摘要:

AbstractThe theca externa of large vesicular ovarian follicles of cats, rabbits and guinea pigs was studied with the electron microscope. Fibroblasts and smooth muscle were observed in all species. In the guinea pig, a third cell type, with characteristics of both fibroblasts and smooth muscle, was present. Myelinated and unmyelinated nerves were observed in the theca externa of cats and guinea pigs. Unmyelinated nerves often contained vesicles and mitochondria and were separated from cellular elements by a space of about 2000 Å. It is suggested that coordinated muscular contractions in the theca externa offer the most reasonable explanation for the extrusion of the ovum. This muscle is probably, at least partially, under local neural control

ISSN:0002-9106    

DOI:10.1002/aja.1001330202

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1972

数据来源: WILEY

摘要:

AbstractLight and electron microscopy were used to study the morphology of adipose cells in newborn Merino lambs (Ovis aries). Postnatal changes in morphology were also examined in naturally fed Merino lambs held at 26°C or at 3°C for up to 32 days from the time of birth, and in lambs fasted for up to three days at 26°C or at 3°C since birth.All adipose cells examined in the newborn lambs showed the morphological characteristics of brown adipose cells; no white adipose cells could be found. The brown adipose tissue in normally fed lambs was replaced progressively by white adipose tissue during the first two or three weeks of life, and this replacement was retarded in the lambs held at 3°C. During replacement a continuous spectrum of cells with morphological characteristics between those of brown and white adipose cells were seen. No degenerating brown adipose cells were observed; and, apart from brown adipose cells, no cells were identified that could have been precursors of white adipose cells. This evidence suggests that in various body regions of lambs white adipose cells are derived from brown adipose cells.Lambs fasted at 3°C or under conditions that approached thermoneutrality (26°C) showed rapid depletion of lipid from brown adipose cells; hence brown adipose tissue of the lamb differs from that in the newborn rabbit in which this tissue is not readily depleted of fat during starvation under thermoneutral cond

ISSN:0002-9106    

DOI:10.1002/aja.1001330203

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1972

数据来源: WILEY

摘要:

AbstractThe heads of the spermatozoa of rabbit, man, and bull are flattened in the dorsoventral plane and exhibit three distinct regions in the head coverings. The anterior one‐half to two‐thirds of the nucleus is covered by the acrosome, the middle of the nucleus by the thinned equatorial segment of the acrosome and the remainder of the head is covered by the postacrosomal segment. Species variation is evident in the head coverings; most prominent are the equatorial bands of the rabbit spermatozoon. The bands are subacrosomal bulges curving around the head; the arms of each band are displaced in the anteroposterior axis and do not cross the midline axis. The equatorial bands are visible in scanning electron micrographs, which also show a serrated junction between the equatorial segment and the postacrosomal reg

ISSN:0002-9106    

DOI:10.1002/aja.1001330204

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1972

数据来源: WILEY

摘要:

AbstractThe postnatal development of the retina in control (CBA/S) and rodless (CBA/Ki) mice was studied by light and electron microscopy. In the control mice, the major increase in retinal thickness occurs between birth and seven days. The inner and outer segments begin to grow into the optic ventricle between seven and ten days with their most rapid growth occurring between 12 to 15 days; by 35 days the retina appears mature. During development, the nuclear layers become thinner while the optic ventricle (layer of rods) and the plexiform layers become thicker. At birth, the mutant or rodless retina is indistinguishable from the control; however, the inner and outer segments fail to develop beyond the primitive seven‐ to ten‐day stage. At 15 days the outer nuclear layer becomes reduced to only a few nuclei in thickness. Many degenerating elements are found in the cavity of the optic ventricle and in the outer nuclear and plexiform layers. By 35 days the mutant retina lacks photoreceptors and is reduced in thickness to less than that at birth. The pigment epithelium is heightened in regions where degeneration is incomplete but becomes highly attenuated in regions where visual cell degeneration is complete. The optic ventricle contains the villous processes of the pigment epithelium and the fringe processes of the Müller cells. The outer limiting membrane is contiguous with remnants of the outer plexiform layer. Between the outer plexiform layer and the inner limiting membrane, the mutant retina is normal in appearance and dimension. The delayed appearance of the smooth endoplasmic reticulum of the pigment epithelium is implicated in the failure of outer segment maturation. The role of both Müller and pigment epithelial cells in removal of the products of retinal degeneration is disc

ISSN:0002-9106    

DOI:10.1002/aja.1001330205

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1972

数据来源: WILEY

摘要:

AbstractThe ultrastructure of fertilization has been studied in rabbit eggs recovered 11 to 15 hours after natural mating. Many sperm passing between the granulosa cells had undergone the acrosomal reaction, but this was not invariable, and, occasionally, intact sperm were present close to the zona pellucida. The cells of the corona radiata sometimes develop pseudopodial processes at the abovular surface and can ingest sperm after natural mating. The bulk of the content of the acrosome and the vesiculated elements formed during the acrosomal reaction, are lost before the sperm penetrates the zona pellucida, at which point the naked inner membrane of the acrosome is brought into intimate apposition with the zona. As the sperm cleaves a path through the zona pellucida, the posterior equatorial segment of the acrosome remains intact, and later persists as such in perivitelline sperm and quite possibly after incorporation of the sperm head into the vitellus.Sperm head entry into the vitellus is a two‐fold process. The fertilizing sperm invariably fuses first with the vitelline membrane over the midposterior region of the head, whereas the rostral or acrosomal portion is drawn into the vitellus while encased by a flattened vesicle; this vesicle is comprised by the persistent inner membrane of the acrosome and externally by vitelline membrane sequestered from the egg surface. Soon after exposure to ooplasm, the sperm nucleus begins to decondense at a variable rate into a web of electron‐dense strands; this process begins in the midposterior region, and then extends rostrally and caudally. At the same time the encasing membranes are reflected away from the anterior region of the nucleus, exposing subacrosomal material to the ooplasm. At this point the perforatorium remains, but this and the associated membranes are presumed to disintegrate eventually within the egg. After decondensation of the nucleus is complete, the faintly staining chromatin becomes enveloped by a series of compressed vesicles which together will form the porous limiting membrane of the male pronucleus.The last region to be incorporated is the sperm tail, the plasma membrane of which is lost as organelles of the tail pass into the ooplasm. During its incorporation, the midpiece engenders some reaction at the egg surface, and the mainpiece sometimes becomes fused with surface processes before it enters the body of the egg. The midpiece then commonly disintegrates, with dispersion of the mitochondrial sheath, whereas the mainpiece usually remains essentially intact until the time of syngamy or bey

ISSN:0002-9106    

DOI:10.1002/aja.1001330206

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1972

数据来源: WILEY

ISSN:0002-9106    

DOI:10.1002/aja.1001330201

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1972

数据来源: WILEY