Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “branching process”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 343 records · Page 19Linked to original sources
PubMed1999

Immunocytological localization of dopamine in the guinea pig retina.

We examined dopaminergic neurons in the guinea pig retina; antisera against tyrosine hydroxylase (TH), dopamine beta-hydroxylase (DBH), phenylethanolamine N-methyltransferase (PNMT) and an antiserum against gamma-aminobutyric acid (GABA) were used. In the present study, two types of amacrine cells were labeled with an anti-TH antiserum. However, no DBH and PNMT immunoreactivities were seen. The type 1 cell had a larger-sized soma located in the inner nuclear layer with processes ramifying mainly in stratum 1 of the inner plexiform layer (IPL). The type 2 cell had a smaller-sized soma and processes branching in stratum 3 of the IPL. The mean densities were 56.4 +/- 11.5/mm2 for the type 1 cell and 166.6 +/- 30.3/mm2 for the type 2 cell. Double immunocytochemistry using an antiserum against GABA revealed that while none of the type 1 cells showed GABA immunoreactivity, all of the type 2 cells displayed GABA immunoreactivity. Our results suggest that, in the guinea pig retina, the type 1 amacrine cells are pure dopaminergic and the type 2 cells are dopaminergic elements that use GABA as their second transmitter.

Age Factors↗
PubMed2006

The probability of treatment induced drug resistance.

We propose a discrete time branching process to model the appearance of drug resistance under treatment. Under our assumptions at every discrete time a pathogen may die with probability 1-p or divide in two with probability p. Each newborn pathogen is drug resistant with probability mu. We start with N drug sensitive pathogens and with no drug resistant pathogens. We declare the treatment successful if all pathogens are eradicated before drug resistance appears. The model predicts that success is possible only if p<1/2. Even in this case the probability of success decreases exponentially with the parameter m=muN. In particular, even with a very potent drug (i.e. p very small) drug resistance is likely if m is large.

Drug Resistance, Microbial↗
PubMed1985

Biomicroscopy of surface deposits resembling foreign-body giant cells on implanted intraocular lenses.

Deposits resembling foreign-body giant cells, which can be seen on specular reflex slit-lamp examination, were studied in vivo with a wide-field specular microscope using a low-power dipping cone lens in three cases of posterior chamber lens implantation. The deposits seen as iris pigment on routine examination showed two types of cell-like figures: round, bipolar or ameboid small figures with long branching processes and round, oval, or bizarre large figures. The large cell type had the pigment particles at the central or paracentral area and vacuole-like structures adjacent to the pigment particles. The specular photomicrographic characteristics were similar to those of fibroblast-like cells and foreign-body giant cells, which had been shown on the surfaces of extracted implanted intraocular lenses by the lens implant cytology technique.

Aged↗
PubMed1988

The microaerophilic respiration of Campylobacter mucosalis.

A model is proposed for the respiratory adaptation to falling oxygen concentration during growth of the microaerophilic bacterium Campylobacter mucosalis. During the early stages of growth, the oxidation of formate is a two-stage branched process involving the production of H2O2 followed by its peroxidatic removal. In later stages of growth, at lower oxygen concentrations, the predominant electron flow is linear to a membrane-bound cytochrome-c oxidase which reduces O2 directly to H2O. Several components of this model have been investigated. H2O2 was produced during formate oxidation and accumulated when electron transfer to the cytochrome-c peroxidase was inhibited. A cytochrome c-553, of the Class 1 types, was purified and shown to be the specific electron donor to both the peroxidase and the membrane-bound oxidase. The levels of this cytochrome c and of the peroxidase were higher in cells harvested early in growth. In later stages of growth, the activity of the membrane-bound oxidase increased. Proton pumping across the membrane was detected with either H2O2 or oxygen as terminal electron acceptor. The novel energy-conserving role of H2O2 in this catalase-negative bacterium is discussed in relation to its microaerophilic nature.

Adaptation, Physiological↗
PubMed1976

A Golgi study of neuronal types in the neostriatum of monkeys.

