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R Salas

Publications and source records attributed to R Salas.

At least 19 recordsLinked to original sources
PubMed2001

Lateral mobility and anchoring of recombinant GABAA receptors depend on subunit composition.

The clustering of type A gamma-aminobutyric acid receptors (GABA(A)R) at discrete and functionally significant domains on the nerve cell surface is an important determinant in the integration of synaptic inputs. To discern the role that the subunits of the GABA(A)R play in determining the receptor's cell surface topography and mobility, the alpha1, beta1, beta3, and gamma2s subunits were transfected into COS7, HEK293, and PC12 cells and the distribution and cell surface mobility of these recombinant receptors were examined. Our results show that alpha1 subunits are retained in the endoplasmic reticulum while beta1 and beta3 subunits are sorted to the plasma membrane where they form clusters. Co-expression and co-assembly of alpha1 and beta3 subunits result in the rescue of intracellular alpha1 subunits, which are transported as alphabeta subunit complexes to the cell surface where they formed clusters. Fluorescence photobleach recovery and single particle tracking of recombinant receptors show that, despite clustering, beta3 subunit homooligomers are mobile within a cell surface domain. Inclusion of alpha1 in beta3 or beta3gamma2s complexes, however, dramatically reduces the receptor's lateral mobility in COS 7 and PC12 cells and anchors GABA(A)Rs on the cell surface, suggesting the formation of a direct link to a component of the cytoskeleton. The mobility of recombinant receptors that include the alpha1 subunit mirrors the mobility of GABA(A)Rs on cell bodies and dendrites of cortical and spinal cord neurons. The results suggest that incorporation of alpha1 subunits give rise to a population of GABA(A)Rs that are immobilized on the cell surface.

Animals↗
PubMed2001

Characterization of enzootic foci of Venezuelan equine encephalitis virus in western Venezuela.

The distribution of the sylvatic subtype ID Venezuelan equine encephalitis (VEE) viruses in the lowland tropical forests of western Venezuela was investigated using remote sensing and geographic information system technologies. Landsat 5 Thematic Mapper satellite imagery was used to study the reflectance patterns of VEE endemic foci and to identify other locations with similar reflectance patterns. Enzootic VEE virus variants isolated during this study are the closest genetic relatives of the epizootic viruses that emerged in western Venezuela during 1992-1993. VEE virus surveillance was conducted by exposing sentinel hamsters to mosquito bites and trapping wild vertebrates in seven forests identified and located by means of the satellite image. We isolated VEE viruses from 48 of a total of 1,363 sentinel hamsters in two of the forests on six occasions, in both dry and wet seasons. None of the 12 small vertebrates captured in 8,190 trap-nights showed signs of previous VEE virus infection. The satellite image was classified into 13 validated classes of land use/vegetation using unsupervised and supervised techniques. Data derived from the image consisted of the raw digital values of near- and mid-infrared bands 4, 5, and 7, derived Tasseled Cap indices of wetness, greenness, and brightness, and the Normalized Difference Vegetation Index. Digitized maps provided ancillary data of elevation and soil geomorphology. Image enhancement was applied using Principal Component Analysis. A digital layer of roads together with georeferenced images was used to locate the study sites. A cluster analysis using the above data revealed two main groups of dense forests separated by spectral properties, altitude, and soil geomorphology. Virus was isolated more frequently from the forest type identified on flat flood plains of main rivers rather than the forest type found on the rolling hills of the study area. The spatial analysis suggests that mosquitoes carrying the enzootic viruses would reach 82-97% of the total land area by flying only 1-3 km from forests. We hypothesize that humans within that area are at risk of severe disease caused by enzootic ID VEE viruses. By contrast, equines could actually become naturally vaccinated, thus preventing the local emergence of epizootic IC VEE virus strains and protecting humans indirectly.

Animals↗
PubMed2001

Spatial dispersion of adult mosquitoes (Diptera: Culicidae) in a sylvatic focus of Venezuelan equine encephalitis virus.

