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Biomedical subjects

A Robertson

Publications and source records attributed to A Robertson.

At least 289 records · Page 16Linked to original sources
PubMed1975

Gene frequency distributions as a test of selective neutrality.

The analysis of differences between loci in the variance of gene frequency over populations within a species has been suggested as a method of detecting natural selection. It is shown that, in the absence of selection, the expected variation over loci depends strongly on the pattern of relationships between populations. The effect of structure within a species is always to increase the variation and therefore to reduce the power of the method.

Biological Evolution↗
PubMed1975

Reduced plasma membrane permeability in a multiple cross-resistant strain of Saccharomyces cerevisiae.

Single nuclear gene inheritance was shown to be responsible for increased resistance to: eight diverse inhibitors of mitochondrial function (antimycin, carbonylcyanide-m-chlorophenylhydrazone, chloramphenicol, oligomycin, tetracycline, triethyltin bromide, triphenylmethylphosphonium bromide and triton-X-165); and an inhibitor of cytoplasmic protein synthesis (cycloheximide). Continuous monitoring of oxygen uptake during respiratory adaptation showed that anerobic pretreatment of resistant cells sensitized respiratory adaptation to chloramphenicol and antimycin. However, since a depression of mitochondrial function by catabolite repression did not result in sensitization to antimycin, alteration of the mitochondrial membrane does not appear to be responsible for resistance to mitochondrial inhibition. Alteration of cellular binding sites was not responsible for resistance since in vitro mitochondrial protein synthesis was sensitive to chloramphenicol and in vitro mitochondrial respiration was sensitive to oligomycin, carbonylcyanide-m-chlorophenylhydrazone, and antimycin. Autoradiography of an ethylacetate-ethanol extract of [14C]chloramphenicol-treated resistant cells indicated that resistance was not due to enzymatic modification of inhibitors. The maintenance of an antimycin-resistant respiration by protoplasts of resistant cells ruled out the involvement of the cell wall in cellular resistance. The reduced transport of [14C]chloramphenicol by resistant cells (1% of normal cells) indicated that a single nuclear gene mutation can alter the permeability of the plasma membrane to many diverse inhibitors.

Anaerobiosis↗
PubMed1975

Cell density dependence of the aggregation characteristics of the cellular slime mould Dictyostelium discoideum.

We have measured fruiting body density and spore formation efficiency in Dictyostelium discoideum as functions of initial cell density. Experiments were performed on agar made up with distilled water and on buffered agar. Minor differences are seen; these are discussed. The functions show 4 regions of density dependence which can be accounted for by changes in aggregation characteristics with density and changes in the efficiency of spore differentiation. The results are discussed in terms of the relaying mechanism for signal propagation controlling cell aggregation. They extend earlier measurements by Bonner & Dodd and by Hohl & Raper, supply data for a quantitative model of the aggregation process, allow estimates of signal range, and show the importance of entrainment between neighbouring centres in defining aggregation territories.

Cell Aggregation↗
PubMed1975

The distribution and elimination of radioactivity in the rat after administration of 14C-4-acetamidophenyl-2-acetoxybenzoate (benorylate).

Following oral administration of 4-acetamido-phenyl-2-acetoxybenzoate (carboxyl-14C) (benorylate) to rats, no gross differences were detected 7.5 h after administration with respect to the distribution of 14C in various tissues, including the upper sections of the small intestine. A high concentration of 14C was found in the lower sections of the intestine 4 h after administration. The 14C in the intestine was present as unchanged benorylate, as detected by thin-layer chromatography, suggesting that benorylate absorption was slow. Intravenous injection of 14C-benorylate to rats showed that the drug had a relatively high elimination rate from the blood with a half-life of 1.9 h. In blood benorylate must be rapidly hydrolysed enzymatically since no 14C-metabolites, other than salicylic acid, could be detected.

Adipose Tissue↗
PubMed1975

The tip of the Dictyostelium discoideum pseudoplasmodium as an organizer.

We have extended Raper's original work on the organizing ability of the tip of the Dictyostelium discoideum slug. Our new results are that tips from all multicellular (pseudoplasmodial) stages act as organizers; that the structure organized by a tip depends on the developmental stage of the cells responding to the tip's signal; that tips from all stages release a qualitatively similar signal which is continuous, most probably a gradient of c-AMP; and that the signal from fruiting-body tips appears stronger than that from conus tips. We discuss these results with reference to the control of morphogenetic movement and patterned differentiation and point out that the D. discoideum tip is analagous to a classical organizer, whose signal is interpreted according to the state of determination of cells in its field of influence.

Cell Differentiation↗
PubMed1975

Influence of vaccination with avirulent herpesvirus on subsequent infection of chickens with virulent Marek's disease herpesvirus.

Vaccination of chickens with turkey herpesvirus (HVT) or attenuated Marek's disease herpesvirus (aMDHV) blocked infection with virulent MDHV (VMDHV) for approximately 5 weeks after contact exposure. However, there was no apparent blockage of infection when challenge virus was administered intraabdominally (IA). Evidence for infection with VMDHV was based on viral isolation by in vivo assay or by detecting precipitins to "A" antigen associated with virulent virus. The HVT stimulated production of neutralizing antibody against VMDHV in a high percentage of chickens, whereas the aMDHV was a comparatively poor inducer of such antibody. Despite this difference, both of the vaccinal viruses conferred protection against development of Marek's disease.

Animals↗
PubMed1974

Symposium No. 10: Animal genetics. Introduction by the Chairman.

On the basis of morphology Chenopodium quinoa of the Andes and C. nuttalliae of Mexico appear to be very closely related species. Artificial hybrids have been secured between the two. It is suggested that both species may have been derived from the same original wild type. A weedy quinoa, C. quinoa var. melanospermum, is known from South America, but as yet a weed race closely related to C. nutalliae has not been reported from Mexico.

Animals↗
PubMed1974

Distribution of pentazocine in blood and brain of the baboon following intravenous injection.

1 In the baboon the blood levels of pentazocine between 1 and 60 min after intravenous injection of 0.5 mg/kg were measured by a gas chromatographic technique. From cerebral arteriovenous differences it was shown that the peak of the brain concentration occurred within 15 min and probably within 10 min of intravenous injection. At the time of peak concentration about 10% of the injected dose was in the brain, while the corresponding value at 60 min was 2%.2 The concentration of pentazocine in the brain was an order of magnitude greater than the concentration in cerebral venous blood both at 5 min and 60 min after injection. No major brain interregional differences were demonstrated. Cerebrospinal fluid from the cisterna magna did not yield values from which the cerebral concentration of pentazocine could be predicted.

Animals↗