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PubMed1995

Childhood leukemia in metropolitan regions in the United States: a possible relation to population density?

Following recent research in Great Britain, the geographic incidence of leukemia and non-Hodgkin's lymphoma among White children in three metropolitan regions of the United States (San Francisco-Oakland, CA; Detroit, MI; and Atlanta, GA) during 1978-82 has been analyzed using census tract-specific data. There was no evidence of a general tendency for cases to cluster geographically, in contrast to results from Britain. Further, rates did not vary with median income or education levels for census tracts. However, there was a statistically significant increasing trend in incidence rates with increasing population density: relative risk for highest relative to lowest category = 1.4 (95% percent confidence interval [CI] = 1.1-2.0) for White population density, and 1.4 (CI = 1.0-2.0) for total population density. The interpretation of these findings is unclear and further investigation is required. It is possible that population density is acting as a surrogate for some virus-related factor.

Adolescent↗
PubMed1982

Population density and fertility in 22 Indian villages.

Do agriculturists in the Third World sometimes adjust to increasing population density by having fewer children? Over-time data (1961-1972) for 22 farm villages in India point to such a possibility. Cross-sectionally, villages with higher density tend to have lower fertility, even with controls for village caste composition, prior fertility, female literacy, and agricultural production. Similarly, the regression coefficient for village density is negative when the cross-sections are "pooled." Population density apparently has an inhibiting effect on fertility in these villages.

Agriculture↗
PubMed1988

Effects of light environment and population density on growth performance of male turkeys: 2. Physiological changes.

This study was designed to determine the effects of intermittent white light [2 h of light (L) followed by 2 h of dark (D) repeated six times per day] vs. diurnal white, blue, and red light (12L:12D), light intensities of 86.1 lx (high) vs. 5.4 lx (low) at high and low population densities, and season of the year on changes in the pineal, pituitary, and adrenal glands and testes of male turkeys. Pineal gland weights were unaffected by any of the factors under study. Pituitary gland weights significantly increased only in 12-wk-old males reared during the fall and winter compared with those reared during the spring and summer, but were unaffected by the imposed light environments or population density. Adrenal glands were significantly larger in males reared under high population density conditions in comparison with those reared under low density housing. The different light environments were ineffective in altering the effects of population density on adrenal response. Intermittent, high intensity light caused precocious sexual development when males were between 12 and 23 wk of age. White light and red-filtered light stimulated testes activity and seminiferous tubule development, whereas blue-filtered light was nonstimulatory.

Adrenal Glands↗
PubMed2000

Hairy chinch bug (Hemiptera: Lygaeidae) damage, population density, and movement in relation to the incidence of perennial ryegrass infected by Neotyphodium endophytes.

Studies examined hairy chinch bug, Blissus leucopterus hirtus Montandon, damage, population density, and movement in stands of perennial ryegrass, Lolium perenne L., containing various proportions of endophyte infected plants (E+). Our main objective was to determine the utility of mixtures containing E+ for management of chinch bugs. Chinch bug damage and population density decreased linearly as the proportion of E+ increased. This trend held true even when chinch bug populations were extremely high. Chinch bug nymphs emigrated more quickly from stands containing 100% E+ than they did from stands containing 50 or 0% E+, whereas adult chinch bug emigration was relatively unaffected by the proportion of E+. Our results indicate that turfgrass mixtures containing E+ can reduce chinch bug damage and population density.

Acremonium↗
PubMed1996

Epidemiology of childhood IDDM in Northern Ireland 1989-1994: low incidence in areas with highest population density and most household crowding. Northern Ireland Diabetes Study Group.

