Showing papers by "University of Seville published in 1994"

Sources of attention-sensitive visual event-related potentials.

Abstract: In a study of the neural processes that mediate visual attention in humans, 32-channel recordings of event-related potentials were obtained from 14 normal subjects while they performed a spatial attention task. The generator locations of the early C1, P1, and Nl components of the visual evoked response were estimated by means of topographic maps of voltage and current source density in conjunction with dipole modelling. The topography of the C1 component (ca. 85 ms post-stimulus) was consistent with a generator in striate cortex, and this component was unaffected by attention. In contrast, the P1 and Nl components (ca. 95 and 170ms) exhibited current density foci at scalp sites overlying lateral extrastriate cortex and were larger for attended stimuli than for unattended stimuli. The voltage topographies in the 75–175 ms latency range were modeled with a 5-dipole configuration consisting of a single striate dipole and left-right pairs of dipoles located in lateral extrastriate and inferior occipito-temporal areas. This model was found to account for the voltage topographies produced by both attended and unattended stimuli with low residual variance. These results support the proposal that visual-spatial attention modulates neural activity in extrastriate visual cortex but does not affect the initial evoked response in striate cortex.

The variable incidence of hip fracture in southern Europe: the MEDOS Study.

Abstract: We assessed the incidence of hip fracture and ecological correlates in residents of 14 communities in six countries of Southern Europe. Hip fracture cases were recorded prospectively in defined catchment areas over a 1-year interval. A retrospective questionnaire was used to assess ecological differences between communities. During a 1-year period of observation a total of 3629 men and women over the age of 50 years were identified with hip fracture from a catchment of 3 million. In all communities the fracture rate increased exponentially with age. There were large and significant differences between centres in the doubling time for hip fracture risk with age and in crude and age-standardized rates. Greater than 4-fold and 13-fold differences in age-standardized risk were found amongst men and women respectively. The lowest rates were observed from Turkey and the highest from Seville, Crete and Porto. Fractures were significantly more frequent among women than men with the exception of three rural Turkish centres. Indeed, in rural Turkey the normal female/male ratio was reserved. Variations in incidence between regions were greater than the differences within centres between sexes, and there was a close and significant correlation between incidence rates for men and those for women in the regions studied. Excess female morbidity increased progressively from the age of 50 years but attained a plateau after the age of 80 years, suggesting a finite duration of the effect of the menopause. The retrospective questionnaire completed by 80% of cases suggested that differences in incidence between the communities studied could not be explained by differences in gonadal status in women. In both men and women cross-cultural associations were found with factors related to age or socioeconomic prosperity, the majority of which disappeared after adjustment for age. We conclude that there are marked and sizeable differences in the incidence rates of hip fracture throughout Southern Europe. The reasons for these differences are not known but affect both men and women, and are likely to be related to lifestyle or genetic factors rather than to differences in endocrine status.

Assimilatory Nitrogen Metabolism and Its Regulation

Abstract: The element nitrogen (N) constitutes about 5–10% of the dry weight of a cyanobacterial cell. The purpose of this chapter is to review the assimilatory pathways which in free-living cyanobacteria lead from different extracellular N-sources to cellular N-containing components. Inorganic nitrogen in the form of ammonium is incorporated into glutamine and glutamate via the glutamine synthetase/glutamate synthase cycle. The glnA gene, encoding glutamine synthetase, has been characterized in a number of cyanobacteria. Glutamate (and glutamine) distribute N to other organic compounds by means of transaminases, and glutamate is itself a precursor of some other nitrogenous metabolites. Ammonium can be taken up from the external medium by the cyanobacterial cell, but it can also be derived from other nutrients, essentially N2, nitrate and urea. Many cyanobacteria are able to fix N2 under aerobic conditions. Strategies for protecting nitrogenase from O2 in cyanobacteria include the temporal separation of nitrogenase activity and photosynthetic O2 evolution, and in some filamentous cyanobacteria, the differentiation of heterocysts (cells specialized in N2 fixation). A detailed characterization of nif genes has only been performed in a heterocyst-forming cyanobacterium. Nitrate reduction has been found to use photosynthetically reduced ferredoxin as an electron donor, and genes encoding nitrate transport and reduction proteins have been identified and shown to constitute an operon. Some amino acids like arginine and glutamine can also contribute N to some cyanobacteria; however, urea and amino acid utilization have been poorly investigated thus far. Pathways of N assimilation in cyanobacteria are induced upon ammonium deprivation, ammonium being the preferred N source. A gene, ntcA, encoding a transcriptional regulator required for expression of proteins subjected to nitrogen control has been identified. A major theme for future research is how information about the N status of the cell is sensed and transduced to the protein(s) effecting regulation of gene expression.

