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Biomedical subjects

D G Cran

Publications and source records attributed to D G Cran.

At least 37 records · Page 2Linked to original sources
PubMed1987

Distribution of spermatozoa in the mare's oviduct.

The morphology of the uterotubal junction (UTJ) and caudal isthmus during the peri-ovulatory period, and the distribution of spermatozoa within the region, were studied in 10 Pony mares. The proximal tip of the uterine horn and caudal 1-2 cm of the isthmus were removed during oestrus or shortly after ovulation from animals mated or artificially inseminated within the previous 24 h. The tissues were incised longitudinally and fixed for scanning electron microscopy. Analysis of micrographs showed deep longitudinal and oedematous folds in the preovulatory samples. After ovulation, much of the folding and oedema disappeared. There was a regional arrangement of ciliated and nonciliated cells and the cilia showed evidence of directional orientation. Occasional spermatozoa were seen in some specimens deep in furrows between folds of the UTJ.

Animals↗
PubMed1985

The distribution of actin in sheep ovaries.

The distribution of actin in sheep ovaries has been examined using immunofluorescent techniques. The germinal epithelium, which contained abundant microfibrils, fluoresced strongly while the underlying stroma was only weakly positive. During early follicular growth a band of fluorescence was associated with the base of those granulosa cells abutting onto the basal lamina. This transitional polarity of actin distribution was correlated with cell shape changes in the basal granulosa.

Actins↗
PubMed1985

Qualitative and quantitative structural changes during pig oocyte maturation.

Pig oocytes were examined at hourly intervals after stimulation with hCG. Meiosis was resumed between 20 and 30 h after hCG. This coincided with a decline in the number of mitochondria and evidence is presented which indicates that this was due to fusion. The number of lipid droplets increased and the volume fraction of large vesicles decreased. Both these organelles maintained a close spatial relationship with the endoplasmic reticulum (ER). Mitochondria were clustered at the periphery of the cell before hCG injection but dispersed with maturation. The volume occupied by large vesicles, 'protein bodies' and Golgi also decreased at the edge of the oocyte with the progression of maturation.

Animals↗
PubMed1985

Effect of rapid warming of boar semen on sperm morphology and physiology.

The effect of rapid dilution (1:8 with BTS or 1:6.5 with KRP) and temperature change on sperm morphology and physiology were studied using boar spermatozoa pre-diluted in BF5 diluent. Rapid dilution of cold semen (5 degrees C) with a warm solution (37 degrees C) caused marked acrosomal changes which were most prominent in the anterior region. The acrosomal damage appeared to be caused mainly by rapid warming. In contrast to rapid cooling, rapid warming had little effect upon motility, glutamic-oxaloacetic transaminase release and respiration.

Animals↗
PubMed1983

Thecal vasculature and oocyte maturation during follicular atresia in the sheep and pig.

During follicular atresia in the sheep and pig there is a marked reduction in the vasculature of the theca interna underlying the membrana granulosa. In the sheep there is no reduction of thecal blood vessels adjacent to the cumulus which remains viable. By contrast, in the pig the cumulus degenerates during atresia and the underlying thecal vasculature is greatly diminished. However, despite loss of contact between the follicle cells and the oocyte, the germinal vesicle remains intact.

Animals↗
PubMed1983

Follicular development in the sheep after priming with PMSG.

The administration of PMSG to sheep early in the oestrous cycle (Days 2 or 3) results in the formation of follicular cysts of varied morphology by Days 8 or 9. These may persist for up to 14 days after injection. If PMSG is given on Day 5 or later approximately 50% of such cysts ovulate. However, when PMSG is given at the beginning of the cycle (Day 2 or 3), the membrana granulosa is lost from the majority of the cysts and the theca interna luteinizes. The major hormone secreted by such luteinized follicles is progesterone. The structure of the steroid-secreting cells of the follicles is similar to that of large luteal cells of granulosa cell origin in cyclic corpora lutea. It is suggested that under suitable luteinizing conditions thecal cells may acquire many of the characteristics of granulosa cells.

