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G Alvarez

Publications and source records attributed to G Alvarez.

At least 19 recordsLinked to original sources
PubMed1999

Lithium protects cultured neurons against beta-amyloid-induced neurodegeneration.

The deposition of beta-amyloid peptide (A beta), the hyperphosphorylation of tau protein and the death of neurons in certain brain regions are characteristic features of Alzheimer's disease. It has been proposed that the accumulation of aggregates of A beta is the trigger of neurodegeneration in this disease. In support of this view, several studies have demonstrated that the treatment of cultured neurons with A beta leads to the hyperphosphorylation of tau protein and neuronal cell death. Here we report that lithium prevents the enhanced phosphorylation of tau protein at the sites recognized by antibodies Tau-1 and PHF-1 which occurs when cultured rat cortical neurons are incubated with A beta. Interestingly, lithium also significantly protects cultured neurons from A beta-induced cell death. These results raise the possibility of using chronic lithium treatment for the therapy of Alzheimer's disease.

Amyloid beta-Peptides↗
PubMed1999

Bednet impregnation for Chagas disease control: a new perspective.

BACKGROUND: To determine the efficacy and acceptability of deltamethrin-impregnated bednets in controlling Chagas disease in South America. METHODS: In three endemic departments of Colombia, a qualitative study on people's knowledge about Chagas disease, vectors, preventive measures and their willingness for collaboration in control operations was undertaken. Additionally, in an entomological study with 100 laboratory-bred Chagas vectors (Rhodnius prolixus), vectors were released for 5 nights (20 each night) in an experimental room, with the human bait protected for one night by an unimpregnated and for four nights by a deltamethrin-impregnated bednet (13 mg/m2). Vectors were stained with fluorescent powder for observation, collected after 10 h exposure in the experimental room and observed for a further 72 h. RESULTS: The study population did not know anything about Chagas disease, but believed the vector to transmit cutaneous leishmaniasis. Therefore willingness to take part in control operations was high. The experimental hut study showed a vector mortality rate of 95% in a room with impregnated nets and of 10% in a room with unimpregnated nets. CONCLUSION: This study opens a new perspective for Chagas disease control in integrated vector borne disease prevention programmes.

Animals↗
PubMed1999

Relevance of sialoglycoconjugates in murine thymocytes during maturation and selection in the thymus.

Differentiation of most T lymphocytes is characterized not only by the variable expression of CD4/CD8 coreceptor molecules and increased surface density of the T cell antigen receptor, but also by changes in the glycosylation pattern of cell surface glycolipids or glycoproteins. In this work we evaluated the changes in the sialylation pattern in thymus sections from normal and dexamethasone treated mice. We used sialic acid specific lectins, such as Sambucus nigra agglutinin (SNA, NeuAcalpha2,6-Gal specific) and Maackia amurensis agglutinin (MAA, NeuAcalpha2,3-Gal specific). Our results indicate that the sialylation pattern was modified during the maturation process of thymic cells. The immature CD4-CD8- and CD4+CD8+ cortical thymocytes were recognized by SNA, whereas the mature single positive (CD4+ or CD8+) medullary cells, preferentially bound MAA lectin. However, in the corticomedullary region we found not only SNA+ cells, but also MAA+ cells. In the thymus of dexamethasone treated mice, the clusters of thymocytes undergoing apoptosis in the cortex were characteristically stained by SNA. These results suggest that in the initial stages of the differentiation pathway, a great number of thymocytes express an alpha2,6 linked sialic acid on their surface and as they progress to more mature stages there is a change in the sialylation pattern to alpha2,3 linked sialic acids probably due to a regulated expression of different sialyltransferases, which could be modulated by the thymic microenvironment.

Animals↗
PubMed1998

Protection by pyruvate and malate against glutamate-mediated neurotoxicity.

