Biomedical subjects

F Barceló

Publications and source records attributed to F Barceló.

At least 19 recordsLinked to original sources

PubMed2001

Heterogeneous DNA binding modes of berenil.

Isothermal titration calorimetry (ITC) profiles of berenil bound to different DNAs show that, despite the strong preference of berenil for AT-rich regions in DNA, it can bind to other DNA sequences significantly. The ITC results were used to quantify the binding of berenil, and the thermodynamic profiles were obtained using natural DNAs as well as synthetic polynucleotides. ITC binding isotherms cannot be simply described when a single set of identical binding sites is considered, except for poly[d(A-T)2]. Ultraviolet melting of DNA and differential scanning calorimetry were also used to quantify several aspects of the binding of berenil to salmon testes DNA. We present evidence for secondary binding sites for berenil in DNA, corresponding to G+C rich sites. Berenil binding to poly[d(G-C)2] is also observed. Circular dichroism experiments showed that binding to GC-rich sites involves drug intercalation. Using a molecular modeling approach we demonstrate that intercalation of berenil into CpG steps is sterically feasible.

Animals↗

PubMed2001

Free radical activity of natural and heat treated amphibole asbestos.

The amphibole minerals amosite and crocidolite were subjected to calcination and to hydrothermal treatment in order to study the effect of these heat treatments on the ability of the minerals to trigger formation of free radicals, which is known to be a main factor causing asbestosis and other asbestos-induced diseases. Free radical activity of the natural and heat treated minerals was studied by using supercoiled DNA (pUC18 plasmid) as a target molecule, and also by means of EPR spectroscopy. It was shown that after calcination of the natural minerals at 1073 K their free radical activity was strongly decreased These results, which may have relevant consequences for asbestos technology, were correlated with concomitant alteration of the structure and surface chemistry of the minerals during calcination.

Asbestos, Amosite↗

PubMed2001

Does the Wisconsin Card Sorting Test measure prefontral function?

This review describes a research program aimed at evaluating the validity and specificity of the Wisconsin Card Sorting Test (WCST), one of the most widely used tests of prefrontal function in clinical and experimental neuropsychology. In spite of its extensive use, voices of caution have arisen against the use of WCST scores as direct markers of prefrontal damage or dysfunction. Adopting a cognitive neuroscience approach, the present research program integrates behavioral, physiological, and anatomical information to investigate the cognitive and neural mechanisms behind WCST performance. The results show that WCST performance evokes conspicuous physiological changes over frontal as well as posterior brain regions. Moreover, WCST scores confound very heterogeneous cognitive and neural processes. This confounding effect may have led many authors to overlook the relative importance of certain dysfunctional states such as those indexed by random errors. These findings strongly suggest that WCST scores cannot be regarded as valid nor specific markers of prefrontal lobe function. However, they do provide some relevant clues to update our current knowledge about prefrontal function. In the long run, the integrative approach of cognitive neuroscience may help us design and develop more valid and sensitive tools for neuropsychological assessment.

Brain Mapping↗

PubMed2000

Attentional set shifting modulates the target P3b response in the Wisconsin card sorting test.

For years the Wisconsin card sorting test (WCST) has been used as a test of frontal lobe function. Recent event-related potential (ERP) research has shown large differences in the amplitude of P3b responses evoked by early and late trials within each WCST series ([8]: Barceló F., Sanz M., Molina V., Rubia FJ. The Wisconsin Card Sorting Test and the assessment of frontal function: A validation study with event-related potentials. Neuropsychologia 1997;35:399-408). In this study, 16 normal subjects performed a WCST adaptation to investigate the role of attentional set shifting in these WCST P3b effects. Two control tasks were designed to examine whether early-late WCST P3b changes reflect category selection (attention) or category storage (memory) operations. Results suggest both a sharp P3b attenuation during shift WCST trials, followed by a gradual P3b build-up during post-shift trials. This P3b modulation could not be attributed to selection or storage of simple sensory stimulus dimensions, nor was it observed when the new rule was externally prompted by the first card in the WCST series. Instead, WCST P3b changes seem related to the endogenously generated shift in the perceptual rule used to sort the cards (i.e., the shift in set). The gradual build-up in P3b amplitude paralleled a progressive improvement in sorting efficiency over several post-shift WCST trials. A model based on formal theories of visual attention and attentional set shifting is proposed to account for these effects. The model offers firm grounds for prediction and bridges the gap between related clinical and experimental evidence.