Animals↗
PubMed1982

Carbon dioxide induced disassembly of gap-junctional plaques.

When sheep ovarian follicle cells are maintained in an O2-rich environment their cells are metabolically coupled, as monitored by observing the exchange of [3H]choline; choline metabolites were detected up to 4 mm from the explant under these control conditions. When the tissues were placed in a CO2-rich environment the cells became uncoupled physiologically and choline metabolites were no longer exchanged. The cells in these two states, coupled and uncoupled, were examined by freeze-fracture. The initial controls were characteristic of ovarian follicular tissue exhibiting large macular plaques with regular outlines composed of PF intra-membranous particles (IMPs), which were arrayed in rows with IMP-free aisles. With uncoupling, the junctional plaques became irregular at the periphery, they became loosely packed and IMPs began to 'stream' out laterally across the membrane. Ultimately they were reduced to negligible IMP clusters or free IMPs. Analyses of the IMPs with an image analyser confirmed that in the uncoupled state the gap-junctional IMPs were dispersed over the membranes. On return to an O2-rich environment, the cells became recoupled as monitored by physiological criteria and in freeze-fracture replicas IMPs reclustered into macular, albeit smaller, plaques. These results support the contention that with uncoupling, gap-junctional particles are free to move and hence may become dispersed over the membrane face, with the possibility of being re-utilized to form junctions anew when conditions for coupling are re-established.

Animals↗
PubMed1981

Selective effect of gonadotrophins on cell coupling, nuclear maturation and protein synthesis in mammalian oocytes.

Individual gonadotrophic hormones were used to examine the degree to which changes in intercellular coupling between somatic and germ cells initiate meiotic maturation, regulate protein synthesis or alter the ultrastructure of the ovine oocyte. Follicle Stimulating Hormone (FSH; 50 ng ml-1) suppressed intercellular coupling to the same extent as that observed during oocyte maturation in vivo. At low concentrations FSH did not, however, initiate resumption of meiosis. By contrast, luteinising hormone (LH; 100-500 ng ml-1) invariably initiated meiosis in oocytes cultured within the follicle but did not disrupt intercellular coupling. We conclude that nuclear maturation is not dependent upon the disruption of cell contact between the oocyte and the surrounding follicle cells. The profile of proteins synthesized by untreated oocytes differed greatly from that of oocytes matured for 18 h in follicles treated with a combination of FSH and LH. Pretreatment of follicles with either FSH or LH at low concentrations resulted in the synthesis of an intermediate and more variable pattern of proteins. No correlation was found between changes in protein synthesis and the extent of junctional communication between the cumulus cells and oocyte. Membrane vesiculation and lysosomal change in the transzonal processes are early structural changes associated with the suppression of intercellular coupling in oocytes. These changes in coupling probably result in the relocation of intracellular organelles in the final stages of oocyte maturation.

Animals↗
PubMed1980

Fate of the theca interna following ovulation in the ewe.

The fate of the theca interna after ovulation was studied in ewes, using light and electron microscopic histology and histochemistry. At the time of ovulation the theca interna was incorporated, apparently completely, into the margin of the developing corpus luteum and into the centres of many infoldings of the follicular wall. There was no evidence of degeneration of the more highly differentiated theca interna cells at or following the time of ovulation. Within 24 h of ovulation, cells derived from the theca interna began migrating from their original sites into the deeper, granulosa-derived areas of the luteal tissue. At later stages cells derived from the theca interna remained concentrated in septa derived from the follicular infoldings, but were also widely distributed throughout the luteal tissue. Structural evidence supported the view that the small luteal cells and fibroblasts of the corpus luteum were derived from the theca interna, and the large luteal cells from the membrana granulosa.

Alkaline Phosphatase↗
PubMed1980

Fine structure of the sheep oocyte during antral follicle development.