Examination of the nestriatum of monkeys prepared by the Golgi-Kopsch perfusion method revealed the presence of at least 6 neuronal types. The spiny type I is medium size with a high density of dendritic spines. The axon extends well beyond the dendritic field and gives off many collaterals. The spiny type II is either medium or large size, has long thick dendrites with a relatively low density of spines, and an axon similar to that of the previous type but with fever collaterals. The aspiny type I is medium size with varicose dendrites and a thin axon arborizing in the immediate vicinity of the soma. The aspiny type II is large, with many thick and thin varicose dendrites. The aspiny type III is medium size with smooth dendrites and an axon ramifying profusely within the dendritic field. The neurogliform cell is small with many branching processes. Findings indicate that the neostriatum has 2 distinct types of spiny neurons with long axons (spiny I and II), some of which may contribute to the efferent system. There are also 2 (aspiny I and III) or perhaps as many as 4 categories (aspiny I, II, III and neurogliform) of typical Golgi type II cells. Large neurons belong to 2 separate populations, one with dendritic spines and a long axon (large version of spiny II), and one with varicosities and presumably a short axon (aspiny II). A realistic interpretation of neurophysiologic data on the neostriatum must take into account all cell types instead of the current view of considering it as a pool of interneurons with few output cells.

Animals↗
PubMed1980

Identification of the interplexiform cell in the dace retina by dye-injection method.

The responses of interplexiform cells in the dace retina were recorded intracellularly and identified morphologically. The response pattern closely resembles the response of bipolar cells and amacrine cells (on- and off-types). Morphologically, the perikaryon of most of these cells lies in the amacrine cell layer, and is usually large in size. Distal and proximal processes arise from the soma directly. The distal process ramifies and extends widely in the outer plexiform layer, but does not make contact with receptor terminals. The proximal process branches and extends widely in the inner plexiform layer. The majority of these cells resembles the dopaminergic interplexiform cells, but a few resemble the glycinergic interplexiform cells in the goldfish retina.

Animals↗
PubMed1981

The noradrenergic system in cultured aggregates of fetal rat brain cells: morphology of the aggregates and pharmacological indices of noradrenergic neurons.

Spherical aggregates formed rapidly in culture by re-aggregation of trypsin-dissociated brain cells from the 17-day-old fetal rat. Over about 10 days in initially random distribution of cells evolved into a 3-layered arrangement; cells with characteristics of neurons were found largely in the intermediate layer. The survival of neuronal and glial cell types was evaluated histologically and verified by electron microscopy, which revealed synaptic and myelin structures that rapidly increased in number after 18 days in culture. Levels of norepinephrine (NE) and dopamine (DA) reached peaks of 9.5 and 4.4 ng/mg protein, respectively, at culture day 21. Uptake of [3H]NE paralleled these amine levels and was blocked by desipramine or pretreatment with either reserpine or 6-OH-DA. Autoradiographs of aggregates labeled with [3H]NE showed a high density of silver grains over cells, apparently neurons, with branching processes traced for 120 micrometer. Previously accumulated [3H]NE was released under depolarizing conditions (high [K+] or vertridine) only in the presence of Ca2+. Release was induced to a lesser extent by kainic greater than glutamic acid. Thus, such aggregates appear to contain catecholaminergic neurons capable of synthesis, uptake and release of NE. The time course of development of these functions supports suggestions that aggregate preparations might be useful in studying neurochemical or morphological aspects of brain development and function in vitro.

Animals↗
PubMed1982

Astrocyte cultures from adult rat brain. Derivation, characterization and neurotrophic properties of pure astroglial cells from corpus callosum.

It has not as yet been routinely possible to derive primary cultures of glial cells from adult rat brain tissue even when adopting strategies that have proven successful with perinatal tissue. We now report that in response to a surgical lesion and a period of postoperative 'priming' in vivo, proliferating cultures of astroglial cells can be derived from the normally quiescent glia of the corpus callosum region of the adult rat brain. In such cultures the predominance of astroglia and the virtual absence of oligodendroglia and neurons has been established by the use of a variety of cell-type specific antisera. Fibroblasts, the only other cell type identified, when not numerous could be successfully eliminated by treatment of the cultures with anti-Thy-1 antibodies and guinea pig complement. Pure astroglial cells from adult brain have been sub-cultured and maintained for up to 4 months in vitro, providing suitable quantities of cells for studies on the trophic interaction between glia and neurons. In long-term culture the adult astrocytes maintain a flattened undifferentiated morphology but readily assume a stellate shape with long branching processes upon the addition of a crude homogenate from bovine pituitary.

Animals↗
PubMed1988

The mechanism of cytosine arabinoside toxicity on quiescent astrocytes in vitro appears to be analogous to in vivo brain injury.