During the period 1989-1994, 462 cases of insulin-dependent diabetes mellitus were registered among children from Northern Ireland aged under 15 years. The estimated completeness of the register was 98.8% (95% confidence interval (CI) 97.7%, 99.9%). A standardised rate of 19.6 (95% CI 17.8, 21.4) per 100 000 person years was obtained, placing Northern Ireland near the top of the range of published incidence in the United Kingdom, with a rate close to that reported for Scotland. In an analysis based on 217 postcode sectors, areas with a high population density and the most material deprivation were observed to have the lowest incidence rates. After inclusion of population density in a Poisson regression analysis, the component of deprivation which was found to be most significant was household crowding. Relative to children living in areas of low population density, there was a reduced risk for children in medium (relative incidence 0.85 (95% confidence limits CI 0.67, 1.09)) and high (0.62 (95% CI 0.48,0.80)) population density areas. Similarly, relative to children living in areas with low levels of household crowding, there was a reduced risk for children in medium (relative incidence 0.73 (95% CI 0.58,0.93)) and high (0.67 (95% CI 0.53, 0.83)) levels of household crowding. Tests for space-time clustering at diagnosis and at birth were negative. A possible explanation for the differences in incidence rate observed in this study is that exposure to infections very early in childhood is a protective factor. Later infections may act as either initiators or promoters of diabetes, but the absence of space-time clustering suggests that no single specific infectious agent is responsible.

Adolescent↗
PubMed1986

Contradistinctive growth responses of cultured rat intestinal epithelial cells to epidermal growth factor depending on cell population density.

The growth response of cultured rat intestinal epithelial (RIE-1) cells to epidermal growth factor (EGF) depends on the cell population density. EGF stimulated the proliferation of RIE-1 cells in dense cultures, but inhibited the proliferation of cells growing at low population densities. In contrast, insulin enhanced RIE-1 cell growth irrespective of the population density. The tumour promoter 12-0-tetradecanoylphorbol 13-acetate (TPA), like EGF, inhibited the proliferation of low-density RIE-1 cells, but differed from EGF in that it did not stimulate the growth of dense cultures.

Animals↗
PubMed2000

Female house mice develop a unique ovarian lesion in colonies that are at maximum population density.

Colonies of house mice reach maximum population density in 120-180 days, irrespective of cage size and initial number of colonizing animals. Reproduction ceases because the females become aggressive and unreceptive to mating. The aggressive behavior is correlated with elevated levels of testosterone (T) and corticosterone (B) (Chapman et al., Phys Behav 64:529-533, 1998). In two of seven strains of mice, females developed ovarian lesions. The occurrence of the lesion in one strain was correlated with the age of the animal and duration of the study. In the second strain, cage size was the determining factor. Lesioned ovaries weighed significantly more than nonlesioned ovaries. The lesion consisted of accumulations of luteal membrane and organelle fragments, and other cellular debris, suggestive of incomplete and prolonged luteolysis. Electron microscopic (EM) analyses revealed the presence of deposits of permanganate-resistant congophilic amyloid fibrils in the intima and smooth muscle cells of luteal thecal arteries. Population females had thymus glands and uteri that weighed significantly less than the same organs from females housed in the breeding colony, whereas the adrenal glands from the population females weighed significantly more. It is proposed that the female aggression is due to high levels of T. It is also proposed that the high levels of B suppress the immune cells involved in normal luteolysis and contribute to the incomplete and prolonged luteolysis.

Aggression↗
PubMed1999

[Estimation of the population density and its significance in gene geography].

A factor of the association between gene geographical data and populations of the mapped region was analyzed. This allowed for correction of the equations for the major statistical parameters of gene geographical maps (mean, variance, etc.) and gene geographical methods of estimating the spatial nonstationarity of data within a mapped region. The proposed approach is based on the use of the population density in a mapped region as a factor reflecting the anisotropy of the geographical space. The population density of the North Eurasian indigenous populations was mapped, and the application of the resulting map was illustrated with an example.

Anisotropy↗
PubMed2004

Population density regulates Drosophila synaptic morphology in a Fasciclin-II-dependent manner.