We studied the spatial localization of mosquitoes in sylvatic focus of Venezuelan equine encephalitis virus in western Venezuela to identify mosquito species potentially involved in the hypothesized transport of viruses out of enzootic foci. The following criteria were used to identify species with potential for virus export: (1) common in the forest and surrounding area, (2) feeding on a wide range of vertebrates; (3) long dispersal capabilities, and (4) established vectorial competence for enzootic or epizootic VEE viruses. CDC traps baited with light/CO2 were operated for four and 12-h intervals to collect mosquitoes at four stations along two forest/open area transects from September to November 1997. We collected 60,444 mosquitoes belonging to 11 genera and 34 species. The most common species were Aedes serratus (Theobald), Ae. scapularis (Rondani), Ae. fulvus (Wiedmann), Culex nigripalus Theobald, Cx, (Culex) "sp", Cx. mollis Dyar & Knab, Cx. spissipes (Theobald), Cx. pedroi Sirivanakarn and Belkin, Psorophora ferox (Humboldt), Ps. albipes (Theobald), and Ps. cingulata (F.). Very few mosquitoes were captured during the (day in the open area outside the forest, suggesting that any virus export from the forest may occur at night. The following mosquitoes seemed to be mostly restricted to the forest habitat: Ae. serratus, Ps. ferox, Ps. albipes, sabethines, Cx. spissipes, Cx. pedroi, Cx. dunni Dyar, and Ae. fulvus. The main species implicated its potential virus export were Cx. nigripalpus, Ae. scapularis, and Mansonia titillans (Walker).

Aedes↗
PubMed2001

Genetic diversity and relationships among Venezuelan equine encephalitis virus field isolates from Colombia and Venezuela.

During field studies of enzootic Venezuelan equine encephalitis (VEE) viruses associated with epizootic emergence, a large number of virus isolates were made in sylvatic foci of Venezuela and Colombia. To rapidly characterize these isolates, antigenic subtypes were determined by means of immunofluorescence and by single-strand conformational polymorphism (SSCP) analysis by use of an 856-bp fragment from the P62 gene, which we used to distinguish genetic variants. Representative isolates were sequenced to assess the sensitivity of SSCP to detect genetic differences. The SSCP analysis distinguished isolates differing by as little as 1 nucleotide; overall, differences of > or = 1 nucleotide were recognized 89% of the time, and the sensitivity to distinguish strains that differed by only 1 or 4 nucleotides was 17 and 57%, respectively. Phylogenetic analyses of representative sequences showed that all recent isolates from the Catatumbo region of western Venezuela and the middle Magdalena Valley of Colombia were closely related to epizootic subtype IAB and IC strains; strains from Yaracuy and Miranda States were more distantly related. Cocirculation of the same virus genotype in both Colombian and Venezuelan foci indicated that these viruses are readily transported between enzootic regions separated by > 300 km. The SSCP analysis appears to be a simple, fast, and relatively efficient method of screening VEE virus isolates to identify meaningful genetic variants.

Aedes↗
PubMed1999

Bioavailability of diclofenac after intramuscular administration to rats with experimental spinal cord injury.

Spinal cord injury (SCI) has been proposed to reduce drug bioavailability after intramuscular administration owing to an impairment in blood flow to paralyzed limbs. To test this hypothesis, we studied diclofenac bioavailability after intramuscular administration in rats with SCI. Female Sprague-Dawley rats were submitted to SCI at the T8 level by contusion and received a 10-mg/kg intramuscular diclofenac dose in the thigh of the right hind limb 24 h after injury. Blood samples were drawn, diclofenac concentration was determined by high-performance liquid chromatography, and whole-blood concentration against time curves were constructed. SCI did not result in a significant change in C(max) and T(max), compared with sham-lesioned controls, suggesting that the rate of drug absorption was not altered. Half-life was prolonged, and therefore area under the curve was greater in SCI than in sham-lesioned animals. Therefore, 24 h after SCI at the T8 level, intramuscular diclofenac bioavailability was not impaired but was actually enhanced. Results suggest that the rate of intramuscular diclofenac absorption is not significantly altered, although its elimination is impaired, during the acute phase of SCI. It then appears that SCI-induced pharmacokinetic alterations are complex, the global bioavailability depending on the sum of SCI effects on absorption, distribution, and elimination. Systematic studies on SCI-induced alterations are thus required to provide information leading to a rational dosing regimen design for SCI patients.

Animals↗
PubMed1999

Genetic and phenotypic changes accompanying the emergence of epizootic subtype IC Venezuelan equine encephalitis viruses from an enzootic subtype ID progenitor.

