Vm) ranges and slopes for spontaneous and evoked hyperpolarizations in both Cx and RE cells. V-I plots from TC cells had similar slopes, but Vm during evoked hyperpolarizations was displaced towards more negative values. 4. Intracellular injection of constant hyperpolarizing current in Cx cells increased the amplitude of the initial part of the depolarizing plateau of the slow oscillation, but decreased the amplitude of the last part. 5. These results suggest disfacilitation to be the dominant mechanism in the membrane of cortical and thalamic cells during the spontaneous long-lasting hyperpolarizations, which shape and synchronize slow oscillations in corticothalamic networks. In Cx and RE cells, the same mechanism underlies thalamically evoked long-lasting hyperpolarizations. By contrast, evoked responses in TC cells show a strong additional hyperpolarizing factor. We propose that GABAB processes are stronger in TC than in Cx neurones, thus rendering the thalamus an easier target for absence-type epileptic phenomena through potentiation of thalamic rebound capabilities.