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At least 145 records · Page 8Linked to original sources
PubMed1979

Chinese hamster ovary cell population density affects intracellular concentrations of calcium-dependent regulator and ability of regulator to inhibit adenylate cyclase activity.

The adenylate cyclase activity [ATP pyrophosphate-lyase (cyclizing), EC 4.6.1.1] of crude Chinese hamster ovary cell membranes was inhibited 30-40% by low concentrations (6-600 ng/ml) of calcium-dependent regulator (CDR). This inhibitory effect was lost at concentrations of CDR above 600 ng/ml. The adenylate cyclase activity of membranes prepared from low population density Chinese hamster ovary cells was not appreciably altered by CDR. However, with increasing cell population density there was a significant increase in the ability of CDR to inhibit cyclic AMP formation. Further, the intracellular levels of CDR determined in the 12,000 x g supernatant and particulate fractions varied inversely with increasing cell population density. As cell number increased from 2 x 10(6) to 10 x 10(6) cells per dish the CDR concentration present in the supernatant fraction increased from 0.4 to 0.8 mug of CDR per mg of protein, while the amount of endogenous CDR associated with the particulate fraction decreased from 0.6 to 0.4 mug of CDR per mg of protein. This suggests that possible changes in the distribution of CDR between the supernatant and membrane fractions might serve as a regulatory mechanism for activities under CDR control.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1977

Population density and the rate of mental illness.

An examination of age specific rates of psychiatric admissions within Brooklyn, New York, indicated that population density may function as an intervening variable in the production of mental illness. Measures of household and family contact were found to be significantly correlated to four rates of hospital utilization. These same measures carried unique components that were also significantly related to service use. Other measures of density such as people per acre and structures per acre were found to be unrelated to the rates of psychiatric utilization. The results of this study suggest that if density does produce mental illness its likely mechanism of action will be routed through household contact.

Adolescent↗
PubMed1983

[Trial of a comparative analysis of methods for determining the population density of the black rat].

Studied was the link between the three most commonly applied methods of the deratization practice, aiming to determine the population density of rodents -- the visual method, the untoxic baits method, and the 24-hour/trap method. The three of them were practically tested and approbated in the conditions of an industrial swine-breeding complex, resp., in various productional sections. Data processing was carried out statistically through the methods of the nonparametric and the correlation analysis and the analysis of variance. It was found that the 24-hour/trap method gave the most minimal quantitative characteristics of the rodent population density, while the method making use of untoxic baits was shown to offer the most highly reproducible results. The differences between the average density values obtained by the three methods were essential. On the other hand, the discrepancies in the character of the link between the results obtained with the use of these methods were probably due to the variations in the activity of rodents. This, in turn, was associated with the use of various technologies in the individual sections, the various forms of rodent activity itself as recorded by each single one of the methods, and the varying density in these sections.

Animal Husbandry↗
PubMed1992

Changes in population density and distribution of Ixodes dammini (Acari: Ixodidae) in Wisconsin during the 1980s.

Changes in the density and distribution of Ixodes dammini, Spielman Clifford, Piesman & Corwin were assessed in Wisconsin by examining hunter-killed deer for ticks in 1981 and 1989. Deer examination sites were distributed widely across the state and included 23 sites in 1981 and 15 sites in 1989; 10 sites were visited both years. Between 1981 and 1989, I. dammini became more abundant throughout its range, and I. dammini range expanded into the southwestern portion of Wisconsin. I. dammini was not found in the eastern one-third of the state. When compared with 1981, the 1989 survey revealed significant increases in the proportion of infested deer in the southwest (Arena), higher levels of infestation of individual deer (number of ticks per individual deer) in the central west (Bangor-W. Salem), and significantly less disparity between the proportions of infested male deer and infested female deer in the north (Spooner) compared with sites farther south. These results are consistent with a pattern of I. dammini range expansion from north to south, followed by an increase in population density in the colonized areas. Dermacentor albipictus Packard was present throughout the range of I. dammini and at sites in the northeastern quadrant of Wisconsin where I. dammini was not found. The range of D. albipictus did not change between the survey years, but its population density increased significantly at sites in the north. There is no evidence for interaction between the two tick species that might affect tick distribution or population density, nor can the greater number of I. dammini found in 1989 be attributed to increased tick activity because of warmer weather; temperatures were cooler in 1989 than 1981.

