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Biomedical subjects

G B Chapman

Publications and source records attributed to G B Chapman.

At least 37 records · Page 2Linked to original sources
PubMed1991

Trial order affects cue interaction in contingency judgment.

Recent research on contingency judgment indicates that the judged predictiveness of a cue is dependent on the predictive strengths of other cues. Two classes of models correctly predict such cue interaction: associative models and statistical models. However, these models differ in their predictions about the effect of trial order on cue interaction. In five experiments reported here, college students viewed trial-by-trial data regarding several medical symptoms and a disease, judging the predictive strength of each symptom with respect to the disease. The results indicate that trial order influences the manner in which cues interact, but that neither the associative nor the statistical models can fully account for the data pattern. A possible variation of an associative account is discussed.

Cues↗
PubMed1990

Cue interaction in human contingency judgment.

Most studies of human contingency judgment have been based on the assumption that frequency information about one predictor is assessed in isolation of information about other predictors. Recent evidence, however, suggests that the judged predictive strength of one cue is influenced by the predictive strengths of other copresent cues. Two experiments demonstrate that stimuli with the same outcome contingencies may nonetheless have different predictive strengths as the result of cue interaction. The first experiment, in which a within-subject design was used, provides a demonstration of blocking. A stimulus presented in compound with a strong predictor was rated as less predictive than another stimulus that was presented in compound with a nonpredictive cue. In the second experiment, cue interactions in conditioned inhibition were examined. A stimulus gained negative predictive strength as the result of compound presentations with a positive predictor when the outcome was not presented. This negative predictor was compared with an otherwise analogous stimulus that was not presented in compound with a positive predictor. These results support the use of animal-conditioning models as accounts of human contingency learning.

Adult↗
PubMed1987

Localization of Plasmodium falciparum histidine-rich protein 1 in the erythrocyte skeleton under knobs.

Plasmodium falciparum parasites that induce knobs in the host erythrocyte membrane (K+ phenotype) synthesize a 90 kDa histidine-rich protein (PfHRP-1), whereas knobless variants do not. A monoclonal antibody (mAb 89) to PfHRP-1, in combination with cryo-thin section immunoelectron microscopy, localized the antigen in the parasitophorous vacuolar space and vesicles within the erythrocyte cytosol. Additional immunoelectron microscopic studies showed that PfHRP-1 was also associated with submembranous electron-dense material under knobs and with microfilaments of the host erythrocyte skeletal network. Immunofluorescence and immunoelectron microscopy of intact, non-fixed K+ infected erythrocytes using mAb 89 and a rabbit antiserum raised against purified PfHRP-1, failed to identify any surface exposed epitopes. These antibodies also failed to block cytoadherence of infected erythrocytes to C32 melanoma cells or to affect macrophage phagocytosis of infected erythrocytes.

Animals↗
PubMed1987

The application of propidium iodide staining to the study of the macronucleus and micronuclei in the suctorian, Heliophrya sp.

Morphological changes in the macronucleus and micronuclei of the ciliated protozoon Heliophrya chapmani were investigated using the nucleic acid-specific stain propidium iodide. The fluorescence patterns of nuclei observed in propidium iodide preparations correspond well with those observed using more conventional DNA-specific methods, such as the Feulgen stain. The advantages of propidium iodide staining (minimal cell loss during staining, rapidity of the staining process, and the avoidance of cell damage during hydrolysis) make this method a quick and efficient alternative in the cytochemical study of the protozoan nucleus.

Animals↗
PubMed1978

Fine structure of the nasal barbel of the channel catfish, Ictalurus punctatus.

Ultrathin sections of the nasal barbel of the channel catfish, Ictalurus punctatus, were studied in the electron microscope and the fine structure was compared to that of barbels of other teleosts and to the mandibular (dentary) barbels of I. punctatus. While the overall histology of the nasal barbel is similar to that of barbels described previously, this study revealed far greater cellular complexity and variability than was previously reported. A layer of stratified epidermal cells rests upon a connective tissue dermis containing a cartilage rod, a large number of nerve fibers and numerous blood vessels, fibroblasts and pigment cells. Taste buds are present in the epidermal layer. This layer was found to contain probably 16 kinds of cell types, several of which may represent transitional stages, in addition to taste bud cells. Observations were made pertaining to innervation and cell types in the taste buds. A new terminology for designating the barbels of I. punctatus is suggested.

Animals↗
PubMed1976

The ultrastructure of implanted trophoblast cells of the yellow agouti mouse.

An electron microscope study of ultrathin sections of trophoblast cells of implanting blastocysts resulting from the crossing of heterozygous yellow agouti mice has been conducted. Several conditions for successful preparation of the blastocysts have been described. These include avoidance of the use of sucrose in the buffers, reduction of specimen washing times and exclusion of propylene oxide from the dehydration procedure. Electron micrographs of cells from a blastocyst considered, on the basis of light microscopy, to be 'abnormal' revealed a cytoplasm with many 'empty' areas and numerous 'vacuolated' mitochondria. Electron micrographs of cells from blastocysts considered to be 'normal' revealed, in one instance, a preponderance of cells with very few of these 'abnormal' features, and, in the other instance, a preponderance of cells with many abnormalities. Both 'normal' blastocysts revealed cellular features usually regarded as either primitive or pathological, namely tight junctions, vacuolated mitochondria and mitochondria with cristae oriented parallel to their long axis. It was generally concluded that the appearance of the blastocysts, in the light microscope, at 100-105 hours of development, could not be used as a valid criterion of normality or abnormality, for, although a blastocyst classified as 'abnormal' under the light microscope appeared 'abnormal' also in the electron microscope, those classified as 'normal' under the light microscope appeared either 'normal' or 'abnormal' in the electron microscope. This disturbing situation may indicate that the electron microscope is diagnosing 'abnormality' before the light microscope. The presence of immature forms of organelles (e.g., vacuolated mitochondria) indicates either a failure to mature or regression. Failure to mature could be benign or of sinister import.