Adult↗

PubMed2000

Prefrontal modulation of visual processing in humans.

Single neuron, evoked potential and metabolic techniques show that attention influences visual processing in extrastriate cortex. We provide anatomical, electrophysiological and behavioral evidence that prefrontal cortex regulates neuronal activity in extrastriate cortex during visual discrimination. Event-related potentials (ERPs) were recorded during a visual detection task in patients with damage in dorsolateral prefrontal cortex. Prefrontal damage reduced neuronal activity in extrastriate cortex of the lesioned hemisphere. These electrophysiological abnormalities, beginning 125 ms after stimulation and lasting for another 500 ms, were accompanied by behavioral deficits in detection ability in the contralesional hemifield. The results provide evidence for intrahemispheric prefrontal modulation of visual processing.

Attention↗

PubMed1999

Electrophysiological evidence of two different types of error in the Wisconsin Card Sorting Test.

The specificity of the Wisconsin Card Sorting Test (WCST) for assessing frontal lobe pathology remains controversial, although lesion and cerebral blood flow studies continue to suggest a role for the dorsolateral prefrontal cortex in WCST performance. Inconsistencies might derive from the extended use of various WCST scores as equivalent indicators of frontal pathology. In this study, event-related potentials (ERPs) were recorded from 32 normal subjects who committed perseverative and non-perseverative errors. Both types of WCST errors evoked anomalous but distinct ERP patterns over frontal lobe regions. Perseverative errors were also associated with a dysfunctional extrastriate response to stimulation. This evidence suggests that perseverative and non-perseverative errors result from disruptions in two different prefrontal neural networks engaged during card sorting.

Adult↗

PubMed1999

Metallic bracket to enamel bonding with a photopolymerizable resin-reinforced glass ionomer.

Enamel acid etching plays an important role in treatment on direct bracket bonding. Several studies have been carried out concerning the damage this procedure causes to the enamel. A valuable alternative seems to be the use of photopolymerizable resin-reinforced glass ionomer without acid etching of enamel. This study compares the strength of bracket debonding, the amount of remnant adhesive on the tooth, and the enamel condition in 3 adhesive systems. Three groups were set; in the first group, a glass ionomer with a photopolymerizable resin reinforce and enamel etching with orthophosphoric acid at 37% was used; in the second group, the same ionomer was used but without acid etching; and in the third group, a photopolymerizable resin was used after etching enamel with orthophosphoric acid at 37%. Debonding strength was determined in MPa; a stereoscopic microscope was used to determine the amount of remnant adhesive on the tooth in accordance to ARI and a scanning electron microscope study was made to observe the enamel conditions, existing in debonding among groups (P <.0001), with etching and without etching. The remnant adhesive on the tooth did not show a significant difference (P = 1.000); greater irregularities were found in the enamel in the etching groups. It was demonstrated that the etching was a critical factor in obtaining adequate adhesion strength and that it alters the enamel conditions. Teeth with ionomer and etching had a greater material remnant.

Acid Etching, Dental↗

PubMed1998

Non-frontal P3b-like activity evoked by the Wisconsin Card Sorting Test.