Animals↗
PubMed2000

[Population density of Eucalyptus urophylla plantation].

This paper dealt with the relationships and correlation models of the population density of 5.6 years old Eucalyptus urophylla plantation with its crown width, diamter at breast height(DBH), tree height, individual standing volume, stand volume, wood properties and survital rate. The results showed that the population density remarkably affected DBH, individual standing volume, crown width, live branch height, stand volume and wood fiber width; but not affect tree height, basic density of wood, and length of wood fibers. It had a positive relationship with stand volume, live branch height and wood fibers width, and a negative relationship with DBH, individual standing volume and crown width. In addition, E. urophylla had a wide range of reasonable density. For short-rotation puplwoods, the optimum planting density of E. urophylla is 2000 individuals per hectare.

Ecology↗
PubMed1978

The estimation of neuronal population density by a robust distance method.

A new "nearest-neighbour" or "distance" method of estimating neurone population density is introduced. The method was originally developed for ecological studies but can be imported into histology without significant modification; changes in population density can be estimated by inverting the measure of area per unit cell (the so-called mean area). Its advantages include tests of randomness for the spatial distribution of the cells at issue and a robustness which can tolerate some departure from a random distribution pattern. To illustrate how the method is applied estimates of neurone density, in terms of "mean area" per cell-point, are made on a montage tracing of the human cerebellar dentate nucleus.

Cell Count↗
PubMed2000

Activity of the antimutagenic enzyme 8-oxo-2'-deoxyguanosine 5'-triphosphate pyrophosphohydrolase (8-oxo-dGTPase) in cultured chinese hamster ovary cells: effects of cell cycle, proliferation rate, and population density.

Mammalian 8-oxo-2'-deoxyguanosine 5'-triphosphate pyrophosphohydrolases (8-oxo-dGTPases), such as MTH1, are believed to play the same antimutagenic role as their bacterial homologues, like MutT. Both decompose promutagenic 8-oxo-dGTP, a product of active oxygen's attack on dGTP. It is not known how 8-oxo-dGTPase expression and function are regulated. Therefore, we investigated the effect of cell population density, proliferation rate, and cell cycle phase on 8-oxo-dGTPase specific activity in cultured Chinese hamster ovary K1-BH4 (CHO) cells. With increasing cell population density (from 30 to 95% confluence), the activity of 8-oxo-dGTPase per milligram protein decreased by 33% (p =.007 by ANOVA) while cells shifted by 9% into the G(0)/G(1) phase, with a 5% drop in cells in S phase. Importantly, inhibition of the cells' proliferation rate by calf serum deprivation caused a more dramatic 23% shift toward the G(0)/G(1) phase and a 25% drop in S phase, but had no effect on 8-oxo-dGTPase activity. Likewise, no differences in the enzyme activity were observed within cell populations of different cell cycle phases separated by centrifugal elutriation. Thus, the present results exclude cell cycle-dependent regulation of 8-oxo-dGTPase activity in CHO cells or its simple dependence on proliferation rate. The observed decrease of 8-oxo-dGTPase activity with increasing cell population density might be related to augmentation of cell-to-cell contact.

Analysis of Variance↗
PubMed2006

Geostatistical analysis of disease data: accounting for spatial support and population density in the isopleth mapping of cancer mortality risk using area-to-point Poisson kriging.

BACKGROUND: Geostatistical techniques that account for spatially varying population sizes and spatial patterns in the filtering of choropleth maps of cancer mortality were recently developed. Their implementation was facilitated by the initial assumption that all geographical units are the same size and shape, which allowed the use of geographic centroids in semivariogram estimation and kriging. Another implicit assumption was that the population at risk is uniformly distributed within each unit. This paper presents a generalization of Poisson kriging whereby the size and shape of administrative units, as well as the population density, is incorporated into the filtering of noisy mortality rates and the creation of isopleth risk maps. An innovative procedure to infer the point-support semivariogram of the risk from aggregated rates (i.e. areal data) is also proposed. RESULTS: The novel methodology is applied to age-adjusted lung and cervix cancer mortality rates recorded for white females in two contrasted county geographies: 1) state of Indiana that consists of 92 counties of fairly similar size and shape, and 2) four states in the Western US (Arizona, California, Nevada and Utah) forming a set of 118 counties that are vastly different geographical units. Area-to-point (ATP) Poisson kriging produces risk surfaces that are less smooth than the maps created by a naïve point kriging of empirical Bayesian smoothed rates. The coherence constraint of ATP kriging also ensures that the population-weighted average of risk estimates within each geographical unit equals the areal data for this unit. Simulation studies showed that the new approach yields more accurate predictions and confidence intervals than point kriging of areal data where all counties are simply collapsed into their respective polygon centroids. Its benefit over point kriging increases as the county geography becomes more heterogeneous. CONCLUSION: A major limitation of choropleth maps is the common biased visual perception that larger rural and sparsely populated areas are of greater importance. The approach presented in this paper allows the continuous mapping of mortality risk, while accounting locally for population density and areal data through the coherence constraint. This form of Poisson kriging will facilitate the analysis of relationships between health data and putative covariates that are typically measured over different spatial supports.