Hypoxia induces voltage-dependent Ca2+ entry and quantal dopamine secretion in carotid body glomus cells.

Abstract: We have investigated the changes of cytosolic [Ca2+] and the secretory activity in single glomus cells dispersed from rabbit carotid bodies during exposure to solutions with variable O2 tension (Po2). In normoxic conditions (Po2 = 145 mmHg; 1 mmHg = 133 Pa), intracellular [Ca2+] was 58 +/- 29 nM, and switching to low Po2 (between 10 and 60 mmHg) led to a reversible increase of [Ca2+] up to 800 nM. The response to hypoxia completely disappeared after removal of external Ca2+ or with the addition of 0.2 mM Cd2+ to the external solution. These same solutions also abolished both the Ca2+ current of the cells and the increase of internal [Ca2+] elicited by high external K+. Elevations of cytosolic [Ca2+] in response to hypoxia or to direct membrane depolarization elicited the release of dopamine, which was detected by amperometric techniques. Dopamine secretion occurred in episodes of spike-like activity that appear to represent the release from single secretory vesicles. From the mean charge of well-resolved secretory events, we estimated the average number of dopamine molecules per vesicle to be approximately 140,000, a value about 15 times smaller than a previous estimate in chromaffin granules of adrenomedullary cells. These results directly demonstrate in a single-cell preparation the secretory response of glomus cells to hypoxia. The data indicate that the enhancement of cellular excitability upon exposure to low Po2 results in Ca2+ entry through voltage-gated channels, which leads to an increase in intracellular [Ca2+] and exocytotic transmitter release.

Factors limiting microbial biomass in the mineral soil and forest floor of a warm-temperate forest

Abstract: Soil respiration and microbial biomass-N, in the forest floor, and in the top 10cm of the mineral soil, was measured in a warm-temperate forest soil in North Carolina (U.S.A.). We amended soils with nitrogen, phosphorus and sucrose at five different samplings from May 1991 to July 1992. Average microbial biomass-N was 463 μg g −1 in the litter layer and 52.3 μg g −1 in the mineral soil. N fertilization increased microbial biomass in the forest floor but in the mineral soil microbial biomass only responded to P fertilization. Phosphatase activity g −1 of organic matter was four times higher in the mineral soil than in the forest floor. Soil respiration increased with N, P and sucrose additions. We found seasonal differences in soil respiration and microbial biomass through the year with a winter minimum and a summer maximum. The limitation of microbial biomass by P in the mineral soil is explained by the decrease of P availability due to P Sorption by Al and Fe sesquioxides in the upper mineral soil, and by P uptake by roots from the forest floor. Our results suggested that in this forest microbial biomass would not act as a major N sink with increased N deposition.

Expression, tissue distribution and subcellular localization of dehydrin TAS14 in salt-stressed tomato plants.