Event related potentials (ERP) were recorded from 29 electrode positions in 10 normal subjects while they performed a simplified version of the Wisconsin Card Sorting Test (WCST). The design focused on ERP differences between early and late trials within each WCST series. Topographic and dipole analyses confirmed the reliability of two ERP signs: one conspicuous mid-parietal P3b wave and one asymmetrical frontal-temporal component. A three-dipole model accounted for these ERP signs with > 90% accuracy even in individual subjects, and suggests a sub-second activation of temporal-parietal and medial temporal association areas during card sorting. The WCST-related P3b wave is proposed to reflect working memory operations such as template matching and template formation during card sorting.

Adult↗

PubMed1998

A theoretical perusal of the satellite DNA curvature in tenebrionid beetles.

The curvature patterns of seven satellite DNAs taken from beetles belonging to the family Tenebrionidae (Coleoptera) were modelled utilising a number of computer programs that describe and plot the curvature profiles of DNA. The theoretical analysis agreed with the experimentally observed curvature of most of these satellite DNAs, and its absence in Tribolium freemani and Tenebrio obscurus satellite I. In many cases, the tenebrionid satellite DNAs lack periodically repeated runs of phased-A-tracts, yet they represent a clear example of curved DNA. The macroscopic curvature of satellites from these closely related organisms confirmed that other sequence elements must be participating in the bending of these DNAs. Our modelling approaches are discussed, together with previous experimental results, in terms of the role played by DNA curvature in the organisation of satellite DNA and the tight compacting of heterochromatin.

Animals↗

PubMed1997

Polymorphic curvature of satellite DNA in three subspecies of the beetle Pimelia sparsa.

The curvature of the monomeric repeats of satellite DNAs from three subspecies of the beetle Pimelia sparsa (Coleoptera, Tenebrionidae) has been analysed. Evidence of curvature was inferred from their retarded migration in native polyacrylamide gels, which was confirmed by direct electron microscopy visualisation. Sequence-comparison analysis, which included sequence alignments and modelling studies, was used to reveal the patterns of local bending and curvature. The effects of the minor-groove-binding drugs distamycin and berenil on the curvature were assayed, and analysed with respect to their (A+T)-rich sequence preferences. Since our study deals with satellite DNAs from closely related organisms (three subspecies), we correlated the differences in sequence, and also the high similarity conserved in the (A+T)-rich regions, with the changes in the patterns of curvature.

Animals↗

PubMed1997

Event-related potentials during memorization of spatial locations in the auditory and visual modalities.

Event-related potential (ERP) studies of working memory have used delayed S1-S2 match-to-sample tasks in which S1 is held in memory for comparison with S2. ERP negativities in the S1-S2 interval have been interpreted either in terms of working memory operations, or in terms of general preparatory motor processing. Two experiments (N = 20 each) were carried out to explore the nature of ERP negativities in a visuospatial memory task and in an auditory spatial memory task, respectively. In the experimental condition, subjects had to memorize the location of S1 (S1-memorize) so as to respond whether S2 appeared in the same spatial location (S2-memorize). In the control condition, subjects were requested to ignore S1 (S1-passive), and to respond whether S2 matched or not a target location predetermined at the beginning of the trial block (S2-pressing). Results support the two main conclusions of Martin-Loeches et al. (Electroenceph. clin. Neurophysiol., 1994, 91: 363-373). Firstly, that the encoding into memory of spatial location is associated with an ERP negative wave over the brain areas putatively associated with the processing of sensory information (i.e. right parieto-occipital for the visual task; fronto-central and left temporal areas for the auditory task). Secondly, the P300 does not seem to be an important ERP feature related to spatial location encoding and retaining into memory. Despite the distinct scalp distribution of these memory-related, modality-specific ERP negativities, they also showed a considerable degree of temporal synchronicity across modalities.

Adolescent↗

PubMed1997

The Wisconsin Card Sorting Test and the assessment of frontal function: a validation study with event-related potentials.

