ISSN:0002-9106    

DOI:10.1002/aja.1001350402

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

年代:1972

数据来源: WILEY

摘要:

AbstractIn the mature placental labyrinth of common myomorph rodents (rat, mouse and hamster) fetal capillaries are separated from maternal blood spaces by trabeculae composed of three distinct cytoplasmic layers. To resolve the controversy regarding the embryonic origin(s) of these layers a correlated light and electron microscopic study was made of the developing placental tissues of the golden hamster during the eighth and ninth days of gestation, the critical period of labyrinth morphogenesis in this species. It was determined that the syncytial inner layer (layer III) of the trabeculae, the layer bordering the fetal capillaries, is derived from the “true” chorionic ectoderm which fuses with the undersurface of the Träger (ectoplacental cone) early on the eighth day of gestation. Both the syncytial middle layer (layer II) and the cellular outer layer (layerI) of the trabeculae, on the other hand, were found to differentiate from the trophoblastic cells of the Träger. Allantoic mesenchyme, which approximates the fused chorionic‐Träger tissues late on day eight and is the source of the fetal capillaries and mesenchyme of the labyrinth, was noted to exert a critical inductive effect on the morphogenesis of syncytial layers II and III. On the basis of fine structure, the developing labyrinth appears not to be a major site for maternal‐fetal transfer of macromolecules nor to be involved to a significant degree in the production of proteins or steroids for

ISSN:0002-9106    

DOI:10.1002/aja.1001350403

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

年代:1972

数据来源: WILEY

摘要:

AbstractThe nerve supply to the alveolar ducts and alveoli of mouse lungs was studied with the electron microscope. In the alveolar ducts, nerve bundles consisting of as many as nine unmyelinated axons surrounded by connective tissue fibers were usually located in the interstitium surrounding the openings of the alveoli. In the alveolar walls, nerve bundles consisting of as many as five unmyelinated axons were located in the interstitium between pneumocytes and the capillaries. The unmyelinated axons contained neurotubules and some mitochondria, and were partially or completely surrounded by Schwann cells. Two distinct types of enlarged nerve endings were identified. The first type contained many small mitochondria and was either associated with the type I pneumocyte or located alone in the interstitium. The second type was packed with numerous large dense‐core vesicles and was in close contact with the type II pneumocyte. It is suggested that the first type of ending is sensory and the second type is motor in functio

ISSN:0002-9106    

DOI:10.1002/aja.1001350404

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

年代:1972

数据来源: WILEY

摘要:

AbstractThe relative density and distribution of acidic negative residues on the plasma membranes of spermatozoa of seven mammalian species were studied using a colloidal iron hydroxide (CIH) labeling technique. The surface distribution of negative residues is discontinuous on mature spermatozoa from the cauda epididymidis or on ejaculated spermatozoa of the rabbit, mongoose, rat, guinea pig and hamster. Tail regions are generally more densely labeled with CIH than head regions, indicating that sperm tails have more acidic negative charges than heads. In these species, the density of the negative surface charge is rather uniform within a particular segment of the spermatozoa and abruptly changes at the junctions to morphologically distinct segments, suggesting that the biochemical properties of the plasma membrane also change at these junctions. In bull (cauda epididymal) and human (ejaculated) spermatozoa, the entire surfaces of spermatozoa are densely labeled with CIH. Comparison of testicular, caput and cauda epididymal spermatozoa of rabbit, bull and hamster suggests that the negative surface charges of spermatozoa increase with epididymal maturation of spermatozoa. A possible chemical nature of the residue(s) has been suggested from neuraminidase digestion and methylation experiments.

ISSN:0002-9106    

DOI:10.1002/aja.1001350405

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

年代:1972

数据来源: WILEY

摘要:

AbstractThe ultrastructure of bone marrow of rats, mice and guinea pigs was studied after fixation by vascular perfusion. Serial sections were examined to determine the structure and site of pores in lining cells. It was concluded that pores are transient structures occurring only in conjunction with migrating blood cells. These pores occur within lining cells and most frequently near junctions of contiguous lining cells. Microfilaments in lining and adventitial cells are described and their possible roles discussed.

ISSN:0002-9106    

DOI:10.1002/aja.1001350406

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

年代:1972

数据来源: WILEY

摘要:

AbstractGuinea‐pigs were injected with either3H‐thymidine or colchicine and killed at various time intervals after the injections. Duration of the over‐all cell cycle and of the G1, S and G2phases was determined with autoradiography for cells in the short, medium and long crypts of the colon as well as for the lower, middle and upper segments of the crypt.The duration of mitosis estimated with the colchicine method increased from the mouth of the crypt downward to the bottom, from about one to three hours. The cells located in the crypt between the mouth and approximately the twentieth cell position have a cell cycle of about 15 hours whereas those located in the crypt section between the twentieth cell position and the bottom have a cell cycle of about 25 hours. This difference is due mainly to a change in the G1phase. The results of planimetry for the first and second waves of labeled mitoses suggest that in the lower segment of medium and long crypts, cells in the G0phase occur. It is concluded that the factor(s) controlling cell cycle duration in the colon crypt appears either at the crypt mouth or n

ISSN:0002-9106    

DOI:10.1002/aja.1001350407

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

年代:1972

数据来源: WILEY

摘要:

AbstractThe effects of embryonic overgrowth on the avian optic tectum were determined during late developmental stages in 121 chick embryos in which overgrowth was induced surgically. The embryos ranged in incubation age from seven days through 21 days and showed a variety of gross brain defects, including fused optic lobes, fusion of one or both optic lobes with a cerebral hemisphere or with the cerebellum, absence or reduction of one optic lobe, convolutions of the tectal wall, and hydrocephalus. At seven days to 11 days of incubation, histological defects of the tectum included irregularities in the migration patterns of neuroblasts and abnormal stratification among the migrated neuroblasts. The most severe defects in the 12‐day through 21‐day tectum were in the stratification of the outer region which corresponds to the adult stratum griseum and fibrosum superficiale, whereas deeper areas of the tectum underwent relatively normal histodifferentiation. Epithelial rosettes were common until the sixteenth day, after which they disappeared almost entirely except for a few occasional ones near the ventricular zone. Preliminary behavioral observations of the defective embryos revealed random motility similar to that in the control embryos, but a failure to achieve the proper hatching position. Of 61 operated embryos maintained until hatching, only one was capable of emerging from the sh

ISSN:0002-9106    

DOI:10.1002/aja.1001350408

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

年代:1972

数据来源: WILEY

摘要:

AbstractThe lateral ventricles and choroid plexuses of an adult and near‐term sheep fetus were examined with scanning electron microscopy. The predominant surface structure of the ependymal cells were cilia arranged in clumps with evidence of metachronic activity. Topographical variations of the ependymal surface are described and discussed according to their role in transport of cerebrospinal fluid and their relation to underlying nervous tissu

ISSN:0002-9106    

DOI:10.1002/aja.1001350409

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.1001350401

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

年代:1972

数据来源: WILEY