Pyruvate and malate (P/M) increase the contribution of mitochondria to neuronal calcium homeostasis. We have now found that cortical neuronal cultures utilize pyruvate preferentially over glucose. The supply of pyruvate and malate protects hippocampal and cortical neurons against delayed cell death occurring 24 h after glutamate exposure. High [Ca2+]i levels attained during and after glutamate exposure were reduced when neurons were incubated in the presence of P/M. At the single cell level, this was reflected in a decrease in the number of neurons that respond to glutamate with high rises in [Ca2+]i. The results suggest that the ability to prevent large increases in [Ca2+]i may underlie the beneficial effects of pyruvate and malate during glutamate excitotoxicity.

Animals↗
PubMed1998

[Coronary spasm and heart arrest caused by ventricular fibrillation].

We report the cases of three young men, heavy smokers, without previous heart disease and who were resuscitated after cardiac arrest due to ventricular fibrillation attributed to coronary spasm. All of them complained of atypical chest pain and the exercise testing, echocardiogram and coronary angiography were normal. The first case was diagnosed by Holter monitoring and by provocative testing with intracoronary ergonovine; the second by provocative testing with intracoronary acetylcholine and the third by Holter monitoring. The patients were treated with a calcium antagonist and/or nitrates and in the follow up they remained asymptomatic.

Adult↗
PubMed1998

Laparoscopic extraperitoneal repair of inguinal hernias.

The world of surgical laparoscopy is evolving. Laparoscopic prosthetic inguinal hernia repair is gaining rapid and wide acceptance. This experience consisted of 144 hernia repairs in 105 patients (40 bilateral, 31 recurrent, and 33 unilateral nonrecurrent hernias), treated through an extraperitoneal laparoscopic repair. When compared with transabdominal repair, operative time and postoperative recovery were similar, with some advantages related to the avoidance of intraabdominal manipulation and potential related complications. In spite of a relatively short follow-up (up to 40 months), there were no recurrences in this series. Morbidity rate was acceptable (16.1%), mainly reported as minor complications. Anatomical and technical skills to perform the operation are required and achieved through training. Extraperitoneal hernia repair with synthetic mesh is safe and feasible, with the advantages of being associated with less pain, rapid return to full activities, and the already proven milder systemic responses following interventional laparoscopy.

Female↗
PubMed1998

Transabdominal or totally extraperitoneal laparoscopic hernia repair?

Laparoscopic repair of inguinal hernias follows some principles that have already proven its efficiency, as a posterior approach and the prosthetic repair that allows a "tension-free" repair with consequent early return to work and low recurrence rate. To determine the most appropriate laparoscopic repair, we compared the transabdominal preperitoneal (TAPP) and the totally extraperitoneal (TEP) approach. Patients undergoing TAPP and TEP were compared regarding technical feasibility and difficulties, time until return to work and follow-up, including intraoperative and postoperative complications. Seventy-eight patients (108 hernias) were submitted to TAPP and 67 (100 hernias) were repaired through TEP. All data were analyzed by Yates-corrected chi-square test to qualitative analysis of each group and p < or = 0.05 was considered significant. Both procedures were indicated mainly for bilateral and/or recurrent hernias (68%). The operative time was shorter in TAPP (not statistically significant). Surgeons complained of more technical difficulties while performing the TEP approach (70% complaints of difficulty in TEP--four conversions to TAPP). There was no difference in hospital stay (mean of 30 h) and return to work (TAPP 7 days and TEP 5.5 days). Regarding the complication rate (TAPP = 20.5% and TEP = 13.5%; not significant), none were related to the pneumoperitoneum technique or its systemic effects. In the TAPP approach, two trocar site hernias occurred, and in the TEP approach, one severe cellulitis occurred, which was managed without surgical intervention. The mean follow-up period for each procedure was not the same, so the recurrence rates are not comparable statistically (rate of 1.85% in TAPP and 0 in TEP). Both techniques are safe and have the same advantages, but TAPP is easier: a better view of the anatomy is achieved, shortening the learning curve. We suggest that TAPP can be an adequate laparoscopic approach to groin hernias. A longer follow-up period and more cases are needed to determine recurrence rates.

Adult↗
PubMed1997

On Fisher's exact test for detecting gametic disequilibrium between DNA polymorphisms.

