SEARCH · Search PubMed

Results for “model system”

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.

SourceResearch connectionFrom yearThrough year

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

At least 973 records · Page 54Linked to original sources

PubMed2001

Timing of breeding in variable environments: tropical birds as model systems.

Animals need to adjust reproductive decisions to environmental seasonality. In contrast to species from the well-studied temperate zones, little is known for tropical birds about the environmental cues that stimulate reproductive activity and the physiological mechanisms that regulate reproduction. I am investigating the environmental and endocrine mechanisms that underlie the timing of reproduction in spotted antbirds from the near-equatorial Panamanian rainforest and in small ground finches from the equatorial arid Galápagos islands. Spotted antbirds live in a fairly predictable seasonal environment and show regular changes in gonad sizes and some reproductive hormones. Despite the small annual variation in photoperiod close to the equator, these birds can measure slight photoperiodic increases and use it to initiate reproductive activity. Spotted antbirds also respond to seasonal changes in food availability, which allows them to flexibly adjust gonad growth to environmental conditions. Testosterone is involved in regulating song and aggressive behavior in these year-round territorial birds, although it can remain at low plasma levels throughout the year. In contrast, small ground finches exposed to a rather unpredictable climate on Galápagos appear to grow their gonads whenever heavy rains fall and have regressed gonads during other times of the year. The lack of a physiological preparation for the breeding season and their response to short-term cues related to rainfall indicate a striking flexibility in the regulation of breeding in small ground finches. I suggest that tropical birds can serve as model systems to study the physiological adaptations to different environments. Unraveling the neuroendocrine mechanisms behind the flexibility in reproductive timing will clarify whether differences found between temperate and tropical birds represent variations of the same basic mechanism or instead reflect a fundamental divergence in physiological control systems.

Animals↗

PubMed1995

Monomeric ferric heme peptide derivatives: model systems for hemoproteins.

Electron paramagnetic resonance spectra of a number of ferric heme peptide derivatives, in aqueous-detergent and various aqueous-alcohol solvent mixtures, have been obtained using samples in the concentration range 0.1-1.0 mM. Some of these were clearly monomeric, homogeneous, mixed-ligand adducts, entirely suitable for use as model systems for hemoprotein spectroscopic studies. As anticipated, the measured EPR parameters were largely independent of solvent environment. Surprisingly, micellar preparations of ferric heme undecapeptide in mildly alkaline solution showed no evidence for the formation of a hydroxide adduct, contrary to a previous report [S. Mazumdar, O. K. Medhi and S. Mitra, Inorg. Chem. 30 700 (1991)].

Amino Acid Sequence↗

PubMedDate not supplied

A unique model system for tumor progression in GBM comprising two developed human neuro-epithelial cell lines with differential transforming potential and coexpressing neuronal and glial markers.

The molecular mechanisms involved in tumor progression from a low-grade astrocytoma to the most malignant glioblastoma multiforme (GBM) have been hampered due to lack of suitable experimental models. We have established a model of tumor progression comprising of two cell lines derived from the same astrocytoma tumor with a set of features corresponding to low-grade glioma (as in HNGC-1) and high-grade GBM (as in HNGC-2). The HNGC-1 cell line is slow-growing, contact-inhibited, nontumorigenic, and noninvasive, whereas HNGC-2 is a rapidly proliferating, anchorage-independent, highly tumorigenic, and invasive cell line. The proliferation of cell lines is independent of the addition of exogenous growth factors. Interestingly, the HNGC-2 cell line displays a near-haploid karyotype except for a disomy of chromosome 2. The two cell lines express the neuronal precursor and progenitor markers vimentin, nestin, MAP-2, and NFP160, as well as glial differentiation protein S100beta. The HNGC-1 cell line also expresses markers of mature neurons like Tuj1 and GFAP, an astrocytic differentiation marker, hence contributing toward a more morphologically differentiated phenotype with a propensity for neural differentiation in vitro. Additionally, overexpression of epidermal growth factor receptor and c-erbB2, and loss of fibronectin were observed only in the HNGC-2 cell line, implicating the significance of these pathways in tumor progression. This in vitro model system assumes importance in unraveling the cellular and molecular mechanisms in differentiation, transformation, and gliomagenesis.