Cluster Analysis↗
PubMed1978

[Effect of microorganism population density on protein metabolism].

The influence of population density of yeasts Candida utilis on the protein synthesis was investigated using 14C-L-leucine. After 15--30 minutes of exposure in 14C-L-leucine, the isotope incorporation into the protein was negligible at subcritical density of cell suspension (10(4)--5X10(5) cells/mm3), but then beginning from the 10(6) cells/mm3 density, a sharp activation of incorporation was observed. With increased incubation time up to 60--120 minutes for high density suspension (more than 10(6) cells/mm3), the degradation of newly-synthesized protein is the more the higher the cell concentrations and incubation time. The changes of protein synthesis intensity seem to be not associated with the influence of such traditional factors as nutrient medium exhaustion, toxicosis, change of hydrogen ion concentration and oxygen deficiency. It is suggested that structurally functional shifts in cells initiated by intercellular interactions may underlie the dependence of protein synthesis on the suspension culture density.

Aerobiosis↗
PubMed2003

Variation in population density of horn flies (Haematobia irritans irritans) (L.) (Diptera: Muscidae) in Nellore cattle (Bos indicus).

The population density of horn flies was evaluated in the year 1998 in the municipality of Araçatuba, São Paulo Brazil, in relation to temperature and rainfall conditions. Two lots of 30 Nellore steers (Bos indicus) were used which had no insecticidal treatment and were naturally infested with horn flies. The infestations were assessed by two counting methods, i.e., the traditional estimate method and the filming method. The highest fly frequencies were recorded in spring, summer, autumn and the lowest frequencies were recorded in winter. The increase in fly number was positively correlated (P<0.05) with rainfall.

Animals↗
PubMed1984

Erythropoietin production in long-term cultures of human renal carcinoma cells. The role of cell population density.

The present studies report the maintenance of erythropoietin (Ep) production in long-term cultures of a human renal carcinoma from a patient with erythrocytosis. The renal carcinoma cells were grown and maintained in monolayer cultures for 7 months. They were serially passaged every 2-3 weeks when the cultured cells reached confluency. Ep levels measured with a sensitive radioimmunoassay in the spent culture media of the cells in the stage of semiconfluent or confluent density were less than 20 and 30 mU/ml, respectively, throughout the period of 15 successive passages. However, when the renal carcinoma cells were maintained in culture without passage after reaching confluency, Ep levels in the spent media of these cells reproducibly showed an exponential increase to more than 300 mU/ml at the time of saturation density. The importance of cell population density in Ep production by the renal carcinoma cell cultures was further confirmed by the observation that the cultures with higher seeding density reached confluency earlier and began an exponential increase in Ep production sooner than those cultures with lower seeding density.

Carcinoma, Renal Cell↗
PubMed1999

A new proposal to adjust Moran's I for population density.

We analyse the effect of using prevalence rates based on populations with different sizes in the power of spatial independence tests. We compare the well known spatial correlation Moran's index to three indexes obtained after adjusting for population density, one proposed by Oden, another proposed by Waldhör, and a third proposed by us in this paper. We find an effect of spatially correlated populations in the type I error probability on the test based on Moran's and Waldhör's indexes. We conclude also that the test proposed by Oden is powerful to test risk heterogeneity, but it has disadvantages when the interest is solely on the spatial correlation of morbidity risks. In this latter case, we recommend using our proposed test which is more powerful than the usual Moran's index applied directly to the rates.

Analysis of Variance↗
PubMed1990

Effects of larval population density on rates of development and interactions between two species of Chrysomya (Diptera: Calliphoridae) in laboratory culture.

