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Biomedical subjects

R Salas

Publications and source records attributed to R Salas.

At least 37 records · Page 2Linked to original sources
PubMed1994

Latin American hemorrhagic fever.

Several viral and bacterial agents are responsible for hemorrhagic fever in Latin America, but there are three agents that are only present in this region: (1) the Junin virus, (2) the Machupo virus, and (3) the Guanaritovirus, members of the Tacaribe complex of the family Arenaviridae and responsible for the Argentinian, Bolivian, and Venezuelan hemorrhagic fever. The clinical manifestations of hemorrhagic fever are similar for the three viruses, mainly myalgia, arthralgia, headache, relative bradycardia, conjunctivitis, nausea, vomiting, diarrhea, and hemorrhagic disorders. In this article, the three viruses, their causes, and manifestations are discussed.

Arenavirus↗
PubMed1993

Field studies on the epidemiology of Venezuelan hemorrhagic fever: implication of the cotton rat Sigmodon alstoni as the probable rodent reservoir.

During February 1992, field studies on the epidemiology of Venezuelan hemorrhagic fever (VHF) were carried out in a rural area of Portuguesa State in central Venezuela. The objective of this work was to determine the prevalence of infection with Guanarito virus, the etiologic agent of VHF, among wild rodents and humans living within an endemic focus of the disease. A total of 234 rodents, representing nine different species, were collected and their spleens were cultured for virus. Thirty-one Guanarito virus isolates were made from two rodent species: 19 from 40 Sigmodon alstoni and 12 from 106 Zygodontomys brevicauda. Guanarito virus antibody rates among these two species were 5.1% and 15.0%, respectively. Nine of the 12 Z. brevicauda that yielded virus from their spleens also had Guanarito virus antibodies in their sera. In contrast, none of the 19 Guanarito virus-positive S. alstoni had antibodies to the virus. These data suggest that S. alstoni usually develops a persistent nonimmunizing infection with Guanarito virus, while Z. brevicauda develops an immunizing infection. Based on knowledge of the behavior of other human pathogenic arenaviruses, these results imply that S. alstoni is the principal rodent reservoir of Guanarito virus in nature. To determine the prevalence of Guanarito virus infection among humans in the same region, 195 people living near one of the rodent collecting sites were bled and their sera were tested for antibodies to the virus. Five individuals (2.6%) had Guanarito virus antibodies; all were adults, and two had been diagnosed previously as having VHF.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1993

[Modulation of electrical coupling of horizontal cells of the retina].

Horizontal cells are electrically coupled in the teleost retina. This coupling is modulated by dopamine, which is in turn liberated from interplexiform amacrine cells. The present review includes studies carried out to elucidate the intracellular mechanisms responsible for such modulation of the resistance of intercellular unions, that results from the action of dopamine on receptors located on the cell membrane. In order to study the effects of possible second messengers, hydrogen ions (H+), cyclic adenosine monophosphate (cAMP) or calcium ions (Ca2+) were injected electrophoretically from multiple microelectrodes that simultaneously allow for voltage recording in the injected cells and in neighboring ones. A resistive hexagonal network model was used to calculate the cell membrane resistance (Rm) and the coupling resistance (Ra) between the two impaled cells. Intracellular injections of Lucifer yellow were used to microscopically verify the changes produced in Ra. The microinjection of either H+ or cAMP led to reduction in coupling ratio and increase in Ra, while Rm was reduced. These changes are similar to those produced by dopamine perfusion of the retina and, equally, are corroborated by the hindrance of diffusion to neighboring cells of the Lucifer yellow injected simultaneously. No changes were detected upon Ca2+ injection, but the chelator EGTA resulted in an increased electrical coupling and Rm reduction. The results reported are consistent with the idea that both H+ and cAMP are second messengers involved in dopamine's modulation of intercellular coupling, which is produced by changes in the resistance of intercellular unions, while Ca2+ would act as a modulator through its effect on the cell membrane resistance.

Animals↗
PubMed1993

Effect of age on progression through temporary prostheses after below-knee amputation.