Aged↗

PubMed2006

Phase changes during hygroscopic cycles of mixed organic/inorganic model systems of tropospheric aerosols.

A correct description of the aerosol's phases is required to determine its gas/particle partitioning, its reactivity and its water uptake and release. In this study, we investigate organic/electrolyte interactions of ammonium sulfate, nitrate and sodium chloride with substances containing carboxylic acids (COOH) and hydroxyl (OH) functional groups. As organic model compounds, we chose polyols with different OH/CHn (n = 0-3) ratios-namely, glycerol, 1,4-butanediol, and 1,2-hexanediol-as well as PEG 400 and a mixture of dicarboxylic acids consisting of malic, malonic, maleic, glutaric, and methylsuccinic acid. Bulk solubility and water activity measurements of these model systems together with a survey of literature data showed that NaCl is a salting-out agent for alcohols and organic acids whereas ammonium nitrate and sulfate exhibited salting-in and salting-out tendencies depending on the nature and number of functional groups as well as on the concentration of the solution. All investigated salts induce a liquid-liquid phase separation in the 1,2-hexanediol/water system. Considering the composition of the tropospheric aerosol, such phase separations might indeed occur frequently when particles in the atmosphere are exposed to varying relative humidity. To complement the bulk experiments, we investigated single particles consisting of ammonium sulfate and dicarboxylic acids as well as of ammonium sulfate and PEG 400 in an electrodynamic balance. Whereas the relative humidities of total deliquescence as well as the water uptake and release of the fully deliquesced particles are in good agreement with the bulk results and represent thermodynamic equilibrium, the water uptake before full deliquescence shows significant deviations. These deviations may be caused by morphological effects.

Journal Article↗

PubMed1965

AUTOIMMUNE DISEASE IN NZB/BL MICE. I. PATHOLOGY AND PATHOGENESIS OF A MODEL SYSTEM OF SPONTANEOUS GLOMERULONEPHRITIS.

This study, based upon 528 laboratory examinations and 16 complete autopsies of NZB/Bl mice, deals with autoimmune manifestations (as shown by hypergammaglobulinemia, Coombs positive hemolytic anemia, and the occasional presence of lupus- and rheumatoid-like factors) and mainly with the pathology and the pathogenesis of glomerulonephritis in these mice, a model system of membranous glomerulonephritis with spontaneous and insidious onset, progression through chronic stages, and almost certainly induced by immunological, and autoimmune, mechanisms. The earliest and lasting histological change was hyaline thickening of the capillary walls and adjacent intercapillary regions of the glomerular tufts, corresponding in location to polysaccharide-rich capillary basement membrane and mesangial materials. Distributed focally and diffusely in the glomerular tuft and eventually sparing no glomerulus, hyaline, granular, and fibrillar ("spongy fiber") materials produced narrowing of capillary lumens by concentric or eccentric encroachment upon them. In the later stages hyaline lobulation and sclerosis of the glomerular tufts occurred. Thus the lesions corresponded to those seen in human focal and diffuse membranous, chronic lobular, and lastly (intracapillary) sclerosing glomerulonephritis. In all instances of glomerulonephritis the glomerular tufts contained selective localizations of mouse immunoglobulins corresponding in distribution to that of the hyaline and (PAS-positive) polysaccharide-rich materials in the focal and diffuse membranous and lobular lesions and in amounts increasing with the severity of glomerular disease. The mouse immunoglobulins were extracted from frozen sections of glomerulonephritic kidneys and were then capable of recombination with glomerular tufts in sections of autologous or isologous glomerulonephritic kidneys from which in vivo localized immunoglobulins had been extracted. The pattern of recombination with glomerular tufts was similar to that of in invo localized immunoglobulins. The extracted immunoglobulins did not show affinity for mouse red cells (in the indirect Coombs test) nor for autologous or isologous cell nuclei (in the immunofluorescence test). The serum of mice with severe glomerulonephritis contained immunoglobulins with in vitro affinity for extracted autologous or isologous glomerular tufts. Thus circulating as well as localized antibodies were demonstrated. The immunogenic materials (autoantigens) may have been formed in the glomerular tufts or accumulated in them from some other source, such as the circulating plasma; however they corresponded in location to polysaccharide-rich capillary basement membrane and mesangial materials. The spleen was identified at the cellular level as the main site of formation of autoantibodies to red cells, as well as the main site of red cell destruction. Some evidence was brought forth suggesting that these autoantibodies were "heavy" or gammaM-globulins. More studies are in progress.

