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Biomedical subjects

J G Thompson

Publications and source records attributed to J G Thompson.

At least 55 records · Page 3Linked to original sources
PubMed1991

Glucose utilization by sheep embryos derived in vivo and in vitro.

Embryos were collected from superovulated donors at various intervals from onset of oestrus, ranging from Day 1.5 to Day 6. In addition, blastocysts obtained from the culture of 1-cell embryos collected in vivo or of oocytes matured and fertilized in vitro were used to assess the effects of in vitro manipulation and culture on glucose utilization. Glycolytic activity was determined by the conversion of [5-3H]glucose to 3H2O, and oxidation of glucose was determined by the conversion of [U-14C]glucose to 14CO2. Glucose utilization increases significantly from the 8-cell stage and during compaction and blastulation. Glucose oxidation was at a relatively low level (5-12% of total utilization) compared with glycolysis. No difference was observed between the glycolytic activity of blastocysts derived from in vivo or in vitro sources. However, glucose oxidation was lower (P less than 0.05) in blastocysts derived from the culture of 1-cell embryos or from oocytes matured and fertilized in vitro. Exogenous tricarboxylic acid cycle substrates (i.e. pyruvate and lactate supplied in the medium) affected the level of glucose oxidation.

2,4-Dinitrophenol↗
PubMed1990

Effect of oxygen concentration on in-vitro development of preimplantation sheep and cattle embryos.

Two-cell sheep embryos and 2-4-cell and 8-cell cow embryos were cultured for 5 days in stoppered test-tubes in Synthetic Oviduct Fluid supplemented with 32 mg BSA/ml. The medium had been previously equilibrated with one of the following O2 concentrations (sheep: 0, 2, 4, 6, 8, 10, 12, 17, 20%; cow: 0, 4, 8, 12, 17, 20%). At the end of culture embryos were examined for morphology and stained to assess numbers of nuclei. Mean (+/- s.e.m.) nuclei/embryo was highest at 8% O2 for sheep embryos (23.6 +/- 3.1), 4% for 2-4-cell cow embryos (23.2 +/- 6.1) and 8% for 8-cell cow embryos (29.6 +/- 5.2). The minimum number of nuclei/embryo occurred at 20% O2 in each case (10.3 +/- 0.9, 10.3 +/- 2.7, 14.5 +/- 2.4, respectively) with similar values also recorded at 0% O2 (10.8 +/- 1.9, 16.5 +/- 6.0, 14.6 +/- 2.4, respectively). Analysis of the proportion of embryos reaching at least the morula stage demonstrated a significant quadratic component for the different oxygen concentrations for sheep (P less than 0.01) and cow (P less than 0.05) embryos. A number of sheep and cow embryos showed abnormalities, suggesting that the culture conditions require further refinement. The results confirm that, under lowered oxygen levels, development of sheep and cattle embryos can occur through the 8- to 16-cell block in a simple defined medium without somatic cell support.

Animals↗
PubMed1989

Development of sheep preimplantation embryos in media supplemented with glucose and acetate.

Two experiments were conducted to examine the effect of supplemental glucose (G; 1.5 mM) and/or acetate (A; 0.5 mM) on the development of early sheep embryos to blastocysts when cultured in vitro in glucose-free synthetic oviductal fluid (SOF)+sheep serum or bovine serum albumin (BSA). In Experiment 1, 2- to 4-cell, 8- to 16-cell and >16-cell embryos were cultured in SOF, SOF+G, SOF+A or SOF+G+A. All media were supplemented with 10% sheep serum. In addition, embryos were cultured in either microdrops under polysiloxane oil or in multiwell dishes. Overall, development to the blastocyst stage was 3%, 30% and 68% for 2- to 4-cell, 8- to 16-cell and >16-cell stages, respectively, suggesting that an 8-cell developmental block existed under our culture conditions. Glucose supplementation had little effect on embryo development, and no overall effect was observed from the addition of acetate. In Experiment 2, 8- to 16-cell embryos were cultured in SOF or SOF+G, both supplemented with BSA. Development to the blastocyst stage was 25% and 18%, respectively. The results show that the presence of glucose or acetate did little to enhance embryonic development in our incubation systems. Further work is required to evaluate fully the energy requirements for development of the early sheep embryo.