Forty six patients that underwent below knee amputation for diabetes, trauma/osteomyelitis or peripheral vascular disease were studied. Healing was estimated by the rate of progression through temporary prostheses as determined weekly by the amputee rehabilitation team (physiatrist, orthopedist, physical therapist, nurse, and prosthetist). For all groups combined, mean days +/- standard error from amputation to above knee cast with pylon and foot (AKPy) were 22.9 +/- 1.9, to below knee cast with pylon and foot (BKPy) 41.6 +/- 2.8 and to laminated temporary prostheses 66.5 +/- 4.5. A regression analysis of these variables on age (range: 29 to 84 yr) showed significant positive correlations for AKPy (r = 0.34, P = 0.0214) and BKPy (r = 0.40, P = 0.0056). An analysis of variance with contrasts (Tukey's protected t) showed significant lower values (P < 0.05) for amputation to BKPy in the trauma/osteomyelitis group when compared to diabetes or peripheral vascular disease and no difference among the last two groups. However, when variables were adjusted for age (analysis of covariance with age as a covariate), the differences among groups disappeared (covariance F(2,44) = 0.9, P > 0.4). In conclusion, age, not the cause of the amputation, correlated with healing after below knee amputation as estimated by the rate of progression through temporary prostheses.

Adult↗
PubMed1991

Venezuelan haemorrhagic fever.

An outbreak of severe haemorrhagic illness began in the municipality of Guanarito, Portuguesa State, Venezuela, in September, 1989. Subsequent detailed study of 15 cases confirmed the presence of a new viral disease, designated Venezuelan haemorrhagic fever. Characteristic features are fever, toxicity, headache, arthralgia, diarrhoea, conjunctivitis, pharyngitis, leucopenia, thrombocytopenia, and haemorrhagic manifestations. Other features include facial oedema, cervical lymphadenopathy, nausea/vomiting, cough, chest or abdominal pain, and convulsions. The patients ranged in age from 6 to 54 years; all were residents of rural areas in central Venezuela, and 9 died. Infection with Guanarito virus, a newly recognised arenavirus, was shown by direct culture or by serological confirmation in all cases. Epidemiological studies suggest that the disease is endemic in some rural areas of central Venezuela and that it is rodent-borne. Venezuelan haemorrhagic fever has many similarities to Lassa fever and to the arenavirus haemorrhagic fevers that occur in Argentina and Bolivia.

Acute Disease↗
PubMed1991

Evidence for direct coupling of primary agonist-receptor interaction to the exposure of functional IIb-IIIa complexes in human blood platelets. Results from studies with the antiplatelet compound ajoene.

Ajoene, (E,Z)-4,5,9-trithiadodeca-1,6,11-triene 9-oxide, is a potent antiplatelet compound isolated from alcoholic extracts of garlic. In vitro, ajoene reversibly inhibits platelet aggregation as well as the release reaction induced by all known agonists. In this paper we show that ajoene has a unique locus of action, that is not shared by any other known antiplatelet compound. For example, ajoene inhibits agonist-induced exposure of fibrinogen receptors, as well as intracellular responses such as activation of protein kinase C and the increase in cytoplasmic free calcium induced by receptor-dependent agonists (collagen, ADP, PAF, low-dose thrombin). On the other hand, with agonists that can by-pass (at least partially) the receptor-transductor-effector sequence, such as high-dose thrombin, PMA, NaF, only the exposure of fibrinogen receptors is blocked by ajoene. Binding of fibrinogen to chymotrypsin-treated platelets is only slightly inhibited by ajoene. The results reported here also show that: (a) ajoene does not act as a calcium chelator, does not impair the initial agonist-receptor interaction and does not influence the basal levels of intracellular inhibitors of platelet activation such as cyclic GMP; (b) the locus of action of ajoene is a yet unknown molecular step that links, in the case of physiological agonists, specific agonist-receptor complexes to the sequence of the signal transduction system on the plasma membrane of platelets. In the case of non-physiological, receptor-independent agonists (PMA, NaF), we can only speculate on the hypothesis that they somehow mimic the effect of the agonist-receptor complexes on the signal transduction system; and (c) the exposure of fibrinogen receptors is not a direct consequence of other intracellular processes. These observations clearly show, for the first time, that the exposure of fibrinogen receptors is a membrane event proximally and obligatorily coupled to the occupancy of other membrane receptors by their agonists without any intervention by the cytoplasmic biochemical processes. Additional results support the involvement of G-proteins in these early events of platelet activation. Furthermore, a role of the beta tau subunits of G-proteins in the exposure of fibrinogen receptors is proposed.