Abstract: We previously isolated and characterized TAS14, and mRNA that is induced in tomato upon osmotic stress or abscisic acid (ABA) treatment and that shares expression and sequence characteristics with other dehydrin genes in different species. Affinity-purified antibodies against TAS14 protein were used to study the expression of TAS14 protein, both in seedlings and mature plants, its tissue distribution and its subcellular localization. TAS14 protein was not detected in 4-day-old seedlings but accumulated after ABA, NaCl or mannitol treatments. In NaCl-treated seedlings, some protein was detectable after 6 h of treatment and reached maximal levels between 24 and 48 h. Concentrations ranging from 5 to 12.5 g/l NaCl induced the protein to similar levels. In salt-stressed mature plants, TAS14 was expressed abundantly and continuously in aerial parts, but only slightly and transiently in roots. Immunocytochemical analysis of salt-treated plants showed TAS14 accumulated in adventitious root primordia and associated to the provascular and vascular tissues in stems and leaves. Immunogold electron microscopy localized TAS14 protein both in the cytosol and in the nucleus, associated to the nucleolus and euchromatin. Since TAS14 is a phosphoprotein in vivo, the classes of protein kinases potentially responsible for its in vivo phosphorylation were tested in in vitro phosphorylation assays. TAS14 protein was phosphorylated in vitro by both casein kinase II and cAMP-dependent protein kinase.

Antiulcer effect of naringin on gastric lesions induced by ethanol in rats

Abstract: This study was designed to determine the gastroprotective properties of naringin on and the involvement of endogenous prostaglandins in mucosal injury produced by absolute ethanol. Oral pretreatment w

Cloning and characterization of a chitinase (CHIT42) cDNA from the mycoparasitic fungus Trichoderma harzianum

Abstract: A cDNA of Trichoderma harzianum (chit42), coding for an endochitinase of 42 kDa, has been cloned using synthetic oligonucleotides corresponding to aminoacid sequences of the purified chitinase. The cDNA codes for a protein of 423 amino acids. Analysis of the N-terminal amino-acid sequence of the chitinase, and comparison with that deduced from the nucleotide sequence, revealed post-translational processing of a putative signal peptide of 22 amino acids and a second peptide of 12 amino acids. The chit42 sequence presents overall similarities with filamentous fungal and bacterial chitinases and to a lesser extent with yeast and plant chitinases. The deduced aminoacid sequence has putative catalytic, phosphorylation and glycosylation domains. Expression of chit42 mRNA is strongly induced by chitin and chitin-containing cell walls and is subjected to catabolite repression. Southern analysis shows that it is present as a single-copy gene in T. harzianum. chit42 is also detected in several tested mycoparasitic and non-mycoparasitic fungal strains.

Antiulcer and gastroprotective effects of quercetin: a gross and histologic study.

Abstract: This study was designed to determine the cytoprotective properties of quercetin and the involvement of endogenous prostaglandins in mucosal injury produced by absolute ethanol. Gastric glands were also analyzed histologically. Oral pretreatment with the highest dose of quercetin (200 mg/kg), 120 min before absolute ethanol, was most effective in necrosis prevention. Subcutaneous administration of indomethacin (10 mg/kg) to the animals treated with quercetin (200 mg/kg) partially inhibited gastric protection. All treated groups showed a marked increase in the amount of gastric mucus although this increase was less in animals pretreated with indomethacin. Total proteins and the hexosamine content decreased in the groups receiving indomethacin. The histomorphometric evaluation of the gastric damage confirmed a significant increase in mucus production accompanied by a parallel reduction of gastric lesions with the highest dose of quercetin tested.

Comparison of Methods to Estimate Dark Respiration in the Light in Leaves of Two Woody Species.

Abstract: Dark respiration in the light was estimated in leaves of two woody species (Heteromeles arbutifolia Ait. and Lepechinia fragans Greene) using two different approaches based on gas-exchange techniques: the Kok method and the Laisk method. In all cases, dark respiration in the light was lower (P < 0.05) than respiration in darkness, indicating that dark respiration was inhibited in the light. Rates of dark respiration in the light estimated by the Laisk method were 52% higher (P < 0.05) than those estimated by the Kok method. Differences between the methods could be explained by the low ambient CO2 concentrations required by the Laisk approach. The mean value of the inhibition of respiration by light for the two species, corrected for the ambient CO2 concentration effect, was 55%. Despite the differences in leaf characteristics between the species, values of the CO2 photocompensation point, at which the rate of photosynthetic CO2 uptake equaled that of photorespiratory CO2 evolution, were very constant, suggesting an excellent consistency in the results obtained with the Laisk approach.