Animals↗

PubMed2006

Impact of extraction conditions on the content of acrylamide in model systems and food.

It has recently been suggested that the analytical methods that have been developed to date for the determination of acrylamide (AA) may underestimate the concentration of AA in certain foods, because significantly higher results were obtained upon extraction of the food matrix under alkaline conditions. The present study employs food (potato, rye) and chemical model systems to better understand the tentative release of AA under high pH extraction conditions. The experimental design is based on the generation of AA in an environment containing an AA-isotopomer, and by comparing the ratio of AA, respectively the AA-isotopomer, after extraction at pHs 7 and 12. The results show that the additional AA released is not due to improved extractability of AA from the food matrix, and should therefore be regarded as an extraction artefact. Strongly alkaline conditions seem to induce net formation of AA from water-soluble precursors formed during thermolysis.

Acrylamide↗

PubMed2001

Behavior modification in primary care: the pressure system model.

The leading causes of death in the United States are predominantly attributable to modifiable behaviors. Patients with behavioral risk factors for premature death and disability, including dietary practices; sexual practices; level of physical activity; motor vehi cle use patterns; and tobacco, alcohol, and illicit sub stance use, are seen far more consistently by primary care providers than by mental health specialists. Yet models of behavior modification are reported, debated, and revised almost exclusively in the psychology literature. While the Stages of Change Model, or Transtheo retical Model, has won application in a broadening array of clinical settings, its application in the primary care setting is apparently quite limited despite evidence of its utility [Prochaska J, Velicer W. Am J Health Promot 1997;12:38-48]. The lack of a rigorous behavioral model developed for application in the primary care setting is an impediment to the accomplishment of public health goals specified in the Healthy People objectives and in the reports of the U.S. Preventive Services Task Force. The Pressure System Model reported here synthesizes elements of established behavior modification theories for specific application under the constraints of the primary care setting. Use of the model in both clinical and research settings, with outcome evaluation, is encouraged as part of an effort to advance public health.

Behavior Therapy↗

PubMed2006

The effect of in ovo ethanol exposure on retina and optic nerve in a chick embryo model system.

Ocular anomalies seen in children with fetal alcohol syndrome (FAS) suggest that ocular structures are sensitive to alcohol exposure during their development. This study was designed to investigate the effect of in ovo ethanol (EtOH) exposure on retinal development and myelinization of optic nerve fibers at an ultra structural level in a chick embryo model system. Prior to incubation, fertilized chicken eggs were injected once with 100 microl of either 0.9% NaCl (vehicle control), or EtOH solutions at different doses (10, 30, or 50%, v:v in 0.9% NaCl) into their air sacs and incubated at 37.5 degrees C and saturation humidity. On day 20 embryos were analyzed in terms of their viability and growth and the optic cups including the optic nerves were dissected out. Specimens were processed for electron microscopy (EM). Results showed that, EtOH significantly decreased the viability of chick embryos (P < 0.045), and caused significant prenatal growth retardation (P < 0.004) in a dose-dependant manner. Light microscopy of semi thin sections revealed that prenatal exposure to EtOH resulted in both retinal degeneration and optic nerve hypoplasia (P < 0.001) in a dose-dependant manner. EM revealed that a dose-dependant decrease in the number of myelinated nerve fibers was profound in groups exposed to EtOH (P < 0.001). Furthermore, the myelin coats observed were thinner than those seen in control embryos. In groups exposed to EtOH myelin sheets were unorganized and contained vacuolar structures in between them. The tissue in between the cells and optic nerve fibers, on the other hand, lost its intact appearance with vacuolar and vesicular structures in between them. In addition, the optic nerve fibers contained granular accumulations in EtOH exposed groups. A dose dependent degeneration was also observed in retinas of EtOH exposed groups. The effect of EtOH was profound in pigment epithelium (PE), inner plexiform layer (IPL), and ganglion cell layer (GC). Mitochondrial deficiencies, and alterations in melanin granule number and distribution dominated the defects seen in PE. On the other hand, EM findings of all the affected layers were suggestive of induced cell death in EtOH exposed groups. Thus, this study suggests retinal development with the emphasis on melanin pigmentation in PE and optic nerve myelinization as potential targets of prenatal EtOH exposure and discusses potential mechanisms of EtOH action on these tissues.

