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Biomedical subjects

Y George

Publications and source records attributed to Y George.

At least 19 recordsLinked to original sources
PubMed1979

Suppressor mutations causing partial reversion in the amiA region of Pneumococcus.

Mutants of an aminopterin-resistant strain of pneumococcus possessing four different suppressor genes have been isolated after mutagenesis with 5-BUdR. The suppressed strains exhibit a partial revertant phenotype since the parental aminopterin resistance remained unchanged but the associated sensitivity to an excess concentration of the branched chain amino acids L-isoleucine, L-valine and L-leucine was diminished almost to the level of the wild-type strain C13. The suppressor mutations had therefore dissociated the two properties associated with a mutation in the amiA cistron, namely aminopterin resistance and isoleucine sensitivity. The suppressor genes reduced the sensitivity to isoleucine of a number of amiA mutants, but had no effect on the level of resistance to a number of unrelated genes conferring resistance to other antibacterial substances. The suppressor mutations themselves did not confer resistance to aminopterin. Mapping of the suppressor mutations by recombination analysis and by clonal analysis showed them to be intragenic lying in the region near to the amiA-r19, amiA-r23, amiA-r17 loci.

Aminopterin↗
PubMed1976

[Ultrastructural variations of synapses in the normal human cerebral cortex].

The numerous synapses in the normal human brain cortex display various aspects. The authors have also observed some electronic type synapses which are more numerous around the pericaryons. The cortical synapses are classed according to their synaptic vesicle richness : synapses with very few vesicles, synapses very rich in vesicles and synapses with a middling vesicular density. With the help of observations on these aspects and on variations of the synaptic cleft and that of the postsynaptic density, the authors advance an hypothesis on synaptic plasticity, the synaptic structures going from a simple intercellular contact (probably non functional) to a completly formed synapse and vice versa.

Adolescent↗
PubMed1975

[Microglia and pericytes of the human cerebral cortex].

Biopsies of normal human cerebral cortex were fixed by aldehydes and their ultrastructure was studied. Two main types of vessels are observed, capillaries and metarterioles, and around them two types of pericytes are described: a microgliocyte-like pericyte which is either surrounded by a nervous basal membrane, or laying outside this membrane; endothelial-like pericytes which are frequently observed inside the metarterioles perivascular space and contain many lysosomes. Endothelial-like pericytes have probably a metabolic function and microgliocyte-like pericytes are more involved in a role of mechanic regulation of the microcirculation. This hypothesis is supported by the observation of a microgliocyte interposed between two endothelial processes and protuding into the vascular lumen.

Cerebral Cortex↗
PubMed1975

[Ultrastructure of cellular features permitting the regulation of human cerebral cortex microcirculation].

Microglia-like cells and endothelial cells may influence capillary blood output. 1) Microglia-like cells are sometimes interposed between two endothelial processes with which they are nexus-linked. In this position, they protude in vascular lumen which is considerably reduced. 2) Endothelial cells present no contractile filaments but their nucleus and surrounding cytoplasm may protude in vascular lumen, constituting a "coussinet-like" structure. Thus, regulation by specialized structures observed by Legait in brain arteries seems to occur even in the smallest ramifications of brain cortical vessels.

Capillaries↗