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Biomedical subjects

D G Cran

Publications and source records attributed to D G Cran.

45 records · Page 3Linked to original sources
PubMed1978

Ultrastructural changes in the theca interna during follicular atresia in sheep.

Sixteen antral follicles, 1.8--4.2 mm in diameter, at various stages of atresia, were studied by electron microscopy. Deletion of theca interna cells by condensation followed by fragmentation (apoptosis), with subsequent engulfment of the fragments by remaining thecal cells, was present at all stages, but was most marked during secondary and tertiary atresia. In primary and secondary atresia, the relative numbers of thecal cells whose cytoplasm was rich in tubular endoplasmic reticulum were higher than in non-atretic follicles of comparable size. During tertiary atresia the number of cell layers in the theca interna was reduced, and cells rich in tubular endoplasmic reticulum became proportionately less numerous. Degenerating cellular material was present within the lumina of thecal capillaries at all stages of atresia. Such material was rarely seen in primary atresia, and increased in incidence progressively in later stages. It was concluded that during atresia a large number of theca interna cells are deleted by apoptosis, and many thecal capillaries become blocked with cellular debris.

Animals↗
PubMed1978

Macroscopic identification and steroidogenic function of atretic follicles in sheep.

The degree of translucency, vascularization of the follicle wall and the integrity of the membrana granulosa, as seen under a stereoscopic microscope, were used to distinguish between non-atretic and atretic isolated follicles. Subsequent histological evaluation showed that both non-atretic and severely atretic follicles could be correctly identified with over 95% accuracy. The concentrations of steroids were measured in both follicular tissue and fluid. The total steroid content of large (3.1-6.0 mm diameter) non-atretic follicles in vivo (115 pmol/follicle) exceeded that of large atretic follicles (54 pmol) and also that of small (2.0-3.0 mm diameter) non-atretic and atretic follicles (6 pmol). Oestrogen accounted for 80%, testosterone 13% and progesterone 7% of the total steroid content in large non-atretic follicles, whereas testosterone accounted for 75% of the steroid content in the other three categories of follicles. A similar pattern is observed when the concentrations of steroids are expressed on the basis of follicular weight. Total oestrogen secretion, as measured by the output of steroid into the culture medium in 24 h, was 937 pmol for large non-atretic, 31 pmol for large atretic, 65 pmol for small non-atretic and 4 pmol for small atretic follicles. In terms of steroid production (pmol/mg tissue), the four follicular categories were equally efficient. However, the type of steroid produced depended on the category of follicle and corresponded to its steroid content.

Animals↗
PubMed1976

Structural changes occurring during atresia in sheep ovarian follicles.

The structural changes that characterize primary, secondary and tertiary atresia in sheep Graafian follicles have been studied by means of histological, histochemical and ultrastructural techniques. In primary atresia vacuoles representing swollen endoplasmic reticulum are prominent along the antral border together with disorganized granulosa cells containing pyknotic nuclei. Phagocytic cells, which increase in number as atresia progresses, were seen within the membrana granulosa and are considered to be transformed granulosa cells. Even in follicles classified as nonatretic, a few antral vacuoles and occasional pyknotic nuclei are present. During secondary atresia there is a large increase in the number of cells with pyknotic nuclei; many of these nuclei had been extruded and had fused to form the characteristic Feulgen-positive atretic bodies found along the edge of the antral cavity. These bodies usually have a diameter of up to 15 mum but occasionally reached as much as 400 mum. A second area of degeneration is frequently present in the membrana granulosa, two or three cell layers from the basal lamina, and it is at this level that exfoliation of granulosa cells occurs in tertiary atresia. In contrast to the membrana granulosa, there are during secondary atresia, only slight indications of degeneration in the cumulus. In tertiary atresia the membrana granulosa is highly disorganized; the atretic bodies are often fewer in number than at earlier stages. The basal lamina remains essentially intact. It is at this stage that the first clear signs of degeneration occur in the theca interna. Despite some disintegration of the cumulus, the integrity of the oocyte is maintained and its nucleus remains vesicular. Changes in the thecal microcirculation may plan a key role in atresia: adjacent to the basal lamina of non-atretic follicles, there is a well-developed capillary network which is significantly reduced as atresia progresses.

Animals↗
PubMed1976

Permeability of ovarian follicles to electron-dense macromolecules.

Ferritin (m.w. 500 000) perfused into the ovarian arteries of sheep permeated the theca interna and was also found in the membrana granulosa of both non-atretic and atretic Graafian follicles. Colloidal gold (m. w. 1 000 000) similarly perfused, was found in the theca interna but not in the granulosa. The results are discussed in terms of the blood-follicle barrier.

Animals↗
PubMed1975

Changes in DNA synthesis during cell growth and chloroplast replication in greening spinach leaf disks.

Spinach leaf disks grown initially in the dark, show increased cell expansion and chloroplast replication when transferred to the light. These changes are accompanied by increases in the total amount of DNA and the incorporation of [3H]thymidine (3H-TdR). Autoradiography of EDTA-separated cells dried on to glass slides was used to follow changes in 3H-TdR incorporation in both chloroplasts and nuclei. Specificity of incorporation was confirmed by nuclease studies. DNA synthesis occurs in both the chloroplasts and nuclei, and is highest just prior to, and during the period of most rapid cell growth and chloroplast replication which occurs shortly after the transfer to the light. Light, however, appears to have a greater and more immediate effect on nuclear DNA synthesis. Though nuclear and chloroplast DNA syntheses follow similar patterns during disk growth, in a given cell, chloroplast DNA synthesis can be separate in time from nuclear DNA synthesis. The increased nuclear DNA synthesis is possibly required to support the increased population of chloroplasts, while chloroplast DNA synthesis is associated with chloroplast division. If the disks are not transferred to the light but kept in darkness, chloroplast 3H-TdR incorporation remains high, though chloroplast division is reduced. Epidermal cells in light-grown tissue also show 3H-TdR incorporation but low rates of chloroplast division. It would appear that chloroplast DNA synthesis in mesophyll cells from light-grown tissue shows a general relation to chloroplast division, but there does not appear to be an obligatory close coupling between the 2 processes.

Autoradiography↗
PubMedDate not supplied

The predetermination of embryonic sex using flow cytometrically separated X and Y spermatozoa.

A review is given of the predetermination of sex in various domestic animals and in the human using sperm samples enriched for X- or Y-chromosome bearing spermatozoa obtained by flow cytometry and cell sorting. A comparison of other putative methods of sperm separation is made. In separating human X and Y spermatozoa, measurements of the DNA content in each individual gamete using the Hoechst fluorochrome 33342 remains the only validated method. The difference in DNA content between human X and Y spermatozoa is approximately 2.8%, and cell sorters have been adapted to take account of this and the asymmetrical nature of the sperm head. DNA analyses and PCR have been used to validate the method for animal spermatozoa. In the human, fluorescence in-situ hybridization (FISH) has confirmed sorting accuracy. Many correctly-diagnosed normal offspring have been born in various animal species and any potential mutagenic or cytotoxic effects are being closely monitored as are the cost and efficiency of the technology.

Animals↗