Neuronal cultures derived from the septal diagonal band region of the embryonic rat brain and grown in a chemically defined medium contained a very small number of contaminating astroglial cells. During the first week in culture, these cells were well dispersed in the form of a single isolated cell with fine fibrous branched processes. Treatment with 4 microM cytosine arabinoside for 24 h failed to kill these astrocytes (most probably present in quiescent form), as judged by glutamine synthetase activity and glial fibrillary acidic protein-positive cell count. On the other hand, the exposure of cultures to cytosine arabinoside resulted in a marked increase in choline acetyltransferase enzyme activity. The overall results, together with our previous findings, are consistent with the proposal that a brief exposure to a relatively low concentration of cytosine arabinoside induces quiescent astrocytes to produce a large quantity of a neurotrophic factor that is involved in the regulation of cholinergic cells.

Animals↗
PubMed1991

Binding sites for 125I ET-1, ET-2, ET-3 and vasoactive intestinal contractor are present in adult rat brain and neurone-enriched primary cultures of embryonic brain cells.

Binding sites for iodinated endothelin (ET)-2, ET-3 and vasoactive intestinal contractor (VIC) were visualised in the adult rat brain using quantitative autoradiography and have a similar anatomical distribution to that of ET-1 and sarafotoxin S6b. Highest densities of binding sites for all 5 labelled peptides were present in the granular layer of the cerebellum. Cross-competition experiments show that at a concentration of 1 microM, unlabelled ET-1, ET-2, ET-3, VIC and sarafotoxin S6b were able to compete for the binding sites detected by each of the iodinated peptides. Binding sites for the ET isoforms were also present after 7-14 days in vitro in neurone-enriched primary cultures derived from embryonic rat cerebellum (16-18 days gestation) in which more than 90% of cells stained with an anti-neurofilament antibody. Using micro-autoradiography to detect the binding sites, an average of 14% of cells in these cultures with a diameter of 9.2 +/- 0.6 microns were associated with high silver grain densities (greater than 400 grains/100 microns). With some of these cells, silver grains were localised over cell bodies and branching processes characteristic of a neuronal phenotype. A second group of cells with high grain densities were more difficult to classify using morphological criteria and may be non-neuronal. The density of silver grains over the remaining cells was low (less than 20 grains/100 microns 2) and was similar to that measured in nuclear emulsion overlying cultures used to assess non-specific binding. These results indicate that binding sites for all ET peptides are present in both adult rat brain and embryonic cerebellar cultures.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1996

The effect of basic fibroblast growth factor on glutamate-injured neuroarchitecture and arachidonic acid release in adult hippocampal neurons.

During development in culture, basic fibroblast growth factor (bFGF) protected immature primary hippocampal neurons against glutamate-induced neurotoxicity. We investigated the effects of bFGF on mature, differentiated rat hippocampal neurons cultured for 10-12 days after an 8-min exposure to 500 microM glutamate. Seven days post-injury, hippocampal cells demonstrated severe reductions in cellular viability and axonal and dendritic outgrowth, which were accompanied by a marked increase in [3H]arachidonic acid (ARA) release from prelabelled neurons. bFGF applied post-injury attenuated cell death and cytoarchitectural destruction at all concentrations used (500 pg/ml, 1, 10, 20 ng/ml). However, neurite elongation and branching processes were only significantly protected by 10 ng/ml bFGF. [3H]ARA release decreased in a dose-related fashion within a concentration range of 1-10 ng/ml bFGF. 20 ng/ml bFGF was not superior to 10 ng/ml bFGF. Therefore, bFGF's neurotropic actions appear to be concentration-dependent. Our data suggest that bFGF applied post-injury may have a neuroprotective potential for mature, differentiated, completely polarized hippocampal neurons.

Animals↗
PubMed1983

Cytoskeletal proteins in cultured secretory cells from rat pituitary.

Cultured cells from female rat pituitaries were examined by immunofluorescence microscopy for the presence of pituitary hormones and for cytoskeletal proteins. The cells attach well to glass coverslips and, when well-dispersed initially, develop networks of branching processes. Their cytoplasm appears granular and shows granular fluorescence when the cells are permeabilized and treated with antisera to pituitary hormones. The cultures contain fibroblasts which are morphologically distinct and much larger than the secretory cells. Consequently, they provide an internal control for cytoskeletal proteins in nonsecretory cells. Fibroblasts have relatively prominent stress fibres. By contrast, the secretory cells have a diffuse cytoplasmic distribution of all cytoskeletal proteins investigated. One cell type, the gonadotrope, which secretes luteinizing hormone and follicle-stimulating hormone, was examined in particular detail.

Actinin↗
PubMed1989

Immunological reactions induced by intracerebral transplantation: evidence that host microglia but not astroglia are the antigen-presenting cells.

