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At least 271 records · Page 15Linked to original sources
PubMed2003

Spatial patterns of mammalian brain aging: distribution of cathepsin D-immunoreactive cell bodies and dystrophic dendrites in aging dogs resembles that in Alzheimer's disease.

Elevated levels of the lysosomal enzyme cathepsin D are found in the early stages of Alzheimer's disease (AD) and co-occur with intraneuronal tangles. The present study tested whether increases in cathepsin D would emerge during aging in another mammalian species. Regional brain patterns of cathepsin D immunostaining were compared in dogs ages 0.35 to 16 years. Accumulations of immunopositive material were evident in neuronal cell bodies in many forebrain sites in middle-age to old dogs (>/=6 years). Three types could be distinguished: (1) dense aggregates with no particular position within the cell body; (2) crescent-shaped "caps" that occupied one pole of the cell body; and (3) very dense "spikes" that extended from the cell body for variable distances into the apical dendrite; these spikes were found in only a few areas, most notably the subiculum and layer V of neocortex. The spikes appeared between ages 2 and 5 years and increased steadily with age thereafter. Spikes were found in the subiculum in the aged human brain but only infrequently; they were, however, present in large numbers in AD brains. These results established that brain aging in dogs is (1) well advanced by middle age, (2) varies markedly across regions, and (3) in at least some of its aspects (dystrophic dendrites) is prominent in areas known to exhibit pathology early in the course of AD. Combined with previous results for rats, these findings indicated that changes in cathepsin D observed in AD, in particular in the temporal lobe, reflect a generalized mammalian pattern of brain aging.

Aged↗
PubMed1980

Temporal and spatial patterns of Purkinje cell formation in the mouse cerebellum.

In an attempt to determine the time of origin and the final localization of Purkinje cells in the cerebellum, pregnant mice were injected with tritiated thymidine successively, four to six times daily, beginning on either day 10, 11, 12, 12.5, 13, or 14 of gestation, considering 6 a.m. on the day when vaginal plugs were found as day 0. Offspring were killed at 30 days of age, and serial sagittal sections of the cerebellum were prepared for autoradiography. Labeled and unlabeled Purkinje cells in the various regions of the cerebellum were counted, and unlabeled ones were considered to be formed earlier than the initiation of the injections. In the medial level of the vermis, the majority of the Purkinje cell population was formed on day 12 of gestation and a few on day 13, whereas the cells in the paravermian and hemispheric portions were formed on days 11 and 12. Thus, a slight lateromedial gradient of the time of Purkinje cell origin was demonstrated. Purkinje cells that were formed after day 12.5 were distributed more in the vermis than in the hemisphere, more in the ventral region of the vermis (lingula, ventral lobule of lobulus centralis, and nodulus) than in the dorsal region (culmen, declive, tuber, pyramis, and uvula), and deep in the vermian fissures, rather than on the surface of the lobules. These findings suggest that postnatally, early maturing regions of the cerebellum may have received many of the later formed Purkinje cells.

Animals↗
PubMed1988

Geometry and spatial patterns in Polysphondylium pallidum.

The formation of secondary sori in whorls of Polysphondylium pallidum provides an attractive model system for the study of symmetry breaking during morphogenesis. Tip-specific antibodies that permit detection of very early stages in this patterning process are available. We have found that the patterns of tip-specific antigen expression vary considerably depending on the size, shape, and developmental stage of the whorl. All of these patterns, however, are well explained by patterning models that rely on short-range autocatalysis and long-range inhibition, as exemplified by reaction-diffusion theories. In the context of reaction-diffusion, we discuss the possible effects of initial conditions, boundary conditions, and nonlinearities on the selection of patterns in P. pallidum whorls.

Models, Theoretical↗
PubMed1990

Developmental regulation and spatial pattern of expression of the structural genes for nitrogenase in the cyanobacterium Anabaena.

Depriving the cyanobacterium Anabaena of fixed nitrogen induces the differentiation of heterocysts at intervals along its filaments. To test whether the oxygen-deficient conditions believed to prevail within mature heterocysts are sufficient, in the absence of fixed nitrogen, to elicit the expression of nitrogenase, PnifHDK was fused transcriptionally to luxAB (encoding luciferase). Expression, monitored from individual cells as light emission, was localized (with a resolution of approximately 1 micron) to differentiated cells, whether or not oxygen was present. Anabaena PCC 7118 is a heterocystless mutant strain that is known to fix nitrogen when deprived of combined nitrogen under anaerobic conditions. Three lines of evidence indicate that the mutant has retained the ability to develop a pattern despite its inability to make heterocysts. First, morphologically distinct cells appear at nonrandom intervals when filaments are starved of nitrogen. Second, these cells, like heterocysts, have little or no phycocyanin-dependent fluorescence. Third, nitrogen-starved filaments fragment, with fragment lengths similar to the spacing normally seen between heterocysts. Expression of PnifHDK-luxAB was largely confined to differentiated cells in the mutant as in the wild-type strain. These results provide evidence for a causal relationship between development and transcriptional events in Anabaena.

