André C. Cordier

The influence of fixation procedure, embedding medium and section thickness on morphometric data in thyroid gland.

SummaryIn this study, the effects of fixation procedures, embedding medium and section thickness on stereological measurements of normal thyroid were analysed. The following conclusions were drawn:A)the use of a single section for the analysis of a lobe is sufficient if this section is located in the central part of the lobe.B)fixation and embedding with glutaraldehyde-Epon leads to a larger shrinkage than Bouin-paraplast, but the difference between the two procedures is not significant.C)osmium post-fixation reduces the shrinkage induced by glutaraldehyde and lowers the axial deformation produced by sectioning.D)Bouins fixative and paraplast embedding induce considerable shrink-age of the interstitial tissue. The shrinkage obtained with glutaraldehyde-Epon is less. However, it is still not known whether this difference is due to the fixative, or to the embedding procedure or to both.E)only in glutaraldehyde and osmium-fixed material, embedded in Epon, can follicles and colloids be assumed to be spherical in shape without significant errors.

Ultrastructure of the thymus in “Nude” mice

The thymus of the “Nude” mouse has been studied with electron microscopy. This thymus is formed of cysts whose walls are formed by ciliated cells, mucous cells, undifferentiated cells, and cells of glandular character. Between the cysts are found undifferentiated cells, mucous acini, and a few plasma cells and mast cells. We have been unable to find some of the structures that are specific for the normal thymus, viz. Hassall bodies, myoid cells, epithelial cells of the cortex, and medullary “cystic” cells of the medulla. The comparison of the normal thymus with the Nude mouse thymus suggests that the deficiency in epithelial cells of the cortical type could be the cause of the absence of lymphocyte multiplication. The deficiency in medullary “cystic cells” might explain the absence of hormonal capacity of the Nude thymus. The primary site of thymic malformation in the nu/nu mouse probably resides in the ectoblastic component of the thymic anlage.

Ciliogenesis and ciliary anomalies in thymic cysts of "nude" mice.

SummaryThe thymus of the “nude” mouse is composed of ciliated cysts. In the adult mouse, different steps of ciliogenesis can be observed. The ciliated cells exhibit several anomalies in the centriole and in the cilium itself; the most important ones are the half-centriole and the compound cilia. An explanation for the occurrence of frequent anomalies in ciliated cells is suggested. Finally, some single cilia are described in fat cells.

Thyroid gland in dwarf mice

SummaryStereological methods were used to compare thyroids of dwarf mice and of their heterozygote littermates. In the thyroid of dwarf mice unorganized cellular masses, adipous tissue and ultimobranchial cysts are abundant. Follicles are small and their distribution function is unimodal. The number of cells per follicle is considerably lowered if compared with the normal. In control mice the distribution function of thyroid follicles is bimodal. These data show that the origin of the thyroid anomaly in dwarf mice is due to a drastic diminution of cell divisions, probably resulting from the lack of growth hormone.

Relationship between ciliary rootlets and smooth endoplasmic reticulum

SummaryIn ciliated cells of thymic cysts in Nude mice, ciliary rootlets are constantly and closely related to smooth endoplasmic reticulum and clear vesicles. This special association suggests that this structure does not play only an anchoring role but must be involved in the general metabolism of the cilium.

Morphometry of nuclear pore complexes in thyroid cells during hyperplasia and involution.

Nuclear pore complexes were analyzed in freeze-fractured replicas of thyroid follicular cells of C3H mice in different physiological states. Thyroid stimulation induced a rapid and simultaneous increase of the nuclear surface and volume and of the total number of pore complexes. The numerical density (Na) of pore complexes increased at the 6th day of stimulation, but after that time the proportion of cells with an increased Na was always higher than the proportion of 3H-labelled nuclei. During thyroid involution, all the nuclear parameters, including the Na, returned to normal values. These results indicate that the total number of pore complexes and their Na are correlated with the cellular activity rather than with the cell cycle. They also suggest that 2 different mechanisms are involved in the generation of pore complexes: first, an addition of new membranes with a low density of pore complexes; later, a formation of new pore complexes in preexisting membranes. However, during involution, parts of the nuclear membranes and pore complexes in the remaining parts disappear synchronously. In freeze-fractured thyroid nuclear membranes, 2 neighbouring pore complexes were always separated by a distance of 105 nm. Clusters of pore complexes were not observed. A comparison of the distances between pore complexes and between randomly generated points never showed any significant differences indicating that pore complexes were randomly distributed.