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PubMed1985

Effect of interferon tested in a model system for organogenesis.

The effect of interferon (IFN) on growth and differentiation was examined in a model system for organogenesis--the embryonic murine kidney and its components. A relatively weak, transient inhibition of thymidine incorporation was recorded during the most active period of DNA synthesis in the presence of IFN at a concentration of 10(5) U/ml. No interference with cytodifferentiation or organogenesis could be shown by the end-point criteria used.

Animals↗
PubMed1972

Polar Indole-3-acetic Acid Diffusion in Nonliving and Model Systems.

Polar indole-3-acetic acid movement was observed in killed plant segments and in artificial model systems. The polar diffusion of indole-3-acetic acid was observed in tissue killed by chemical or physical means in an agar-plant system and in a multicelled Plexiglas dialysis chamber containing hypocotyl tissue gradients or gradients of anion exchange material.It was suggested that polar indole-3-acetic acid movement in excised segments may be a reflection of the diffusion of indole-3-acetic acid through asymmetric gradients of materials with binding characteristics somewhat similar to ion exchange.

Journal Article↗
PubMed1983

The development, using poly(Hg-U) in a model system, of a new method to visualize cytochemical hybridization in fluorescence microscopy.

The development, using a model system, of a new method for the detection of cytochemical (in situ) hybrids is described. The method is based on the mercuration of nucleic acids with mercuric acetate. To facilitate hybridization, the acetate ligand is replaced by the CN- ion. In the hybrids formed, the CN- is exchanged for trinitrophenyl(TNP)-glutathione. The TNP-glutathione is subsequently detected by indirect immunofluorescence using anti-TNP antibodies. The feasibility of the approach was investigated using Sepharose- or Sephadex-bound poly(A) and mercurated poly(U). Poly(Hg-U) did hybridize with poly(A)-Sepharose, provided that the acetate ligand was replaced with CN-. The TNP-glutathione hapten thus synthesized bound effectively to mercury-Sepharose but not to amino-Sepharose when the reaction was performed in the dark. Furthermore, binding of TNP-glutathione to Sephadex-bound poly(A) . poly(HG-U) hybrids was detectable with indirect immunofluorescence using anti-TNP antibodies. The fluorescence intensity measured was dependent on the amount of poly(Hg-U) present and on the dilution of the antibody. Nonspecific binding was very low. Calibration of the number of fluorescein molecules found after the complete reaction was performed with fluorescein isothiocyanate-labeled poly(U). It was determined that one fluorochrome molecule per two nucleotides had been obtained, in close agreement with the theoretically expected number. The sensitivity of the method, when applicable to microscopic preparations, is comparable to in situ hybridization with 3H-labeled nucleic acids with a specific activity of 4 x 10(8) dpm/micrograms (two 3H-isotopes per nucleotide) and an exposure time of 1 day. Extension of the method to the cRNA-DNA system and its application to microscopic preparations is under investigation.

Chemical Phenomena↗
PubMed2002

Profiling of drugs for membrane activity using liposomes as an in vitro model system.

The increasing size of chemical libraries being analyzed by high-throughput screening results in a growing number of active compounds that need to be assessed before moving forward in the drug development process. As a consequence, more rapid and highly sensitive strategies are required to accelerate the process of drug discovery without increasing the cost. Due to the fact that significant numbers of compounds from combinatorial libraries are hydrophobic in nature, approaches are needed to evaluate the potentialfor these compounds to interfere with the functions of biological membranes. The liposome system was used to detect agents that act as follows: (i) ionophores able to induce specific ion permeability, e.g., valinomycin for K+ and protonophoric uncouplers for H+; (ii) ion antiporters which exchange H+ for other ions, e.g., nigericin; (iii) agents that form low specificity ion channels in the membrane, e.g., gramicidin; and (iv) detergents and other membrane-disrupting agents. We propose using this liposome assay during the drug development process to identify compounds that have membrane activity and, as a consequence, produce a biological effect by altering the physico-chemical properties of the cell membrane rather than interacting with a protein target. Screening of a representative set of biologically-active compounds (198) indicated that the majority of systemic antimicrobial drugs, but not topical drugs, lack membrane activity in this model system.

Animals↗
PubMed1995

A soft systems approach to designing an information system model to be used as a tool support in the prevention and control of sexually transmitted diseases in a health jurisdiction of Mexico.

