No abstract

A h e structural analysis of fetal mouse ovaries reveals the presence of intercellular bridges between developing oocytes. These bridges, which connect two or more oocytes, are most frequently seen prior to the dictyate stage of meiotic prophase. The intercellular connections are limited by a tri-laminar membrane which is continuous with the oocyte plasmalemma. A characteristic feature of all bridges is the presence of an electron-dense material on the cytoplasmic side of the limiting membrane. Since this dense material is a constant and conspicuous component of the entire bridge, identscation of these connections is possible in all planes of section. In cross section, the bridges are usually cylindrical, while in longitudinal section, a variety of configurations are observed. Oocytes connected by intercellular bridges exhibit a highly developed Golgi complex which is frequently localized in the region of the cytoplasmic continuities. Vesicular elements, apparently derived from the Golgi, are routinely observed within the boundaries of the bridges. Other cytoplasmic organelles, including rough and smooth endoplasmic reticulum, free ribosomes and mitochondria, are also seen in these bridges. The presence of these vesicles and organelles within intercellular bridges suggests that these connections may provide a means for transfer of organelles and other substances from one oocyte to another. It may be, therefore, that intercellular bridges are important for the nourishment and maturation of certain selected oocytes as well as for the synchronization of meiotic events.True intercellular bridges were first demonstrated between developing spermatogenic cells in the adult cat testis by Burgos and Fawcett ('55), and subsequently in the testis of a variety of other species (Fawcett, Ito and Slautterback, '59). The results of these investigations led Fawcett ('61 ) to speculate that intercellular bridges are responsible for the precise synchronization of development of the male gamete. Intercellular bridges have also been noted between developing oocytes in rat (Franchi and Mandl, '62), hamster (Weakley, '66, '67) rabbit (Zamboni and Gondos, '68) and human ovaries (Stegner, '67). The significance of these bridges in the ovary has been briefly commented upon only by Zamboni and Gondos ('68). These authors suggest that bridges between developing oocytes, as in the testis, may provide a method for their synchronous development. They further suggest that those oocytes which do not lose their intercellular connections are destined to degenerate.The present investigation is a comprehensive study on the morphology of intercellular bridges in the developing mouse J. MORPH., 127: 307-340. ovary and is an attempt to further clarify their function in the female gonad. MATERIALS AND METHODSAlbino female mice of the ICR strain were caged with fertile males of the same strain. The females were examined daily for evidence of a successful copulation and those animals which had a vaginal plug were isolated. The morning on which a...

A variety of human tendons have been studied at the electron microscope level. The fibers of these tendons are composed of collagen fibrils that average 1,750 A and 600 A in diameter. A third population that measures 100 A in diameter may represent immature collagen or filaments that are incorporated into tendon elastic fibers. The larger collagen fibrils vary in ratio with respect to one another, and are connected by interfibrillar bridges which in some cases appear to extend through the substance of the fibril. The collagen fibrils of the paratenon are less-well organized than those of the tendon proper and average 600 A in diameter. Tendons that exhibit the property of lateral stretch (plantaris and palmaris) were compared at the ultrastructural level with tendons that do not have this property. No differences between the two tendon types could be determined in normal or spread preparations, indicating that the differences in physical characteristics are a result of fiber rather than fibril organization.

An experiment designed to study the effects of the copper IUD on the virgin rat uterus has revealed the presence of intracellular collagen fibrils in control uteri and in uteri that have contained a copper IUD for three months. The cells containing the collagen are found in the stroma in close proximity to the uterine epithelium. The collagen is found within membrane-bound cytoplasmic vacuoles that vary in morphology. In some cases the fibrils are tightly packed and linear, with no other material evident in the vacuole. In other examples, the fibrils are randomly arranged and the vacuoles contain a punctuate material which is characteristic of phagolysosomes. Finally, cytoplasmic vacuoles are seen which contain ill-defined debris and poorly-visualized structures that exhibit a periodicity, suggesting a terminal phase of fibril breakdown. All animals were sacrificed in metestrus, and the results indicate that intracellular collagen is present in the nulliparous rat uterus at this stage of the cycle. In addition, this phenomenon does not appear to be influenced by the presence of a copper IUD over a period of three months.