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C Burn

Publications and source records attributed to C Burn.

8 recordsLinked to original sources
PubMed2001

Information processing during hypnotically suggested sex change.

During hypnotically suggested sex change, 36 real (12 virtuoso and 24 high hypnotizable) and 18 simulating (low hypnotizable) individuals listened to a story involving a male and a female character. They subsequently reported their experience and recall of the story. Virtuosos were less likely than highs and simulators to identify with the character consistent with their suggested sex. However, virtuosos recalled more information about the character consistent with their suggested sex than did highs and simulators. The authors discuss the findings in terms of attention and the selective processing of information during hypnosis. They conclude that character identification was not the major factor that influenced the recall of virtuosos and suggest that virtuosos may have processed aspects of the information in a more self-referential way and thus encoded and recalled it more effectively.

Adult↗
PubMed1995

Prediction of the initial slope of the acute clonogenic survival curve by the post-irradiation behaviour of cytochalasin-induced polykaryons.

We have investigated the behaviour of 11 lines of cultured cells in a survival assay whose endpoint is the ability of cells to become polyploid when incubated in the presence of cytochalasin B (CB). Single cells were induced by CB to form polykaryons after irradiation, and, by analogy with the colony-forming assay, the survival of polykaryon-forming units (PFUs) was defined as the fraction of cells able to achieve a given DNA content (at least 16C in most experiments). There was a radiation dose-dependent reduction in PFU survival, which, following the appearance of cells containing at least 16C DNA, was not markedly dependent upon the sampling time. In all cases, PFUs appeared to be more radioresistant than clonogens, especially at high dose. In 9/11 lines the PFU dose-response curves were exponential, while in two there was a pronounced curvature (quadratic parameter). There was a highly significant positive correlation between PFU response and the corresponding clonogenic initial slope. We suggest that in polykaryons the opportunity for the mechanical loss of DNA fragments may be reduced because the cells do not divide, and therefore that DNA damage resulting from chromosome aberrations may be less important in PFUs than in clonogens. Consequently, PFUs may express lesions not directly associated with mechanical gene loss. This assay may yield an alternative estimate for the clonogenic initial slope, and could be of use where colony-forming assays fail due to incomplete cell monodispersion.

Animals↗
PubMed1995

Variation in radiosensitivity due to cell age and split-dose recovery in polykaryons induced by cytochalasin.

We have investigated the properties of an in vitro cell survival assay that uses as its endpoint the ability to form polyploid cells (polykaryons) in the presence of cytochalasin B (CB). The criterion for survival is that a polykaryon-forming unit (PFU) must reach the arbitrary DNA content of at least 16C. The age-dependence of PFU sensitivity to 137Cs irradiation was determined using V79-379A cells synchronized at mitosis. Cells assayed as PFUs demonstrated much less variation in radiosensitivity with age than did clonogens, but the changes in curve shape were qualitatively similar. In both assays mitotic cells yielded an exponential survival curve while that obtained at 5 h (mid-late S) had a marked quadratic component. Owing to the small overall variation in PFU survival with age, at doses greater than about 25 Gy the surviving fraction at 5 h was lower than in mitosis. In both V79-379A and HeLa S3 cells, PFUs demonstrated a capacity for split-dose recovery and yielded recovery ratios at 2.6 at 50 Gy in V79 and 1.5 at 20 Gy in HeLa. Since these ratios were much lower than in clonogens at the same dose, we suggest that this is consistent with an association that we have previously demonstrated between PFU response and the clonogenic initial slope. In an attempt to clarify the DNA lesions to which PFUs may be sensitive, we determined PFU response following exposure to 254-nm UV irradiation. In contrast with ionizing radiation, PFU response to UV was very similar to that of clonogens. This suggests that following UV exposure the absence of cytokinesis in polykaryons may confer less protection than in the case of ionizing radiation, possibly due to fundamental differences in the spectrum of DNA lesions produced.

Animals↗
PubMed1993

The survival of cytochalasin-induced polykaryons following exposure to cytotoxic agents.