The purpose of this work is to present the preliminary results of research in progress on the design of an information system model that is capable of supporting prevention and control activities related to sexually transmitted diseases (STD) in a Mexican health jurisdiction. The project is being developed in the following five phases: 1) informetric indicators on the prevention and control of STD; 2) information flow models representing the access and use of information by the actors involved in the activities; 3) system analysis; 4) system design; and 5) implementation. Bibliometric/scientometric techniques have been applied to conduct the first phase of the project. A soft systems approach is to be conducted throughout phases 2-5. Austin and Kendall and Kendall criteria are to be used for system analysis, design, and implementation. Expected products and benefits include: a) a bibliographic database on the prevention and control of STD in Mexico; b) science policy indicators to improve decision making; c) an information system model/prototype; and d) the development of the soft systems methodology, as applied to improving information-problem-situations in a health system.

Databases, Bibliographic↗
PubMed2000

Sorting and transport in C. elegans: aA model system with a sequenced genome.

In the past few years, yeast and cultured cells have been the model systems of choice for the study of protein sorting and transport. Recently, there has been a surge in research in these areas in Caenorhabditis elegans, with advances in experimental techniques and genomics. New in vivo assays that monitor endocytosis and neuronal transport have been used to delineate roles for several genes in these processes.

Animals↗
PubMed2002

Brain tumor invasion model system using organotypic brain-slice culture as an alternative to in vivo model.

PURPOSE: The primary cause of local recurrence and therapeutic failure in the treatment of malignant gliomas is the invasion of tumor cells into the surrounding normal brain. While it is known that malignant gliomas infiltrate diffusely into regions of normal brain, it is frequently very difficult to unequivocally identify the solitary invading glioma cell in histopathological preparations, or in experimental glioma models. We have developed an experimental invasion assay system, which allows us to track the solitary invasive glioma cell, using human brain tissue obtained from routine craniotomies for seizures or trauma. METHODS: This tissue is cut into 1-mm thick slices and cultured in the upper chamber of Transwell culture dishes on top of a 0.4- micro m pore size polyester membrane, which is fed on medium provided in the lower chamber. Glioma cells are stably transfected with vectors containing a green fluorescent protein (GFP) cDNA. Stable, high-level expression GFP transfectants were selected by direct visualization under fluorescence microscope. In addition, various tumor spheroids are stained with vital dye, DiI, to track the invading cells. GFP-expressing glioma cells or stained spheroids were then implanted on the center of the brain slice, and the degree of brain tumor invasion into the brain tissue was evaluated at different time points by optical sectioning using a confocal microscope. RESULTS: We observed that GFP-expressing glioma cells or stained spheroids could be readily tracked and followed with this model system. Individual tumor cells that exhibited green or red fluorescence could be identified and their migration path through the brain slices unequivocally followed. CONCLUSION: This experimental invasion system may be of considerable utility in studying the process of brain tumor invasion and in evaluating its invasiveness in individual brain tumor because it not only provides a better representation of extracellular matrix molecules normally encountered by invading glioma cells, but also provides the fluorescent tag applied to the tumor cells.

Astrocytoma↗
PubMed2005

Quantifying in vivo somatic mutations using transgenic mouse model systems.

This chapter describes the use of the bacteriophage cII positive selection assay with the MutaMouse transgenic model system. The assay is similar to others involving a transgenic target, including the cII and lacI assays in the Big Blue(R) Mouse, lacZ in the MutaMouse, and the gpt delta assay. Briefly, high-molecular-weight DNA is purified from the tissue of interest and used as substrate during in vitro packaging reactions, in which the lambda transgenes are excised from the genome and assembled into viable phage. Phage containing the mutational targets are then adsorbed into an appropriate bacterial host, and mutations sustained in vivo are evidenced by either standard recombinant screening or selection assays. Mutant frequencies are reported as the ratio of mutant phage to total phage units analyzed. The lambda-based transgenic mouse assays are used to study and characterize in vivo mutagenesis, as well as for mutagenicity assessment. The models permit the enumeration of mutations sustained in virtually any tissue of the mouse and are sensitive and robust. Application of the assays is simple, not requiring resources beyond those commonly found in most academic laboratories.

