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Biomedical subjects

G Meyer

Publications and source records attributed to G Meyer.

At least 397 records · Page 22Linked to original sources
PubMed1984

A rapidly light-induced chloroplast protein with a high turnover coded for by pea nuclear DNA.

Among the translation products obtained in vitro with mRNAs isolated from etiolated grown pea, or after different times of illumination following the etiolation, a 24000-Mr protein has been observed in the very early phase of greening; its occurrence culminates at 2-4 h after the start of illumination. From these data it is concluded that the corresponding mRNA appears in and disappears from the poly(A)-containing RNA population within hours. The protein product has been characterized as the precursor for a 17000-Mr chloroplast protein; by means of post-translational transport in vitro, the processed product becomes bound to chloroplast membranes. A product of the same size can also be labeled in vivo with a maximum of incorporation of label at 6-8 h after illumination. This product decays with a half-life of about 5 h. These findings imply a regulatory function of the 17000-Mr protein during the process of greening, possibly by synchronization of nuclear and chloroplast genomes. Other possibilities are considered.

Biological Transport↗
PubMed1984

Methotrexate-vindesine association in the treatment of head and neck cancer influence of vindesine on methotrexate's pharmacokinetic behavior.

Determination of methotrexate (MTX) kinetics after an IV bolus (50 mg/m2) allows prediction of the steady-state plasma level of this drug during a constant infusion. This prediction allows high-dose MTX (HD-MTX) therapy without major toxicity. Patients with head and neck carcinoma received HD-MTX and vindesine (VDS) infusions concomitantly. The therapeutic survey of these patients showed that the predicted plasma level of MTX was not achieved in the presence of VDS. Moreover, the computed dose of MTX had to be increased by a larger amount if the MTX plasma clearance after the identification IV push was low (less than 9 l/h). In the presence of VDS, the creatinine clearance is lower than when MTX is infused alone, and MTX renal elimination is identical (MTX or MTX + VDS infusions). Thus it seems that the decrease of the MTX plasma level during MTX-VDS infusion could be due to an increase of cellular incorporation.

Adult↗
PubMed1984

A type of apparently axonless granule cell in the cat auditory cortex.

In the auditory areas (A I, A II and the posterior ectosylvian gyrus) of the cat, unusually small granule cells apparently lacking an axon are described. They are exclusively located in layer 2/3 and sometimes impregnate in groups of 4 or 5, being probably quite frequent. Some morphological differences between granule cells of young and adult cats are noted.

Aging↗
PubMed1984

Positional dependence of enterocyte membrane potential in hamster and rabbit enterocytes.

A technique is described allowing microelectrode impalement of enterocytes located at known positions along intestinal villi from rabbits and hamsters. Using this technique a 5 mV hyperpolarization in membrane potential is shown to occur as enterocytes migrate over the basal third of intestinal villi. The villus structure of the hamster ileum is similar to the rabbit, but the enterocyte lifespan in these two tissues differs considerably (enterocyte migration rates of 17.6 and 6.3 microns hr-1 for hamster and rabbit respectively). A correlation was found between the position an enterocyte occupied on the crypt-villus axis and the developmental state of the membrane potential. No such correlation existed when making comparisons on a time basis. These results are discussed both in terms of what is now known concerning different aspects of enterocyte development and in relation to what type of control mechanism might be generally responsible for initiating differentiation in this tissue.

Animals↗
PubMed1984

Developmental changes in intra-enterocyte cation activities in hamster terminal ileum.

Intracellular Na+ and K+ activities have been determined under visual control in enterocytes located at known positions along hamster ileal villi in vitro. The intracellular K+ activity found in enterocytes migrating over the basal third of villi was significantly less than that found in older enterocytes (83 and 113 mM respectively). The intracellular Na+ activity remained unaffected by the state of enterocyte development (32 mM throughout). Extracellular K+ and Na+ activities measured close to the luminal surface of the intestine were always similar to those measured in the bulk of the bathing medium. There was, however, a small difference in K+ activity detected between the bulk solution and solution near the luminal surface of enterocytes (3 . 4 and 3 . 6-3 . 7 mM respectively). Na+ activity in the villus core was also similar to that of the bathing medium. The brush border membrane content of sucrase-isomaltase, determined cytochemically, was found to increase rapidly as enterocytes migrated over the basal third of the villus and to plateau at a point roughly equivalent to that where intracellular K+ activities became maximal. The numerous ways by which enterocytes might control their intracellular K+ concentrations during development are emphasized. Attention is nevertheless drawn to the close correspondence seen between different aspects of brush border membrane development and the ability of enterocytes to maintain high internal concentrations of K+.