Antibodies, Monoclonal↗
PubMed1991

Left ventricular aneurysm and intraventricular thrombi. Investigation and surgical correlations.

Formation of a left ventricular aneurysm and intraventricular thrombus represents one of the dreaded sequelae of coronary artery disease and acute myocardial infarction. The present emphasis is to reduce the incidence by reduction of cholesterol and fats, elimination of smoking, improved detection and control of hypertension and diabetes mellitus. Earlier diagnosis is available with stress testing and other noninvasive techniques. Cardiac catheterization allows detection of occlusive lesions. The CASS and other studies increasingly prove that percutaneous angioplasty and coronary artery bypass surgery improve life expectancy and implicitly should reduce the incidence of acute myocardial infarction. In the setting of the latter, thrombolytic agents may reduce the amount of myocardial injury. Despite these measures, formation of left ventricular aneurysms remains a common occurrence. Diagnosis and management are critical issues to the cardiac surgeon.

Cardiac Catheterization↗
PubMed1990

Retinal neurotransmitter interaction as reflected in horizontal cell spatial behaviour.

The effects of 5-hydroxytryptamine (5-HT) and its precursors 5-hydroxytryptophan (5-HTP) and L-tryptophan (L-Tryp) on the spatial properties of horizontal cells were studied in the isolated and perfused retina of the teleost Eugerres plumieri. All three compounds produce a contraction of the receptive field, evaluated by the ratio of responses evoked by local and distant light stimuli. This is the result of cell uncoupling, revealed by the hindrance to diffusion of intracellularly injected Lucifer yellow. Similar effects are produced by dopamine (DA) and the effectiveness is DA much greater than 5-HT greater than 5-HTP greater than L-Tryp. All these effects are blocked by Haloperidol. HPLC studies of endogenous DA release reveal that it occurs when isolated retinas are incubated with 50 mM potassium, 10 microM 5-HT or 5-HTP, but is not found with up to 1 mM L-Tryp. The results indicate that indolaminergic cells induce the release of DA from interplexiform cells, which in turn uncouples horizontal cells in the fish retina.

5-Hydroxytryptophan↗
PubMed1990

Results of emergent versus elective cardiac transplantation procedures.

Twenty-six patients underwent emergent (Group I) and 34 patients elective (Group II) cardiac transplantation (C. Tx.) from June 1985 through June 1989. Age, sex, etiology, presence of diabetes, renal failure and pulmonary artery pressures were comparable for both groups (P greater than 0.5). Twenty-two patients were in New York Heart Association (NYHA) Class IV for Group I and 17 for Group II. Group I included 12 patients on inotropic agents, five on intra-aortic balloon pump (IABP) and one on IABP and cardiopulmonary bypass (CPB). Elective patients were stable at home. Location of the donor heart and mean ischemic times were comparable for both groups. Early mortality (within 30 days) included four patients for Group I and two for Group II. There were four late deaths for Group I patients and six for Group II. Four deaths were due to infection, six to rejection, two to malignancy, two neurological and one each to suicide and multisystem failure. Immunosuppression regimen was similar for both groups. The number and severity of early and late rejection episodes were similar despite blood group crossing in 11 patients for Group I (P less than .01). Incidence of infection was comparable. Favorable lifestyles were comparable, including employment of 12 patients for Group I and 16 for Group II. Cumulative survival for the entire series was 70% at two years. The study indicates that the results of emergent and elective cardiac transplantation procedures are equally gratifying, that mortality is mainly related to rejection and sepsis complications and blood group crossing does not significantly increase the number of rejection episodes.

Bacterial Infections↗
PubMed1989

Cyclic adenosine monophosphate as a second messenger in horizontal cell uncoupling in the teleost retina.