Nonrandom associations between DNA polymorphisms are commonly tested by Fisher's exact test in spite of it is seriously conservative. Theoretical statistical studies have shown that the exact test with Tocher's correction does not present this problem but Tocher's correction is never used by experimentalists for detecting gametic associations. We have examined the practical consequences of using these two alternative tests for the detection of nonrandom associations in populations. A total of 1566 pairs of RFLPs of eleven gene regions and sixteen populations from previously published human and Drosophila disequilibrium data were examined. The analysis reveals remarkable differences between the two tests for detecting gametic associations. In some gene regions, the exact test with Tocher's correction detects a percentage of significant associations between RFLPS which is twice or three times higher than that detected by the exact test without correction. Therefore, the widely used exact test can be seriously underestimating disequilibrium in populations. In addition, the study shows that the standard chi-square test for independence in 2 x 2 tables detects a similar percentage of significant associations between RFLPs than Tocher's test.

Animals↗
PubMed1997

Epidemic Venezuelan equine encephalitis in La Guajira, Colombia, 1995.

In 1995, the first Venezuelan equine encephalitis (VEE) outbreak in Colombia in 22 years caused an estimated 75,000 human cases, 3000 with neurologic complications and 300 fatal, in La Guajira State. Of the state's estimated 50,000 equines, 8% may have died. An epizootic IC virus, probably introduced from Venezuela, was rapidly amplified among unvaccinated equines. Record high rainfall, producing high densities of vector Aedes taeniorhynchus, led to extensive epidemic transmission (30% attack rate) in the four affected municipalities. Native Wayuu Indians, constituting 24% of the state's population, were at increased risk of infection (risk ratio, 3.3; 95% confidence interval, 2.2-5.3). Epidemiologic studies found no evidence of human-to-human transmission. A higher-than-expected number of abortions during the outbreak confirmed a previously suspected abortifacient role of VEE infection. Pesticide applications and a mass equine vaccination program contributed to preventing the outbreak's spread south of La Guajira.

Adult↗
PubMed1997

Conditions for protected inversion polymorphism under supergene selection.

Conditions for protected inversion polymorphism under the operation of both karyotype and supergene selection in a viability model have been analytically determined. When supergene selection (the effect of recombination in homokaryotypes lowering the mean fitness of their offspring) is acting on gene arrangements and there is no karyotype selection, it is demonstrated that a polymorphic stable equilibrium is reached by the population, which is a function of only the recombination effects in homokaryotypes. Under both supergene and karyotype selection the degree of dominance (h) of karyotype selection is critical to produce a protected inversion polymorphism. In general, the opportunity for protected polymorphism increases as the degree of dominance decreases. For small s values, the conditions for protected polymorphism are r > 2sh and c > 2s(h-1), where r and c are the average loss of viability for offspring of ST/ST and IN/IN homokaryotypes, respectively. These findings suggest that supergene selection may be an important balancing mechanism contributing to the maintenance of inversion polymorphism.

Chromosome Inversion↗
PubMed1997

[Transient ischemic attacks in Chilean patients and their relationship with the country's pattern of cerebrovascular disease].

BACKGROUND: It has been postulated that in Chile, transient ischemic attacks (TIA) are much less frequent than in Caucasian populations. A lesser frequency of these attacks would be due to a higher frequency of intracranial atheromas, whereas an abundance of TIA would be a result of a higher prevalence of extracranial atheromas. AIM: To study the history of TIA in a group of Chilean patients with an acute episode of cerebrovascular disease. PATIENTS AND METHODS: One hundred forty nine patients admitted to a Neurology service of a public hospital in Santiago, with an acute stroke, were studied. Patients and close relatives were interrogated about previous symptoms of TIA using a structured questionnaire. RESULTS: One hundred nine patients had an ischemic and 40 patients a hemorrhagic stroke. Twenty patients with ischemic stroke had a history of TIA (18%). Fifteen out of 74 patients without a cardiac source of emboli (20%) and five out of 35 cases with an embolic source (14%) had a TIA preceding their stroke. Three out of 40 patients (8%) with hemorrhagic stroke had a history of TIA. CONCLUSIONS: This study does not support nor reject the hypothesis of a Chilean pattern of cerebrovascular disease unlike that found in Northern Caucasians.