The structure and distribution of organelles within oocytes of developing antral follicles were studied qualitatively and quantitatively. In the smallest category of follicle (0.2-0.4 mm diam.) the Golgi was present in a peripheral position, the endoplasmic reticulum was distended and mitochondria were intimately associated with it. Processes from surrounding cumulus cells were in contact with the oolemma which was thrown up into slender villi, increasing the oocyte surface area 5-fold. In these and all subsequent follicles the oocyte cytoplasm contained numerous 30 nm particles or vesicles. As the follicles grew to about 2.0 mm the mitochondria became located in a peripheral band, interior to which were numerous large vesicles, and the villi became shorter and thicker. In follicles > 2.0 mm the mitochondrial band was largely dispersed and cortical granules rested close to the oolemma. Little structural change was then observed until late oestrus. In oocytes from preoovulatory follicles at this stage an internal dense zone was formed in the zona pellucida. Most of the cumulus cell processes degenerated and most mitochondria assumed a hooded appearance.

Animals↗
PubMed1979

The fine structure of the cumulus oophorus during follicular development in sheep.

The cumulus and membrana granulosa of non-atretic ovarian follicles from primordial up to a stage shortly before ovulation were studied by electron microscopy. The follicular cells of primordial follicles were undifferentiated and rested on a thick basal lamina. In secondary follicles the endoplasmic reticulum had proliferated forming an anastomosing network. In early antral and antral follicles (0.5--2.0 mm dia.) the ER was composed of short cisternae, the mitochondria had elongated and gap junctions were first observed. In late antral follicles (3.0--5.9 mm dia.) gap junctions were frequent. In the cumulus the glycogen was associated with electron lucent areas whereas in the granulosa it was invariably associated with membranes. In large antral follicles large membrane bound bodies were present in the basal cells of the cumulus. At early oestrus a distinctive mitochondrial morphology was noted in the granulosa but not elsewhere in the follicles. At mid oestrus numerous annular nexuses were present in the granulosa but not in the cumulus. At late oestrus numerous lipid droplets were formed in both cumulus and granulosa, the boundary with theca interna became indistinct and the basal lamina became incomplete.

Animals↗
PubMed1979

Regeneration of atretic sheep ovarian follicles in vitro.

Large (4--6 mm diam.) and small (2--3 mm) atretic follicles were removed from sheep ovaries during the luteal phase of the cycle and maintained in organ culture without hormonal supplementation for up to 5 days. The structure, cell dynamics and steroid-producing capacity of the follicles were compared with those of non-atretic follicles of similar size. The granulosa layer of the atretic follicles invariably regenerated in culture, increasing in thickness more than 2- and 4-fold in large and small follicles respectively. This could not be accounted for by cell division which remained low throughout the culture period. In contrast, non-atretic follicles showed high mitotic activity during the first 24 h in culture: this was not associated with an increase in granulosa thickness in large follicles although there was a 4-fold increase in small ones. An increase in internuclear spacing, a measure of cell size plus intercellular space, partly accounted for the increase in granulosa thickness in atretic follicles. Even when granulosa cells remained in close apposition there was an almost total absence of gap junctions, a prominent feature in the granulosa of non-atretic follicles both in vivo and in vitro. Pyknotic nuclei and atretic bodies rapidly disappeared from the regenerating granulosa layer. The theca interna was restored in culture to a state ultrastructurally closely resembling that of non-atretic follicles in vivo. Total steroid secretion (oestradiol-17beta, testosterone plus progesterone) into the culture medium (pmol.mg tissue-1.24 h-1) was the same for atretic and non-atretic follicles of comparable size. There was, however, a marked difference in the type of steroid produced, largely related to a loss of aromatizing capacity in atretic follicles. The predominant steroid secreted by large non-atretic follicles was oestrogen, with slightly smaller amounts of testosterone, whereas the principal steroid secreted by large atretic follicles was progesterone. In small non-atretic and atretic follicles, the predominant steroid was testosterone, but the non-atretic follicles also secreted appreciable amounts of oestrogen. Addition of FSH to the culture medium did not restore aromatizing capacity to the atretic follicles.