Aerobiosis↗
PubMed1984

The effects of Janus Green B on the temporal and spatial pattern of feather germ morphogenesis.

The normal timing and appearance of feather germs was perturbed by injecting the dye Janus Green B into the amniotic fluid of chick embryos at late stage 28, prior to the first appearance of feather germs. This treatment prevented feather germ morphogenesis in some regions while elsewhere it delayed normal morphological development. The Janus Green B effect lasted for approximately 98 hours. Feather regions, which normally form epidermal placodes during the period of treatment, showed the longest delays in subsequent feather germ formation and were the most likely to remain featherless. These results suggest that the epidermal placode stage is critical for feather germ formation. Janus Green B appears to prevent feather germ morphogenesis by interfering with development prior to this critical stage. Since severely affected regions fail to recover their capacity to form feather germs, even after the period of sensitivity to the dye, a limited period of competence is suggested for feather germ formation.

Animals↗
PubMed1989

Spatial patterns of gene expression in preimplantation mouse embryos.

The distribution of total polyadenylated RNA and mRNAs from the beta-actin, fibronectin, and cytokeratin Endo A genes was examined in preimplantation mouse embryos using in situ hybridization of riboprobes to RNA in sections of embryos. Polyadenylated RNA was found in the cytoplasm of all cells of blastocyst-stage embryos, whereas the specific mRNAs displayed three distinct patterns of expression: uniform throughout the embryo (beta-actin), enriched in the inner cell mass (fibronectin), and enriched in the trophectoderm (Endo A). In eight-cell embryos, the polyadenylated RNA was more concentrated in nuclei than in the cytoplasm (as noted previously), although this was not the case in blastocysts, nor was it true for the specific mRNAs that were examined. These experiments demonstrate that there is localized gene expression in the early mouse embryo, which correlates with the formation of the trophectoderm and the inner cell mass.

Actins↗
PubMed2002

A numerical approach to the study of spatial pattern formation in the ligaments of arcoid bivalves.

In this paper, we employ the novel application of a reaction-diffusion model on a growing domain to examine growth patterns of the ligaments of arcoid bivalves (marine molluscs) using realistic growth functions. Solving the equations via a novel use of the finite element method on a moving mesh, we show how a reaction-diffusion model can mimic a number of different ligament growth patterns with modest changes in the parameters. Our results imply the existence of a common mode of ligament pattern formation throughout the Arcoida. Consequently, arcoids that share a particular pattern cannot be assumed, on this basis alone, to share an immediate common ancestry. Strikingly different patterns within the set can easily be generated by the same developmental program. We further show how the model can be used to make quantitatively testable predictions with biological implications.

Animals↗
PubMed1993

Temporal and spatial patterns of expression of c-fos, zif/268, c-jun and jun-B mRNAs in rat brain following seizures evoked focally from the deep prepiriform cortex.

Using in situ hybridization, we previously investigated (17) the regional pattern of c-fos mRNA increases in the brain following convulsive seizures elicited from a highly circumscribed epileptogenic site located in the deep prepiriform cortex. In this paper, we focus on the hippocampus and examine mRNAs encoding other immediate early genes (IEGs), namely c-jun, jun-B, and zif/268, for changes following the focally evoked seizures. Although the anatomic distribution of increases in each IEG mRNA was qualitatively comparable, the temporal analysis indicated that increases in zif/268 mRNA appeared prior to the other genes studied. Each of the mRNAs reached a maximum increase by 30 min and declined to basal levels within 3 h following seizure initiation. The data indicate that these four IEGs respond in a coordinated fashion to propagated seizure activity with increases in mRNA and, furthermore, that increased expression of all four genes appears to occur in the same cell types in the hippocampus.

Animals↗
PubMed1997

Differential spatial patterns of Fos induction following generalized clonic and generalized tonic seizures.

The expression of generalized clonic and generalized tonic seizures has been suggested to result from the activation of different and independent neuronal circuits. Using the induction of the c-fos protein (Fos) as a marker of neuronal activity, we identified brain structures that are differentially associated with the expression of electroconvulsive shock-induced generalized clonic and generalized tonic seizures. Expression of either seizure phenotype resulted in a similar bilaterally symmetrical increase in Fos immunoreactivity in many forebrain structures, including the bed nucleus of the stria terminalis, hippocampal dentate gyrus, amygdala, and piriform cortex, compared to controls. However, following tonic hindlimb extension (THE), the degree of labeling in specific thalamic, hypothalamic, and brain stem areas was significantly greater than that of either controls or animals exhibiting clonic seizures. While a greater number of neurons in the hypothalamus (e.g., ventromedial nucleus), subparafascicular thalamic nucleus, peripeduncular area, deep medial superior colliculus, dorsal and lateral central gray, and paralemniscal nuclei were robustly labeled following THE, noticeably fewer cells were immunoreactive following face and forelimb clonic seizure behaviors. These differences were also found to be independent of the stimulus magnitude. In animals stimulated with the same current intensity but expressing either of the two seizure phenotypes, the pattern of Fos induction was consistent with the seizure phenotype expressed. These results demonstrate that specific subsets of neurons are differentially activated following the expression of different generalized seizure behaviors and that activity in discrete mesencephalic and diencephalic structures is more frequently associated with the expression of generalized tonic seizures than with the expression of generalized clonic seizures.