Abnormalities, Drug-Induced↗

PubMedDate not supplied

The National Institute on Disability and Rehabilitation Research burn model system database: a tool for the multicenter study of the outcome of burn injury.

Advances in critical care and surgical management have significantly improved survival after burn injury over the past several decades. However, today, survival alone is an insufficient outcome. In 1994, the National Institute on Disability and Rehabilitation Research (NIDRR) created a burn model system program to evaluate the long-term sequelae of burn injuries. As part of this multicenter program, a comprehensive demographic and outcome database was developed to facilitate the study of a number of functional and psychosocial outcomes after burns. The purpose of this study is to review the database design and structure as well as the data obtained during the last 10 years. This is a descriptive study of the NIDRR database structure as well as the patient data obtained from the four participating burn centers from 1994 to 2004. Data obtained during hospitalization and at 6, 12, and 24 months after discharge were reviewed and descriptive statistics were calculated for select database fields. The database is divided into several subsections, including demographics, injury complications, patient disposition, and functional and psychological surveys. A total of 4600 patients have been entered into the NIDRR database. To date, 3449 (75%) patients were alive at discharged and consented to follow-up data collection. The NIDRR database provides an expansive repository of patient, injury, and outcome data that can be used to analyze the impact of burn injury on physical and psychosocial function and for the design of interventions to enhance the quality of life of burn survivors.

Adolescent↗

PubMed1989

Histochemical blockade of the antigen-antibody reaction using immunoperoxidase demonstration of lysozyme in paneth cells and lamina propria mononucleocytes of human small intestine as a model system.

Nitrosation and acetylation, two histochemical blocking procedures for amino groups, were used to establish the extent to which these groups intervene in the antigen-antibody reaction in immunohistochemistry. We used the peroxidase-antiperoxidase method (PAP) to demonstrate lysozyme in Paneth cells and in lamina propria mononucleocytes of human small intestine as a model system. We studied the relationship of these groups to fixation, concentration of the primary antiserum, and length of blockade, as well as the possibility of reversing blockade as proof of specificity. Our findings support the contention that amino groups are also an important factor in antigen-antibody binding, even in fixed tissue. Fixatives influence the binding process in many ways, with acetylation producing a more successful result than nitrosation in tissue fixed in Bouin without acetic acid, whereas the reverse is true in formaldehyde-fixed tissue.

Acetates↗

PubMed2003

Lactobacillus strains isolated from Danbo cheese as adjunct cultures in a cheese model system.

Isolates of Non-Starter Lactic Acid Bacteria (NSLAB) from six ripened Danbo cheeses of different ages and of different brands were examined. Special emphasis was on the genus Lactobacillus with the aim of investigating their role in cheese maturation. Thirty-three isolates were typed by the PCR-based method, Randomly Amplified Polymorphic DNA (RAPD). Ten RAPD types were found and 70% of the isolates were of RAPD types found in more than one cheese. The different RAPD types were identified to species level by Temporal Temperature Gradient Gel Electrophoresis (TTGE). Most of the isolates were identified as Lactobacillus paracasei (76%), but also Lactobacillus curvatus, Lactobacillus plantarum, Lactobacillus rhamnosus and some taxa originating from the starter culture were detected. In one cheese, no lactobacilli were found. One strain of the most frequent Lactobacillus RAPD type from each of the five cheeses with a Lactobacillus flora was used as adjunct cultures in a cheese model system. Four of the five adjuncts were re-isolated during ripening. Two adjunct containing model cheeses received higher flavour scores than the control while two other were associated with off-flavours. The two model cheeses with off-flavour had a similar microflora and both were after 13 weeks of ripening dominated by a strain identified as L. plantarum.