The immunological reactions to embryonic cerebellar xenografts (n = 16) and allografts (n = 8) in host rat brain were studied after 2, 4, and 6 weeks of survival and compared to a control group consisting of 10 rats with isografts. Indirect immunofluorescence was performed on fresh frozen brain sections using antibodies against antigen presenting cells (Ia/Ox-6+ cells) and T helper (W3/25+) cells. Massive infiltrations of both cell types were found within xenografts. Ia antigen was present in the walls of small vessels near the transplant as well as in the ventricles on supra- and subependymal cells. In host tissue surrounding the grafts, Ox-6+ immunoreactivity was also observed in a population of cells ranging from an irregular rod-like shape with short branching processes to more rounded cell bodies with retracted processes. The appearance of these cells was characteristic of microglia. These cells were GFAP-negative. These cellular reactions were associated with rejection of the grafts. In contrast, the allografts survived, but nevertheless cells expressing Ox-6+ and to a lesser extent W3/25+ immunoreactivity were found along the injection needle tract and in damaged host tissue surrounding the grafts. No Ox-6+ perivascular infiltrations were seen. Some staining was also found within the allografts, mainly associated with damaged tissue. Ox-6+ ramified cells were also observed. Both Ox-6+ and W3/25+ immunoreactivity decreased with the time of survival. Host and donor GFAP-positive astrocytes did not express Ox-6+ molecules, and therefore probably were not involved in presenting antigen to effector cells. The control isografts also survived very well, but nevertheless Ox-6+ and less widespread W3/25+ cells were present in surrounding injured host tissue. Ox-6+ perivascular infiltration was not found in the host brain of animals with isografts. Ox-6+ and W3/25+ immunoreactivities were present primarily in graft areas that appeared damaged, often closely associated with injured host tissue. These results indicate that the process of implantation of grafts and associated brain injury induces enhanced Ia/Ox-6+ immunoreactivity, primarily on microglia in brain parenchyma surrounding grafts, and suggest that host microglia may substantially contribute to the initiation of immune reactions against intracerebral grafts. Despite this predisposition to an immunological response, only in the case of xenografts did these reactions, with the addition of Ox-6+ perivascular cuffing and cell infiltrations within the grafts, lead ultimately to graft rejection.

Animals↗
PubMed1978

Robustness of life table methods in large populations--a study by computer simulation.

The robustness of the product life table estimator of the survival function was studied for large populations under perturbations in the age distribution, changing levels of mortality and changing patterns of fertility. A macrosimulation system, based on a class of stochastic population models called generalised age-dependent branching processes, was used to carry out the numerical investigations. Aside from drastic perturbations in the age distribution and changes in levels of mortality, the product life table estimator of the survival function was found to be robust in large populations, under a variety of conditions.

Age Factors↗
PubMed1989

Fixation probabilities for advantageous mutants: a note on multiplication and sampling.

If the average number of gametes produced by the individual is small, as may be the case for haploid organisms, then sampling with and without replacement can lead to considerable differences in the fixation probabilities of mutant alleles. As a function of the population size N, these probabilities converge quickly to the survival probabilities given by branching processes with Poisson or Bernoulli offspring distributions.

Biological Evolution↗
PubMed1992

The effect of preferential mixing on the growth of an epidemic.

The spread of infection in a community stratified into classes, where individuals have a preference for either within- or between-class contact, is discussed. The effect of such classification is assessed through the comparison of heterogeneous epidemic models with corresponding homogeneous models. Stratification of the community is modeled via a multitype branching process approximation to the epidemic. This allows us to conveniently study its effect through such quantities as the epidemic threshold parameter and the probability of a major outbreak. Attention is focused on the model of May and Anderson; however, a number of other heterogeneous structures reflecting preferential mixing are also studied.

Communicable Diseases↗
PubMed1978

Myxoma of the mandible--a fibroblastic tumor.

A case of myxoma of the mandible is described. The tumor was examined by both light and electron microscopy. Histochemistry showed an abundant acid mucopolysaccharide stroma, embedded in which were stellate cells with branching processes. Ultrastructurally, these cells were seen to be fibroblasts. Occasional myofibroblasts were seen in the tumor. No odontogenic epithelium was identified, and this component was not thought to be important in the histogenesis of the tumor.

Adolescent↗
PubMed1983

Some stochastic models for plasmid copy number.

Some stochastic models for the copy number of plasmids in a cell line are studied. When considering the behavior of copy number in the whole cell line, the theory of multitype branching processes is appropriate. Attention is paid to the cure rate in the cell line, and the asymptotic fractions of cells containing a given number of plasmids. These quantities are used to compare the models numerically.

DNA Replication↗