The reduction in the receptive field of horizontal cells of the teleost Eugerres plumieri observed upon dopamine (DA) superfusion is thought to be due to cell uncoupling. The possible mechanisms by which activation of DA receptors modify the electric coupling between horizontal cells were studied in the present work. It was found that the effect of DA in different preparations is mediated by a modification of intracellular concentration of cAMP and H+. The effects of intracellular injection of cAMP and H+ were studied in retinal horizontal cells of the teleost E. plumieri. A triple microelectrode was used to inject the ion iontophoretically, to pass current pulses, and to record voltages from the same cell, while a fourth microelectrode was used to record voltages from a neighboring cell in the same retinal layer. Responses evoked by light spots and annuli were evaluated simultaneously. Coupling ratios between neighboring horizontal cells ranged from 0.22 to 0.45. The intercellular resistance (Rc), 0.5-3.5 x 10(6) ohms, and that of the remaining cell membrane resistance (Rm), 2.5-18 x 10(6) ohms, were calculated by means of a passive electrical model that has a hexagonal array. The microinjection of H+ with injection current from +5 to +30 nA for 40 to 100 sec led to temporary and reversible light response reduction. The coupling ratio between two impaled cells was reduced by about 30%, and intercellular resistance (Rc) increment was 320% while cell membrane resistance (Rm) did not change consistently. There was also a temporary and reversible Rm reduction (70-85%) and an Rc increment of 170-330% when cyclic adenosine monophosphate was iontophoretically injected with current from -30 to -40 nA for 50 to 170 sec. The coupling ratio between two impaled cells was reduced by about 40%, and light responses recorded from the injected cell showed a reduction in amplitude with the same time course as that of the resistive changes. The injection of Lucifer yellow into a horizontal cell under normal conditions always results in pronounced fluorescence for more distant cells; however, under constant injection of H+ or cAMP only the injected cell is fluorescent, which provides direct evidence of the reduction in the effectiveness of coupling between horizontal cells. The observed effects of intracellular H+ or cAMP injection correspond to the resistive changes in Rc and coupling ratio that occur in the horizontal cell network upon superfusion with a dopamine (DA) solution.

Animals↗
PubMed1988

Identification of horizontal cells generating different spectral responses in the retina of a teleost fish (Eugerres plumieri).

Six different types of spectral responses were recorded from horizontal cells under mesopic conditions in perfused retina, isolated from the dark-adapted mojarra (Eugerres plumieri). They were tentatively termed photopic Lr-, Lg1-, Lg2-, Lb-, and C-type, and scotopic L-type. The Lr-, Lg-, and Lb-type responses showed a maximum peak at 605, 550, and 516 nm respectively, while the C-type was composed of hyperpolarizing potentials in response to shorter wavelengths and depolarizing potentials in response to longer wavelengths (so-called R/G-type). The scotopic L-type has a peak at 516 nm in the spectral response and a slow decay phase in the waveform response. Following a brief period of diffuse illumination, it was found that the Lg1-type response is altered to the Lr-type, while both Lg2- and Lb-type responses change to the C-type. Intracellular marking with Lucifer or Procion yellow identified the cellular origins of different response types: external (He) and medial horizontal (Hm) cells for the Lr-type, internal horizontal (Hi) cells for the C-type, and rod-horizontal (Hr) cells for the scotopic L-type. Only He cells were found to possess an axon, while dye coupling was seen between axonless Hm, Hi, or Hr cells but not between He cells. The morphology of these fluorescent dye-marked cells was the same as that of the respective cells observed in Golgi-stained materials.

Animals↗
PubMed1978

Considerations on the possible structrual basis of neuronal integrated functions.

Different types of dendro-dendritic and dendro-somatic contacts in several species are described. They are classified in five varieties: (a) parallel dendro-dendritic contacts; (b) crossed dendro-dendritic contacts; (c) perisomatic interdendritic contacts; (d) perivascular interdendritic contacts; (e) dendro-somatic contacts. It is hypothetically postulated, in agreement with other authors, that the structurally differentiated interdendritic and dendro-somatic contacts could act as functional junctions for the electrotonic spread of stimuli between neighbour neuronal elements.

Action Potentials↗