Animals↗
PubMed1983

Axonal patterns and topography of short-axon neurons in visual areas 17, 18, and 19 of the cat.

In a Golgi study of short-axon cells in areas 17, 18, and 19 of the adult cat, 21 main axonal arborization patterns are distinguished and related to laminar position and dendritic morphology. Multipolar neurons exclusive to layer 2/3 exhibit the greatest diversity of axons: These may be arranged in a local tuft, a single descending stem with recurrent collaterals, a columnar descending plexus, horsetaillike bundles, a dense intralaminar plexus, or a varicose local arbor. Multipolar cells of layers 2--5 may have local basket or chandelier axons or a neurogliform axonal plexus, and axons in layer 4 may branch into a columnar basket plexus. Two types of multipolar cells are described in layers 5 and 6. Also, neurons with a bitufted dendritic tree have different axonal patterns: cone-shaped axons, arcade axons, profuse ascending plexuses, and columnar or diffuse ascending and descending arbors. The axons of bitufted cells in layer 6 ascend or form a local tuft. Finally, giant bitufted cells with local axons, bitufted or multipolar cells with horizontal axons, and bipolar cells are described. The neuronal types established on the basis of their axonal arbor are compared to previous classifications of cortical neurons. The location of neurons thus classified has been recorded and evaluated. Most cells show no topographical specificity and occur indistinctly in the three visual areas, while two types are exclusive to area 17. Horsetail neurons accumulate at the 17/18 and 18/19 borders. Multipolar cells of layer 2/3 with a dense intralaminar plexus and chandelier cells are concentrated in the region where the central visual field is represented.

Animals↗
PubMed1983

Karyometric changes in the subcommissural organ of male mice after gonadectomy.

A karyometric study of the ependymal cells of the subcommissural organ (SCO) was made in male albino mice castrated at 20 days and examined at 25, 35, 45, 55 and 85 days of life, and in control groups of the respective ages. The values of the nuclear areas and perimeters of SCO cells as well as those of the global volume of the SCO are significantly lower in the experimental groups, and the nuclear membrane shows less invaginations. No changes are observed after gonadectomy in the subjacent thalamic ependyma.

Androgens↗
PubMed1983

Immunomodulation by NPT 15392 in cancer patients under chemotherapy.

A clinical trial of NPT 15392, a purine derivative, was run in ten head and neck cancer patients presenting signs of immunosuppression and undergoing repeated chemotherapy. A battery of ten tests was used to assess the immune status of the subjects. Those tests included skin tests, lymphocyte investigations (count, E-rosetting, membrane fluorescence and lymphoblastic transformation) and determination of serum levels of C'3 fraction of complement and IgA. The drug induced transitory, immune stimulation during or after treatment without any side effects. NPT 15392 seemed to selectively exert an action on T lymphocytes. Inasmuch as transitory, immune stimulation and secondary immune depression were noted after treatment, the therapeutic protocol for use of this drug should be reexamined.

Adjuvants, Immunologic↗
PubMed1983

Different sodium chloride cotransport systems in the apical membrane of rabbit gallbladder epithelial cells.

The kinetics of Cl- influx from the lumen to the cell and the paracellular pathway was examined in isolated rabbit gallbladder by measuring 36Cl uptake (45 s) and by correcting it for the extracellular space with 3H-sucrose. The paracellular fraction of the influx was studied by incubating the tissue in Na+-free saline or in solutions containing 25 mM SCN-; the kinetics turned out to be hyperbolic. The cellular fraction of the influx comprised three components. The first was immediately Na+-dependent and insensitive both to exogenous and endogenous cell bicarbonate; its sigmoidal kinetics revealed the presence of a carrier with three Cl- binding sites cooperating positively with one another, with strong interaction factors. The second cellular component was immediately Na+-dependent and sensitive to endogenous cell bicarbonate; the kinetics was hyperbolic with a maximum at 20 mM Cl- concentration and a substrate inhibition from 20 to 130 mM; it was completely inhibited by 10(-4)M acetazolamide. The third cellular component was slowly Na+-dependent and slowly sensitive to exogenous bicarbonate; its kinetics was hyperbolic, without substrate inhibition in the tested Cl- concentration range. On this basis, the presence of three Na+-Cl- cotransports is suggested: i) on a single carrier without any exchange with H+ and HCO3-, ii) on a single carrier with an exchange with H+ and HCO-, and, and iii) on two separate carriers in exchange with H+-and HCO3-.

Acetazolamide↗