Acute Disease↗
PubMed1997

[Copper intake and blood levels as risk factors for atheromatous disease].

BACKGROUND: Copper is part of antioxidant enzymes and could have a cardiovascular protective effect. A higher cardiovascular risk has been associated with high as well as low plasma copper levels. AIM: To search for differences in copper intake and plasma levels between patients with coronary artery or cerebrovascular diseases and normal subjects. PATIENTS AND METHODS: Zinc and copper intake, plasma levels and serum lipid levels were measured in 20 patients with cerebrovascular disease, 20 patients with an acute myocardial infarction and 40 subjects hospitalized for elective surgery, that served as controls. RESULTS: Copper and zinc intake was below recommended allowances in all subjects. Serum zinc and copper levels did not differ in the three study groups. In patients with myocardial infarction a weak correlation was found between serum copper and total cholesterol (r = 0.24; p < 0.05) and LDL cholesterol (r = 0.31; p < 0.05). CONCLUSIONS: No differences in copper levels were found in subjects with atherosclerosis and controls. The correlation between serum copper and cholesterol deserves further investigation.

Aged↗
PubMed1996

Measuring selective effects of modifier gene polymorphisms on the Bare locus of Drosophila subobscura.

An attempt to quantify the effects of modifier gene polymorphisms on the operation of natural selection on a major locus has been carried out. The modifier system we have investigated is constituted by a set of polygenic modifier loci affecting the morphological expression of the Bare (Ba) bristle mutant of Drosophila subobscura. Ba is a dominant mutant that is lethal in homozygous condition and both the polygenic modifiers and Ba are located on the O chromosome of this species. Experimental populations were found with Ba/+ individuals and two different types of populations were started according to their modifier genetic background: populations with wild O chromosomes of either high or low modifier effect (cages H and L, respectively). Fitness estimates (total fitness, viability and fertility) for genotypes of the Ba locus were obtained under the two different modifier backgrounds. In the populations with high modifier background the total fitness of the Ba/+ heterozygote was very similar to that of the +/+ homozygote (fitness equal to 1). However, in cages with low modifier background a strong selection against the Ba/+ heterozygote was detected (average of total fitnesses over generations was 0.66 +/- 0.10), and fertility appears to be the fitness component responsible for this effect (mean fertility was 0.55 +/- 0.08). These findings demonstrate that modifier gene polymorphisms affecting the expression of the Ba mutant may be associated with large selective effects on the major locus.

Animals↗
PubMed1996

Time-series analysis of seasonal changes of the O inversion polymorphism of Drosophila subobscura.

We have studied seasonal variation (spring, early summer, last summer and autumn) of inversion polymorphisms of the O chromosome of Drosophila subobscura in a natural population over 15 years. The length of the study allowed us to investigate the temporal behavior (short-term seasonal changes and long-term directional trends) of the O arrangements by the powerful statistical method of time series analysis. It is shown that the O inversion polymorphisms varied on two different time scales: short-term seasonal changes repeated over the years superimposed on long-term directional trends. All the common arrangements (O3+4+7, Osr, O3+4+8) showed significant cyclic seasonal changes, and all but one of these arrangements (O3+4+7) showed significant long-term trends. Moreover, the degree of seasonality was different for different arrangements. Thus, O3+4+7 and OST showed the highest seasonality, which accounted for approximately 61 and 47% of their total variances, respectively. The seasonal changes in the frequencies of chromosome arrangements were significantly associated with the seasonal variation of the climate (temperature, rainfall, humidity and insolation). In particular, O3+4+7 and OST, the arrangements with the greatest seasonal component, showed the strongest association with all climatic factors investigated, especially to the seasonal changes of extreme temperature and humidity.

Animals↗