Animals↗
PubMed1996

Spatial pattern formation during aggregation of the slime mould Dictyostelium discoideum.

Stream formation and spiral wave behaviour during the aggregation of Dictyostelium discoideum (Dd) are studied in a model based on the Martiel-Goldbeter equations for cAMP relay, combined with chemotactic motion of Dd cells. The results show that stream formation occurs if the turnover rate of intracellular cAMP is increased. This increase in the turnover rate of cAMP[in] leads to a dependence of the speed of the cAMP wave on the cell density. We propose that this dependence of wave speed on cell density is the underlying mechanism for stream formation. Besides stream formation, increasing the turnover rate of cAMP[in] also results in a spiral wave period that decreases during aggregation, a phenomenon that is commonly observed in situ. Furthermore, the dependence of wave speed on cell density is measured empirically. The speed of the cAMP wave is found to decrease as the wave travels from high to low cell density. This indicates that in situ, wave speed does depend on cell density.

Animals↗
PubMed1999

A mathematical model for outgrowth and spatial patterning of the vertebrate limb bud.

A new model for limb development which incorporates both outgrowth due to cell growth and division, and interactions between morphogens produced in the zone of polarizing activity (ZPA) and the apical epidermal ridge (AER) is developed and analysed. The numerically-computed spatio-temporal distributions of these morphogens demonstrate the importance of interaction between the organizing regions in establishing the morphogenetic terrain on which cells reside, and because growth is explicitly incorporated, it is found that the history of a cell's exposure to the morphogens depends heavily on where the cell originates in the early limb bud. Because the biochemical steps between morphogen(s) and gene activation have not been elucidated, there is no biologically-based mechanism for translating the spatio-temporal distributions of morphogens into patterns of gene expression, but several theoretically plausible functions that bridge the gap are suggested. For example it is shown that interpretation functions based on the history of a cell's exposure to the morphogens can qualitatively account for observed patterns of gene expression. The mathematical model and the associated computational algorithms are sufficiently flexible that other schemes for the interactions between morphogens, and their effect on the spatio-temporal pattern of growth and gene expression, can easily be tested. Thus an additional result of this work is a computational tool that can be used to explore the effects of various mutations and experimental interventions on the growth of the limb and the pattern of gene expression. In future work we will extend the model to a three-dimensional representation of the limb and will incorporate a more realistic description of the rheological properties of the tissue mass, which here is treated as a Newtonian fluid.

Animals↗
PubMed2001

Bimodality for plant sizes and spatial pattern in cohorts: the role of competition and site conditions.

The well-known size bimodality in cohorts of plants is revisited with methods emphasizing generic modeling. A link between bimodality and interface growth in nonequilibrium statistical physics is emphasized: the development of bimodality is understood as a phase transition like interface roughening. A specific model is proposed, inspired by gap models. It is used to illustrate generic results, to understand the end point of mean field approximation and aggregation of variables, and to discuss the role of site and competition for the development of a social hierarchy within a forest stand, in a wider ecological context.

Cohort Studies↗
PubMed1979

Spatial patterns for an interaction-diffusion equation in morphogenesis.

A certain interaction-diffusion equation occurring in morphogenesis is considered. This equation is proposed by Gierer and Meinhardt, which is introduced by Child's gradient theory and Turing's idea about diffusion driven instability. It is shown that slightly asymmetric gradients in the tissue produce stable striking patterns depending on its asymmetry, starting from uniform distribution of morphogens. The tool is the perturbed bifurcation theory. Moreover, from a mathematical point of view, the global existence of steady state solutions with respect to some parameters is discussed.

Cell Differentiation↗
PubMed2001

Temporal and spatial pattern of infant mortality in Germany after unification.

OBJECTIVES: After unification in 1990 the two parts of Germany underwent a complex process that has led to convergence of infant mortality. The pattern of change did, however, differ in east and west. This study investigates whether these differences conceal a complex pattern of heterogeneity at the regional level. METHODS: Examination of routine data on infant, neonatal and postneonatal mortality. Time trends in the 16 federal states of Germany (Länder) from 1991 to 1997 were studied using a log-linear model. RESULTS: In 1991, infant mortality was higher in almost all eastern Länder than in the west. By 1997, this east-west gap had disappeared. Over this period, infant mortality fell in all Länder but one. The decline was steepest in the east, ranging from 31% to 52%. Improvements were largely due to steep declines in both neonatal and postneonatal mortality. CONCLUSIONS: This study shows that, at the time of unification, there was an almost complete demarcation between east and west, a pattern that disappeared by 1997. There is, however, still a substantial regional variation in infant mortality that is largely determined by postneonatal mortality.

Germany↗