Revue canadienne de biologie experimentale最新文献

Hypophysectomy of brook trout (Salvelinus fontinalis) results in a decrease in retinal porphyropsin in animals maintained for one month under continuous light. After one month in continuous darkness, retinal porphyropsin decreases to zero percent in all hypophysectomized fish. The effect of hypophysectomy is reversed by treatment with 1 mg/liter of L-thyroxine in the aquarium water for one month. The results indicate that light-induced changes in visual pigment proportions are partly dependent upon factors regulated by the pituitary.

Spontaneously active explanted rat ventricle cells show 4 to 7 h after explantation fast rising TTX sensitive action potentials but 24 h after explantation, electrogenesis is determined by slow rising. Mn sensitive action potentials. Because 4 to 7 h after explantation the electrical properties of the cells resemble more those of the tissue they were derived from than of cells 24 h after explantation, we conclude that the occurrence of slow rising action potentials is not directly related to the method of tissue disintegration but develops gradually after explantation.

A step-by-step technique leading to the preparation of a full-crown with diffusion chamber in the cat, is presented. The crown is built according to the routine clinical technique. The diffusion chamber is prepared and sealed with the help of a specially adapted screw. A vital stain locked in the diffusion chamber did not show any leakage in the oral cavity, even after 3 months. Such a device could easily help to study the action of toxins and isolated antigens on the animals dental pulp.

Most strains of Neisseria gonorrhoeae are rapidly eliminated from the peritoneal cavity of mice following an experimental infection. However, we could modify the rate of clearance of N. gonorrhoeae by preteating (48 h) the mice with sublethal doses of Staphylococcus aureus coagulase-positive strains which provoke the rapid appearance of activated phagocytes; we showed that these have increased activities of their B-galactosidase and their enzymes able to reduce nitroblue tetrazolium (NBT). Presumably, these activated phagocytes participated in the more efficient elimination of N. gonorrhoeae cells from the peritoneal cavity, that is 3 log units instead of 1 for the control, within the first 2 hours after their injection. There was no increase in the clearance of N. gonorrhoeae from the peritoneal cavity of mice when these were pretreated with cyclophosphamide. The use of enzyme-treated staphylococci (protoplasts) showed that some component of the coagulase-positive S. aureus cell wall seems responsible for the stimulation observed. This modulation of the response of mice to N. gonorrhoeae could serve as an improved method to evaluate the virulence of different N. gonorrhoeae strains.

It has been observed that biological systems have different sensitivities to various radiation qualities. Moreover, the relative response depends on the dose level of the applied radiation. In this context the radiosensitivity of Med-fly, Ceratitis capitata Wied., cells, to gamma-rays and neutrons, has been tested by observing cell population growth and mortality. Fast neutron doses ranged between 1.5 and 25 rad, a region of particular interest in radiation protection studies; the 60Co gamma-ray dose values were between 300 and 5 000 rad. The experimental results show a much higher radiosensitivity of these cells to fast neutrons than to gamma-rays, and indicate a dependence of the RBE values on the neutron-dose levels. Furthermore, there was a certain dependence on radiation quality for the morphological damage. Dose-effect relationships are analyzed for both neutrons and gamma-rays and the results are discussed.

In rod outer segments, most lipids are phospholipids. Among the fatty acid chains of these phospholipids, half are polyunsaturated. Despite their tendency to get oxidized, we have succeeded to purify those phospholipids by a preparative method and to measure their individual area-pressure isotherms at argon-water interface. The analysis of those isotherms reveals that membranes formed from these phospholipids must be highly fluid and should molecular movements in the membrane.

Factors and mechanisms governing selection of oviposition sites, in natural conditions, by female mosquitoes, are not well known. Laboratory tests show that a large number of very diverse environmental factors can attract or stimulate females to oviposit at a particular site (biophysical parameters, microorganisms, decomposing organic matter of different types). Pheromones produced by eggs, larvae or nymphs, depending on genera and species, seem to play an equally active role. A critical review of the main works as well as an account and a prospective of current knowledge in this field are presented and discussed.

A total of 267 passerine birds distributed among 37 species were netted during spring 1980 and summer 1981 in the Laurentian and Montreal areas. All the cloacal swabs collected at that time wer free of influenza viruses. Three and five days after oral administration of avian or human influenza A virus strains, 108 isolates were obtained from 42 of 134 passerine birds. Positive samples were recovered mainly from the respiratory and the digestive tract and also from liver. Spleen and kidneys. Viral replication is cells from trachea, lungs, gizzard and caecum was detected by indirect immunofluorescence using a monoclonal antibody to influenza A virus nucleoprotein. Viral transmission from inoculated to non inoculated birds placed in the same cages was not observed. On the other hand a similar experimental inoculation of young mallard ducks showed that extensive viral transmission occurred from inoculated to non inoculated ducklings and that infection was found exclusively in the digestive tract. Furthermore viruses were detected in samples of drinking water from all cages containing infected ducks. Passerine birds do not represent an important reservoir of influenza viruses but might contribute to the formation and spreading of recombinants potentially pathogenic for man and animals.

The striate structure of the dilator iris muscle of diving and non-diving ducks was studied by light and electron microscopy. The myofibrils of both muscles are highly organized and resemble the typical appearance of fast striate muscle. The larger relative size of the dilator in the diver cannot be explained on the basis of differences in accommodation but is likely due to a difference in speed and magnitude of pupil changes.

The wild type strains and DNA-repair deficient mutant strains of B. subtilis were exposed to ozone. The results show that the lethal effect of ozone is greatly influenced by factors such as ozone concentration, treatment time, growth phase, and treatment of medium. The recA and recC loci seem to be most important and perhaps the polA and uvrA loci may also be required, but the recB and recD loci are not required for the repair of DNA-damase induced by ozone in B. subtilis.