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Biomedical subjects

C Galera

Publications and source records attributed to C Galera.

At least 19 recordsLinked to original sources
PubMed2004

Attentive mechanisms in visual search.

Selective attention can be employed to a restricted region in space or to specific objects. Many properties of this attentional window or spotlight are not well understood. In the present study, we examined the question whether the putative shape of the attentional spotlight can be determined by endogenous cueing within a visual search paradigm. Participants searched for a target among distractors, which were arranged within a vertical or horizontal rectangle. The shape of this rectangle was cued endogenously in a valid or invalid way. Response times (RTs) to correct identification of target orientation were recorded. In Experiment 1, the difference between valid and invalid RTs demonstrated that cueing resulted in elongated attentional areas. This was true only for a group of experienced psychophysical participants, whereas a group of inexperienced participants were not able to use cueing in this way. In Experiment 2, the line motion illusion was used to examine the spatial properties of the attended area. The results confirmed for both experienced and inexperienced participants that attention was confined to the cued elongated area only. We present converging evidence for an attentional spotlight whose shape can be adjusted flexibly by appropriate endogenous cueing.

Adult↗
PubMed2001

The HCL gene of Medicago truncatula controls Rhizobium-induced root hair curling.

The symbiotic infection of the model legume Medicago truncatula by Sinorhizobium meliloti involves marked root hair curling, a stage where entrapment of the microsymbiont occurs in a chamber from which infection thread formation is initiated within the root hair. We have genetically dissected these early symbiotic interactions using both plant and rhizobial mutants and have identified a M. truncatula gene, HCL, which controls root hair curling. S. meliloti Nod factors, which are required for the infection process, induced wild-type epidermal nodulin gene expression and root hair deformation in hcl mutants, while Nod factor induction of cortical cell division foci was reduced compared to wild-type plants. Studies of the position of nuclei and of the microtubule cytoskeleton network of hcl mutants revealed that root hair, as well as cortical cells, were activated in response to S. meliloti. However, the asymmetric microtubule network that is typical of curled root hairs, did not form in the mutants, and activated cortical cells did not become polarised and did not exhibit the microtubular cytoplasmic bridges characteristic of the pre-infection threads induced by rhizobia in M. truncatula. These data suggest that hcl mutations alter the formation of signalling centres that normally provide positional information for the reorganisation of the microtubular cytoskeleton in epidermal and cortical cells.

Acetyltransferases↗
PubMed2000

Genetic analysis of calcium spiking responses in nodulation mutants of Medicago truncatula.

The symbiotic interaction between Medicago truncatula and Sinorhizobium meliloti results in the formation of nitrogen-fixing nodules on the roots of the host plant. The early stages of nodule formation are induced by bacteria via lipochitooligosaccharide signals known as Nod factors (NFs). These NFs are structurally specific for bacterium-host pairs and are sufficient to cause a range of early responses involved in the host developmental program. Early events in the signal transduction of NFs are not well defined. We have previously reported that Medicago sativa root hairs exposed to NF display sharp oscillations of cytoplasmic calcium ion concentration (calcium spiking). To assess the possible role of calcium spiking in the nodulation response, we analyzed M. truncatula mutants in five complementation groups. Each of the plant mutants is completely Nod- and is blocked at early stages of the symbiosis. We defined two genes, DMI1 and DMI2, required in common for early steps of infection and nodulation and for calcium spiking. Another mutant, altered in the DMI3 gene, has a similar mutant phenotype to dmi1 and dmi2 mutants but displays normal calcium spiking. The calcium behavior thus implies that the DMI3 gene acts either downstream of calcium spiking or downstream of a common branch point for the calcium response and the later nodulation responses. Two additional mutants, altered in the NSP and HCL genes, which show root hair branching in response to NF, are normal for calcium spiking. This system provides an opportunity to use genetics to study ligand-stimulated calcium spiking as a signal transduction event.

Calcium↗
PubMed2000

Four genes of Medicago truncatula controlling components of a nod factor transduction pathway.