Animals↗
PubMed1979

Effect of exogenous gonadotrophin (PMSG) on the antral follicle population in the sheep.

Follicles were obtained from the ovaries of four groups of 15 ewes. Ewes in the control group were ovariectomized on the 12th day of the oestrous cycle. The other ewes were all given PMSG on the 12th day of the cycle; some were ovariectomized 24 or 40 h later, the others were given prostaglandin followed by hCG and were ovariectomized 6 or 12 h after the hCG injection. All follicles greater than 2 mm in diameter were measured and examined macroscopically for signs of atresia. Some were subjected to detailed morphological examination, the pattern of steroid secretion was determined in others. All the evidence from these three approaches suggested that, in vivo, reversal of the atretic process ('rescue') plays no part in the increase in the number of follicles observed following administration of PMSG.

Animals↗
PubMed1979

The small luteal cell of the sheep.

Corpora lutea of sheep were examined by electron microscopy at day 10 of the oestrous cycle and at days 15, 25, 50, 100, 125 and 140 of pregnancy. Small luteal cells were present in all corpora lutea, and were two to three times as numerous as large luteal cells. The former were irregular in shape, with tapering cytoplasmic processes. Their major cytoplasmic organelles were a predominantly smooth endoplasmic reticulum, mitochondria with tubular and lamellar cristae, and one or more Golgi complexes. The enzyme delta 5-3 beta-hydroxysteroid dehydrogenase was present in their cytoplasm. Small luteal cells were often interposed between large luteal cells and capillaries, and formed close, complex surface relationships with large luteal cells. Small and large luteal cells differed in many ways, including the restriction of numerous approximately 0.2 micron cytoplasmic granules to the large cells, and no cells of intermediate structure were observed. These features of small luteal cells suggest a steroid hormone synthetic function, and direct interaction with large luteal cells.

3-Hydroxysteroid Dehydrogenases↗
PubMed1978

Ultrastructure of the theca interna of ovarian follicles in sheep.

The theca interna of non-atretic ovarian follicles from 2.0 mm in diameter up to the stage shortly following ovulation was studied by light and electron microscopy. In follicles less than 3.0 mm in diameter, the theca interna consisted of about 8-12 layers of flattened cells, together with many capillaries and small bundles of collagen. Two main forms of cellular differentiation were seen. These were towards either fibroblast-like cells or presumed steroidogenic cells whose cytoplasm contained large amounts of predominantly smooth tubular endoplasmic reticulum, to which some ribosomes were attached. The majority of cells were of relatively undifferentiated or intermediate structure. In larger follicles up to the early stages of oestrus the theca interna cells became larger and less flattened, and cells rich in tubular endoplasmic reticulum became proportionately more numerous. By 18 h after the onset of oestrus the theca interna was oedematous, and many cells possessed pseudopodia. Many cells also contained numerous lipid droplets, but there were no signs of thecal cell degeneration or death. Shortly after ovulation the basal lamina of the membrana granulosa was incomplete, and it became more difficult to distinguish between theca and granulosa layers. Structural heterogeneity, with two major cell types and cells of intermediate structure, was present at all stages. It was concluded that: (1) the theca interna of 2.0-2.9 mm follicles contained many cells whose structure was compatible with a steroidogenic capacity; (2) changes in the differentiated thecal cells up to the early stages of oestrus were quantitative rather than qualitative, and suggestive of an increased steroidogenic capacity; (3) the accumulation of lipid in many cells of the theca interna by 18 h after the onset of oestrus probably reflected a reduction in steroidogenic activity; and (4) there was no evidence of any structural specialization to facilitate the transport of steroids from the theca interna to the membrana granulosa.

Animals↗