Animals↗
PubMed1986

Significance of immune responses to mucosal carcinogens: a hypothesis and a workable model system.

Carcinogens must enter the tissues before neoplastic transformation of cells can occur. The present report describes the 2-AAF model system being used to test our hypothesis that development of mucosal immunity to carcinogens will interfere with their passage through mucosal epithelial cells. The 2-AAF model is ideal for testing this hypothesis. 2-AAF is a carcinogen which passes through the intestinal epithelium following oral administration, is transported to the liver and is there metabolized with the ultimate formation of hyperplastic nodules and neoplasms. Further, neoplasms form at other sites including the ear duct, gastrointestinal tract and the lungs. Our studies indicate that 2-AAF alone given orally does not elicit an immune response. However, 2-AAF is immunogenic when conjugated to carrier proteins and administered in CFA. Such conjugates of 2-AAF are not carcinogenic when administered in doses needed to achieve a systemic immune response in rats. Future studies will document the optimal conditions required to stimulate mucosal immunity to 2-AAF and the effect of such immunity on carcinogenesis in this model.

2-Acetylaminofluorene↗
PubMed2006

The short-lived fish Nothobranchius furzeri as a new model system for aging studies.

Genetic and pharmacological research on aging is hampered by the lifespan of available vertebrate models. We recently initiated studies on Nothobranchius furzeri, a species with a maximum life expectancy in captivity of just three months which represents the shortest documented captive lifespan for a vertebrate. Further research on N. furzeri has demonstrated that 1. Short lifespan is tied with explosive growth and accelerated sexual maturation. 2. Short lifespan is correlated with expression of age-related behavioral and histological changes. 3. Lifespan and expression of age-related markers can be modulated by water temperature. 4. Resveratrol, a drug characterized for its life-extending action in Caenorhabditis elegans and Drosophila, increases lifespan and retards expression of age-related markers. 5. Aging-related genes can be easily isolated by homology cloning. Finally, different populations or species of Nothobranchius show large-scale differences in captive lifespan. In the last three years, N. furzeri has moved from biological curiosity to a promising model system for drug validation. Furthermore, this species occupies a favorable position in the Teleost's "tree of life". It is very close to the Japanese Medaka, and close to the pufferfishes and stickleback and might represent a very useful model for comparative genomics of aging.

Aging↗
PubMed2006

Acoustic emission analysis and experiments with physical model systems reveal a peculiar nature of the xylem tension.

Advanced acoustic emission analysis, special microscopic examinations and experiments with physical model systems give reasons for the assumption that the tension in the water conducting system of vascular plants is caused by countless minute gas bubbles strongly adhering to the hydrophobic lignin domains of the xylem vessel walls. We ascertained these bubbles for several species of temperate deciduous trees and conifers. It is our hypothesis that the coherent bubble system of the xylem conduits operates as a force-transmitting medium that is capable of transporting water in traveling peristaltic waves. By virtue of the high elasticity of the gas bubbles, the hydro-pneumatic bubble system is capable of cyclic storing and releasing of energy. We consider the abrupt regrouping of the wall adherent bubble system to be the origin of acoustic emissions from plants. For Ulmus glabra, we recorded violent acoustic activity during both transpiration and re-hydration. The frequency spectrum and the waveforms of the detected acoustic emissions contradict traditional assumptions according to which acoustic emissions are caused by cavitation disruption of the stressed water column. We consider negative pressure in terms of the cohesion theory to be mimicked by the tension of the wall adherent bubble system.

Acoustics↗
PubMed1984

GABA neurons in the mammalian central nervous system: model for a minimal basic neural unit.

My current working models of nervous system function place particular emphasis on the roles of inhibitory GABAergic neurons in information processing in the central nervous system. It is proposed that in behavioral sequences, innate or learned, preprogrammed neural circuits are released to function at varying rates and in various combinations largely by disinhibition of pacemaker neurons whose activities are under the dual tonic inhibitory control of GABAergic local circuit neurons and projection command neurons. According to this view, disinhibition is permissive and excitatory input to pacemaker neurons has mainly a modulatory role. Disturbances in GABAergic function probably occur in a variety of neurologic and psychologic disorders.

Afferent Pathways↗
PubMedDate not supplied

Feeding behavior of Aplysia: a model system for comparing cellular mechanisms of classical and operant conditioning.