Bacterial Typing Techniques↗

PubMed1995

Alpha-fetoprotein and the acute phase response. A study using acute pelvic inflammatory disease as a model system.

Alpha-fetoprotein (AFP) is used as a tumor marker for hepatomas and germ cell tumors. In healthy non-pregnant adults the serum concentration (S-AFP) is very low and we examined whether it was affected when the acute phase response was activated, using patients with acute pelvic inflammatory disease (PID) as a model system. In 70 PID patients the median S-AFP was 1.2 kIU/l (range: 0.5-5.9 kIU/l), within the normal range. S-AFP did not correlate with the clinical grade of disease nor with the serum concentrations of acute phase reactants and albumin. Thus, S-AFP is not significantly affected by activation of the acute phase response and presence of infection should not per se interfere with the use of S-AFP as a tumor marker. However, a negative correlation was found with the serum concentration of alpha-2-macroglobulin (P = 0.05), but whether this has any biological significance remains to be clarified.

Acute-Phase Proteins↗

PubMed1985

Effect of beta-receptor blockade on anxiety with reference to the three-systems model of phobic behavior.

14 phobic subjects were given propranolol (Inderal), atenolol (Tenormin) and placebo in a double-blind fashion according to a repeated measurement design. Subjects were exposed to their source of fear while their anxiety and cardiovascular responses (heart rate, blood pressure and peripheral temperature) were recorded. In accordance with the Three-Systems Model of fear and phobias, the subjects were divided into two groups of high and low physiological reactors, operationalized by the cardiovascular items in their anxiety pattern from a revised version of the Autonomic Perception Questionnaire (APQ). It was found that beta-blockade had the predicted effect on heart rate and peripheral temperature while diastolic blood pressure was unaffected. The systolic blood pressure finally was lowered for the low cardiovascular reactors. The subjectively rated anxiety rose consistently during exposure. There was no general effect of the beta-blocking drugs on subjective anxiety. For the high cardiovascular reactors propranolol was associated with a higher anxiety level.

Adult↗

PubMed1991

Does cholesterol screening result in negative labeling effects? Results of the Massachusetts Model Systems for Blood Cholesterol Screening Project.

Several previous studies that looked at the effects of labeling individuals as hypertensive found increases in psychosocial distress, diminished feelings of well-being, or absenteeism. Other studies found no such effects. Thus far, similar studies relating to labeling for high blood cholesterol levels have not been published. The Massachusetts Model Systems for Blood Cholesterol Screening Project investigated whether labeling effects occurred as a result of the community-based screening, education, and referral programs it conducted in Worcester and Lowell. Nine questions concerning perceptions of physical and psychological well-being were asked on a questionnaire given to screening participants. The same questions were asked as part of a follow-up questionnaire given to all individuals identified as having high blood cholesterol levels at one of the screenings. Comparison of the baseline and follow-up results did not demonstrate significant overall negative effects among any age, sex, racial, income, or educational groups. On the contrary, responses to many of the questions revealed small but statistically significant improvements in perceptions of physical and psychological well-being. The absence of negative labeling effects may be attributable to the positive, supportive approach to participant counseling taken by the project.

Adult↗

PubMed2006

Status of complete proteome analysis by mass spectrometry: SILAC labeled yeast as a model system.

