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Biomedical subjects

A Reyes

Publications and source records attributed to A Reyes.

At least 37 records · Page 2Linked to original sources
PubMed2001

Influence of dendritic conductances on the input-output properties of neurons.

A fundamental problem in neuroscience is understanding how a neuron transduces synaptic input into action potentials. The dendrites form the substrate for consolidating thousands of synaptic inputs and are the first stage for signal processing in the neuron. Traditionally, dendrites are viewed as passive structures whose main function is to funnel synaptic input into the soma. However, dendrites contain a wide variety of voltage- and time-dependent ion channels. When activated, the currents through these channels can alter the amplitude and time course of the synaptic input and under certain conditions even evoke all-or-none regenerative potentials. The synaptic input that ultimately reaches the soma is likely to be a highly transformed version of the original signal. Thus, a key step in understanding the relationship between synaptic input and neuronal firing is to elucidate the signal processing that occurs in the dendrites.

Action Potentials↗
PubMed2001

Broad band spectral measurements of EEG during emotional tasks.

Broad band spectral measurements were calculated on EEG recordings of 40 healthy male university students during emotional tasks using the emotion induction technique. Emotional stimuli were sentences with positive valence (joy of love), with negative valence (frustration) and neutral situation. Broad band measurements showed that delta and beta bands reflected better the differences by emotional state. Hemispheric differences associated to emotional states were obtained only for mean frequency data. Higher delta frequencies at left frontopolar, right frontal, parietal and temporal and higher beta frequencies at left frontotemporal and temporal were related to love. Meanwhile higher delta frequencies especially at left frontopolar and temporal regions and lower beta frequencies at midline frontal (Fz) and central (Cz) leads were associated to frustration. These findings suggest that narrow band measurements may reflect more efficiently EEG changes during emotional tasks.

Adult↗
PubMed2001

Negative remodeling at the ostium of the left circumflex artery.

We report an ostial lesion with negative remodeling. Coronary angiography revealed a 60% stenosis at the ostium of the left circumflex artery (LCX). Intravascular ultrasound (IVUS)-guided directional atherectomy followed by stenting was planned. However, IVUS images revealed no significant stenosis and negative remodeling at the ostium of the LCX. The lesion did not undergo intervention.

Coronary Angiography↗
PubMed2001

[Distribution of hepatitis C virus genotypes among the hemodialysis population in the province of Alicante].

UNLABELLED: Hepatitis C virus (HCV) genotypes are irregularly distributed among the different geographic area and groups at risk. OBJECTIVE: To study the different HCV genotypes and subtypes of hemodialyzed patients from Alicante. METHODS: We studied 640 patients on haemodialysis (HD) and we determined the RNA-HCV and the genotypes in the 120 patients with antibodies against HCV (HCV-Ab). We compared the results with the genotypes of 1,370 patients from other groups at risk in the same geographic area. RESULTS: RNA-HCV was not found in the serum in 15% (18/120) of the patients on HD who were HCV-Ab positive. Prevalence of the different genotypes in the 102 patients with positive viral RNA was the following: 1b: 56.8% (58/102), 1a: 19.6% (20/102), 3: 17% (17/102), 2a-2c: 1.9 (2/102), 2b: 0.9% (1/102) 4: 2.9 (3/102), 5: 0.9% (1/102). In conclusion, the genotype 1b was the most frequent in the patients studied in all these areas, and was the same as in the rest of the country. This genotype has been associated with the most severe hepatic disease and poor response to treatment, affecting the prognosis of these patients. The most frequent genotypes in HD in Alicante were 1b, 3 and 1a. HCV genotypes distribution among the HD units was not uniform in the different geographic areas. HCV genotypes distribution in the HD population is similar to other groups at risk from the same geographic area.

Adult↗
PubMed2000

Evolution of the mitochondrial genetic system: an overview.