Genetic analysis of the Drosophila larval neuromuscular junction has identified some of the key molecules that regulate synaptic plasticity. Among these molecules, the expression level of Fasciclin II (FasII), a homophilic cell adhesion molecule, is critically important for determining the final form of the neuromuscular junction. Genetic reduction of FasII expression by 50% yields more elaborate nerve terminals, while a greater reduction in expression, to 10% of wild-type, yields a substantial reduction in the nerve terminal morphology. Importantly, regulation of FasII expression seems to be the final output for several genetic manipulations that transform NMJ morphology. In an effort to understand the importance of this regulatory pathway in the normal animal, we have undertaken studies to identify environmental cues that might be important for initiating FasII-dependent changes in synaptic plasticity. Here we report on the relationship between larval population density and synaptic morphology, synaptic strength, and FasII levels. We raised Drosophila larvae under conditions of increasing population density and found an inverse exponential relationship between population density and the number of synaptic boutons, the number of branches, and the length of branches. We also observed population-dependent alteration in FasII levels, with lower densities having less FasII at the synapse. The correlation between density and morphological change was abrogated in larvae constitutively expressing FasII, and in wild-type larvae grown on soft culture medium. Together these data show that environmental cues can induce regulation of FasII. Interestingly, however, the quantal content of synaptic transmission was not different among the different population densities, suggesting that other factors contribute to maintaining synaptic strength at a defined level.

Animals↗
PubMed2002

Protein kinase Cepsilon mediates PMA-induced growth inhibition of low population density NIH 3T3 fibroblasts.

Phorbol 12-myristate-13-acetate (PMA), a potent tumor promoter and activator of most protein kinase C (PKC) isotypes, was found to significantly inhibit the growth of low population density (1-5% confluency) NIH 3T3 cells. Higher cell population density (above 10% confluency) provided protection from this growth inhibitory effect of PMA. PMA-induced growth arrest is accompanied by an elevation in the level of p21(Cip1) protein, along with cell cycle arrest at the G1/S transition. Activation of PKC is required for this growth inhibitory response since the pan PKC inhibitor GF109203 blocked this effect of PMA. However, the classical PKC inhibitor Gö6976 had no effect, strongly suggesting the involvement of novel PKC isotypes (delta and/or epsilon). Overexpression of PKCepsilon, but not PKCdelta, was found to potentiate PMA-induced growth inhibition. Overexpression of a kinase-inactive dominant-negative mutant of PKCepsilon (K437R) decreased the growth inhibitory effect of PMA and also blocked the PMA-induced increase in the level of p21(Cip1) protein. Taken together, these results indicate that PMA has a cell population density-dependent effect on the growth of NIH 3T3 cells and that the PMA growth inhibitory effect at low cell population density is mediated through activation of PKCepsilon.

3T3 Cells↗
PubMed1988

Population density functions: a differential equation approach.

"This paper introduces a new mathematical technique to describe population density functions. Two length scales, which characterize the variation of these density functions within a region, are identified. A differential equation is derived and asymptotic solutions obtained. Two specific techniques, the method of matched asymptotic expansions and the method of multiple scales, are introduced and illustrated by application to population densities at both the metropolitan and regional levels."

Demography↗
PubMed1986

Modulation of the population density of identifiable epidermal Langerhans cells associated with enhancement or suppression of cutaneous immune reactivity.

The epidermis on the backs or ears of DBA/2 mice treated for 7 days with a 20% concentration of monobenzyl ether of hydroquinone (MBEH) had a significantly greater population density of ATPase- and Ia-positive cells compared with control mice treated with diluent. There was no decrease or increase in ATPase- or Ia-positive cells at sites distal from the treated tissue. This increase in population density of Langerhans cells was associated with a significant increase in functional afferent immune reactivity measured by allergic contact hypersensitivity. We also found evidence for enhanced efferent immune reactivity. Animals treated on the ears for 7 days with MBEH were sensitized to DNFB on untreated back. MBEH treated ears with more Ia-positive Langerhans cells demonstrated a threefold greater increase in swelling after the DNFB challenge than the control mice. Results of other studies suggest that the afferent and efferent enhanced immune reactivity produced by MBEH are local effects. We postulated that MBEH produced its effects by activating the oxidation of arachidonic acid (AA) to prostaglandins. To test this, we applied AA to mouse skin. AA has a biphasic effect on epidermal Langerhans cells: in low doses it increases their number; in high amounts it decreases the number of identifiable cells with either the Ia or the ATPase technique. An increased population density of identifiable epidermal Langerhans cells induced with AA was correlated with an increase in afferent and efferent immune reactivity. In contrast, reduction of Langerhans cells with larger amounts of AA suppress the afferent and efferent limb of the immune response. DNFB applied to skin with decreased Langerhans cell density from AA induced a state that mimics immune tolerance. The findings are significant because we report the only method to either increase or decrease the population density of Langerhans cells: and to modulate up or down the afferent or efferent limbs of the cutaneous immune response. Our results also suggest that the Langerhans cell may be involved in the efferent limb of the immune efferent response. These effects may be modulated in part by products of AA metabolism.