Recent studies have indicated that epizootic Venezuelan equine encephalitis (VEE) viruses can evolve from enzootic, subtype ID strains that circulate continuously in lowland tropical forests (A. M. Powers, M. S. Oberste, A. C. Brault, R. Rico-Hesse, S. M. Schmura, J. F. Smith, W. Kang, W. P. Sweeney, and S. C. Weaver, J. Virol. 71:6697-6705, 1997). To identify mutations associated with the phenotypic changes leading to epizootics, we sequenced the entire genomes of two subtype IC epizootic VEE virus strains isolated during a 1992-1993 Venezuelan outbreak and four sympatric, subtype ID enzootic strains closely related to the predicted epizootic progenitor. Analysis by maximum-parsimony phylogenetic methods revealed 25 nucleotide differences which were predicted to have accompanied the 1992 epizootic emergence; 7 of these encoded amino acid changes in the nsP1, nsP3, capsid, and E2 envelope glycoprotein, and 2 were mutations in the 3' untranslated genome region. Comparisons with the genomic sequences of IAB and other IC epizootic VEE virus strains revealed that only one of the seven amino acid changes associated with the 1992 emergence, a threonine-to-methionine change at position 360 of the nsP3 protein, accompanied another VEE virus emergence event. Two changes in the E2 envelope glycoprotein region believed to include the major antigenic determinants, both involving replacement of uncharged residues with arginine, are also candidates for epizootic determinants.

Amino Acid Sequence↗
PubMed1999

Dengue virus structural differences that correlate with pathogenesis.

The understanding of dengue virus pathogenesis has been hampered by the lack of in vitro and in vivo models of disease. The study of viral factors involved in the production of severe dengue, dengue hemorrhagic fever (DHF), versus the more common dengue fever (DF), have been limited to indirect clinical and epidemiologic associations. In an effort to identify viral determinants of DHF, we have developed a method for comparing dengue type 2 genomes (reverse transcriptase PCR in six fragments) directly from patient plasma. Samples for comparison were selected from two previously described dengue type 2 genotypes which had been shown to be the cause of DF or DHF. When full genome sequences of 11 dengue viruses were analyzed, several structural differences were seen consistently between those associated with DF only and those with the potential to cause DHF: a total of six encoded amino acid charge differences were seen in the prM, E, NS4b, and NS5 genes, while sequence differences observed within the 5' nontranslated region (NTR) and 3' NTR were predicted to change RNA secondary structures. We hypothesize that the primary determinants of DHF reside in (i) amino acid 390 of the E protein, which purportedly alters virion binding to host cells; (ii) in the downstream loop (nucleotides 68 to 80) of the 5' NTR, which may be involved in translation initiation; and (iii) in the upstream 300 nucleotides of the 3' NTR, which may regulate viral replication via the formation of replicative intermediates. The significance of four amino acid differences in the nonstructural proteins NS4b and NS5, a presumed transport protein and the viral RNA polymerase, respectively, remains unknown. This new approach to the study of dengue virus genome differences should better reflect the true composition of viral RNA populations in the natural host and permit their association with pathogenesis.

3' Untranslated Regions↗
PubMed1999

[Chemical composition and digestibility of the protein of 20 ecotypes of Pijiguao (Bactris gassipaes) of the Venezuelan Amazon].

Precooked flour (80 degrees C x 3 hours) from the pulp of 20 ecotypes of Pijiguao cultivated in the Amazon area of Venezuela and dried at 80 degrees C for 3 hours was manufactured for the purpose of developing an alternative method of conservation of the fruit for human consumption and for the purpose of contributing to the study of the germoplasm through the assessment of its chemical characterization by applying the AOAC methods. The results showed a wide statistical variability (p < 0.05) among the ecotypes in relation to the fat content (5.13%-17.30%), protein content (5.00%-8.30%), starch content (29.13%-56.40%), and dietetic fiber content (8.10%-21.00%). Likewise, significant differences in the carotenoid content (3.46-40.06 mg/100 g) and the vitamin C content (6.60 to 51.60 mg/100 g) were also detected. The digestibility "in vitro" of the protein was high (88.10%-91.90%). In addition color was analyzed in a tristimulus color meter and the data varied between L = 65.07 to 81.84; a = 0.18 to 13.96 y b = 18.30 to 38.82. Orange, yellow, and beige were observed Pijiguao precooked flour is a potential source of dietetic carotenoids, vitamin C, fat, and starch.