BACKGROUND: Mass spectrometry has become a powerful tool for the analysis of large numbers of proteins in complex samples, enabling much of proteomics. Due to various analytical challenges, so far no proteome has been sequenced completely. O'Shea, Weissman and co-workers have recently determined the copy number of yeast proteins, making this proteome an excellent model system to study factors affecting coverage. RESULTS: To probe the yeast proteome in depth and determine factors currently preventing complete analysis, we grew yeast cells, extracted proteins and separated them by one-dimensional gel electrophoresis. Peptides resulting from trypsin digestion were analyzed by liquid chromatography mass spectrometry on a linear ion trap-Fourier transform mass spectrometer with very high mass accuracy and sequencing speed. We achieved unambiguous identification of more than 2,000 proteins, including very low abundant ones. Effective dynamic range was limited to about 1,000 and effective sensitivity to about 500 femtomoles, far from the subfemtomole sensitivity possible with single proteins. We used SILAC (stable isotope labeling by amino acids in cell culture) to generate one-to-one pairs of true peptide signals and investigated if sensitivity, sequencing speed or dynamic range were limiting the analysis. CONCLUSION: Advanced mass spectrometry methods can unambiguously identify more than 2,000 proteins in a single proteome. Complex mixture analysis is not limited by sensitivity but by a combination of dynamic range (high abundance peptides preventing sequencing of low abundance ones) and by effective sequencing speed. Substantially increased coverage of the yeast proteome appears feasible with further development in software and instrumentation.

Amino Acid Sequence↗

PubMed1996

Zwitterionic phospholipids enhance aspirin's therapeutic activity, as demonstrated in rodent model systems.

We have recently reported that the Gl toxicity of aspirin is markedly reduced when the drug is preassociated with the zwitterionic phospholipid dipalmitoylphosphatidycholine (DPPC) before intragastric administration. The present study was designed to determine whether the biological availability and therapeutic activity of aspirin were affected by chemically associating the drug with DPPC. To evaluate this, we compared the kinetics of entry of labeled aspirin into the blood, after intragastric administration of the drug in the free and lipid-associated states; we also tested the ability of the above formulations to inhibit fever, inflammation and pain in appropriate rodent model systems. We found that although the Gl absorption of free aspirin and that of the aspirin/DPPC complex were similar, in all three rodent models the complex had significantly greater antipyretic, anti-inflammatory and analgesic efficacy than aspirin alone. Dose-response analyses employing the fever model demonstrated that potency of aspirin to reduce fever was increased 5 to 10-fold when the aspirin was intragastrically administered in the lipid-associated state. We conclude that the therapeutic activity of aspirin to inhibit fever, inflammation and pain is remarkably enhanced when the drug is intragastrically administered in chemical association with the zwitterionic phospholipid DPPC. A number of molecular mechanisms have been proposed to explain the observed phospholipid-dependent increase in aspirin's therapeutic activity.

1,2-Dipalmitoylphosphatidylcholine↗

PubMed1987

The human tumor clonogenic assay as a model system in cell biology.

The human tumor stem cell (clonogenic) assay (HTCA) is a soft agar system designed for growing fresh human tumor specimens in vitro. The assay has been extensively used in studies both of individual patients' response to chemotherapy and for screening new agents. The technical limitations of this assay have been extensively discussed. The use of this test as a model system to study fundamentals of tumor cell growth has not been stressed. The potentials and limitations of this assay for the study of the regulation of tumor growth are presented.

Cell Cycle↗

PubMed1996

Inhibition of matrix metalloproteinase 9 expression by a ribozyme blocks metastasis in a rat sarcoma model system.

Matrix metalloproteinases (MMPs) have been implicated in tumor progression, but the exact roles that each member of this family may play in contributing to the behavior of malignant tumors are only beginning to be understood. MMP-9 (gelatinase B or the 92-kDa gelatinase/type IV collagenase) expression has been associated with metastasis in a variety of model systems including that of rat sarcomas generated by transformation of rat embryo cells with rasH and myc. To determine the effect that expression of MMP-9 has in this system, we inhibited the expression of MMP-9 using a hammerhead ribozyme. Introduction of an expression vector for a ribozyme directed against the rat MMP-9 mRNA sequence into a metastatic rat embryo cell line transformed by rasH and myc (2.10.10) that constitutively secretes MMP-9 resulted in the absence of detectable MMP-9 mRNA and loss of released 92-kDa gelatinase activity. These cells were no longer metastatic in a lung colonization assay but retained tumorigenicity. Introduction of an expression vector for a control hammerhead ribozyme had no effect. These data document the requirement for MMP-9 expression in metastasis in this system.

Animals↗