Rearing of Chrysomya megacephala (F.) and Chrysomya rufifacies (Macquart) in pure cultures at seven different population densities (larvae per gram of liver) demonstrated an inverse relationship between density and the duration of the larval stage. In pure cultures, larval mortality rates decreased with increasing density until an optimum density was reached (8 larvae/g liver for C. megacephala and 10 larvae/g liver for C. rufifacies), then decreased directly with density. Puparial and adult weights varied inversely with density for both species in pure cultures. Internal feeding mass temperatures were above ambient temperatures for all cultures, with maximum temperatures recorded in cultures with 20 and 40 larvae/g liver for G. rufifacies and C. megacephala, respectively. In paired encounters, larvae of C. rufifacies were cannibalistic and predatory on C. megacephala larvae after the first instar. In mixed cultures of these two species, the larval mortality of C. rufifacies remained relatively stable, whereas the larval mortality of C. megacephala increased directly with population density.

Analysis of Variance↗
PubMed1997

Lack of concordance between mtDNA gene flow and population density fluctuations in the bank vole.

The genetic structure of bank voles Clethrionomys glareolus was determined from analyses of mitochondrial DNA (mtDNA) sequences, and compared with previous data on geographical synchrony in population density fluctuations. From 31 sample sites evenly spaced out along a 256-km transect in SE Norway a total of 39 distinct mtDNA haplotypes were found. The geographical distribution of the haplotypes was significantly non-random, and a cladistic analysis of the evolutionary relationship among haplotypes shows that descendant types were typically limited to a single site, whereas the ancestral types were more widely distributed geographically. This geographical distribution pattern of mtDNA haplotypes strongly indicates that the range and amount of female dispersal is severely restricted and insufficient to account for the previously observed synchrony in population density fluctuations. We conclude that geographical synchrony in this species must be caused by factors that are external to the local population, such as e.g. mobile predators.

Animals↗
PubMed1992

Population density pattern and change in the city of Riyadh, Saudi Arabia.

"This paper examines and assesses the changes in the population density pattern in the city of Riyadh, the capital of Saudi Arabia where the city has undergone dramatic changes in its physical as well as its social structure. Analysis of data revealed a decline in population density at an exponential rate from the city center with variation between city sectors and zones. The city's rapid horizontal expansion and dispersal of population is the result of factors such as increases in city population and in size and number of single family dwellings, widening of streets, rise in income and residential mobility rates, mass use of automobiles, change in family size, zoning regulations, leapfrogging, and huge governmental city development projects."

Asia↗
PubMed1981

Effect of population density on growth and development of Taenia hydatigena in dogs.

Groups of puppies were infected with either one, five, 10, 20 or 40 cysticerci of Taenia hydatigena and necropsied 70 days later. The number of worms recovered from each group was proportional to the number of cysticerci fed. Individual weights of worms decreased significantly with increasing numbers. The lengths of worms and relative numbers of pregravid and gravid proglottids also decreased with increasing population density. Gravid segments were present on some worms at all population densities.

Animals↗
PubMed2002

Effects of relative humidity, temperature, and population density on production of cuticular hydrocarbons in housefly Musca domestica L.

The production of cuticular hydrocarbons by both males and females of Musca domestica L. under very wet conditions (90% relative humidity) compared to the production at 50 and 20% relative humidity is delayed up to at least 3 days after emergence from the pupae. Eight days after emergence, however, males contain the same amounts of hydrocarbons at 90, 50, and 20% relative humidity, whereas females at 90% still possess less of these substances than at 50 and 20%. It is suggested that this is due to the fact that males, being more active than females, need more cuticular hydrocarbons to prevent water loss. No indication is found that relative humidity has a different effect on the production of the sex pheromone, muscalure [(Z)-9-tricosene] by females than on the production of the other hydrocarbons. Male and female flies produce more hydrocarbons at 35 degrees C than at 20 degrees C. On females, the relative amounts of nonacosane and methyl- and dimethylnonacosanes are significantly higher at 35 degrees C than at 20 degrees C. Female flies produce some (Z)-9-tricosene after eight generations at low population density in contrast to females at high population density, which did not produce muscalure. We suggest that because of the relatively large contribution to the total population, the properties of a small number of females are likely to be expressed sooner in the next generations of small populations than in those of large populations.

Animals↗