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Biomedical subjects

B R Scott

Publications and source records attributed to B R Scott.

At least 55 records · Page 3Linked to original sources
PubMed1977

Mechanistic state vector model for cell killing by ionizing radiation.

By use of the mechanistic state vector model (MSV model) it is demonstrated that under circumstances where cell division during irradiation is unlikely: 1. A cell survival curve (dose-log surviving fraction curve) that is exponential can be obtained even though some of the surviving cells may have nonlethal damage. Exponential survival curves are said to have zero curvature. 2. In some cases, in the absence of a mixed population, the slope of a single-dose survival curve may decrease in magnitude, as the dose increases for a range of doses. These curves are said to show negative curvature for that range of doses. Fractionating the dose or decreasing the dose rate may result in enhanced cell killing. 3. The initial slope of a mammalian cell survival curve should be independent of the dose rate and number of dose fractions provided that the number of cells having lethal damage builds up to a steady level during the post irradiation time regime. The magnitude of the initial slope will depend on properties of the cells and on properties of the radiation. 4. A nonzero initial slope in the cell survival curve, after exposure to low linear energy transfer (LET) radiation, may be due to biology, rather than physics.

Animals↗
PubMed1977

The induction of mutations to 2-thioxanthine resistance in inhibitor depleted conidia of Aspergillus nidulans by gamma-radiation in the presence of oxygen or nitrogen.

A strain of Aspergillus nidulans has been used to study the inactivating and mutagenic effect of 60Cogamma-rays in the presence of oxygen or nitrogen. Mutation was studied by the 2-thioxanthine system which selectively detects forward mutation at a number of gene loci (at least 16). Mutants resistant to conidial pigmentation effects of 2-thioxanthine can be divided into four main classes (2TxR, hx, uaY and cnx) and three of these classes (hx, uaY and cnx) can be further characterized at the gene level. The results demonstrate the existence of a marked differential forward mutational response of gene loci in Aspergillus conidia which is dependent upon whether gamma-irradiation in aqueous suspension was carried out in the presence of oxygen or of nitrogen: this effect is independent of the dose of radiation exposure. The specificity for mutation is altered by the presence of the self-inhibitor of germination for the anoxic treatment but not the oxic irradiation. The implication of different oer's (oxygen enhancement ratios) for mutation induction in different classes or genes for the mechanism and type of damage induced by the two radiation conditions are discussed.

Aspergillus nidulans↗
PubMed1976

UV mutagenesis in inhibitor depleted conidia of Aspergillus nidulans.

UV treated conidia of a strain of Aspergillus nidulans (meth Gl. biAl) depleted of germination inhibitory substances have been examined for inactivation and mutation induction at groups of suppressor gene loci defining three classes of methionine revertants. An exponential decline in the colony forming ability and quadratic increase in mutation frequency (for each class of revertant) as the incident dose increased were observed. The induced mutation frequency for each class and the loss of colony forming ability of the conidia are greater in the absence than in the presence of these self-inhibitors of germination. However, the relative frequencies of the individual classes of revertants did not differ whether the inhibitory substances were present or not. Liquid holding effects leading to increases in survival and mutation have been observed, but the relative frequencies of the individual revertant classes remain unchanged.

Aspergillus nidulans↗