Mitochondria, semi-autonomous organelles possessing their own genetic system, are commonly accepted to descend from free-living eubacteria, namely hydrogen-producing alpha-proteobacteria. The progressive loss of genes from the primitive eubacterium to the nucleus of the eukaryotic cell is strongly justified by the Muller rachet principle, which postulates that asexual genomes, like mitochondrial ones, accumulate deleterious and sublethal mutations faster than sexual genomes, like the nucleus. According to this principle, the mitochondrial genome would be doomed to death; instead, we observe that the mitochondrial genome has a variable size and structure in the different organisms, though it contains more or less the same set of genes. This is an example of genetic conservation versus structural diversity. From an evolutionary point of view the genetic system of organelles is clearly under strong selective pressure and for its survival it needs to utilize strategies to slow down or halt the ratchet. Anyway, the mitochondrial genome changes with time, and the rate of evolution is different for both diverse regions of the mtDNA and between lineages, as demonstrated in the case of mammalian mt genomes. We report here our data on the evolution of the mitochondrial DNA in mammals which demonstrate the suitability of mtDNA as a molecular tool for evolutionary analyses.

Animals↗
PubMed2000

Long-branch attraction phenomenon and the impact of among-site rate variation on rodent phylogeny.

The phylogenetic relationships among major lineages of rodents is one of the issues most debated by both paleontologists and molecular biologists. In the present study, we have analyzed all complete mammalian mitochondrial genomes available in the databases, including five rodent species (rat, mouse, dormouse, squirrel and guinea-pig). Phylogenetic analyses were performed on H-strand amino acid sequences by means of maximum-likelihood and on H-strand protein-coding and ribosomal genes by means of distance methods. Also, log-likelihood ratio tests were applied to different tree topologies under the assumption of rodent monophyly, paraphyly or polyphyly. The analyses significantly rejected rodent monophyly and showed the existence of two differentiated clades, one containing non-murids (dormouse, squirrel and guinea-pig) and the other containing murids (rat and mouse). Long-branch attraction between murids and the outgroups could not be responsible for the existence of two different rodent clades, as no significant differences in evolutionary rate have been observed, except in the case of the squirrel, which shows a lower rate. The impact of among-site rate variation models on the phylogeny of rodents has been evaluated using the gamma distribution model. Results have shown that relationships among rodents remained unchanged, and the general topology of the tree was not affected, even though some branches were not properly resolved, most likely due to a lack of fit between estimated and real rate heterogeneity parameters.

Animals↗
PubMed2000

Performance of small-scale CHO perfusion cultures using an acoustic cell filtration device for cell retention: characterization of separation efficiency and impact of perfusion on product quality.

Several small-scale Chinese hamster ovary (CHO) suspension cultures were grown in perfusion mode using a new acoustic filtration system. The separation performance was evaluated at different cell concentrations and perfusion rates for two different CHO cell lines. It was found that the separation performance depends inversely on the cell concentration and perfusion rate. High media flow rates as well as high cell concentrations resulted in a significant drop in the separation performance, which limited the maximal cell concentration achievable. However, packed cell volumes of 10% to 16% (corresponding to 3 to 6. 10(7) cells/mL) could be reached and were maintained without additional bleeding after shifting the temperature to 33 degrees C. Perfusion, up to 50 days, did not harm the cells and did not result in a loss of performance of the acoustic filter as often seen with other perfusion systems. Volumetric productivities in perfusion mode were 2- to 12-fold higher for two cell lines producing two different glycoproteins when compared to fed-batch or batch processes using the same cell lines. Product concentrations were in the range of 20% to 80% of batch or fed-batch culture, respectively. In addition, using the protease-sensitive product rhesus thrombopoietin, we could show that cultivation in perfusion mode drastically reduced proteolysis when compared to a batch culture without addition of protease inhibitors such as leupeptin.

Acoustics↗
PubMed2000

The influence of temperature upon the hydrolysis of cellobiose by beta-1,4-glucosidases from Aspergillus niger.