Ascorbic Acid↗
PubMed1997

Origins of horizontal cell spectral responses in the retina of marine teleosts (Centropomus and Mugil sp).

Intracellular recording and marking of horizontal cells (HCs) were carried out in isolated retinas of marine teleosts (Centropomus and Mugil sp.) to identify the cellular origins of different spectral types of S-potential. The spectral responses recorded under mesopic conditions were classified into four types: photopic L, biphasic C(R/G), biphasic C(G/R), and scotopic L(sL). Intracellular marking with Lucifer yellow (LY) or Procion yellow (PY) revealed that in the Centropomus retina an L-type response was recorded from H1 and H2 cells, C(R/G)-type from H3 cells, and sL-type from H4 cells. However, in 20% of microelectrode penetrations from the photoreceptor surface, the sequential order of response appearances was found to be L-, sL-, and C(R/G)-types. In this species, thick dendritic processes of H3 and H4 cells are distributed at the same level as the cell body. In the Mugil retina, on the other hand, L-type response was recorded from H1 cells, C(G/R)-type from H2 cells, C(R/G)-type from H3 cells, and sL-type from H4 cells, this sequential arrangement being very regular. In both species, the cone-connected H1 cells are small and possess an axon, while the two other cone HCs as well as rod-connected H4 cells are axonless. Earlier (Negishi et al., 1988) and present findings indicate that there is a wide variety of HC morphology and functional organization in the teleost retina.

Animals↗
PubMed1997

Hyperphosphatasemia: CT assessment.

Hyperphosphatasemia is a rare disorder of uncertain cause. A 39-year-old male exhibiting striking skeletal deformities consisting of enlargement of the skull, enlargement and bowing of the long bones, neurosensorial symptoms and elevated alkaline phosphatase is the subject of this report. In the past, the radiological workup has been limited to plain films. We advocate CT in the assessment of neurological signs and symptoms which may complicate this disease.

Adult↗
PubMed1996

Re-emergence of epidemic Venezuelan equine encephalomyelitis in South America. VEE Study Group.

BACKGROUND: Venezuelan equine encephalomyelitis (VEE) virus has caused periodic epidemics among human beings and equines in Latin America from the 1920s to the early 1970s. The first major outbreak since 1973 occurred in Venezuela and Colombia during 1995, and involved an estimated 75,000 to 100,000 people. We report an epidemiological and virological investigation of this epidemic. METHODS: Virus isolates were made in cell culture from human serum, human throat swabs, and brain tissue from aborted and stillborn human fetuses, as well as from horse brain tissue and pooled mosquito collections. Human sera were also tested for VEE-specific antibodies. The serotypes of VEE isolates were identified by antigen assays, and viruses were characterised genetically by sequencing PCR products generated from the E3 and E2 genes. Phylogenetic analyses were done to determine evolutionary relations with respect to previous epidemic/epizootic and enzootic VEE virus isolates. Mosquito collections were made to identify possible vectors, and clinical findings were determined by direct observation of patients visiting hospitals and clinics in affected regions, and by inspecting patient records. Equine vaccination and vector control were used in an attempt to halt the spread of the outbreak. FINDINGS: Most affected people had an acute, self-limited febrile illness of 3 to 4 days duration. However, convulsions were often seen in children, and abortions and fetal deaths occurred in pregnant women infected with VEE virus. Antigenic characterisation of 12 virus isolates spanning the temporal and spatial range of the outbreak indicated that all are VEE serotype IC. Phylogenetic analysis revealed that all of the 1995 viruses were closely related to serotype IC viruses isolated during a large VEE outbreak that occurred in the same regions of Colombia and Venezuela from 1962-1964. A 1983 mosquito isolate from north central Venezuela was also closely related to the 1995 isolates. INTERPRETATION: This outbreak was remarkably similar to one that occurred in same regions of Venezuela and Colombia during 1962-1964. Symptoms of infected patients, estimated mortality rates, meteorological conditions preceding the epidemic, and seasonal patterns of transmission were all very similar to those reported in the previous outbreak. In addition, viruses isolated during 1995 were antigenically and genetically nearly identifical to those obtained during 1962-1964. These findings suggest that the epidemic resulted from the re-emergence of an epizootic serotype IC VEE virus. Identification of a similar virus isolate in mosquitoes in Venezuela in 1983, 10 years after epidemic/epizootic VEE activity ceased, raises the possibility of a serotype IC enzootic transmission cycle in northern Venezuela.

