Influence de la méthode de fixation sur l'observation des divisions cellulaires dans l'adénohypophyse du rat mâle

Résumé Les mitoses de l'adénohypophyse du rat mâle ont été examinées comparativement après fixation par perfusion et après fixation par immersion.Après fixation par perfusion la répartition topographique des mitoses dans le parenchyme est homogène, et l'index mitotique est de 1,85 pour 1 000 cellules.Après fixation par immersion, la densité des mitoses décroit de la périphérie vers le centre, et l'index mitotique n'est que de 0,80 mitoses pour 1 000 cellules.La lenteur de pénétration du fixateur pendant l'immersion est tenue pour principal responsable des différences observées. Elle entraîne une modification de l'aspect des mitoses, telle que plus de la moitié d'entre elles ne sont pas identifiables et échappent aux comptages.

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Influence of fixation on the observation of mitoses in the male rat adenohypophysis

Summary The mitoses of the adenohypophysis in male rats have been observed comparatively after fixation by perfusion and fixation by immersion.After fixation by perfusion, the topographic distribution of mitoses throughout the parenchyma is homogenous and the mitotic index is 1.85 for 1 000 cells.After fixation by immersion, the density of the mitoses is decreasing from the periphery towards the center and the mitotic index is only 0.80 for 1 000 cells.The slow penetration of the fixative during fixation by immersion is considered to be the main cause in the differences observed. This slow action causes a modification in the aspect of the mitoses, and more than fifty percent of them cannot be identified and escape to the counts.

Avec la collaboration technique de Mademoiselle J. Rameau.     

Alterations of the mitotic index of c cells and follicular cells of the rat thyroid during the circadian rhythm and after exposure to cold

Summary Using the colchicine technique we found that the mitotic indices of follicular as well as of C cells of rat thyroids showed a weakly marked circadian rhythm with highest values at 19.30 and lowest values at 13.30. Under the influence of cold there occurred a rhythmically significant augmentation of mitoses of both follicular and C cells, the former reaching a peak of up to about four times their corresponding control values, the latter barely reaching the double. For this reason, it seems improbable that C cells play an important role in thermoregulation.     

Brassica napus pollen development during generative cell and sperm cell formation

Summary Brassica napus pollen development during the formation of the generative cell and sperm cells is analysed with light and electron microscopy. The generative cell is formed as a small lenticular cell attached to the intine, as a result of the unequal first mitosis. After detaching itself from the intine, the generative cell becomes spherical, and its wall morphology changes. Simultaneously, the vegetative nucleus enlarges, becomes euchromatic and forms a large nucleolus. In addition, the cytoplasm of the vegetative cell develops a complex ultrastructure that is characterized by an extensive RER organized in stacks, numerous dictyosomes and Golgi vesicles and a large quantity of lipid bodies. Microbodies, which are present at the mature stage, are not yet formed. The generative cell undergoes an equal division which results in two spindle-shaped sperm cells. This cell division occurs through the concerted action of cell constriction and cell plate formation. The two sperm cells remain enveloped within one continuous vegetative plasma membrane. One sperm cell becomes anchored onto the vegetative nucleus by a long extension enclosed within a deep invagination of the vegetative nucleus. Plastid inheritance appears to be strictly maternal since the sperm cells do not contain plastids; plastids are excluded from the generative cell even in the first mitosis.