We have made experimental studies into the enzymatic hydrolysis of cellobiose within the temperature range of 40 degrees C to 70 degrees C at pH 4.9, by using beta-1,4-glucosidase from Aspergillus niger. At 70 degrees C there was significant enzyme deactivation, which could be fitted to a potential deactivation model with values of n equal to 1.09 and k(d) to 0.1564 (g/l)(-0.09) min(-1), whereas the rate of hydrolysis could be fitted to the Michaelis-Menten equation. Between 40 degrees C and 60 degrees C we noted a substrate inhibition and that the CEC compound formed contributed to glucose production. The apparent activation energies had values of 4.66, 8.45, 4.82, and 3.99 kJ/mol for the kinetic constants k(a) and k(a2) the Michaelis constant and the substrate inhibition constant, respectively.

Journal Article↗
PubMed2000

Separation of polyamines, conjugated to DNA, by reversed-phase high-performance liquid chromatography.

Genomic DNA was isolated from the lichen Evernia prunastri in order to analyze by high-performance liquid chromatography the occurrence of polyamines conjugated to the macromolecule. The acid-insoluble (PH) fraction of this DNA contained mainly conjugated spermidine, although small amounts of free putrescine and spermidine were also present. The PH fraction of DNA also contained conjugated evernic acid, the main phenol produced by this lichen species. Conjugation of polyamines to calf thymus DNA was carried out under in vitro conditions. Conjugation was to spermidine and mainly to spermine and produced DNA compactation. Evernic acid enhanced the action of polyamines in order to produce DNA aggregation.

Animals↗
PubMed2000

Three maize root-specific genes are not correctly expressed in regenerated caps in the absence of the quiescent center.

The quiescent center is viewed as an architectural template in the root apical meristem of all angiosperm and gymnosperm root tips. In roots of Arabidopsis thaliana (L.) Heynh., the quiescent center inhibits differentiation of contacting initial cells and maintains the surrounding initial cells as stem cells. Here, the role of the quiescent center in the development of the maize (Zeca mays L.) root cap has been further explored. Three maize root-specific genes were identified. Two of these were exclusively expressed in the root cap and one of them encoded a GDP-mannose-4,6-dehydratase. Most likely these two genes are structural, tissue-specific markers of the cap. The third gene, a putative glycine-rich cell wall protein, was expressed in the cap and in the root epidermis and, conceivably is a positional marker of the cap. Microsurgical and molecular data indicate that the quiescent center and cap initials may regulate the positional and structural expression of these genes in the cap and thereby control root cap development.

Amino Acid Sequence↗
PubMed2000

Auditory event-related potentials in poor readers.

Although poor readers (PR) are considered the major group among reading-disabled children, there are not event-related potentials (ERP) studies reported of PR on the subject. In this study, attentional and memory processes were studied in an auditory oddball task in PR and normal controls. ERP to auditory stimuli were recorded in 19 leads of the 10/20 system, using linked earlobes as references, in 20 normal children (10 female) and 20 PR (10 female) of the same age (10-12 years old). Two pure tones (1000 and 3000 Hz) were used in an oddball paradigm. No significant differences were observed in the amplitudes and latencies of N100 between the groups. However, N200 to frequent stimuli and P200 to both frequent and infrequent stimuli were of higher amplitude in poor readers than in normal children. There were no differences between groups in the latency and amplitude of P300. The results suggest that PR use more attentional resources in the components occurring before P300 to both frequent and infrequent stimuli than the normal children, and this finding is particularly marked for PR girls.

Child↗
PubMed2000

Primary task demands modulate P3a amplitude.

Auditory event-related brain potentials (ERPs) were recorded from 10 subjects in two different conditions: (1) subjects were required to reorder five visually presented letters in order to form a word and provide a verbal response (task condition); (2) subjects were presented with a control stimulus with the same physical characteristics as the experimental stimulus, but containing just one type of letter (i.e., AAAAA). Subjects had to verbally respond to such stimuli by saying "A" (control condition). Tones of 1000 Hz (standard) and 1050 Hz (deviant) were also presented to the subjects in a 85%-15% probability paradigm 2 s before, during and 8 s after the presentation of the visual stimuli. Recordings were obtained from Fpz, Fz, Cz and Pz vs. linked ears. Auditory ERPs to the auditory stimuli after the presentation of the visual letter string and during the performance of the task were averaged for the standard and deviant tones in both conditions. Only correct responses were considered for the averages. The N100 was affected by stimulus type (standard vs. deviant) but not by condition (task vs. control); however, larger P3a waves were observed during the control than during the task condition. No significant differences between conditions were observed in the mismatch negativity (MMN) latency range. These results suggest that primary task demands modulate involuntary attention processing.