Performance of goldfish trained in allocentric and egocentric maze procedures suggests the presence of a cognitive mapping system in fishes

Abstract: Goldfish were trained to obtain food in a four-arm maze placed in a room with relevant spatial cues. Four experimental conditions were run: allocentric, egocentric, egocentric + allocentric, and control. Relative to controls, all groups were able to solve the different tasks with high accuracy after 1 week of training. Subsequent transfer tests revealed place and response strategies for allocentric and egocentric groups, respectively, and both types of strategies for the ego-allocentric group. Moreover, the allocentric group showed the capacity to choose the appropriate trajectory toward the goal, even from novel starting points, presumably by using the distal cues as a whole. The results suggest that, in addition to using egocentric strategies, goldfish are able to solve spatial tasks on the basis of allocentric frames of reference and to build complex spatial cognitive representations of their environment.

Eye position and eye velocity integrators reside in separate brainstem nuclei.

Abstract: Two types of central nervous system integrators are critical for oculomotor performance. The first integrates velocity commands to create position signals that hold fixation of the eye. The second stores relative velocity of the head and visual surround to stabilize gaze both during and after the occurrence of continuous self and world motion. We have used recordings from single neurons to establish that the "position" and "velocity" integrators for horizontal eye movement occupy adjacent, but nonoverlapping, locations in the goldfish medulla. Lidocaine inactivation of each integrator results in the eye movement deficits expected if horizontal eye position and velocity signals are processed separately. These observations also indicate that each brainstem compartment generates and stores these signals. Consequently, each integrator exhibits functional autonomy. Therefore, we propose that the intrinsic electrophysiological properties of the constituent neurons in each brainstem subnucleus may be sufficient for producing integrator rhythmicity.

The reaction time of drivers and the stability of traffic flow

Abstract: In this work, a condition for any traffic flow model is proposed: the consistency condition. An expression for the reaction time of drivers as a function of traffic density is derived from this condition. The changes introduced in the Payne model by the adoption of this expression for the reaction time are investigated. A comparison analysis of the resulting Payne model with others proposed by several authors and with the Simple Continuum Model is carried out. This analysis leads to the conclusion that the results of the Payne model are almost identical to those given by the Simple Continuum Model. Finally, the stability of traffic flow is studied by linearizing the Payne model and the car-following models modified by the adoption of the new formulation for the reaction time. The analysis shows that the inclusion of stochastic terms in the models would be necessary to explain instability phenomena in traffic flow.

Production of halocin is a practically universal feature of archaeal halophilic rods

Abstract: Antagonisms among members of nine phenons of halobacteria were detected by combining two methods based on the double layer technique. Inhibitory activities were not due to phages. The protein nature of the inhibitors indicated that they were halocins. With only one exception, all strains tested exhibited inhibitory activity against other halobacteria due to the production of halocins. A very wide range of activity spectra was detected and the numerical comparative analysis showed little grouping, due to the scarce similarities between them. This indicates that many different halocins are produced by this heterogeneous group of micro-organisms. Our results show that halocin production should be considered as a practically general feature of halobacteria.

A CNN universal chip in CMOS technology

Abstract: This paper describes the design of a CNN universal chip in a standard CMOS technology. The core of the chip consists of an array of 32/spl times/32 completely programmable CNN cells. Input image can be loaded in optical or electrical form. Accuracy is in the range of 7-8 bit and cell density is of 33 cells/mm/sup 2/. >

A new type of glutamine synthetase in cyanobacteria: the protein encoded by the glnN gene supports nitrogen assimilation in Synechocystis sp. strain PCC 6803.