Animals↗
PubMed1970

Intracytoplasmic membrane structures in Vibrio marinus.

An electron microscope study of Vibrio marinus strains MP-1, an obligate psychrophile, and PS-207, a moderate psychrophile, revealed numerous intracellular membranous structures. The structures were found to occur more frequently in V. marinus strain MP-1 than in strain PS-207. The frequency of occurrence and complexity of structure were related to age of the culture. In early logarithmic phase, cells revealed invaginations of the plasma membrane. More complex membrane forms, found in late logarithmic and stationary phase, were either myelin-like sheaths, for which the term "myelemma" is proposed, or membranes randomly arranged throughout the cells. The complex membrane forms were not observed to be directly connected with the plasma membrane. However, they were often found in approximation to the plasma membrane or associated with vacuoles and circular membrane profiles. Individual membranes were of a tripartite structure and of dimensions similar to the cell wall and plasma membrane.

Bacteriological Techniques↗
PubMed1970

Effect of low temperature on the growth and fine structure of Bacillus subtilis.

Logarithmically growing cultures of Bacillus subtilis transferred from 37 to 15 C present atypical growth curves, and ultrathin sections of such cells reveal structural modifications involving mesosome deterioration and double cell wall formation. After a time, optical density and viable count increase, and cells regain the appearance typical of control cells, indicating a recovery from thermal stress. Subcultures of such recovered cells continue to grow well at 15 C. Cultures transferred from 37 to 12 C show atypical growth and fine structure, although no recovery from this stress is seen. Cultures previously grown at 15 C continue to grow at 12 C, and, furthermore, do not show the ultrastructural alterations seen in similar cells with a 37 C thermal history. The results of these studies suggest that low temperatures induce structural modifications in B. subtilis, that the response of a population to thermal stress may change during the period of the stress, and that thermal history may influence the response of a population to thermal stress.

Adaptation, Physiological↗
PubMed1969

Morphology and round body fermation in Vibrio marinus.

The morphology of Vibrio marinus MP-1 was studied by phase and electron microscopy. The ultrastructure of the vibrio form of V. marinus was found to be typically gram-negative with a trilaminar plasma membrane and cell wall. The coccoid or round bodies noted in otherwise pure cultures of V. marinus were frequently found in early and late stationary phase of growth. The round bodies in ultrathin section were found to contain at least one, and often three or four, cell units. Three types of round bodies were observed in ultrathin section, each differing in size and behavior: "spherules," "spheres" or the "round body," and "giant cells" or "macrospheres." The round bodies appeared to be associated with, or to result from, the constrictive cell division of V. marinus.

Cell Division↗
PubMed1968

Fine structure of selected marine pseudomonads and achromobacters.

The fine structure of more than 20 marine pseudomonads and more than 15 achromobacters was examined. Under the conditions extant, clear differences between members of these two groups were seen. The pseudomonads displayed the characteristic gram-negative morphology: the cell wall was irregularly undulant and the cytoplasmic membrane more nearly planar, ribonucleoprotein (RNP) particles were loosely packed throughout the periphery of the cytoplasm, and the deoxyribonucleic acid (DNA) was axially disposed. Cell division appeared to be by constriction. Some strains characteristically produced evaginations or blebs of the cell wall. Occasionally, thick, densely stained ring structures were seen which are possibly analogous to mesosomes. In contrast, the achromobacters demonstrated a regularly undulant outer cell wall element and a planar inner wall. The cytoplasmic membrane was thin and not readily observed. RNP particles were densely stained and tightly packed in the cytoplasm; the DNA was most often lobate in disposition. Cellular division was mediated by the formation of a septum which consisted of the cytoplasmic membrane and the inner element of the cell wall. Mesosomes were observed in all of the strains examined. Dense inclusion bodies were also seen in many strains.

Alcaligenes↗
PubMed1968

Variation in the fine structure of a marine achromobacter and a marine pseudomonad grown under selected nutritional and temperature regimes.

Certain features of the fine structure of a marine achromobacter and a marine pseudomonad were dependent upon the conditions of growth. Cells of achromobacter grown at 10 C in a low peptone-seawater (SW) medium displayed the characteristic morphology of the achromobacter: a regularly undulant outer element of the cell wall and a planar inner element, tightly packed ribonucleoprotein (RNP) particles in the cytoplasm, deoxyribonucleic acid (DNA) disposed in a lobate manner, and dense inclusion bodies. Few mesosomes, however, were seen. Cells of achromobacter grown at 10 C in a high peptone-SW medium had larger and more highly organized mesosomes. At 22 C, in a low peptone-SW medium, no mesosomes were seen, but the inclusions were more frequently seen and were larger in the achromobacter cells. At 22 C, in a high peptone-SW medium, these cells revealed the greatest variation in cellular morphology. They contained both small and large mesosomes, or no mesosomes, and both small and large inclusions, or no inclusions. Pseudomonad cells at 10 C in a low peptone-SW medium revealed a typical gram-negative morphology: double-layered, irregularly undulant cell wall; more nearly planar cytoplasmic membrane; densely stained, lightly packed RNP particles; finely fibrillar, axially disposed DNA; simple mesosomes. At 10 C, in a high peptone-SW medium, pseudomonad cells revealed associated strands of material and intracytoplasmic ringlike structures. At 22 C, in a low peptone-SW medium, pseudomonad cells had a more undulant cell-wall and a more nearly planar cytoplasmic membrane. At 22 C, in a high peptone-SW medium, these cells revealed prominent blebs of the cell wall.

Alcaligenes↗