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Cordier, André C.; Haumont, Stanislas M.
doi: 10.1002/aja.1001570303pmid: 7405870
In the NMRI mouse embryo, the thymus develops from the third endodermal pouch and the third ectodermal cleft. The cervical vesicle, formed not by the closure of the sinus cervicalis but by an invagination of the dorsal segment of the ectoderm between the third and fourth branchial clefts, contributes to the formation of the thymus. The intense proliferation of the ectoderm of the third cleft on the eleventh day covers the endodermal part.
Farr, Andrew G.; Cho, Yongock; de Bruyn, Peter P. H.
doi: 10.1002/aja.1001570304pmid: 7405871
The internal structure of cells lining the lymphatic sinus of the lymph node includes the presence of large bristle‐coated vesicles, transfer tubules, and vesicular organelles for the uptake and intracellular disposition of endocytosed material. The lining cells of the sinuses phagocytose particulate material from the lymph in the same manner as the sinusoidal endothelium of the bone marrow takes up particulates from the blood and, thus, are similar in this respect to the endothelial lining of the bone marrow sinusoids.
doi: 10.1002/aja.1001570305pmid: 6773409
The purpose of this study was to examine developmental changes in the amnion with regard to: (1) the fine structure of the epithelial cells, (2) the nature and permeability of the intercellular junctions, and (3) the structure of extracellular matrix components in the subepithelial compartment. Comparisons were made between amnion from 26‐72 and 146‐170 days of gestation. Early in gestation, epithelial cells were squamous and had few apical microvilli; late in gestation, cells were cuboidal with numerous microvilli and a well‐developed glycocalyx. Epithelial cells from early gestation had large glycogen stores, well‐developed Golgi apparatus, granular ER, and relatively few 10 nm cytoplasmic filaments. Later, cells were similar except for less glycogen, somewhat more lipid droplets, and numerous 10 nm cytoplasmic filaments. Lateral cell borders were complexly interdigitated at both ages and desmosomes were the predominant type of cell junction. Occasional tight junctions were observed early in gestation; no tight junctions were observed near term. After exposure to peroxidase in vitro, reaction product was present in the intercellular spaces, and the epithelial cells demonstrated very limited pinocytosis. Early in gestation, the basal cell surface was smooth, had no specialized junctions, and was underlain by a complete basal lamina (BL). Late in gestation, the basal surface was thrown into numerous folds, had hemidesmosome‐like junctions, and an incomplete BL. Early in gestation, the BL contained ruthenium red‐positive particles; later, these particles were absent. Early in gestation, the BL had a layer of interstitial collagen fibrils beneath it; late in gestation, a thick layer of 12 nm microfibrils was interposed between the BL and the interstitial collagen. The microfibrillar layer appeared at about 72 days of gestation, when it was apparently formed between the basal cell surface and the partially detached basal lamina.
Chiras, Daniel D.; Greenwald, Gilbert S.
doi: 10.1002/aja.1001570306pmid: 7190774
To quantify thymidine incorporation into DNA in the ovary of the intact, cyclic hamster, hamsters were injected at different times throughout the four‐day estrous cycle (day 1 = day of ovulation; day 4 = proestrus). Animals were killed one hour after injection. One ovary was prepared for liquid scintillation counting of DNA and the other for autoradiographic analysis.
doi: 10.1002/aja.1001570307pmid: 6105822
Fetal (18 days postcoitum) and neonatal (3‐day) pancreatic explants were grown in organ culture with or without supplementation with corticosterone (0.1 μg/ml). After 0, 4, and 8 days of culture, the specific hormone‐positive, islet cell volumes were determined by the use of immunocytochemical and morphometric methods. The insulin, glucagon, and somatostatin contents of the explants were estimated by radioimmunoassays. In the fetal explants, all of the islet cell populations increased in volume and the content of each of the hormones increased over an 8‐day period of culture. Supplementation with corticosterone resulted in a restriction of the increases of the alpha and delta cell volumes and in the somatostatin content of the explants. In the neonatal explants, the volumes of the alpha and delta cells and the glucagon and somatostatin contents decreased over a 4‐day culture period. The presence of corticosterone in the culture medium preserved these cells and their hormone content. Co‐culture of 18‐day fetal and 3‐day neonatal pancreata in control medium for 8 days resulted in a significant decrease in the content of all three of the islet hormones in the fetal explants. These results suggest that a substance harmful to the islet cells is released from the degenerating acinar cells. Thus, the effects of the steroid on the islets may be mediated through its effects on the acinar tissue.
Mato, Masao; Ookawara, Shigeo; Kurihara, Kyoichi
doi: 10.1002/aja.1001570308pmid: 7405872
Exogenous substances such as trypan blue and horseradish peroxidase administered intraventricularly are taken up by granular pericytes in cerebral fine vessels. These cells are provided with elongated and complicated infoldings. Pinocytotic vesicles occur often along the infoldings, and ends of infoldings are swollen and assume vesicular shapes. The specific morphology of the granular perithelial cells is considered to favor a removal of metabolic wates in cerebral tissue.
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