Abstract: A new glutamine synthetase gene, glnN, which encodes a polypeptide of 724 amino acid residues (M(r), 79,416), has been identified in the unicellular cyanobacterium Synechocystis sp strain PCC 6803; this is the second gene that encodes a glutamine synthetase (GS) in this cyanobacterium The functionality of this gene was evidenced by its ability to complement an Escherichia coli glnA mutant and to support Synechocystis growth in a strain whose glnA gene was inactivated by insertional mutagenesis In this mutant (strain SJCR3), as well as in the wild-type strain, the second GS activity was subject to regulation by the nitrogen source, being strongly enhanced in nitrogen-free medium Transcriptional fusion of a chloramphenicol acetyltransferase (cat) gene with the 5'-upstream region of glnN suggested that synthesis of the second Synechocystis GS is regulated at the transcriptional level Furthermore, the level of glnN mRNA, a transcript of about 2,300 bases, was found to be strongly increased in nitrogen-free medium The glnN product is similar to the GS subunits of Bacteroides fragilis and Butyrivibrio fibrisolvens, two obligate anaerobic bacteria whose GSs are markedly different from other prokaryotic and eukaryotic GSs However, significant similarity is evident in the five regions which are homologous in all of the GSs so far described The new GS gene was also found in other cyanobacteria but not in N2-fixing filamentous species

Smart-pixel cellular neural networks in analog current-mode CMOS technology

Abstract: This paper presents a systematic approach to design CMOS chips with concurrent picture acquisition and processing capabilities. These chips consist of regular arrangements of elementary units, called smart pixels. Light detection is made with vertical CMOS-BJT's connected in a Darlington structure. Pixel smartness is achieved by exploiting the cellular neural network paradigm, incorporating at each pixel location an analog computing cell which interacts with those of nearby pixels. We propose a current-mode implementation technique and give measurements from two 16 x 16 prototypes in a single-poly double-metal CMOS n-well 1.6-/spl mu/m technology. In addition to the sensory and processing circuitry, both chips incorporate light-adaptation circuitry for automatic contrast adjustment. They obtain smart-pixel densities up to 89 units/mm/sup 2/, with a power consumption down to 105 /spl mu/W/unit and image processing times below 2 /spl mu/s. >

Changes of ploidy during the Azotobacter vinelandii growth cycle.

Abstract: This work was supported by grant PB89/0627 from the DGICYT of the Government of Spain. R.M. was a predoctoral fellow under the PFPI program of the Regional Government of Andalusia (Junta de Andalucia), Spain.

Mobile robot trajectory planning with dynamic and kinematic constraints

Abstract: This paper presents methods for planning mobile robot trajectories by considering the kinematic and dynamic constraints on the vehicle motion. The resulting path is smooth and quasilinear in curvature variations. The maximum value of the curvature can be assured to be smaller than the value given by the constraints. Furthermore, speeds along the path are planned subject to the kinematic and dynamic constraints. The resulting trajectories provide ideal conditions for high precision path tracking and positioning. In the paper we present the application of the proposed methods to RAM-1, a new mobile robot designed and built for indoor and outdoor industrial environment. >

Disorder-induced vibration-mode coupling in SiO2 films observed under normal-incidence infrared radiation.

Abstract: We have investigated the strongest infrared absorption mode in silicon oxide films obtained at low temperatures (anodic and plasma oxides). The asymmetric stretching transverse mode of the Si-${\mathrm{O}}_{4}$ tetrahedra, centered at 1070 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$, exhibits an interesting multiple-resonance structure on the high-energy side of the infrared spectrum. A transverse-optical (TO) mode at 1200 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ and a longitudinal-optical (LO) mode at 1150 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$, both modes associated with a LO-TO frequency splitting, and another longitudinal-optical mode at 1250 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$, associated also with a LO-TO splitting of the 1250- and 1070-${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ peaks are also observed. An important increase in the intensity of the multiple-resonance feature, attributed to the water concentration present during the oxidation process, is observed. This effect is related to the increase in the short-range disorder in silicon oxide films attributed to OH and ${\mathrm{H}}_{2}$O incorporation during growth. In addition, x-ray-photoelectron-spectroscopy measurements reflect the influence of this short-range disorder on the O 1s and Si 2p core-level and valence-band spectra.