The Wisconsin Card Sorting Test (WCST) is generally regarded as the prototype of abstract reasoning task and has been routinely used to assess frontal lobe function in a variety of clinical and research contexts. However, there are growing concerns that the WCST fails to discriminate frontal patients from those with lesions in other brain regions or from normals. Event-related potentials (ERP) from frontal, fronto-temporal, temporal, parietal and occipital areas were recorded during the performance of a computerized version of the WCST in order to explore frontal versus non-frontal ERP indexes during WCST activation. The task protocol was contrived to focus on the differences between early and late trials of each WCST series. Cognitive processes underlying these two task conditions have been described as extradimensional and intradimensional shifts in attention, respectively. Differences between early and late WCST trials appeared as soon as 120 msec poststimulus and were associated with a negative field potential centred at the fronto-temporal region of the left hemisphere. Significantly larger amplitudes of the posterior P3b wave for late as compared with early WCST trials also lent support to claims of a strong involvement of working memory mechanisms during WCST performance. Results are discussed in terms of the implications for the utility of ERP measures in clinical neuropsychology.

Adult↗

PubMed1997

Purification and characterization of ferritin from alfalfa seeds.

Ferritin from alfalfa (Medicago sativa) seeds was isolated, purified, and characterized. The apparent molecular mass of the native protein was found to be 560 kDa. Electrophoresis in denaturing gradient polyacrylamide-SDS gels revealed subunits of 28-26.5 kDa. The average iron cores were 4 nm in diameter and contained about 1400 iron atoms, with an iron-to-phosphorus ratio of 4:1. N-terminal amino acid sequencing of the 28 kDa subunit revealed close homology with other plant proteins. Immunochemical analysis using polyclonal antibodies raised against pea-seed ferritin has confirmed, in agreement with previous reports, that plant proteins share common epitopes.

Amino Acid Sequence↗

PubMed1997

Sources and topography of supramodal effects of spatial attention in ERP.

This study aimed to finding modality-independent event-related potentials (ERP) modulations related to spatial attention by minimising several possible methodological constrains which may account for the rareness of this finding in past spatial attention ERP research. ERP were recorded while subjects performed a shifting spatial attention task of either auditory, visual or mixed (both auditory and visual) modality. Task requirements and stimulation devices were identical for either modality. Stimuli could appear (80%, valid trials) or not (invalid trials) at predicted locations, and subjects had to perform a speeded response to every stimulus. Reaction time benefits were found for valid trials. Instead of the usually found enhancement of sensory-evoked modality-specific components for valid trials, ERP showed modality-independent modulations as a function of attention. They consisted of a fronto-central activity starting 240 ms after stimulus onset and originated in the anterior cingulate gyrus, followed 40 ms later by a bilateral parietal cortex activation. These processes would be reflecting the activity, respectively, of the anterior and posterior attention systems postulated in Posner's model (Posner and Peterson 1990), which showed a higher degree of participation during invalid trials. P300-like processes were also observed for invalid trials. These results demonstrate that supramodal effects of spatial attention of ERP can be obtained. Furthermore, they extend Posner's model by indicating the timings of implication of the attention subsystems.

Acoustic Stimulation↗

PubMed1997

Ferritin adsorption on amosite fibers: possible implications in the formation and toxicity of asbestos bodies.

In order to investigate how endogenous iron can be deposited in vivo on inhaled mineral fibers during early stages of formation of asbestos bodies, in vitro experiments were performed on the adsorption of ferritin onto amosite asbestos. The mineral dust was found to adsorb the protein from an aqueous solution containing 0.3 mg/ml horse spleen ferritin. In order to simulate physiological conditions the aqueous solution was adjusted with 150 mM saline. Polyacrylamide-SDS gel electrophoresis of the desorbed protein showed subunits of approximately 13 and 15 kD, aside from the 20-kD subunit present in the native protein. This suggests that as a result of interactions between ferritin molecules and the solid surface of the mineral fibers, the protein iron core may be released or partially exposed. Data indicate these interactions may have implications in the observed mineral fiber toxicities.

Adsorption↗

PubMed1997

Electrophysiological measures of cognition in biological psychiatry: some cautionary notes.