Feeding behavior of Aplysia provides an excellent model system for analyzing and comparing mechanisms underlying appetitive classical conditioning and reward operant conditioning. Behavioral protocols have been developed for both forms of associative learning, both of which increase the occurrence of biting following training. Because the neural circuitry that mediates the behavior is well characterized and amenable to detailed cellular analyses, substantial progress has been made toward a comparative analysis of the cellular mechanisms underlying these two forms of associative learning. Both forms of associative learning use the same reinforcement pathway (the esophageal nerve, En) and the same reinforcement transmitter (dopamine, DA). In addition, at least one cellular locus of plasticity (cell B51) is modified by both forms of associative learning. However, the two forms of associative learning have opposite effects on B51. Classical conditioning decreases the excitability of B51, whereas operant conditioning increases the excitability of B51. Thus, the approach of using two forms of associative learning to modify a single behavior, which is mediated by an analytically tractable neural circuit, is revealing similarities and differences in the mechanisms that underlie classical and operant conditioning.

Adaptation, Physiological↗
PubMed1988

A model system illustrating the isolation and enrichment of a rare population of tumour cells in bone marrow.

A model system employing a modified nylon matrix is described for the separation of rare cells titrated into either a leukaemic cell line or normal bone marrow. A 75- to 125-fold enrichment and recovery of the rare cell population was achieved, starting from an initial level of 0.014 to 0.2% of the total population. The rare cell population was identified by pre-labelling with Hoechst 33342, which intercalates into the DNA, and renders cells highly fluorescent. Separation and recovery of cells was totally dependent on the use of a panel of monoclonal antibodies binding to the labelled population. The nylon matrix, precoated with an anti-mouse immunoglobulin, traps the cells coated with monoclonal antibodies, and these can be released simply by gentle manipulation of the matrix. The matrix employed has been shown to not specifically trap committed bone marrow progenitors as determined by CFU-GM, BFU-E and CFU-GEMM assays. The use of this technique should simplify the isolation of rare tumour cells metastasizing to bone marrow.

Affinity Labels↗
PubMed2001

Compressive deformation and damage of muscle cell subpopulations in a model system.

To study the effects of compressive straining on muscle cell deformation and damage an in vitro model system was developed. Myoblasts were seeded in agarose constructs and cultured in growth medium for 4 days. Subsequently, the cells were allowed to fuse into multinucleated myotubes for 8 days in differentiation medium, resulting in a population of spherical myoblasts (50%), spherical myotubes (35%), and elongated myotubes (15%) with an overall viability of 90%. To evaluate cell deformation upon construct compression half-core shaped constructs were compressed up to 40% strain and the resulting cell shape was assessed from confocal scans through the central plane of spherical cells. The ratio of cell diameters measured parallel and perpendicular to the axis of compression was used as an index of deformation (DI). The average DI of myoblasts decreased with strain level (0.99+/-0.03, 0.70+/-0.04, and 0.56+/-0.10 at 0%, 20%, and 40% strain), whereas for myotubes DI decreased up to 20% strain and then remained fairly constant (0.99+/-0.06, 0.55+/-0.06, 0.50+/-0.11). The discrepancy in DI between spherical myoblasts and myotubes at 20% strain was explained by the relative sensitivity of the cell membrane to buckling, which is more pronounced in the myotubes. Sustained compression up to 24 h at 20% strain resulted in a significant increase in cell damage with time as compared to unstrained controls. Despite differences in membrane buckling no difference in damage between myoblasts and spherical myotubes was observed over time, whereas the elongated myotubes were more susceptible to damage.

Animals↗
PubMed2006

Animal-based national surveillance for zoonotic disease: quality, limitations, and implications of a model system for monitoring rabies.

Surveillance for zoonotic diseases among wildlife is a research and public health challenge. The inherent limitations posed by the requisite human-animal interactions are often undefined and underappreciated. The national surveillance system for animal rabies in the United States was examined as a model system; reporting of animal rabies is legally mandated, each case of rabies is laboratory confirmed, and data have been consistently collected for more than 50 years. Factors influencing the monthly counts of animal rabies tests reported during 1992-2001 were assessed by univariate and multivariable regression methods. The suitability of passively collected surveillance data for determining the presence or absence of the raccoon-associated variant of rabies within states and within individual counties was assessed by determining critical threshold values from the regression analyses. The size of the human population and total expenditures within a county accounted for 72% and 67%, respectively, of the variance in testing. The annual median number of rabies tests performed was seven for counties without rabies, 22 for counties with non-raccoon rabies, and 34 for counties with raccoon rabies. Active surveillance may be required in locales with sparse human populations when a high degree of confidence in the status of rabies is required.