Using CHO-K1, HeLa S3 and two Walker lines (WR and WS) differentially sensitive to cis-diamminedichloroplatinum(II) (cisplatin), the survival after exposure to cisplatin, mitomycin C, vinblastine, vincristine or cytosine arabinoside has been determined either of clonogens or of cells rendered polyploid by post-exposure incubation in the presence of cytochalasin B (CB). It is suggested that the inhibition of cytokinesis by CB permits an assessment to be made of the fraction of damage whose expression is cell division-related, possibly including that resulting from a loss or malsegregation of genetic material. It was found that the response of polykaryons in comparison to clonogens was both agent- and cell line-dependent. After cisplatin exposure, polykaryon survival (defined as the ability to accumulate at least 16C DNA) declined exponentially with dose and was qualitatively, and to some extent quantitatively, similar to that observed previously after irradiation. In HeLa S3, giant cells induced by 10-20Gy irradiation in the absence of CB exhibited a radiation dose-dependent reduction in the relative frequency of highly polyploid cells which was similar to that observed in CB-induced polykaryons.

Animals↗
PubMed1990

Flow cytometric studies of the survival of cytochalasin-induced polyploidy in Chinese hamster ovary cells.

A method has been developed to estimate the post-irradiation survival of cytochalasin B-induced polyploidization of adherent Chinese hamster ovary cell using the flow cytometer. After exposure to radiation, surviving cells are allowed to become polyploid in the presence of cytochalasin, and are detached using trypsin, fixed by the addition of glutaraldehyde and stained using mithramycin. DNA content distributions are polymodal, and the absolute number of cells per culture in any given ploidy class is estimated by reference to a non-fluorescent bead internal standard, detected using forward scatter. Post-irradiation survival is defined as the ability to reach a given DNA content, and is reduced exponentially with dose. A bioassay to determine optimum cytochalasin concentrations can be derived from the relative size of the 2C (G0/G1) peak in the DNA content distribution. At culture densities greater than about 8 x 10(4) cell/cm2 the relative number of cells reaching at least 16C is reduced, but this inhibition is partially reversible by an increase in the medium glucose concentration, but not by the use of cytochalasin D or dihydro B.

Animals↗
PubMed1987

Evaluation of pulmonary artery pressure and resistance by pulsed Doppler echocardiography.

Pulsed Doppler echocardiography was used to examine the relation between pulmonary valve motion and pulmonary artery (PA) flow velocity patterns in 39 adults. In 16 patients with normal PA pressure (mean pressure less than 20 mm Hg), PA flow velocity accelerated slowly to a peak flow velocity at midsystole (time to peak flow velocity, or acceleration time = 134 +/- 20 ms [mean +/- standard deviation]), followed by a slow deceleration to the end of ejection, producing a "dome-like" appearance. In contrast, in 23 patients with elevated PA pressure (mean pressure 20 mm Hg or more), flow velocity accelerated rapidly to a peak flow velocity in early systole (acceleration time = 88 +/- 25 ms, p less than 0.01), followed by rapid flow velocity deceleration to a nadir in midsystole. In 13 of these patients, a transient increase in flow velocity occurred in late systole, producing a "spike and dome" appearance. In patients with an acceleration time of 120 ms or less, there was a negative linear correlation with mean PA pressure, expressed by the equation: mean PA pressure = 90 - (0.62 X acceleration time). The standard error of the estimate was 8.3 mm Hg. A similar negative linear correlation was found between PA acceleration time and total pulmonary resistance. Using a PA acceleration time of 100 ms or less resulted in a 78% sensitivity and a 100% specificity for detection of elevated PA pressure. Although this Doppler method cannot precisely estimate PA pressure, it can be helpful in separating patients with normal pressure from those with elevated PA pressure.

Adult↗
PubMed1979

Echocardiographic measurements in normal subjects: evaluation of an adult population without clinically apparent heart disease.

In order to determine normal echocardiographic values for older subjects, we studied 136 adults (78 men and 58 women, 20 to 97 years of age) without evidence of cardiovascular disease. When patients were subdivided into six age groups, progressive changes were found in mean normal values for various parameters. Specifically, when the oldest group (over 70 years) was compared with the youngest group (21-30 years), significant (p less than 0.01) increases in aortic root (22 percent) and left atrial (16 percent) dimensions, in ventricular septal (20 percent) and left ventricular free-wall (18 percent) thicknesses, and in estimated left ventricular mass (15 percent) were noted. In addition, a significant (p less than 0.01) decrease in mean mitral E-F slope (43 percent) and slight decreases in mean left ventricular systolic and diastolic internal dimensions (5 and 6 percent, respectively; p less than 0.05) were noted. Left ventricular ejection fraction and percentage fractional shortening were found to be independent of age. These data have been used to derive regression equations that are related to both age and body surface area. The regression equations can be used to calculate mean normal values and 95 percent prediction intervals for echocardiographic measurements in adults.

Adult↗