Research into the electrophysiological correlates of mental illness is currently expanding, largely because of the availability of relatively inexpensive and powerful computers. However, improvements in technology do not always lead to enhanced methodological procedures; thus, there are concerns over the proper interpretation of the results of these investigations. Our argument is that electroencephalographic (EEG) research into psychopathology of psychiatric diseases should adopt a cognitivist model of mental dysfunction rather than a neurologist model of brain disease. Cognitive science has significant potential as an integrative framework for theorizing and researching psychiatric disorders and their treatment. Models of human cognitive functioning have rather special and unique features; these will make their impact upon the nature of both the analysis and interpretation of EEG data. The adoption of a sound model of brain function has implications for the methods to be used at different successive stages of the research process. We address a number of methodological requirements pertaining to: the recording and analysis of EEG signals, the laboratory context, the nature of the tasks, and the attribution of obtained effects. However, there are grounds for great caution. Even if the mapping of electrical changes in brain activity leads to a good approximation of the temporal and spatial dynamics of higher brain function, exploitation of such information presupposes a deeper understanding of both human cognition and the physiological basis of the EEG than is often displayed in the literature. To demonstrate this fundamental point, we draw a number of comparisons between traditional neurological approaches to brain assessment and contemporary cognitive psychophysiology.

Cognition↗

PubMed1995

A psychophysiological inquiry into the nature of the Sokolovian orienting response comparator model: skin conductance and EEG data.

The mechanisms which trigger the orienting response (OR) are still the subject of lively debate. Sokolov (1990) proposes the development of a multidimensional model of the physical parameters of stimulation. Recent OR research has shown that the skin conductance OR (SCOR) is related to task demands and controlled processing, although this is not so clear for central physiological indexes of orienting. Seventy-three subjects performed visual discriminations of stimuli within a warning-stimulus paradigm. The physical complexity of stimuli and their task relevance were manipulated within subjects, while the nonspecific effects of workload were controlled with a group factor. SCORs were measured concurrently with 1-s epochs of EEG alpha and theta power from Fz, Cz, Pz, and Oz. Neither index was reliably affected by the physical complexity of stimulation alone. However, both higher task relevance and higher workload significantly increased the magnitude of EEGORs and SCORs. Task averages of central and autonomic activity showed an overall pattern of covariation, but a second-by-second breakdown of EEG spectra suggests that the SCOR may be an aggregate of the activation of diverse brain mechanisms responsible for physiological orienting. The results are consistent with a model of orienting as a continuous dimension of resource allocation to anticipated and current task demands, rather than with the abrupt dichotomy between voluntary and involuntary orienting. Implications for the classical OR Sokolovian model are discussed.

Analysis of Variance↗

PubMed1994

Calorimetric and spectroscopic studies on the poly[d(GA).d(CT)] structural polymorphism induced by zinc.

The interaction of zinc (II) with poly[d(GA).d(CT)] and salmon testes DNA has been investigated by Differential Scanning Calorimetry (DSC) and Circular Dichroism (CD). We have detected and energetically characterized the existence of two different structural forms in poly[d(GA).d(CT)] which behave differently during a DSC experiment. The overall melting of DNA shows two calorimetric transitions at different temperatures. Moreover, the presence of zinc, at an input ratio of ion to nucleotide (r) above two, renders a complex DSC profile which is characterized by a negative enthalpy transition. Besides, the low-temperature transition observed in the presence of zinc is practically reversible after re-cooling/re-heating cycles. Nevertheless, the high-temperature transition characterized by a negative delta H degree cal does not appear in re-heating experiments, and remains stable below 100 degrees C. A calorimetric negative enthalpy transition is also found using salmon DNA in the presence of zinc ions. It seems that the combination of a temperature effect and zinc binding might induce the production of a stable metal-DNA complex, which can also be detected by changes in some bands in the CD profiles. The experimental results show that the presence of DNA structures and binding processes involving a negative calorimetric enthalpy contribution might be more widespread than previously reckoned.

Animals↗