Adolescent↗
PubMed1996

Effects of glutamic acid and related agents on horizontal cells in a marine teleost retina.

Excitatory amino acids (EAAs) such as glutamic and aspartic acids, considered as the most likely neurotransmitters at the photoreceptor-horizontal cell synapse of teleost retinas, as well as agonists such as kainic acid and several of their antagonists, were applied to isolated and superfused retinas of the teleost Eugerres plumieri. Intracellular recordings from horizontal cells reveal that EAA receptors are of the kainate-quisqualate type. There is competitive inhibition between the agonist and antagonist agents used, and under their combined effect, the synapse under study remains operational, in a functional state, able to modulate the horizontal cell membrane potential upon retinal illumination.

Animals↗
PubMed1996

Fractal analysis of spinal dorsal horn neuron discharges by means of sequential fractal dimension D.

The present study describes a new method for converting a typical point process, such as a train of neuronal action potentials (spikes), into a planar curve which is then processed by means of a fast algorithm to calculate and display the fractal dimension D values of each of a sequence of blocks having an equal and preselectable number of interspike intervals, hence the term sequential fractal dimension D (SFD). This method is fast, does not require special computing facilities, and provides a continuous, high temporal resolution display of the neuronal discharge complexity along the course of spontaneous activity or event relating changes. The method affords insight into short duration changes in neuronal behaviour in a way independent of its discharge rate. SFD analysis of spike trains from spinal dorsal horn neurons suggests that the neuronal response to a given stimulus can be expressed as changes in the discharge pattern complexity, thus revealing a novel sensory coding strategy.

Action Potentials↗
PubMed1996

[Electrical status epilepticus during sleep].

INTRODUCTION: Sleep electrical status epilepticus (SESE) is a rare entity whose diagnosis depends or showing spike and wave complexes on the EEG during more than 85% of the duration of NoREM sleep. Typically it presents in children, most of whom have subjacent epilepsy. It is currently accepted that SESE is asymptomatic, although its persistence may give rise to severe neuropsychological sequelae. There are no references to sleep disorders in these patients. We present the case of a seven year old girl with SESE, hypersomnia and secondary nocturnal enuresis. CLINICAL CASE: The seven year old patient had a past history of simple partial crises with motor symptoms. There was progressive hypersomnia and nocturnal enuresis. The polysomnogram showed SESE. The Test for Multiple Latencies in Sleep (TMLS) showed pathological diurnal somnolence. HLA DR2 typing was negative. Neuropsychological study showed severe alterations in the language area, with a normal intelligence quotient. CONCLUSIONS: The new findings presented suggested that SESE is an intrinsic sleep disorder and not merely an EEG pattern. Since it occurs in children, sometimes with neuropsychological deficits, systematic TMLS should be done. The association of hypersomnia, changes in immediate visual memory and autistic regression suggest involvement of the limbic system.

Brain↗
PubMed1994

Description of Guanarito virus (Arenaviridae: Arenavirus), the etiologic agent of Venezuelan hemorrhagic fever.

This paper characterizes Guanarito virus, the etiologic agent of Venezuelan hemorrhagic fever. Based on its morphology and antigenic properties, Guanarito virus appears to be a new member of the Tacaribe complex of the genus Arenavirus, family Arenaviridae. Complement fixation and indirect fluorescent antibody tests showed that Guanarito virus and its antiserum are broadly cross-reactive with other members of the Tacaribe complex, but it can be differentiated from other members of the complex by neutralization test. Guanarito virus causes mortality in suckling mice and adult guinea pigs, but not in adult mice. Inoculated rhesus monkeys developed viremia and became ill; however, they subsequently recovered and responded with production of antibody. To date, all isolates of Guanarito virus have come from sick persons or wild rodents living within a single geographic focus in the central plains of Venezuela.

Adult↗