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R B Azevedo

Publications and source records attributed to R B Azevedo.

12 recordsLinked to original sources
PubMed2001

A power law for cells.

Darwin observed that multiple, lowly organized, rudimentary, or exaggerated structures show increased relative variability. However, the cellular basis for these laws has never been investigated. Some animals, such as the nematode Caenorhabditis elegans, are famous for having organs that possess the same number of cells in all individuals, a property known as eutely. But for most multicellular creatures, the extent of cell number variability is unknown. Here we estimate variability in organ cell number for a variety of animals, plants, slime moulds, and volvocine algae. We find that the mean and variance in cell number obey a power law with an exponent of 2, comparable to Taylor's law in ecological processes. Relative cell number variability, as measured by the coefficient of variation, differs widely across taxa and tissues, but is generally independent of mean cell number among homologous tissues of closely related species. We show that the power law for cell number variability can be explained by stochastic branching process models based on the properties of cell lineages. We also identify taxa in which the precision of developmental control appears to have evolved. We propose that the scale independence of relative cell number variability is maintained by natural selection.

Animals↗
PubMed2001

Magnetic resonance of a dextran-coated magnetic fluid intravenously administered in mice.

Magnetic resonance was used to investigate the kinetic disposition of magnetite nanoparticles (9.4 nm core diameter) from the blood circulation after intravenous injection of magnetite-based dextran-coated magnetic fluid in female Swiss mice. In the first 60 min the time-decay of the nanoparticle concentration in the blood circulation follows the one-exponential (one-compartment) model with a half-life of (6.9 +/- 0.7) min. The X-band spectra show a broad single line at g approximately 2, typical of nanomagnetic particles suspended in a nonmagnetic matrix. The resonance field shifts toward higher values as the particle concentration reduces, following two distinct regimes. At the higher concentration regime (above 10(14) cm(-3)) the particle-particle interaction responds for the nonlinear behavior, while at the lower concentration regime (below 10(14) cm(-3)) the particle-particle interaction is ruled out and the system recovers the linearity due to the demagnetizing field effect alone.

Animals↗
PubMed2001

Testing life-history pleiotropy in Caenorhabditis elegans.

Much life-history theory assumes that alleles segregating in natural populations pleiotropically affect life-history traits. This assumption, while plausible, has rarely been tested directly. Here we investigate the genetic relationship between two traits often suggested to be connected by pleiotropy: maternal body size and fertility. We carry out a quantitative trait locus (QTL) analysis on two isolates of the free-living nematode Caenorhabditis elegans, and identify two body size and three fertility QTLs. We find that one of the fertility QTLs colocalizes with the two body size QTLs on Chromosome IV. Further analysis, however, shows that these QTLs are genetically separable. Thus, none of the five body size or fertility QTLs identified here shows detectable pleiotropy for the assayed traits. The evolutionary origin of these QTLs, possible candidate loci, and the significance for life-history evolution are discussed.

Animals↗
PubMed2001

Regulation of antioxidant enzyme activities in male and female rat macrophages by sex steroids.

Human and animal immune functions present sex dimorphism that seems to be mainly regulated by sex hormones. In the present study, the activities of the antioxidant enzymes total superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GSH-Px) were measured in intraperitoneal resident macrophages from adult male and female rats. In addition to comparing males and females, we also examined the regulation of these enzyme activities in macrophages by sex steroids. GSH-Px activity did not differ between male and female macrophages. However, both total SOD and CAT activities were markedly higher in females than in males (83 and 180%). Removal of the gonads in both males and females (comparison between castrated groups) increased the difference in SOD activity from 83 to 138% and reduced the difference in CAT activity from 180 to 86%. Castration and testosterone administration did not significantly modify the activities of the antioxidant enzymes in male macrophages. Ovariectomy did not affect SOD or GSH-Px activity but markedly reduced (48%) CAT activity. This latter change was fully reversed by estrogen administration, whereas progesterone had a smaller effect. These results led us to conclude that differences in the SOD and CAT activities may partially explain some of the differences in immune function reported for males and females. Also, estrogen is a potent regulator of CAT in macrophages and therefore this enzyme activity in macrophages may vary considerably during the menstrual cycle.

Animals↗
PubMed2001

[Prevalence of and factors associated with hepatitis B virus markers in a rural population of central Brazil].

OBJECTIVE: To carry out a survey of hepatitis B virus seroepidemiology in a municipality in central Brazil, on the border of two large ecosystems, the cerrado (savanna) and the Amazon River basin. METHODS: The municipality studied, Nova Mutum, is located in the north central portion of the Brazilian state of Mato Grosso. The study sample of 754 individuals included persons from families, selected at random, who were living in the municipality's urban center as well as all the individuals living in a nearby rural village. Ages ranged from 2 to 79 years. All eligible individuals were interviewed. Blood was collected and used to assess hepatitis B virus markers by enzyme-linked immunosorbent assay. RESULTS: Hepatitis B virus infection was found in 232 individuals, or 31% of them; 19 of them (3%) were HBsAg-positive. Of the 754 persons, 149 of them (20%) who reported having been vaccinated against hepatitis B and who presented anti-HBs positivity were classified as vaccine responders. With the multivariate analysis, the variables found to be associated with exposure to hepatitis B virus were having begun sexual relations, having been vaccinated against yellow fever with a needle-free jet injection gun (for the age group < 20 years), and being an immigrant from southern Brazil (> 20 years). Vaccine coverage was low among individuals older than 10 years. The largest share of susceptible individuals (74%) were found in the age group of 11 to 20 years. CONCLUSIONS: Our data suggest that hepatitis B virus vaccine coverage in Brazil should be extended to include teenagers in populations that have a low to moderate hepatitis B virus prevalence. It is likely that our results can be extrapolated to other areas of Latin America with a similar epidemiological pattern.