Rhizobium nodulation (Nod) factors are lipo-chitooligosaccharides that act as symbiotic signals, eliciting several key developmental responses in the roots of legume hosts. Using nodulation-defective mutants of Medicago truncatula, we have started to dissect the genetic control of Nod factor transduction. Mutants in four genes (DMI1, DMI2, DMI3, and NSP) were pleiotropically affected in Nod factor responses, indicating that these genes are required for a Nod factor-activated signal transduction pathway that leads to symbiotic responses such as root hair deformations, expressions of nodulin genes, and cortical cell divisions. Mutant analysis also provides evidence that Nod factors have a dual effect on the growth of root hair: inhibition of endogenous (plant) tip growth, and elicitation of a novel tip growth dependent on (bacterial) Nod factors. dmi1, dmi2, and dmi3 mutants are also unable to establish a symbiotic association with endomycorrhizal fungi, indicating that there are at least three common steps to nodulation and endomycorrhization in M. truncatula and providing further evidence for a common signaling pathway between nodulation and mycorrhization.

Gene Expression Regulation, Plant↗
PubMed2000

Stimulus segmentation in the visual search task.

Four experiments were conducted in order to study the segmentation process in a visual search task with relevant stimuli (target and distractors) randomly distributed among textural elements. The basic idea was that a parallel segmentation process of the relevant stimuli would contribute to the overall reaction time independently of the contribution of the number of relevant stimuli. In the first experiment, with relevant stimuli and textural elements that differed in the orientation of their component lines, texture presence interacted with number of relevant stimuli and with target presence. These results were not favorable to the parallel segmentation hypothesis. In the second and third experiments, in which the relevant and the textural stimuli differed in orientation and in the luminance contrast of their component lines, the results support a parallel segmentation process for the higher contrast conditions. In these experiments, the effect of texture presence was greater on target-absent than on target-present trials. Experiment 4 shows that the search can be restricted to the high-contrast relevant stimuli when the number of these stimuli is constant and the number of textural stimuli changes from trial to trial. The present results suggest that the relevant stimuli can be segmented in parallel and then submitted to a restricted analysis, even when they are scattered among textural stimuli.

Adolescent↗
PubMed1999

Effect of training on the ability of dual-task coordination.

Within the framework of the working memory model proposed by A. Baddeley and G. Hitch, a dual-task paradigm has been suggested to evaluate the capacity to perform simultaneously two concurrent tasks. This capacity is assumed to reflect the functioning of the central executive component, which appears to be impaired in patients with dysexecutive syndrome. The present study extends the investigation of an index ("mu"), which is supposed to indicate the capacity of coordination of concurrent auditory digit span and tracking tasks, by testing the influence of training on the performance in the dual task. The presentation of the same digit sequence lists or always-different lists did not differently affect the performance. The span length affected the mu values. The improved performance in the tasks under the dual condition closely resembled the improvement in the single-task performance. So, although training improved performance in the single and dual conditions, especially for the tracking component, the mu values remained stable throughout the sessions when the single tasks were performed first. Conversely, training improved the capacity of dual-task coordination throughout the sessions when dual task was performed first, addressing the issue of the contribution of the within-session practice to the mu index.

Adult↗
PubMed1999

Effect of practice and span length on the dual-task coordination executive test.

The measure "mu", proposed as an index of the ability to coordinate concurrent box-crossing (BC) and digit-span (DS) tasks in the dual task (DT), should reflect the capacity of the executive component of the working memory system. We investigated the effect of practice in BC and of a change in the digit span on mu by adding previous practice trials in BC and diminishing, maintaining or increasing the digit sequence length. The mu behavior was evaluated throughout three trials of the test. Reported strategies in digit tasks were also analyzed. Subjects with diminished span showed the best performance in DT due to a stable performance in DS and BC in the single- and dual-task conditions. These subjects also showed a more stable performance throughout trials. Subjects with diminished span tended to employ effortless strategies, whereas subjects with increased span employed effort-requiring strategies and showed the lowest means of mu. Subjects with initial practice trials showed the best performance in BC and the most differentiated performance between the single- and dual-task conditions in BC. The correlation coefficient between the mu values obtained in the first and second trials was 0.814 for subjects with diminished span and practice trials in BC. It seems that the within-session practice in BC and the performance variability in DS affect the reliability of the index mu. To control these factors we propose the introduction of previous practice trials in BC and a modification of the current method to determine the digit sequence length. This proposal should contribute to the development of a more reliable method to evaluate the executive capacity of coordination in the dual-task paradigm.

