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  • Title: The ultrastructure of the trophoblastic layer of the degu (Octodon degus) placenta: a re-evaluation of the 'channel problem'.
    Author: Kertschanska S, Schröder H, Kaufmann P.
    Journal: Placenta; 1997; 18(2-3):219-25. PubMed ID: 9089785.
    Abstract:
    Previous studies on immersion-fixed specimens of the haemomonochorial labyrinthine chorioallantoic placenta of the degu have made visible channels or pores which completely crossed the trophoblastic layer; for the first time hints for an open connection between maternal blood spaces and fetal interstitium were demonstrated in a placenta. This important finding was re-evaluated by means of transmission electron microscopy paying particular attention to the influence of the mode of fixation and of ischaemic periods prior to fixation. Thirty placentae from seven near-term degu (estimated gestational age 80-90 days) were fixed at various times (5-45 min) after maternal death. Placentae were perfused in situ via the aorta/uterine arteries or the umbilical vein with 2.2 per cent phosphate-buffered glutaraldehyde (n = 7, ischaemic periods < 5-45 min) or lanthanum hydroxide/osmium tetroxide (n = 7, ischaemic periods < 5 min), or were immersion-fixed in 2.2 per cent phosphate-buffered glutaraldehyde (n = 16, ischaemic periods 10-45 min). In material with brief ischaemic periods (n = 3, 5-10 min) no open connections between the maternal blood lacunae and fetal interstitium could be detected. Instead, occasional foci of trophoblast reduced to a thickness of 0.1 micron were found. After ischaemic periods exceeding 10 min, the thin trophoblastic diaphragms had partly disappeared resulting in complete transtrophoblastic pores. It is likely, therefore, that visible trophoblastic pores or channels in the degu placenta are ischaemic artefacts. Application of lanthanum hydroxide from the fetal circulation showed that a branching system of membrane-lined tubules (15-50 nm wide) intruded the trophoblast from its basal side, as has been reported for the guinea-pig and human placenta. It remains to be investigated whether these invaginations belong to a continuous transtrophoblastic channel system.
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