Journal Article↗
PubMed1985

Inferences and recall at ages four and seven.

Inferences and recall at ages 4 and 7 were studied as a function of the cause of a target event, the presence and timing of questions prior to recall, and the type of inference demanded by the questions. 7-year-olds inferred and recalled well with stories containing any of the causal connections employed in the study. 4-year-olds performed better when physical causes, rather than either psychological causes or enabling relations, connected events. Timing of questions did not affect the 7-year-olds' inferences, but asking questions interfered with their recall. Questions about story events aided the 4-year-olds' ability to make inferences and to recall, especially when causal connections were least specified and when questions were asked following the story. 4- and 7-year-olds also differed in responding to demands for 3 specific types of inference. 4-year-olds produced significantly more unconstrained inferences than logical or constrained informational inferences. 7-year-olds were most responsive to logical inference questions, and produced significantly more logical than constrained inferences.

Child↗
PubMed1980

The effects of retinal eccentricity and orientation on perceived length.

An experiment was performed to examine the effects of line orientation and retinal locus on the perceived length of a single line. Thirty-five male and female undergraduate volunteers each monocularly judged the length of five test lines presented in two orientations (horizontal and vertical) at five different retinal loci. Displacement of horizontal lines from the fovea on either the horizontal or vertical meridian produced decreases in perceived size. The perceived length of vertical lines, however, decreased only with displacements on the vertical meridian.

Humans↗
PubMed1978

The role of apparent depth and context in the perception of the Ponzo illusion.

The role of apparent depth features and the proximity of the test lines to the adjacent contours in the actuation of the Ponzo illusion was examined. Six versions of the Ponzo figure were employed: a standard Ponzo figure and five modified figures in which the test lines varied in orientation (horizontal or vertical) and in location (inside or outside the converging contours). Both manipulations resulted in a significant decrease in the magnitude of the illusion in comparison to the standard Ponzo figure. The results suggest that the Ponzo illusion is significantly affected by contextual factors.

Depth Perception↗
PubMed1978

Effect of perspective and slant on perception of apparent size and distance.

An experiement was performed to re-examine the role of linear perspective and floor slant on apparent size and distance scales. Misleading perspective cues did not alter the observers' apparent distance scales but did influence the absolute magnitude of distance judgments; floor slant exerted little influence on apparent distance scales or the absolute magnitude of distance judgments. Neither perspective nor slant manipulation reliably affected apparent size scales or exerted more than a minor influence on the absolute magnitude of size judgments.

Cues↗
PubMed1977

The perception of brief temporal intervals: power functions for auditory and visual stimulus intervals.

Two experiments were performed to examine the role of method of estimation and the employment of a standard stimulus on the judged duration of auditory and visual stimuli presented for brief temporal intervals (0.25 to 5.0 s). The results indicate that the relationship between judged and physical duration is nearly direct and linear. Psychophysical methodology and stimulus modality exerted little influence on the obtained power functions.

Acoustic Stimulation↗
PubMed1975

The role of figure orientation and apparent depth in the perception of the horizontal-vertical illusion.

An experiment was performed which examined the role of figural orientation directly, and the role of an inappropriately invoked size-constancy mechanism indirectly, in the actuation and magnitude of the horizontal-vertical illusion. When the vertical line of the stimulus figure was aligned above the horizontal line, the illusory effect was significant and positive; in contrast, when the vertical line was located below the horizontal line, the illusion was negative. Under the assumption that a vertical line can appear as a foreshortened line in depth, these findings support an explanation based on the operation of a misapplied size-constancy mechanism.

Depth Perception↗