Adolescent↗
PubMed1997

Specific flavonoids promote intercellular root colonization of Arabidopsis thaliana by Azorhizobium caulinodans ORS571.

The ability of Azorhizobium caulinodans ORS571 and other diazotrophic bacteria to internally colonize roots of Arabidopsis thaliana has been studied. Strains tagged with lacZ or gusA reporter genes were used, and the principal colonization sites were found to be the points of emergence of lateral roots, lateral root cracks (LRCs). High frequencies of colonization were found; 63 to 100% of plants were colonized by ORS571, and 100% of plants were colonized by Herbaspirillum seropedicae. After LRCs were colonized, bacteria moved into intercellular spaces between the cortical and endodermal cell layers. Specific flavonoids, naringenin and daidzein, at 5 x 10(-5) M, significantly promoted colonization by ORS571. By using a nodC and a nodD mutant of ORS571, it was shown that neither Nod factors nor NodD are involved in colonization or flavonoid stimulation of colonization. Flavonoids did not appear to be stimulating LRC colonization by their activity as nutritional factors. LRC and intercellular colonization by H. seropedicae was stimulated by naringenin and daidzein at the same concentration that stimulated colonization by ORS571.

Arabidopsis↗
PubMed1996

Inositolphosphoglycans and diacyglycerol are possible mediators in the glycogenic effect of GLP-1(7-36)amide in BC3H-1 myocytes.

A potent glycogenic effect of GLP-1(7-36)amide has been found in rat hepatocytes and skeletal muscle, and specific receptors for this peptide, which do not seem to be associated with the adenylate cyclase-cAMP system, have been detected in these tissue membranes. On the other hand, inositolphosphoglycan molecules (IPGs) have been implicated as second messengers of the action of insulin. In this work, we have found, in differentiated BC3H-1 myocytes, specific binding of [125I]GLP-1(7-36)amide, and a stimulatory effect of the peptide on glycogen synthesis, confirming the findings in rat skeletal muscle. Also, GLP-1(7-36)amide modulates the cell content of radiolabelled glycosylphosphatidylinositols (GPIs) and increases the production of diacylglycerol (DAG), in the same manner as insulin acts, indicating hydrolysis of GPIs and an immediate and short-lived generation of IPGs. Thus, IPGs and DAG could be mediators in the glycogenic action of GLP-1(7-36)amide in skeletal muscle.

Animals↗
PubMed1996

Inositolphosphoglycans are possible mediators of the glucagon-like peptide 1 (7-36)amide action in the liver.

A potent glycogenic effect for GLP-1(7-36)amide has been found in rat hepatocytes and skeletal muscle, and the specific receptors detected for GLP-1(7-36)amide in these tissue membranes do not seem to be associated to adenylate cyclase. On the other hand, inositolphosphoglycan molecules (IPGs) have been implicated as second messengers in the action of insulin. In a human hepatoma cell line (HEP G-2), we have observed the presence of [125I]GLP-1(7-36)amide specific binding, and a stimulatory effect of the peptide upon glycogen synthesis, confirming the findings in isolated rat hepatocytes. Also, GLP-1(7-36)amide modulates the cell content of radiolabelled glycosylphosphatidylinositols (GPIs), in the same manner as insulin, indicating hydrolysis of GPIs and an immediate and short-lived generation of IPGs. Thus, IPGs could be mediators in the GLP-1(7-36)amide glycogenic action in the liver.

Animals↗
PubMed1995

Glucagon-like peptide-1 binding to rat skeletal muscle.