Adolescent↗
PubMed2000

Cellular basis of wing size variation in Drosophila melanogaster: a comparison of latitudinal clines on two continents.

We investigated the cellular basis of two extensive, continuous, latitudinal, genetic, body size clines of Drosophila melanogaster by measuring wing area and cell size in the wing blade of adult flies reared under standard, laboratory conditions. We report that the contribution of cell size to an Australian cline is much smaller than that to a South American cline. The data suggest that neither cell size nor cell number were the targets of selection, but rather wing area itself, or a trait closely related to it. We hypothesize that the differences between the continents were caused by differences in the initial pattern of genetic variation for the cell traits and/or by the direction of selection on the source populations of the clines. Despite large differences between continents in the cellular basis of the latitudinal variation, multiple regression analysis, using the individual variation within populations, showed that the relationship between cell size and cell number was changed with latitude in the same way in the two clines. The relative contribution of cell number to wing area variation increased with latitude, probably because of compensatory interactions with cell size as a consequence of the latitudinal increase in cell number. Our findings are discussed in relation to the cellular basis of evolutionary change in laboratory thermal selection lines and natural populations along latitudinal clines.

Analysis of Variance↗
PubMed1997

Genetic and environmental responses to temperature of Drosophila melanogaster from a latitudinal cline.

Field-collected Drosophila melanogaster from 19 populations in Eastern Australia were measured for body size traits, and the measurements were compared with similar ones on flies from the same populations reared under standard laboratory conditions. Wild caught flies were smaller, and latitudinal trends in size were greater. Reduced size was caused by fewer cells in the wing, and the steeper cline by greater variation in cell area. The reduction in size in field-collected flies may therefore have been caused by reduced nutrition, and the steeper cline may have been caused by an environmental response to latitudinal variation in temperature. No evidence was found for evolution of size traits in response to laboratory culture. The magnitude of phenotypic plasticity in response to temperature of development time, body size, cell size and cell number was examined for six of the populations, to test for latitudinal variation in plasticity. All characters were plastic in response to temperature. Total development time showed no significant latitudinal variation in plasticity, although larval development time showed a marginally significant effect, with most latitudinal variation at intermediate rearing temperatures. Neither thorax length nor wing size and its cellular components showed significant latitudinal variation in plasticity.

Adaptation, Physiological↗
PubMed1996

Administration of fish oil by gavage increases the activities of hexokinase, glucose-6-phosphate dehydrogenase, and citrate synthase in rat lymphoid organs.

1. The effect of administration of fish oil by gavage on key enzyme activities of glucose metabolism of the thymus, spleen, and mesenteric lymph nodes was investigated. 2. The activities of hexokinase, glucose-6-phosphate dehydrogenase, and citrate synthase in the lymphoid organs were markedly raised due to a daily administration of fish oil by gavage (0.4% of body weight). 3. These findings indicate that the therapeutic utilization of fish oil does affect the metabolism of the lymphoid organs, and possibly immune function; however, the mechanism involved remains to be investigated.

Animals↗
PubMed1995

Cellular basis and developmental timing in a size cline of Drosophila melanogaster.

We examined 20 Drosophila melanogaster populations collected from a 2600-km north-south transect in Australia. In laboratory culture at constant temperature and standard larval density, a genetic cline in thorax length and wing area was found, with both traits increasing with latitude. The cline in wing area was based on clines in both cell size and cell number, but was primarily determined by changes in cell number. Body size and larval development time were not associated among populations. We discuss our results in the context of selection processes operating in natural and experimental populations.

Analysis of Variance↗
PubMed1989

Patterns of marihuana smoking among Brazilian students.

Changes in frequency of marihuana smoking over time were investigated by interviewing forty-seven Brazilian students from São Paulo between 18 and 24 years old, of both sexes. From their report, it was concluded that the course of smoking frequency follows two predominant patterns. In one of them, the 'Stable Pattern', subjects report increasing consumption up to a peak frequency where they remain for a relatively long and stable period of time. In the other one, the 'Descending Pattern', subjects report a gradual increase up to a peak, followed by a clear decline in rate of use. Two other patterns were also detected in a small number of subjects. The diversity of patterns identified stresses the difficulty in predicting the course of marihuana smoking frequency by young people. The relationship between marihuana smoking and the use of other drugs was also investigated. The only drugs that were reported to be regularly consumed by the majority of subjects were alcohol and tobacco, while 90% of the subjects reported having tried at least one other illegal drug.

Adult↗
PubMedDate not supplied

Adaptation and constraint in the evolution of Drosophila melanogaster wing shape.

We have taken advantage of parallel instances of natural selection on body size in Drosophila melanogaster to investigate constraints and adaptation affecting wing shape. Using recently developed techniques for statistical shape analysis, we have examined variation in wing shape in similar body size clines on three continents. Gender-related shape differences were constant among all populations, suggesting that gender differences represent a developmental constraint on wing shape. In contrast, the underlying shape varied significantly between continents and shape change within each cline (i.e., between small and large body size populations) also varied between continents. Therefore, variation at these two levels presumably results from either drift or natural selection. Functional considerations suggest that shape variation between the continents is unlikely to be adaptive. However, cline-related shape change, which we show has a significant allometric component, may be adaptive. The overall range of wing shape variation, across a large range of wing size, is extremely small, and the possibility that wing shape is subject to stabilizing selection (or canalization) is discussed.

Adaptation, Physiological↗