Acoustic Stimulation↗
PubMed2000

Acetylcholinesterase-amyloid-beta-peptide interaction and Wnt signaling involvement in Abeta neurotoxicity.

Previous studies have indicated that acetylcholinesterase (AChE) promotes amyloid-beta-peptide (Abeta) fibril formation and AChE-Abeta complexes increase Abeta-dependent neurotoxicity. Here we present evidence for the: i) identification of the AChE motif that promotes amyloid formation, ii) in vivo effect of AChE on brain plaque formation, and iii) connection between AChE-Abeta neurotoxicity and the Wnt signal transduction pathway. Computer modeling, stereotaxic infusions and cell biological techniques were used to study the above problems. Results indicated that a 3.4 kDa AChE peptide promotes Abeta fibril formation. AChE infusion into rat hippocampus determines the appearance of anti-Abeta and thioflavine-S positive plaques, and AChE-Abeta toxicity on hippocampal cultures was blocked by lithium, an activator of the Wnt cascade. We suggest that AChE-Abeta/Abeta dependent neurotoxicity may result in loss of function of Wnt signaling components, and open the possibility that lithium may be considered as a candidate for therapeutic intervention in Alzheimer's disease pathology.

Acetylcholinesterase↗
PubMed2000

Lineage-specific evolutionary rate in mammalian mtDNA.

The existence of a lineage-specific nucleotide substitution rate in mammalian mtDNA has been investigated by analyzing the mtDNA of all available species, that is, 35 complete mitochondrial genomes from 14 mammalian orders. A detailed study of their evolutionary dynamics has been carried out on both ribosomal RNA and first and second codon positions (P12) of H-strand protein-coding genes by using two different types of relative-rate tests. Results are quite congruent between ribosomal and P12 sites. Significant rate variations have been observed among orders and among species of the same order. However, rate variation does not exceed 1.8-fold between the fastest (Proboscidea and Primates) and the slowest (Perissodactyla) evolving orders. Thus, the observed mitochondrial rate variations among taxa do not invalidate the suitability of mtDNA for drawing mammalian phylogeny. Dependence of evolutionary rate differences on variations in mutation and/or fixation rates was examined. Body size, generation time, and metabolic rate were tested, and no significant correlation was observed between them and the taxon-specific evolutionary rates, most likely because the latter might be influenced by multiple overlapping variable constraints.

Animals↗
PubMed1999

Evolutionary genomics in Metazoa: the mitochondrial DNA as a model system.

One of the most important aspects of mitochondrial (mt) genome evolution in Metazoa is constancy of size and gene content of mtDNA, whose plasticity is maintained through a great variety of gene rearrangements probably mediated by tRNA genes. The trend of mtDNA to maintain the same genetic structure within a phylum (e.g., Chordata) is generally accepted, although more recent reports show that a considerable number of transpositions are observed also between closely related organisms. Base composition of mtDNA is extremely variable. Genome GC content is often low and, when it increases, the two complementary bases distribute asymmetrically, creating, particularly in vertebrates, a negative GC-skew. In mammals, we have found coding strand base composition and average degree of gene conservation to be related to the asymmetric replication mechanism of mtDNA. A quantitative measurement of mtDNA evolutionary rate has revealed that each of the various components has a different evolutionary rate. Non-synonymous rates are gene specific and fall in a range comparable to that of nuclear genes, whereas synonymous rates are about 22-fold higher in mt than in nuclear genes. tRNA genes are among the most conserved but, when compared to their nuclear counterparts, they evolve 100 times faster. Finally, we describe some molecular phylogenetic reconstructions which have produced unexpected outcomes, and might change our vision of the classification of living organisms.

Animals↗