We have found [125I]glucagon-like peptide-1(7-36)-amide-specific binding activity in rat skeletal muscle plasma membranes, with an estimated M(r) of 63,000 by cross-linking and SDS-PAGE. The specific binding was time and membrane protein concentration dependent, and displaceable by unlabeled GLP-1(7-36)-amide with an ID50 of 3 x 10(-9) M of the peptide; GLP-1(1-36)-amide also competed, whereas glucagon and insulin did not. GLP-1(7-36)-amide did not modify the basal adenylate cyclase activity in skeletal muscle plasma membranes. These data, together with our previous finding of a potent glycogenic effect of GLP-1(7-36)-amide in rat soleus muscle, and also in isolated hepatocytes, which was not accompanied by a rise in the cell cyclic AMP content, lead use to believe that the insulin-like effects of this peptide on glucose metabolism in the muscle could be mediated by a type of receptor somehow different to that described for GLP-1 in pancreatic B cells, where GLP-1 action is mediated by the cyclic AMP-adenylate cyclase system.

Adenylyl Cyclases↗
PubMed1994

Two cases of laryngeal leishmaniasis in patients infected with HIV.

A high incidence of visceral leishmaniasis has been documented in HIV-infected patients in endemic areas. In these patients, atypical locations and a chronic course of the disease are more frequent. Two AIDS patients with laryngeal leishmaniasis are reported. These cases are believed to be the first of this type documented in the literature. The possible pathogenic mechanisms of the disease are discussed. Infection with Leishmania donovani may eventually be described for every organ containing phagocytic cells.

Acquired Immunodeficiency Syndrome↗
PubMed1994

Local and global factors of similarity in visual search.

Effects of the similarity between target and distractors in a visual search task were investigated in several experiments. Both familiar (numerals and letters) and unfamiliar (connected figures in a 5 x 5 matrix) stimuli were used. The observer had to report on the presence or absence of a target among a variable number of homogeneous distractors as fast and as accurately as possible. It was found that physical difference had the same clear effect on processing time for familiar and for unfamiliar stimuli: processing time decreased monotonically with increasing physical difference. Distractors unrelated to the target and those related to the target by a simple transformation (180 degrees rotation, horizontal or vertical reflection) were also compared, while the physical difference was kept constant. For familiar stimuli, transformational relatedness increased processing time in comparison with that for unrelated stimulus pairs. It was further shown in a scaling experiment that this effect could be accounted for by the amount of perceived similarity of the target-distractor pairs. For unfamiliar stimuli, transformational relatedness did have a smaller and less pronounced effect. Various comparable unrelated distractors resulted in a full range of processing times. Results from a similarity scaling experiment correlated well with the outcome of the experiments with unfamiliar stimuli. These results are interpreted in terms of an underlying continuum of perceived similarity as the basis of the speed of visual search, rather than a dichotomy of parallel versus serial processing.

Adult↗
PubMed1991

Relationship between D-glucose oxidation and glycolysis in tumoral pancreatic islet cells with either rapid or decreased cell growth.

The relationship between glucose oxidation and glycolysis was examined in tumoral pancreatic islet cells with either rapid or decreased cell growth. In the control RINm5F cells, the utilization of D-[5-3H]glucose progressively augmented at increasing concentrations of D-glucose (0.2 to 16.7 mM), whereas D-[6-14C]glucose oxidation reached its maximal value at about 3.0 mM D-glucose. The 14CO2/3HOH ratio progressively decreased at increasing hexose concentrations, being about 5-times higher at 0.2 than 10.0-16.7 mM. These experiments were repeated in cells cultured in the presence of D,L-alpha-difluoromethylornithine, which inhibits RINm5F cell proliferation. At 0.2 mM D-glucose, 14CO2 output was severely decreased but 3HOH production little affected, resulting in a marked fall of the 14CO2/3HOH ratio. On the contrary, at 16.7 mM D-glucose, 3HOH formation was more markedly decreased than 14CO2 output, resulting in an increased 14CO2/3HOH ratio. These findings provide a model for the interference of cell growth with D-glucose metabolism in islet cells. Rapid growth causes a preferential stimulation of the Krebs cycle relative to glycolysis at a low glucose concentration, whilst increasing glycolysis more than oxidation at high concentrations of the hexose.

Animals↗