Animals↗
PubMed1984

Studies on the biosynthesis of cartilage proteoglycan in a model system of cultured chondrocytes from the Swarm rat chondrosarcoma.

Biosynthesis of cartilage proteoglycan was examined in a model system of cultured chondrocytes from a transplantable rat chondrosarcoma. Extensive modification with the addition of chondroitin sulfate glycosaminoglycan, N-linked oligosaccharide, and O-linked oligosaccharide is required to convert a newly synthesized core protein precursor into a proteoglycan. Kinetic analyses revealed the presence of a large pool of core protein precursor (t 1/2 approximately 90 min) awaiting completion into proteoglycan. The large t 1/2 of this pool allowed kinetic labeling experiments with a variety of radioactive precursors to distinguish between early biosynthetic events associated primarily with the rough endoplasmic reticulum from late events associated primarily with the Golgi apparatus. The results of a series of experiments indicated that the addition of N-linked oligosaccharide chains occurs early in the biosynthetic process in association with the rough endoplasmic reticulum, whereas the initiation and completion of O-linked oligosaccharides occurs much later, at about the same time as chondroitin sulfate synthesis. This also indicated that keratan sulfate chains, when present in the completed molecule, are added in the Golgi apparatus, as they are probably built on oligosaccharide primers closely related to the O-oligosaccharide chains. Furthermore, when 3H-glucose was used as the precursor, the entry of label into xylose, the linkage sugar between the core protein and the chondroitin sulfate chain, was found to occur within 5 min of the entry of label into galactose and galactosamine in the remainder of the chondroitin sulfate chain. This indicated that the initiation and completion of the chondroitin sulfate chain occurs late in the pathway probably entirely in the Golgi apparatus. Thus, proteoglycan synthesis can be described as occurring in two stages in this system, translation and N-glycosylation of a core protein precursor which has a long half-life in the rough endoplasmic reticulum, followed by extensive rapid modification in the Golgi complex in which the majority of glycosaminoglycan and oligosaccharide chains are added to the core protein precursor with subsequent rapid secretion into the extracellular matrix.

Animals↗
PubMed1990

Effects of monosaccharides and disaccharides on the formation of food mutagens in model systems.

The formation of the mutagenic imidazoquinoxalines (MeIQx, DiMeIQx) was studied using a modification of a previous model system. Creatine or creatinine (0.9 mmole) was heated together with glycine (0.9 mmole) and various sugars (0.45 mmole) dissolved in diethylene glycol and water (3 ml, 5:1) for up to 15 min at 180 degrees C. This system produced the same amount of mutagenicity after 10 min at 180 degrees C as a previous one during 2 h of reflux boiling at 128 degrees C. MeIQx (4 nmole/mmole creatin(in)e) was the major mutagen produced together with minor amounts of DiMeIQx, both 4,8- and 7,8-DiMeIQx according to HPLC-MS. A few other mutagenic peaks were also separated on HPLC, but they were not identified. Varying the concentration (0-2.4 mmole) and type of monosaccharides and disaccharides greatly affected the yields of all the mutagenic compounds. Sugar in molar amounts lower than the creatin(in)e concentration increased the yield until an optimum was reached. In higher concentrations the formation of all the mutagens was markedly reduced. The same was found for glucose, fructose, sucrose, and lactose, though the monosaccharides showed the most pronounced inhibitory effects. The inhibition of the formation of the mutagenic compounds by an excess of sugars is proposed to be an effect of Maillard reaction products, which may block the formation of imidazoquinoxalines by attacking creatine. Support for this mechanism is given by data showing a lower recovery of unreacted creatine with increasing concentration of glucose and also by an inhibitory effect on the formation of these mutagens after adding a typical Maillard reaction product, 5-hydroxymethyl-2-furfural.

Chromatography, High Pressure Liquid↗