Adjuvants, Immunologic↗
PubMed1997

Seasonality of birth in schizophrenia: the effect of regional population density.

It has been suggested that winter birth in urban areas may be associated with an increased risk of schizophrenia. Data on 4139 patients with a hospital diagnosis of schizophrenia were obtained from a survey of public departments of psychiatry in metropolitan France. Place of birth was classified according to the administrative subdivision of French territory into 95 'départements'. Density of population in the decade and in the département of birth was identified using successive census data. A 20% excess (OR, 1.20; 95% CI, 1.03-1.40; p = 0.02) of winter births (January-March) was found among patients born in highly densely populated areas (> 136 inhabitants/km2) compared to those born in other areas. These results suggest that seasonal early environmental risk factor(s) linked to schizophrenia predominantly operate in urban areas.

Adolescent↗
PubMed1993

Relation between population density and cancer incidence, Illinois, 1986-1990.

Many investigators have examined urbanization gradients in cancer rates. The authors used incidence data for 1986 through 1990 from the Illinois State Cancer Registry, a large, population-based incidence registry, to identify race-specific, urban-rural trends in cancer rates. Using population density, they categorized an urbanization gradient into four groups. Five-year, average annual age-adjusted, site-specific incidence rates were calculated for all sex-race strata within each population density group. Monotonic and statistically significant cancer incidence trends across all race-sex groups were found for cancers of the esophagus, liver, lung, female breast and cervix, male prostate, nervous system, non-Hodgkin's lymphomas, and all cancers combined. No trend was observed for blacks that was not also seen for whites; however, significant trends for cancer of the pancreas and Hodgkin's disease were seen for whites but not for blacks. Colon cancer in males was the only sex-specific trend in cancer that can occur in both sexes. Analytic studies for sites with consistent urban-rural trends across all race-sex groups may be fruitful in identifying the aspect of population density, or other unmeasured factor, that contribute to these trends.

Female↗
PubMed2001

Population density methods for large-scale modelling of neuronal networks with realistic synaptic kinetics: cutting the dimension down to size.

Population density methods provide promising time-saving alternatives to direct Monte Carlo simulations of neuronal network activity, in which one tracks the state of thousands of individual neurons and synapses. A population density method has been found to be roughly a hundred times faster than direct simulation for various test networks of integrate-and-fire model neurons with instantaneous excitatory and inhibitory post-synaptic conductances. In this method, neurons are grouped into large populations of similar neurons. For each population, one calculates the evolution of a probability density function (PDF) which describes the distribution of neurons over state space. The population firing rate is then given by the total flux of probability across the threshold voltage for firing an action potential. Extending the method beyond instantaneous synapses is necessary for obtaining accurate results, because synaptic kinetics play an important role in network dynamics. Embellishments incorporating more realistic synaptic kinetics for the underlying neuron model increase the dimension of the PDF, which was one-dimensional in the instantaneous synapse case. This increase in dimension causes a substantial increase in computation time to find the exact PDF, decreasing the computational speed advantage of the population density method over direct Monte Carlo simulation. We report here on a one-dimensional model of the PDF for neurons with arbitrary synaptic kinetics. The method is more accurate than the mean-field method in the steady state, where the mean-field approximation works best, and also under dynamic-stimulus conditions. The method is much faster than direct simulations. Limitations of the method are demonstrated, and possible improvements are discussed.

Cell Count↗